聚锆碳硅烷陶瓷先驱体的制备与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷(PDMS)热解制得的液相产物聚硅碳硅烷(PSCS)与乙酰丙酮锆(Zr(AcAc)4)反应,制备了含锆SiC陶瓷纤维的先驱体聚锆碳硅烷(PZCS).选用液相PSCS作为反应原料,可使锆元素在先驱体中分布更加均匀,并能防止Zr(AcAc)4在反应过程中升华.实验合成的PZCS化学式为SiC1.94HxO0.066Zr0.0104,数均分子量Mn=200~400,再成型性良好.反应机理研究表明,反应过程中存在PSCS裂解重排反应,Si—H键在反应中显示出很高的活性,PZCS分子量的增加是PSCS形成的Si—H键与Zr(AcAc)4的配位基发生交联反应的结果.利用PZCS制备的Si—Zr—C—O陶瓷纤维平均强度2.6GPa,平均直径11μm,性能优异.

YNTHESIS AND CHARACTERIZATION OF POLYZIRCONOCARBOSILANE PRECURSOR

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%.