Thermodynamic modelling of the Ca–O system including 3rd generation description of CaO and CaO2

Abstract

A complete thermodynamic description of the Ca-O system is proposed including 3 rd generation modelling of crystalline CaO, liquid and amorphous CaO, and crystalline CaO2. Compared to previous modellings, a more robust description of the thermodynamic properties of the binary phases is achieved using data recently obtained by density functional theory calculations and molecular dynamics simulations. The heat capacity of crystalline CaO is reassessed, leading to a noticeably higher value below the melting point compared to previous modellings and resulting in a slightly higher standard entropy. It is highlighted that the parameters given in terms of polynomial functions of temperature that were employed so far in 3 rd generation models to describe anharmonic contributions in the heat capacity of compounds were not suited to satisfactorily describe the thermodynamic properties of crystalline CaO. It is suggested that this observation can be generalized to most refractory oxides. Alternative terms are proposed in the Gibbs energy function that give more flexibility in fitting the experimental data and lead to more numerically reasonable values for the parameters. The liquid and amorphous CaO phase is described using the two-state model, leading to a significant improvement in the description of its heat capacity. The description of crystalline CaO2 is also improved as only estimates of the thermodynamic properties of the compound were available in previous modellings of the system. Finally, phase equilibria data on the Ca-CaO liquidus is reviewed, and it is highlighted that slight discrepancies in the relatively low temperature measurements can lead to significantly different descriptions of the liquid phase.

Solar-Assisted Approach for the Synthesis of Nanoadsorbents for Biogas Desulfurization Using Wastes

“…On the other hand, the evaporation of targets containing Mg favors the presence of high percentages of MgO compared to the corresponding Ca phases. For instance, when marble and dolomite targets were used, MgO was the major crystal phase (54.4 and 48.2 %wt., respectively), whereas CaO content was found much lower despite its higher percentage in the initial material due to the challenges of thermally evaporating the CaeO system [34]. In these samples, spontaneous hydration of CaO seems to be inhibited with the percentage of Ca(OH) 2 lying under 5 %wt.…”

Current Status and Future Scope of Phase Diagram Studies

“…To expand the temperature range using the Einstein function, the third-generation database is intensively constructed. [66][67][68][69][70][71]…”

A Third Generation Calphad Description of Fe: Revisions of Fcc, Hcp and Liquid

“…[24][25][26][27] Alongside this, a number of thermodynamic descriptions of unary and binary systems have been assessed for the next generation of Calphad descriptions. [27][28][29][30][31][32][33][34] The first attempt to use the suggested models was for describing the thermodynamic data of Fe. [35] However, that thermodynamic description was assessed at the very early stages of developing the new generation of Calphad descriptions.…”