Understanding the behaviour of glazes-New Test possibilities

Abstract

The glasses are intrinsically complex systems, quite difficult to study because their structure has no long range order and they are not in a thermodynamically stable state. Ceramic glazes are undoubtedly far more complex than glasses because in most cases they are composed of glassy and crystalline phases that interact, develop and disappear during the firing cycle. Only few compositions can be considered as glasses, while most of them can be described as glassy matrix embedding crystalline phases and separation phases. A full understanding of the physical-chemical behaviour of a glaze is often out of reach of ceramic technologies that are mostly concerned with a good comprehension of the practical behaviour of the glaze in an actual industrial firing cycle. This is the reason why the direct observation of the behaviour of the glaze during the actual firing cycle is considered one of the most powerful research tools available to the ceramic technologist. The most important features of this analytical technique are: first - to be able to follow the behaviour of the glaze sample at the same temperature gradient as well as in the industrial kiln; second - to use a sample as small as possible to be close enough to the behaviour of the glaze layer on the ceramic ware. The automatic hot stage microscope MISURA meets these requirements with an unsurpassed heating rate of 80°C/min and the possibility of magnifying up to 200 times the sample in the furnace. This means that it is possible to run firing cycles over some dozen minutes with glaze samples as thin as 500 microns.