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Synthesis Conditions of Cobalt Aluminate Nano-Sized Powder
Sh. Salem, S.H. Jazayeri, F. Bondioli, A. Allahverdi, M. Shirvani
Abstract
The effect of the conditions applied for the synthesis of cobalt aluminate powder on the thermal behaviour of a typical transparent frit was investigated. The nano-sized cobalt aluminate spinels were prepared with the combustion method. The powders were synthesized at a pH of 2.5, 7.0, 10.5 and a fuel ratio of 0.56 and 0.75 using cobalt and aluminium nitrates and glycine as fuel. The obtained gels were calcined at 800 and 1000 °C. 2 wt% calcined powders were added to an industrial transparent frit and the thermal behaviour of the modified glazes was studied by means of hot stage microscopy (HSM). The thermal properties are described in terms of height percentage and contact angle. All samples began to shrink close to 700 °C and reached a minimum value at around 1330 °C. The synthesis of powder at acidic and neutral pH with a low content of fuel led to a significant change in the height percentage and an expansion was observed between 940 and 1040 °C. The HSM data were analyzed with the Vogel-Fulcher-Tamman equation and the influence of the synthesis conditions on the molten viscosity was evaluated. The results indicated that the synthesis of cobalt aluminate gel at neutral pH in the presence of a low fuel ratio and calcination at 1000 °C provides the best conditions from an industrial point of view.
Keywords
Cobalt aluminate, glaze; melting, hot stage microscopy, viscosity
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