Non-isothermal sintering with concurrent crystallization of polydispersed soda-lime-silica glass beads

We test the Clusters model for non-isothermal sintering of crystallizing polydispersed particles against experimental data obtained under different conditions. We demonstrate that the model predicts the densification curves for two distinct size distributions of devitrifying soda-lime-silica glass having spherical particles. For each system a minimum heating rate can be found, so that for higher rates the compacts always reach maximum density, while for lower heating rates crystallization inhibits densification. In the latter case, the residual porosity increases with decreasing heating rate. We discuss the results taking into account several complicating factors, such as pre-existing surface crystals, the average number of necks per particle, compositional shifts due to crystallization, temperature gradients and degassing during sintering. Finally, we discuss the physical and processing parameters that determine whether sintering will be favorable over crystallization. (C) 2003 Elsevier B.V. All rights reserved.