Ablation and oxidation resistance properties of C/C composites densified by xylene pyrocarbon using LaCl3 as a catalyst and resin carbon
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摘要: 采用薄膜沸腾（CVI）法，以LaCl3催化热解二甲苯、浸渍树脂及热处理后获得密度为1.72~1.73 g/cm3的炭/炭（C/C）复合材料。应用氧-乙炔火焰和静态空气氧化法测试材料的烧蚀与氧化性能，XRD、SEM研究烧蚀及氧化面的物相组成与形貌。结果表明，随着催化剂含量由0升高至15 wt%，材料的烧蚀和氧化失重率先减小后增大。高温氧化环境中表面形成的La2O3层可减缓材料的氧化，催化生长的纳米丝状碳增强了基体抗剥蚀能力，使得催化剂添加后材料的质量和线烧蚀率较未添加时分别降低7.6%~15.2%和10.7%~20.0%，氧化失重率减少17.7%~38.5%。催化剂含量6 wt%和10 wt%下材料的性能较佳；含量超过10 wt%后，基体中各向同性结构热解炭较厚，导致材料抗烧蚀氧化性能降低。热处理温度由1 800℃升高至2 250℃时，材料的抗烧蚀氧化性能提高。Abstract: Carbon/carbon composites with densities of 1.72-1.73 g/cm3 were prepared by densification with pyrocarbon produced from xylene using a LaCl3-catalyzed film boiling chemical vapor infiltration method, followed by resin impregnation, carbonization and graphitization. The ablation and oxidation resistance of the composites were respectively tested by an oxyacetylene torch and air oxidation methods. The phase composition and morphology of the ablated and oxidized surfaces were studied by XRD and SEM, respectively. Results show that the ablation rate and oxidation loss exhibit minima at catalyst contents from 0 to 15 wt%. During the ablation and oxidation, the La2O3 film formed from LaC2 oxidation protects the composites from further oxidation. Catalytically-formed carbon nanofilaments prevent mechanical separation of the carbon fibers from the matrix. As a result, mass ablation and volume ablation rates and the weight loss of the composites due to oxidation are decreased by 7.6%-15.2%, 10.7%-20.0% and 17.7%-38.5%, respectively compared with those formed without the catalyst. The composites produced at catalyst contents of 6 and 10 wt% have higher ablation and oxidation resistance than samples with 0, 3 and 15 wt% contents. Both the thicker isotropic pyrocarbon when the catalyst content is more than 10 wt% and the lower fraction of carbon nanofilaments when the catalyst content is less than 6 wt% are unfavorable for the improvement of the ablation and oxidation resistance properties. The ablation and oxidation resistance of the composites are improved by graphitization from 1 800℃ to 2 250℃.
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Key words:
- Carbon/carbon composites /
- Rare earth La /
- Ablation /
- Oxidation
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