The influence of quenching rates on the microstructure and properties of plasma-dissociated zircon

Abstract

The physical nature of what is usually described as “plasma-dissociated” zircon is very much dependent on the rate of quenching of the molten material after it has passed through or around the plasma. A product composed of small particles is rapidly cooled and the dominant microstructure is that of tiny crystallites of monoclinic zirconia intimately intergrown with a matrix of amorphous silica. If, as a consequence of the layout of the device itself, the product is in a more massive form, then the cooling rates in the interior are slower and considerable grain growth occurs. The zirconia forms segregations of comparatively large grains which, though still surrounded by silica, lack the intimate intergrowth we now find to be necessary to impart certain unique properties recently shown to be of interest to the ceramic colour, refractory and metallurgical industries. There is a continous relationship between microstructure and quenching rate, whether the samples come from the same or different plasma furnaces.