INFLUENCE OF THE MICROSTRUCTURE ON THE POLISHING PROCESS OF PORCELAIN TILES

Nowadays the concern with the conservation of the natural sources of raw materials is in evidence, generating a notorious environmental awareness worldwide. For a long time, the society discusses the importance of environmentally friendly products. In this context, the ceramic tiles sector is perfectly capable of absorbing a range of industrial wastes in ceramic tiles compositions. Since the last two decades, research has been carried out aiming at obtaining eco-friendly ceramic tiles, including porcelain stoneware tiles, from industrial wastes as alternative raw materials. However, most of these investigations on the technical feasibility of the insertion of industrial waste were focused on technological and mechanical performance. The behavior regarding the glossiness gain of eco-friendly ceramic tiles remains unknown both in the field of scientific research and in the industrial scope. Thus, the present work aims to evaluate the influence of the microstructural features, caused by the insertion of industrial wastes, on the final surface quality, considering the polishing process. For this purpose, eco- friendly porcelain stoneware tiles compositions were developed from different industrial wastes from the state of Rio Grande do Norte, Brazil. The surface characteristics prior to polishing were characterized and 3D mapped, in order to obtain an estimate of the minimum thickness to be removed during the polishing process. Values of material removal of 1.08 up to 2.37% of the initial thicknesses were found to mitigate the roughness and waviness effects of the samples. During the polishing process, the kinematic parameters were kept constant, as well as the polishing time intentionally saturated, aiming to ensure that the microstructural difference is the only variable to be related to the final glossiness reached. In total, six eco-friendly compositions were polished, three of them with different proportions (5, 10 and 15 wt.%) of the waste from the breakage of bricks and roof tiles and another three from different proportions (10, 15 and 20 wt.%) of the waste from the beneficiation of primary kaolin ore. The surface quality of the compositions was characterized by determination of glossiness and roughness curves as well as the morphology of the samples. The patterns were compared to a waste-free composition. The experimental results have shown that it was possible to raise the glossiness level of 59 gloss units, for the composition waste-free, to levels between 66 and 72 gloss units reached for the eco-friendly porcelain tiles. These values are close to those generally found in commercial porcelain tiles. Such results are able to validate the potential of using industrial wastes as alternative raw materials for the production of polished ecological porcelain tiles and enable the direct transfer of knowledge to the productive sector, contributing to the diversification of the Brazilian industrial matrix in the direction of technologically more advanced products, of greater added value and ecologically correct.