Gel-casting Was Used For Preparing Complex Shaped Corrosion Resistant Alumina Ceramic

Gel-casting was used for preparing complex shaped corrosion resistant alumina ceramic parts. Investigation was conducted into the preparing method and development of the microstructure of the gel-casted green body. The influences of various factors on the properties of the slurry such as pH of the slurry, dispersant, solid loading, particle size and the influences on gelation process and hence the structure of the casted bodies of the factors including the concentration of the monomer solution, solidification temperature, pH of the slurry, the amount of the initiator and catalyst for the polymerization were studied. Complex shaped corrosion resistant alumina ceramic parts were prepared successfully through optimization of the preparation parameters of the system.The results of the study shows that alumina slurries possesses different properties at different pH. Good dispersion can be obtained at pH 8 to 10. The viscosity increases with the solid loading of the slurry. For better dispersion of different solid loading the addition of the dispersant should be controlled in appropriate range.The addition of MgO as sintering aid in the forms of magnesium nitrate, magnesium sulphate and magnesium carbonate influences the fluidity while it will have no influence if added in the form of magnesite.The rate of solidification process increases with the concentration of the monomer solution, gelation temperature and the amount of the initiator and catalyst. The controlling of the solidification rate is important for the properties of the shaped bodies because flaws may appear if the solidification proceeds too fast.The corrosion resistance of alumina ceramics depends on the homogeneity of microstructure, the density as well as the amount and composition of the grain boundary phase. Products with dense homogeneous structure posses high corrosion resistance. Better corrosion resistance of the products can be obtained with higher alumina content and less grain boundary phase because corrosion occurs mainly on the grain boundary.The results show also that the state of dispersion of the particles in the slurry has great influence on microstructure of the formed bodies. Good dispersion leads dense and homogeneous microstructure which assures high corrosion resistance of the final products.