The effect of SiO2 and Cr2O3 additions on the crystallisation behaviour and magnetic properties of a B2O3–BaO–Fe2O3 glass

Differential thermal analysis, X-ray diffractometry and scanning electron microscopy with energy dispersive spectroscopy were used to study the crystallisation of a glass with a composition of 45% BaO, 30% B2O3 and 25% Fe2O3 (mol%), to which 10–30% SiO2 was added replacing B2O3. The effect of 1 mol% Cr2O3 as a nucleation agent also was studied. The magnetic properties of some specimens also were measured with a vibrating sample magnometer. It was found that while the addition of >10 mol% SiO2 prevented formation of barium hexaferrite, the main magnetic phase, Cr2O3, greatly enhanced surface crystallisation. All specimens revealed glass in-glass phase separation, which in the presence of Cr2O3 was more extensive and on a much finer scale. The latter specimens, in the form of pressed glass frits heat treated 1 h at 723 °C, showed a coercive force of Hc=4150 Oe and saturation magnetisation of Ms=9.92 emu/g.