Oxidation And Ablation Properties Of Low-Cost C/C-SiC Composites Prepared By Precursor Impregnation And Pyrolysis Method

C/C-SiC composites,prepared by precursor impregnation pyrolysis（PIP）with polycarbosilane（PCS）as SiC precursor,have excellent properties in terms of oxidation resistance,ablative resistance,wear resistance and structural load bearing,which are widely used in aerospace and braking fields.However,the price of PCS was extremely expensive,resulting in the high cost of preparing C/C-SiC composites by PIP method,which limited the further development and application of the composites.In order to solve this problem,low cost ethyl hexanosilicate（TEOS）,silica Sol（SiO₂）and polymethyl silane（PMS）as silicon source,boron phenolic resin（BPR）,glucose(C₆H₁₂O₆)and phenolic resin as carbon source,through the carbothermal reduction,sol-gel and PIP methods,C/C-SiC composites were prepared on the basis of C/C composites,and the fabrication cost,microstructure,mechanical,oxidation and ablation properties of the composites were investigated.Main research results are as follows:（1）Employing the cost-saving SiC precursor（TEOS-BPR）,C/C-SiC composites were prepared by carbothermal reduction method.The results show that during the heat treatment process of TEOS-BPR,the unique structure of SiO₂ phase enveloping C phase is formed,which is beneficial to fully generate SiC in the carbothermal reduction reaction and make part of SiC ceramics contain C nucleus.The C nucleus plays an active role in the oxidation and ablation process.After 36h static oxidation at high temperature,the weight loss rate of C/C-SiC composites was 8 wt%.After ablation for 90s,the linear ablation rate and mass ablation rate of the composites were 13.50±3.30μm/s and 0.141±0.015 mg/s,respectively.（2）In-situ SiC particles and nanofibers were grown in C/C preforms by using cost-saving precursor(SiO₂-C₆H₁₂O₆)through sol-gel method,and the compacted C/C-SiC composites were obtained.The results show that,compared with the nubby SiC generated by PCS pyrolysis,in-situ grown SiC particles and nanofibers of the composites were more continuous and could fill the tiny pores of the non-woven layer,which is beneficial to form a continuous and compact SiO₂ layer during ablation.Moreover,compared with C/C-SiC composites prepared by using PCS,the composites show more excellent anti-oxidation and anti-ablation properties.After 36h static oxidation at high temperature,the weight loss rate of the composites decreased by 0.3 wt%.After ablation for 120s,the linear ablation rate and mass ablation rate of the composites decreased by32.74%and 57.00%,respectively.（3）PMSC was obtained by modifying PMS with phenolic resin,which not only solved the problem of residual Siin the pyrolysis products of PMS,but also increased the ceramic yield.Compared with the composites prepared by using PCS,the cost of the C/C-SiC composites prepared by using PMSC was lower.Moreover,a small amount of MLG was introduced to mdify C/C-SiC composites,enhancing their oxidation and ablation properties.When the MLG content was 2.13 wt%,the weight loss rate of the composites decreased by 3.1 wt%after 36 h static oxidation.After ablation for 120 s,the mass and linear ablation rates of the composites decreased by 58.51%and 35.16%,respectively.（4）In the process of oxidation and ablation,La_9.33Si₆O₂₆ absorbed SiO₂ and transformed into La₂Si₂O₇ with a more stable structure,which increased the viscosity of molten SiO₂,reduced its evaporation and denudation,and enhanced the oxidation and ablation properties of C/C-SiC composites.When the content of La_9.33Si₆O₂₆ was 19.16 wt%,the composites did not lose weight after 100h static oxidation,but gained weight by 1wt%,the linear and mass ablation rates of the composites decreased by 81.15%and 95.00%after ablation for 120 s,respectively.92 figures 23 tables 174 references...