Study On Synthesis Process Of Large Production Of SiC/SiO₂Coaxial Nanocable

In this dissertation, combined with the product yield and microstructure, we systematically studied the synthesis process of high quality SiC/SiO2coaxial nanocable based on a homemade three-chamber continuous production of vacuum controlled atmosphere furnace, with synthesing large number of high quality SiC/SiO2coaxial nanocable as the goal and looking forward to its industrial production and applications. The synthesis process was constantly optimized and the growth mechanism was discussed.Firstly, we systematically studied the holding time, CH4ventilation time, CH4ventilation rate, CH4ventilation dynamic changes and the temperature of the raw materials into the furnace on the mass production of SiC/SiO2coaxial nanocable using the Si powder, SiO2powder and the CH4as raw materials by chemical vapor reaction. An optimization process of synthesising large scale SiC/SiO2coaxial nanocable was obtained:pre-milled Si powder and silica powder mixture (n(Si): n(SiO2)=1.5:1) as the silicon source, high purity methane gas as the carbon source,0.05mol-L"1nickel nitrate ethanol solution as the catalyst,1270℃as the synthesis temperature, the holding time is60min, CH4ventilation rate is about250sccm, the temperature of the raw materials into the furnace is less than400℃. The product reach gram level, the diameter of the obtained SiC/SiO2nanocable is about50-90nm, the single crystal SiC core diameter is about30-40nm and the amorphous SiO2layer thickness is about15-25nm。Secondly, we systematically studied the influence of the holding time, the amount of catalyst, the temperature of the raw materials into and out the furnace on the mass production of SiC/SiO2coaxial nanocable using the Si, SiO2and graphite mixture powders as the raw materials by chemical vapor reaction combined with the carbothermal reduction. The optimization of the process parameters are as follows: Si powder, SiO2powder and graphite powder mixed milled (n(Si):n(SiO2)=1.5:1, n(C):n(Si+SiO2)=1.5:1), synthesis temperature1270℃,0.05mol·L-1nickel nitrate ethanol solution uniformly dropping4-12ml, holding time120-240min, the temperature of the raw materials into and out the furnace were maintained under500℃and1000℃, respectively. The synchronization precipitation VLS growth mechanism proposed reasonablely to explan the phenomenon in the experiments and betterly to guide the progress of the synthesis experiment. The product reach one gram, the diameter of the obtained SiC/SiO2nanocable is about50-100nm, the core is about20-40nm and the amorphous layer thickness is about20-30nm。Finally, with graphite powders as solid carbon source and methane as gaseous carbon source, a optimization preparation process of synthesising large number of high quality SiC/SiO2coaxial nanocable was obtained:n(C):n(Si+SiO2)=1.5:1, synthesis temperature1270℃,0.05mol·L-1nickel nitrate ethanol solution uniformly dropping4ml, the holding time120min, methane ventilation rate100-250seem, the temperature of the raw materials into and out the furnace were maintained under500℃and1000℃,respectively. The formation mechanism of large area SiC/SiO2coaxial nanocable is described based on the special structure of the home-made graphite reactor and the VLS mechanism. The product stable in more than one gram, the diameter of the obtained SiC/SiO2nanocable is about60-80nm, the core is about25-35nm and the amorphous layer thickness is about15-20nm。In addition, here we preliminary explored using Si, SiO2powder, activated carbon, methane and polycarbosilane as the raw materials prepared SiC/SiO2coaxial nanocables, and the growth mechanism of the product was discussed.The synthesis process promotes the industrialization of SiC/SiO2coaxial nanocable as well as laid solid experimental and theoretical basis on the industrialization production of SiC and other one dimensional nanomaterials.