Uranium Monosulfide. The Ferromagnetic Transition. The Heat Capacity and Thermodynamic Properties from 1.5° to 350°K

Abstract

The heat capacity of uranium monosulfide was measured from 1.5° to 22°K by an isothermal (isoperibol) method and from 6° to 350°K by an adiabatic technique. The ferromagnetic transition at 180.1°K has a characteristic lambda shape and associated magnetic ordering entropy and enthalpy increments of 1.62 ± 0.2 cal °K−1mole−1 and 231 ± 20 cal mole−1, respectively, over the temperature range 0° to 230°K. The correlation of the thermal data with magnetic studies is discussed. The heat capacity below 9°K is represented by Cp = 5.588 × 10−3T + 2.627 × 10−4T3 / 2 + 6.752 × 10−5T3cal°K−1mole−1Cp=5.588×10−3T+2.627×10−4T3∕2+6.752×10−5T3cal°K−1mole−1, in which the successive terms represent conduction electronic, magnetic, and lattice contributions. Values of the entropy [S°], enthaply function [(H° − H°0) / T][(H°−H°0)∕T], and Gibbs‐energy function [(G° − H°0) / T][(G°−H°0)∕T] are 18.64 ± 0.005, 8.94 ± 0.002, and − 9.70 ± 0.02 cal °K−1 mole−1, respectively, at 298.15°K. The Gibbs energy of formation at 298.15°K is − 72.9 ± 3.5 kcal mole−1