Characterisation of Binary Phase Mixtures of Magnesium-Aluminate Spinel and Calcium-Aluminates Using Time-Gated Raman Spectroscopy

Abstract

The modification of MgO·Al₂O₃ spinel inclusions into less detrimental mixture phases of CaO–MgO–Al₂O₃ plays an essential role in refining calcium-treated aluminium killed steels. This study uses Raman spectroscopy for the characterisation of binary phase samples that contain MgO·Al₂O₃ spinel and calcium aluminate (CaO)_x–(Al₂O₃)_y phases. Samples were synthesised from MgO·Al₂O₃ spinel (MA), Al₂O₃ and calcium aluminate phases to achieve binary samples of CA–MA, C3A–MA, C12A7–MA and Al₂O₃–MA with varying phase fractions. The study also examined the possibility of a slight variation for non-stoichiometric spinel samples below the 1600°C region in an MgO–Al₂O₃ binary system. The relative intensities of the Raman band were used for the quantification of the phase fractions. For a quantitative prediction, linear regression calibration models were identified for each of the studied systems. This work demonstrates the use of Raman spectroscopy for the characterisation of calcium aluminate phases of CA, C3A, C12A7 and magnesium aluminate spinel phases along with Al₂O₃ and its potential application in inclusion characterisation.