Towards Rational Design of Porcelain Tile Glazes

Abstract

The complexity of porcelain tile glaze compositions translates into equally complex behaviour during firing in which, concurrently or in partially overlapping form, very different processes develop, such as the dissolution of crystalline phases, the crystallisation of new phases, and sintering phenomena. This complexity, and the scarcity of studies relating to the subject, make it extremely difficult to formulate such glaze compositions scientifically and efficiently. The present study analysed the physico-chemical transformations that occurred during the firing of these glazes, focusing in particular on the sintering process and its kinetics. A kinetic model was developed, first, which describes the sintering of complex glaze compositions (containing more than five components) with significant frit contents (45–70%) that devitrify crystalline phases during firing. A second, more comprehensive kinetic model was then developed, involving a formal multi-step kinetic model that encompassed even more complex glaze compositions (up to nine components), to calculate the effective viscosity of the glaze melt. This property was compared, on the one hand, with the effective viscosity obtained experimentally by hot stage microscopy (HSM) and, on the other, with that estimated theoretically from the chemical and mineralogical composition of the material, at different temperatures. The results obtained by the two methods exhibited very good agreement. The concept of effective viscosity provides a better understanding of the role played by the different glaze constituents and the firing conditions in sintering, enabling more rational design of these materials.