Sintering Behaviour of Clays for Ceramics Production

Abstract

The natural raw materials suitable for the production of ceramics consist of several families of minerals. Hydrated aluminosilicates, or clay minerals, are the most abundant in the surface portion of the earth’s crust and are fundamental components of the ceramic body. The main characteristic of clay minerals is their ability to interact with water: they are highly hygroscopic, absorbing water easily and retaining it very strongly. The presence of water molecule retained around the crystal structure gives clay minerals their most important property for the purpose of the ceramic production process, i.e. plasticity, which allows to mould the clay into the required shape. During firing, clays undergo some transformations which can be simply listed as: loss of the crystalline water (dehydroxylation), sintering and newborn crystalline phases growth. The study of the properties of clays during the entire firing process can provide extremely useful information: clays sintering behaviour strongly influences the whole ceramic body sintering behaviour. In fact, depending on the clay adopted in the body formulation, a great variability in firing behaviour may be observed. Unfortunately, most of the thermal analysis techniques available until now show some limits just in correspondence of the sintering processes.