Influence of B₂O₃ on the Production of Pure, Gel-Processed Mn-Zn Ferrites

Abstract
The influence of B₂O₃ on the microstructure and magnetic properties of pure Mn-Zn ferrites has been investigated. A citrate gel processing route was employed to produce highly homogeneous Mn-Zn (Mn_0,57Zn_0,35Fe_2,08O₄) ferrites undoped or doped with B₂O₃ (0-2.5wt%). The results show that B₂O₃ doping does not benefit the magnetic properties of these ferrites, but promoted grain growth significantly. The initial permeability (µ_i) of undoped samples has been determined to be about 2400. It sharply drops at 0.1-0.15wt% B₂O₃ doping levels to 1200-800, and rises back to a maximum value (~2600) at 0.25wt% doping level. Further increases in B₂O₃ doping level give further decreases in initial permeability. The power loss (P_L) is increased with B₂O₃, content, although a second minimum value of P_L is found at 0.25wt% doping level. The changes in magnetic properties are closely related to the observed microstructure. A uniform microstructure of 9.6±0.7µm. pore-free grains is observed in undoped ferrites, whereas at 0.1-0.15wt% B₂O₃ doping levels discontinuous grain growth is observed. A uniform microstructure with a grain size (39.5±3.3µm) is obtained at the 0.25wt% doping level, beyond which the average grain size decreases with further increases in B₂O₃ and a general increase in porosity occurs.