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
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
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
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
Using coal fly ash slurry samples supplemented with different amounts of Al_2O_3,we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach,which is a popular method suitable for industrial app...Using coal fly ash slurry samples supplemented with different amounts of Al_2O_3,we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach,which is a popular method suitable for industrial application.The microstructure,phase composition,and compressive strength of the sintered samples were investigated.Mullite was identified in all of the prepared materials by X-ray diffraction analysis.The microstructure and compressive strength were strongly influenced by the content of Al_2O_3.As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40,the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased.A further increase in the Al_2O_3 content resulted in a decrease in the compressive strength of the sintered samples.The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.展开更多
Mullite nanowhiskers with Al-rich structure were prepared by molten salt synthesis at 1000°C for 3 h in air using silica, amorphous silica, and ultrafine silica as the silica sources. The phase and morphology of ...Mullite nanowhiskers with Al-rich structure were prepared by molten salt synthesis at 1000°C for 3 h in air using silica, amorphous silica, and ultrafine silica as the silica sources. The phase and morphology of the synthesized products were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. A thermogravimetric and differential thermal analysis was carried out to determine the reaction mechanism. The results reveal that the silica sources play an important role in determining the morphology of the obtained mullite nanowhiskers. Clusters and disordered arrangements are obtained using common silica and amorphous silica, respectively, whereas the use of ultrafine silica leads to highly ordered mullite nanowhiskers that are 80-120 nm in diameter and 20-30 μm in length. Considering the growth mechanisms, mullite nanowhiskers in the forms of clusters and highly ordered arrangements can be attributed to heterogeneous nucleation, whereas disordered mullite nanowhiskers are obtained by homogenous nucleation.展开更多
In order to enhance the fracture toughness of mullite, three-dimensional braided carbon fiber reinforced mullite(C/mullite) composites were prepared using the Al2O3-SiO2 sol with a high solid content as raw material. ...In order to enhance the fracture toughness of mullite, three-dimensional braided carbon fiber reinforced mullite(C/mullite) composites were prepared using the Al2O3-SiO2 sol with a high solid content as raw material. Mullitization behavior of the sol was characterized. Then, the microstructure, mechanical properties and oxidation resistance of C/mullite composites were investigated. It is found that the SiO2-rich mullite with desirable sintering shrinkage can be synthesized at 1 300 ℃ from the sol with an Al2O3/SiO2 mass ratio of 1:1. The C/mullite composites with a total porosity of 21.5% were fabricated by repeating 18 cycles of vacuum impregnation-drying-heat treatment, showing a flexural strength of 234.5 MPa and a fracture toughness of 13.1 MPa·m1/2. Since carbon fibers were protected by compact matrix, the C/mullite composites show favorable oxidation resistance during 1 200 ℃-1 600 ℃ even if an open porosity of 10.3% was detected.展开更多
To reduce the burning loss and the spalling and to improve energy efficiency,the mullite composite lining plates were used to replace cast steel or alloy lining in rotary coke tanks for coke dry quenching equipment.Th...To reduce the burning loss and the spalling and to improve energy efficiency,the mullite composite lining plates were used to replace cast steel or alloy lining in rotary coke tanks for coke dry quenching equipment.The results show that:the dense mullite composite lining plate in the cone part has the density of 2.20 g·cm^(-3) and the wear test,s volume loss of 4.08 cm^(3),and the light weight mullite composite lining plate in the straight cylinder part has the density of 1.95 g·cm^(-3) and the wear test,s volume loss of 17.6 cm^(3).After using,there is no shrinkage gap,no burn loss or holes in the plates,indicating good sealing of the mullite composite lining plates.The lining plate for the cone part has low burning loss,without spalling for more than half a year.The outer surface temperature of coke tanks adopting the cast steel or the alloy lining is 480 to 570℃,while that of the ones adopting mullite composite lining plates is 120 to 170℃,showing a largely improved insulating property.Adopting mullite composite lining plates on the basis of the current coke tank cage,the lining plates can be timely treated and wholly replaced,improving the service life and reducing the maintenance workload.展开更多
Different mixtures of Moroccan silica-alumina geomaterials were used for the preparation of refractory ceramics. A formula of composition (M2) has allowed obtaining a good quality of refractory. Addition of a small qu...Different mixtures of Moroccan silica-alumina geomaterials were used for the preparation of refractory ceramics. A formula of composition (M2) has allowed obtaining a good quality of refractory. Addition of a small quantity of carbon (1%) to the M2 formula has substantially improved the quality of the refractory. The morphological, textural and mineralogical evolution, through SEM and XRD shows that the addition of carbon, which plays a catalytic role, favors the crystallization of andalusite. Then, from 1200°C, the andalusite starts to transform to primary mullite needles. At 1400°C, the mullite becomes the major mineral phase beside cristobalite and vitreous phase.展开更多
Enrichment of schist mined in Morocco resulted in an extract essentially made of andalusite, quartz and muscovite, which was investigated with the aim to synthesize mullite refractory materials. X-ray diffraction anal...Enrichment of schist mined in Morocco resulted in an extract essentially made of andalusite, quartz and muscovite, which was investigated with the aim to synthesize mullite refractory materials. X-ray diffraction analysis was used to assess phase transformations upon heating at different temperatures. Mullite formation starts as early as 1200℃ and seems almost total at 1450℃. This process correlates with a weak shrinkage (3.5% at 1450℃) and the formation of an important glass phase. Green compacts obtained by unidirectional pressing the extract powder were heated under air in the temperature range 1200℃ - 1600℃. Chemical and mechanical properties of these materials were investigated and correlated with their microstructure.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.
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Using coal fly ash slurry samples supplemented with different amounts of Al_2O_3,we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach,which is a popular method suitable for industrial application.The microstructure,phase composition,and compressive strength of the sintered samples were investigated.Mullite was identified in all of the prepared materials by X-ray diffraction analysis.The microstructure and compressive strength were strongly influenced by the content of Al_2O_3.As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40,the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased.A further increase in the Al_2O_3 content resulted in a decrease in the compressive strength of the sintered samples.The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material.
基金the New Century Excellent Talents in Universities (No. NECT-12-0779)the Fundamental Research Funds for the Central Universities (No. FRF-SD-13-006A)the Program for Changjiang Scholars and Innovative Research Team in Universities (No. IRT1207) for financial support
文摘Mullite nanowhiskers with Al-rich structure were prepared by molten salt synthesis at 1000°C for 3 h in air using silica, amorphous silica, and ultrafine silica as the silica sources. The phase and morphology of the synthesized products were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. A thermogravimetric and differential thermal analysis was carried out to determine the reaction mechanism. The results reveal that the silica sources play an important role in determining the morphology of the obtained mullite nanowhiskers. Clusters and disordered arrangements are obtained using common silica and amorphous silica, respectively, whereas the use of ultrafine silica leads to highly ordered mullite nanowhiskers that are 80-120 nm in diameter and 20-30 μm in length. Considering the growth mechanisms, mullite nanowhiskers in the forms of clusters and highly ordered arrangements can be attributed to heterogeneous nucleation, whereas disordered mullite nanowhiskers are obtained by homogenous nucleation.
基金Funded by the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology(No.SAST2015043)the Open Foundation of Science and Technology on Thermostructural Composite Materials Laboratory(No.614291102010117)the National Natural Science Foundation of China(No.11572277)
文摘In order to enhance the fracture toughness of mullite, three-dimensional braided carbon fiber reinforced mullite(C/mullite) composites were prepared using the Al2O3-SiO2 sol with a high solid content as raw material. Mullitization behavior of the sol was characterized. Then, the microstructure, mechanical properties and oxidation resistance of C/mullite composites were investigated. It is found that the SiO2-rich mullite with desirable sintering shrinkage can be synthesized at 1 300 ℃ from the sol with an Al2O3/SiO2 mass ratio of 1:1. The C/mullite composites with a total porosity of 21.5% were fabricated by repeating 18 cycles of vacuum impregnation-drying-heat treatment, showing a flexural strength of 234.5 MPa and a fracture toughness of 13.1 MPa·m1/2. Since carbon fibers were protected by compact matrix, the C/mullite composites show favorable oxidation resistance during 1 200 ℃-1 600 ℃ even if an open porosity of 10.3% was detected.
文摘To reduce the burning loss and the spalling and to improve energy efficiency,the mullite composite lining plates were used to replace cast steel or alloy lining in rotary coke tanks for coke dry quenching equipment.The results show that:the dense mullite composite lining plate in the cone part has the density of 2.20 g·cm^(-3) and the wear test,s volume loss of 4.08 cm^(3),and the light weight mullite composite lining plate in the straight cylinder part has the density of 1.95 g·cm^(-3) and the wear test,s volume loss of 17.6 cm^(3).After using,there is no shrinkage gap,no burn loss or holes in the plates,indicating good sealing of the mullite composite lining plates.The lining plate for the cone part has low burning loss,without spalling for more than half a year.The outer surface temperature of coke tanks adopting the cast steel or the alloy lining is 480 to 570℃,while that of the ones adopting mullite composite lining plates is 120 to 170℃,showing a largely improved insulating property.Adopting mullite composite lining plates on the basis of the current coke tank cage,the lining plates can be timely treated and wholly replaced,improving the service life and reducing the maintenance workload.
文摘Different mixtures of Moroccan silica-alumina geomaterials were used for the preparation of refractory ceramics. A formula of composition (M2) has allowed obtaining a good quality of refractory. Addition of a small quantity of carbon (1%) to the M2 formula has substantially improved the quality of the refractory. The morphological, textural and mineralogical evolution, through SEM and XRD shows that the addition of carbon, which plays a catalytic role, favors the crystallization of andalusite. Then, from 1200°C, the andalusite starts to transform to primary mullite needles. At 1400°C, the mullite becomes the major mineral phase beside cristobalite and vitreous phase.
基金the Centre d’Etude et de Re-cherche des Phosphates Mineraux(Cerphos,Morocco)for their collaboration and financial support.
文摘Enrichment of schist mined in Morocco resulted in an extract essentially made of andalusite, quartz and muscovite, which was investigated with the aim to synthesize mullite refractory materials. X-ray diffraction analysis was used to assess phase transformations upon heating at different temperatures. Mullite formation starts as early as 1200℃ and seems almost total at 1450℃. This process correlates with a weak shrinkage (3.5% at 1450℃) and the formation of an important glass phase. Green compacts obtained by unidirectional pressing the extract powder were heated under air in the temperature range 1200℃ - 1600℃. Chemical and mechanical properties of these materials were investigated and correlated with their microstructure.
