Study On Preparation Technology Of Silicon Carbide Powders With Controlled Particle Size And Morphology

SiC ceramics have excellent mechanical properties,oxidation resistance,wear resistance,thermal stability,thermal shock resistance and chemical corrosion resistance,and the thermal expansion coefficient is small,the thermal conductivity is large.Some SiC ceramic products with specific structure,such as SiC ceramic membranes,often need small particle size and high sphericity in order to meet the requirements of application.Therefore,it is very important to prepare SiC powders with controllable particle size and morphology.In order to promote the research and application of SiC ceramic membranes,the research topic is the study on preparation technology of silicon carbide powders with controlled particle size and morphology.In this paper,SiC powders were prepared by carbothermal reduction,the controllability of particle size and morphology of SiC powders was studied by controlling sintering temperature,holding time,firing mode and silicon source type,the aim is to understand the reaction mechanism of carbothermal reduction reaction,to master the key factors to control the particle size and morphology of SiC powders,and to provide the SiC powders with controllable particle size and high sphericity for practical production of SiC ceramic membranes.The main contents are described as follows:(1)Effects of sintering temperature and doping on particle size and morphology of SiCSiC was prepared by carbothermal reduction in a horizontal vacuum sintering furnace with microsilica powders and glucose as the main raw materials.The effects of different calcination temperatures on the phase,particle size and morphology of SiC were investigated,and the effects of niobium doping on the morphology of SiC were further studied.The results show that: When calcined at 1300℃,1400℃ and1500℃ for 2 h,the obtained products are 3C-SiC,the SiC of this crystalline form belongs to β-SiC.With the increase of temperature,the degree of crystallization of the product increases,the particle size increases,and the morphology changes from irregular shape to polygon,the morphology and particle size of SiC can be effectively influenced and controlled by controlling the reaction temperature.At 1400℃,theproduct can inherit the morphology of microsilicon powders.Niobium doping causes the product to exist in the form of adhesion,and rod-like SiC appears in the product,at this point,the product has obvious behavior of crystal growth and crystal merger.The particle morphology and grain size of SiC can also be controlled by doping niobium powders,and the reaction temperature can be lowered by doping.However,due to the heterogeneity of morphology,the SiC prepared by doping is not suitable for practical application.(2)Effect of holding time on particle size and morphology of SiC and study on reaction mechanismUsing microsilica powders and glucose as main raw materials,the influence of heat preservation time(60min,120 min,180min)on SiC was investigated by using three-temperature tube furnace at 1300℃ and 1400℃ and the formation mechanism of SiC whiskers and powders was studied.The results show that: At 1300℃,the carbothermal reduction reaction has not taken place yet,and when the holding time is prolonged,the carbothermal reduction reaction still does not take place.At 1400℃ for60 min,SiC was formed in the product,at 1400℃ for 120 min,the amount of SiC increased and SiC was able to inherit the morphology and particle size of the microsilica powders,at 1400℃ for 180 min,the yield of SiC continues to increase,but the particle size does not change much.The formation of whiskers in the product SiC mainly follows the gas-liquid-solid(VLS)and gas-gas(VV)mechanism,the formation of SiC powders mainly follows the mechanism of solid-solid(SS)and gas-solid(VS).(3)Effect of silicon source type and particle size on particle size and morphology of SiCSiC powders were prepared by using 1μm and 3μm gas phase silica and 0.5μm and 1μm precipitated silica as silicon sources,the effects of type,morphology and particle size of silicon source on the particle size and morphology of SiC were studied.The results show that: At 1400℃ for 120 min,the morphology and particle size of SiC powders were inherited from that of silicon source.It is feasible to prepare SiC with controllable morphology by changing the type and particle size of silicon source.(4)Preparation of Nano-sized SiC by Sol-Gel method combined withCarbothermal reduction methodUsing tetraethyl orthosilicate(TEOS)as the main raw material,the morphology particle size controllable silicon sol was prepared by controlling the hydrolysis temperature and the amount of ammonia water by the sol-gel method.The key factors affecting the morphology of silica sol and the influence of the particle size of silica sol on the morphology of SiC powders were explored.The results show that: The hydrolysis temperature and the amount of ammonia do not affect the morphology of the silica sol,the prepared silica sol is spherical.With the increase of hydrolysis temperature,the particle size of silica sol increased first and then decreased.With the increase of ammonia content,the particle size of silica sol increased first and then decreased.The SiC powders with controllable particle size and high sphericity can be prepared by using 0.2 μm and 0.6 μm silica sol as silicon source.