To broaden the application of SiO_(2) sol-bonded castables,using micro-or nano-Al_(2)O_(3) powder and SiO_(2) gel powder as the main raw materials,the effects of CaO impurity on the formation of mullite by the reactio...To broaden the application of SiO_(2) sol-bonded castables,using micro-or nano-Al_(2)O_(3) powder and SiO_(2) gel powder as the main raw materials,the effects of CaO impurity on the formation of mullite by the reaction of Al_(2)O_(3) and SiO_(2) at different temperatures(1350,1400,1500,and 1600℃)in different atmospheres(oxidation atmosphere and reduction atmosphere)were studied.The results show that in the oxidizing atmosphere,the introduction of CaO can promote the formation of mullite.When the temperature increases from 1350℃to 1600℃,the amount of mullite formed gradually increases.In the reducing atmosphere,the introduction of CaO is not conducive to the formation of mullite,and the amount of mullite decreases with the increasing temperature.The smaller the particle size of Al_(2)O_(3),the more easily it reacts with SiO_(2) gel powder to form mullite.展开更多
Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testin...Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.展开更多
In order to improve the high-temperature performance of mullite ceramic materials,mullite ceramic bodies were placed in closed containers with AlF_(3)·3H_(2)O powder and kept at 1 600 ℃ for 6 h.AlF_(3)·3H_(...In order to improve the high-temperature performance of mullite ceramic materials,mullite ceramic bodies were placed in closed containers with AlF_(3)·3H_(2)O powder and kept at 1 600 ℃ for 6 h.AlF_(3)·3H_(2)O reacts with O_(2) to produce gaseous compounds AlOF and F,which penetrate into the bodies,promote Al2O3 and SiO_(2) to form mullite whiskers,and strengthen the mullite ceramic materials.The results show that the mullite ceramics have enhanced hot strength,increased bulk density and declined apparent porosity by adding a certain amount of AlF_(3)·3H_(2)O in a closed container.When the addition of AlF_(3)·3H_(2)O is 6%,the bulk density of the ceramic material reaches the maximum and the apparent porosity is the lowest;and when the addition of AlF_(3)·3H_(2)O is 8%,the hot strength of the material is the highest.展开更多
Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents ...Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents and their additions(mass fraction of 0,5%,10%,15%and 20%,respectively)on the properties of the microporous mullite aggregates were analyzed by XRD,SEM and Image-Pro Plus software.The results show that the comprehensive performance of the sample with 10%rice husk powder is the best:the closed porosity is 7.1%;the bulk density is 2.63 g·cm^(-3);the compressive strength is 122 MPa;the median pore size is 15.16μm;and the thermal conductivity at 500℃is 2.30 W·m^(-1)·K^(-1).展开更多
To protect carbon materials from oxidation, mullite/SiC coatings were prepared on graphite by chemical vapor reaction (CVR) and slurry sintering. The XRD analyses show that the phase of the outer-layer coating is comp...To protect carbon materials from oxidation, mullite/SiC coatings were prepared on graphite by chemical vapor reaction (CVR) and slurry sintering. The XRD analyses show that the phase of the outer-layer coating is composed of SiO2 and mullite, and the inner-layer coating is mainly composed of β-SiC. The anti-oxidation behavior of the coating and the Rockwell hardness (HRB) of the coating after oxidation were investigated. The oxidation test shows that the as-prepared multi-layer coating exhibits excellent antioxidation and thermal shock resistance at high temperature. After oxidation at 1150 ℃ for 109 h and thermal shock cycling between 1150 ℃ and room temperature for 12 times, the mass gain of the coated sample is 0.085%. Meanwhile, the indentation tests also demonstrate that the as-prepared coating has good bonding ability between the layers.展开更多
用挤压铸造方法制备了Mullite/Al Cu Si复合材料。用硬度 (HB)测试仪、差示扫描量热仪 (DSC)和显微镜研究含Si量变化和Mullite纤维对Al Cu Si合金时效硬化行为的影响 ;元素Si、Mullite纤维以及二者同时存在对Al Cu Si合金时效析出序列...用挤压铸造方法制备了Mullite/Al Cu Si复合材料。用硬度 (HB)测试仪、差示扫描量热仪 (DSC)和显微镜研究含Si量变化和Mullite纤维对Al Cu Si合金时效硬化行为的影响 ;元素Si、Mullite纤维以及二者同时存在对Al Cu Si合金时效析出序列的影响。结果表明 :Si和Mullite纤维明显抑制了Al Cu合金GP区的形成 ;随着含Si量增加 ,Al Cu Si合金的时效硬化过程加快 ;Mullite纤维对Al Cu和Al Cu Si合金的时效硬化过程都具有加速作用 ,同时提高了基体合金的时效硬度 ,但相对而言 ,Mullite纤维对无Si的Al Cu合金的时效硬化加速作用更为明显一些。展开更多
Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired te...Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.展开更多
Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, mor...Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H20 and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H20, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of A1F3·3H20. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.展开更多
Decomposition kinetics of mullite and corundum in coal fly ash with highly alkaline solution was studied.The effects of the reaction temperature and reaction time on decomposition rates of mullite and corundum and alu...Decomposition kinetics of mullite and corundum in coal fly ash with highly alkaline solution was studied.The effects of the reaction temperature and reaction time on decomposition rates of mullite and corundum and alumina extraction efficiency were investigated.The results show that increasing reaction temperature and reaction time increases the decomposition rates of mullite and corundum and alumina extraction efficiency,with the decomposition temperature of mullite lower than that of corundum.After 90 min reaction at 220℃,more than 100 g alumina was extracted when recycling 1 L of alkaline solution.The decomposition processes of mullite and corundum corresponded with the shrinking unreacted core model,and the reaction rate was under chemical reaction control,with the activation energies of mullite and corundum being 67.46 and 161.82 kJ/mol,respectively.展开更多
In this research,the mullite material with sludge from aluminum profile factory and pyrophyllite as primary raw materials was prepared. Based on the optimal formula,optimal calcining temperature and holding time deter...In this research,the mullite material with sludge from aluminum profile factory and pyrophyllite as primary raw materials was prepared. Based on the optimal formula,optimal calcining temperature and holding time determined in the research,effects of Na2SiF6 mineralizer on crystal structure,microstructure and properties of mullite were discussed to determine the optimal addition of Na2SiF6 mineralizer. With XRD and SEM methods,crystal structure and microstructure of the test samples were characterized; with Rietveld Quantification method,contents of various crystal phases in the test samples were determined; properties of the test samples were tested. In combination with the structural and property analysis results,the optimal Na2SiF6 addition was determined to be 2%. Correspondingly,the content of solid solution of mullite-Al4.59Si1.41O9.7 was 96.9wt%,the bulk density was 2.10 g/cm3,the degree of porosity was 27.0%,the water absorption rate was 12.8%,the rupture strength was 24.30 MPa and primary thermal-shock rupture strength retention rate was 87.4%.展开更多
The waste slag from aluminum profile factory and silicon fine powder from ferroalloy factory were utilized as the main raw materials to synthesize mullite solid solution Al4＋2xSi2-xO10-x/2, whose defect formation mec...The waste slag from aluminum profile factory and silicon fine powder from ferroalloy factory were utilized as the main raw materials to synthesize mullite solid solution Al4＋2xSi2-xO10-x/2, whose defect formation mechanism, crystalline phase composition, crystal cell parameters, microstructures and morphologies were characterized in detail by XRD and SEM. The results show that because of the ultrafine particle size of the materials, the content of mullite solid solution synthesized by this method is higher than that by regular method. Keywords： waste slag from aluminum factory, silicon fine powder, mullite, solid solution展开更多
基金This work was financially supported by National Natural Science Foundation of China(Nos.52172031 and 51872266).
文摘To broaden the application of SiO_(2) sol-bonded castables,using micro-or nano-Al_(2)O_(3) powder and SiO_(2) gel powder as the main raw materials,the effects of CaO impurity on the formation of mullite by the reaction of Al_(2)O_(3) and SiO_(2) at different temperatures(1350,1400,1500,and 1600℃)in different atmospheres(oxidation atmosphere and reduction atmosphere)were studied.The results show that in the oxidizing atmosphere,the introduction of CaO can promote the formation of mullite.When the temperature increases from 1350℃to 1600℃,the amount of mullite formed gradually increases.In the reducing atmosphere,the introduction of CaO is not conducive to the formation of mullite,and the amount of mullite decreases with the increasing temperature.The smaller the particle size of Al_(2)O_(3),the more easily it reacts with SiO_(2) gel powder to form mullite.
基金Funded by the National Key Research and Development Program of Science and Technology of China(No.2018YFB1501002)。
文摘Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.
基金supported by the National Natural Science Foundation of ChinaKey Projects of Henan United Fund(NSFCNo.U1904217).
文摘In order to improve the high-temperature performance of mullite ceramic materials,mullite ceramic bodies were placed in closed containers with AlF_(3)·3H_(2)O powder and kept at 1 600 ℃ for 6 h.AlF_(3)·3H_(2)O reacts with O_(2) to produce gaseous compounds AlOF and F,which penetrate into the bodies,promote Al2O3 and SiO_(2) to form mullite whiskers,and strengthen the mullite ceramic materials.The results show that the mullite ceramics have enhanced hot strength,increased bulk density and declined apparent porosity by adding a certain amount of AlF_(3)·3H_(2)O in a closed container.When the addition of AlF_(3)·3H_(2)O is 6%,the bulk density of the ceramic material reaches the maximum and the apparent porosity is the lowest;and when the addition of AlF_(3)·3H_(2)O is 8%,the hot strength of the material is the highest.
文摘Microporous mullite aggregates were prepared from bauxite by dry pressing and firing at 1700℃for 3 h with corn starch,PMMA microspheres or rice husk powder as the porogenic agent.The effects of some porogenic agents and their additions(mass fraction of 0,5%,10%,15%and 20%,respectively)on the properties of the microporous mullite aggregates were analyzed by XRD,SEM and Image-Pro Plus software.The results show that the comprehensive performance of the sample with 10%rice husk powder is the best:the closed porosity is 7.1%;the bulk density is 2.63 g·cm^(-3);the compressive strength is 122 MPa;the median pore size is 15.16μm;and the thermal conductivity at 500℃is 2.30 W·m^(-1)·K^(-1).
基金Project (2012M511752) supported by China Postdoctoral Science FoundationProject (2011CB605801) supported by the National Basical Research Program of China+3 种基金Project (2012QNZT004) supported by the Fundamental Research Funds of the Central Universities, ChinaProject supported by the Freedom Explore Program of Central South University, ChinaProject (CSUZC2012026) supported by the Open-End Fund for the Valuable and Precision Instruments of Central South University, ChinaProject supported by the Postdoctoral Science Foundation of Central South University, China
文摘To protect carbon materials from oxidation, mullite/SiC coatings were prepared on graphite by chemical vapor reaction (CVR) and slurry sintering. The XRD analyses show that the phase of the outer-layer coating is composed of SiO2 and mullite, and the inner-layer coating is mainly composed of β-SiC. The anti-oxidation behavior of the coating and the Rockwell hardness (HRB) of the coating after oxidation were investigated. The oxidation test shows that the as-prepared multi-layer coating exhibits excellent antioxidation and thermal shock resistance at high temperature. After oxidation at 1150 ℃ for 109 h and thermal shock cycling between 1150 ℃ and room temperature for 12 times, the mass gain of the coated sample is 0.085%. Meanwhile, the indentation tests also demonstrate that the as-prepared coating has good bonding ability between the layers.
文摘用挤压铸造方法制备了Mullite/Al Cu Si复合材料。用硬度 (HB)测试仪、差示扫描量热仪 (DSC)和显微镜研究含Si量变化和Mullite纤维对Al Cu Si合金时效硬化行为的影响 ;元素Si、Mullite纤维以及二者同时存在对Al Cu Si合金时效析出序列的影响。结果表明 :Si和Mullite纤维明显抑制了Al Cu合金GP区的形成 ;随着含Si量增加 ,Al Cu Si合金的时效硬化过程加快 ;Mullite纤维对Al Cu和Al Cu Si合金的时效硬化过程都具有加速作用 ,同时提高了基体合金的时效硬度 ,但相对而言 ,Mullite纤维对无Si的Al Cu合金的时效硬化加速作用更为明显一些。
基金Project(N100302002)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(20100471467)supported by the China Postdoctoral Science Foundation
文摘Zirconia-mullite-corundum composites were successfully prepared from fly ash,zircon and alumina powder by a reaction sintering process.The phase and microstructure evolutions of the composite synthesized at desired temperatures of 1 400,1 500 and 1 600°C for 4 h were characterized by X-ray diffractometry and scanning electronic microscopy,respectively.The influences of sintering temperature on shrinkage ratio,apparent porosity and bulk density of the synthesized composite were investigated.The formation process of the composites was discussed in detail.The results show that the zirconia-mullite-corundum composites with good sintering properties can be prepared at 1 600°C for 4 h.Zirconia particles can be homogeneously distributed in mullite matrix,and the zirconia particles are around 5μm.The formation process of zirconia-mullite-corundum composites consists of decomposition of zircon and mullitization process.
基金financially supported by the Project of the Science and Technology Creative Team of Universities in Jiangxi Province,China(No.00008713)the Open Foundation of Jiangxi Key Laboratory for Advanced Copper and Tungsten Materials(No.2013-KLP-04)
文摘Mullite whiskers were facilely prepared by sintering kyanite at high temperature, with the addition of AlF3·3H20. The as-prepared whiskers have been characterized systematically in terms of phase composition, morphology, and structure. Results showed that the morphology and size of mullite whiskers were strongly depended on the content of AlF3·3H20 and sintering temperature. At temperatures in the range of 1 100 to 1 500 ℃ with 4 wt% addition of AlF3·3H20, the well-shaped mullite whiskers were obtained. For an instance, the mullite whiskers with 5-10 μm in length and 0.1-0.2 μm in cross-section could be formed at 1 400 ℃, with 4 wt% addition of A1F3·3H20. Moreover, results showed that the addition of mullite whiskers into ceramic matrix enhanced its fracture toughness significantly.
基金Project(2013CB632601)supported by the National Basic Research Program of China
文摘Decomposition kinetics of mullite and corundum in coal fly ash with highly alkaline solution was studied.The effects of the reaction temperature and reaction time on decomposition rates of mullite and corundum and alumina extraction efficiency were investigated.The results show that increasing reaction temperature and reaction time increases the decomposition rates of mullite and corundum and alumina extraction efficiency,with the decomposition temperature of mullite lower than that of corundum.After 90 min reaction at 220℃,more than 100 g alumina was extracted when recycling 1 L of alkaline solution.The decomposition processes of mullite and corundum corresponded with the shrinking unreacted core model,and the reaction rate was under chemical reaction control,with the activation energies of mullite and corundum being 67.46 and 161.82 kJ/mol,respectively.
基金Sponsored by the Fujian Provincial Reform and Development Commission
文摘In this research,the mullite material with sludge from aluminum profile factory and pyrophyllite as primary raw materials was prepared. Based on the optimal formula,optimal calcining temperature and holding time determined in the research,effects of Na2SiF6 mineralizer on crystal structure,microstructure and properties of mullite were discussed to determine the optimal addition of Na2SiF6 mineralizer. With XRD and SEM methods,crystal structure and microstructure of the test samples were characterized; with Rietveld Quantification method,contents of various crystal phases in the test samples were determined; properties of the test samples were tested. In combination with the structural and property analysis results,the optimal Na2SiF6 addition was determined to be 2%. Correspondingly,the content of solid solution of mullite-Al4.59Si1.41O9.7 was 96.9wt%,the bulk density was 2.10 g/cm3,the degree of porosity was 27.0%,the water absorption rate was 12.8%,the rupture strength was 24.30 MPa and primary thermal-shock rupture strength retention rate was 87.4%.
基金This work was supported by the "863" Program (No. 2003AA322020)
文摘The waste slag from aluminum profile factory and silicon fine powder from ferroalloy factory were utilized as the main raw materials to synthesize mullite solid solution Al4＋2xSi2-xO10-x/2, whose defect formation mechanism, crystalline phase composition, crystal cell parameters, microstructures and morphologies were characterized in detail by XRD and SEM. The results show that because of the ultrafine particle size of the materials, the content of mullite solid solution synthesized by this method is higher than that by regular method. Keywords： waste slag from aluminum factory, silicon fine powder, mullite, solid solution
