Crystallisation behaviour, microstructure and magnetic properties of BaO–Fe2O3–B2O3–SiO2 glass ceramics

Differential thermal analysis, X-ray diffractometry and scanning electron microscopy with energy dispersive spectroscopy were used to study the crystallisation of glass ribbons with a composition of 35% BaO, 35%Fe2O3, 20%B2O3 and 10% SiO2 (mol%) prepared via cooling the melts between steel rollers. The magnetic properties of specimens were also measured with a vibrating sample magnetometer. Heat treatment of glass specimens both in the form of bulk (ribbon) or pressed powders at their respective DTA exo-peak temperatures of 722 and 702 °C led to the formation of BaFe12O19 and BaB2O4 as the only crystalline phases. The pressed powders showed the finest and the broadest size distribution of acicular and platelet particles in the 0.1–2.5 μm range. The glass ribbons heat treated in one-stage exhibited the most uniform distribution of platelet particles of 0.9 μm mean size, while a two-stage heat treatment led to a bimodal size distribution of platelet particles. All specimens showed nearly identical values of saturation magnetisation of Ms = 25–27 emu/g while the coercivity values varied between Hc = 2800–3800 Oe.