The latter observation is attributed to different particle characteristics of the rice husk ash : The particle size distribution as measured by laser granulometry (d50 = 11.1 d90 = 39.8) of the rice husk ash was significantly coarser than the particle size distribution of previously investigated silica feedstock - microsilica and a residue from chlorosilane produntion, which had d50 = 0.2-1.0 mm and 6.8 mm, respectively.