Phase transformations in Higher Manganese Silicides

This work is an investigation of the phase transformations of the Higher Manganese Silicides in the temperature range [100–1200 °C]. Several complementary experimental techniques were used, namely in situ X-ray Diffraction (XRD), Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). The evolution of both the lattice parameters and the thermal expansion coefficients was determined from in situ XRD measurements. The stability of the samples was investigated by thermal analysis (DTA) and Cp measurements (DSC). This study shows that Mn27Si47 which is the stable phase at room temperature and under atmospheric pressure undergoes a phase transformation at around 800 °C. Mn27Si47 is transformed into Mn15Si26. This phase transformation seems to be of a second order one. Indeed it was not evidenced by DTA and by contrast it appears on the Cp curve.

► The phase transitions of the Higher Manganese Silicides were investigated.
► The samples were characterised by XRD, DTA and DSC.
► Mn27Si47 is the stable phase at room temperature and under atmospheric pressure.
► At around 800 °C, Mn27Si47 is transformed into Mn15Si26.
► The phase transition is of a second order.