21 research outputs found
The thermodynamic properties of the f-elements and their compounds. Part II. The Lanthanide and Actinide Oxides
A comprehensive review of the thermodynamic properties of the oxide compounds of the lan- thanide and actinide elements is presented. The available literature data for the solid, liquid and gaseous state has been analysed and recommended values are presented. In case experimental data
are missing, estimates have been made based on the trends in the two series, which are extensively discussed.JRC.E.3-Materials researc
Single-ion values for ionic solids of both formation enthalpies, ÎfH(298)ion, and Gibbs Formation Energies, ÎfG(298)ion
Formation enthalpies, ÎfH(298), are essential thermodynamic descriptors of the stability of materials, with many available from the numerous thermodynamic databases. However, there is a need for predictive methods to supplement these databases with missing values for known and even hypothetical materials, and also as an independent check on the not-always reliable published values. In this paper, we present 34 additive single-ion values, ÎfH(298)ion, from the formation enthalpies of 124 ionic solids, including an extensive group of silicates. In addition, we have also developed an additive set of 29 single-ion formation Gibbs energies, ÎfG(298)ion, for a smaller group of 42 materials from within the full set, constrained by the limited availability of the corresponding experimental data. Such single-ion values may be extended among related materials using simple differences from known thermodynamic values, but always with critical consideration of the results.Using the excellent available data for silicates, we propose that the solid-state silicate ion formation enthalpies can be estimated as âÎfH(298)silicate/kJ molâ1= â252[n(Si) + n(O)] â 27, where n(X) represents the number of species X in the silicate. More speculatively, we estimate the contribution per silicon and oxygen species as â490 and â184 kJ molâ1, respectively. Similarly, âÎfG(298)silicate/kJ molâ1= â266[n(Si) + n(O)] â 7, with the contribution per silicon and oxygen species being â140 and â300 kJ molâ1, respectively. We compare and contrast these results with the extensive collection of âmodified lattice energyâ (MLE) ion parameters from the M.S. thesis of C. D. Ratkey. Our single-ion formation enthalpies and the MLE parameters may be used in complementary predictions. While lattice energies, UPOT, entropies, So298, and heat capacities, Cp,298, of ionic solids are reliably estimated as proportional to their formula volumes (using our Volume-Based Thermodynamic, VBT, procedures), this is not the case in general for thermodynamic formation properties, other than within select groups of related materials