scholarly journals Thermodynamic Stabilities of U(VI) Minerals: Estimated and Observed Relationships

1996 ◽  
Vol 465 ◽  
Author(s):  
Robert J. Finch
Keyword(s):  
Gibbs Energy ◽  
Reaction Pathways ◽  
Free Energies ◽  
Fine Grained ◽  
Surface Energies ◽  
Stability Diagrams ◽  
Activity Diagrams ◽  
Mineral Stability ◽  
Mineral Compositions

ABSTRACTGibbs free energies of formation (ΔG°ƒ) for several structurally related U(VI) minerals are estimated by summing the Gibbs energy contributions from component oxides. The estimated ΔG°f values are used to construct activity-activity (stability) diagrams, and the predicted stability fields are compared with observed mineral occurrences and reaction pathways. With some exceptions, natural occurrences agree well with the mineral stability fields estimated for the systems Sio2-Cao-Uo3-UOH2O and Co2-caO-UO3-H2O providing confidence in the estimated thermodynamic values. Activity-activity diagrams are sensitive to small differences in ΔG°f values, and mineral compositions must be known accurately, including structurally bound H2O. The estimated ΔG°f values are not considered reliable for a few minerals for two major reasons: (1) the structures of the minerals in question are not closely similar to those used to estimate the ΔG°f* values of the component oxides, and/or (2) the minerals in question are exceptionally fine grained, leading to large surface energies that increase the effective mineral solubilities.

Dynamic Modeling of Reaction Pathways on the Gibbs Energy Surface

2000 ◽  
Vol 39 (2) ◽  
pp. 508-517 ◽  
Author(s):  
Srinivas R. Vuddagiri ◽  
Kenneth R. Hall ◽  
Philip T. Eubank
Keyword(s):  
Gibbs Energy ◽  
Dynamic Modeling ◽  
Energy Surface ◽  
Reaction Pathways

A theoretical evaluation of mineral stability in Don Juan Pond, Wright Valley, Victoria Land

1997 ◽  
Vol 9 (1) ◽  
pp. 92-99 ◽  
Author(s):  
G.M. Marion
Keyword(s):  
Experimental Data ◽  
Eutectic Temperature ◽  
High Water ◽  
Don Juan ◽  
Theoretical Evaluation ◽  
Antarctic Lakes ◽  
Stability Diagrams ◽  
Subzero Temperatures ◽  
Mineral Stability ◽  
Victoria Land

Don Juan Pond, located in the Wright Valley, Victoria Land, is unique for several reasons. It is the most saline of the Antarctic lakes, being a near-saturated CaCl2 solution. As a consequence of this high salinity, Don Juan Pond generally remains unfrozen in winter, even at temperatures below -50°C. Don Juan Pond is the site where antarcticite (CaCl2·6H2O) was first identified forming naturally. The objective of this paper is to demonstrate the utility of a chemical thermodynamic model (FREZCHEM) by developing theoretical stability diagrams for ice, halite (NaCl), hydrohalite (NaCl·2H2O), and antarcticite in Don Juan Pond, using experimental data collected on 34 days between 1961 and 1983. The composition of Don Juan Pond at the calculated eutectic temperature (-51.8°C) was CaCl2 = 3.72 mol kg−1 and NaCl = 0.50 mol kg−1, which is similar but not identical to a pure NaCl–CaCl2–H2O system. The low eutectic temperature and high CaCl2 concentrations of Don Juan Pond account for lack of freezing during winter. The model is compatible with the experimental data, and predicts the formation of ice during rare high water periods, halite, and antarcticite. These solid phases have all been reported from Don Juan Pond. The model also predicts the formation of hydrohalite at subzero temperatures; hydrohalite has never been observed at Don Juan Pond, but this may simply reflect that most sampling was done during the summer when halite is thermodynamically more stable than hydrohalite. The FREZCHEM model may prove useful in elucidating the physicochemical behaviour, the origin of salinity, and the evolution of Antarctic lakes.

Evaluation of Thermodynamic Properties of Cerium in Liquid Cadmium Cathode Within LiCl-KCl Salt System

2016 ◽  
Author(s):  
Dalsung Yoon ◽  
Supathorn Phongikaroon
Keyword(s):  
Thermodynamic Properties ◽  
Gibbs Energy ◽  
Intermetallic Compounds ◽  
Linear Trend ◽  
Open Circuit ◽  
Salt System ◽  
Free Energies ◽  
Enthalpy And Entropy ◽  
Molten Salt System

Thermodynamic properties of Ce-Cd intermetallic compound were investigated in LiCl-KCl-CeCl3-CdCl2 molten salt system at various temperatures. Six Ce-Cd intermetallic compounds, CeCd, CeCd2, CeCd3, Ce13Cd58, CeCd6, and CeCd11 could be observed via cyclic voltammetry (CV) and the relative Gibbs free energies for the intermetallic formations were estimated by the analysis of the anodic peaks in the CV experiments. Furthermore, an open circuit chronopotentiometry which is known as a suitable method for measuring thermodynamic values of intermetallic compounds were performed. The linear trends of the relative Gibbs free energies were found by using potential difference from CV and CP methods. It can be noted that CV method can be easy and fast tool to estimate relative Gibbs energy for intermetallic compounds of Cd-Ms (metals). For the determination of standard Gibbs free energy, enthalpy, and entropy for the intermetallic formation, CP results were used. The linear trend of the Gibbs energy were obtained against temperature changing from 698 K to 823 K. From the linear relationship, the enthalpy and entropy of the formation were calculated.

Filler-Elastomer Interactions. Part I: Silica Surface Energies and Interactions with Model Compounds

1991 ◽  
Vol 64 (4) ◽  
pp. 559-576 ◽  
Author(s):  
Meng-Jiao Wang ◽  
Siegfried Wolff ◽  
Jean-Baptiste Donnet
Keyword(s):  
Functional Groups ◽  
Phenyl Ring ◽  
Silica Surface ◽  
Rubber Matrix ◽  
Low Molecular Weight ◽  
Free Energies ◽  
Model Compounds ◽  
Surface Energies ◽  
Surface Areas ◽  
Degree Of Unsaturation

Abstract Inverse gas-solid chromatography, operated at infinite dilution, has been used to assess the surface energies of silicas, both fumed and precipitated. The dispersive components of the surface free energies of the silicas were calculated from the free energies of adsorption, corresponding to the —CH2— group, obtained from n-alkane adsorption. The specific components of the surface energies were evaluated separately by comparison of the free energies of adsorption of polar probes with those of n-alkanes, based on the surface areas covered by the probe molecules. The results indicate that while the dispersive components of silica surface energies is somewhat higher for the fumed silicas, the specific components are much higher for precipitated silicas, probably resulting from the higher silanol concentration on their surfaces. Moreover, the interaction able to take place between rubber matrix and the silicas are also estimated chromatographically from the adsorptions of low-molecular-weight analogs of elastomers. The free energies and enthalpies indicate that the interactions of functional groups with the fillers decrease in the order of nitrile, phenyl ring, double bond. The saturated rubber analogs show lower interactions with silicas. The lowest interactions of iso-alkanes imply poor interactions between butyl rubber and the fillers. As expected, the experimental data reflect an attenuation of polymer-silica interactions with decreasing content of functional groups and degree of unsaturation in NR, BR, SBR, and NBR.

The Origin of Saline Groundwaters in Granitic Rocks: Evidence From Hydrothermal Experiments

1985 ◽  
Vol 50 ◽  
Author(s):  
David Savage ◽  
Mark R. Cave ◽  
Antoni E Milodowski
Keyword(s):  
Fluid Phase ◽  
Granitic Rocks ◽  
Plagioclase Feldspar ◽  
Natural Systems ◽  
Stability Diagrams ◽  
Hydrothermal Experiments ◽  
Mineral Stability ◽  
Solid Phases ◽  
Chemical Conditions ◽  
The Stability

AbstractHydrothermal rock-water experiments at 80°, 150° and 250° C have been carried out to investigate the origin of saline groundwaters in the Carnmenellis Granite, Cornwall, UK which have previously been attributed to be derived via dissolution of biotite and plagioclase feldspar by dilute meteoric groundwaters. The nature of product fluid and solid phases in the experiments was dominated by the dissolution of plagioclase and potassium feldspars, coupled with the precipitation of laumontite, calcite and smectite. However, the release of chloride from the rock was minimal, suggesting minor dissolution of the major chloride bearing mineral, biotite. The relative inertness and stability of biotite during the experiments was borne out by direct physical observation of reacted biotites and by consideration of the fluid phase composition in terms of thermodynamic mineral stability diagrams. It is concluded that the experimental and natural systems are buffered under different chemical conditions, which may be due to acidity generated via oxidation of localised sulphide zones within the granite and absent in the experiments. Dissolution of biotite may be an important mechanism for enhancing the salinity of groundwaters in granitic rocks if groundwaters are buffered to be outside the stability of biotite and convective circulation is significant.

An igneous-textured clast in the Peace River meteorite: insights into accretion and metamorphism of asteroids in the early solar system

2013 ◽  
Vol 50 (1) ◽  
pp. 14-25 ◽  
Author(s):  
Christopher D.K. Herd ◽  
Jon M. Friedrich ◽  
Richard C. Greenwood ◽  
Ian A. Franchi
Keyword(s):  
Solar System ◽  
Isotope Composition ◽  
Parent Body ◽  
Early Solar System ◽  
Element Abundances ◽  
Fine Grained ◽  
Peace River ◽  
Petrology And Geochemistry ◽  
Mineral Compositions ◽  
The Impact

The mineralogy, petrology, and geochemistry of an igneous-textured clast in the Peace River L6 chondrite meteorite was examined to determine the roles of nebular processes, accretion, and parent-body metamorphism in its origin. The centimetre-scale clast is grey and fine grained and is in sharp contact with the host chondrite. Two sub-millimetre veins cut across both the clast and host, indicating that the clast formed prior to the impact (shock) event(s) that produced the numerous veins present in the Peace River meteorite. The clast and host are indistinguishable in terms of mineral compositions. In contrast, there are differences in modal mineralogy, texture, as well as trace element and oxygen isotope composition between the clast and host. These differences strongly suggest that the clast was formed by impact melting of LL-group chondritic material involving loss of Fe–FeS and phosphate components, followed by relatively rapid cooling and incorporation into the Peace River host meteorite. Subsequent metamorphism on the Peace River parent body caused recrystallization of the clast and homogenization of mineral compositions and thermally labile element abundances between the clast and host. Shock metamorphism, including formation of shock melt veins, occurred post-metamorphism, during fragmentation of the L chondrite parent body. The results suggest that the formation of the Peace River parent asteroid included the incorporation of material from other asteroids and that the pre-metamorphic protolith was a breccia. Accordingly, we propose that the Peace River meteorite be reclassified as a polymict breccia.

Silicate Mineralogy of the Middle Zone Cumulates and Associated Gabbroic Rocks from the Insch Intrusion, NE Scotland

1988 ◽  
Vol 52 (366) ◽  
pp. 309-322 ◽  
Author(s):  
W. J. Wadsworth
Keyword(s):  
Principal Components ◽  
Intermediate Position ◽  
Middle Zone ◽  
Lower Zone ◽  
Fine Grained ◽  
Geographical Variations ◽  
Mineral Compositions ◽  
Complex Relationships ◽  
A Minor ◽  
Block Faulting

AbstractThe Middle Zone (MZ) of the Insch intrusion lies in a geographically intermediate position between the Lower Zone (LZ) and Upper Zone (UZ) cumulate sequences, but is more complicated than either in comprising two intricately associated, but texturally distinct, components, the MZ cumulates and the fine-grained granular gabbros (FGG). In addition, there is a minor group of porphyritic granular gabbros (PGG), containing abundant plagioclase phenocrysts. A further variety of gabbroic rock, namely quartz-biotite norite (QBN) occupies a similarly intermediate position in the Boganclogh extension of the main Insch mass. These principal components (MZ cumulates, FGG, and QBN) show considerable mineralogical overlap with each other and with the lower part of the UZ succession (UZa). Unlike the UZ rocks, they are essentially olivine-free (apart from the most basic granular gabbros) and consist mainly of plagioclase, orthopyroxene, and Ca-rich clinopyroxene, with accessory Fe-Tioxides and minor interstitial biotite and/or hornblende. Mineral compositions are in the range An70–55 (plagioclase), En71–44 (opx), and Ca46Mg42Fe12 to Ca45Mg30Fe25 (cpx), but in detail each rock group can be characterized mineralogically as well as texturally. It is concluded that the MZ cumulates and FGG (including PGG) are essentially complementary, formed in different locations, and under slightly different conditions, but in the same magma chamber. The complex relationships between them, and the apparently haphazard geographical variations in mineral compositions, may be the combined results of the magmatic events, possibly including the movement of large xenolithic fragments, and later block faulting. The substantial compositional overlap of the more evolved MZ cumulates by UZa is explained in terms of replenishment by magma of slightly more primitive (and potentially olivine-bearing) composition after the deposition of the MZ. The Boganclogh QBN is believed to represent a more hydrous fraction of the Insch MZ magma.

An interactive spreadsheet for graphing mineral stability diagrams

1995 ◽  
Vol 21 (1) ◽  
pp. 175-185 ◽  
Author(s):  
Dean L. Biddle ◽  
Harry J. Percival ◽  
David J. Chittleborough
Keyword(s):  
Stability Diagrams ◽  
Mineral Stability

scholarly journals Multi-stage Reactive Formation of Troctolites in Slow-spreading Oceanic Lithosphere (Erro–Tobbio, Italy): a Combined Field and Petrochemical Study

2019 ◽  
Vol 60 (5) ◽  
pp. 873-906 ◽  
Author(s):  
Valentin Basch ◽  
Elisabetta Rampone ◽  
Laura Crispini ◽  
Carlotta Ferrando ◽  
Benoit Ildefonse ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Oceanic Lithosphere ◽  
Rock Interaction ◽  
Crystallographic Preferred Orientation ◽  
Compositional Evolution ◽  
Fine Grained ◽  
Interaction Processes ◽  
Multi Stage ◽  
Mineral Compositions ◽  
Melt Composition

Abstract Many recent studies have investigated the replacive formation of troctolites from mantle protoliths and the compositional evolution of the percolating melt during melt–rock interaction processes. However, strong structural and geochemical constraints for a replacive origin have not yet been established. The Erro–Tobbio impregnated mantle peridotites are primarily associated with a hectometre-size troctolitic body and crosscutting gabbroic dykes, providing a good field control on melt–rock interaction processes and subsequent magmatic intrusions. The troctolitic body exhibits high inner complexity, with a host troctolite (Troctolite A) crosscut by a second generation of troctolitic metre-size pseudo-tabular bodies (Troctolite B). The host Troctolite A is characterized by two different textural types of olivine, corroded deformed millimetre- to centimetre-size olivine and fine-grained rounded undeformed olivine, both embedded in interstitial to poikilitic plagioclase and clinopyroxene. Troctolite A shows melt–rock reaction microstructures indicative of replacive formation after percolation and impregnation of mantle dunites by a reactive melt. The evolution of the texture and crystallographic preferred orientation (CPO) of olivine are correlated and depend on the melt/rock ratio involved in the impregnation process. A low melt/rock ratio allows the preservation of the protolith structure, whereas a high melt/rock ratio leads to the disaggregation of the pre-existing matrix. The mineral compositions in Troctolite A define reactive trends, indicative of the buffering of the melt composition by assimilation of olivine during impregnation. The magmatic Troctolite B bodies are intruded within the pre-existing Troctolite A and are characterized by extreme textural variations of olivine, from decimetre-size dendritic to fine-grained euhedral crystals embedded in poikilitic plagioclase. This textural variability is the result of olivine assimilation during melt–rock reaction and the correlated increase in the degree of undercooling of the percolating melt. In the late gabbroic intrusions, mineral compositions are consistent with the fractional crystallization of melts modified after the reactive crystallization of Troctolites A and B. The Erro–Tobbio troctolitic body has a multi-stage origin, marked by the transition from reactive to fractional crystallization and diffuse to focused melt percolation and intrusion, related to progressive exhumation. During the formation of the troctolitic body, the melt composition was modified and controlled by assimilation and concomitant crystallization reactions occurring at low melt supply. Similar processes have been described in ultraslow-spreading oceanic settings characterized by scarce magmatic activity.

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