Set Of Thermodynamic Data Research Articles

Theoretical study on gas‐phase reactions during chemical vapor deposition of TixAl1–xN from TiCl4, AlCl3, and NH3

AbstractFcc‐TixAl1–xN (TiAlN) coatings synthesized via chemical vapor deposition (CVD) reduce cutting tool wear. Although CVD conditions reportedly influence coating quality, no quantitative guidelines are yet available. To quantitatively study the film‐forming mechanism of TiAlN CVD, the gas composition over the surface must be known. Therefore, we developed a gas‐phase elementary reaction model for TiAlN CVD derived from TiCl4/AlCl3/NH3. First, we constructed a novel thermodynamic dataset including molecules that contained both Ti and Al, and calculated the equilibrium composition. Thermal equilibrium calculations in the gas phase showed that the most stable species were AlCl3 and TiCl3 rather than TiCl4. An elementary reaction model was constructed based on the kinetics of the gas‐phase species that were generated. Kinetic analysis revealed that gas‐phase reactions were largely absent under our reactor conditions. The thermal equilibrium calculations indicated that TiCl4 may have given rise to TiCl3. Thus, other reaction pathways of TiCl4 to TiCl3 were explored. We calculated the reaction rate constants of 12 reactions of Ti species and added them to the model, which revealed that TiCl4 decomposed to TiCl3 via TiCl3NH2. Under our conditions, TiCl4 and TiCl3NH2 are the major Ti species and AlCl3 and AlCl2NH2 are the major Al species, which suggests that some of these species may form films. Unlike in the earlier reaction model, NH2 and H radicals were produced, which may have contributed to the surface reactions. For reactors with large Surface/Volume ratio of reactor, the effects of gas‐phase reactions should be considered. Our reaction model enables estimation of the partial pressures of reactor gas species and will therefore aid study of the TiAlN deposition mechanism.

Development of a consistent geochemical model of the Mg(OH)2–MgCl2–H2O system from 25°C to 120°C

The formation of magnesium chloride-hydroxide salts (magnesium hydroxychlorides) has implications for many geochemical processes and technical applications. For this reason, a thermodynamic database for evaluating the Mg(OH)2–MgCl2–H2O ternary system from 0 °C–120 °C has been developed based on extensive experimental solubility data. Internally consistent sets of standard thermodynamic parameters (ΔGf°, ΔHf°, S°, and CP) were derived for several solid phases: 3 Mg(OH)2:MgCl2:8H2O, 9 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2:4H2O, 2 Mg(OH)2:MgCl2: 2H2O(s), brucite (Mg(OH)2), bischofite (MgCl2:6H2O), and MgCl2:4H2O. First, estimated values for the thermodynamic parameters were derived using a component addition method. These parameters were combined with standard thermodynamic data for Mg2+(aq) consistent with CODATA (Cox et al., 1989) to generate temperature-dependent Gibbs energies for the dissolution reactions of the solid phases. These data, in combination with values for MgOH+(aq) updated to be consistent with Mg2+-CODATA, were used to compute equilibrium constants and incorporated into a Pitzer thermodynamic database for concentrated electrolyte solutions. Phase solubility diagrams were constructed as a function of temperature and magnesium chloride concentration for comparisons with available experimental data. To improve the fits to the experimental data, reaction equilibrium constants for the Mg-bearing mineral phases, the binary Pitzer parameters for the MgOH+ — Cl− interaction, and the temperature-dependent coefficients for those Pitzer parameters were constrained by experimental phase boundaries and to match phase solubilities. These parameter adjustments resulted in an updated set of standard thermodynamic data and associated temperature-dependent functions. The resulting database has direct applications to investigations of magnesia cement formation and leaching, chemical barrier interactions related to disposition of heat-generating nuclear waste, and evaluation of magnesium-rich salt and brine stabilities at elevated temperatures.

Calculation of Littlewood predominance diagrams for metal electrodeposition from molten chlorides using CALPHAD software and databases

Littlewood predominance diagrams are maps of phase stability with a potential in the ordinate and a pO2− on the abscissa. pO2− is the negative logarithm of the activity of O2− ions.In the current work, a new method for calculation of Littlewood predominance diagrams is presented. The method is particularly suitable for software and databases constructed according to the CALPHAD (CALculation of Phase Diagrams) methodology. This enhances the consistency of the calculations and enables inclusion of elaborate descriptions of non-stoichiometric phases. The calculation is based on Gibbs energy minimization so that identification of relevant reaction equations is not needed as input.A thermodynamic database with all the relevant phases, including metals, chlorides, oxides and oxychlorides is a perquisite for the calculation. The calculation results depend on the thermodynamic modeling and data. However, the algorithm does not depend on the details of the thermodynamic models used. That is, the same calculation method is applied irrespective of the thermodynamic model chosen. Sample calculations are given for the simple Mg-Cl-O system and for the more-complex Ca-Ti-Cl-O system. We use thermodynamic datasets published in the literature, as well as a small CALPHAD database for the Ca-Ti-Cl-O system constructed in the course of the present work.

Rapid generation of massive thermodynamic datasets using frequency comb spectroscopy.

We demonstrate massively parallel spectroscopic measurements of 12C2H2 using an optical frequency comb. This allows for the rapid and simultaneous estimation of self-broadening and self-shifting of more than 50 optical transitions between 1512 and 1538nm. The use of a temperature-controlled sealed gas cell allows us to measure both pressure- and temperature-mediated broadening and shifting. We present the results for the pressure-mediated self-broadening and self-shifting coefficients for 59 optical lines that make up the v1 + v3 combination band and a selection of hot bands. Our ability to measure the broadening of numerous transitions allows for the confirmation of prior work that shows that there is no measurable vibrational dependence across all acetylene bands, despite the strong dependence of the broadening coefficient on the rotational number. We also present an extensive measurement of the temperature dependence of the self-broadening for each of these 59 lines. This work shows the revolutionary power afforded by the frequency combs for rapid generation of large datasets related to thermodynamic variations of the key spectroscopic parameters of important gases.

Modeling the Global Water Cycle—The Effect of Mg‐Sursassite and Phase A on Deep Slab Dehydration and the Global Subduction Zone Water Budget

AbstractWe study the interplay of the thermal structure within subducted oceanic slabs together with the stability fields of hydrous phases that control slab dehydration and the amount of water transported into the deeper mantle. We implement different published thermodynamic data for phase A and Mg‐sursassite into a model of 56 subduction zones and evaluate the effect of these phases on the global water budget. We modeled vertical fluid fluxes within the slab such that dehydration‐derived fluid was allowed to react with fluid‐undersaturated rocks in other parts of the slab. The effect of Mg‐sursassite on the global water budget is limited, because the Clapeyron slope of this dehydration reaction is steeper than most pressure‐temperature trajectories in subduction zones. Two sets of published thermodynamic data for phase A yield significantly different values for the amount of deeply subducted water, ranging between 8 × 108 Tg/Ma and 1.4 × 109 Tg/Ma. In some subduction zones, the differences span several orders of magnitude. The absolute modeled amount of deeply subducted water strongly depends on the depth and intensity of slab mantle hydration, but a comparison of modeled and experimental data indicates that the thermodynamic dataset that yielded higher values is more reliable and should be implemented in future thermodynamic models. Our results show that the stable phases around the choke point as well as the slope and position of the phase A‐out reaction influence the deep water release from the slab, but the slope and position of the phase A dehydration reaction mainly control the recycling of water into the deep mantle.

Phase stabilities and thermodynamic properties of crystalline phases in CaO–SiO2–H2O above 100 °C

The current study revises the phase diagram of the CaO–SiO2–H2O system at saturated steam pressure between 100 and 250 °C by combining experimentally observed phase relations, solubility data and thermodynamic restrictions. A new self-consistent thermodynamic dataset for crystalline C-S-H phases is reported. The dataset revises known thermodynamic properties and derives values for phases for which no data have been published up to now. Chemical compositions and molar volumes of the phases were updated based on recent crystal structure refinements. Additionally, thermodynamic properties are deduced for hydroxylellestadite, scawtite and spurrite as they are relevant for autoclaved concrete and metamorphism/metasomatism of rocks. Portlandite dominates together with hillebrandite, xonotlite and low-quartz the equilibrium phase assemblage up to 250 °C. If the formation of the latter three phases is delayed by kinetic reasons, numerous metastable phases can occur.

Growth and Stability of Stratiform Carrollite (CuCo2S4) in the Tenke-Fungurume Ore District, Central African Copperbelt

Abstract Carrollite (CuCo2S4) is the main ore mineral of the critical battery metal cobalt, yet, surprisingly, detailed characterization of its thermodynamic properties and of its trace element contents remain sparse in the scientific literature. To fill these knowledge gaps, we generated the first thermodynamic data set for carrollite using well-characterized samples obtained from the stratiform sulfide mineralization style at Fungurume 88 deposit in the Democratic Republic of Congo. Detailed mineralogical investigation of these same samples suggests that carrollite has limited ability to incorporate other ‘sweetener’ elements (except Cu and Ni) by substitution mechanisms. Modeling using CHNOSZ 2.0.0. software and an integrated Cu-Co-S-O thermodynamic data set provides insights into the stability of carrollite relative to other Co-bearing minerals under physicochemical conditions relevant to the Central African Copperbelt. Further exploration of these models indicates that dropping redox potential in the mineralizing system is insufficient to explain the mineral-scale and deposit-scale zonation patterns commonly observed in Cu-Co deposits of the Central African Copperbelt. Instead, factors such as increasing pH, decreasing T, decreasing sulfur activity, or some combination of changing physicochemical parameters may need to be invoked to explain these zonation trends. At the Fungurume 88 deposit, the absence of linnaeite (Co3S4) suggests that ore precipitation occurred at temperatures cooler than 211 °C. From our pH-logfO2 diagrams, and relative to higher temperatures, such a lower T regime is marked by a greater degree of offset between the modeled Cu and Co solubility contours, thus facilitating a more differentiated and zoned distribution of these two metals at the deposit scale. Our models are offered to the geoscience community as exceptionally useful tools for modeling and visualizing the Cu-Co-S-O systematics and may be applied to a variety of geological and geometallurgical questions in the Central African Copperbelt and other deposits elsewhere.

Thermochemistry of SinOx(OH)y Vapor Species from Quantum Chemical Calculations.

The thermochemistry of the Si-O-H system has been extensively studied both experimentally and theoretically due to its importance in chemical processes, degradation of silica-protected materials in combustion, and geological processes. In this paper, we review past studies and use quantum mechanical methods to generate a new data set. Molecular geometries were generated with DFT using the B3LYP functional. Energetics were calculated with RCCSD(T) methods extrapolated to the complete basis set (CBS/45) limit. Particular attention was given to the treatment of the vibrational modes. A rigid rotor model was used, corrections for anharmonicity were applied, and the Pitzer-Gwinn treatment of the hindered rotation of the M-OH groups was applied. The generated enthalpies of formation at 298 K are compared to those of experiments and other calculations. Generally, the agreement is good. A set of thermodynamic data (enthalpy of formation at 298 K, entropy at 298 K, and heat capacity polynomial to 3000 K) is presented for SiOH, SiO(OH), Si(OH)2, SiO(OH)2, Si(OH)3, Si(OH)4, Si2O(OH)6, and Si3O2(OH)8. These can be added to any of the common computational thermodynamics packages. The application of these data to high-temperature corrosion and geological problems is discussed.

Experimental study and thermochemical assessment of the reciprocal system Li+, K+//Cl−, CO32−

In this work a new thermodynamic dataset of the reciprocal system Li+, K+//Cl−, CO32− was generated by using Calphad method with FactSage. After collecting and analyzing the available thermodynamic data in the literature, experiments were designed to improve the comprehensiveness of the new database. Specifically, Differential Thermal Analysis (DTA) was used (1) to confirm the eutectic temperature of the K2CO3–KCl system, (2) to check the solid solubility in the K2CO3–Li2CO3 system and (3) to measure the phase equilibria of the diagonal sections (i.e. Li2CO3–(KCl)2 and K2CO3–(LiCl)2) in the reciprocal system. In addition, the heat capacity of the intermediate compound LiKCO3 was measured by three types of Differential Scanning Calorimetry (DSC) and its phase transformation was studied by High temperature X-ray Diffractometry (HTXRD). Based on the literature data and the present experimental results, the thermodynamic data on pure LiCl, all sub-binary systems and the reciprocal system were reassessed in the new database, which can be used to calculate and predict the thermodynamic properties of the salt mixtures in the reciprocal system Li+, K+//Cl−, CO32− more precisely and reliably.

Hydrogeochemical impact of Opalinus Clay system shown in migration lengths of uranium

Abstract. Models and simulations allow a prognosis of how processes in the geosphere might occur in the future by considering physical and chemical processes. They are the only way to test future scenarios and hypotheses and to evaluate how a repository site will develop over a period of a million years, e.g. by quantifying potential radionuclide migration in the hydrogeological system of the containment providing rock unit. An example is used to demonstrate the extent to which simulated migration lengths can vary for a million years, depending on the model concept and on the underlying data and parameters. In the case of uranium in the potential host rock Opalinus Clay (Switzerland), the range extends from 5 m, by applying experimentally determined transport parameters, over 50 m, using process-based approaches and taking hydrogeology into account, and up to 80 m, depending on the thermodynamic data set used. The degree of reliability of the models is derived from comparison with laboratory tests, data from boreholes and underground laboratories or natural analogues. This is the only way to assess the simulation results. In addition, indications can be provided regarding where new data need to be collected. So our task is to find an answer to the following question: how accurate do the models for the repository site search have to be in order to produce resilient and robust forecasts? To reduce the uncertainty related to the migration length of uranium in the Opalinus Clay, the calcite carbonate ion and the hydrogeological system at a potential disposal site need to be known, whereas the quantity of clay minerals plays a subordinate role, as long as it is enough, which is the case in argillaceous formations.

Thermodynamic Modelling and Experimental Study of Nasicon Sub-Systems for Application as Solid State Electrolyte

Solid state electrolytes are crucial for enhancement of the safety and practicability of batteries. NASICON ( Na Super Ionic Conductor) is proposed as replacement for β″-Al2O3 [1], because of its excellent structural strength and conductivity which is attributed to its structure wherein Na migrates in 3D voids providing ionic conductivity of 0.2 S·cm-1 (300 °C). Furthermore, the processing temperature is relatively low (~700 °C), and high Na abundance makes it cheaper than Li-ion batteries.The NASICON phase with formula Na1+xZr2SixP3-xO12 [0≤x≤3] is found to be conductive and is a part of the complex Na2O-SiO2-P2O5-ZrO2 system. For a successful material design, thermodynamic properties (phase equilibria, heat capacity, stability, etc.) for all subsystems must be known, and for prediction of the properties, a reliable and consistent database is imperative. To accomplish these milestones, a thermodynamic database of the quaternary oxide system including the NASICON phase is being developed using Calculation of Phase Diagrams (CALPHAD) method.As part of this development, underlying binary systems such as Na2O-ZrO2 and ternary systems such as ZrO2-SiO2-P2O5 are studied. After preliminary results, the phase diagram construction is in progress with DTA/TG, XRD, and the experimental data along with literature values after critical analysis will be utilized for generation of Gibbs energies for all phases in the system. Using the thermodynamic dataset obtained, phase equilibria are predicted in agreement with the experimental data. The current state of work will be presented.

Long‐Term Variation of Dust Devils in East Asia During 1959–2021

AbstractDust devils play an important role in dust transport by carrying it from the surface into the atmosphere, especially in summer. However, information on how dust devils changed in the past decades and what caused these changes remains lacking. Based on thermodynamic criteria and ERA5 reanalysis data set, this study investigated the long‐term variation of favorable conditions for dust devil occurrence in East Asia over the past 63 years and defined it as potential dust devil and dusty plume (PDDP) occurrence in hours. Annual mean frequency of PDDP in East Asia was approximately 217.2 hr from 1959 to 2021. An overall downward trend in PDDP frequency has been found over 63 years in East Asia among which strong PDDPs drop significantly at the fastest rate while the weak ones dropped insignificantly. Moreover, PDDP frequency in the Gobi Desert increased but they decreased in the Taklimakan Desert. The monthly variation of PDDP shows a single‐peak structure with a tendency for the peak to move from June to July. For the diurnal changes, PDDP mainly occurred between 10:00 and 16:00 at local time (LT), with over 60% of them happening between 12:00 LT and 14:00 LT. We also found a negative correlation between precipitation and PDDP occurrence. This study provides a comprehensive understanding of favorable conditions for dust devil occurrence in East Asia over the past decades, which is of great importance to further evaluate its impact on climate, environment as well as ecosystem.

Tin transport and cassiterite precipitation from hydrothermal fluids

Cassiterite (SnO2) is the main ore mineral of tin in magmatic–hydrothermal tin deposits, but tin transport and precipitation mechanisms from hydrothermal fluids remain poorly understood. We critically evaluated aqueous tin speciation in hydrothermal fluids from extensive experimental data and thermodynamic modeling. Sn(II) chloride complexes in hydrothermal fluids exist mainly as SnCl+, SnCl2(aq), and SnCl3−. The revised Helgeson–Kirkham–Flowers model parameters of these three tin species and two tin ions (Sn4+ and Sn2+) were derived from the correlation algorithms among these parameters, and the standard molar properties of cassiterite were optimized to be internally consistent with the available thermodynamic dataset. These thermodynamic parameters, together with the available equilibrium constant equation of Sn(IV) chloride complexes, could reproduce the available solubility data of cassiterite in acidic solutions at 400–700 °C under oxygen fugacity (fO2) levels buffered by hematite–magnetite (HM) or nickel–nickel oxide (NNO). These comparisons allow modeling chemical systems of SnO2–NaCl–HCl–H2O (liquid phase) to examine tin transport and cassiterite precipitation mechanisms under tin-mineralizing conditions: 300–500 °C, 50–150 MPa, 2 molal NaCl, and fO2 levels from QFM (quartz–fayalite–magnetite) to HM. Sn(II) chloride complexes are commonly interpreted to dominate in aqueous tin speciation under fO2 = NNO, but our modeling results indicate that considerable contents of Sn(IV) chloride complexes also exist in those reduced fluids with high HCl contents, consistent with recent in situ high-temperature experiments and molecular dynamic simulations. The Sn(II)/Sn(IV) ratios in fluids depends on fO2, temperature, and HCl contents. A considerable amount of Sn(IV) possibly exist in an early mineralization stage even under fO2 = NNO; if so, redox reactions are unnecessary to precipitate cassiterite from these mineralizing fluids. We find that even if the fO2 levels are constant, simple cooling can alter mineralizing fluids to be more oxidized (e.g., from QFM to HM) and cause cassiterite precipitation, indicating that oxidizing agents are not necessary as previously thought. This explains why cassiterite can precipitate in host rocks (e.g., sandstone or quartzite) that do not provide oxidizing agents. A simple rise in fO2 levels and pH neutralization (e.g., greisenization) also cause cassiterite precipitation. Cassiterite solubility in oxidized acidic hydrothermal fluids (NNO < fO2≤HM) is high enough to account for the tin contents of fluid inclusions from typical tin deposits, but the mineralization potential of oxdized fluids is inferior to reduced fluids (fO2≤ NNO) under the same conditions.

The solubility of oxygen in water and saline solutions

Oxygen is one of the key reaction partners for many redox reactions also in the context of nuclear waste disposal. Its solubility influences radionuclides’ behavior, corrosion processes and even microbial activity. Therefore, a reliable calculation of the solubility of molecular oxygen in aqueous solutions is relevant for any safety assessment. Available geochemical speciation and reactive transport programs handle these data very differently. In some codes, the hypothetical equilibrium between dissolved oxygen and water is used to balance redox reactions. Equilibrium constants are given in “temperature grids” for up to 573.15 K. In other cases, temperature functions for the solubility of gaseous oxygen in water are given, without any reference to a valid temperature range. These settings become even more complicated when used in the context of modeling equilibria in high-saline solutions applying the Pitzer formalism. This raised the question about the experimental foundation of equilibrium constants given in such data files and their validity for the solubility of molecular oxygen in saline solutions. For this article, a thorough literature review was conducted with respect to the solubility of molecular oxygen in pure water and saline solutions. From these primary experimental O2 solubility data a temperature-dependent Henry’s law function as well as temperature-dependent binary and ternary Pitzer ion-interaction coefficients were derived. An internally consistent set of thermodynamic data for dissolved oxygen is presented, along with statements about its validity in terms of temperature and, as far as Pitzer interaction coefficients are concerned, of solution composition. This self-consistent activity-fugacity model containing thermodynamic data, Henry’s law temperature equation, and Pitzer interaction coefficients is capable of providing a more accurate description of redox transformations, allowing a reduction of conservatism in safety assessment calculations, not only in the context of a nuclear repository. The model reproduces well the reliable experimental data available, and is capable to predict the oxygen solubility in complex solution media. The temperature functions used to describe Henry’s constant and the Pitzer interaction coefficients are consistent with the implementation in commonly used geochemical computational programs, allowing direct use without further modification.

Phase equilibrium modelling of partial melting in the upper mantle: A comparison between different modelling methodologies and experimental results

Recent advances in thermodynamic modelling now allow phase equilibrium studies of partial melting in mafic and ultramafic sources under upper mantle conditions. This potentially offers several advantages over experimental investigations, including the fact that capsule-sample interactions are avoided, there is no uncertainty over the volatile content of the charge, the process is much faster, and open system behaviour can be investigated with relative ease. Two different thermodynamic datasets are in common use for phase equilibrium investigations of mantle rocks, compiled alongside a range of constantly evolving phase solution models. This study compares the results of published experimental studies on partial melting in the upper mantle with phase equilibrium modelling results from the popular pMELTS software (Ghiorso et al., 2002), which uses an embedded dataset from Berman (1988), and with results from the Rcrust software (Mayne et al., 2016), which uses the dataset of Holland & Powell (2011). The aim of this comparative study is to investigate the suitability of each combination of software specific calculation routines, thermodynamic datasets and phase solution models to provide a viable alternative to conventional experimental techniques when studying magma genesis from the upper mantle. The main points of interest are how the phase assemblages, proportions, and compositions predicted by the modelling compare with those produced in the experiments. The set of experimental results used for comparison includes both peridotitic and eclogitic compositions, investigated over a pressure range of 1.0–3.0 GPa and a temperature range of 1165–1950 °C. The results indicate that using the Holland & Powell (2011) dataset and appropriately selected phase solution models provides the best match with experimental results in terms of melt volume, melt composition and the assemblage of coexisting phases produced during partial melting under upper mantle conditions.

The Fibrolite Problem: Implications for Reaction Overstep Studies

Abstract Despite several experimental studies the phase relations in aluminosilicates, especially involving the high-temperature polymorph, are not well understood. The widespread occurrence of fibrolite before sillimanite in rocks is described as the ‘fibrolite problem’. Fibrolite is considered to have higher free energy than sillimanite because of the excess surface energy contribution due to the higher surface/volume ratio. Equilibrium thermodynamics fails to reconcile the stability of fibrolite, with higher free energy, at lower temperatures than sillimanite. The existing literature invokes reaction kinetics to suggest that the low energy of {110} faces leads to acicular fibrolite growth rather than prismatic sillimanite. Here the ‘fibrolite problem’ is discussed from a perspective of high nucleation rates and hindered growth rates. An analog to fibrolite-sillimanite crystallization is suggested in the crystallization of mullite, a member of the Al2O3-SiO2 system. The crystallization of fibrolite in rocks shifts the position of the sillimanite producing reactions from the equilibrium PT depending upon the ΔS and ΔV of the reaction. Thermodynamic datasets calibrated using such natural samples tend to produce accurate predictions for sillimanite stability in geological terranes but inherently possess a reaction overstep and hence should be used carefully while quantifying reaction oversteps.

Enthalpy, heat capacity and thermal expansivity measurements of MgSiO3 akimotoite: Reassessment of its self-consistent thermodynamic data set

Enthalpy, isobaric heat capacity (CP) and thermal expansivity (α) of MgSiO3 akimotoite were re-determined by drop-solution calorimetry, differential scanning calorimetry and high-temperature powder X-ray diffraction measurement, respectively. From the obtained α, thermal Grüneisen parameter of MgSiO3 akimotoite was constrained to be 1.3. Using isochoric heat capacity by lattice vibrational model calculation and the Grüneisen relation equation, α and CP above maximum measurement temperature and the temperature derivative of isothermal bulk modulus were optimized by the least squares fitting to an existing P–V–T dataset which makes these parameters self-consistent. The obtained thermodynamic data set for MgSiO3 akimotoite was used to calculate the akimotoite–bridgmanite phase equilibrium boundary in MgSiO3 and high-pressure phase relations in Mg2SiO4. The result shows the stability field of the phase assemblage of MgSiO3 akimotoite + MgO below about 1400 K and around 23 GPa, suggesting the phase transition from ringwoodite to bridgmanite + ferropericlase via akimotoite + ferropericlase in cold subducted slabs.

MAGEMin, an Efficient Gibbs Energy Minimizer: Application to Igneous Systems

AbstractPrediction of stable mineral equilibria in the Earth's lithosphere is critical to unravel the tectonomagmatic history of exposed geological sections. While the recent advances in geodynamic modeling allow us to explore the dynamics of magmatic transfer in solid mediums, there is to date no available thermodynamic package that can easily be linked and efficiently be accounted for the computation of phase equilibrium in magmatic systems. Moreover, none of the existing tools fully exploit single point calculation parallelization, which strongly hinders their applicability for direct geodynamic coupling or for thermodynamic database inversions. Here, we present a new Mineral Assemblage Gibbs Energy Minimizer (magemin). The package is written as a parallel C library, provides a direct Julia interface, and is callable from any petrological/geodynamic tool. For a given set of pressure, temperature, and bulk‐rock composition magemin uses a combination of linear programming, extended Partitioning Gibbs Energy and gradient‐based local minimization to compute the stable mineral assemblage. We apply our new minimization package to the igneous thermodynamic data set of Holland et al. (2018), https://doi.org/10.1093/petrology/egy048 and produce several phase diagrams at supra‐solidus conditions. The phase diagrams are then directly benchmarked against thermocalc and exhibit very good agreement. The high scalability of magemin on parallel computing facilities opens new horizons, for example, for modeling reactive magma flow, for thermodynamic data set inversion, and for petrological/geophysical applications.

Thermodynamic properties of the novel photocatalyst BiSbO4 phase determined from 1.8 K to 1073 K

Growing interest in BiSbO4 application as the superior photocatalytic material leads to the problem of its thermodynamic stability. However, its thermodynamic properties have not been determined so far. In order to provide this data five experimental methods followed by critical data evaluation were used. BiSbO4 samples were obtained by the solid state synthesis. Low-temperature heat capacity data were obtained with physical property measurement system (PPMS) and standard entropy S0298.15 = 127.1 (±2.0) J/(mol·K) was derived. Next, using differential thermal analysis/differential scaning calorimetry method (DTA/DSC), high-temperature heat capacity of BiSbO4 phase has been measured and is given in the form of Maier-Kelley equation. Metal oxide equilibration established three phase equilibrium characterized by constant temperature and pO2. Finally, employment of the e.m.f. cell with the solid electrolyte gave Gibbs free energy change of the reaction Bi + O2+ 1/2Sb2O4 = BiSbO4. Then, the Third Law analysis provided the standard heat of formation of BiSbO4 from elements equal to ΔH0f,298.15 = −859.50 (±3.57) kJ/mole. This set of thermodynamic data allowed the calculation of the oxide Cp, heat content, S0T and μ0T, which are given in the range of temperature from 298.15 to 1100 K.

The potential––pH diagram for rhenium

The aqueous chemistry of rhenium is of importance for the hydrometallurgical processes involving rhenium alloys, for the leaching of rhenium from its ores and alloys, and for the electrochemical deposition of thin rhenium films. This study aims to present the chemical and electrochemical equilibria in the Re – H2O system in the form of the Pourbaix diagram. The existing variants of the Pourbaix diagrams for rhenium available in the literature were reviewed; it was shown that they significantly differ from each other in the composition and the values of the thermodynamic activities of rhenium species. The thermodynamic properties of aqueous rhenium species, including the standard Gibbs energies of formation and the standard electrode potentials of half-cell reactions involving it, were collected and analysed. The compounds of rhenium (+7) and rhenium (+6) not isolated in the free aqueous state, and rhenium hydride compounds were discussed. The self-consisted set of thermodynamic data for further calculations was obtained. Using these data, the basic chemical and electrochemical equilibria involving aqueous rhenium species at the temperature of 298 K and the air pressure of 1 bar were calculated. For the first time the potential – pH diagram for the Re – H2O system at the temperature of 298 K, the air pressure of 1 bar and the different activities of rhenium species in the solution were constructed. The influence of thermodynamic activities of aqueous rhenium compounds on the stability of rhenium oxides was discussed. It was shown that rhenium trioxide ReO3 is thermodynamically stable only in concentrated solutions (at the activities of rhenium species not less than 10–6 М), rhenium dioxide ReO2 loses the stability at the activities of rhenium species less than 10–8 М, and rhenium sesquioxide Re2O3 does so at the activities of rhenium species not less than 10–14 М. The necessity of the measurement of the stability constants of ortho- and mesorhenate anions, as well as nonahydridorhenates for a deeper understanding of the aqueous rhenium chemistry was discussed.