Silica aerogel due to the high specific surface area, nanometer level pores and low density of the micro structure, had excellent heat-insulating properties. But the characteristics of silica aerogel with low density ...Silica aerogel due to the high specific surface area, nanometer level pores and low density of the micro structure, had excellent heat-insulating properties. But the characteristics of silica aerogel with low density and high voidage resulted in poor mechanical properties. In order to improve the strength of materials and meet the actual needs, in this paper the heat-insulating composite material was made from the silica aerogel and mullite fiber. This kind of composite material mainly contented of mullite fiber, formed macro block structure, that gas gel is coated and filled with mullite fiber. Furthermore, the composite material had good strength and kept excellent thermal stability at 600°C. In addition the density of composite decreased with the increasing of the gas gel content.展开更多
Alumina-silica composite coatings were prepared on the surface of graphite paper by CVD using AlCl3/SiCl4/H2/CO2 as precursor in the temperature range of 300 to 550℃. XRD and SEM were used to examine the phase comp...Alumina-silica composite coatings were prepared on the surface of graphite paper by CVD using AlCl3/SiCl4/H2/CO2 as precursor in the temperature range of 300 to 550℃. XRD and SEM were used to examine the phase composition and the microstructure of the coating, respectively. The results indicate that the dense, uniform and adherent alumina-silica composite coating can be prepared on graphite paper substrate by CVD at 550℃ using SiCl4/AlCl3/CO2/H2. The alumina-silica composite coating is composed of a number of spherical particles. Each particle is composed of a number of fine-particle. The phase of the 550℃ composite coating includes γ-alumina containing amorphous silica. The content of Cl element in composite coating decreases with the increase of the deposition temperature. The analysis results of morphology and growth mechanisms of the CVD alumina-silica indicate that the condensation within the boundary layer will be more likely to lead to the formation of gel-particles. The gel-particles size decreases with the increase of deposition temperature in the range of 300550℃. Surface reaction is the main path to generate deposition products at 550℃.展开更多
Silica aerogel composites have promising applications in high-temperature heat storage insulation.However,the impact of high temperatures and moisture on their insulation performance remains unclear.To reveal the infl...Silica aerogel composites have promising applications in high-temperature heat storage insulation.However,the impact of high temperatures and moisture on their insulation performance remains unclear.To reveal the influences of high temperature and moisture absorption property on the heat transfer of silica aerogel composites,an experimental and numerical study was conducted to explore the micromorphology,thermophysical parameters,moisture absorption characteristics,and temperature response.The service temperature limit of the silica aerogel composite has been clarified.Measurements have conducted for the thermal conductivity,specific heat capacity,thermal diffusivity,specific surface area,density,porosity,and pore size distribution of the heated silica aerogel composite(at temperatures of 600,800,1,000,1,100 and 1,200℃).The moisture absorption characteristic curve at 20℃ has been obtained.Thermal testing of silica aerogel composites under varying heating temperatures and moisture content has been completed.Additionally,a numerical method has been developed to calculate the temperature curve of moist silica aerogel composites.The insulation performance of silica aerogel composite with varying moisture contents depends on the game between thermal conductivity and latent heat.Compared with the negative effect of the moisture content on insulation performance,the positive influence of moisture evaporation and heat absorption is dominant in situations involving temperatures higher than the phase transition temperature.展开更多
The reduction of volume of silica glass during aluminum reactive penetration was observed experimentally. The liquid aluminum infiltrates easily into the cavities while the released silicon is solved in the liquid alu...The reduction of volume of silica glass during aluminum reactive penetration was observed experimentally. The liquid aluminum infiltrates easily into the cavities while the released silicon is solved in the liquid aluminum, and Al/Al2O3 composites could be obtained. The experimental results show that Al/Al2O3 composites can be transformed into Al2O3 grains by oxygen in the cavities of Al/Al2O3 composites during the longer penetration treatment. The formation of alumina is a sintering process, in which liquid aluminum, particulate alumina and oxygen play an important role. The transformtion process has shown that there is a relationship of σAl2O3-Al2O3 2O3-Al, where σAl2O3-Al2O3 is the grain boundary energy of alumina, and σAl2O3-Al is the interface energy between aluminum and alumina. The formation temperature by aluminum reactive penetration is much lower than that by sintering.展开更多
The fused cast alumina-zirconia-silica(AZS)refractory is an indispensable material of the glass melting furnace,because of its outstanding corrosion resistance and low pollution to glass production.The exudation is on...The fused cast alumina-zirconia-silica(AZS)refractory is an indispensable material of the glass melting furnace,because of its outstanding corrosion resistance and low pollution to glass production.The exudation is one important index to evaluate the performance of fused cast AZS refractory products.In order to study the effects of chemical composition and microstructure on the exudation of fused cast AZS refractory materials,three types of fused-cast AZS refractory bricks(AZS33#,AZS36#and AZS41#)were selected from several companies as the research object,and their composition,bulk density,apparent porosity,the value of exudation,static corrosion rate and microstructure were discussed.The results show that the chemical composition,especially the content of SiO2 and Na2O,and the distribution of zirconia would greatly affect the content and viscosity of glass phase,thus affecting the glass exudation.This work will provide technical reference for the development of low exudation AZS refractories.展开更多
文摘Silica aerogel due to the high specific surface area, nanometer level pores and low density of the micro structure, had excellent heat-insulating properties. But the characteristics of silica aerogel with low density and high voidage resulted in poor mechanical properties. In order to improve the strength of materials and meet the actual needs, in this paper the heat-insulating composite material was made from the silica aerogel and mullite fiber. This kind of composite material mainly contented of mullite fiber, formed macro block structure, that gas gel is coated and filled with mullite fiber. Furthermore, the composite material had good strength and kept excellent thermal stability at 600°C. In addition the density of composite decreased with the increasing of the gas gel content.
文摘Alumina-silica composite coatings were prepared on the surface of graphite paper by CVD using AlCl3/SiCl4/H2/CO2 as precursor in the temperature range of 300 to 550℃. XRD and SEM were used to examine the phase composition and the microstructure of the coating, respectively. The results indicate that the dense, uniform and adherent alumina-silica composite coating can be prepared on graphite paper substrate by CVD at 550℃ using SiCl4/AlCl3/CO2/H2. The alumina-silica composite coating is composed of a number of spherical particles. Each particle is composed of a number of fine-particle. The phase of the 550℃ composite coating includes γ-alumina containing amorphous silica. The content of Cl element in composite coating decreases with the increase of the deposition temperature. The analysis results of morphology and growth mechanisms of the CVD alumina-silica indicate that the condensation within the boundary layer will be more likely to lead to the formation of gel-particles. The gel-particles size decreases with the increase of deposition temperature in the range of 300550℃. Surface reaction is the main path to generate deposition products at 550℃.
基金supported by the National Natural Science Foundation of China(Grant Nos.:52006168 and 12102056).
文摘Silica aerogel composites have promising applications in high-temperature heat storage insulation.However,the impact of high temperatures and moisture on their insulation performance remains unclear.To reveal the influences of high temperature and moisture absorption property on the heat transfer of silica aerogel composites,an experimental and numerical study was conducted to explore the micromorphology,thermophysical parameters,moisture absorption characteristics,and temperature response.The service temperature limit of the silica aerogel composite has been clarified.Measurements have conducted for the thermal conductivity,specific heat capacity,thermal diffusivity,specific surface area,density,porosity,and pore size distribution of the heated silica aerogel composite(at temperatures of 600,800,1,000,1,100 and 1,200℃).The moisture absorption characteristic curve at 20℃ has been obtained.Thermal testing of silica aerogel composites under varying heating temperatures and moisture content has been completed.Additionally,a numerical method has been developed to calculate the temperature curve of moist silica aerogel composites.The insulation performance of silica aerogel composite with varying moisture contents depends on the game between thermal conductivity and latent heat.Compared with the negative effect of the moisture content on insulation performance,the positive influence of moisture evaporation and heat absorption is dominant in situations involving temperatures higher than the phase transition temperature.
基金This project was supported by the National Natural Science Foundation of China!(Grant No.59474013)
文摘The reduction of volume of silica glass during aluminum reactive penetration was observed experimentally. The liquid aluminum infiltrates easily into the cavities while the released silicon is solved in the liquid aluminum, and Al/Al2O3 composites could be obtained. The experimental results show that Al/Al2O3 composites can be transformed into Al2O3 grains by oxygen in the cavities of Al/Al2O3 composites during the longer penetration treatment. The formation of alumina is a sintering process, in which liquid aluminum, particulate alumina and oxygen play an important role. The transformtion process has shown that there is a relationship of σAl2O3-Al2O3 2O3-Al, where σAl2O3-Al2O3 is the grain boundary energy of alumina, and σAl2O3-Al is the interface energy between aluminum and alumina. The formation temperature by aluminum reactive penetration is much lower than that by sintering.
文摘The fused cast alumina-zirconia-silica(AZS)refractory is an indispensable material of the glass melting furnace,because of its outstanding corrosion resistance and low pollution to glass production.The exudation is one important index to evaluate the performance of fused cast AZS refractory products.In order to study the effects of chemical composition and microstructure on the exudation of fused cast AZS refractory materials,three types of fused-cast AZS refractory bricks(AZS33#,AZS36#and AZS41#)were selected from several companies as the research object,and their composition,bulk density,apparent porosity,the value of exudation,static corrosion rate and microstructure were discussed.The results show that the chemical composition,especially the content of SiO2 and Na2O,and the distribution of zirconia would greatly affect the content and viscosity of glass phase,thus affecting the glass exudation.This work will provide technical reference for the development of low exudation AZS refractories.
