INFLUENCE OF B2O3 ON THE PRODUCTION OF PURE, GEL-PROCESSED MN-ZN FERRITES

The influence of B2O3 on the microstructure and magnetic properties of pure Mn-Zn ferrites has been investigated. A citrate gel processing r oute was employed to produce highly homogeneous Mn-Zn (Mn0.57Zn0.35Fe2 .08O4) ferrites undoped or doped with B2O3 (0-2.5wt%). The results sho w that B,O, doping does not benefit the magnetic properties of these f errites, but promoted grain growth significantly. The initial permeabi lity (mu(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 ri ses back to a maximum value (similar to 2600) at 0.25wt% doping level. Further increases in B2O3 doping level give further decreases in init ial permeability. The power loss (P-1) is increased with B2O3 content, although a second minimum value of P-L is found at 0.25wt% doping lev el. The changes in magnetic properties are closely related to the obse rved microstructure. A uniform microstructure of 9.6+/-0.7 mu m, pore- free grains is observed in undoped ferrites, whereas at 0.1-0.15wt% B2 O3 doping levels discontinuous grain growth is observed. A uniform mic rostructure with a grain size (39.5+/-3.3 mu m) is obtained at the 0.2 5wt% doping level, beyond which the average grain size decreases with further increases in B2O3 and a general increase in porosity occurs.