Enthalpy of Mixing of Sodium Borosilicate Glasses by DSC Analysis

An easy-to-use method to determine the enthalpy of mixing (ΔHmix) from the differential scanning calorimetry (DSC) heating curve of demixed borosilicate glasses of the composition zSiO2 (1-z)(0.16Na2O·0.84B2O3) with z = 0.775, 0.55 and 0.424 is presented. It is shown that ΔHmix results from the area under the endothermic mixing event of the DSC heating curve, but that ΔHmix can also be used to approximate the initial compositions of the boron-rich and silica-rich domains that exhibit the glass transition temperatures Tg1 and Tg2 of the DSC upscans.