Preparation of Ceramic Powders by Spray Roasting Method

Abstract

A new method preparing pure and homogeneous fine oxide powders was developed, and its detail was discussed.
Inflammable solution of nitrate dissolved in ethanol was sprayed into the refractory tube with compressed air and then ignited leading to the oxide powders. The products oxide powders were introduced to the scrubber through the cooling pipe in order to separate the powders from gaseous bodies.
By this method, NiO and CoFe₂O₄ powders were obtained and their particle size, crystallite size and magnetic properties were investigated and the effects of nitrate concentration of mixed solution on their properties were discussed.
Results were obtained as follows.
1) The mixture of large sphere particles (0.5-2.0μ) and very fine crystallites (<200Å) were obtained. The ratio of large sphere particles to fine crystallits increased with the nitrate concentration of more than 0.014 mol/l.
2) The mean crystalline grain size calculated from line broadening of X-ray diffraction increased with the concentration of nitrate, from 430 Å at 0.0008 mol/l to 830 Å at 0.21 mol/l.
3) The coercive force of CoFe₂O₄ powders decreased rapidly with temperature, from 400 Oe at 30°C to 200 Oe at 100°C, and above 100°C the coericve force decreased monotonically. At room temperature the coercive force increased with decreasing grain size but above 100°C the relation was reversed.