Effects of debinding atmosphere on the microstructure and sintering densification of nickel ferrite

Microsized nickel ferrite (NiFe2O4) powders were synthesized by molten salt synthesis in KCl flux using Fe2O3 and NiO as raw materials. The binder burnout process of the compact containing 1.2 wt% poly vinyl alcohol was performed in air and N2 atmospheres, followed by sintering in N2 atmosphere. The effects of debinding atmosphere on the microstructure and sintering densification of NiFe2O4 were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS) and X-ray photoelectron spectroscopy (XPS). Metallic Ni particles were found uniformly distributed on the surface of NiFe2O4 particles debound in N2 atmosphere. The densifications of the samples sintered at 1150 °C and 1300 °C were 90.7% and 97.2% respectively when the binder burnout process was performed in N2 atmosphere. They increased by 15% and 6.7% respectively compared with those debound in air. The temperature for the debound sample to reach a densification of 90% was 150 °C lower in N2 atmosphere than that in air. Also the average grain size of NiFe2O4 and Fe/Ni ratio in NiFe2O4 phase of the sintered samples debound in N2 atmosphere showed a significant increase, compared with those debound in air.