On models to describe the volume in the context of establishing high-pressure Gibbs energy databases. (September 2022)

• Record Type: Journal Article
• Authors: Deffrennes, Guillaume; Joubert, Jean-Marc; Oudot, Benoit
• Is Part Of: Calphad. Volume 78(2022)
• Publication Date: 2022-09
• Subjects: High pressure -- Modeling -- Volume -- CALPHAD -- EOS; Phase diagrams -- Data processing -- Periodicals; Thermochemistry -- Data processing -- Periodicals; Diagrammes de phases -- Informatique -- Périodiques; Thermochimie -- Informatique -- Périodiques; Thermodynamica; Electronic journals; 541.363
• DOI: 10.1016/j.calphad.2022.102435
• Languages: English
• ISSNs: 0364-5916

Abstract

Abstract: High-pressure Gibbs energy approaches are promising for establishing multi-component thermodynamic databases. However, so far, they have often been considered unsuccessful, because of their tendency to lead to unphysical extrapolations of the thermodynamic properties at elevated temperatures and pressures. Beyond this symptom, the root causes of the problem are rarely investigated. In this work, it is identified that these shortcomings are caused by (i) an inconsistent treatment of the SGTE method of extrapolation, and (ii) an insufficient knowledge of the models to describe the volume that are the key to extend CALPHAD databases toward high pressures. Because the first step toward solving the problem is to focus on the later issue, several models to describe the volume that are built upon the Grover empirical law are investigated, namely, the Lu-Grover, Joubert-Lu-Grover, Jacobs-Grover, and the Anand-Saxena-Grover approaches. In addition, an original description built upon the concept of thermal pressure, and a new scheme based on the equivalence between temperature and pressure when computing the volume are discussed. For each of these models, limitations and possibilities are identified from a practical standpoint. Highlights: Gibbs energy models for high pressures tend to lead to unphysical extrapolations. These shortcomings primarily come from the description of the volume. For five models to describe the volume, limitations and possibilities are discussed. Two new models lead to reasonable extrapolations at high pressures and temperatures.