Synthesis Of SiC Precursors Containing Zirconium, Tantalum And Hafnium To Prepare The SiC Fibers

In order to improve the high-temperature resistance and oxidation-resistance performance of SiC ceramic,introducing hetero-elements in the preparation process of SiC ceramic precursor to synthesis hetero-elements containing SiC ceramic precursor has become the mainstream of high-performance SiC ceramic materials.In this work,three preceramic polymers-Polyzirconocarbosilane(PZCS), Polytantalocarbosilane(PTCS) and Polyhafnocarbosilane(PHCS) were synthesized.The corresponding Si-Zr-C-O ceramic fibers,Si-Ta-C-O ceramic fibers and Si-Hf-C-O ceramic fibers were prepared.The reaction conditions,structure and reaction mechanism of PZCS,PTCS PHCS were studied in details.The composition,structure,high-temperature and oxidation-resistance properties of the ceramic fibers were also studied.PZCS was synthesized by the reaction of LPCS and Zr(AcAc)₄(4 wt%～8 wt%).At reaction temperature 390～450℃and pyrolysis temperature 480～520℃for 6～8h,PZCS melts at 160～270℃and exits good spinnability.The reaction yield is 50.4%and the ceramic yield of PZCS is 82.4%Si-Zr-C-O fibers were obtained from PZCS,whose chemical formula is SiC_1.24H_xO_0.56Zr_0.0129.The average diameter of the fibers is 11μm,the average tensile strength is 2.5 GPa.Si-Zr-C-O fibers have good high-temperature-resistant performance.Processing at 1450℃and 1600℃,the tensile strength retention rate is 72%and 36%respectively.The chemical formula of Si-Zr-C-O fibers is SiC_0.99H_xO_0.1Zr_y after processing at 1800℃.Si-Zr-C-O fibers also have good oxidation-resistance properties.After processing 20 hours at 1000℃in the air, the tensile strength retention rate is 71.2%,after processing 100 h,the tensile strength retention rate is 50%.PTCS was synthesized by the reaction of LPCS and Ta(AcAc)(OEt)₄(4 wt%～10 wt%).At reaction temperature 450℃and pyrolysis temperature 500℃for 6～12h,PTCS melts at 180～260℃and exits good spinnability.The reaction yield is 66.4%and the ceramic yield is 84.2%.Si-Ta-C-O fibers were obtained from PTCS,whose chemical formula is SiC_0.63H_xO_0.55Ta_y.The average diameter of the fibers is 20μm,the average tensile strength is 1.9 GPa.Si-Ta-C-O fibers have good high-temperature-resistant perfomance.After processing at 1450℃and 1600℃,the tensile strength retention rate is 47%and 32%respectively.The chemical formula of Si-Ta-C-O fibers is SiC_1.19H_xO_0.056Ta_y after processing at 1800℃. Si-Ta-C-O fibers have good oxidation-resistance properties.After processing 20 hours at 1000℃in the air,the tensile strength retention rate is 56.82%,after processing 100h,the tensile strength retention rate is 60.5%.PHCS was synthesized by the reaction of LPCS and Hf(AcAc)₄(2 wt%～15 wt%).At reaction temperature 450℃and pyrolysis temperature 500℃for 14h,PTCS melts at 160～300℃and exits good spinnability.The reaction yield is 67.2%and the ceramic yield of PHCS is 83.9%,much higher than PCS.Si-Hf-C-O fibers were obtained from PHCS,whose chemical formula is SiC_1.48H_xO_1.17Hf_y.The average diameter of the fibers is 14μm,the average tensile strength is 1.8GPa.Si-Hf-C-O fibers had good high-temperature-resistant perfomance. After processing at 1450℃and 1600℃,the tensile strength retention rate is 61%and 39%. The chemical formula of Si-Hf-C-O fibers is SiC_1.13H_xO_0.06Hf_y after processing at 1800℃. Si-Hf-C-O fibers have good oxidation-resistance properties.After processing 20 hours at 1000℃in the air,the tensile strength retention rate is 74.0%,after processing 100 h,the tensile strength retention rate is 46.1%.As discussed above,the overall performance of Si-Zr-C-O fibers is the best among the three kinds hetero-elements containing ceramic fibers.