Determination of onset temperature of melting in binary alloys using unit root test in differential scanning calorimetry

One of the important functions in differential scanning calorimetry (DSC) measurements is to determine the phase transition temperature of materials. In this study, we propose a statistical approach to determine the onset temperature of melting in multiphase alloys using the heating curve of DSC. The melting temperature determined using the extrapolation method is noticeably different from the detectable onset temperature of the reaction. The stationarity of the baseline (of the DSC curve) enables the detection of the onset temperature using statistical method without assumptions of shape of the heat absorption peak; the onset temperature of melting is the point where the baseline loses stationarity which was determined in augmented Dickey-Fuller test in this study. The method was validated by melting a potential eutectic reference alloy (Ag-40Cu in atomic percent), which has an invariant melting temperature at the eutectic composition. The onset temperatures of eutectic and congruent melting of a few binary alloys (Co-13Nb, Ni-41Nb, Ni-45Pd) were determined using this method and compared with the melting temperature obtained using the extrapolation method. The present study provides an improved methodology to evaluate the accurate phase transition temperature of a material.