Prediction Of Pressure Dependence Research Articles

Pressure dependence of thermodynamic interaction parameters for binary solid solution phases: An atomistic simulation study

The effect of pressure on the interaction parameters (enthalpy of mixing) of face-centered cubic (FCC) and body-centered cubic (BCC) binary solid solution phases has been investigated using atomistic simulations at 0 K based on semi-empirical interatomic potentials (the second nearest-neighbour modified embedded-atom method: 2NN MEAM). First, it is confirmed that the 2NN MEAM interatomic potentials reproduce the pressure dependence of enthalpy and molar volume of pure elements in excellent agreement with thermodynamic modelling and experimental data. The prediction of pressure dependence is then extended to binary solid solutions. It is shown that the pressure dependence of binary interactions is clearly correlated with the sign of excess volume of corresponding solid solution phases. That is, the enthalpy of mixing shifts toward the positive direction with pressure if the excess volume shows a positive deviation from the linear average of constituent elements, while it shifts toward the negative direction in the opposite case. The results can be interpreted well by the functional form for the pressure dependence of Gibbs free energy of solution phases. An atomistic computational approach to estimate the pressure dependence of the excess volume of solution phases is also proposed.

Molecular Force Parameters through Thermal Diffusion to Ensure the Model Independency of Column Calibration Factor

Using Ar 36 –Ar 40 as calibrating gas, the simultaneous determination of thermal diffusion factors α T 's at two available experimental temperatures as well as the prediction of pressure dependence of ln q e at an intermediate temperature is possible for some isotopic inert gas mixtures in terms of column calibration factor F s (CCF) of a given column. The variation of α T with \bar T is then used to estimate the force parameters of the molecules only to ensure the reliability of the proposed temperature dependence of α T . The experimental α T 's due to Maxwell and Slieker shape factors are also calculated for comparison with those by the CCF method as well as by theoretical ones based on elastic collisions among the molecules. It seems that α T 's by CCF method play an important role in determining the force parameters of molecules indicating thereby the model independency of F s as a sensitive α T measuring parameter.