Polybenzimidazole containing ether bond（OPBI） was reinforced with silicon carbide whisker（m Si C） modified by 3-aminopropyltriethoxysilane（KH550）, and then doped with phosphoric acid（PA） to obtain OPBI/m Si C/...Polybenzimidazole containing ether bond（OPBI） was reinforced with silicon carbide whisker（m Si C） modified by 3-aminopropyltriethoxysilane（KH550）, and then doped with phosphoric acid（PA） to obtain OPBI/m Si C/PA membranes. These OPBI/m Si C/PA membranes have excellent mechanical strength and oxidative stability and can be used for high temperature proton exchange membrane（HT-PEM）. The tensile strength of OPBI/m Si C/PA membranes ranges from 27.3 to 36.8 MPa, and it increases at first and then decreases with the increase of m Si C content. The high m Si C content and PA doping level contribute to improving the proton conductivity of membranes. The proton conductivity of PBI/m Si C-10/PA membrane is 27.1 m S cm-1 at 170℃ without humidity, with an increase of 55.7% compared with that of OPBI/PA membrane. These excellent properties make OPBI/m Si C/PA membranes promising membrane materials for HT-PEM applications.展开更多
The thermal expansion behaviors of commercially-available SiC whisker reinforced pure aluminum composites subjected to different heat treatments were studied. The results indicated that the thermal expansion behaviors...The thermal expansion behaviors of commercially-available SiC whisker reinforced pure aluminum composites subjected to different heat treatments were studied. The results indicated that the thermal expansion behaviors were greatly affected by heat treatment. To explain the results, the microstructures and thermal mismatch stresses in the matrix of the composite were examined by the transmission electron microscope and X-ray diffraction, respectively. The results show that the dislocation density and thermal mismatch stresses in the matrix of the composites water-quenched from 600°C are much higher than those of the composite slowly cooled from 600°C. The analysis suggests that the coefficients of thermal expansion (CTE) are closely related to the change of thermal mismatch stresses and the yield strength of the matrix of the composite. The comparison of the coefficients of thermal expansion between experiments and calculations suggests that the temperature behaviors of CTE of SiC/Al composite agree better with those of Kerner's model within lower temperature range.展开更多
The pitch was dried and modified with 1 mass%nickel nitrate and 10 mass% Si powder successively,then carbonized in Ar atmosphere at 900,1 000,1 100,1 200,1 300,and 1 400 ℃,respectively. Effects of carbonization tempe...The pitch was dried and modified with 1 mass%nickel nitrate and 10 mass% Si powder successively,then carbonized in Ar atmosphere at 900,1 000,1 100,1 200,1 300,and 1 400 ℃,respectively. Effects of carbonization temperature on phase composition and microstructure of Ni-catalyzed silicon modified pitch were studied by XRD,FESEM and EDS,and the growth mechanism of Si C whiskers was discussed as well. The results show that Si C whiskers form in the carbonized products of modified pitch processed in Ar atmosphere at 1 000,1 100,1 200,1 300,or 1 400 ℃; its length is about1- 6 μm; its growth mode is apical growth,and its growth mechanism accords with V- L- S mechanism.展开更多
SiC whiskers were synthesized by carbothermal reduction of silicon nitride, α-Si3N4 and β-Si3N4 powders were used as silicon sources, and graphite, active carbon and black carbon as carbon sources, as well as boron ...SiC whiskers were synthesized by carbothermal reduction of silicon nitride, α-Si3N4 and β-Si3N4 powders were used as silicon sources, and graphite, active carbon and black carbon as carbon sources, as well as boron oxide as catalyst. The synthesized SiC whiskers were characterized by XRD and SEM. The results showed that the synthesizing temperature should be above 1716 K; the decomposition of Si3N4 was the limited step in the synthesis of SiC whiskers; and catalyst not only offered the liquid condition, but also restricted the growth of SiC whiskers along one dimension. LS mechanism seems to explain well the growth of SiC whiskers.展开更多
The cemented carbide material (YG10F) with different additions of TiC whisker (0%, 0.3%, 0.6%, mass fraction) was prepared by different techniques. The effect of TiC whisker addition on the density, microhardness and ...The cemented carbide material (YG10F) with different additions of TiC whisker (0%, 0.3%, 0.6%, mass fraction) was prepared by different techniques. The effect of TiC whisker addition on the density, microhardness and toughness of the experimental material was investigated. The results indicate that after the wet-milling for 8 h and sintering in vacuum at 1 440 ℃, the toughness of YG10F is remarkably improved and meanwhile higher microhardness is obtained by 0.3% TiC whisker addition. Preliminary analysis suggests that the main toughening mechanism of TiC whisker in YG10F is whisker pull-out and bridging phenomena.展开更多
A new way to prepare SiC whiskers through the induction of carbon fiber was suggested. With the processing steps of opening furnace firstly and then shutting it, rice hall, as the only raw material, was carbonified to...A new way to prepare SiC whiskers through the induction of carbon fiber was suggested. With the processing steps of opening furnace firstly and then shutting it, rice hall, as the only raw material, was carbonified to get excess quantity of Si in rice hull. After a certain catalyzer was added, SiC whiskers were prepared by means of the induction of carbon fiber. The component and morphology of the whisker were analyzed by XRD, SEM and TEM. The results reveal that the diameters of the whiskers range in 0.5-2μm and their lengths in 100-500μm. The whiskers are straightβ-SiC crystals with smooth surface. The whisker is homogeneous and its productivity is 100%. Two kinds of formation mechanisms, both VLS mechanism and vapor formation mechanism, are involved during the growth of the whiskers. But the vapor formation mechanism relatively plays a key role.展开更多
A thin layer of poly(vinyl alcohol)(PVA) was coated on the surface of silicon carbide whiskers(SCWs)and crosslinked by glutaraldehyde, and then these modified whiskers(mSCWs) were incorporated into high density polyet...A thin layer of poly(vinyl alcohol)(PVA) was coated on the surface of silicon carbide whiskers(SCWs)and crosslinked by glutaraldehyde, and then these modified whiskers(mSCWs) were incorporated into high density polyethylene(HDPE) to prepare HDPE/mSCW composites with a high thermal conductivity.The thermal conductivity, mechanical properties, heat resistance, thermal stability and morphology of HDPE/mSCW and HDPE/SCW composites were characterized and compared. The results reveal that the thermal conductivity of both HDPE/SCW and HDPE/mSCW composites increases with the increase of filler loading, and reaches a maximum of 1.48 and 1.69 W/(m K) at 40 wt% filler loading, which is 251.20% and 300.75% higher than that of HDPE, respectively. Significantly, HDPE/mSCW composites have a higher thermal conductivity than their HDPE/SCW counterparts with the same filler loading. In addition, the heat resistance, Young’s modulus and yield strength of both HDPE/SCW and HDPE/mSCW composites are also improved compared with that of HDPE. mSCW can be homogenously dispersed in the HDPE matrix, which contributes to the formation of thermally conductive networks by the inter-connection of mSCWs.展开更多
基金financially sponsored by the Kunlun Scholar Award Program of Qinghai Provincethe Fundamental Research Funds for the Central Universities (WD1315012)
文摘Polybenzimidazole containing ether bond（OPBI） was reinforced with silicon carbide whisker（m Si C） modified by 3-aminopropyltriethoxysilane（KH550）, and then doped with phosphoric acid（PA） to obtain OPBI/m Si C/PA membranes. These OPBI/m Si C/PA membranes have excellent mechanical strength and oxidative stability and can be used for high temperature proton exchange membrane（HT-PEM）. The tensile strength of OPBI/m Si C/PA membranes ranges from 27.3 to 36.8 MPa, and it increases at first and then decreases with the increase of m Si C content. The high m Si C content and PA doping level contribute to improving the proton conductivity of membranes. The proton conductivity of PBI/m Si C-10/PA membrane is 27.1 m S cm-1 at 170℃ without humidity, with an increase of 55.7% compared with that of OPBI/PA membrane. These excellent properties make OPBI/m Si C/PA membranes promising membrane materials for HT-PEM applications.
文摘The thermal expansion behaviors of commercially-available SiC whisker reinforced pure aluminum composites subjected to different heat treatments were studied. The results indicated that the thermal expansion behaviors were greatly affected by heat treatment. To explain the results, the microstructures and thermal mismatch stresses in the matrix of the composite were examined by the transmission electron microscope and X-ray diffraction, respectively. The results show that the dislocation density and thermal mismatch stresses in the matrix of the composites water-quenched from 600°C are much higher than those of the composite slowly cooled from 600°C. The analysis suggests that the coefficients of thermal expansion (CTE) are closely related to the change of thermal mismatch stresses and the yield strength of the matrix of the composite. The comparison of the coefficients of thermal expansion between experiments and calculations suggests that the temperature behaviors of CTE of SiC/Al composite agree better with those of Kerner's model within lower temperature range.
文摘The pitch was dried and modified with 1 mass%nickel nitrate and 10 mass% Si powder successively,then carbonized in Ar atmosphere at 900,1 000,1 100,1 200,1 300,and 1 400 ℃,respectively. Effects of carbonization temperature on phase composition and microstructure of Ni-catalyzed silicon modified pitch were studied by XRD,FESEM and EDS,and the growth mechanism of Si C whiskers was discussed as well. The results show that Si C whiskers form in the carbonized products of modified pitch processed in Ar atmosphere at 1 000,1 100,1 200,1 300,or 1 400 ℃; its length is about1- 6 μm; its growth mode is apical growth,and its growth mechanism accords with V- L- S mechanism.
文摘SiC whiskers were synthesized by carbothermal reduction of silicon nitride, α-Si3N4 and β-Si3N4 powders were used as silicon sources, and graphite, active carbon and black carbon as carbon sources, as well as boron oxide as catalyst. The synthesized SiC whiskers were characterized by XRD and SEM. The results showed that the synthesizing temperature should be above 1716 K; the decomposition of Si3N4 was the limited step in the synthesis of SiC whiskers; and catalyst not only offered the liquid condition, but also restricted the growth of SiC whiskers along one dimension. LS mechanism seems to explain well the growth of SiC whiskers.
基金Project(550108) supported by the Natural Science Foundation of Jiangxi Province, China
文摘The cemented carbide material (YG10F) with different additions of TiC whisker (0%, 0.3%, 0.6%, mass fraction) was prepared by different techniques. The effect of TiC whisker addition on the density, microhardness and toughness of the experimental material was investigated. The results indicate that after the wet-milling for 8 h and sintering in vacuum at 1 440 ℃, the toughness of YG10F is remarkably improved and meanwhile higher microhardness is obtained by 0.3% TiC whisker addition. Preliminary analysis suggests that the main toughening mechanism of TiC whisker in YG10F is whisker pull-out and bridging phenomena.
基金Project(50225210) supported by the National Natural Science Foundation of China for Distinguished Young Scholars Project(03H53044) supported by the Aeronautic Science of China
文摘A new way to prepare SiC whiskers through the induction of carbon fiber was suggested. With the processing steps of opening furnace firstly and then shutting it, rice hall, as the only raw material, was carbonified to get excess quantity of Si in rice hull. After a certain catalyzer was added, SiC whiskers were prepared by means of the induction of carbon fiber. The component and morphology of the whisker were analyzed by XRD, SEM and TEM. The results reveal that the diameters of the whiskers range in 0.5-2μm and their lengths in 100-500μm. The whiskers are straightβ-SiC crystals with smooth surface. The whisker is homogeneous and its productivity is 100%. Two kinds of formation mechanisms, both VLS mechanism and vapor formation mechanism, are involved during the growth of the whiskers. But the vapor formation mechanism relatively plays a key role.
基金financially sponsored by the National Natural Science Foundation of China(No.U1507123)the Foundation of Qinghai Science and Technology Department(No.2017-HZ-803)+1 种基金the Thousand Talents Program of Qinghai ProvinceKunlun Scholar Award Program of Qinghai Province
文摘A thin layer of poly(vinyl alcohol)(PVA) was coated on the surface of silicon carbide whiskers(SCWs)and crosslinked by glutaraldehyde, and then these modified whiskers(mSCWs) were incorporated into high density polyethylene(HDPE) to prepare HDPE/mSCW composites with a high thermal conductivity.The thermal conductivity, mechanical properties, heat resistance, thermal stability and morphology of HDPE/mSCW and HDPE/SCW composites were characterized and compared. The results reveal that the thermal conductivity of both HDPE/SCW and HDPE/mSCW composites increases with the increase of filler loading, and reaches a maximum of 1.48 and 1.69 W/(m K) at 40 wt% filler loading, which is 251.20% and 300.75% higher than that of HDPE, respectively. Significantly, HDPE/mSCW composites have a higher thermal conductivity than their HDPE/SCW counterparts with the same filler loading. In addition, the heat resistance, Young’s modulus and yield strength of both HDPE/SCW and HDPE/mSCW composites are also improved compared with that of HDPE. mSCW can be homogenously dispersed in the HDPE matrix, which contributes to the formation of thermally conductive networks by the inter-connection of mSCWs.
