Sintering and rounding kinetics of irregular glass particles

Reference Presenter Authors
10-075 Raphael Midea Cuccovia Vasconcelos Reis Reis, R.M.(Fluminense Federal University); Barbosa, A.J.(INVAP- SE); Ghussn, L.(UERJ-FAT); Ferreira, E.B.(University of São Paulo); Zanotto, E.D.(Federal University of São Carlos (UFSCar)); Viscous sintering of glassy powders has been used for many years for the fabrication of numerous products. The viscous sintering kinetics have been modeled for a variety of conditions, which usually start with an idealized particle or geometric assumption. For the initial stage of densification, in which a neck between a pair of spherical particles grows and the particle’s centers approach each other, the classical model of Frenkel (for two equally sized spherical particles) has been assumed and extensively used. In practice, however, actual glass particles are rarely spherical, and it is known that irregular particles sinter 2 to 5 times faster than spherical ones. Also, even in the early stages, the shrinkage rate of irregular particles is not linear with time, as for spherical particles, and hence a better description is needed. In this paper we compare the shrinkage of spherical and irregular glass particles of two different compositions – diopside (MgO.CaO.2SiO2) and soda-lime-silica glasses during sintering. The sintering rate of irregular particles is initially higher, but tends to reach that of their spherical counterparts, which we attribute to particle rounding. We assume that the smaller radius of curvature of the irregular particle edges control the sintering rate, and these local radii increase as the particles round off. We propose a model for the growth kinetics of their radius of curvature and apply it to Frenkel’s model. The calculated curves with the modified sintering model describe the experimental shrinkage of irregular diopside and soda-lime-silica glass particles and also explain their sintering anisotropy. These findings provide a significant step towards the description of sintering kinetics of jagged glass particles.
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