Effect of calcination condition of nano-sized cobalt-aluminate pigment on glazing of ceramic body by transparent frit

In present investigation the effect of calcination time of nano-sized CoAl2O4 pigment on thermal behaviour of a typical transparent frit was investigated. The nano-sized cobalt-aluminate spinels were prepared by combustion method and calcined for 1 and 2 h at 800 and 1000 ˚C. The calcined powders were added to an industrial transparent frit and the thermal behaviours of modified glazes were studied by hot stage microscopy, HSM. The thermal properties are described in terms of height percentage and contact angle as a function of temperature. In order to obtain the parameters of Vogel-Fulcher-Tamman equation, the glass transition temperature, softening point and the temperature where samples form a half-sphere shape during HSM analysis were measured and the molten phase viscosity was predicted as a function of temperature. The results indicated that the calcination of cobalt–aluminate at 1000 ˚C during 1 h provides the best thermal properties.