Effects of metal ions on the morphology and structure of haematite particles produced from forced hydrolysis reaction
The effects of metal ions (CuII, NiII, CoII and CrIII) 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 (XMe), 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 XMe=0.8. On the other hand, spherical haematite particles with a few double-spherical particles were formed for the system doped with CrIII at XCr≤0.04 but no pure haematite particle was produced above this concentration. TEM and XRD suggested that the haematite particles formed at XCu≤0.4 and XCr≤0.04 are polycrystalline with an enlarged c edge length in the unit cell, though the diamond-like particles produced at XCu≥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.