Correlation between the morphology of cobalt oxalate precursors and the microstructure of metal cobalt powders and compacts

Abstract

Metal cobalt powders of well-controlled size and morphology were synthesized by thermal decomposition under hydrogen of precipitated cobalt oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strength of the metal compacts was measured. A precipitation from ammonium oxalate and oxalic acid gives rise to the formation of β-CoC2O4·2H2O particles of parallelepipedic and acicular morphology, respectively. An increase in the length to diameter ratio of the precursor particles favours an entanglement of the elementary grains during the thermal decomposition. Therefore, irregular and rough metal particles have been obtained. This specific morphology favours a mechanical interlocking of the particles during the compaction, leading to high values of green density and green strength of the metal compacts.