Binder C, - Sic-b <sub> 4 </ Sub> C Carbon / Ceramic Composites And Self-healing Antioxidant Properties

Carbon materials have been widely used in high temperature environments owing to their some properties such as low density, refractory, excellent thermal stability and high strength in high temperature. However, the oxidation of carbon in high temperature has greatly restricted its use in air, therefore, increasing oxidation resistance of carbon materials in high temperature has invariably been the task for MSB reserchers for several decades. The study on C-SiC-B4C carbon/ceramics composites is just one of many endeavours to solve the problem on oxidation of carbon materials. Being different from the anti-oxidation method of coating, C-SiC-B4C composites feature self-healing when resist oxidation.When grounded into fine powders, green petroleum cokes with some content of volatiles can be directly molded and sintered without any additionally added binder. This special self-sintered raw carbon marerials can be fabricated into isotropic carbon marerials with high strength and high buck density. In this essay, based on the above mentioned study on binderless molding and self-sintering of green cokes, C-SiC-B4C carbon/ceramics composites are successfully manufactured as follows: the Nanjing green petroleum cokes with 12% content of volatiles as carbon precusor, added by different contents of SiC, B4C ceramic powders, are mixed and ball-milled together; obtained carbon/ceramics composite powders are then molded and sintered at temperature as high as 1600℃. The density and strength of C-SiC-B4C composites are measured, and the conditions which should be meeted for manufacturing the composites with high density are also discussed. By the XRD phase analysis of the pre-sintered and sintered composites and the SEM image of fracture microstructures of the composites, the sintering process and the sintering mechanism of the composites are investigated in detail.The anti-oxidation behaviours of C-SiC-B4C composites are tested at temperatures ranged from 700℃ to 1300℃. The results show that a solid self-healing anti-oxidation protective layer will form over the surface of composites when oxidized at 1100℃~1200℃; and when oxidized at temperature of 1300℃, the self-healing protective layer will change into liquid state or semi-liquid state and the anti-oxidation property of the composites will get worse. The composition ofself-healing anti-oxidation protective layer is SiO2B2O3 solid solution or boronsilicate glass, which is formed via the oxidation of SiC and B4C. The factors affecting the formation of self-healing anti-oxidation protective layer include relative density of the composites, the content of SiC and B4C, the ratio value of SiC/B4C and oxidation temperature etc., and the effect of sintering process on the enhancement of density of composites and then on the enhancement of anti-oxidation property is especially emphasized. Finally the surface morphorgy of self-healing anti-oxidation protective layer is observed through SEM and the thickness of the layer is also measured.