Effects of pre-heating temperature for polycarbosilane on preparing capsule with drop-tower technique

The SiC hollow microspheres with the diameter of 200-400 μm and the thickness of 3-5 μm were fabricated by drop-tower technique using polycarbosilane (PCS) as raw material, and the best furnace conditions and the effects of pre-heating temperature on preparing capsules were investigated in this paper. The obtained microspheres were characterized to study the relationships between their productivities, qualities and the pre-heating temperatures. The results show that the microspheres fabricated at 500 ℃ with 25%Ar and 75%He as the inner furnace gas condition possess the highest capsule productivity, and the best sphericity, concentricity and surface finishment. Furthermore, some of the PCS with low molecular weight and other small molecules were eliminated in the pre-heating treatment process, which could reinforce the polymerization degree of PCS and enhance the thermo-stability and ceramic yield of the raw materials. Therefore, the productivity of the microspheres promotes while the surface roughness decreases with the increasing of pre-heating temperature at the best inner furnace condition. Especially, the microspheres prepared with PCS pre-heating at 350 ℃ possess the greatest quality. (authors)