Study the Physical Properties of Ceramic Tile by Adding Dolomite and Magnesite as Refractory Materials to Engobe Compound

Water absorption measurement is one of the factors for evaluation of constructional ceramics. The tile components are glaze, engobe and biscuit. The engobe makes a flat surface on ceramic which improves glaze quality and beauty. Water absorption decreases beauty of ceramic and it may separate glaze from the biscuit. The amount of porosity in the structure of the engobe and biscuit affect water absorption. Holes and capillaries increase probability of water movement from the biscuit to the ceramic tile’s surface. Thus changing the engobe components is a way for controlling water movement to the surface. In recent study, the effects of addition of two kinds of refractory materials such as magnesite (MgCO3) and dolomite (CaMg(CO3)2) on water absorption property of ceramic were studied. After sample preparation, engobe and glaze were coated on the biscuit and the ceramic was heated in the furnace at 1134˚C for 42 minutes. Samples were evaluated by X-ray diffraction (XRD), scanning electron microscope (SEM), flexural strength, shrinkage and water absorption methods. The colorimetric measurements for ceramic tile surface were carried out using CIE-L*a*b* standard. The results show that after addition of magnesite and dolomite to the engobe, water absorption decreased. Also, a high shrinkage is carried out for the samples and the flexural strength increases while the brightness (L*) decreases. The SEM micrographs show that after addition of these materials, the particles in the engobe layer are sintered and block the capillaries. Thus they can prevent water diffusion to the glaze surface.