催化反应制备碳化硅纳米粉体的密度泛函理论计算及实验研究

Density Functional Theory Calculation and Experimental Study of Catalytic Synthesis SiC Nano Powders

以Si_(55),Si_(43)M_(12)和Si_(37)M_(18)(M=Fe,Co或Ni)团簇为模型,采用密度泛函理论(DFT)研究了Fe,Co及Ni纳米团簇催化硅粉转化为SiC的机理.计算结果表明,Fe,Co及Ni纳米催化剂先与Si形成合金,拉长并弱化Si—Si键的强度,起到活化Si粉的作用;合金的形成有利于C原子的吸附及Si原子和C原子间的反应;Fe的催化能力强于Co和Ni.在此基础上,以Si粉和酚醛树脂为原料,以Fe,Co及Ni硝酸盐为催化剂前驱体,通过微波加热反应制备了3C-SiC纳米粉体.研究了催化剂种类、反应温度、催化剂用量和反应时间等对制备3C-SiC纳米粉体的影响.结果表明,催化剂Fe,Co和Ni的加入均可显著降低3C-SiC的合成温度.当以2.0%(质量分数)的Fe为催化剂时,Si粉在1100℃下反应30 min后即可全部转化为3C-SiC纳米粉体;而在相同条件下,无催化剂时Si粉的完全转化温度为1250℃;Fe的催化效果优于Co和Ni,与DFT计算结果吻合.

Taking Si_（55）,Si_（43）M_（12） and Si_（37）M_（18）（ M = Fe,Co or Ni） cluster as models,density functional theory（ DFT） was used to investigate the catalytic mechanism of Fe,Co and Ni catalysts on the formation of SiC using Si and C as starting materials. The results show that Fe,Co and Ni nano catalysts will form alloy with Si first,and then elongate the bond length of Si—Si and weaken its bond strength,finally activate Si powder. The formation of alloy is favorable to the adsorption of C atom,and then accelerate the reaction process between Si and C atoms. The catalytic performance of Fe is better than Co and Ni. On this basis,3C-SiC nano powders were synthesized by a microwave reaction method using silicon powders and phenolic resin as raw materials,and ferric/cobalt/nickel nitrate as catalyst precursor. The effects of catalyst type,heat treatment temperature,catalyst content and holding time on the preparation of 3C-SiC were investigated. Results indicated that the addition of Fe,Co and Ni significantly decreased the synthesis temperature of 3C-SiC. Si powder can completely transform into 3C-SiC at 1100 ℃ for 30 min using 2. 0% Fe as catalyst. In contrast,for the sample without any catalysts,corresponding temperature was as high as 1250 ℃. Moreover,the experiment results also indicated that the catalytic performance of Fe is better than Co and Ni,which is in consistent with the DFT calculations.