Minerale und Phasenbeziehungen im pseudotern�ren System Tl2SAs2S3Sb2S3 bei tiefen Temperaturen (original) (raw)
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Mineralogy and Petrology, 1995
The experimental determination of phase relations in the pseudoternary system T12S-As2S3-Sb2S 3 below 200 °C is practically impossible, especially so under dry condensed conditions. As thallium sulfosalts are naturally formed at low temperatures equilibrium phase assemblages at 100 and 200 °C were calculated by application of thermochemical approximations for the free enthalpies of formation of the sulfosalts. A comparison of the calculated conode configurations with the results of syntheses under dry condensed conditions at 200 °C yielded good agreement between experiment and calculations. Zusammenfassung M inerale und Phasenbeziehungen im pseudotern~ren System TI 2 S-As 2 S 3-Sb 2 S 3 bei tiefen Temper atur en Die Ableitung der Phasenbeziehungen im pseudotern/iren System TI2S-AszS3-Sb2S 3 ffir Temperaturen unterhalb 200 °C, insbesondere unter trockenen Bedingungen, ist auf experimentellem Weg praktisch nicht m6glich. Da die Thalliumsulfosalze als tieftemperierte Mineralbildungen anzusehen sind, wurden die stabilen Gleichgewichtsassoziationen bei 100 und 200 °C unter Verwendung thermodynamischer N/iherungen fiir die freie Bildungsenthalpie der Sulfosalze berechnet. Ein Vergleich der berechneten Konodenverl/iufe mit den Ergebnissen von Versuchen unter trocken kondensierten Bedingungen bei 200°C ergab gute lJbereinstimmung zwischen Experiment und Berechnung.
The experimental determination of phase relations in the pseudoternary system T12S-As2S3-Sb2S 3 below 200 °C is practically impossible, especially so under dry condensed conditions. As thallium sulfosalts are naturally formed at low temperatures equilibrium phase assemblages at 100 and 200 °C were calculated by application of thermochemical approximations for the free enthalpies of formation of the sulfosalts. A comparison of the calculated conode configurations with the results of syntheses under dry condensed conditions at 200 °C yielded good agreement between experiment and calculations.
Chemical Engineering Division, thermochemical studies annual report, July 1973--June 1974
1974
Standard enthalpies of formation have been determined for the following compounds: Cs2U207(c), 8-Na2U04(c), BaU04(c), HI(aq), CsN03(c), Cs2C03(c), CsCl(c), RbCl(c), Cs2Cr04(c), and Cs2Cr207(c). Preliminary reaction calorimetric studies of WS 2 and Li-Al alloys are described. High-temperature enthalpies and other thermodynamic properties are reported for~and 8-Na2U04(c); Cs2U04(c), and Al203 (c) • SUMMARY In connection with continuing studies of the thermodynamics of chemical. reactions in nuclear reactors, t.Hf values have been obtained for Cs2U207, ~-and 8-Na2U04, and BaU04. A thermodynamic analysis indicates that Cs 2 uo 4 is likely to be the dominant species formed in oxide fuel + Cs reactions. The enthalpy of the ~to 8-Na2U0 4 transition at 298.15 K has been determined. In a variety of thermochemical cycles, t.Hi(I-,aq) is a key component. Current critical compilations assign the rather large uncertainty of ± 0.2 kcal mol-l to this value. The present study has reduced the uncertainty to± 0.02 kcal mol-1 • CsN03 Previous determinations of the enthalpy of solution and, hence, of the enthalpy of formation, of CsN03 were rather uncertain. Current studies have yielded a new precise value for t.Hf(CsNQ3). By combining solubility and enthalpy of solution data, the standard entropy, S 0 (CsN0 3), has been deduced. The thermodynamic properties of Cs 2 C03 are of interest in connection with seed loss in the coal-fired MHD process. The enthalpy of solution of Cs 2 C03 in 0.5M CsOH was measured, and the standard enthalpy of formation, t.H£(Cs2C03, c, 298.15 K), was derived.
The Journal of Chemical Thermodynamics, 2005
The chemical reaction equilibrium constant for the formation of pyrosulfite from bisulfite in aqueous solutions f2HSO À 3 ðaqÞ S 2 O 2À 5 ðaqÞ þ H 2 OðlÞg was determined for temperatures from (313 to 353) K from ATR-IR-spectroscopic and calorimetric investigations of the system (Na 2 S 2 O 5 + H 2 O), resulting in ln K = À10.226 + 2123.6/(T/K), D r G m ¼ ð7:69 AE 0:33Þ kJ Á mol À1 ; D r H m ¼ ðÀ17:7 AE 0:5Þ kJ Á mol À1 (on the molality scale). Furthermore, some ATR-IR-spectroscopic results on liquid mixtures of (NH 3 + SO 2 + H 2 O) at T = 313 K are presented, revealing considerable amounts of pyrosulfite.
Prediction of enthalpies of formation of hydrous sulfates
A method for the prediction of the enthalpies of formation DH°f for minerals of hydrous sulfates is proposed and is decomposed in the following two steps: (1) an evaluation of DH°f for anhydrous sulfates based on the differences in the empirical electronegativity parameter D H O = M z+ (c) characterizing the oxygen affinity of the cation M z+ ; and (2) a prediction of the enthalpy of hydration based on the knowledge of the enthalpy of dissolution for anhydrous sulfates. The enthalpy of formation of sulfate minerals from constituent oxides is correlated to the molar fraction of oxygen atoms bound to each cation and to the difference of the oxygen affinity D H O = M z+ (c) between any two consecutive cations. The D H O = M z+ (c) value, using a weighing scheme involving the electronegativity of a cation in a given anhydrous sulfate, is assumed to be constant. This value can be calculated by minimizing the difference between the experimental enthalpies and calculated enthalpies of formation of sulfate minerals from constituent oxides. The enthalpy of hydration is closely related to the nature of the cation in the anhydrous salt, to the number of water molecules in the chemical formula and to the enthalpy of dissolution for the anhydrous salt. The results indicate that this prediction method gives an average value within 0.55% of the experimentally measured values for anhydrous sulfates and 0.21% of the enthalpies of hydration or hydrous sulfates. The relationship between D H O = M z+ (sulfate), which corresponds to the electronegativity of a cation in a sulfate compound, and known parameter D H O = M z+ (aq) was determined. These determinations allowed the prediction of the electronegativity of some anhydrous transition metal double sulfate and contributed to the prediction of the enthalpy of formation for any hydrous double sulfate. With a simplified prediction of the entropy of a hydrous sulfate, calculations of Gibbs free energy of formation can be evaluated and contribute to the knowledge of the stability of some hydrous sulfates in different environmental conditions such as temperature or air moiety. Therefore, to check the reliability of the predictive model, stability fields for some hydrous ferric sulfates such as pentahydrate ferric sulfate, lawsonite, kornelite, coquimbite, and quenstedtite vs. temperature and relative humidity were studied and compared with experimental measurements.
American Mineralogist, 2013
The stability of clay minerals is an important factor in assessing the durability of containment barriers for deep waste storage. In that context, the complete thermodynamic data set of three 2:1 ferro-magnesian clay minerals have been determined at 1 bar and from 2 to 520 K, using calorimetric methods. The studied clay samples were, respectively, the Na-saturated saponite Sap-Ca-1, Na 0.394 K 0.021 Ca 0.038 (Si 3.569 Al 0.397 Fe 3+ 0.034 )(Mg 2.948 Fe 2+ 0.021 Mn 0.001 )O 10 (OH) 2 , the Ca-saturated nontronite NAu-1, Ca 0.247 K 0.020 (Si 3.458 Al 0.542 )(Mg 0.066 Fe 3+ 1.688 Al 0.268 Ti 0.007 )O 10 (OH) 2 , and the Ca-saturated Santa Olalla vermiculite, Ca 0.445 (Si 2.778 Al 1.222 )(Al 0.192 Mg 2.468 Fe 3+ 0.226 Fe 2+ 0.028 Ti 0.018 Mn 0.007 )O 10 (OH) 2 .
Computers & Geosciences, 1992
A~traet-Recent advances in theoretical geochemistry permit calculation of the standard molal thermodynamic properties of a wide variety of minerals, gases, aqueous species, and reactions from 1 to 5000 bar and 0 to 1000°C. The SUPCRT92 software package facilitates practical application of these recent theories, equations, and data to define equilibrium constraints on geochemical processes in a wide variety of geologic systems. The SUPCRT92 package is composed of three interactive FORTRAN 77 programs, SUPCRT92, MPRONS92, and CPRONS92, and a sequential-access thermodynamic database, SPRONS92.DAT. The SUPCRT92 program reads or permits user-generation of its two input files, CON and RXN, retrieves data from the direct-access equivalent of SPRONS92.DAT, calculates the standard molal Gibbs free energy, enthalpy, entropy, heat capacity, and volume of each reaction specified on the RXN file through a range of conditions specified on the CON file, and writes the calculated reaction properties to the output TAB file and, optionally, to PLT files that facilitate their graphical depiction. Calculations can be performed along the liquid side of the H20 vaporization boundary by specifying either temperature (T) or pressure (P), and in the single-phase regions of fluid H20 by specifying either T and P, T and H20 density, T and log K, or P and log K. SPRONS92.DAT, which contains standard molal thermodynamic properties at 25°C and 1 bar, equation-of-state parameters, heat capacity coefficients, and phase transition data for approximately 500 minerals, gases, and aqueous species, can be augmented or otherwise modified using MPRONS92, and converted to its direct-access equivalent using CPRONS92.