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

The influence of B203 on the microshucture and magnetic properties of pure Mn-Zn ferrites has been investigated. A citrate gel processing route was employed to produce highly homogeneous Mn-Zn (MQ,~,Z~.,F~,,OJ ferrites undoped or doped with B203 (0-2.5wt%). The results show that B203 doping does not benefit the magnetic properties of these femtes, but promoted grain growth significantly. The initial permeability (k) of undoped samples has been determined to be about 2400. It sharply drops at 0.1-0.15wt% B203 doping levels to 1200-800, and rises back to a maximum value (-2600) at 0.25wt% doping level. Further increases in B203 doping level give further decreases in initial permeability. The power loss (P,) is increased with B20, content, although a second minimum value of P, is found at 0.25wt% doping level. The changes in magnetic properties are closely related to the observed microstructure. A uniform microstructure of 9 .6f0 .7~. pore-free grains is observed in undoped ferrites, whereas at 0.1-0.15wt% B20, doping levels discontinuous grain growth is observed. A uniform microstructure with a grain size (39.5f3.3pm) is obtained at the 0.25wt% doping level, beyond which the average grain size decreases with further increases in B203 and a general increase in porosity occurs.