The Influence of Particle Size Distribution on the Performance of Ceramic Particulate Suspensions Maria da Graça Rasteiro*, Albano Jorge** DOI: 10.1002/ppsc.200601042 In memoriam of Professor Dr. Brian Scarlett 1 Introduction Glaze suspensions are complex mixtures of different particulate materials, essentially frit and kaolin. The frits can have different compositions, but are always a solid mixture of oxides of several metals, depending on the final properties required for the glaze (hardness, optical properties, etc.). Therefore, in such a complex mixture, interactions between the particles are very intricate and are strongly affected by the size of the particles. In addition, the preparation of ceramic glaze suspen- sions requires that an adequate flow behavior is maintained. Therefore, several parameters have to be rigorously controlled, e.g., particle size and solids con- centration, composition of the suspension, ionic charge of the liquid, etc. On the other hand, it is quite usual in the ceramics industry for the glaze suspension to lose its suitable flow characteristics with time. That can be caused by the dissolution of the glaze or by the sedimen- tation of the particles, which result in agglomeration or deagglomeration of the solids. This can result in difficult problems for industry, mainly when the process is irre- versible. These effects have been observed by several authors [1], but some authors have recently begun to study the relation between the release of cations by the frit and the changes detected in the rheological behavior of the glaze, in a more systematic manner [2,3]. This work focuses attention on the influence of the size of the particles on the quality and stability of glaze sus- pensions, since particle size has the strongest affect on the rheology and performance of these suspensions, aside from the frit composition. In this paper, results are presented for two glaze formula- tions prepared with two different commercial frits of dis- tinct composition. The glazes were prepared in a Part. Part. Syst. Charact. 24 (2007) 101–107 101 * Prof. M. G. Rasteiro (corresponding author), Chemical Engi- neering Department, Coimbra University, Pólo II, Pinhal de Marrocos, 3030-290 Coimbra (Portugal). E-mail: mgr@eq.uc.pt ** Eng. A. Jorge, Colorobbia Portugal, Anadia (Portugal). Abstract During the preparation of ceramic glaze suspensions it is necessary to guarantee that the suspension possesses the required properties, with several parameters having to be rigorously controlled, e.g., particle size and solids concentration, composition of the suspension and ionic charge of the liquid. This study focuses attention on the influence of particle size distribution on three important properties of glaze suspensions: rheological behavior, opacity and reflectance characteristics and tendency to dissolve. In this paper, results are presented for two glaze formulations prepared with two different commer- cial frits of distinct composition. The glazes were pre- pared in a laboratory ball mill and the grinding time was adjusted for each formulation, in order to obtain suspen- sions with different particle size (at least three different grinding times). The rheological behavior is strongly dependent on the particle size and also on changes in the interactions between the particles, caused by modifi- cations in the cationic content of the suspending medium, as a result of frit dissolution, which is also influenced by the size of the particles. Keywords: glaze, grinding, particle size distribution, reflectance, rheology © 2007 WILEY-VCH Verlag GmbH & Co. KGaA,Weinheim http://www.ppsc-journal.com