Thermal properties and crystallization of MgO-FeOx-P2O5 glasses.

Differential scanning calorimetry (DSC), dilatometry and X-ray diffraction have been used to study thermal behavior and stability of glasses prepared simultaneously in Al₂O₃ or Pt crucibles in compositional series (40 − <italic>x</italic>)MgO-<italic>x</italic>Fe₂O₃-60P₂O₅ within the concentration range of <italic>x</italic> = 0-40 mol% Fe₂O₃. Mössbauer spectra showed that all glasses with Fe₂O₃ contained both Fe(II) and Fe(III) ions. The contamination glasses from alumina crucibles ranged from 0.3 to 0.9 mol% Al₂O₃. The replacement of MgO by Fe₂O₃ resulted in a gradual decrease in glass transition temperature and dilatometric softening temperature, whereas thermal expansion coefficient did not change significantly. The DSC curves showed that all glasses crystallize on heating in the broad temperature range ≈ 560-900 °C. Crystallization temperature decreases with increasing Fe₂O₃ content. The highest tendency toward crystallization was found for the glass containing 40 mol% Fe₂O₃. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were Mg(PO₃)₂, Fe(PO₃)₃, Fe₃(P₂O₇)₂ and FePO₄. All thermoanalytical studies showed differences in thermal behavior of glasses prepared in Al₂O₃ or Pt crucibles. [ABSTRACT FROM AUTHOR]