Magnetic and colouring performaces of Co²⁺ ion doped magnetite powders synthesised using isothermal gaseous reduction

Abstract

Co²⁺ ion doped magnetite Fe₃O₄ powders were synthesised through isothermal gaseous reduction of hematite Fe₂O₃. X-ray diffraction results indicated that a single magnetite phase formed with 20CO–80CO₂ (%) gas composition annealed at 1000°C for 2 h. The phase accompanied with a minor amount of cobalt ferrite CoFe₂O₄ with varying the Co²⁺ ion content from 1·0 to 7·0%. The cobalt incorporation strongly influenced on the crystallite size, microstructure, magnetic properties and colorimetric performance. Vibrating sample magnetometer (VSM) evinced that pure magnetite phase as a soft magnetic material changed to hard magnetic material as the result of cobalt ferrite (CoFe₂O₄) phase formation. A saturation magnetisation (60·0 emu g⁻¹) achieved for the pure magnetite phase. The coercive force increased from 41·7 Oe for pure phase to 476·7 Oe at 7%Co²⁺ ion doped magnetite. Meanwhile, addition of 2% Co²⁺ ion found to enhance the coloring properties of the magnetite. The colouring properties of CIE-L*a*b* and X, Y, Z colour measurements were near a commercial black pigment. However, the results demonstrated the visibility of using 2%Co²⁺ doped magnetite spinel powders as black magnetic ceramic pigments.

Keywords:

• Pigments
• Ferrites
• Powders
• Doping
• Synthesis
• Magnetic properties