Thermochemical Equilibrium Modeling Indicates That Hg Minerals Are Unlikely to Be the Source of the Emissivity Signal on the Highlands of Venus

Several of the highlands of Venus exhibit unexpectedly low radar emissivity compared to that of the lowlands. The source has been hypothesized to be a mineral with a high dielectric constant. Recently HgTe (coloradoite) has been suggested to explain the low emissivity signal; however, little research has been completed to verify its stability on Venus. In this project, we used a Gibbs free energy minimization software to investigate whether HgTe, as well as HgS and HgSe, can form at simulated highland conditions. According to our calculations, approximately 1.3 wt% of mercury in the crust needs to be outgassed in order for HgS to be stable at 4 km in altitude. In addition, approximately 250 ppb of tellurium in the crust needs to be outgassed for HgTe to precipitate at the same altitude. The required mercury abundance for HgSe to be stable at this altitude is less, approximately 0.6 wt%; however, this is significantly larger than the 10–90 ppb generally present in basaltic rocks on Earth. Therefore, Hg-bearing minerals are likely not the source of the low radar emissivity signal.

Mixed oxide growth on combinatorial aluminium–gadolinium alloys — a thermodynamic and first-principles approach

Metal surfaces covered with oxides have attracted considerable scientific attention in various applications. In particular, anodic films fabricated by cost-effective anodizing have been widely used in nano-structured engineering to provide various surface functionalities. However, understanding of alloy film stability, having individual elements with widely varying structures and morphologies, is very limited due to lack of thermodynamic information and effects of electrolyte chemistry. This requires many tedious efforts on a trial and error basis in selecting suitable electrolytes that can produce the protective film at high efficiency on alloys having mixed chemistries. It is, therefore, crucial to develop a combination of high throughput theoretical analysis and automated rapid localized electrochemical probing that provides a fast and simple solution for electrolyte choice and paves the way to the remarkable expansion of industrial applications of oxides. Herein, we demonstrate that combinatorial Al–Gd alloys covering 1.0 to 10.0 at.% Gd can be oxidized into ultra-thin anodic films of controlled thickness through a selection of electrolyte based on thermodynamics (phosphate buffer with a pH of 8.20). We propose that growth of anodic films on alloys at high efficiency is possible if Gibbs free energy minimization criteria would be systematically contemplate. Graphical abstract

An autonomous petrological database for geodynamic simulations of magmatic systems

Self-consistent modelling of magmatic systems is challenging as the melt continuously changes its chemical composition upon crystallization, which may affect the mechanical behaviour of the system. Melt extraction and subsequent crystallization create new rocks while depleting the source region. As the chemistry of the source rocks changes locally due to melt extraction, new calculations of the stable phase assemblages are required to track the rock evolution and the accompanied change in density. As a consequence, a large number of isochemical sections of stable phase assemblages are required to study the evolution of magmatic systems in detail. As the state-of-the-art melting diagrams may depend on nine oxides as well as pressure and temperature, this is a 10-D computational problem. Since computing a single isochemical section (as a function of pressure and temperature) may take several hours, computing new sections of stable phase assemblages during an ongoing geodynamic simulation is currently computationally intractable. One strategy to avoid this problem is to pre-compute these stable phase assemblages and to create a comprehensive database as a hyperdimensional phase dia- gram, which contains all bulk compositions that may emerge during petro-thermomechanical simulations. Establishing such a database would require repeating geodynamic simulations many times while collecting all requested compositions that may occur during a typical sim- ulation and continuously updating the database until no additional compositions are required. Here, we describe an alternative method that is better suited for implementation on large-scale parallel computers. Our method uses the entries of an existing preliminary database to estimate future required chemical compositions. Bulk compositions are determined within boundaries that are defined manually or through principal component analysis in a parameter space con- sisting of clustered database entries. We have implemented both methods within a massively parallel computational framework while utilizing the Gibbs free energy minimization program Perple X. Results show that our autonomous approach increases the resolution of the ther- modynamic database in compositional regions that are most likely required for geodynamic models of magmatic systems.

Decomposition Characteristics of SF6 under Arc Discharge and the Effects of Trace H2O, O2, and PTFE Vapour on Its By-Products

The research on decomposition characteristics of SF6 and its by-products have great significance to the operation, maintenance, condition assessment and fault diagnosis of power equipment. In this paper, the particle composition models of SF6, SF6/polytetrafluoroethylene (PTFE), SF6/PTFE/O2, SF6/PTFE/H2O, and SF6/PTFE/O2/H2O were established by using Gibbs free energy minimization method, and the effects of trace H2O and O2 impurities and PTFE vapour on SF6 by-products were studied by the models. In order to verify the correctness of the simulation results, a series of breaking experiments were carried out on a 40.5 kV SF6 circuit breaker, and a gas chromatograph was used to detect and analyse the SF6 by-products. It was found that when PTFE vapour is involved in the arc plasma, the main by-product after arc quenching is CF4, and the molar fractions of C2F6 and C3F8 are very low. When O2 is involved, the main by-products are SOF2, SO2 and SO2F2, and a small amount of CO and CO2 was also produced. When H2O is involved, the main by-products in simulation are SOF2, SO2 and HF, and a small amount of SO2, CO2, CO, SO2F2 and H2 was also produced. The experimental results are in good agreement with the above results.

Thermodynamics Study on Liquid Phase Catalytic Exchange for Water Detritiation

Liquid phase catalytic exchange (LPCE) is one of the key technologies for tritium removal of tritiated water, such as effluents from Fukushima nuclear power plant. Although former researchers have widely studied this process theoretically, the reported results differ from each other due to different assumptions and parameters adopted. In this work, the principle of Gibbs free energy minimization is applied, with only basic physical properties and no more other assumptions involved. The predictions of isotope exchange are more accurate, and the average error between calculation results and experimental data reduces from 4.45%~6.65% to 2.17%. Then the catalytic exchange behaviors are systematically investigated in the protium-deuterium (H-D) system, and the influence of the cascade processes are emphatically analyzed. The method established in this paper could be applied to catalytic exchange systems for tritium separation, which is essential for the development of water detritiation.

An autonomous petrological database for geodynamic simulations of magmatic systems

SUMMARY Self-consistent modelling of magmatic systems is challenging as the melt continuously changes its chemical composition upon crystallization, which may affect the mechanical behaviour of the system. Melt extraction and subsequent crystallization create new rocks while depleting the source region. As the chemistry of the source rocks changes locally due to melt extraction, new calculations of the stable phase assemblages are required to track the rock evolution and the accompanied change in density. As a consequence, a large number of isochemical sections of stable phase assemblages are required to study the evolution of magmatic systems in detail. As the state-of-the-art melting diagrams may depend on nine oxides as well as pressure and temperature, this is a 10-D computational problem. Since computing a single isochemical section (as a function of pressure and temperature) may take several hours, computing new sections of stable phase assemblages during an ongoing geodynamic simulation is currently computationally intractable. One strategy to avoid this problem is to pre-compute these stable phase assemblages and to create a comprehensive database as a hyperdimensional phase diagram, which contains all bulk compositions that may emerge during petro-thermomechanical simulations. Establishing such a database would require repeating geodynamic simulations many times while collecting all requested compositions that may occur during a typical simulation and continuously updating the database until no additional compositions are required. Here, we describe an alternative method that is better suited for implementation on large-scale parallel computers. Our method uses the entries of an existing preliminary database to estimate future required chemical compositions. Bulk compositions are determined within boundaries that are defined manually or through principal component analysis in a parameter space consisting of clustered database entries. We have implemented both methods within a massively parallel computational framework while utilizing the Gibbs free energy minimization program Perple_X. Results show that our autonomous approach increases the resolution of the thermodynamic database in compositional regions that are most likely required for geodynamic models of magmatic systems.

Thermodynamic Analysis of Aqueous Phase Reforming of Sorbitol

The objectives of this study were to investigate the most thermodynamically favoured reaction pathway during APR of sorbitol. The thermodynamic analysis of APR of sorbitol was studied using ASPEN Plus V8.0 by applying Gibbs free energy minimization principle, operating at different temperatures (300–800 K), pressure (10–30 bar) and sorbitol concentration (1%, 3%, 5%, 10%, 15% and 20%). The simulation model was validated by comparing the results with the existing work conducted by Serentis and Tsiakaras. The results obtained show that the mol fraction and trend of H2, CO2 and CH4 for both cases are almost similar to the existing work. Therefore the simulation model was validated. Five main reaction pathways of APR of sorbitol were identified and intermediates of each reaction pathway were defined according to their stages and their composition was analyzed. The result obtained show that the decarbonylation reaction (pathway 2) is the most thermodynamically favoured pathway with a total dry basis percentage of 21%.

Phlogopite-Forming Reactions as Indicators of Metasomatism in the Lithospheric Mantle

Phlogopite is widely accepted as a major mineral indicator of the modal metasomatism in the upper mantle within a very wide P–T range. The paper reviews data on various phlogopite-forming reactions in upper-mantle peridotites. The review includes both descriptions of naturally occurring reactions and results of experiments that model some of these reactions. Relations of phlogopite with other potassic phases, such as K-richterite, sanidine and K-titanates, are discussed. These data are taken as a basis for thermodynamic modeling of the phlogopite-forming reactions for specific mantle rocks in terms of log(aH2O) − log(aK2O) diagrams (pseudosections) using the Gibbs free energy minimization. These diagrams allow estimation of potassium-water activity relations during metasomatic transformations of mantle rocks, prediction sequences of mineral assemblages with respect to these parameters and comparison of metasomatic processes in the rocks of different composition. This approach is illustrated by examples from peridotite xenoliths from kimberlites.