Mechanical modification of silica powders

Abstract

Two types of silica powder with different structures, one crystalline (C1) and one amorphous (A1) were mechanically treated using a planetary type mill. Three different rotation speeds (100, 200, 300 rpm), milling times (15, 30, 60 min) and ball sizes (1, 5, 10mm) were used. The structure and morphology of the powders did not change by milling. The effect of milling conditions on particle size distribution was investigated. By the milling treatment the original particle size of both powders could be effectively reduced. For the amorphous powder rotation speeds of 200 and 300 rpm and prolonged milling causes the formation of a broad range of particles of larger sizes. This behavior is not observed for the crystalline powder. The surface activity of raw and treated powders was measured as the amounts of dissolved Si4+ ion into ammonia solution. For the crystalline powder the smallest ball size, 1mm, was the most changing in the amount of dissolved Si4+ for all milling speeds and milling times and its changing increased by increasing both rotation speed and milling time. In the case of the amorphous powder the 5mm ball size was the most effective for 100 and 200 rpm rotation speeds almost independently of the milling time. A possible activation reaction mechanism occurring during the milling process is also discussed. The findings indicate that from a technical and economical point of view as the low total energy consumption for milling with 15 min milling time at 200 rpm with a 5mm ball will be sufficient to considerably reduce the particle size and increase the specific surface activity of the amorphous powder making it suitable for different applications in non-firing ceramics processing. © 2012 The Ceramic Society of Japan. All rights reserved.