Production of transparent suspensions by real grinding of fused corundum

Suspensions containing ceramic nanoparticles (x(90)<30 nm) are supposed to have an important property: transparency, this opens up a wide field of applications, especially scratch resistant or UV-absorbing films. Common processes for preparing transparent suspensions are based on dispersing aggregates produced by pyrolysis or precipitation. However, in this paper the possibility to produce transparent suspensions by real grinding in a stirred media mill is shown. The grinding of fused corundum down to values near the grinding limit is a very time and energy consuming process. According to the property of transparency, the grinding media wear is one of the greatest challenges to overcome. Therefore, a two-step grinding process was introduced to keep the wear values as low as possible. To produce a transparent suspension by real grinding, the operation mode and operating parameters have to be chosen very carefully, since the amount and size of the wear particles as well as the width of the product particle size distribution determines whether a suspension turns transparent or stays opaque. (C) 2011 Elsevier B.V. All rights reserved.