Chemical vapor deposition of coiled ceramics

1)详细考察了螺旋状碳纤维的制备条件。a）发现少量的硫化氢、磷等杂质对螺旋状碳纤维的生长是必不可少的。H_2S杂质的最佳浓度为0.06- 0.09vol %。b）卷曲碳纤维的最大产率在约700 ° C下在最佳杂质浓度下获得（约30%）。c）线圈长度随着反应时间的增加线性增加，直至60分钟。乙炔和丙酮杂质的流量对螺旋状碳纤维的生长没有影响。2）探讨了螺旋状碳纤维的生长机理。结果表明，镍催化剂的存在对螺旋状碳纤维的生长是必不可少的。提出了一种新的螺旋状碳纤维生长机理-“尖端准VLS机理”。3）通过对螺旋状碳纤维进行气相渗硅，制备了螺旋状碳化硅纤维，也可通过有机加压剂与四氯化碳和氢气在1300-1400 ℃下反应。通过在1100-1300 ℃下对螺旋状碳纤维进行气相渗钛，制备了螺旋状碳化钛纤维。

1) Preparation conditions of the coiled carbon fibers have been examined in detail.a) It was found that a small amount of impurities such as hydrogen sulfide, phosphorus trichloride, it was indispensable for the growth of the coiled carbon fibers. The optimum concentration of the H_2S impurity was determined to be 0.06-0.09 vo1%.b) The maximum yield of the coiled carbon fibers (about 30 %) was obtained at about 700^ﾟC under an optimum impurity concentration.c) The coil length increased linearly with increasing reaction time up to 60 min.d) The flow rate of acetylene and acetone impurities did not affected on the growth of the coiled carbon fibers.2) Growth mechanism of the coiled carbon fibers was discussed. It was observed that presence of nickel catalyst was indispensable for the growth of the coiled carbon fibers. We proposed a new growth mechanism "tip quasi-VLS mechanism" for the growth of the coiled carbon fibers.3) The coiled silicon carbide fibers have been prepared by the vapour phase siliconizing of the coiled carbon fibers, and also by the reaction of an organic presusrsor with carbon tetrachloride and hydrogen at 1300-1400^ﾟC.4) The coiled titanium carbide fibers have been prepared by the vapor phase titanizing of the coiled carbon fibers at 1100-1300^ﾟC.