Iron thermodynamic properties

PS Brereton, FJM Verhagen, ZH Zhou, MWW Adams. Effect of iron-sulfur cluster environment m modulating the thermodynamic properties and biological function of ferredoxm from Pyrococcus furiosus. Biochemistry 37 7351-7362, 1998. 

For the cytochrome c-plastocyanin complex, the kinetic effects of cross-linking are much more drastic while the rate of the intracomplex transfer is equal to 1000 s in the noncovalent complex where the iron-to-copper distance is expected to be about 18 A, it is estimated to be lower than 0.2 s in the corresponding covalent complex [155]. This result is all the more remarkable in that the spectroscopic and thermodynamic properties of the two redox centers appear weakly affected by the cross-linking process, and suggests that an essential segment of the electron transfer path has been lost in the covalent complex. Another system in which such conformational effects could be studied is the physiological complex between tetraheme cytochrome and ferredoxin I from Desulfovibrio desulfuricans Norway the spectral and redox properties of the hemes and of the iron-sulfur cluster are found essentially identical in the covalent and noncovalent complexes and an intracomplex transfer, whose rate has not yet been measured, takes place in the covalent species [156]. 

Diakonov, I. Khodakovsky I. Schott, J. Sergeeva, E. (1994) Thermodynamic properties of iron oxides and hydroxides. I. Surface and bulk thermodynamic properties of goethite (a-FeOOH) up to 500 K. Fur. J. Min. 6 967-983... 

From the above it is likely that sulfate is reduced before ferric iron. This is contrary to what one would expect from the thermodynamic properties of Fe(III) compounds and sulfates. This may be caused by... 

We now see that mitochondria contain a variety of molecules—cytochromes, flavins, ubiquinone, and iron-sulfur proteins—all of which can act as electron carriers. To discuss how these carriers cooperate to transport electrons from reduced substrates to 02, it is useful to have a measure of each molecule s tendency to release or accept electrons. The standard redox potential, E°, provides such a measure. Redox potentials are thermodynamic properties that depend on the differences in free energy between the oxidized and reduced forms of a molecule. Like the electric potentials that govern electron flow from one pole of a battery to another, E° values are specified in volts. Because electron-transfer reactions frequently involve protons also, an additional symbol is used to indicate that an E° value applies to a particular pH thus, E° refers to an E° at pH 7. 

Perfetti, E., Pokrovski, G.S., Ballerat-Busserolles, K. et al. (2008) Densities and heat capacities of aqueous arse-nious and arsenic acid solutions to 350 °C and 300 bar, and revised thermodynamic properties of As(OH)3°(aq), AsO(OH)3°(aq) and iron sulfarsenide minerals. Geochimica et Cosmochimica Acta, 72(3), 713-31. 

Passivation potential — A metal turns passive if the electrode potential is shifted above the passivation potential Ep into the passive range of the -> polarization curve (Fig. 1). This critical potential depends on the thermodynamic properties of the metal. In many cases it equals the value deduced from the thermodynamic data for the formation of an oxide layer of the metal in aqueous electrolytes according to Eq. (1). This reaction is - pH dependent by -0.059 V/pH. In some cases it corresponds to the oxidation of a lower valent to a higher valent oxide (Eq. (2)). For iron the passivation potential in acidic electrolytes has been explained by Eq. (3). 

The second form of precipitation cannot be understood from the thermodynamic properties of the solution the solution is undersaturated, even so, precipitation takes place on the surface. This process is called surface precipitation. In this case there are three possibilities. One of them is when the precipitate is formed in a monomolecular layer. The second possibility is coprecipitation, when a component in low concentration coprecipitates with another component in high concentration if it can be built into the crystal lattice (Section 1.2.4). In this case, the thickness can be higher than that in the monolayer. For example, cesium ions in very low concentration coprecipitate with iron and magnesium containing carbonates (Konya et al. 2005 Chapter 3, Section 3.1.2). These types of surface precipitation can quantitatively be described by the adsorption equations (Section 1.3.4.1). 

We have worked out a sufficiently precise and reliable system of consistent thermodynamic constants (Mel nik, 1972) especially for analysis of the conditions of formation of iron ores. In this work, in addition to the constants of crystalline minerals, data on the stability and thermodynamic properties of the original finely dispersed amorphous or cryptocrystalline iron, magnesium, and silica sediments were systematized for the first time. Such sediments are metastable solid phases which in nature are converted into stable crystalline minerals during diagenesis and low-rank metamor-... 

The conversion of goethite or iron hydroxides into hematite has been investigated experimentally in a great number of works, and the results obtained are rather diverse. Even at room temperature hematite often forms along with goethite, especially in acid and neutral environments. Apparently both these phases are characterized by similar thermodynamic properties and the AGj value of the reaction of dehydration of a-FeOOH at moderate temperatures is not large. 

Desai, P.D., Thermodynamic Properties of Iron and Silicon. Journal of Physical and Chemical Reference Data, 1986.15(3) p. 967-983. 

For thermodynamic analysis of the corrosion of iron alloys in supercritical water, the above computer program was modified based upon standard thermodynamic property extrapolation methods. 

Gronvold, F., Heat capacities and thermodynamic properties of the iron selenides Fei o4Se, FevSeg, and Fe3Se4 from 298 to 1050°K, Acta Chem. Scand, 22, (1968), 1219-1240. Cited on pages 325, 326, 327, 329. 

For example, a species distribution and mineral solubility model generated by a program depends on the values of the thermodynamic properties used for the species and solids involved. The equilibrium constants for amorphous ferric iron hydrous oxide vary by several orders of magnitude (Stumm and Morgan, 1981). By using one value,... 

The variability of FeOOH thermodynamic properties is a result of the metastability of freshly precipitated ferric iron phases (chapter 7.4.2.1, Fig. 7.10). 

The thermal functions of Zr(g) listed in Table V-7 are those derived by [85CHA/DAV] (or calculated from those values listed by [85CHA/DAV]). The equations listed above for the heat capacity of zirconium gas and equations for other thermodynamic properties derived from these equations reproduce the values listed in Table V-7 to within 0.5%. As is evident from the data presented in the table, the heat capacity exhibits a maximum at about 435 K and a minimum at 975 K. This behaviour also occurs for other metals such as titanium and iron. 

In this chapter we will describe the fundamental coordination chemistry, solution thermodynamic properties, and transport properties of these primary iron-transport agents the siderophores and transferrins. 

Bourdin, E., Aubreton, J., Fauchais, P. Equilibrium composition and thermodynamic properties of C—Hj, CH and CH4—plasmas, computation of their reducing action on iron oxyde FbjOj. In IH" Intemat. Symp. plasma Chemistry, Limoges July 1977, Proc. 

Rates of formation, and of dissociation, of dimeric iron(m) complexes of cydta, edta, and hedta have been determined as a function of pH. This represents a contribution to the knowledge of the kinetic behaviour associated with M-O-M and M-OH-M systems, to complement the long-known thermodynamic properties of such complexes. T-Jump studies of the dimerisation of iron(m)-edta show one relaxation, ascribed to the equilibrium... 

Experimental investigations of the thermodynamic properties Cr-Fe-Nb alloys have not been reported. Thermodynamic data for liquid, ferrite and austenite of some iron-based systems were optimized by [1998Mie] in order to give a more accurate representation of phase equilibria between these phases in multieomponent steels. But for the Cr-Fe-Nb system, the auflior has noted fliat a eareM examination of the system is necessary in order to get a reliable prediction of die partitioning tendency of niobium. 

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