Phase Equilibrium of n-Nonane + n-Decane for Low-Temperature Thermal Energy Storage: Insights into Odd-Even Effects

The present article presents the solid-liquid phase diagram of a binary system composed of an n-alkane with an odd number of carbon atoms, namely, n-nonane (n-C₉), with an even-numbered one, namely n-decane (n-C₁₀). This work is part of a series of phase equilibrium studies on n-alkanes for low-temperature thermal energy storage (TES) applications. The ultimate purpose of this work is to investigate the adequacy of this binary system to be used as a Phase Change Material (PCM) at low temperatures. Additionally, along the equilibrium studies on linear alkanes, an interesting feature has emerged: the solid-liquid phase diagrams of binary n-alkane systems apparently show a striking dependence on the odd or even number of carbon atoms in their chains. The phase diagram for the system n-C₉ + n-C₁₀ has primarily been obtained using Differential Scanning Calorimetry (DSC), whose results have been complemented by Hot-Stage Microscopy (HSM) and low-temperature Raman Spectroscopy results. The DSC analysis provided both the temperature and enthalpy values for the observed solid-liquid and solid-solid phase transitions. The n-C₉ + n-C₁₀ binary system seems to display a peritectic solid-liquid phase diagram at low temperatures. The peritectic temperature found was 222.41 K, with a peritectic composition around x _nonane = 0.60. Those results confirmed the initial suggestions that this would be a peritectic system, based on previously observed odd-even effects on phase equilibrium behavior of alkane mixtures. The goal of this work is to extend new insights into the solid-liquid phase equilibrium behavior of the binary system n-C₉ + n-C₁₀, a topic not yet covered in the literature. This information, consequently, provides practical and essential information on the potential use of this system as PCM for low-temperature TES applications. Additionally, it contributes to support the important discussion on the effect of odd-even number of carbons of the individual n-alkanes in the solid-liquid phase equilibrium behavior of their binary mixtures. The solid-liquid diagram of this system is being published for the first time, as far as the authors are aware.

The online version contains supplementary material available at 10.1007/s10765-025-03531-7.