Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resu...Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’.展开更多
In the process of synthesis of nanometer SiC precursors with sol-gel of SiO2 and lignin , the products of all sizes required can be controlled by the concentration of reac-t ants , pH, temperature, reaction and ageing...In the process of synthesis of nanometer SiC precursors with sol-gel of SiO2 and lignin , the products of all sizes required can be controlled by the concentration of reac-t ants , pH, temperature, reaction and ageing time , and so on . The best conditions in this research are : the concentration of Na2SiO3 and organic matters are 4. 50% and 26.4% respectively, pH = 3.3 , T = 65℃ , ageing time is 30min , dried at 150 ℃ , the size of SiC precursors is about 2.0μm .展开更多
A highly branched polycarbosilane bearing allyl groups has been prepared by a one-pot synthesis with chloromethyltrichlorosilane, chloromethylmethyldichlorosilane and allyl chloride as the starting materials. The resu...A highly branched polycarbosilane bearing allyl groups has been prepared by a one-pot synthesis with chloromethyltrichlorosilane, chloromethylmethyldichlorosilane and allyl chloride as the starting materials. The resultant polymer, with the approximate formula [SiH1.2(CH3)0.71(CH2CHCH2)0.09CH2]n, has been characterized by 1H, 13C, and 29Si NMR, GPC, TG and elemental analysis. It could be cross-linked thermally at 170 °C in the absence of oxygen. Pyrolysis of the polymer gave a ceramic with a yield of about 70%.展开更多
Oligo（methylsilylene）-ethynylene polymer with crosslinkable ethynyl unit in the main chain was synthesized by condensation ofα,ω-dicholorooligo（methylsilane） with dilithioacetylene.The as-synthesized polymer was...Oligo（methylsilylene）-ethynylene polymer with crosslinkable ethynyl unit in the main chain was synthesized by condensation ofα,ω-dicholorooligo（methylsilane） with dilithioacetylene.The as-synthesized polymer was characterized by GPC,FT-IR and NMR.The results showed ethynyl group was successfully introduced to the polymer main chain.The ceramic yield was dramatically increased by the cross-polymerization of ethynyl group,and the excess silicon of PMS was compensated.Nearstoichiometric （C/Si=1.17） and partial crystallizationβ-SiC monoliths were obtained by pressureless pyrolysing PSPA at 1200℃in a high yield（73.6 wt%）.展开更多
基金Project (No. 2004C31044) supported by the Science & TechniqueProject of Zhejiang Province, China
文摘Silicon carbide (SiC) ceramic with YAG (Y3Al5O12) additive added by sol-gel method was liquid-phase sintered at different sintering temperatures, and the sintering mechanism and microstructural characteristics of resulting silicon carbide ceramics were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and elemental distribution of surface (EDS). YAG (yttrium aluminum garnet) phase formed before the sintering and its uniform distribution in the SiC/YAG composite powder decreased the sintering temperature and improved the densification of SiC ceramic. The suitable sintering temperature was 1860 °C with the specimen sintered at this temperature having superior sintering and mechanical properties, smaller crystal size and fewer microstructure defects. Three characteristics of improved toughness of SiC ceramic with YAG added by sol-gel method were microstructural densification, main-crack deflection and crystal ‘bridging’.
文摘In the process of synthesis of nanometer SiC precursors with sol-gel of SiO2 and lignin , the products of all sizes required can be controlled by the concentration of reac-t ants , pH, temperature, reaction and ageing time , and so on . The best conditions in this research are : the concentration of Na2SiO3 and organic matters are 4. 50% and 26.4% respectively, pH = 3.3 , T = 65℃ , ageing time is 30min , dried at 150 ℃ , the size of SiC precursors is about 2.0μm .
文摘A highly branched polycarbosilane bearing allyl groups has been prepared by a one-pot synthesis with chloromethyltrichlorosilane, chloromethylmethyldichlorosilane and allyl chloride as the starting materials. The resultant polymer, with the approximate formula [SiH1.2(CH3)0.71(CH2CHCH2)0.09CH2]n, has been characterized by 1H, 13C, and 29Si NMR, GPC, TG and elemental analysis. It could be cross-linked thermally at 170 °C in the absence of oxygen. Pyrolysis of the polymer gave a ceramic with a yield of about 70%.
基金financial support of the National Science Foundation of China(No. 50903086)the Chinese Academy of Sciences
文摘Oligo（methylsilylene）-ethynylene polymer with crosslinkable ethynyl unit in the main chain was synthesized by condensation ofα,ω-dicholorooligo（methylsilane） with dilithioacetylene.The as-synthesized polymer was characterized by GPC,FT-IR and NMR.The results showed ethynyl group was successfully introduced to the polymer main chain.The ceramic yield was dramatically increased by the cross-polymerization of ethynyl group,and the excess silicon of PMS was compensated.Nearstoichiometric （C/Si=1.17） and partial crystallizationβ-SiC monoliths were obtained by pressureless pyrolysing PSPA at 1200℃in a high yield（73.6 wt%）.
