Preparation of silica ceramic cores by the preceramic pyrolysis technology using silicone resin as precursor and binder

A facile and effective preceramic pyrolysis technology was used to prepare the fused silica ceramic cores, among which fused silica powders were used as the raw materials and the silicone resin with -Si-O-Si- as the main chains was used as the precursor. Effects of the silicone resin content and sintering temperature on the properties of fused silica ceramic cores were researched. Results showed that the silicone resin powders had the good cohesiveness, which was beneficial for directly shaping the silica ceramic cores. The organic to inorganic transformation of silicone resin occurred with the increase of temperature, forming the amorphous SiO2 at the temperature less than 1250 degrees C and the cristobalite by the crystallization process of amorphous SiO2 at the temperature more than 1250 degrees C. Based on TG analysis, it was found that the ceramic yield (SiO2) of silicone resin had 83.55wt%. In green bodies, the silicone resin was mainly coated on the surface of fused silica particles via the function of pressing force. After the pyrolysis process was completed, the silicone resin formed some small amorphous silica particles, which was coated on the surface of raw fused silica and filled into the gaps between fused silica particles. With the increase of silicone resin content, the apparent porosity gradually increased, and bending strength showed a decreasing trend. The increasing temperature from 1200 degrees C to 1300 degrees C promoted the densification of silica ceramic cores when the silicone resin content was the same. However, the highest bending strength was obtained at 1250 degrees C. Further increasing temperature was detrimental to the bending strength of silica ceramic cores owing to the microcracks caused by the surface crystallization of fused silica to cristobalite.