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2025
Volume: 53 Issue 3
21 Article(s)
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Effect of Gypsum Type on Flowability of Cement Pastes with Superplasticizer
SHU Xin, ZHANG Qianqian, YANG Yong, and RAN Qianping
IntroductionAppropriate workability is a key to ensuring the smooth pouring, building of concrete, and quality of the project. However, in practical applications, the workability of concrete often undergoes unexpected drastic changes in the early mixing stage, such as rapid loss of flowability, false set and so on. TheIntroductionAppropriate workability is a key to ensuring the smooth pouring, building of concrete, and quality of the project. However, in practical applications, the workability of concrete often undergoes unexpected drastic changes in the early mixing stage, such as rapid loss of flowability, false set and so on. The change of flowability of cement paste overtime in the early stage is mainly related to the early hydration of cement and the adsorption behavior of superplasticizer. Cement pastes with different mineral compositions can exhibit different change rules overtime. In the early stage of hydration, especially in the first hour, the hydration reaction of tricalcium aluminate (C3A) mainly occurs. Since the reaction of C3A with water is extremely rapid, a large amount of calcium sulfate is incorporated into cement, and gypsum dihydrate (G, CaSO4·2H2O) is usually the most important source of calcium sulfate. Although the existing studies focus on the influence of gypsum types on the hydration of C3A, the fundamental reasons are still need to be explored.In this paper, the effect of gypsum types was considered to elucidate the fundamental reasons behind the drastic changes in early flowability of fresh concrete. Five cements were prepared using clinker combined with different types of gypsum (i.e., G, gypsum dihydrate and H, hemihydrate gypsum). The study focused on the time-dependent changes in the flowability of pastes within the first hour, and examined the processes such as adsorption of superplasticizer, dissolution of mineral phase and precipitation of hydration products, thus analyzing the intrinsic mechanisms behind the time-dependent changes in flowability.MethodsBased on the content of C3A in the clinker, four types of cements with a single gypsum type were prepared via adding G and H, respectively, at two molar ratios of SO42⁻ to C3A of 0.5 and 1.5, and one type of cement with mixed gypsum was prepared at a molar ratio of SO42⁻ to C3A of 1.5 and a molar ratio of G to H of 2. In the test, the water binder ratio was fixed at 0.3, and the amount of PC was adjusted to achieve the similar initial flowability (i.e., (250 ± 5) mm at 2 min). At 2, 5, 10, 20, 30 and 60 min after adding water, the paste was taken out for various tests (i.e., flow spread, analysis of interstitial liquid, adsorption and hydrated sample preparation).The flow spread of paste was tested according to the Chinese standard GB/T 8077—2012. The adsorption behavior of PC and the concentrations of [Ca] and [S] in the interstitial liquid were obtained by TOC and inductively coupled plasma mass spectrometry (ICP-MS) on the interstitial liquid obtained by centrifugation. The hydration was stopped with cold isopropyl alcohol (5 ℃) to perform the microscopic analysis on the hydrated sample, including differential scanning calorimetry (DSC) and surface area measurement by BET based on nitrogen adsorption.Results and discussionFor five groups of cement pastes with the similar initial flowability, the addition of G leads to a rapid loss of flowability in the first 10 min, and increasing the amount of G can reduce the loss of flowability. The addition of H also leads to a rapid loss of flowability in the first 10 min, but then the flowability slowly increases. Moreover, the higher the amount of H added is, the more significant loss of flowability in the first 10 min and the greater the subsequent increase of flowability will be.For cement with only G added, the precipitation of ettringite mainly occurs in the first hour, and AFt rapidly forms in the first 5 min and then increases slowly. However, for cement with H, two processes occur simultaneously, i.e., ettringite precipitation and H dissolution -G precipitation. H promotes the formation of ettringite, and the ettringite content in the paste is higher than that with only G added.For cement with only G added, the precipitation of ettringite leads to a large increase in the specific surface area of the system, which in turn causes the loss of paste flowability over time. For cement with H added, the precipitation of ettringite and large-sized G leads to a rapid loss of the early flowability of the paste, but the gradually decreasing sulfate ion concentration in the interstitial liquid is conducive to the adsorption of PC on the surface of the mineral phases, which in turn leads to a reverse increase in the subsequent flowability.ConclusionsThe dissolution of mineral phases and the precipitation/growth of hydration products were key factors causing the drastic changes in early fluidity of the paste. For cement pastes containing dihydrate gypsum, the formation of ettringite led to a significant increase in the specific surface area of the samples, causing a time-dependent loss in fluidity. In contrast, for cement paste containing hemihydrate gypsum, in addition to ettringite, the precipitation of large-sized dihydrate gypsum accelerated the early loss of flowability. However, the gradually decreasing concentration of SO42- was conducive to the adsorption of superplasticizer, thus leading to an increase in flowability of paste..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 09, 2025
- Vol. 53, Issue 3, 497 (2025)
Graphene Oxide-coated Sand for Enhancing Chloride Resistance of Cement-based Materials
FENG Ganlin, LUO Shengyu, LUO Qiling, and LONG Wujian
IntroductionIn coastal engineering, the durability of reinforced concrete structures is often compromised due to the corrosion of steel reinforcements caused by chloride ingress. This issue significantly affects the safety and longevity of these structures. In concrete materials, the interfacial transition zone (ITZ) bIntroductionIn coastal engineering, the durability of reinforced concrete structures is often compromised due to the corrosion of steel reinforcements caused by chloride ingress. This issue significantly affects the safety and longevity of these structures. In concrete materials, the interfacial transition zone (ITZ) between the cement matrix and aggregates is a critical point, affecting the pathways and rates of chloride ion diffusion. Although previous studies demonstrate that the incorporation of nanomaterials can enhance the durability of cement-based materials, the uneven dispersion and agglomeration of these nanomaterials restrict their effectiveness. In this paper, a modification method was proposed via coating graphene oxide (GO) onto aminated sand particles to improve the dispersion of GO within cement-based composites, thereby enhancing their durability. This approach could have a promising potential for extending the service life of coastal engineering structures.MethodsIn this study, a GO dispersion was firstly prepared and dispersed by ultrasound. Subsequently, a specific chemical treatment method was employed to coat GO onto standard sand surfaces, creating aminated functionalized sand (GO-MAs). The preparation process of GO-MAs included sand pretreatment, amination, and chemical bonding with GO. In the experiments, cement-based composites with different GO contents (i.e., 0.1%, 0.3%, 0.5% by mass) were prepared with high-performance polycarboxylate superplasticizers to enhance GO dispersion. The chloride ion resistance of these composites was evaluated by rapid chloride migration (RCM) tests and natural chloride diffusion tests. In addition, the mechanisms of GO-coated sand enhancing the microstructural properties of cement-based materials, particularly the ITZ, were analyzed by mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and thermogravimetric analysis (TG/DTG).Results and discussionThe experimental results indicate that the incorporation of GO significantly reduces the chloride ion penetration depth and migration coefficient in cement-based materials. At GO content of 0.3%, the chloride ion penetration depth and diffusion coefficient when using the method of using GO-coated sand can be reduced by 24.8% and 18.5%, respectively. The MIP tests further reveal that the size of harmful pores (i.e., greater than 50 nm) is decreased by 36.8%, indicating that GO-coated sand effectively improves the pore structure of cement-based materials, reduces porosity, and enhances material density. The microstructural analysis results reveal that GO-coated sand primarily enhances the performance of cement-based composites via optimizing the ITZ. The coupling agent forms stable chemical bonds with the sand surface, while the covalent bonding of amide bonds between GO and the coupling agent improves the dispersion of GO and promotes ITZ hydration, reducing defects and cracks, thereby enhancing resistance to chloride ion transport. The microstructural morphology analysis shows that the samples without GO have more and larger pores, while the samples with GO-coated sand exhibit significantly fewer and denser pores. The EDS analysis indicates that GO-coated sand promotes the enrichment of hydration products at the ITZ interface of cement-based materials, enhancing the ITZ density. Based on the XRD and TG/DTG analysis, GO-coated sand promotes the hydration reaction of cement, thus generating more hydration products, especially C-S-H and Ca(OH)2 crystals. The formation and arrangement of these hydration products play a crucial role in maintaining a high alkaline environment within cement matrix and protecting a passivation film on the steel surface. The qualitative comparative analysis of the crystallographic orientation index of Ca(OH)2 crystals indicates that GO-coated sand reduces the number of Ca(OH)2 crystals perpendicular to the interface in the ITZ, optimizing the directional arrangement of Ca(OH)2 crystals in the ITZ, which is beneficial for strengthening the weak interface and enhancing its density.ConclusionsThe method of using GO-coated sand effectively could enhance the resistance of cement-based materials to chloride ion erosion, and the optimal effect occurred at a GO content of 0.3%. This modification method optimized the ITZ through a “dual-bond effect,” reducing porosity and increasing material density, thereby enhancing the barrier against chloride ions. This research could provide an effective technical approach to improving the durability of cement-based materials and offers important scientific evidence for the protection of concrete structures in coastal engineering. A future research needed to explore the long-term performance of GO-coated sand under different environmental conditions and its application effects in practical engineering, thus providing comprehensive theoretical support and technical guidance for the modification and engineering application of cement-based materials..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 09, 2025
- Vol. 53, Issue 3, 505 (2025)
Effect of Citric Acid and Citrates on Hydration and Setting Performance of Cement
LI Huanhuan, LU Zichen, YOU Ziyang, ZHANG Liheng, and SUN Zhenping
IntroductionRetarders are necessary in construction projects such as long-distance transportation, high-temperature construction in summer and large-volume concrete construction. However, in practical applications, abnormal setting phenomena such as rapid or non-setting of concrete often occur due to the possibly incorIntroductionRetarders are necessary in construction projects such as long-distance transportation, high-temperature construction in summer and large-volume concrete construction. However, in practical applications, abnormal setting phenomena such as rapid or non-setting of concrete often occur due to the possibly incorrect or excessive mixing, which can affect the progress of the project and cause economic losses. It is thus of great significance for accurately regulating the setting and hardening properties of cement-based materials to clarify the cement hydration process and its mechanism under the action of retarders. Citric acid (CA) and its salts (mainly sodium citrate (SC) and potassium citrate (PC)) are commonly used as retarders. However, there are still some controversies about their effect and mechanism in the existing studies. In this paper, CA, SC and PC with different dosages and addition methods were used to clarify the effect and mechanism of these retarders on cement hydration and solve the problem of abnormal setting during the use of such retarders. Their effects on the setting time of cement paste, hydration heat, and adsorption capacity under the action of different sulfate carriers (anhydrite (AH) and hemihydrate (HH)) were investigated. In addition, the possible mechanism was also analyzed.MethodsA fixed water-to-cement mass ratio of 0.4 was used. The dosage of citric acid and its salt was calculated based on a mass ratio of citrate to cement, and the dosage of citrate ion was 0.045%, 0.090%, 0.180% and 0.360% (mass fraction), respectively. Two addition methods were used, i.e., W addition method and S addition method. For W addition method, the retarders were first dissolved in water and then mixed with cement. For S addition method, the retarders were first mixed with cement as a solid powder, and then the mixture was added to water. Two kinds of cement with different types of sulfate carriers were prepared, i.e., AH-contained cement prepared with anhydrite and HH-contained cement prepared with hemihydrate.The setting time was measured according to the Chinese standards GB/T 1346—2011. The hydration of cement paste at (25.00±0.02) ℃ was measured by a model TAM Air 8-channel isothermal calorimeter (Newcastle, DE, USA). The adsorption capacity of different retarders after hydrating for 5 min was measured by a model TOC-L total organic carbon analyzer (Shimadzu Co., Japan). The change in conductivity when AH and HH dissolved in CA, SC and PC solutions with a citrate concentration of 0.047 6 mol/L was determined by a model FE38 conductivity meter (Mettler Toledo Co., Switzerland). In addition, the ionic concentrations of calcium and sulfate during the dissolving process were measured by a model 5800 inductively coupled plasma emission spectrometer (Agilent Co., USA).Results and discussionThe effect of retarders on the cement hydration process can be affected by different addition methods, dosages, cations of retarders and different sulfate types in cement. For cement with different sulfate carriers, the setting time of HH-contained cement is longer than that of AH-contained cement regardless of the dosage of retarder and the addition method used. The abnormal rapid setting phenomenon of retarder can occur in the AH-contained cement rather than in HH-contained cement. Regardless of the type of retarders used, the initial dissolution capacity of HH is greater than that of AH. For different addition methods, the retarder with S addition method shows a greater retarding ability. The effect of citric acid and citrates indicates that the retarding ability of PC is greater than that of SC.The results of hydration heat show that a phenomenon of abnormal rapid setting in AH-contained cement can be caused due to the rapid hydration of the aluminate-containing phase. The results of conductivity and ionic concentration indicate that HH quickly dissolves and releases sufficient sulfate ions, thus inhibiting a rapid reaction of C3A and avoiding the occurrence of rapid setting. Moreover, the ability of PC to promote the dissolution of sulfate carrier is greater than that of SC possibly due to its greater complexing ability with calcium ions. Therefore, the complexation can play an important role in determining the effect of retarders.ConclusionsThe type of sulfate carrier in cement could change the effect of citric acid/citrate. For AH-contained cement, there existed a phenomenon of first retarding and then rapid setting with the increase of retarder dosage. Such a phenomenon was avoided in HH-contained cement. The addition method of citric acid/citrate greatly changed its effect. The S addition method of retarders enhanced its retarding ability. The adsorption and complexation of citric acid/citrate with calcium ions both played an important role in determining the cement hydration process..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 09, 2025
- Vol. 53, Issue 3, 519 (2025)
Mechanism of K2HPO4 Improving Early Strength of Magnesium Silicate Hydrate Cements
LENG Difei, LI Xiangguo, LV Yang, and LI Neng
IntroductionMagnesium silicate hydrate (M-S-H) cement is a low-carbon cementitious material. This paper discusses the mechanism of dipotassium phosphate (DKP) accelerating the hydration of hydrated magnesium silicate cement, and confirms that the introduction of DKP accelerated the formation of M-S-H gel due to the alkIntroductionMagnesium silicate hydrate (M-S-H) cement is a low-carbon cementitious material. This paper discusses the mechanism of dipotassium phosphate (DKP) accelerating the hydration of hydrated magnesium silicate cement, and confirms that the introduction of DKP accelerated the formation of M-S-H gel due to the alkali induction effect and K-struvite seed crystal induction effect. This improves the compressive strength and subsequent strength of hydrated magnesium silicate cement, which can increase 3.25, 13.78, 22.23, 34.58 MPa and 37.96 MPa at the age of 1, 3, 7, 14 d and 28 d, respectively. Meanwhile, different additives can induce the formation of different M-S-H crystal phases. The acceleration of the hydration process by these additives is confirmed through X-ray diffraction (XRD), 29Si nuclear magnetic resonance spectroscopy (NMR), scanning electron microscopy (SEM) and density functional theory calculations. M-S-H is the main source of strength for hydrated magnesium silicate cement, and this paper also emphasizes that suitable additives can induce a faster formation of M-S-H structures with stronger cementitious properties, thereby improving the hydration rate and early compressive strength of magnesium silicate hydrate cements, and further expanding the application range of magnesium silicate hydrate cements.MethodsMgO: SF mass ratio for preparing MSHC samples was 40 : 60 (i.e., the amount of substance was 1:1), the water/cement (w/c) ratio was 0.45, the SHMP content was 1% (mass fraction) of the total solid mass, and the samples were all cured at 25 ℃ and 95% RH for 28 d. When the samples were cured at different ages (i.e., 1, 3, 7, 14 d and 28 d), they were broken into small pieces with the particle sizes of 1-3 cm and soaked in isopropyl alcohol to stop their further hydration. The broken samples were dried in a vacuum drying oven at 40 ℃ until there was no more mass loss.The crystal phases of the samples were determined by a model Empyrean Rietveld X-ray diffractometer (XRD, Malvern Panalytical Co., The Netherlands). The morphology of the samples was analyzed by a model JSM-IT300 scanning electron microscope (SEM, JEOL Ltd., Japan). The nuclear magnetic resonance map of the samples was analyzed by a model Advance III 400 nuclear magnetic resonance spectroscope (NMR, Bruker Co., Germany).This work was also analyzed based on density functional theory calculations (DFT). All the models were geometrically optimized and subsequent calculations were performed by a software named Vienna Ab-initio Simulation Package (VASP). The projection enhanced plane wave method (PAW) was used in the calculation, and the cutoff energy was set to 500 eV, which was obtained after the convergence test. The exchange-correlation potential was approximated by Perdew-Burke-Ernzerhof (PBE) under generalized gradient approximation (GGA). A 15×15×9 K-point grid was used to sample the first Brillouin region for the stress-strain calculation. Young’s modulus and Poisson’s ratio of each M-S-H crystal phase were calculated via vaspkit.Results and discussionThe DKP increases the compressive strength of MSHC by 3.25, 13.78, 22.23, 34.58 MPa and 37.96 MPa at 1, 3, 7, 14 d and 28 d, respectively. This mechanism is since the DKP induces the formation of more suitable M-S-H crystal phase with a higher mechanical strength, and the DKP accelerates the hydration rate of M-S-H, especially the early hydration rate. The SEM images confirm the acceleration effect of the DKP on the hydration. The results of Rietveld XRD and DFT calculation indicate that the DKP can induce the formation of M-S-H crystal structure with a greater gellability. The M-S-H crystal phase-D induced by SHMP is of the lowest Young’s modulus and the highest Poisson's ratio. Also, its M-S-H crystal phase generation is rather small, compared with other groups, resulting in its lowest theoretical compressive strength. The M-S-H principal crystal phase induced by DKP is a superhydrous phase B, which is of the highest Young’s modulus and the lower Poisson’s ratio, leading to the highest theoretical compressive strength. This indicates that the DKP induces the formation of M-S-H crystalline phase with a greater compressive strength. The main crystal phase of M-S-H induced by KOH and K-struvite are talc and anthophyllite, respectively, which are of higher Young’s modulus and lower Poisson’s ratio, thus improving the compressive strength.ConclusionsThe admixture DKP could improve the compressive strength of MSHC via inducing the MSHC system to generate more suitable and higher mechanical strength M-S-H crystal phase, accelerating the hydration process of MSHC, and increasing the compressive strength of MSHC samples (i.e., 3.25, 13.78, 22.23, 34.58 MPa and 37.96 MPa) at different ages (i.e., 1, 3, 7, 14 d and 28 d). The results by Rietveld X-ray diffraction refinement showed that different admixtures induced the hydration of MSHC to form different M-S-H crystal phases, which could affect the cement strength. The DKP induced M-S-H to form a superhydrous phase B, which was a M-S-H crystal phase with a high Young’s modulus and a low Poisson’s ratio. This was one of the mechanisms due to the DKP enhancing MSHC. This wor'k indicated that suitable admixtures could induce the formation of M-S-H crystal structure with a greater cementitious property, thereby improving the hydration rate and early strength of MSHC..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 09, 2025
- Vol. 53, Issue 3, 531 (2025)
Inhibition Effect and Mechanism of Zeolitic Imidazolate Frameworks MOF Corrosion Inhibitors in Reinforced Mortar
WANG Yangyang, HU Jie, HUANG Haoliang, WEI Jiangxiong, and YU Qijun
IntroductionChloride induced corrosion damage of the embedded reinforcement is one of primary reasons for the deterioration of concrete structures in civil engineering. Admixing organic corrosion inhibitors are considered as an effective way to halt the corrosion damage of the embedded reinforcement for its convenient IntroductionChloride induced corrosion damage of the embedded reinforcement is one of primary reasons for the deterioration of concrete structures in civil engineering. Admixing organic corrosion inhibitors are considered as an effective way to halt the corrosion damage of the embedded reinforcement for its convenient use and high cost-efficiency. However, the corrosion inhibition efficiency of conventional corrosion inhibitors exists due to the limited amount of adsorption functional groups in molecular structures. It is thus essential to develop novel corrosion inhibitors with a great adsorption capacity to satisfy the efficient corrosion protection of reinforcement concrete in harsh marine conditions. As typical crystalline hybrid materials, metal-organic frameworks (MOFs) are self-assembled via coordination between metal nodes and organic ligands. Zeolitic imidazolate frameworks (ZIF-8, a representative MOF material) exhibit many heteroatoms and π-electron system, thus enabling its interaction and high corrosion inhibition potential for reinforced concrete. In this study, ZIF-8 corrosion inhibitors were synthesized and its inhibition effect for reinforced mortar was investigated. In addition, the characteristics of the reinforcement/mortar interface were also evaluated by image analysis based on scanning electron microspcopy (SEM) images and chloride titration.MethodsIn the experiments, 0.60 g Zn(NO3)2⋅6H2O was dissolved in 4.5 mL deionized water. 11.50 g 2-methylimidazole was dissolved in 40.0 mL deionized water. The zinc nitrate solution above was then added into 2-MeIm solution in dropwise under stirring. After stirring for 24 h, white ZIF-8 corrosion inhibitors were collected via centrifugation at 10 000 r/min and then cleaned with deionized water for three times. The water to cement (w/c) ratio was 0.5 and the sand to cement (s/c) ratio was 3. The dosage of ZIF-8 corrosion inhibitors was 0% (blank), 0.2%, 0.4% and 0.8% per dry cement weight in mortar specimen, respectively. The reinforcement electrode was centrally embedded in cylindrical mortar specimen (Φ50×100 mm). The reinforced mortar specimens were then half-immersed in 3.5% (mass fraction) NaCl solution (i.e., 25±1 ℃ and 60±5% relative humidity). The chemical composition, thermal stability, morphology, and specific surface area of ZIF-8 corrosion inhibitors were determined by Fourier transform infrared spectroscopy, thermal gravimetric analysis (TG), field emission scanning electron microscopy (FE-SEM) and N2 physisorption, respectively. Electrochemical workstation was used to evaluate the electrochemical behavior of the reinforced mortar during 210 d immersion with three electrode systems. The morphologies and chemical elements of the reinforcement were characterized by FE-SEM combined with energy dispersive spectroscopy (EDS). The compositions of product film on the reinforcement surface were evaluated by X-ray photoelectron spectroscopy. The total porosity at the reinforcement/mortar interface was obtained by image analysis based on the FE-SEM images acquired in backscattered electrons (BSE) mode. Chloride content in mortar matrix within 2 mm from the embedded reinforcement surface was measured by a potentiometric titrator.Results and discussionZIF-8 is prepared by a facile and eco-friendly solvent method. The negative OCP shift of the embedded reinforcement is dramatically prolonged by the admixed ZIF-8 corrosion inhibitors. The more pronounced beneficial effect is relevant to a higher dosage of ZIF-8 corrosion inhibitors. Corrosion initiation time for the embedded reinforcement in mortar specimens is delayed by 8.3%-43.3% at 0.2%-0.8% (mass fraction) ZIF-8 corrosion inhibitors. The corrosion damage of the reinforcement embedded in mortar specimens with ZIF-8 corrosion inhibitors merely occurs after 180 d immersion. ZIF-8 corrosion inhibitors can fill in the pore space in cement matrix due to small particle size (i.e., 75 nm), and the bulk mortar resistance of the reinforced mortar are continuously reduced with immersion age. Compared to the blank specimen, a higher resistance of the formed product layer and a lower capacitance of the formed product layer are relevant to the specimens with ZIF-8 corrosion inhibitors at the same immersion stage. Meanwhile, a higher charge transfer resistance and a lower electric double-layer capacitance are also related to the specimens with ZIF-8 corrosion inhibitors at the same immersion stage. Besides, a lower anodic current density appears for the embedded reinforcement in a mortar with ZIF-8 corrosion inhibitors, and this beneficial effect is more pronounced for a higher dosage of ZIF-8 corrosion inhibitors. The inhibition efficiency is 62.1% in a reinforced mortar in the presence of 0.8% (mass fraction) ZIF-8 corrosion inhibitors after 180 d immersion. The reduced dimensions and increased packing density of the corrosion products occur for the specimen with a higher dosage of ZIF-8 corrosion inhibitors. The chemisorption of ZIF-8 corrosion inhibitors is confirmed by the formation of coordination bond between nitrogen atoms in ZIF-8 corrosion inhibitors and iron atoms on the reinforcement surface. Furthermore, the enhanced peak intensity of Fe2O3 and FeOOH, together with the reduced peak intensity of FeO appear for the specimen with 0.8% ZIF-8 corrosion inhibitors. The porosity of cement matrix at the reinforcement/mortar interface is reduced by 9.8 % and the chloride content in the vicinity of the embedded reinforcement is efficiently reduced by 28.6% with the admixed ZIF-8 corrosion inhibitors in mortar specimen.ConclusionsThe corrosion initiation time of the embedded reinforcement in mortar was efficiently prolonged by 8.3%-43.3% in the presence of 0.2%-0.8% ZIF-8 corrosion inhibitor. ZIF-8 corrosion inhibitors could reduce the corrosion current density and increase the charge transfer resistance and polarization resistance of the embedded reinforcement after corrosion initiation. The inhibition efficiency of 0.8% ZIF-8 corrosion inhibitors was maintained at 62.1% after 180 d immersion in 3.5% NaCl solutions. ZIF-8 corrosion inhibitors exhibited an effective adsorption on the reinforcement surface, thus reducing chloride content on the reinforcement surface. Also, more highly protective products (FeOOH and Fe2O3) could form on the reinforcement surface. ZIF-8 corrosion inhibitors refined the pore structure at the reinforcement/mortar interface and reduced chloride content at the vicinity of the reinforcement. For specimen with 0.8% ZIF-8 corrosion inhibitors, the porosity of cement matrix at the reinforcement/mortar interface was reduced by 9.8%, and the chloride content of cement matrix in the vicinity of reinforcement was declined by 28.6%..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 09, 2025
- Vol. 53, Issue 3, 539 (2025)
Research Progress on Chemical Admixtures for Improving Durability of Structural Concrete
CAI Jingshun, LI Hua, SHU Xin, SHAN Guangcheng... and RAN Qianping|Show fewer author(s)
Concrete durability is recognized as a worldwide problem. With global warming and harsh service environment, the problem of premature failure of structural concrete durability becomes more prominent. Chemical admixtures as the key components of concrete show significant technical advantages in improving the microstructConcrete durability is recognized as a worldwide problem. With global warming and harsh service environment, the problem of premature failure of structural concrete durability becomes more prominent. Chemical admixtures as the key components of concrete show significant technical advantages in improving the microstructure and durability of structural concrete. This review represents research progress on the durability enhancement admixtures for the innovation of concrete durability enhancement technology and the development of low-carbon and sustainable society.Some admixtures used for concrete crack control (i.e., expanding agent, water evaporation inhibitor, heat of hydration inhibitor) are described. The addition of nanomaterials and polymers as well as the use of monomer in-situ polymerization are summarized. In addition, SAP, osmotic crystallization and expansion agents for realizing the self-healing of cracks are also discussed.Air entraining agent, pore hydrophobic agent and nano-pore compacting agent are summarized to enhance concrete microstructure, thus solving the durability failure problem of concrete under freeze-thaw, sulfate attack and chloride ion attack.Corrosion inhibitor is inducted. Recent research progress on organic rust inhibitors, green rust inhibitors and intelligent rust inhibitors is reviewed, and the existing problems of current rust inhibitors are summarized, and the development direction of future rust inhibitors is prospected.Summary and ProspectsDurability failure is a challenge facing the sustainable development of society. How to improve the durability of structural concrete with low cost and high efficiency is a key problem to be solved. This review represents the research progress on durability enhancing admixtures in concrete crack control, microstructure regulation and reinforcement rust resistance improvement, and points out the existing problems of various admixtures.1) Concrete crack control is a premise of structural concrete durability improvement. However, how to further improve the effectiveness and adaptability of admixtures according to the changes of concrete material system characteristics and environmental requirements is a major development direction. In addition, toughness enhancement and self-healing admixtures are still in the research stage, and the key properties are still unclear. How to realize the application needs, further reveal the structure-activity relationship of key materials and achieve the improvement of toughness and self-healing properties is a problem worthy of in-depth study.2) The control of concrete microstructure is a key to improving the durability of concrete. Air entraining agent, pore hydrophobic agent and nano-pore compacting agent are effective technical means to enhance concrete microstructure, which can solve the durability failure problem of concrete under freeze-thaw, sulfate attack and chloride ion attack. However, for coupled corrosion environment, there are still insufficient mutual adaptability of various admixtures applied together, and a further research is needed. In addition, the relations among air entrainment agent, pore hydrophobic agent, nano densifier, cement hydration, stable regulation/optimization of pore structure, and the resulting durability impact mechanism are still unclear, which need to be further investigated.3) The improvement of rust resistance of steel bars is a fundamental to the improvement of structural concrete durability. Inorganic and organic rust inhibitors are important components of rust inhibitors, and the reasonable use of different kinds of rust inhibitors is a key to achieve the improvement of rust resistance performance of steel bars in complex systems. The corrosion protection and repair of structural concrete can be improved via different application methods such as internal mixing, external coating, electromigration and pressure penetration. The future development direction of rust inhibitors can be green and intelligent, but it still needs to be further studied in combination with practical applications.Although the durability of concrete is extremely complex, admixtures have some technical advantages in improving the durability of concrete. In the future, it is necessary to further analyze the micro-action mechanism and structure-activity relationship of admixtures, and propose an effective method of structural design and preparation of admixtures by theoretical calculation (i.e., molecular simulation, artificial intelligence and other theoretical analysis). Also, slow and controlled release technologies such as microcapsule coating, layered and porous material loading are used with the characteristics of cement hydration to enhance the durability and improve the adaptability of admixtures to cement concrete, thus realizing the efficient use of admixtures in concrete systems at regular and fixed points, avoiding the influence of admixtures on cement hydration, microstructure formation and long-term performance，and achieving an accurate control of structural concrete durability throughout the life cycle..
Journal of the Chinese Ceramic Society
- Publication Date: Feb. 08, 2025
- Vol. 53, Issue 3, 553 (2025)
Polycarboxylate Superplasticizers: Structural Design, Application Technology, and Future Directions
ZHANG Yue, XIAO Yuchong, MA Chenyu, Plank Johann... and SHI Caijun|Show fewer author(s)
The global concrete industry is actively committed to promoting energy conservation and carbon emission reduction. This trend accelerates the widespread application of low-carbon binders. As a technology of low-carbon binders continues to advance, the development of polycarboxylate-based superplasticizer (PCE) suitableThe global concrete industry is actively committed to promoting energy conservation and carbon emission reduction. This trend accelerates the widespread application of low-carbon binders. As a technology of low-carbon binders continues to advance, the development of polycarboxylate-based superplasticizer (PCE) suitable for low-clinker or clinker-free binding systems becomes increasingly important. This review represents the classification, the principle of structural design, synthetic methods, and performance characteristics of PCE. The latest development and technological innovation of PCE are described, in particular emphasizing on some challenges faced by PCE in specific application scenarios of low carbon blended cementitious system. The review also looks ahead to the technological prospects of PCE and its key development directions in achieving the low-carbon transformation of the concrete industry.PCE is a polymer designed via introducing different monomer types into its molecular main chain. These monomers include methoxy polyethylene glycol methacrylate (MPEG), allyl polyoxyethylene ether (APEG), methallyl polyoxyethylene ether (HPEG), isopentenyl polyethylene glycol ether (IPEG), and 4-hydroxybutyl vinyl polyoxyethylene ether (VPEG), each imparting distinct physical and chemical properties to PCE. For instance, MPEG-based PCE exhibits a remarkable water reduction rate and has a higher viscosity, thus restricting its application due to time-consuming synthesis. In contrast, VPEG-based PCE requires shorter synthetic time and lower reaction temperature, which demonstrates superior flowability and slump retention, making it suitable for application scenarios requiring prolonged water retention. Besides the choice of monomer types, the structural design of PCE involves other factors, i.e., molecular weight, charge density, and side chain length, etc.. These factors collectively determine the performance of PCE in cement-based materials, including workability, strength development, and long-term durability. The modifications to the main chain of PCE such as silane or phosphate groups can enhance sulfate resistance and adsorption capacity. Lignin-based framework modification of PCE employs readily available raw materials but performs better than traditional PCEs. Anionic side chain modifications and those with large terminal groups can significantly alter PCE’s slump retention and clay tolerance. The development of C-S-H-PCE greatly improves the early strength performance of concrete.Regarding the synthesis methods, PCE is typically prepared through free radical polymerization, which can be conducted in aqueous solution or via emulsion or microemulsion. The determination of synthesis conditions, i.e.. temperature, pressure, catalyst type, and agent concentration are crucial for achieving high-performance PCE. Also, adjusting the monomer ratio of polymer formulation can further enhance PCE performance to meet specific engineering requirements. Other PCE synthesis techniques encompass reversible addition-fragmentation chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). Compared to the simplest approach of free radical polymerization that cannot precisely control molecular weight and structural sequences, the RAFT process allows for customized PCE molecular structures through RAFT agents. The structure-activity relationship between molecular architecture and dispersion performance can be established via continuously innovating PCE synthesis methods e.g., RAFT and ATRP, thus facilitating the development of highly efficient and eco-friendly PCE polymers.In response to the increasing demands for the sustainability of construction industry, the carbon footprint of PCE additives is accurately assessed, whereby the sources of carbon emissions during PCE production and application are identified. Consequently, green high-performance PCEs begin to be developed, delivering remarkable water-reducing efficiency and obtaining other properties such as improvement of early strength and reduction in dry-shrinkage cracks. Particularly for the development of low carbon cementitious systems, the application of PCE is crucial but currently encounters serious compatibility issues. For instance, some issues related to dispersion failure of PCE in alkali-activated cementitious materials remain unclear. Ensuring desirable workability and adaptability of PCE in low carbon binders is a challenge posed in these systems.Summary and ProspectsTo address these challenges, some solutions are explored. On one hand, the molecular structure of PCE is improved to enhance its stability and adaptability in complex environments. On the other hand, some concepts from nanotechnology and smart materials are proposed to develop self-healing PCE products. These innovative studies can improve the overall performance of concrete and pave some effective pathways for the green development of the construction industry. Polycarboxylate superplasticizers play a vital role in driving the concrete industry towards energy saving and emission reduction. A future research will focus on enhancing PCE performance, cost reduction, and expanding its application fields. With the advancement of technology and the guidance of innovative thinking, we can believe that PCE will play an even greater role in promoting sustainable development in the construction industry..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 16, 2025
- Vol. 53, Issue 3, 574 (2025)
[in Chinese]
Journal of the Chinese Ceramic Society
- Publication Date: Mar. 10, 2025
- Vol. 53, Issue 3, 1 (2025)
Divalent Sm Doped Fluorosilicate Glass with Metallic Al as A Reduced Agent
WANG Changjian, QIAO Xusheng, FAN Xianping, and DENG Renren
IntroductionSm2+ ion exhibits a broad absorption band in the ultraviolet-visible region due to its 5d state absorption, which can be tuned by crystal field effects and co-doping with other ions without causing self-absorption during 4f→4f emission transitions. Sm2+ ion also holds significant research interest in fieldsIntroductionSm2+ ion exhibits a broad absorption band in the ultraviolet-visible region due to its 5d state absorption, which can be tuned by crystal field effects and co-doping with other ions without causing self-absorption during 4f→4f emission transitions. Sm2+ ion also holds significant research interest in fields such as fluorescence lighting, photocatalysis, scintillation, temperature sensing, pressure sensing, and radiation dose monitoring. Fluorosilicate glasses doped with Sm2+ ions have promising applications in optical storage and information encryption. However, the efficient reduction of Sm3+ ion to Sm2+ ion remains a challenge due to the relatively low reduction potential of Sm3+/Sm2+. This paper proposes a simple and cost-effective method for preparing Sm2⁺-doped fluorosilicate glass in ambient air atmosphere.MethodsThe nominal base molar composition was 52SiO2-16Al2O3-6AlF3-7.5BaF2-18NaF-0.5Sm2O3. Al particles were added to a raw material at different mass fractions (i.e., 0%, 0.04%, 0.08%, 0.20%, 0.60%, and 0.80%, respectively). 25 g of analytical-grade raw material was mixed in required proportions and ground in an agate mortar for 15 min. The ground mixed material was placed in an alumina crucible covered with alumina and graphite plates and heated in a high-temperature elevator furnace in air at 1 550 ℃ for 30 min. Afterwards, the molten glass was poured onto a graphite plate and rapidly pressed flat using a stainless steel mold to form glass samples. These glass samples were labeled as G0, G0.04, G0.08, G0.20, G0.60, and G0.80, corresponding to the amount of elemental Al added in the raw materials. Finally, the glass samples were cut and polished to a thickness of 1 mm for the spectral measurements.To investigate the effect of annealing temperature on the stability of Sm2+ ion, the samples G0.04 and G0.60 were selected for heat-treatment at 440, 460, 480, 500 and 520 ℃, respectively. We also investigated the effect Sm2+ doping concentration on the luminescence properties of glass samples. To ensure the effective reduction of Sm ions, the concentration of Sm ions in the glass samples was varied at a metallic Al content of 0.80%. The nominal molar composition of the glass was 52SiO2-16Al2O3-6AlF3-7.5BaF2-18NaF-xSm2O3 (i.e., x=0, 0.062, 0.125, 0.250, 0.500, and 1.000, respectively).Results and discussionAt Sm doping amount of 1% (in mole fraction), the characteristic emission of Sm2+ increases, while that of Sm3+ decreases with increasing Al content in the raw materials. At Al doping content of 0.60% (in mass fraction), the characteristic emission peak of Sm3+ ion completely disappears. These results demonstrate that the incorporation of metal Al during glass melting enables efficient, stable and controllable conversion of Sm3+ ion to Sm2 ion.At Al doping content of 0.04%, no crystallization peaks appear in either the original sample or the heat-treated samples at various temperatures. However, at Al doping content of 0.60%, the crystallization peaks appear even before heat-treatment, corresponding to the diffraction plane (220) of Si. The addition of metallic Al in the raw materials can affect the crystallization behavior of the glass. The sample G0.04 exhibits a dramatic decrease in the fluorescence intensity as the heat treatment temperature increases. During this process, a reversal phenomenon occurs in the relative intensities of the fluorescence peaks at 600 nm and 683 nm.This indicates that some of the Sm2+ ions in the G0.04 sample were oxidized during the heat treatment process. In contrast, for the sample G0.60, the relative intensities of the fluorescence peaks at 683 nm and 600 nm remain unchanged after heat- treatment at various temperatures. An increase in Al doping content contributes to maintaining the stability of the Sm2+ valence state at higher temperatures. This phenomenon may be attributed to the formation of a number of low-valence silicon species surrounding Sm2+ ions in the glass at a greater Al doping content. This arrangement potentially prevents the oxidation of Sm2+ ion by Si4+ ion during heat-treatment.The results show that the transmittance of the glass samples in the 300-600 nm range rapidly decreases, and the absorption bands gradually red-shift towards longer wavelengths as Sm doping content increases. Under 350 nm excitation, the fluorescence intensity at 683 nm gradually increases with increasing Sm doping content. However, it suddenly decreases when the Sm doping concentration reaches 1% (in molar fraction, same hereafter), which can be attributed to concentration quenching. The effect of concentration quenching on the luminescence is further corroborated by the fluorescence lifetime decay curves. As the Sm2+ concentration in the samples increases, the fluorescence lifetime at 683 nm gradually decreases.ConclusionsSm2+-doped fluorosilicate luminescent glasses were prepared via adding an appropriate amount of metallic aluminum as a reducing agent in raw materials. The results showed that Sm3+ could be fully reduced when Al doping content reached 0.60% (in mass fraction, same hereafter). Furthermore, the influence of heat treatment temperature on Sm2+ stability was investigated. The oxidation of Sm2+ during heat-treatment could be prevented at Al doping content of 0.60%. In addition, the impact of Sm2+ doping content on the luminescence performance was also explored. The fluorescence intensity of the sample reached its maximum value at Sm doping content of 0.5% (in molar fraction)..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 09, 2025
- Vol. 53, Issue 3, 586 (2025)
Pyrophotocatalytic Performance of g-C3N4/NaNbO3 Composite Material for Degradation of Mixed Dyes
XU Li, DENG Shuwen, ZHOU Xiaoju, WANG Huifeng, and HU Zhenglong
Extanded AbstractIntroductionWith the rapid development of industry, the discharge of dye wastewater from the textile and printing industries poses a huge threat to aquatic ecosystems and human health. Exploring efficient catalytic technologies to reduce water pollution is highly anticipated. Photocatalysis, as an effiExtanded AbstractIntroductionWith the rapid development of industry, the discharge of dye wastewater from the textile and printing industries poses a huge threat to aquatic ecosystems and human health. Exploring efficient catalytic technologies to reduce water pollution is highly anticipated. Photocatalysis, as an efficient and environmentally friendly advanced oxidation technology for decomposing organic dyes, has attracted considerable attention. However, the low utilization rate of solar energy and severe photogenerated carrier recombination restrict the practical application of photocatalysis. In addition to solar energy, the thermal energy generated by cold-hot alternation can be also used as a clean and renewable energy source to induce positive and negative charges and generate pyroelectric potential, thereby achieving pyrocatalysis. Combining pyrocatalysis with photocatalysis can simultaneously collect solar energy and alternating heat energy, and the pyroelectric potential can serve as an internal driving force for dissociating photo generated exciton. This work constructed g-C3N4/NaNbO3 composite materials for the absorption of g-C3N4 to visible light to enhance the utilization efficiency of sunlight. The Mott-Schottky curve was obtained by electrochemical workstation to analyze the conduction type and flat band potential of g-C3N4 and NaNbO.MethodsA hydrated NaNbO3 sample was obtained via hydrothermal reaction at 160 ℃ for 4 h with Nb2O5 and NaOH as raw materials. The hydrated NaNbO3 prepared was then mixed, ground with a certain mass of melamine powder (in a mass ratio of 1:2), and sintered at 500 ℃ for 2 h to obtain g-C3N4/NaNbO3 composite material. The phase, morphology, and optical properties of the product was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet-visible spectroscopy (UV-Vis). The pyrophotocatalytic performance of g-C3N4/NaNbO3 composite materials was evaluated via degrading mixed dyes (i.e., methylene blue MB, methyl orange MO, rhodamine RhB, and acid orange AO7) under light irradiation and cold-hot cycling. The environmental adaptability of g-C3N4/NaNbO3 composite materials was analyzed by changing the concentration, pH value, and water source of the mixed dye solution. The stability of g-C3N4/NaNbO3 composite material was estimated through five repeated uses and the XRD patterns before and after use. The influence of g-C3N4/NaNbO3 on the degradation performance of the mixed dyes was analyzed via adding different active substance trapping agents, and the main active species in the catalytic reaction was determined. The work function was calculated based on density functional theory (DFT) to analyze the electron transfer after contacting g-C3N4 and NaNbO3.Results and discussionThe g-C3N4/NaNbO3 composite material prepared by a two-step method of hydrothermal and mixed sintering is sheet-like g-C3N4 covering the surface of NaNbO3 nanorods with the diameters of 100-300 nm. The photocatalytic degradation efficiencies of g-C3N4, NaNbO3, and g-C3N4/NaNbO3 composite materials for RhB are 19%, 71%, and 84%, respectively. Combined with the pyroelectric catalysis, the photocatalytic efficiency of g-C3N4/NaNbO3 increases to 97.3%. The results show that the formation of g-C3N4 and NaNbO3 composites can enhance the photocatalytic performance, and the pyroelectric potential generated by temperature fluctuations can further separate the photo-generated electron hole pairs, thus improving the photocatalytic degradation efficiency. Under illumination and cold-hot cycling, g-C3N4/NaNbO3 exhibits a pyrophotocatalytic degradation efficiency of 96.9% for mixed dyes, with a degradation reaction rate of 0.038 6 min-1. The degradation efficiency of g-C3N4/NaNbO3 decreases with the increase of initial concentrations of mixed dye solution (i.e., 2×10-5 mol/L, 4×10-5 mol/L, 6×10-5 mol/L and 8×10-5 mol/L). The pyro-photocatalytic degradation efficiency of the mixed dye is 96.9%, 70.8%, and 54.3% when the pH value of the solution is 2.6, 7.1 and 11, respectively, indicating that g-C3N4/NaNbO3 composite catalyst is suitable for working in acidic and neutral environments. Also, g-C3N4/NaNbO3 composite material has a better catalytic activity in deionized water and tap water, while its pyrophotocatalytic performance reduces in river water and lake water. The experimental results of adding sacrificial agents show that ·O2−, ·OH, and h+ are all active substances in the thermal electric photocatalytic degradation, among which ·O2− and ·OH play a particularly significant role in the catalytic degradation. The results of UV-Vis spectra, the Mott-Schottky curve and DFT calculations indicate that g-C3N4/NaNbO3 composite material broadens the absorption range of the solar spectrum, forms an S-type heterojunction, and the pyroelectric potential generated by the pyroelectric effect promotes the dissociation of photo generated carriers, thus improving the pyrophotocatalytic performance.ConclusionsThe constructed g-C3N4/NaNbO3 composite material utilized a wide solar spectral absorption range and a photothermal effect of g-C3N4. The formation of S-type heterojunction between g-C3N4 and NaNbO3 was conducive to the separation and migration of photo generated carriers. Also, the pyroelectric potential induced by temperature fluctuation could result in band bending, and further promoted the separation of photo generated carriers in NaNbO3, demonstrating an enhanced pyrophotocatalytic performance. This work could provide an efficient catalyst that simultaneously utilized solar energy and environmental thermal energy to achieve sewage treatment and environmental remediation..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 20, 2025
- Vol. 53, Issue 3, 594 (2025)
Effect of Boron Content on Microstructure and Electromagnetic Properties of SiBCN Ceramics
CHEN Pingan, HONG Sizeng, LI Xiangcheng, ZHU Yingli, and CHEN Fu
IntroductionAn issue of electromagnetic pollution has escalated with the proliferation of electronic devices, thus posing a significant threat to human health and electronic equipment. Consequently, there is an increasing interest in materials possessing robust electromagnetic wave absorption capabilities. Based on theIntroductionAn issue of electromagnetic pollution has escalated with the proliferation of electronic devices, thus posing a significant threat to human health and electronic equipment. Consequently, there is an increasing interest in materials possessing robust electromagnetic wave absorption capabilities. Based on the absorption mechanisms of electromagnetic wave materials, they can be categorized into dielectric loss and magnetic loss types. The loss mechanisms of magnetic loss materials encompass damping and hysteresis losses. Dielectric loss materials absorb electromagnetic waves through polarization and electrical conductivity losses, typically having elevated dielectric constants. Such materials include ferroelectrics, metal oxides, and inorganic ceramics. Polymer-derived ceramics (PDCs) represent a pivotal technology for the design and fabrication of functional ceramics. This methodology effectively harnesses the advantages of both polymer and ceramic materials. In contrast to conventional ceramic preparation techniques that consume energy, PDCs enable the production of ceramic materials with tunable elemental compositions and controllable crystalline structures through meticulous design and synthesis of the molecular structures of polymer precursors, coupled with precise control in the pyrolysis process. In this paper, polyborosilazanes with different boron contents were synthesized via modulating the quantity of added boron source. The impact of boron content on the structure and properties of polyborosilazanes and the phase composition/microstructure of ceramics was investigated.Methods20 g of n-hexane was added to a reaction flask in ice bath. Methyl dichlorosilane, vinylmethyl dichlorosilane, boron trichloride, and hexamethyldisilane were sequentially added to the reaction flask at different molar ratios. The mixture was stirred in an argon atmosphere for 24 h. The temperature was then raised to 100 ℃ and maintained for 3 h to remove n-hexane and other by-products. Subsequently, the temperature was further increased to 160 ℃, and maintained for 3 h. The mixture was subjected to three cycles of filtration to obtain a light yellow resin-like polyborosilazane. A series of polyborosilazanes with different boron contents were prepared at different amounts of boron trichloride added. The samples synthesized with boron and nitrogen in a molar ratio of 1:6, 1.3:6.0, and 1.5:6.0 were named as P-BTC-1, P-BTC-1.3, and P-BTC-1.5, with boron contents of 3%, 4%, and 5% (in mass), respectively. The obtained precursor samples were subjected to curing treatment. The curing conditions involved heating in an argon atmosphere at a rate of 2 ℃/min at 280 ℃ for 2 h. Afterwards, the cured samples were heated in an argon atmosphere at a rate of 5 ℃/min at 1000 ℃ for 1 h, and then heated at a rate of 2 ℃/min at 1600 ℃, for 2 h to obtain samples P-BTC-1-1600, P-BTC-1.3-1600, and P-BTC-1.5-1600, respectively.The chemical bonds and functional groups in the samples were identified by a model Vertex 70 Fourier transform infrared spectrometer (FT-IR, Bruker Co., Germany). 1H, 13C, and 11B were determined by a model Avance NEO 600 nuclear magnetic resonance spectrometer (NMR, Bruker Co., Germany). The phase composition of the ceramic samples was determined by a model X'Pert MPD Pro X-ray diffractometer (XRD, Philips Co., the Netherlands) with Cu Kα radiation source, scanning angles ranging from 10° to 90°. The microstructure of the ceramic samples was analyzed by a model 400 Nano scanning electron microscope (SEM, Nova Co., USA), and the elemental composition analysis of the samples was performed by an energy dispersive spectrometer (EDS, INCA Energy Co., UK). The thermal decomposition process of the polyborosilazane was analyzedby a model STA 449 F3 thermal analyzer (Netzsch Co., Germany). The electromagnetic parameters of the materials were tested by a model E5071C vector network analyzer (Keysight Tech., Co., USA).Results and discussionA series of polyborosilazanes were synthesized via controlling the amount of boron, resulting in SiBCN ceramics with different atomic compositions. Boron effectively suppresses the fracture of Si—N bonds and the formation of Si—C bonds, inhibits the decomposition of Si3N4 and the generation of SiC as well as facilitates the transformation of amorphous carbon into graphite carbon, thereby increasing the proportion of graphite carbon in SiBCN ceramics. The polarization losses generated by various dielectric crystals such as Si3N4, SiC and graphite carbon enhance the electromagnetic wave absorption performance of SiBCN ceramics. At a boron content of 5% (in mass), the minimum reflection loss reaches -55.67 dB at 8 GHz for a thickness of 3.5 mm.Conclusions1) In the precursor synthesis process, the precursor structure became more stable with an increase in boron content, mainly composed of chemical bonds such as Si—N, B—N, Si—C, Si—H, N—H, and C—H. The ceramic yield increased from 56% to 66.7%.2) After heat treatment at 1600 ℃, boron in polyborosilazanes suppressed the decomposition of Si₃N₄ and the formation of SiC in SiBCN ceramics, and enabled the control of the conductive phase and dielectric loss phase in SiBCN ceramics, thereby enhancing the impedance matching performance of the ceramics to electromagnetic waves. The polarization losses generated by various dielectric materials such as Si3N4, SiC and graphite carbon further enhanced the electromagnetic wave attenuation performance of SiBCN ceramics. At a boron content of 5%, SiBCN ceramics exhibited a minimum reflection loss of -55.67 dB at 8 GHz for a thickness of 3.5 mm, indicating that SiBCN ceramics could be an excellent candidate material in the field of electromagnetic wave absorption..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 17, 2025
- Vol. 53, Issue 3, 607 (2025)
Corrosion Resistance of Gd-doped La2(Zr0.7Ce0.3)2O7 Ceramic Materials to V2O5 + Na2SO4 Molten Salts
QU Xiaofu, XIE Min, SONG Xiaowei, ZHANG Yonghe... and WANG Zhigang|Show fewer author(s)
IntroductionOne of the major reasons for the failure of thermal barrier coating materials is the corrosion caused by the reaction between aeroengine thermal barrier coating materials (TBC) and V2O5+Na2SO4 in fuel under high-temperature service conditions. Conventional TBCs are difficult to meet the increasingly harsh hIntroductionOne of the major reasons for the failure of thermal barrier coating materials is the corrosion caused by the reaction between aeroengine thermal barrier coating materials (TBC) and V2O5+Na2SO4 in fuel under high-temperature service conditions. Conventional TBCs are difficult to meet the increasingly harsh high-temperature service environment. It is thus necessary to develop new and more corrosion-resistant thermal barrier coating materials. Among the materials to replace conventional TBC, La2(Zr0.7Ce0.3)2O7(LZC) ceramics are considered as potential TBC candidates due to their high sintering resistance, low thermal conductivity and high thermal expansion coefficient. Also, the thermal conductivity of LZC can be effectively reduced by using Re3+ with large mass and small radius doping at La3+. Therefore, the modified (La0.5Gd0.5)2(Zr0.7Ce0.3)2O7 (LGZC) doped with Gd3+, which is a rare-earth element and has a smaller ionic radius, can further reduce the thermal conductivity of the material and improve the mechanical properties of the material through fine-grain strengthening. However, the existing reports on the hot corrosion resistance of V2O5+Na2SO4 molten salt of LZC and LGZC materials are more limited to the strong corrosive properties at < 1050 ℃, while the actual service temperature of the coating often exceeds 1200 ℃.MethodsIn this work, ZrO2, La2O3, Gd2O3, CeO2 and other oxide powders were used as raw materials, and LZC and LGZC ceramic samples were prepared by a high-temperature solid-state reaction method. A typical mixed salt of V2O5+Na2SO4 (in a molar ratio of 1:1) was used as a corrosive medium. V2O5 and Na2SO4 powders were mixed. The mixed powder was evenly spread on the surface of the ceramic sample at a concentration of 10 mg/cm2, and then the coated ceramic sample was placed in a box-type resistance box and treated at 900, 1000, 1100 and 1250 ℃ for 5 h for thermal corrosion, respectively.The phase composition of LZC and LGZC samples before and after hot corrosion was determined by a model D8 X-ray diffractometer (XRD, Bruker Co., Germany). The microstructure and morphology were characterized by a model Sigma 500scanning electron microscope (SEM, ZEISS Co., Germany) equipped with energy dispersive spectrometer (EDS).Results and discussionLZC and LGZC ceramic specimens with a single pyrochlorite structure were synthesized. After corrosion, the diffraction peak of LGZC reduces, compared to that of LZC ceramic samples. There are mainly (La, Ce, Gd) VO4, t-ZrO2 and m-ZrO2 on the surface according to the SEM images and EDS results. The content of (La,Ce,Gd) VO4 increases with the increase of temperature in the range of 900-1100 ℃, and decreases after corrosion at 1250 ℃. From the micromorphology after corrosion, the ceramic surface of LZC specimens after corrosion at 900-1100 ℃ is mainly rod-like grains and granular clusters, while LGZC has more rod-like grains rather than granular grains. After corrosion at 1250 ℃, the surface of the LGZC specimen is granular crystals with intracrystalline pores. LZC and LGZC both forman obvious corrosion layer at 900-1100 ℃, and the thickness of the corrosion layer increases with the increase of temperature, and the corrosion layer becomes the thickest at 1100 ℃ (i.e., 38 μm and 35 μm), respectively. However, after corrosion at 1250 ℃, the corrosion layer does not form and the corrosion depth decreases, and the darker molten salt penetrates further downward, showing two completely different microscopic morphologies. Also, the corrosion depth of LGZC is smaller than that of LZC at different temperatures.ConclusionsLZC and LGZC ceramic materials reacted with V2O5+Na2SO4 at 900-1100 ℃ to form a relatively dense corrosion reaction layer, and the corrosion reaction degree increased with the increase of temperature, and the reaction was most intense at 1100 ℃. The hot corrosion mechanism of LZC and LGZC ceramic materials at 900-1250 ℃ followed Lewis’s acid-base law and Gibbs's free energy. The relative alkalinity of LGZC decreased, and the corrosion depth of LGZC was smaller than that of LZC at different temperatures due to the doping of Gd2O3. The corrosion resistance of ceramic materials was reflected in the corrosion depth, the smaller the corrosion depth, the stronger the corrosion resistance of the ceramic materials. Therefore, LGZC was more resistant to V2O5+Na2SO4 corrosion than LZC in this case. After the temperature increased to 1250 ℃, neither of the two samples formed a dense corrosion reaction layer, and the corrosion depth was smaller than that after corrosion at 1100 ℃ because the viscosity of NaVO3 decreased with the increase of the corrosion temperature to 1250 ℃ and blocked the pores in a short time, thus preventing a further penetration of the molten salt..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 16, 2025
- Vol. 53, Issue 3, 620 (2025)
Effect of Configuration Entropy on Resistance of Rare-earth Zirconate Ceramics to CaO-MgO-Al2O3-SiO2
WANG Xiaobo, HE Zhiyong, YANG Xiao, WANG Feng... and ZHANG Qifu|Show fewer author(s)
IntroductionThermal barrier coatings (TBCs) are capable of effectively isolating high-temperature gases, protecting the turbine blade matrix, reducing blade surface temperatures, and consequently enhancing aero engine thrust. TBCs with a thickness ranging from 100 to 500 m in conjunction with internal turbine blade cooIntroductionThermal barrier coatings (TBCs) are capable of effectively isolating high-temperature gases, protecting the turbine blade matrix, reducing blade surface temperatures, and consequently enhancing aero engine thrust. TBCs with a thickness ranging from 100 to 500 μm in conjunction with internal turbine blade cooling can decrease the surface temperature of the superalloy by 100-300 ℃. In recent decades, yttrium-stabilized zirconia (YSZ) containing 7%-8% (by mass) is widely utilized as a material for thermal barrier coatings (TBCs) due to its superior properties. With the increasing demands for thrust-to-weight ratio, weight reduction, and stability in aviation turbine engines, the surface temperature of blade is expected to surpass 1300 ℃. When the operating temperature exceeds 1200 ℃, the YSZ coating undergoes the phase transformation and sintering. For cooling, it transitions from the tetragonal phase to the monoclinic phase, leading to coating volume expansion. Moreover, calcium- magnesium-alumino-silicate (CMAS) compounds derived from dust, sand, and volcanic ash can melt on the TBC surface, causing a severe erosion and ultimately leading to coating failure. The existing CMAS erosion becomes a challenge for TBCs. It is thus necessary for the evolving requirements of future turbine engine development to develop novel thermal barrier coating materials. Recent studies focus on new TBCs materials, including rare-earth zirconates, phosphates, and hafniates, which exhibit an enhanced CMAS erosion resistance, compared to YSZ. In this paper, the CMAS erosion resistance of rare-earth zirconates was investigated.MethodsY2Zr2O7 (H1), (Y0.5Gd0.5)2Zr2O7 (H2), (Y0.33Gd0.33Er0.33)2Zr2O7 (H3), (Y0.25Gd0.25Er0.25Yb0.25)2Zr2O7 (H4), (Y0.2Gd0.2Er0.2 Yb0.2Lu0.2)2Zr2O7 (H5) were synthesized by a solid-state synthesis method at 1650 ℃ for 10 h. The glass phase was prepared according to the classical composition of 33CaO-9MgO-13Al2O3-45SiO2. In the CMAS erosion resistance test, CMAS powder was uniformly applied to ceramic discs at a density of 20 mg/cm2. The discs were then placed in a crucible and maintained in an air atmosphere at 1300 ℃ for 5 h to conduct the erosion experiment. Subsequently, the samples were sectioned along the centerline, and the cross-sections were ground and polished to achieve a surface roughness of 1 μm, facilitating the observation of the morphology and thickness of the eroded layer. To analyze the reaction products of different zirconate ceramics during CMAS erosion, CMAS powder was mixed with five types of zirconate ceramic powders at a mass ratio of 1:1 and heated in an air atmosphere at 1300 ℃ for 5 h.Results and discussionAll the five rare-earth zirconate ceramics exhibit a single, defective fluorite structure. After five rare-earth zirconate ceramics are eroded at 1300 ℃ for 5 h, the CMAS erosion depths are ranked as H2 > H3 > H1 > H4 > H5. Despite the fact that the CMAS corrosion resistance of rare-earth zirconate ceramics does not improve with increasing entropy, the CMAS corrosion resistance of high-entropy rare-earth zirconate ceramics is superior to that of low- and medium-entropy ceramics. After heating at 1300 ℃ for 5 h, the erosion depth of H5 is only 22 μm. The mechanism of resistance to CMAS erosion in rare-earth ceramics can be elucidated through the "dissolution-reprecipitation" mechanism. Upon interaction between rare-earth zirconate ceramics and CMAS, RE3⁺ and Zr₄⁺ dissolve from the ceramic matrix into the CMAS melt. RE3⁺ ions with larger ionic radii (such as Gd3⁺ and Y3⁺) react with Ca2⁺ and Si₄⁺ in the CMAS to form RE-apatite. Conversely, RE3⁺ ions with smaller ionic radii (such as Er3⁺, Yb3⁺, and Lu3⁺) preferentially incorporate into ZrO2 lattice, forming a fluorite-structured RE-ZrO. When the precipitation rates of RE-apatite and RE-ZrO2 exceed the erosion rate of CMAS, a dense protective layer forms, effectively preventing further CMAS erosion. The average rare-earth ion radius and optical basicity both affect the corrosion resistance of five rare-earth zirconate ceramics to CMAS.ConclusionsY2Zr2O7, (Y0.5Gd0.5)2Zr2O7, (Y0.33Gd0.33Er0.33)2Zr2O7, (Y0.25Gd0.25Er0.25Yb0.25)2Zr2O7, and (Y0.2Gd0.2Er0.2Yb0.2Lu0.2)2Zr2O7 were synthesized by a high-temperature solid-state reaction method. These five rare-earth zirconate ceramics exhibited a defective fluorite crystal structure. The analysis of the mechanism of resistance to CMAS erosion in these ceramics revealed that the erosion layer consisted of two distinct layers, i.e., an infiltration layer and a reprecipitation layer. The reprecipitated layer primarily comprised near-spherical fluorite-structured RE-ZrO2 and RE-apatite crystalline pillars, forming a dense barrier that prevented further CMAS penetration into the substrate. The impact of configurational entropy on the CMAS corrosion resistance of these five rare-earth zirconate ceramics was investigated. The CMAS corrosion depths were found to be H2 > H3 > H1 > H4 > H5, and H5 exhibited the optimum CMAS corrosion resistance, showing a corrosion depth of only 22 μm after heating at 1300 ℃ for 5 h. The findings indicated that while the resistance to CMAS erosion in rare-earth zirconate ceramics did not strictly increase with increasing configurational entropy, high-entropy rare-earth zirconate ceramics demonstrated a superior resistance. compared to low- and medium-entropy counterparts. In addition, the CMAS corrosion resistance of rare-earth zirconate ceramics was influenced by both configurational entropy and the radius of rare earth ions. A concept of optical basicity was introduced to evaluate the corrosion resistance of five rare-earth zirconate ceramics against CMAS. Under identical conditions, a larger optical basicity difference (ΔΛ) between the rare earth zirconate ceramics and CMAS resulted in a higher reaction rate and deeper erosion by CMAS. The optical basicity could serve as a valuable reference for selecting new thermal barrier coating materials..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 16, 2025
- Vol. 53, Issue 3, 630 (2025)
Determination of Firing Temperature of Low-Temperature Ceramics by Rod Expansion Method
YANG Changan, CAO Zhichao, LUO Hongjie, ZHU Jianfeng... and SHI Pei|Show fewer author(s)
IntroductionThermal expansion analysis is a most widely used method for determining the firing temperature of ancient ceramics, which infers the original firing temperature of ancient ceramics via analyzing the inflection point of the thermal expansion curve. However, for the pottery at an original firing temperature tIntroductionThermal expansion analysis is a most widely used method for determining the firing temperature of ancient ceramics, which infers the original firing temperature of ancient ceramics via analyzing the inflection point of the thermal expansion curve. However, for the pottery at an original firing temperature that is lower than the formation temperature of glass phase, the inflection point on the thermal expansion curve is actually the formation temperature of glass phase rather than original firing temperature. To solve a problem of inaccurate determination of low-temperature pottery firing temperature by a thermal expansion method, clay samples fired at different temperatures were prepared with clay as a raw material, and analyzed by X-ray diffraction (XRD), synchronous comprehensive thermal analyzer (TG-DTA), and scanning electron microscopy (SEM). In addition, the first derivative curve corresponding to the top rod thermal expansion curve of clay samples fired at different temperatures fitted to the dehydroxylation expansion peak of kaolinite, and the relationship curve between the dehydroxylation expansion peak of kaolinite and the original firing temperature was also obtained.MethodsA clay as a raw material was processed by grinding, screening, drying, pressing, and sintering at different temperatures. Afterwards, the cylindrical samples with a diameter of 5 mm and a length of 25 mm were prepared with clay by polishing. The thermal behavior of clay raw materials was determined by thermogravimetry-differential thermal analysis (TG-DTA). The chemical composition, phase composition, and microstructure of the raw materials and the samples fired at different temperatures were characterized by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The linear expansion or contraction process of the samples during the refiring process at different firing temperatures was tested by a thermal expansion instrument.Results and discussionThe XRF spectra show that the chemical composition of raw materials and samples at different firing temperatures is the similar. The XRD patterns and TG-DTA analysis of raw materials indicate that the dehydroxylation of kaolinite occurs at 300-600 ℃. Based on the XRD patterns, the phases in clay samples fired at different temperatures are consistent with those in clay raw materials. At < 900 ℃, the characteristic diffraction peak intensity of kaolinite in clay samples fired at different temperatures changes with the increase of firing temperature. The SEM images show that the typical layered structure of kaolinite in clay raw material begins to lose its structural hydroxyl groups and gradually transforms into metakaolinite, and this transformation gradually deepens as the firing temperature increases. The results of the thermal expansion test of clay samples fired at different temperatures indicate that there is a linear relationship between the dehydroxylation expansion peak of kaolinite on the first derivative curve of thermal expansion and its original firing temperature. This linear relationship can be expressed by a formula, i.e., A= -2.278 481 7×10-6T+3.337 870 9×10-3. To verify the accuracy of the formula, the thermal expansion test of clay samples is conducted using a push rod, and the calculated firing temperature is not significantly different from its original firing temperature, which are 41℃ and 35 ℃, respectively. The push rod thermal expansion method can be thus used to determine the original firing temperature of low-temperature pottery made from clay.ConclusionsBefore the glass phase formation temperature, kaolinite in the sample could lose the hydroxyl group in its structure and gradually transform into metakaolinite as the firing temperature increases, thus causing the expansion of the thermal expansion curve. The intensity of the thermal expansion peak of kaolinite dehydroxylation gradually decreased as the firing temperature increased. The first-order derivatives of the thermal expansion curves of the samples fired at different temperatures were taken, fiting the kaolinite dehydroxylation peak. This linear relationship with the firing temperature could be expressed by a formula, i.e., A= -2.278 481 7×10-6T+3.337 870 9×10-3. The clay samples fired at 550 ℃ and 650 ℃ were used for the thermal expansion curves, respectively. The clay samples fired at 550 ℃ and 650 ℃ were used to verify the reasonableness of the fitting formula. It was indicated that the firing temperature of low-temperature pottery made of clay could be determined by the top bar thermal expansion method..
Journal of the Chinese Ceramic Society
- Publication Date: Dec. 31, 2024
- Vol. 53, Issue 3, 640 (2025)
Preparation and Microwave Absorption Properties of Spinel/Rock Salt (Fe0.2Co0.2Ni0.2Cu0.2Zn0.2)CoxOy High-Entropy Ceramics
WANG Zhongyi, REN Yumei, YANG Shuai, XI Tong... and ZHANG Rui|Show fewer author(s)
IntroductionWith the rapid development of wireless communication technology, electromagnetic waves are regarded as a main medium for energy and information transmission. Absorbing materials, as a focus of scientific research in recent years, play a key role in effectively reducing electromagnetic radiation pollution inIntroductionWith the rapid development of wireless communication technology, electromagnetic waves are regarded as a main medium for energy and information transmission. Absorbing materials, as a focus of scientific research in recent years, play a key role in effectively reducing electromagnetic radiation pollution in the environment, thereby reducing the negative effect of electromagnetic waves. The design of absorbing materials follows the principles of "thin, light, wide, and strong" to meet practical applications. At present, there are various types of absorbing materials, mainly including magnetic metals, polymer based composite materials, ferrites, and carbon-based materials. However, all the materials have their limitations. For instance, magnetic materials have a superior performance, but they have a poor oxidation resistance, which are prone to eddy current losses, thus affecting the absorption efficiency. The preparation cost of polymer-based composite materials is high, and their application fields are limited. Ferrite materials have an insufficient temperature stability and a high surface density. In addition, carbon-based materials suffer from poor impedance matching and narrow absorption frequency bands. These inherent limitations hinder a widespread applicability of absorbing materials in diverse application scenarios. Therefore, developing novel absorbing materials with superior oxidation resistance and high-temperature stability has an important practical significance.MethodsHigh-entropy multiphase oxide ceramics was prepared by a solid-state reaction method. In the preparation process, FeO, CoO, NiO, CuO, ZnO and Co2O3 as raw materials in a molar ratio of 1:1:1:1:1:5 were ground with anhydrous ethanol in a mill at 200 r/min for 8 h, and then dried at 80 ℃ to obtain a mixed powder. Subsequently, 8 g of the mixed powder was pressed into a round billet with a diameter of 30 mm at 10 MPa. The obtained round billet was then heated and reacted in a model BR-12N muffle furnace at different temperatures (i.e., 800, 900, 1000 ℃ and 1100 ℃) for 6 h to obtain the samples of (Fe0.2Co0.2Ni0.2Cu0.2Zn0.2)CoxOy high-entropy ceramics (HEO), which were named samples HEO-800, HEO-900, HEO-1000, and HEO-1100, respectively.Results and discussionThe results show that the obtained samples HEO-800, HEO-900, HEO-1000, and HEO-1100 all exhibit spinel and rock salt phases, as well as pore structures and irregular blocks. The degree of crystallization gradually increases with increasing temperature, which can be attributed to the accelerated diffusion of atoms at the interface and the gradual increase in grain size due to the presence of oxygen vacancies. The XPS analysis indicates that the high-entropy multiphase oxide ceramics sintered at different temperatures all have oxygen vacancies, and the maximum oxygen vacancies occur at 900 ℃. The conductivity test shows that the sample HEO-900 has the maximum conductivity. The electromagnetic wave absorption test results reveal that the RLmin values of the samples HEO-800, HEO-900, HEO-1000, and HEO-1100 are -9.85, -36.14, -13.73 dB, and -4.61 dB, respectively. The sample HEO-900 obtained via sintering at 900 ℃ has the optimum absorbing property. Except for the sample HEO-900, the reflection loss of other samples is not high mainly due to the weak dielectric loss caused by low oxygen vacancy, while the magnetic loss is opposite to the dielectric loss. The magnetic loss and dielectric loss synergistically promote the improvement of absorption performance of the material. In addition, the impedance matching area also firstly increases and then decreases as the temperature increases. The impedance area of the sample HEO-900 is relatively large, indicating that there are more electromagnetic waves incident on the interior of the material and the absorption efficiency increases.ConclusionsThe results indicated that oxygen vacancies were easily generated in (Fe0.2Co0.2Ni0.2Cu0.2Zn0.2)CoxOy high-entropy ceramics due to the multivalent state and multiple transformations of element Co, which was conducive to electron transfer. The presence of multiphase structure and oxygen vacancies increased the dielectric loss of the material and the interface polarization and defect polarization of the system, thus significantly improving the absorption capacity of electromagnetic waves. This study found that the sample HEO-900 sintered at 900 ℃ had the optimum absorption performance (i.e., the RLmin value of -36.14 dB and an optimal bandwidth of 2.86 GHz at a matching thickness of 3.0 mm and a frequency of 9.37 GHz)..
Journal of the Chinese Ceramic Society
- Publication Date: Dec. 27, 2024
- Vol. 53, Issue 3, 647 (2025)
Preparation of Al2O3-ZrO2 Nanostructured Amorphous Composites by Phase Transformation Assisted Flash Sintering
WANG Shuhuai, WANG Jianglin, YANG Yongkang, JIA Ziqi... and XU Xiqing|Show fewer author(s)
IntroductionNanostructured amorphous composites are novel materials composed of nanostructured amorphous matrix and precipitated nanocrystalline phases. However, their preparation requires large and expensive equipment. Flash sintering (FS) ensures a rapid densification at low temperatures and offers an effective approIntroductionNanostructured amorphous composites are novel materials composed of nanostructured amorphous matrix and precipitated nanocrystalline phases. However, their preparation requires large and expensive equipment. Flash sintering (FS) ensures a rapid densification at low temperatures and offers an effective approach for the preparation of nanostructured amorphous composites with simple and economical equipment. The amorphous powders by FS show denser microstructures, compared to the crystalline powders by FS. The phase transition from a metastable phase to a stable phase during the sintering process can expedite atomic diffusion and particle rearrangement, thereby promoting structural densification. In this paper, nanostructured amorphous powders in three systems, i.e., Al2O3-La2O3(AL), Al2O3-La2O3-ZrO2(ALZ) and Al2O3-ZrO2(AZ), were prepared by a sol-gel method and densified into dense bulks via flash sintering. The flash sintering behaviors of these different systems were compared, and the promotion of phase transformation on the densification was discussed.MethodsThe three systems of amorphous powders, i.e., AL, ALZ, and AZ, were synthesized via a sol-gel method and subsequently calcined at 600 ℃ for 1 h. Before flash sintering, the powders were consolidated into cylindrical green bodies (ϕ8 mm×2.3 mm) through uniaxial compression molding at 500 MPa. A platinum wire and electrodes were used to establish electrical connections between a DC power supply and the sample in electric fields of 1000 V/cm and 1600 V/cm, and a heating rate of 10 ℃/ min. At a predetermined maximum current of 0.26 A/cm2, the control mode of the power supply was swiftly switched from voltage control to current control. The voltage and current both were measured by a digital electrical multimeter. After continuous energizing for 60 s, the furnace and power supply both were powered off and naturally cooled to ambient temperature.Results and discussionThe powders of AL, AZ and ALZ all exhibit weak and broad scattering peaks without any detectable crystallization peaks, indicating their amorphous nature. The average particle sizes of the AL, AZ and ALZ powders are 13.7, 6.7 nm and 11.6 nm, respectively. Flash sintering occurs in each system at an electric field intensity of 1000 V/cm with increasing current density. Among the flash-sintered ceramics samples, the sample AZ shows the maximum crystallinity of 69.82% and the relative density of 89%. The crystallinity and relative density of the sample AZ further increase when the electric field intensity increases to 1 600 V/cm. The densification during flash sintering is enhanced by crystallization as crystallization promotes the atomic diffusion and particle rearrangement. Based on the high-resolution transmission electron microscopy images, the uniform precipitation of nanocrystalline phases within an amorphous matrix in the flash-sintered sample AZ with the average particle sizes of 8.74 nm for nanocrystalline regions and 3.15 nm for amorphous regions.ConclusionsThis study conducted an investigation on the flash sintering behavior of three amorphous nanopowders (i.e., AL, AZ and ALZ), and examined the relationship between densification and phase transition. Flash sintering occurred in each nanopowder at an electric field intensity of 1000 V/cm, and the sample AZ exhibited the maximum crystallinity of 69.82% and relative density of 89%. The crystallinity and relative density of the AZ sample further increased to 74.11% and 96%, respectively, when the electric field intensity increased to 1600 V/cm. This study confirmed a positive correlation between crystallization and densification during flash sintering as crystallization and phase transition accelerated atomic diffusion and particle rearrangement, thereby enhancing ceramic densification. The HRTEM images of the sample AZ after flash sintering at 1600 V/cm revealed the uniform precipitation of nanocrystalline phases within an amorphous matrix, indicating that low-temperature rapid preparation of nanostructured amorphous composites was achieved via phase transformation-assisted flash sintering..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 07, 2025
- Vol. 53, Issue 3, 658 (2025)
Modified Seafoam Fibers for Improving Fire Performance of Non-Intumescent Fire Coatings
XUE Yonggang, GAO Jinbao, LIU Yicen, FANG Yunchao, and LI Yan
IntroductionSteel building is a form of construction. Non-intumescent fireproofing materials have superior fireproofing effects and can provide effective fireproofing and thermal insulation protection for steel structures. However, the modification and innovation of non-intumescent fireproofing materials are insufficieIntroductionSteel building is a form of construction. Non-intumescent fireproofing materials have superior fireproofing effects and can provide effective fireproofing and thermal insulation protection for steel structures. However, the modification and innovation of non-intumescent fireproofing materials are insufficient in China at present. Seafoam has a good thermal stability and a low thermal conductivity, having a thermal insulation effect, which can be used as a filler for fireproof coating or fireproof board. Seafoam can effectively improve the fire resistance of fireproof coating or fireproof board. Seafoam mineral fibers dispersed in a low concentration solution can form a stable high-viscosity suspension, so they can be dispersed and modified with other fillers and added to fireproof coating or fireproof board slurry. Therefore, the fire performance of seafoam fiber fireproofing materials can be improved. In this work, a modified seafoam fiber was added to fireproof coatings for improving the fire performance of non-intumescent fireproof coatings. This modified fiber as a kind of modified fiber was prepared via mixing seafoam fiber, magnesium hydroxide fiber and silicon oxide fiber under high-speed mixing and adding polymer modifier. In addition, the physical and chemical properties and fire performance of the finished product were also analyzed.MethodsIn this work, 5-70 mm hydromagnesite fibers were ground in a mill to obtain the fibers with the lengths of < 5 mm. Subsequently, 1-5 mm seafoam fibers and 3-6 mm silicon oxide fibers were selected, and 50% seafoam fibers, 30% hydromagnesite fibers, 8% silicon oxide fibers, 5% organic bentonite, 1% polymer water-absorbent resins, 1% starch ether, 5% hydroxypropyl methyl cellulose ether were mixed as raw materials in a dry mixer for 30 min to obtain the modified seafoam fibers. The modified seafoam fibers were analyzed based on the physical phase characterization. Cement, kaolin, modified fiber, and fire protection additives in different weight ratios were added to the dry mixer and stirred for 300 s, and then an expanded vermiculite was added to the mixer and stirred for 120 s, and six groups of fireproofing coating samples were obtained. Afterwards, the samples were then stirred slowly in a cement sand mixer according to a mass ratio of fireproofing coating:707 emulsion: water of 1.0:0.2:0.8 and mixed for 5 min to make the mixture homogeneous. After mixing, the fire resistance, bond strength and compressive strength of the samples were characterized.Results and discussionBased on the fire resistance test analysis of fireproofing materials doped with six different contents of modified seafoam fibers (i.e., 10%, 12.5%, 15%, 17.5%, 20% and 22.5%), the fireproofing and thermal insulation properties of fireproofing coatings are gradually improved with the increase in the addition of modified seafoam fibers. Their fireproofing and thermal insulation properties enhance with the increase in the doping of modified seafoam fibers, indicating that modified seafoam fibers play a key role in the fireproofing coatings. Seafoam fibers play a key role in fireproof coatings. The fireproof performance is obviously better than that of two commercial fireproof materials. The analysis by X-ray diffraction patterns shows that Mg(OH)2 is added to the modified seafoam fiber. According to the TG-DTG analysis, Mg(OH)2 decomposes into MgO during the heat process, and MgO is a kind of superior heat-insulating and insulating material, indicating that the modified seafoam fibers greatly improve the fire-insulating and heat-insulating performance. The FTIR analysis shows that there are a large number of Si—O—Si bonds in the sample, and that there is a large number of Si—O—Si bonds in the sample. There are a lot of Si—O—Si bonds in the sample, so that the modified seafoam fibers maintain its original adsorption and rheological properties. The appearance and morphology of the fireproof coating after combustion show that the silicon oxide fibers improve the crack resistance of the fireproof coating.ConclusionsIn this paper, the modified seafoam fiber was prepared via mixing seafoam fiber, magnesite fiber, silicon oxide fiber and some polymer modifiers in a certain proportion. The modified seafoam fiber had a better fireproofing and thermal insulation performance, the magnesite fiber could further reduce the thermal conductivity of the material, and the silicon oxide fiber could ensure that the fireproofing coating was not easy to crack. To meet the national standards of bonding strength and compressive strength of the basis, the fireproof coating with 20% of the modified seafoam fibers had the optimum fire insulation performance. At the effective fire prevention time of 185 min, the coating had a bonding strength of 0.042 MPa and a compressive strength of 0.461 MPa. Compared with some other commercial fireproofing materials, the coating had a fireproofing effect and some application prospects..
Journal of the Chinese Ceramic Society
- Publication Date: Dec. 30, 2024
- Vol. 53, Issue 3, 666 (2025)
Progress on B4C-SiC Ceramics Prepared by Reaction Sintering
ZHANG Wei, ZHANG Jin, DUAN Chunlei, GENG Hao, and HAN Yang
Boron carbide-silicon carbide (B4C-SiC) ceramics have the performance of B4C and SiC, which have low density, high melting point, high hardness, high elastic modulus, good wear resistance, high thermal tolerance, excellent chemical stability, etc.. Compared with B4C ceramics, B4C-SiC ceramics possess a higher fracture Boron carbide-silicon carbide (B4C-SiC) ceramics have the performance of B4C and SiC, which have low density, high melting point, high hardness, high elastic modulus, good wear resistance, high thermal tolerance, excellent chemical stability, etc.. Compared with B4C ceramics, B4C-SiC ceramics possess a higher fracture toughness and a lower cost. Compared with SiC ceramics, B4C-SiC ceramics have a higher hardness and a lower density. B4C-SiC ceramics can be widely used in modern high-technology industries, such as aerospace, military, mechanical and automotive engineering, chemical industry, nuclear energy, high-temperature thermoelectric conversion, tribology, aviation, etc. due to their outstanding properties. In particular, the materials with the combination of high hardness and low density are more desirable than the materials without this characteristic. B4C-SiC ceramics are suitable for use as lightweight structural materials and rotating tribo-components.Despite numerous advantages, B4C-SiC ceramics are difficult to sinter to obtain high densification because of the high covalent bond ratios of both B4C and SiC. The existing preparation methods of B4C-SiC ceramics mainly include pressureless sintering, hot-press sintering, and spark plasma sintering. Although these methods can produce dense B4C-SiC ceramics with a good performance, the sintering temperature is relatively high. In order to reduce the sintering temperature of B4C-SiC ceramics, the reaction sintering method is developed to produce B4C-SiC ceramics. The preparation method of reaction sintered B4C-SiC ceramics is similar to that of SiC ceramics produced by reaction sintering, in which the molten Si with an appropriate fluidity infiltrates into a porous green/partially sintered body composed of only B4C, the mixture of B4C and free C, B4C-SiC-C, or B4C-SiC powders at high temperatures. The molten Si infiltrated reacts with C either from free C or B4C to form SiC, the reaction leads to a volume expansion occupying partial pores in the preform. The remaining excess pores in the preform are filled with molten Si after the reaction, making the reaction sintered B4C-SiC ceramics dense. The preparation of reaction sintered B4C-SiC ceramics is actually an in-situ chemical reaction. For the characteristics of reaction sintered B4C-SiC ceramics, B4C, SiC formed, and residual Si particles can interconnect into a uniform and intense three-dimensional network at low sintering temperatures without any applied pressure, and near-net shaped products with zero shrinkage can be produced. Also, fine reactive starting powders capable of being densified are not required, thus reducing the cost of raw materials.The preparation method of reaction sintering is different from other preparation methods to obtain B4C-SiC ceramics. The microstructure of reaction sintered B4C-SiC ceramics has its own characteristics. The core-rim structure occurs in the reaction sintered B4C-SiC ceramics. Firstly, B4C cores surrounded by a thick B12(B, C, Si)3 envelope are formed, and there is an intense bonding between B4C and B12(B, C, Si)3. Until now, there is still a heated debate on the formation mechanisms responsible for B12(B, C, Si)3 rim. The core-rim structure of B4C is formed in B4C-SiC ceramics produced via a conventional reaction sintering route. However, there is no core-rim structure of B4C in the reaction sintered B4C-SiC ceramics prepared by microwaves assisted processing method in Ar-H2 atmosphere. Secondly, When the preform containing α-SiC is used to prepare the reaction sintered B4C-SiC ceramics, the core-rim structure of primary α-SiC surrounded by secondary β-SiC rim also appears besides the core-rim structure of B4C surrounded by B12(B, C, Si)3 rim., SiC grains with different morphologies, i.e., plate-like shape and polygonal shape, can be in-situ generated via depending on the carbon source.The mechanical properties of reaction sintered B4C-SiC ceramics are crucial for their applications, which are affected by many factors, such as phase composition and content, microstructure, raw materials, sintering temperature, etc.. The ratio of B4C to SiC affects the mechanical properties of reaction sintered B4C-SiC ceramics. Moreover, there is some residual phases in the resulting B4C-SiC ceramics, eventually in the presence of excessive C or Si. The addition of excessive C in the green body will lead to insufficient Si to completely react with C, forming residual C. In contrast, residual Si is formed when free C added is insufficient or Si is excessive. The presence of C or Si is not conducive to the mechanical properties of reaction sintered B4C-SiC ceramics. The mechanical properties of reaction sintered B4C-SiC ceramics are related to their microstructure. The morphology and size of grains as well as the characteristics of grain boundaries directly determine the mechanical properties of reaction sintered B4C-SiC ceramics. The kinds and purity of raw materials and the sintering temperature also have an impact on the mechanical properties of reaction sintered B4C-SiC ceramics.Summary and prospectsThe preparation of B4C-SiC ceramics via reaction sintering is a low-cost method, and this route is suitable for large-sized and complex-shaped products. Although significant progress is achieved in the preparation of reaction sintered B4C-SiC ceramics, some challenges still remain in the scientific research and practical application. The reaction sintered B4C-SiC ceramics have reached the industrial production stage; however, the residual Si phase with low hardness and stiffness contained in the B4C-SiC ceramics can lead to a decrease in the performance, restricting their applications in the high-temperature field. New methods and processes still need to be explored to produce low Si or Si free reaction sintered B4C-SiC ceramics. The formation mechanism of the microstructure of reaction sintered B4C-SiC ceramics and its effect on the mechanical properties of B4C-SiC ceramics are unclear yet, and the further in-depth exploration is needed through theoretical calculations and characterization techniques. The existing investigation for reaction sintered B4C-SiC ceramics mostly focuses on conventional mechanical properties evaluation, and other mechanical properties are seldom reported. The impact strength and tribological properties of reaction sintered B4C-SiC ceramics also need to be investigated deeply..
Journal of the Chinese Ceramic Society
- Publication Date: Feb. 07, 2025
- Vol. 53, Issue 3, 675 (2025)
Research Progress on High-Temperature Ceramic Protective Coatings on C/C Composite Materials
WANG Luyan, LIU Rongjun, WANG Yanfei, LI Duan, and MIAO Huaming
C/C composite materials have several advantages, i.e., low density, high thermal conductivity, low thermal expansion coefficient, and resistance to ablation, which can be used in various fields such as aerospace and nuclear chemical engineering. However, the susceptibility of C/C composite materials to oxidation in higC/C composite materials have several advantages, i.e., low density, high thermal conductivity, low thermal expansion coefficient, and resistance to ablation, which can be used in various fields such as aerospace and nuclear chemical engineering. However, the susceptibility of C/C composite materials to oxidation in high-temperature environments is a primary concern for their further application. One effective solution is the fabrication of high-temperature oxidation-resistant ceramic coatings on the surface of C/C composite materials. The existing high-temperature oxidation-resistant ceramic coatings for C/C composites are gradually transited from single-layer to multi-layer. Typically, these composite coatings consist of three components, i.e., a mitigating layer, an intermediate layer and a sealing layer. The mitigating layer serves to alleviate the thermal expansion coefficient mismatch between the substrate and the coating, while an oxygen-blocking layer characterized by a low oxygen diffusion rate prevents external oxygen from penetrating the substrate. The sealing layer with low porosity, high-temperature fluidity, and self-healing properties protects against environmental medium erosion.This review categorizes the existing high-temperature oxidation-resistant coatings of C/C composites based on different oxidation resistance mechanisms of ceramic coatings, i.e., ceramic coatings based on self-healing glass phase protection mechanisms, ceramic coatings based on enhanced glass phase protection mechanisms, and antioxidant coatings based on composite glass phases. The ceramic coatings based on enhanced glass phase protection mechanisms are further divided into ion-enhanced glass phases, microporous-inclusion structure enhanced glass phases, and particle-enhanced glass phases. In the self-healing glass phase protection mechanism coatings, SiO2 and B2O3 are the most common glass phases. However, single-layer SiO2 or B2O3 coatings are restricted in their application at > 1000 ℃ due to the volatilization of the generated B2O3 glass phase. It is thus necessary to incorporate both silicides and borides into the coating to facilitate the formation of a silicon-boron glass phase from their high-temperature oxidation products (i.e., SiO2 and B2O3), thereby enhancing the oxidation resistance at > 1000 ℃. In addition, SiOC glass phases can also improve oxidation resistance at > 1000 ℃.In ion-enhanced glass phases, Ta and Hf ions exhibit significant reinforcement effects on the glass phase. Specifically, Ta ions due to its intense ionic complexation form a coral-like oxide framework with Hf ions, acting as a supporting scaffold in the Ta-Hf-Si-O glass phase. This enhances the viscosity and strength of the glass layer and the oxygen barrier capability of the coating. Hf cations diffuse into the SiO2 lattice, creating more stable chemical bonds that increase the thermal stability of SiO2 glass, allowing the glass phase to continue protecting the substrate from oxidation in a wider temperature range for an extended period. In microporous-inclusion structure enhanced glass phases, the microporous structure can inhibit crack propagation, while the inclusion structure can suppress the tendency for coating cracking, thereby also enhancing oxidation resistance. A research indicates that SiC-Si coatings with microporous structures can protect C/C composites from oxidation at 1500 ℃ for 846 h, with a mass loss of only 0.16%. In particle-enhanced glass phases, the SiO2 glass phase generated upon oxidation of the coating becomes stable due to the incorporation of Zr compound particles as reinforcing phases, reducing the formation of cracks in the glass phase. This results in superior high-temperature oxidation resistance. For instance, La2O3-modified ZrB2-SiC coatings yield a Zr compound particle distribution in La-Si-O glass that forms a dense oxidation film, demonstrating the oxidation resistance at 1500 ℃ for 550 h and at 1600 ℃ for 107 h, while enduring 50 thermal cycles from 1500 ℃ to room temperature with a mass gain of 0.35%. Researchers develop the coatings that can resist oxidation at 1700 ℃ for 415 h based on the aforementioned antioxidant mechanism.In coatings based on composite glass phases, silicate and aluminate composite glass phases synergistically utilize the advantages of different glass phases. In addition to exhibiting self-healing functions, they also possess a superior oxidation resistance, remaining stable under high-temperature and oxidative conditions. Moreover, elements such as Zr, Y, and Al can capture oxygen molecules, forming a stable oxide layer that further protects the C/C substrate from oxidation damage. In addition, this review also represents the specific preparation processes and oxidation resistance effects for coatings based on oxide-generated glass phase protection mechanisms, enhanced glass phase protection mechanisms, and silicate glass phase coatings.Summary and ProspectsThis review offers a prospective outlook on the development of oxidation-resistant coatings for C/C composites. Firstly, novel reinforcing phases, such as one-dimensional and two-dimensional materials, can be doped to design and optimize the synthesis of ultra-high-temperature oxidation-resistant ceramic materials via efficient artificial intelligence approaches. This involves more complex combinations of the existing oxidation-resistant coatings or mechanisms to actively explore new systems of oxidation-resistant coatings for C/C composites capable of withstanding at > 1700 ℃. Secondly, constructing a complete and reliable performance database for the existing C/C composite oxidation-resistant coatings can elucidate the related protective mechanisms, establish reasonable evaluation mechanisms, and explore key control methods, thereby providing design parameters and theoretical support for practical applications. Finally, a research should focus on the adaptability of oxidation-resistant coatings on C/C composite components of various sizes and configurations, optimizing preparation processes, revealing critical control factors, forming stable process control pathways, and developing relevant process standards..
Journal of the Chinese Ceramic Society
- Publication Date: Jan. 02, 2025
- Vol. 53, Issue 3, 688 (2025)
Progress on High-Temperature Wave-Transmitting Materials in Microwave Sintering
LIU Bingyan, YIN Hongfeng, TANG Yun, REN Xiaohu... and YUAN Hudie|Show fewer author(s)
Industrial operations lead to energy consumption and environmental pollution with the economy development. In developed countries, the thermal efficiency of ceramic kilns in ceramic industry reaches over 50%, while in China it is only about 28%. Combined with the pollution reduction and carbon reduction in recent yearsIndustrial operations lead to energy consumption and environmental pollution with the economy development. In developed countries, the thermal efficiency of ceramic kilns in ceramic industry reaches over 50%, while in China it is only about 28%. Combined with the pollution reduction and carbon reduction in recent years, the gradual development of industrial kilns towards green and intelligent direction becomes an inevitable trend in the context of dual carbon. As is well known, microwave energy can reduce energy consumption and greenhouse gas emissions in drying processes. Microwave sintering technology is also regarded as a ‘new generation sintering technology of the 21st century‘. This technology is an efficient and environmentally friendly method used in metallurgy, powder and ceramics preparation due to its advantages such as volumetric heating, selective heating, time-saving and high efficiency. Compared with conventional sintering methods, a coupling effect between microwaves and materials is utilized in microwave sintering process, thereby producing dielectric loss, converting microwave energy into thermal energy. The microwave sintering furnace mainly involves microwave generator, waveguide tube and sintering chamber. In the operation, the microwave generated by the microwave generator is transmitted through a wave guide, thus entering the sintering chamber after passing through multiple layers of insulation, interacting with the material in the crucible, generating dielectric loss inside the material and converting microwave energy into thermal energy. For this purpose, some imperative requirements put forward for the selection of furnace lining materials. In addition to conventional fire resistance, the lining material used for microwave sintering furnaces also has good wave transmission properties. However, the existing research on transparent materials mostly focus on aircraft radome, and there is still a lack of systematic introduction on wave-transparent materials used in microwave sintering furnaces.This review briefly introduces the working principle of microwave sintering technology and the wave transmission mechanism of materials, and summarizes several common types of high-temperature wave transmitting materials like ceramic firebrick, ceramic fiberboard, ceramic aerogel. Among them, ceramic aerogels have typically nano-pores of up to 90%, which can reduce the dielectric constant of the material significantly. Ceramic fiberboard has a low density and thermal conductivity. However, the application of these two materials is limited due to their lower operating temperatures. Ceramic firebrick with its superior mechanical properties and high-temperature stability shows a broad application prospect in fused silica, alumina, silicate and phosphate ceramics, and these materials with porous structures are more widely used because of the lower dielectric constant of air. Some influencing factors on the dielectric properties of materials are described. Combination with the mechanical properties and dielectric properties of materials, the performance of each ceramic is analyzed, and the advantages and disadvantages of different high-temperature wave transmitting materials are given. Among them, aluminum silicate ceramic shows a promising application prospect in the lining materials for microwave furnace. However, the comprehensive properties of the material in the industrial microwave frequency range still need to be further investigated.Summary and prospectsAlthough the favourable dielectric property of ceramic aerogel and fiberboard is proved in the selection of lining materials for microwave sintering, some problems of operating temperature still remain in the practical application. For ceramic firebrick, compared with nitride ceramics (i.e., Si3N4、SiAlON and Si2N2O), some porous oxides ceramics (i.e., fused quartz, alumina, silicate and hosphate ceramics) become a research hotspot because of the lower cost and better antioxidant properties. All the materials show some advantages in mechanical properties and dielectric properties. For instance, fused quartz with relatively stable dielectric properties has a lower operating temperature. Alumina ceramics have a higher operating temperature, but their thermal shock resistance needs to be improved and its dielectric properties have a temperature dependence. Mulite ceramics have excellent characteristics such as high melting point (i.e., 1830 ℃), low thermal expansion coefficient (i.e., 4.5×10-6 K-1), and low thermal conductivity, which can be used in air at 1750 ℃ without high temperature oxidation. In addition, mulite ceramics also have the superior dielectric properties (i.e., ε is about 3-6, tanδ is about 10-3). Some refractory materials with mullite as a main component are commonly used as lining materials in conventional high-temperature furnace. Furthermore, according to the existing studies, the increase of porosity can effectively reduce the dielectric constant of materials, and has a negative impact on the mechanical properties of materials. In this case, mullite ceramics are easy to form grains with acicular morphology during sintering, which is beneficial to maintaining high mechanical properties of the material at a high porosity. However, some challenges still remain in the scientific researches and practical application, such as some related studies on the dielectric properties at high temperatures are limited at <1200 ℃, but it is far from enough for the lining materials of microwave kiln, in which the working temperature can often reach 1700 ℃. The change of the transmittance of materials at higher temperatures is still of great research value. Also, it is necessary to optimize the dielectric constant test system at high temperatures. Finally, some novel material systems of oxides ceramic in a largescale need to be further explored for the microwave sintering application. Meanwhile, exploring the relevance between microstructure and properties and further accelerating the upgrading and application of ceramic based wave-transmitted materials in microwave sintering technology become some research hotspots, which can reduce the pollution and carbon emissions caused by the use of industrial kilns and lay a foundation for the realization of ’carbon neutrality’..
Journal of the Chinese Ceramic Society
- Publication Date: Dec. 27, 2024
- Vol. 53, Issue 3, 700 (2025)
High-Temperature Insulating Materials Tolerant to Water: Preparation, Properties and Applications
JIAN Yang, JIANG Yonggang, FENG Junzong, LI Liangjun... and FENG Jian|Show fewer author(s)
Novel high-temperature thermal insulation materials (i.e., ceramic fiber insulation materials and aerogels) become research hotspots due to their low density, low thermal conductivity, and superior thermal insulation properties. Ceramic thermal insulation materials can be classified into two categories, i.e., rigid cerNovel high-temperature thermal insulation materials (i.e., ceramic fiber insulation materials and aerogels) become research hotspots due to their low density, low thermal conductivity, and superior thermal insulation properties. Ceramic thermal insulation materials can be classified into two categories, i.e., rigid ceramic thermal insulation tiles and flexible ceramic fiber thermal insulation blankets. Ceramic thermal insulation materials serve as one of the primary thermal protection materials on the surfaces of aerospace equipment due to their superior characteristics such as porosity, low thermal conductivity, high-temperature stability, and excellent mechanical properties. Aerogel is a lightweight material with a nano-porous structure. At atmospheric pressure, silica aerogel has the lowest thermal conductivity among any other insulators. In various applications, aerogel increasingly replaces more conventional materials. The skeleton and porous morphology of aerogel can be controlled in a nanoscale to provide various remarkable physical properties, such as ultra-low density, intense adsorption capacity, ultrahigh specific surface area, and ultralow thermal conductivity.However, the most existing thermal insulation materials are generally isotropic and hydrophilic, significantly limiting their applications in humid environments. The widely used high-temperature thermal insulation materials are typically porous structures, and their nanopores and high specific surface areas contribute to reducing thermal conductivity through a gas-phase heat transfer, thus having superior thermal insulation performance. Nevertheless, their thermal conductivity increases, and this trend intensifies with increasing ambient humidity when porous materials absorb moisture in humid environments, leading to a degraded thermal insulation performance. Moreover, in a direct contact with water, the nanoporous structure of the materials can collapse under capillary forces, causing a significant increase in thermal conductivity.This review comprehensively represents the implementation methods and performance aspects of water resistance for three commonly used high-temperature thermal insulation materials, i.e., ceramic fiber thermal insulation tiles, ceramic fiber thermal insulation blankets, and silica aerogel. The ceramic fiber thermal insulation tiles enhance their high-temperature stability and water resistance through the application of high-emissivity coatings. The ceramic fiber thermal insulation blankets achieve a water resistance via electrostatic spinning and surface modification techniques. For silica aerogel thermal insulation materials, their water resistance is improved via modifying their surfaces with organic hydrophobic groups and adopting hydrothermal-assisted drying methods. This review also identifies some challenges for the improvement of the existing materials and provides an outlook on the future development directions.Summary and ProspectsThis review represents the research advancements in high-temperature insulation materials (i.e., water-resistant ceramic fiber insulation tiles, insulation blankets, and aerogels). Some strategies for enhancing their water resistance, such as the application of high-emissivity coatings, chemical vapor deposition, and modification with organic hydrophobic groups, are described. These materials possess a significant application potential at multiple fields due to their low density, robust water resistance, and efficient thermal insulation properties. Nevertheless, some challenges persist in maintaining water resistance at high temperatures, simplifying manufacturing processes, and developing novel materials. A future research should prioritize enhancing the water resistance of materials at elevated temperatures, streamlining production processes, and innovating novel materials. In addition, the stability and durability of these materials in practical applications also need to be further investigated to facilitate the technological advancements and industrial upgrading..
Journal of the Chinese Ceramic Society
- Publication Date: Dec. 27, 2024
- Vol. 53, Issue 3, 718 (2025)
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