Study on Thermodynamics and Kinetics for the Reaction of Magnesium Diboride and Water by Microcalorimetry

Abstract

An exothermic reaction between MgB₂ and water was observed in our laboratory at high temperature, although no obvious reaction occurred at room temperature. The reaction process of MgB₂ and water was therefore studied by using microcalorimetry. The results showed that the reaction enthalpies of MgB₂ with water and the formation enthalpies of MgB₂ at <i>T</i> = (323.15, 328.15, 333.15 and 338.15) K are (–313.15, –317.85, –322.09, –329.27) kJ?mol^–1, and (–238.96, –237.73, –236.50, –234.30) kJ●mol^–1, respectively. The standard enthalpy of formation and standard molar heat capacity of MgB2 obtained by extrapolation method are –245.11 kJ●mol^–1 and 246 J●mol^–1●K^–1, respectively. The values of activation energy <i>E</i>, pre-exponential factor A and the reaction order for the reaction of MgB₂ and water over the temperature range from 323.15 K to 338.15 K are 50.80 kJ●mol^–1, 10^4.78 s^–1 and about 1.346, respectively. The positive values of Δ<i>G</i>^≠ and Δ<i>H</i>^≠ and negative value of Δ<i>S</i>^≠ indicate that the reaction can take place easily above 314.45 K.