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 help of the heat transfer equations. The heating power and cooling rate are discovered 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 to cause an obvious temperature fluctuation with time. Our work presents a physical foundation for understanding the phase-transition characteristics of molecular solid at the micrometer scale and introduces novel strategies for in-situ measuring phase-transition temperature of fusion fuels at low temperatures.