The precipitation of PbFe12O19 hard magnetic phase in PbO-SiO2-B2O3-Fe2O3 glass-ceramics

The present work is focused on investigating the crystallization process of the hard magnetic PbFe ₁₂O ₁₉ phase in PbO-SiO ₂-B ₂O ₃-Fe ₂O ₃ system. In this regard, different composition of (60-x)PbO-(x)SiO ₂–15B ₂O ₃–25Fe ₂O ₃ ( x = 0, 10, 20, 30) (mol.%), were melted and quenched in cooled water. The annealing process was done in as-quenched samples in temperature range of 300 to 700 °C for 5 h. According to achieved results, fully glassy structure only formed in 30PbO-30SiO ₂–15B ₂O ₃–25Fe ₂O ₃ system and the microstructure of quenched samples in other studied compositions was combination of Fe ₂O ₃, Fe ₃O ₄ and amorphous phases. The glassy phase in 30PbO-30SiO ₂–15B ₂O ₃–25Fe ₂O ₃ system exhibited one-stage crystallization on heating and its crystallization activation energy was estimated to be about 520 kJ/mol. The crystallization process in this system is governed by a three-dimensional diffusion-controlled growth. The highest value of coercivity was achieved of about 1450 Oe in annealed sample at 700 °C for 5 h.