Estimation of Thermal Properties of Sulphides using DFT
Sulphides have a large impact on the mechanical properties and corrosion behavior of steels. It is thus of great importance to be able to predict the formation of sulphides. To make this possible it is important to have an understanding of the thermodynamics related to sulphides. A suitable way to predict the thermodynamics is by using computational thermodynamics, more specifically the CALPHAD-method. This method has been shown to be a very efficient way to predict thermodynamic behavior of various materials. One of the most widely used models within the CALPHAD-method is the compound energy formalism (CEF), which is used to describe solution phases. In CEF the so-called end-member energies is a very important part. The end-member energies are the description the Gibbs energy of stable, metastable as well as hypothetical end-states which exist for a specific phase. However, there are uncertainties on how to describe the end-member energies of various metastable sulphide structures by extrapolating existing experimental data. An alternative to using experiments is to perform DFT calculations to obtain information regarding the thermal properties at 0 K. The thermal properties at finite temperatures can be predicted using the Debye-Grüneisen model. This methodology has been used successfully to predict the thermal properties of for example carbides. The aim of this work is to calculate the thermal properties of the stable and metastable structures of CaS, CrS, FeS, MgS, MnS, and NiS.