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We used the Clusters model to study the densification kinetics and resulting porosity of a compact of polydispersed soda-;lime-;silica glass spheres. In addition to the physical data (viscosity, surface tension, particle size distribution) required by the Clusters model, for the first time in glass-;sintering studies, we took extra variables into account: the average number of necks per sphere, the effects of pre-;existing crystals on the particle surfaces, and sample size. The model predicted both the densification kinetics and the resulting pore-;size distribution of sintered compacts. A cross section of a porous sample displayed a porosity pattern that agreed with computer-;simulated cross sections, whose pore-;size distributions was calculated via the Clusters model using a Monte Carlo technique. Its capacity to predict both density and pore-;size distribution makes the Clusters model a valuable tool for designing sintered glasses with any desired microstructure.

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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.