Study On Preparation Of High Solid Loading SiC Slurry And Colloidal Molding Method

Covalent ceramic materials like silicon carbide (SiC) have been recognized as potential candidates for high temperature structural applications, because of their superior thermal, mechanical, chemical and electrical characteristics. Their widespread application is, however, limited by the critical and complicated manufacturing technologies of brittle ceramics and the low reliability to the material's properties. With wet or colloidal processing method, which has the advantages of easy control of agglomeration, impurities, and the defects, ceramics can be produced with high reliability and complicated shapes. The problem, which must be solved firstly, is the preparation for the low viscosity, homogeneous concentrated ceramic suspension of which solid loading is higher than 50% solid volume fraction. The surface modification of fine ceramic powders is the optimal method to improve the dispersity of ceramic powders.The dissertation describes an organic-coating method for changing the surface properties of ceramics powder. The modified organosilane coupling agent can bond with Si-OH which is on the surface of SiC powder. This covering layer will change the chemical constitution and surface properties of the SiC powder, that will consequently improve the dispersity of the SiC fine powder in water. A various of analysis methods such as FTIR, XPS, TEM, XRD and TG-DSC are used to detect the substance and the structure of the covering on the SiC powder surface. In this paper, the size distribution, exterior configuration and colloidal properties of the powder are analyzed. The dispersion and stability mechanism of modified powder are also studied. The effects of technologic parameters and package substances on the dispersity of modified powders are carefully investigated.The low viscosity (855.6mPa.S) and homogeneous concentrated SiC suspension with 58vol% is prepared with the addition of dispersant by using the modified fine powders. The high solid loading and low viscosity suspension,which will be applied to slip casting to manufacture SiC, is prepared by using fine modified SiC powder mixed with coarse powder properly through the redressal of pH value and the addition of defoaming agent. The highest density of green body prepared by slip casting may reach 2.58g/cm3, which is about 80.4%of theoretical density of the SiC material.