Crystallization Behaviour of Willemite Crystalline Glazes in Presence of NiO, TiO2 and Fe2O3

Crystalline glazes based on the willemite crystals (Zn2SiO4) were prepared in presence of nickel oxide, titanium oxide and iron oxide by two step heating process, i.e. glaze firing at 1200 degrees C and crystallization above differential thermal analysis crystallization peak temperature. The mechanism of crystallization of the glazes was determined. The result showed that titanium and iron oxides induced a bulk crystallization mechanism in the glaze while in the presence of nickel oxide crystallization of willemite was initiated from the surface layer. Willemite got crystallized randomly as spherulites in the nickel bearing glazes when it was applied on a horizontal substrate. However, it was crystallized as grape-like clusters in the vertical surfaces.