In the single firing process for the production of ceramic tiles, the appearance of the "black core" defect occurs under determined conditions of raw materials and parameters of the industrial process. It was then decided to investigate the effects of an oxygen enriched atmosphere for minimizing the occurrence of defects such as "black core", with the goal of reducing the firing cycle. A complete physical and chemical characterization of the used raw materials was carried out. Raw material samples were fired in an electrically heated laboratory kiln of the chamber type. It presents controlled atmosphere and is able to simulate the fast firing process. Flows of pure oxygen and/or of oxygen blends were continuously introduced into the kiln, using two different methods. The tendency for eliminating the "black core" was assessed by measuring the ratio between the "black core" volume and the overall volume of the sample. The results, obtained upon the use of the proposed method of oxygen addition, show that the effect of the oxygen enriched atmosphere follows the equations determined by the kinetic models of the oxi-reduction reactions, which in this case determines the pattern of elimination of the "black core" defect as a function of the atmosphere modified by the oxygen introduced into the kiln. This indicates that besides improving the quality of the final product, it is possible to increase the productivity, reducing the firing cycle.
ceramic tiles; kiln atmosphere; quality; oxidation; oxygen enrichment
