Preparation And Performance Of TaC Ceramic Coatings On Graphite Via Slurry Sintering

TaC coating resists chemical attack by corrosive liquids and gases at very high temperatures.There are increasing acceptance in sealing and protecting graphite hardware from hot ammonia,hydrogen,hydrochloric acid,and molten metal used in compound semiconductors epitaxial processes such as metal-organic chemical vapor deposition?MOCVD?and physical vapor transport?PVT?.This paper aims at the demand of semiconductor crystal preparation and the research of TaC coating,we carried out the project“Preparation and performance of TaC ceramic coatings on graphite via slurry sintering”.The TaC slurry powders was synthesized via solvothermal treatment,and the TaC coatings was prepared via slurry-sintering method.Some intrinsic properties of TaC coatings,such as the hardness,the elasticity modulus,the bonding strength.The high-temperature stability and anti-chemical attack were investigated.The highly dispersed and homogeneous TaC slurry powder was synthesized via solvothermal treatment with Tantalum chloride served as metal source and acetylacetone used as carbon source.We controled the solvothermal treatment parameters,such as the temperature,the treatment time and the concentration to optimize the composition of the O and C,and to obtain the highly dispersed and homogeneous TaC slurry powder.The result showed that the preferential process parameters of TaC slurry powder were:the temperature and holding time of solvothermal treatment were 200?and 12h,respectively.Besides,the Ta⁵⁺concentration was 0.4mol/L,and the rate of Tantalum chloride and acetylacetone was1:1.In this case,the obtained TaC slurry powder was highly dispersed with ball shape,in which the mean diameter of 1?m,the specific surface area was 121.9m²/g,and the pore width was 3.110nm.The TaC coating was prepared on graphite via slurry-sintering method,which was dense,single phase and good crystallinity.Steady suspension was prepared through exploring the influence of solid content and additive on stability of suspension and the influence of sintering atmosphere,sintering temperature and sintering time on the morphology,composition and structure of TaC coating was studied.The preferential process parameters of TaC slurry suspension were:solid content was 15wt%,and the content of PVB was 0.4wt%.The preferential sintering parameters were:the sintering atmosphere was vacuum,the sintering temperature was 2000?and the sintering time was 1h.The microstructure and mechanical properties of TaC coating was characterized systematicly.TaC coating was 10-20?mand the coating had an isotropic granular structure,showing no cracks or pinholes penetrating through the coatings.The hardness and elasticity modulus of TaC coating was investigated via nanoindentation.The hardness was 15.35GPa and and the elasticity modulus was 195.1GPa.The TaC coating had a bonding strength with graphite substrate because of the reaction.The bonding strength was bettert han the tensile strength of graphite substrate.The application performance of TaC coating were evaluated,the result showed that the coating had a good high-temperature stability and anti-chemical attack.The TaC coating was heated at 2200?,2400?and 2600?for 1h,with Ar atmosphere environment.The result showed that the composition,phase and structure of TaC coating maintained good stability after heat treatment.The grain size of TaC coating kept a stable value.TaC coating was tested for 2h in the grow environment of AlN crystal?2300?,Al vapor,N₂ atmosphere?,the coating kept whole structure without crack and spall.The weight-loss rate of TaC coating was 0.1 g/m²?h,which had a good consistency with the literature report.