Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their ...Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.展开更多
在变电站现场开展GIS内电压互感器误差校验时,会面临试验一次回路长、GIS管道电容量随管道长短变化等问题,现有试验设备操作复杂且效率低下。通过研究升压试验操作时不同电感补偿方案的影响因素,设计研制了标准电压互感器与带中压补偿...在变电站现场开展GIS内电压互感器误差校验时,会面临试验一次回路长、GIS管道电容量随管道长短变化等问题,现有试验设备操作复杂且效率低下。通过研究升压试验操作时不同电感补偿方案的影响因素,设计研制了标准电压互感器与带中压补偿试验变压器一体化试验设备,并将其固定安装于新型现场互感器校验车。试验设备使用SF6气体作为绝缘介质。升压装置采用谐振试验变压器,并与标准电压互感器装配于同一气室内部。标准电压互感器设计了特殊结构用于改善系统的不均匀电场分布问题,同时提升了设备使用带中压补偿试验变压器的补偿效果。标准电压互感器与升压器同室对测量结果影响等技术难题得到了有效解决。试验设备配合电动可调电抗器进行试验操作,满足了500 k V电压等级GIS内电压互感现场全电压检测要求,具有可靠性高、操作简便等优点。展开更多
BN-SiO-SiAlON composite ceramics were successfully prepared by the means of hot pressed sintering.Xe plasma flow generated by HallThruster was used for sputtering the surface of the samples in order to evaluate the pl...BN-SiO-SiAlON composite ceramics were successfully prepared by the means of hot pressed sintering.Xe plasma flow generated by HallThruster was used for sputtering the surface of the samples in order to evaluate the plasma erosion resistance.XRD,TEM,SEM,and LSCM were used to characterize the phase composition and morphologies of as-made composite ceramics before and after Xe plasma erosion.The ceramics were composed of h-BN,fused silica,and SiAlON,which maintained structuralstability during the process of Xe plasma sputtering.In conclusion,comparing with BN-SiOcomposite ceramics,the plasma erosion rate of BN-SiO-SiAlON composite ceramics decreases significantly at first then rises with the increase of AlN addition.Erosion pits can be observed by using SEM on the surface after plasma sputtering,which demonstrates that the BN grains have dropped off the surface.In addition,mechanicaldenudation by high-speed Xe ions is recognized as the injury mechanism for the BN-matrix composite materials.展开更多
基金National Natural Science Foundation of China (52072088, 52072089)Natural Science Foundation of Heilongjiang Province (LH2023E061)+1 种基金Scientific and Technological Innovation Leading Talent of Harbin Manufacturing (2022CXRCCG001)Fundamental Research Funds for the Central Universities (3072023CFJ1003)。
文摘Hexagonal boron nitride(h-BN)ceramics have become exceptional materials for heat-resistant components in hypersonic vehicles,owing to their superior thermal stability and excellent dielectric properties.However,their densification during sintering still poses challenges for researchers,and their mechanical properties are rather unsatisfactory.In this study,SrAl_(2)Si_(2)O_(8)(SAS),with low melting point and high strength,was introduced into the h-BN ceramics to facilitate the sintering and reinforce the strength and toughness.Then,BN-SAS ceramic composites were fabricated via hot press sintering using h-BN,SrCO_(3),Al_(2)O_(3),and SiO_(2) as raw materials,and effects of sintering pressure on their microstructure,mechanical property,and thermal property were investigated.The thermal shock resistance of BN-SAS ceramic composites was evaluated.Results show that phases of as-preparedBN-SAS ceramic composites are h-BN and h-SrAl_(2)Si_(2)O_(8).With the increase of sintering pressure,the composites’densities increase,and the mechanical properties shew a rising trend followed by a slight decline.At a sintering pressure of 20 MPa,their bending strength and fracture toughness are(138±4)MPa and(1.84±0.05)MPa·m^(1/2),respectively.Composites sintered at 10 MPa exhibit a low coefficient of thermal expansion,with an average of 2.96×10^(-6) K^(-1) in the temperature range from 200 to 1200℃.The BN-SAS ceramic composites prepared at 20 MPa display higher thermal conductivity from 12.42 to 28.42 W·m^(-1)·K^(-1) within the temperature range from room temperature to 1000℃.Notably,BN-SAS composites exhibit remarkable thermal shock resistance,with residual bending strength peaking and subsequently declining sharply under a thermal shock temperature difference ranging from 600 to 1400℃.The maximum residual bending strength is recorded at a temperature difference of 800℃,with a residual strength retention rate of 101%.As the thermal shock temperature difference increase,the degree of oxidation on the ceramic surface and cracks due to thermal stress are also increased gradually.
基金funded by the National Postdoctoral Program for Innovative Talents (Grant No. BX20190095)National Key Research and Development Program (Grant No. 2017YFB0310400)+1 种基金Financial support from the National Natural Science Foundation of China (Grant No. 51621091, 51472059)China’s Postdoctoral Science Fund (Grant No. 2019M660072, LBH-Z19141) were also appreciated
文摘在变电站现场开展GIS内电压互感器误差校验时,会面临试验一次回路长、GIS管道电容量随管道长短变化等问题,现有试验设备操作复杂且效率低下。通过研究升压试验操作时不同电感补偿方案的影响因素,设计研制了标准电压互感器与带中压补偿试验变压器一体化试验设备,并将其固定安装于新型现场互感器校验车。试验设备使用SF6气体作为绝缘介质。升压装置采用谐振试验变压器,并与标准电压互感器装配于同一气室内部。标准电压互感器设计了特殊结构用于改善系统的不均匀电场分布问题,同时提升了设备使用带中压补偿试验变压器的补偿效果。标准电压互感器与升压器同室对测量结果影响等技术难题得到了有效解决。试验设备配合电动可调电抗器进行试验操作,满足了500 k V电压等级GIS内电压互感现场全电压检测要求,具有可靠性高、操作简便等优点。
基金Funded by the National Natural Science Funds for Distinguished Young Scholar(No.51225203)the National Natural Science Foundation of China(Nos.51372050 and 50902030)
文摘BN-SiO-SiAlON composite ceramics were successfully prepared by the means of hot pressed sintering.Xe plasma flow generated by HallThruster was used for sputtering the surface of the samples in order to evaluate the plasma erosion resistance.XRD,TEM,SEM,and LSCM were used to characterize the phase composition and morphologies of as-made composite ceramics before and after Xe plasma erosion.The ceramics were composed of h-BN,fused silica,and SiAlON,which maintained structuralstability during the process of Xe plasma sputtering.In conclusion,comparing with BN-SiOcomposite ceramics,the plasma erosion rate of BN-SiO-SiAlON composite ceramics decreases significantly at first then rises with the increase of AlN addition.Erosion pits can be observed by using SEM on the surface after plasma sputtering,which demonstrates that the BN grains have dropped off the surface.In addition,mechanicaldenudation by high-speed Xe ions is recognized as the injury mechanism for the BN-matrix composite materials.
