This work had as its objective to evaluate the firing behavior of a kaolinitic clay incorporated with phonolite aiming at semiporous pressed ceramic tiles. Compositions were prepared with addition of 20 and 40 wt.% of phonolite to a kaolinitic clay. For comparison, an industrial ceramic body from Santa Gertrudes, State of S. Paulo, was also evaluated. Cylindrical specimens were prepared by uniaxial pressure at 25 MPa followed by firing at temperatures varying from 1050 to 1200 ºC. The fired specimens were submitted to the following tests: linear shrinkage and water absorption as function of the firing temperature. The microstructural evaluation of the compositions was accomplished by X-ray diffraction and scanning electron microscopy. The results showed that the phonolite addition significantly improve the sintering of the clay, mainly, above 1150 ºC with sharp decrease of the porosity. Although the clay/phonolite mixtures showed higher amount of alkaline oxides as compared with the industrial ceramic tile body, the required water absorption of 10% for semiporous tiles was only reached at temperatures around 80 ºC higher than the industrial body.
phonolite; kaolinitic clay; ceramic tiles
