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

摘要

The kinetics of formation of NiFe_2O_4 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 NiFe_2O_4 nanoparticles in a superparamagnetic state as determined from M?ssbauer spectroscopy. In general, heat treatment at high temperature leads to a nanocomposite rich in NiFe_2O_4. In air, annealing at 1173 K for 8 h favored the formation of the magnetically ordered NiFe _2O_4 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 NiFe_2O_4 spinel structure stabilized for temperatures up to 873 and 773 K, respectively, however, decomposition of the NiFe_2O_4 phase into other undesired structures was observed above 873 K.