Terminal Solid Phases Research Articles

Thermodynamic modeling of the Ag–Sr system

The CALPHAD method was employed to model thermodynamic properties of the Ag–Sr system. The liquid phase was treated as a substitutional model (Ag,Sr), with the excess molar Gibbs free energy expressed by the Redlich–Kister formula. All the intermetallic phases were modeled as stochiometric compounds. The solubilities of Ag and Sr in the terminal solid phases were not considered due to their negligible values. Calculated results were then compared with available data from existing literatures. A set of self-consistent thermodynamic parameters of the Ag–Sr binary system was obtained.

Solubility and Stability Regions of Barium Selenites and Barium Selenates in Aqueous Solution at 25 °C

The Ba-Se(IV)-H2O and Ba-Se(VI)-H2O systems were studied by equilibrating mixtures of barium hydroxide (Ba(OH)2.8H2O) with selenious acid (H2SeO3) or selenic acid (H2SeO4) solution at 25 °C for one month. The equilibration in the neutral and alkaline ranges was carried out under an atmosphere of nitrogen to exclude atmospheric carbon dioxide. Analysis of the terminal solid phases and the associated solution from each experiment for barium and selenium showed the existence of two barium selenites, BaSeO3 (Se(IV)<0.075M) and BaSe2O5 (Se(IV)>0.075M), in the Ba-Se(IV)-H2O system and two barium selenates, BaSeO4 (Se(VI)<14M) and BaSe2O7 (Se(VI)>14M), in the Ba-Se(VI)-H2O system. The stability and solubility regions for these compounds were also determined as a function of pH. The solubility products and conditional free energies of formation for the low solubility BaSeO3 and BaSeO4 phases were calculated from the solubility data obtained.On a étudié les systèmes Ba-Se(IV)-H2O et Ba-Se(VI)-H2O en équilibrant des mélanges d’hydrate de baryum (Ba(OH)2.8H2O) avec une solution d’acide sélénieux (H2SeO3) ou d’acide sélénique (H2SeO4) à 25 °C, pendant un mois. On a effectué l’équilibrage, dans les domaines neutre et alcalin, sous une atmosphère d’azote afin d’exclure le bioxyde de carbone atmosphérique. L’analyse des phases solides terminales et de la solution associée résultant de chaque expérience pour le baryum et le sélénium a montré l’existence de deux sélénites de baryum, BaSeO3 (Se(IV) <0.075M) et BaSe2O5 (Se(IV)>0.075M), dans le système Ba-Se(IV)-H2O et de deux sélénates de baryum, BaSeO4 (Se(VI)<14M) et BaSe2O7 (Se(VI)>14M), dans le système Ba-Se(VI)-H2O. On a également déterminé les régions de stabilité et de solubilité de ces composés, en fonction du pH, et l’on a calculé les produits de solubilité et les énergies libres conditionnelles de formation des phases BaSeO3 et BaSeO4 à faible solubilité, à partir des données de solubilité obtenues.