Solid–liquid phase transitions of deuterium under microspherical confinement

We investigated the solid–liquid phase transition of deuterium (D2) in microspheres using relaxation calorimetry. By developing a point-by-point analysis method for the temperature–time curves, we identified a sudden change in heat during the solid–liquid phase transition and determined the phase-transition temperature with the help of the heat-transfer equations. The heating power and cooling rate were found to affect the solid–liquid phase-transition temperature, while the spatially nonuniform distribution of D2 within microspheres is deduced to result in multiple liquid–solid transition processes, causing an obvious temperature fluctuation with time. Our work presents a physical foundation for understanding the phase-transition characteristics of molecular solids at the micrometer scale and introduces novel strategies for in situ measurement of the phase-transition temperature of fusion fuels at low temperatures.