Grain growth of zircon pigment in tile glaze

Glazes for ceramic materials are often opacified by a zircon pigment. The increase in optical density is related to the number and size of pigment particles, which are well dispersed in the glass. Mechanical dispersion by grinding of a fine zircon powder in a raw glaze mixture results in an unoptimised pigment dispersion in the melted glassy phase at high temperature. A significant reduction in the number of particles and a simultaneous large increase in their size is observed. fit this case the optical glaze density does not attain the expected value and a very large quantity of zircon must be added. In the present work it is shown that a large part of the zircon reacts with the glass phase during firing. Simultaneously, the remaining zircon grains undergo a large increase in grain size by Ostwald ripening through the liquid phase. This process is characterised by a low activation energy (79+/-1 kJ mol(-1)) and a short diffusion path for Zr through the liquid phase between neighbouring grains. The path length is shorter than the size of the larger grains. In the usual firing range, both populations of smaller and larger grains vary in size, the smaller grains favouring growth of the larger grains.