SiC nanowires and SiC/SiO2 core-shell structural nanowires were synthesized via a simple thermal evaporation of CoxSiy melts at the temperature of 1500?C. The morphologies and yields of those SiC nanowires can be tuned by altering the composition of CoxSiy. Nanowires obtained by thermal evaporation of Co Si are composed of SiC/SiO2 core-shell nanostructures with lengths up to several hundreds of micrometers, diameters of 4050 nm, and the thickness of amorphous SiO2 wrapping shell about 20 nm. SiC nanowires prepared by thermal evaporation of Co Si2 and Co2 Si melt are found to be hexagonal-prism-shaped nanorods, and the diameter of those nanorods is about 150 nm and the length is about 10 microns. All the SiC nanowires obtained possess [111] preferred growth direction with a high density stacking faults and twin defects. Taking into consideration the binary alloy diagram of Co Si and the participation of oxygen, we propose the vapor-solid growth mechanism of SiC nanowires and discuss the effect of the supersaturation of Si O on the morphology and yields of SiC nanowires.
碳化硅(SiC)纤维具有高强度、高模量、耐高温、抗蠕变、抗氧化等优异性能,是增强耐高温陶瓷基复合材料的关键材料。介绍了先驱体法制备3代SiC纤维的发展历程:从第1代高氧碳含量SiC纤维发展到第2代低氧高碳含量SiC纤维,再到第3代近化学计量比SiC纤维,SiC纤维的微结构从非晶到微晶显著变化,纤维的耐热性能也显著提高。重点比较了第3代近化学计量比SiC纤维(Hi-Nicalon Type S纤维、Tyranno SA和Sylramic纤维等)的性质,结果表明:SiC纤维的热稳定性由近化学计量比SiC微晶的致密度和微结构决定,Sylramic和Tyranno SA纤维的组成和微结构可通过控制Si-C-O纤维的碳热还原反应来实现,烧结助剂的采用及陶瓷烧结工艺的有效应用可提高纤维的致密度。Hi-Nicalon Type S纤维的组成和微结构取决于聚碳硅烷分解过程中特定的气氛和温度。简介了SiC纤维的研究进展并讨论了其发展趋势。
