Complementary Study to Determine the Thermodynamic Properties of Wüstite in Deep Earth Layers up to 140 GPa

Abstract

In this research was studied the change of Debye temperature with pressure change of the purpôleFeO, this is based on previous values of the elastic properties of this oxide, which were available in the study by S.Tlili et al 2017. And based on the idea of linear change of this parameter between every two successive pressure values, their values are determined for specific pressure values from the PREM model. Therefore, we were able to continue studying some parameters of the thermodynamic properties with changes in temperature and at these pressures. These parameters are represented by two energies internal and free, heat capacity and entropy. We found a clear effect of the Debye temperature on the phase transformation of the oxide, its value is estimated at 712.01 K at zero pressure and its values for its B1 phase are always increasing and greater than its values for its B8 phase, which increases to only 120 GPa. Moreover, at the same pressure and at a temperature of 300 K, the values of the studied thermodynamic parameters respectively are: 5.61, -3.34 kJoule/mole, 38.32 and 35.08 kJoule/K.mole, the same as before. The values of energy and heat capacity at constant volume increase in the same direction as the change with increasing temperature, in addition to the change in pressure, which increases the values of these parameters decrease. As for entropy, it takes the same change as the three parameters until a limit close to the end of the Earth’s upper mantle and the beginning of the Earth’s lower mantle, to begin to reverse the direction of all of that.