B-C掺杂SiC纤维的制备及其性能研究

Boron-carbon doped Silicon Carbide Fibers: Preparation and Property

以聚碳硅烷、聚硼硅氮烷和二甲苯可溶沥青为原料通过低温共混得到了一种B-C掺杂SiC前驱体,再经熔融纺丝、预氧化以及高温热处理制得B-C掺杂SiC纤维。采用红外光谱(IR)、X射线衍射(XRD)、扫描电镜(SEM)等手段对B-C掺杂SiC前驱体及其纤维的组成和微观结构进行了分析和表征,主要研究了热处理温度对纤维组成、结构、力学性能和抗氧化性能的影响。结果表明:硼的引入有效地抑制了高温热处理过程中SiC晶粒的长大,提高了C掺杂SiC纤维的稳定性; B-C掺杂碳化硅纤维经1600℃处理后主要由β-SiC组成,并含有少量的O、B和N。B-C掺杂SiC纤维抗氧化性能优于C掺杂SiC纤维,这主要归因于掺杂纤维在高温氧化过程中形成的硼硅酸盐玻璃膜对其内部的沥青炭起到了很好的氧化防护作用。

The B-C doped SiC precursor was obtained by blending of polycarbosilane, polyborosilicate and xylene soluble pitch at low temperature. The resulted precursor was melt-spun into precursor fibers. The B-C doped silicon carbide fibers were finally obtained by pre-oxidation and high temperature heat-treatment of the precursor fibers successively. The composition and microstructure of B-C doped SiC precursor and its fibers were characterized by IR, XRD and SEM. Effect of the heat-treatment temperature on the composition, structure, mechanic property and oxidation resistance was studied. The results show that the introduction of boron in SiC fibers restrains the growth of SiC grains at high temperature treatment effectively, and simaltaneously improves the thermal stability of the C-doped SiC fibers. B-C doped silicon carbide fibers obtained by heating the pre-oxidized fibers at 1600 ℃ were mainly composed of β-SiC and a small amount of O, B and N. B-C doped SiC fibers ownse better oxidation resistance than the C-doped SiC fibers, which can be attributed to the formation of borosilicate film during the high-temperature oxidation of the B-C doped SiC fibers. This film plays a role effectively in preventing the pith carbon in the doped fibers from oxidation.