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

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.