Effects of metal ions on the morphology and structure of haematite particles produced from forced hydrolysis reaction

Abstract

The effects of metal ions (Cu^II, Ni^II, Co^II and Cr^III) on the morphology and structure of haematite particles, produced from a forced hydrolysis reaction of FeCl₃–HCl at various concentrations of metal ions ranging from 0–0.8 in Me/(Fe+Me) atomic ratio (X_Me), were investigated by various means. Spherical and a few double-spherical haematite particles were altered to diamond-shaped particles with increase in the concentration of divalent metal ions accompanied by a reduction of particle size up to X_Me=0.8. On the other hand, spherical haematite particles with a few double-spherical particles were formed for the system doped with Cr^III at X_Cr≤0.04 but no pure haematite particle was produced above this concentration. TEM and XRD suggested that the haematite particles formed at X_Cu≤0.4 and X_Cr≤0.04 are polycrystalline with an enlarged c edge length in the unit cell, though the diamond-like particles produced at X_Cu≥0.6 exhibited a single-crystal nature. TG and FTIR indicated that the haematite particles produced with metal ions are hydrohaematite and contain OH^– ions in the lattice. The rate of phase transformation from β-FeOOH to haematite was closely related to the crystal lattice distortion and the amounts of the lattice OH^– ions which affected the morphology and structure of the haematite particles. Part of the dopants were incorporated into the particles and were concentrated in the particle surface phase.