Synthesis of Fibrous Cobalt Oxalate by a Double-Jet Process: Morphology and Growth Control

Abstract

Cobalt oxalate particles with a fibrous shape were prepared by a double-jet process with CoCl2 solution and (NH4)2C2O4 + NH3·H2O solution. The formation mechanism of the fibrous cobalt oxalate and the effects of temperature, pH value, feeding rate, ion concentration and PVP25 addition on the particle morphology and particle size were studied in this work. There were two kinds of cobalt oxalate precipitations in the Co2+-NH3-C2O42−-H2O system. When free ammonia was sufficient in this system, C2O42− and Co(NH3) n 2+ (n = 1,2,…,6) would combine to form fibrous Co(NH3)1.5C2O4·2H2O precipitation, otherwise square columnar β-CoC2O4·2H2O formed. The changes in nucleation and growth supersaturation had a great effect on particle morphology and size. The fibrous morphology of cobalt oxalate was formed by the Ostwald ripening mechanism.