Silica powder, process for its production, and composition employing it

摘要

A silica powder containing an ultrafine powder in an amount of from 0.1 to 20 mass % and having an average sphericity of at least 0.85, wherein the ultrafine powder has, as the particle size measured by a dynamic light scattering particle size distribution measuring apparatus, an average particle size of from 150 to 250 nm, less than 10 mass % of the ultrafine powder having a particle size of at most 100 nm being less than 10 mass % (not including 0 mass %) and from 10 to 50 mass % of the ultrafine powder having a particle size exceeding 100 nm and not exceeding 150 nm.