Study On Preparation Of SiC Ceramic By Colloidal Molding Method

In recent years, it has become possible for the preparation of peculiar shape, homogeneous microstructure materials with high capabilities and reliability through new colloidal consolidation techniques. To carry out those techniques, the problem must be solved firstly is the preparation for the low viscosity, homogeneous concentrated ceramic suspensions of which solid loading is higher than 50% solid volume fraction (50vol%). Surface modification of ceramic powders is the optimal method to improve powders dispersity.An organic-coating system was designed in this dissertation to modify the surface of silicon carbide (SiC) fine powders. The system included two sections: one was the basic layer formed by silane coupling reagents; the other was the organic polyelectrolyte acting as a dispersion functional layer. On the SiC powder surface, silane bonded with Si -OH and then grafted the acrylamide polymer. This covering layer changed the chemical constitution and surface properties of the SiC powders, which resulted in the improvement of the SiC fine powder's dispersity in water. A variety of analyses methods such as X-ray diffraction (XRD) , The rmogravimetric and Differential scanning calorimetry (TG-DSC) Transmission electron microscope (TEM) and Fourier transform infrared spectroscopy (FTIR) were used to detect the substance and structure of the covering on the SiC powder surface. In this paper, the colloidal behaviors of the powders were analyzed in detail. A syntactic model of modified powder when it dispersed in the deionized water was advanced. The dispersion and stability mechanism of modified powder was studied. The effects of various package substances and modification parameters on the dispersity of modified powders were deeply investigated too.Using modified SiC fine powders simply, the SiC suspension with 55vol% solid loading could be obtained. The low viscosity, homogeneous concentrated SiC ceramic suspension was prepared while fine modified SiC powder mixed with coarse powder (90-98 u m in diameter) properly through the pH valuemodification, and the suspension was applied to slip casting to manufacture SiC ceramic. The highest density of green body prepared by slip casting may approach to 2.53g/cm3 which is about 78.8% of theoretical density of the SiC material. When modified SiC powder mixed with carbon black, the solid loading of suspension would be about 60vol%. The densities of green body approach to 2.01 g/cm3 and 1.76 g/cm3 when the green bodies were prepared through filter pressing method and starch in situ consolidation molding method respectively. The mechanical properties of green bodies prepared by the three kinds of colloidal consolidation molding methods are relatively high. Among which the flexural strength is about 5.0 MPa.