Pure and M-doped Co3O4 (M = Cr, Fe, Mg, Zr) powders with a nanometre size and a narrow size distribution were prepared by spray pyrolysis from a spray solution with citric acid and ethylene glycol. The precursor powders with a hollow and thin walled structure were turned to nano-sized Co3O4 powders after post-treatment. The mean size of the pure Co3O4 powders post-treated at a temperature of 600 oC was 77 nm. On the other hand, the mean sizes of the doped Co3O4 powders with a doping concentration of 3 mol.% were changed from 24 to 63 nm. The Mg-doped Co3O4 powders had the minimum mean size. The mean sizes of the Mg-doped Co3O4 powders with doping concentrations of 1 and 5 mol.% were 60 and 61 nm. The mean sizes of the Mg-doped Co3O4 powders with a doping concentration of 3 mol.% post-treated at temperatures of 700 and 800 oC were 63 to 102 nm.

Keywords: Spray pyrolysis, Cobalt oxide, Nano powders, Gas phase reaction, Black matrix, Display material.