Study On Gel Casting Process Of Silicon Nitride Combined With Silicon Carbide Material

In order to prepare the profiled silicon nitride bonded silicon carbide material,the SiC and Si powders were used as the main raw materials to study the gel casting process of SiC/Si powder..The main contents include:Optimization and surface treatment of raw materials SiC and Si powder,study of preparation and rheological SiC/Si composite slurry,influence of gel injection molding process factors on properties of SiC/Si blanks,etc.The pHase composition,morpHology and particle size distribution of SiC and Si powder were studied in the raw material and Si surface treatment.SiC and Si powders with pure pHase,rounded particle shape,and concentrated particle size distribution were selected as experimental materials for the subject,and the selected Si powders were surface pre-oxidized and compared with different treatment methods;The zeta potentials of SiC and Si powders at different pH values were studied.The results show that the absolute value of zeta potential is the largest when the pH value of Si powder after surface oxidation treatment is 8-9,and the absolute value of Zeta potential is the largest when the pH value of SiC powder is 10.Preparation of a slurry with high solid content and good fluidity is the key to gel injection molding.In the third part,the effect of SiC particle size on the properties of SiC/Si slurry is studied.The results show:The particle size of the SiC powder has a great influence on the rheology and stability of the slurry.The best particle size is 100 mesh/10%,240 mesh/41%,1200 mesh/7%,5000 mesh/21%;In this paper,six dispersants such as sodi?m hexametaphosphate,sodi?m tripolyphosphate,sodi?m polyacrylate,sodi?m citrate,polyvinylpyrrolidone and CE-64 were selected for comparative study.The effects of the type and amount of dispersant on the properties of SiC/Si slurry were analyzed.The results show:When polyvinylpyrrolidone and CE-64 were added in combination,the dispersion effect on the slurry was the best,and the optim?m addition amount was 0.30%of polyvinylpyrrolidone and 0.10%of CE-64.In this paper,the acrylamide system is used as the gel system.The effect of the amount of acrylamide monomer,N,N'-methylenebisacrylamide crosslinker and ammoni?m persulfate initiator on the properties of the green body in the system was studied.The results showed that when the total addition amount of the monomer and the crosslinking agent was 10%-20%,the performance of the green body was the best when the initiator ammoni?m persulfate was added in an amount of 0.6%.This paper also discusses the process factors such as vacu?m exhaust time and drying system in gel injection molding process.The results show that vacu?m evacuation is beneficial to increase the density of the green body.With the increase of vacu?m exhaust time,the apparent porosity of the green body is signif-icantly reduced.At the end of this paper,suggestions and prospects for the follow-up work on this topic are presented.