Suitable temperature assignment for liquidus line in SLE investigation by DSC

Abstract

The solid–liquid equilibria (SLE) of two binary mixtures of organic stabilizers for energetic materials, viz. N-(2-methoxyethyl)-p-nitroaniline + 2-nitrodiphenylamine (S1) and N-(2-methoxyethyl)-p-nitroaniline + 1,3-diethyl-1,3-diphenylurea (S2), have been determined using differential scanning calorimetry at three heating rates β (0.5, 1, and 2 K min−1). The liquidus line has been predicted using four characteristic points of the mixture melting curve as follows: the maximum peak temperature (Ttop), the temperature proposed by the German Society of Thermal Analysis (TGEFTA), the inflection point temperature (Tinf), and the endset temperature (Tendset) obtained at β= 1 K min−1 and by extrapolating the three heat flow curves at β= 0 K min−1. The melting temperatures of pure compounds and the eutectics have been identified from the onset temperature obtained at β= 0 K min−1. The quality of the prediction has been evaluated by the computation of the global quality factor from SLE consistency tests and by the estimation of the uncertainty associated with each investigated temperature. It was found that the inflection point displays the highest quality factors and the lowest uncertainties. Moreover, and for practical purposes, the inflection temperature obtained at β= 1 K min−1 generated more consistent data and lowest uncertainties than the other temperatures obtained even at β= 0 K min−1.