Gel Mould Injection Molding Process And High Density Of Magnesium Oxide Ceramics In Direction Of The Research

Presently high purity and density magnesium oxide is the purity of99.5%, density of3.43~3.47g/cm3and density of96.9%. High purity and density magnesium oxide has excellentacid and alkali resistance and electrical insulation, good light through, high thermalconductivity and thermal expansion coefficient at the high temperature. MgO ceramics is atypical kind of refractory materials, which can keep stability in the oxidation atmosphere orunder nitrogen at2400, and Fe, Zn, Pb, Cu, Mn and other metal can not reduce it.Magnesium oxide ceramic has been fabricated by water-based gel-casting. The gel-castingand its applied in the preparation of high-density magnesium oxide ceramic have been studiedin this paper. The main contents include: the pretreatment of magnesium oxide powder, thekey technologies of preparation the low viscosity and high solid content slurry in thegel-casting, new method of drying ceramic body and the sinter of obtaining dense ceramicbody. Great attentions have been focused on pre-sintering temperature and influences surfacemodification on the hydration activity, grain size and specific surface area of raw materials.And the effects of pH value, dispersant contents, milling time, solid content and other factorson the slurry viscosity of MgO have also been investigated in this article. The results showthat with the pre-burn treatment temperature raising the particle size of MgO powderdecreases and then increases and the specific surface area first increases and then decreases.At600~800MgO powder has minimum particle size, maximum surface area and moderateactivity in this experiment. Due to the presence of organic compounds stearic acid modifiedtreatment can be effective in reducing the water adsorption of MgO powder surface. Whenthe pH is9.5~11, the addition of dispersant is2.8~3.2wt.%, and milling time is6~9h, thedispersion is the best. Preparation of slurry with54vol%high solid content and viscosity only755mPa s is fully able to meet the requirements of gel-casting.After curing gel the green body gel contains a lot of water, which should be dischargedin the process of drying. The traditional air-drying prone to concentration gradient that makesthe all parts of dried green body unevenly, resulting in the structural stress and residual stress, and leads to the green body having warp, fracture and other defects. The replacement dried of gel-casting green body at room temperature by liquid desiccant can release the stress, and the maximum degree of reduction or even elimination of these structural defects. The magnesiumoxide gel-casting green body drying test has been carried out with40vol%,45vol%,50vol%and54vol%, respectively, the results show that the drying rate decreases with the amount of solid phase increasing and accelerates with the increase the concentration of liquid desiccant. The green body after drying does not appear warping, cracking, peeling and other defects.With thermal analysis of MgO ceramic green body, the suitable sintering system has been confirmed. In this experiment the best sintering temperature of MgO ceramic is1650℃, the density reaches3.50g/cm3that is97.76%of theoretical density, and bending strengthcan reach HOMPa, good thermal stability, sintering body macro-defect-free, and microstructure homogeneous.