Influence of heat-treatment environment on Ni-ferrite nanoparticle formation from coconut water precursor

Abstract

The kinetics of formation of NiFe2O4 nanoparticles were investigated where the nanoparticles were produced by the proteic-sol–gel method using coconut water followed by annealing in (i) air, (ii) air in the presence of boron nitride (BN), or (iii) nitrogen. The sample dried at 473 K for 5.5 h was composed of small disordered NiFe2O4 nanoparticles in a superparamagnetic state as determined from Mossbauer spectroscopy. In general, heat treatment at high temperature leads to a nanocomposite rich in NiFe2O4. In air, annealing at 1173 K for 8 h favored the formation of the magnetically ordered NiFe2O4 inverse spinel structure, with bulk characteristics and average crystal sizes of approximately 66 nm. In a nitrogen atmosphere and in compacted BN powder under air atmosphere, the NiFe2O4 spinel structure stabilized for temperatures up to 873 and 773 K, respectively, however, decomposition of the NiFe2O4 phase into other undesired structures was observed above 873 K.