New method to prepare iron particles with different morphologies: a way to get high green strength metal compacts

摘要

Metal iron powders of well controlled size and morphology were synthesised by thermal decomposition under hydrogen of precipitated ferrous oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strengths of compacts were measured.The precipitation of beta-FeC_2O_4.2H_2O oxalate from ammonium oxalate gives rise to the formation of spherical particles by aggregation of elongated grains. Thermal decomposition of this oxalate from 400 to 500 deg C under hydrogen permits metal iron particles with a rough surface to be obtained. Decomposition occurring above 500 deg C induces a smoothness of the particle surface. Metal particles synthesised at 500 deg C show both surface roughness and micrometer sized primary grains. This specific microstructure has allowed the highest value of compact green strength (31.7 MPa) to be obtained.Acicular shaping of the beta-FeC_2O_4.2H_2O particles precipitated from oxalic acid involves, after decomposition, an increase in the surface roughness and shape irregularity of the metal particles, owing to an entanglement of the elementary grains. An exceptional value (about 60 MPa) for the metal compact green strength was thus obtained for this type of powder.