Abstract:Fine nickel ferrite precursors NiFe₂(C₂O₄)₃·6H₂O were obtained via co-precipitation method with low grade nickel matte as the raw material. Thermodynamic analysis of NiCl₂-FeCl₂-(NH₄)₂C₂O₄-H₂O system for precipitation identified that the theoretical optimum co-precipitation pH value is 2, and has strong complexation with Ni²⁺ and Fe²⁺ ions. Based on these theoretical considerations, the effects of parameters on the precipitation rates and precursors size were investigated systematically. The results show that the optimum co-precipitation conditions are pH=2, temperature 45 °C, 1.2 times theoretical amount of (NH₄)₂C₂O₄ dosage and 3% PEG400 addition. Under these conditions, the precipitation rates of Ni²⁺ and Fe²⁺ are both over 99.8%, with the precursors size of 1-2 um. Furthermore, X-ray diffraction (XRD) and thermogravimetry-differential thermal analysis (TG-DTA) demonstrate that the precursors are single-phase solid solution, wherein the nickel/iron atoms are replaced by the iron/nickel atoms reciprocally.

Key words: nickel ferrite; ferrite; magnetic materials; co-precipitation; low grade nickel matte