Thermodynamic properties for metal oxides from first-principles

Thermodynamic Modeling and Experimental Investigation of the System Fe–Ti–O-K for Ilmenite Used as Fluidized Bed Oxygen Carrier

“…Thermodynamic calculations determine the chemical equilibrium by minimizing Gibbs free energy considering thermodynamic data for various phases and compounds. In this work, the database for pure substances (FactPS), oxide solutions (FToxid), and relevant compounds from other sources were integrated with a user-defined database and utilized along with additional thermal data for compounds previously shown to be important within the potassium–oxygen carrier systems namely, KTi 8 O 16 and K x Fe x Ti 1– x O 2 where x = 0.85 or 0.4 . In case of conflicting data, priority was given to FToxid, FactPS and last the user-defined database.…”

“…In these cases, it is possible to expand the thermodynamic database using first-principles calculations. The method used in this article has been published separately, 15 and entails computing the reaction energies by using density functional theory (DFT) and calculating the phononic contribution to the heat capacity using harmonic approximation. Using the procedure presented by Benisek and Dachs, 22 the results from the first-principles calculations were combined with experimental data from NIST-JANAF thermochemical tables.…”

“…The method has been used previously and provided results in excellent agreement with experimental data for other iron-oxides, especially FeTiO 3 . 15,16 FactSage requires that the temperature dependence of the specific heat capacity is provided as the sum of power functions…”

“…5 As a result of the potassium migration and interactions, several potassium titanates have been mentioned as possible products 4 In the published investigations the uptake of potassium has been measured and the obtained values vary from 2−4 wt % 5,6,14 and up to 10 wt %. 13 From thermodynamic calculations conducted for the interactions of K 2 O with ilmenite, K 2 Ti 6 O 13 is commonly found as the most stable product, 13,15,16 while studies using phase analysis with Xray diffraction (XRD) usually find the formation of priderite. 4,5,11−13 Even though the existing studies provide a certain understanding of the mechanism of potassium diffusion, they do not provide the mechanism behind the formation of different titanates which could explain the different observed uptake mechanisms of potassium by ilmenite.…”

“…In the published investigations the uptake of potassium has been measured and the obtained values vary from 2–4 wt % ,, and up to 10 wt % . From thermodynamic calculations conducted for the interactions of K 2 O with ilmenite, K 2 Ti 6 O 13 is commonly found as the most stable product, ,, while studies using phase analysis with X-ray diffraction (XRD) usually find the formation of priderite. ,,− Even though the existing studies provide a certain understanding of the mechanism of potassium diffusion, they do not provide the mechanism behind the formation of different titanates which could explain the different observed uptake mechanisms of potassium by ilmenite. Understanding potassium diffusion and interactions, as well as predicting maximum potassium uptake is crucial to decide the residence time of the material in the plant and to plan for optimal operational conditions and rate of replacement of bed material.…”