SYNTHESIS AND CHARACTERIZATION OF POLYZIRCONOCARBOSILANE PRECURSOR

Abstract

In order to improve the properties of SiC ceramic fibers polyzirconocarbosilane (PZCS),the precursor of Si—Zr—C—O ceramic fibers, was synthesized by the reaction of zirconium acetylacetonate (Zr(AcAc)_4) at 420℃ with polysilacarbosilane (PSCS),which was prepared by the thermolysis and condensation of polydimethylsilane (PDMS).By the use of liquid PSCS,Zr could be distributed uniformly,and the sublimation of Zr(AcAc)_4 could also be avoided.The empirical formula of PZCS was SiC_ 1.94 H_xO_ 0.066 Zr_ 0.0104 ,the number-averaged molecular weight is in the range of 1300～2500.When the reaction of PSCS with Zr(AcAc)_4 proceeded,an enormous decrease in the number of Si—H bonds in PSCS was observed.The reaction mechanism was found to be that the increase of the molecular weight of PZCS was related to the cross-linking reaction of Si—H bonds with Zr(AcAc)_4,which led to the generation of Si—O—Zr.There exists SiC_4 and SiC_3H structure in PZCS.The ceramic yield of PZCS was 82.4%.We got the Si—Zr—C—O ceramic fibers using PZCS,whose chemical formula was SiC_ 1.24 H_xO_ 0.56 Zr_ 0.0129 .The average tensile strength was 2.6 GPa,the average diameter was 11 μm.Si—Zr—C—O fibers have good high-temperature-resistant performance.Processing at 1450℃ and 1600℃,the tensile strength retention rate was 72% and 36% respectively.Si—Zr—C—O fibers also have good oxidation-resistance properties.After processing 20 h at 1000℃ in the air,the tensile strength retention rate was 71.2%,after processing 100 h,the tensile strength retention rate was 50%.