Development of Composite Phase Change Material for Preventing Spontaneous Combustion of Coal and Its Thermo-Physical Properties

In order to further study the application of phase change materials in inhibitors to prevent spontaneous combustion of coal, AlNH4(SO4)2·12H2O and MgSO4·7H2O were used as raw materials to obtain binary eutectic by melt impregnation. The phase transition temperature of the new material is around 70 °C, which is in the critical temperature range of the coal oxidation process. The material melts and absorbs the heat of coal during the phase change, so that the temperature of the coal is lower than the critical temperature. At the same time, it penetrates into the pores of the coal to isolate oxygen and achieves the effect of blocking the self-heating process of coal oxidation. The experimental results point out that as the proportion of AlNH4(SO4)2·12H2O in the binary eutectic increases, the better the material fusion becomes. The phase transition temperature decreases sharply at first and then slowly increases and stabilizes. The latent heat of change fluctuates back and forth between 260 and 290 J/g and then obviously decreases. Weight loss is basically between 20 and 40%. The optimization experiment pointed out that the best result is when the content of AlNH4(SO4)2·12H2O is 57.6%. Under this amount, the latent heat of phase transition is 298.67 J/g, the phase transition temperature is 65.88 °C, the weight loss rate is 27.2%, and the undercooling degree is 7.1 °C.