Use of rhyolite as flux in porcelain tile production

The use of rhyolite from a local source as an alternative fluxing agent in a commercial porcelain stoneware formulation was investigated. The experimental work was achieved in two parts: in the first part, standard tests were applied to the porcelain tiles obtained from the experimental bodies incorporated with varying amounts of rhyolite (up to 12 wt. %) as a substitution of albite in the standard formulation after single fast-firing under industrial conditions. Reactions during firing were studied by thermal analysis (DTA/TGA/DTG). The vitrification behaviour of the standard and rhyolite containing bodies was evaluated using a double-beam optical non-contact dilatometer. ln addition, XRD was used to analyse the phases formed after firing. SEM was also employed in order to observe the microstructural characteristics of the selected fired bodies with respect to increasing rhyolite content. In the second part, the most suitable rhyolite containing formulation was further developed by modifying its clay fraction for cost saving purposes. Physical, thermal and optical properties of the all the investigated bodies such as water absorption, linear firing shrinkage, bulk density, linear thermal expansion coefficient and chromatic coordinates were measured. According to the results, it was possible to incorporate rhyolite into a porcelain stoneware formulation as a fluxing agent and to obtain meaningful technological properties.