Study on the Precipitation Process of SrFe₁₂O₁₉ from a Glass

Abstract

Crystallization of a SrO-B₂O₃-SiO₂-Fe₂O₃ glass was investigated to elucidate the precipitation process of SrFe₁₂O₁₉ from the glass matrix.
The results obtained are as follows; an unidentified crystal phase, X-phase, precipitates by heating the glass in the temperature range from T_g (546°C) to 750°C. The X-ray diffraction lines of the X-phase are well indexed with assuming a cubic unit cell with α=7.584Å. In the temperature range from 650°C to 750°C, 4SrO⋅B₂O₃⋅SiO₂ precipitates in the vicinity of the glass surface and gradually grows toward the inside of the glass.
SrFe₁₂O₁₉ co-precipitates with 4SrO⋅B₂O₃⋅SiO₂ in the temperature range from 750°C to 850°C. 4SrO⋅B₂O₃⋅SiO₂ has crystallized rapidly in the whole region of the glass and no X-phase is observed in that temperature range. The amount of SrFe₁₂O₁₉ with heating time changes relatively in the same manner as that of 4SrO⋅B₂O₃⋅SiO₂. Based on these results, hexagonal platelets of SrFe₁₂O₁₉ with a dimension of%cong; 0.3μm are obtained as a precipitate from the glass by the heat-treatment at 800°C for 5 hr.