Study On The Structure And Properties Of Ultrafine Coal Based ?-SiC Powder

With the excellent chemical stability,high electronic mobility,low dielectric constan and high hardness properties,the silicon carbide become one of the most promising semiconductor materials.Nanometer silicon carbide powder is favored by people of all fields since the high purity,small range of particle size distribution,specific surface area and other excellent features.Ningxia is a big province for silicon carbide production,however,the price of silicon carbide is relatively low for the most massive production.The cost of the production can be increased as the block silicon carbide turn into silicon carbide powder by airflow pulverization.In this dissertation,Taixi coal that derived from Rujigou of Ningxia province was used as the main carbon source for synthesizing of nano ?-SiC with different methods,and several material propertied such as phases,and morphology were characterized.The study supplied theoretical and practical basis for preparation procedure of SiC powder in Ningxia province.The experimental research and results are summarized as follows:1.The influence of carbon source ash content on SiC powder1)Sodium silicate and different ash content of Taixi coal(6%,10%,20%)were used as silicon and carbon sources,Taixi coal were treated via different acid,and synthesized irregular granular and linear ?-SiC by carbothermic method at 1450?,the particle size distribution in 300?500 nm.In addition,the amount of ash and the different kinds of acid treatment had a great influence on the morphology and size of the samples.2)Sodium silicate was used as silicon source,no ash removal and ash removal coal were used as carbon sources,Fe(NO3)3·9H2O was used as catalyst for preparation of silicon carbide.The size and morphology were different for the synthesized ?-SiC as the carbon particle size was kept certain.A rod like morphology of silicon carbide was produced,the higher crystallinity and smaller particle size of the product can be obtained when the ash removal coal was used.The regular arranged lattice fringes can be clearly seen from HR-TEM images,which further showed that the crystallinity of the product was high,in addition,the distance between the two adjacent frings was 0.25 nm,which was consistent with the value to the(111)lattice planes of 3C-SiC.3)When using 100 mesh de-ashing coal as carbon source,the product size distribution in 0.6?1.2?m,using 200 mesh de-ashing coal as carbon source,the product size distribution in 0.3?1.0 ?m,the result indicated that the size of reaction raw material can controlled the product size to a certain extent.2.The preparation of P-SiC by microwave sintering1)Taixi coal and sodium silicate were used as raw materials,Fe(N03)3.9H20 was used as catalyst,high crystallinity and purity single phase nano P-SiC particles were synthesized at 1600 0C for 60 min by microwave sintering,the specific surface area was 16.606 m2/g,and the yield of the product reached to 75.7%and diameter ranged from70 nm to 300 nm.2)FT-IR and XPS spectral analysis further illustrated the target product was synthesized,high resolution transmission electron microscopy showed that the interplanar spacing of the two adjacent frings was 0.25 nm,which was consistent with the(111)lattice planes of ?-SiC and[111]was the growth direction of ?-SiC.TGA curve showed that the product had good thermal stability and strong oxidation resistance below 800 ?.3)During the reaction process,the particles of nano ?-SiC were synthesized with the vapor-liquid-solid(VLS)mechanism,and nano ?-SiC whiskers were synthesized following by vapor-solid(VS)mechanism.The schematic diagram and the reaction equations of ?-SiC can be used to explain the growth mechanism.3.The influence of the construction of the precursor on the ?-SiC1)Taixi coal and sodium silicate were used as raw materials,Fe(N03)3·9H20 was used as catalyst.The precursor was obtained through infrared drying and freeze drying after adding HCl to removed Na2O to the mixture of sodium silicate and Taixi coal.Green and uniform size silicon carbide powders were synthesized at 1450? for 5 h and under the protection of argon.The specific surface area of product is 13.597 m2/g when the precursor via infrared diying,the particle size distribution is range from 200 to 300 nm,the specific surface area of product is 4.878 m2/g when the precursor via freeze drying,the particle size distribution is 100?200 nm.2)When the mixture of sodium silicate and Taixi coal was added surfactant rather than adding HCI to removed Na2O,then the gel adopted infrared drying,nanoscale ?-SiC were synthesized by carbothermic method at 1450?,the morphology of product was loose skeletal.The average particle size was around 200?300 nm,specific surface area was 11.927 m2/g.4.Purification of secondary SiC1)Ultrasonic purification saved time compared with traditional purification,greatly reduced the amount of mixed acid,and acid can be recycled.Thereby,the pure water,wastewater and the cost can be reduced.2)Both the amount of impurities and types were different for the powder and particle samples.Hence,the products should be purified separately.Compared with the powder samples,particle samples not only need to crush but also go through two steps acid pickling,which leads to the complex craft and high energy consumption.The powder samples purification process is simple and low cost.