Iron is a key indicator of "oxygen fugacity," which is a measurement of the past oxidation levels of a planetary body.
|
|
"Oxygen fugacity is as important as pressure and temperature constraints for determining which minerals will be dominant in the interior of a planet," said Doyle.
|
|
The fugacity capacity constant (Z) is used to help describe the concentration of a chemical in a system (usually in mol/m3Pa). Hemond and Hechner-Levy (2000) describe how to utilize the fugacity capacity to calculate the concentration of a chemical in a system. Depending on the chemical, fugacity capacity varies. The concentration in media 'm' equals the fugacity capacity in media 'm' multiplied by the fugacity of the chemical.
|
|
For a better understanding of the fugacity capacity concept, heat capacity may provide a precedent for introducing Z as a capacity of a phase to absorb particular quantity of chemical. However, phases with high fugacity capacity do not necessarily retain high fugacity. In calculations of fugacity capacity key factors would be (a) the nature of the solute (chemical), (b) the nature of the medium or compartment, (c) temperature.
|
|
The fugacity is most useful in mixtures. It does not add any new information compared to the chemical potential, but it has computational advantages. As the molar fraction of a component goes to zero, the chemical potential diverges but the fugacity goes to zero. In addition, there are natural reference states for fugacity (for example, an ideal gas makes a natural reference state for gas mixtures since the fugacity and pressure converge at low pressure).
|
|
For a condensed phase (liquid or solid) in equilibrium with its vapor phase, the chemical potential is equal to that of the vapor, and therefore the fugacity is equal to the fugacity of the vapor. This fugacity is approximately equal to the vapor pressure when the vapor pressure is not too high.
|
|
The form carbon takes depends on its oxidation state, which depends on the oxygen fugacity of the environment. Carbon dioxide and carbonate are found where the oxygen fugacity is high. Lower oxygen fugacity results in diamond formation, first in eclogite, then peridotite, and lastly in fluid water mixtures. At even lower oxygen fugacity, methane is stable in contact with water, and even lower, metallic iron and nickel form along with carbides. Iron carbides include Fe3C and Fe7C3.
|
|
These were two outstanding problems of theoretical thermodynamics. In two long and ambitious theoretical papers in 1900 and 1901, Lewis tried to provide a solution. Lewis introduced the thermodynamic concept of activity and coined the term "fugacity". ; the term "fugacity" is coined on p. 54.
|
|
For a chemical system at equilibrium, the fugacity of the chemical will be the same in each media/phase/compartment. Therefore equilibrium is sometimes called "equifugacity" in the context of these calculations.D. MacKay & S. Paterson. 1991. Evaluating the Multimedia Fate of Organic Chemicals: a Level III Fugacity Model.
|
|
In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas which has the same temperature and molar Gibbs free energy as the real gas. Fugacities are determined experimentally or estimated from various models such as a Van der Waals gas that are closer to reality than an ideal gas. The real gas pressure and fugacity are related through the dimensionless fugacity coefficient .
|
|
Multimedia fugacity model is a model in environmental chemistry that summarizes the processes controlling chemical behavior in environmental media by developing and applying of mathematical statements or "models" of chemical fate. Most chemicals have the potential to migrate from the medium to medium. Multimedia fugacity models are utilized to study and predict the behaviour of chemicals in different environmental compartments. The models are formulated using the concept of fugacity, which was introduced by Gilbert N. Lewis in 1901 as a criterion of equilibrium and convenient method of calculating multimedia equilibrium partitioning.
|
|
Fayalite can also react with oxygen to produce magnetite + quartz: the three minerals together make up the "FMQ" oxygen buffer. The reaction is used to control the fugacity of oxygen in laboratory experiments. It can also be used to calculate the fugacity of oxygen recorded by mineral assemblages in metamorphic and igneous processes. Molar volume vs.
|
|
Fugacity is another predictive criterion for equilibrium among phases that has units of pressure. It is equivalent to partial pressure for most environmental purposes. It is the absconding propensity of a material. BCF can be determined from output parameters of a fugacity model and thus used to predict the fraction of chemical immediately interacting with and possibly having an effect on an organism.
|
|
216, 218. It is often convenient to use the quantity \phi=f/P, the dimensionless fugacity coefficient, which is 1 for an ideal gas.
|
|
The fugacity of chemicals is a mathematical expression that describes the rates at which chemicals diffuse, or are transported between phases. The transfer rate is proportional to the fugacity difference that exists between the source and destination phases. For building the model, the initial step is to set up a mass balance equation for each phase in question that includes fugacities, concentrations, fluxes and amounts. The important values are the proportionality constant, called fugacity capacity expressed as Z-values (SI unit: mol/m3 Pa) for a variety of media, and transport parameters expressed as D-values (SI unit: mol/Pa h) for processes such as advection, reaction and intermedia transport.
|
|
If the crystal is additionally softer, the fugacity will increase further... and so on and so forth. David Nelson, Bertrand Halperin and independently Peter Young formulated this in a mathematically precise way, using renormalization group theory for the fugacity and the elasticity: In the vicinity of the continuous phase transition, the system becomes critical – this means that it becomes self-similar on all length scales \gg a . Executing a transformation of all length scales by an factor of l , the energy E \to E(l) and fugacity y \to y(l) will depend on this factor, but the system has to appear identically, simultaneously due to the self similarity. Especially the energy function (Hamiltonian) of the dislocations have to be invariant in structure.
|
|
Analogously, expressions involving gases can be adjusted for non- ideality by scaling partial pressures by a fugacity coefficient. The concept of activity coefficient is closely linked to that of activity in chemistry.
|
|
The word fugacity is derived from the Latin fugere, to flee. In the sense of an "escaping tendency", it was introduced to thermodynamics in 1901 by the American chemist Gilbert N. Lewis and popularized in an influential textbook by Lewis and Merle Randall, Thermodynamics and the Free Energy of Chemical Substances, in 1923. ; the term "fugacity" is coined on p. 54. The "escaping tendency" referred to the flow of matter between phases and played a similar role to that of temperature in heat flow.
|
|
This reference pressure is called the standard state and normally chosen as 1 atmosphere or 1 bar. Accurate calculations of chemical equilibrium for real gases should use the fugacity rather than the pressure. The thermodynamic condition for chemical equilibrium is that the total chemical potential of reactants is equal to that of products. If the chemical potential of each gas is expressed as a function of fugacity, the equilibrium condition may be transformed into the familiar reaction quotient form (or law of mass action) except that the pressures are replaced by fugacities.
|
|
The gas fugacity coefficients are mostly set to unity (ideal gas assumption), but for vapor-liquid equilibria at high pressures (i.e. > 10 bar) an equation of state is needed to calculate the gas fugacity coefficient for a real gas description. Determination of NRTL parameters from LLE data is more complicated than parameter regression from VLE data as it involves solving isoactivity equations which are highly non- linear. In addition, parameters obtained from LLE may not always represent the real activity of components due to lack of knowledge on the activity values of components in the data regression.
|
|
Lewis believed that fugacity was the fundamental principle from which a system of real thermodynamic relations could be derived. This hope was not realized, though fugacity did find a lasting place in the description of real gases. Lewis’ early papers also reveal an unusually advanced awareness of J. W. Gibbs's and P. Duhem's ideas of free energy and thermodynamic potential. These ideas were well known to physicists and mathematicians, but not to most practical chemists, who regarded them as abstruse and inapplicable to chemical systems. Most chemists relied on the familiar thermodynamics of heat (enthalpy) of Berthelot, Ostwald, and Van’t Hoff, and the calorimetric school.
|
|
Carbides are predicted to be more likely lower in the mantle as experiments have shown a much lower oxygen fugacity for high pressure iron silicates. Cohenite remains stable to over 187 GPa, but is predicted to have a denser orthorhombic Cmcm form in the inner core.
|
|
The sequence of phosphate transformations ended with the formation of cyrilovite within the F-apatite factures and the replacement of F-apatite by lipscombite and crandillite-group minerals. Weathering-related cyrilovite, lipscombite, and crandillite-group minerals were formed by percolating meteoric waters under increasing oxygen fugacity.
|
|
Fate prediction using fugacity modeling has shown that fatty alcohols with chain lengths of C10 and greater in water partition into sediment. Lengths C14 and above are predicted to stay in the air upon release. Modeling shows that each type of fatty alcohol will respond independently upon environmental release.
|
|
Heat of reaction is not, of course, a measure of the tendency of chemical changes to occur, and Lewis realized that only free energy and entropy could provide an exact chemical thermodynamics. He derived free energy from fugacity; he tried, without success, to obtain an exact expression for the entropy function, which in 1901 had not been defined at low temperatures. Richards too tried and failed, and not until Nernst succeeded in 1907 was it possible to calculate entropies unambiguously. Although Lewis’ fugacity-based system did not last, his early interest in free energy and entropy proved most fruitful, and much of his career was devoted to making these useful concepts accessible to practical chemists.
|
|
Environmental Science and Technology. 25(3):427. :C_m = Z_m \cdot f where Z is a proportional constant, termed fugacity capacity. This equation does not necessarily imply that C and f are always linearly related. Non-linearity can be accommodated by allowing Z to vary as a function of C or f.
|
|
65 Fractional crystallization in silicate melts (magmas) is complex compared to crystallization in chemical systems at constant pressure and composition, because changes in pressure and composition can have dramatic effects on magma evolution. Addition and loss of water, carbon dioxide, hydrogen, and oxygen are among the compositional changes that must be considered. For example, the partial pressure (fugacity) of water in silicate melts can be of prime importance, as in near-solidus crystallization of magmas of granite composition. The crystallization sequence of oxide minerals such as magnetite and ulvospinel is sensitive to the oxygen fugacity of melts, and separation of the oxide phases can be an important control of silica concentration in the evolving magma, and may be important in andesite genesis.
|
|
Quartz is found only in the most strongly peralkaline rocks. Mafic minerals may include aegirine, fayalite, aenigmatite, ilmenite, and sodic amphibole (often arfvedsonite or ferrorichterite).White, J.C., Ren, M., and Parker, D.F., 2005, "Variation in mineralogy, temperature, and oxygen fugacity in a suite of strongly peralkaline lavas and tuffs, Pantelleria, Italy." The Canadian Mineralogist, vol.
|
|
If organism-specific fugacity values are available, it is possible to create a food web model which takes trophic webs into consideration. This is especially pertinent for conservative chemicals that are not easily metabolized into degradation products. Biomagnification of conservative chemicals such as toxic metals can be harmful to apex predators like orca whales, osprey, and bald eagles.
|
|
Feldspars, the most common group of minerals in the Earth's crust, are aluminosilicates. Aluminium also occurs in the minerals beryl, cryolite, garnet, spinel, and turquoise. Impurities in Al2O3, such as chromium and iron, yield the gemstones ruby and sapphire, respectively. Native aluminium metal can only be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes.
|
|
Epidotes are found in variety of geologic settings, ranging from mid-ocean ridge to granites to metapelites. Epidotes are built around the structure [(SiO4)(Si2O7)]10− structure; for example, the mineral species epidote has calcium, aluminium, and ferric iron to charge balance: Ca2Al2(Fe3+, Al)(SiO4)(Si2O7)O(OH). The presence of iron as Fe3+ and Fe2+ helps understand oxygen fugacity, which in turn is a significant factor in petrogenesis., pp.
|
|
Jonathan Mwe di Malila uses strong, vibrant and unbroken colours. Inspired by Fauvism and Pop-Art he aims to counteract the fugacity of impressionistic paintings to give the artwork more duration. Many of his paintings include African or congolese elements, combined with everyday objects, subjects and situation to create a funny content. His main Medium is oil, which he often combines with acrylics or typically African fabrics, such as African wax prints.
|
|
During metamorphism, sulfur and nickel within the olivine lattice are reconstituted into metamorphic sulfide minerals, chiefly millerite, during serpentinization and talc carbonate alteration. When metamorphic olivine is produced, the propensity for this mineral to resorb sulfur, and for the sulfur to be removed via the concomitant loss of volatiles from the serpentinite, tends to lower sulfur fugacity. In this environment, nickel sulfide mineralogy converts to the lowest-sulfur state available, which is heazlewoodite.
|
|
Doing so resulted in the formations of magnesite, siderite, and numerous varieties of graphite. Other experiments—as well as petrologic observations—support this claim, indicating that magnesite is actually the most stable carbonate phase in most part of the mantle. This is largely a result of its higher melting temperature. Consequently, scientists have concluded that carbonates undergo reduction as they descend into the mantle before being stabilised at depth by low oxygen fugacity environments.
|
|
Donald Mackay, (born 30 October 1936) is a Canadian scientist and engineer specializing in environmental chemistry. He was a member of the faculty of Chemical Engineering and Applied Chemistry at the University of Toronto and the founding director of the Canadian Environmental Modelling Centre at Trent University. He has developed several multimedia fugacity models. Mackay has stressed that principles of good practice also need to be adopted for chemical assessments, especially in a regulatory context.
|
|
Site-specific characteristics have a major influence on contaminant bioavailability and no standardized tests have been developed. However, there are a number of chemical and biological tests used to estimate bioavailability including a direct measurement of contaminant bioaccumulation in earthworms (Eisenia fetida). Estimates of bioavailability can also be obtained from chemical solid-phase soil extractions. Fugacity modelling of bioavailability is based on the solubility and partitioning of compounds into aqueous and non-aqueous phases.
|
|
244x244pxThe equilibrium reaction involving diamond is424x424px Mg_2Si_2O_6+2MgCO_3\rightleftharpoons2Mg_2SiO_4+2C(Diamond)+2O_2. Examining the oxygen fugacity of the upper mantle and transition enables us to compare it with the conditions (equilibrium reaction shown above) required for diamond formation. The results show that the logfO_2 is usually 2 units lower than the carbonate-carbon reaction which means favoring the formation of diamond at transition zone conditions. It has also been reported that pH decrease would also facilitate the formation of diamond in Mantle conditions.
|
|
These include: octanol-water partition coefficients (KOW), bioconcentration factors (BCF), bioaccumulation factors (BAF) and biota-sediment accumulation factor (BSAF). Each of these can be calculated using either empirical data or measurements as well as from mathematical models. One of these mathematical models is a fugacity-based BCF model developed by Don Mackay. Bioconcentration factor can also be expressed as the ratio of the concentration of a chemical in an organism to the concentration of the chemical in the surrounding environment.
|
|
About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Native iron is also rarely found in basalts that have formed from magmas that have come into contact with carbon-rich sedimentary rocks, which have reduced the oxygen fugacity sufficiently for iron to crystallize. This is known as Telluric iron and is described from a few localities, such as Disko Island in West Greenland, Yakutia in Russia and Bühl in Germany.
|
|
The differences between minerals can be used to estimate the temperature of equilibration. The δ13C and δ34S of coexisting carbonates and sulfides can be used to determine the pH and oxygen fugacity of the ore-bearing fluid during ore formation. In most forest ecosystems, sulfate is derived mostly from the atmosphere; weathering of ore minerals and evaporites also contribute some sulfur. Sulfur with a distinctive isotopic composition has been used to identify pollution sources, and enriched sulfur has been added as a tracer in hydrologic studies.
|
|
Geothermobarometry relies upon understanding the temperature and pressure of the formation of minerals within metamorphic and igneous rocks, and is particularly useful in metamorphic rocks. There are several methods of measuring the temperature or pressure of mineral formation relying on chemical equilibrium between metamorphic minerals or by measuring the chemical composition of individual minerals. Thermobarometry relies upon the fact that mineral pairs/assemblages vary their compositions as a function of temperature and pressure. There are numerous extra factors to consider such as oxygen fugacity and water activity (roughly, the same as concentration).
|
|
The modal ratio of olivine:pyroxene is oddly low for an H5 ordinary chondrite; typical values are ~1.31, and yet modal analyses indicate the ratio for Mason Gully is as low as 0.84. Plagioclase abundance is also lower than typical values, but Fe(Ni)-metal abundances are higher than average for the H5 group. Metamorphic temperatures were determined based upon the measured oxygen fugacity, using the two-pyroxene and olivine-spinel geothermometry methods. The two-pyroxene approach yielded temperatures between 865 °C - 900 °C, whilst the olivine- spinel approach yielded a temperature of 705 °C.
|
|
Magmatic olivine generally has up to ~4000 ppm Ni and up to 2500 ppm S within the crystal lattice, as contaminants and substituting for other transition metals with similar ionic radii (Fe2+ and Mn2+). Millerite structure During metamorphism, sulfur and nickel within the olivine lattice are reconstituted into metamorphic sulfide minerals, chiefly millerite, during serpentinization and talc carbonate alteration. When metamorphic olivine is produced, the propensity for this mineral to resorb sulfur, and for the sulfur to be removed via the concomitant loss of volatiles from the serpentinite, tends to lower sulfur fugacity. This forms disseminated needle like millerite crystals dispersed throughout the rock mass.
|
|
The Ti3+/Ti4+ ratio in armalcolite can serve as an indicator of fugacity (effective partial pressure) of oxygen during the mineral's formation. It also allows one to distinguish lunar and terrestrial armalcolite, as Ti3+/Ti4+ = 0 for the latter.Grant Heiken, David Vaniman, Bevan M. French Lunar sourcebook: a user's guide to the moon, CUP Archive, 1991, , pp. 148–149 Since armalcolite's formula is (Mg,Fe2+)Ti2O5, it follows the general formula of XY2O5 where the X=(Mg and Fe2+), Y=Ti, and O is oxygen. Both X and Y sites are octahedrally coordinated and the radius ratio between the cations and the anions in armalcolite are at three to five ratio equaling 0.6 making the structure octahedral. Armalcolite is a titanium-rich mineral that falls under the magnesianferropseudobrookite mineral group with Fe2+Ti2O5 and MgTi2O5 as end members.
|
|