Construction of a Room-Temperature Eutectic Binary Phase Diagram by Use of Differential Scanning Calorimetry

A eutectic system is a mixture of two or more substances, displaying a melting temperature lower than its standalone components. The eutectic composition displays the lowest melting temperature of all mixtures. Typically, a eutectic system is used as an example of binary phase diagrams to demonstrate to undergraduate students. Herein, the liquidus and solidus define regions in the phase diagram where the mixture is either a liquid, a solid, or a combination of both. This experiment aims to construct the binary phase diagram of a mixture of menthol (M) and lauric acid (LA) by measuring the thermal properties of a wide range of compositions utilizing differential scanning calorimetry (DSC). The solidus and liquidus are uniquely located below room temperature. The eutectic melting temperature is around 12°C, while the standalone menthol and lauric acid components melt at 36 and 48°C, respectively. This allows the visual demonstration of the compositions in all of the defined regions in the binary phase diagram. Furthermore, the theory of cryoscopy is utilized to predict the liquidus of the phase diagram. The comparison with the experimentally determined melting temperatures allows the undergraduate students to reflect on the reliability of the derived equation.