Effect of calcined colemanite addition on properties of porcelain tile

In this study, the possibility of using calcined-colemanite as an alternative fluxing agent in a body mixture used for porcelain tile was investigated. For this aim, a part of industrial spray-dried powders was replaced with the colemanite calcined by microwave-assisted heating (MACC) in varying amounts (up to 3 wt. %). The tile compositions prepared with different proportions of MACC addition were pressed uniaxially at 15 MPa, and the shaped tiles were then fired at 1220 °C for 50 min in an industrial roller kiln. Physical and mechanical tests, X-ray diffractometer (XRD), and scanning electron microscopy (SEM) analyses were performed to examine the effects of MACC addition on porcelain tile’s technical properties and phase development. The results revealed that the porcelain tiles having 0.5 wt. % of MACC had better technical properties, i.e., lower water absorption (0.09%) and porosity (0.22% for apparent porosity and 7.25% for closed porosity), and higher bending strength (66.04 MPa) than that of others. Consequently, the MACC addition promoted a low-viscosity liquid phase during firing, resulting in a significant microstructural improvement by decreasing the closed porosity and increasing the bulk density and flexural strength.