Development of red wall tiles by the dry process using Brazilian raw materials

This work presents the results of a study concerning the processing of red wall tile composed of clay, calcareous, and quartz from Brazil. The formulation prepared by dry process was optimized depicting the effect of the calcareous addition (12-18 mass%) on the densification behaviour during the firing process. The samples were unidirectionally dry pressed in a die with rectangular cavity and fired in air at temperatures ranging from 1080 to 1200 °C using a fast-firing cycle. The samples were characterized before and after firing. The development of the microstructure was followed by XRD and SEM. The densification was measured by three parameters: linear shrinkage, water absorption, and flexural strength. The results revealed that the red wall tile bodies containing abundant calcareous fired above 1000 °C form gehlenite and anorthite. Moreover, the densification behaviour was found to be influenced by the calcareous content and sintering temperature. The microstructure is constituted of a network of small dense zones interconnected with a porous phase. It was also found that the requirements specified in the Brazilian tile standards concerning the BIII class tiles were fulfilled, depending on calcareous content and sintering temperature.