Thermodynamics of iron

As mentioned previously, siderophores must selectively bind iron tightly in order to solubilize the metal ion and prevent hydrolysis, as well as effectively compete with other chelators in the system. The following discussion will address in more detail the effect of siderophore structure on the thermodynamics of iron binding, as well as different methods for measuring and comparing iron-siderophore complex stability. The redox potentials of the ferri-siderophore complexes will also be addressed, as ferri-siderophore reduction may be important in the iron uptake process in biological systems. 

In order to progress with steels, it was necessary to pursue semi-empirical methods (Weiss and Tauer 1956, Tauer and Weiss 1958) which culminated in fire seminal paper describing the thermodynamics of iron (Kaufman et al. 1963). This included the concept of two different nuignetic states for f.c.c. iron, which had been applied to rationalise the Invar properties of iron-nickel alloys (Weiss 1963). However, this concept was viewed with considerable scepticism. Some support... 

Boness, D. A., J. M. Brown, and A. K. McMahan (1986). The electronic thermodynamics of iron under Earth core conditions. Phys. Earth Planet. Int. 42, 227 0. 

N. A. Stephenson, A. T. Bell, Effects of methanol on the thermodynamics of iron(III) [tetrakis (pentafluorophenyl)]porphyrin chloride dissociation and the creation of catalytically active species for the epoxidation of cyclooctene, Inorg. Chem. 45 (2006) 5591. 

The structural and functional properties of the iron and sulfide donor proteins (frataxin and IscS/NifS, respectively) that mediate [2Fe-2S] cluster assembly on the scaffold protein ISU/IscU are reviewed in light of the developing mechanistic understanding of cluster biosynthesis. The structural information now available for each class of protein provides a context for understanding recent measurements of die kinetics of cluster assembly and the thermodynamics of iron binding and scaffold-partner interactions. The protein NFU is discussed as a mediator of persulfide bond cleavage to yield inorganic sulfide for cluster assembly. 

Jacobson, N.S., Mehrotra, G.M. (1993) Thermodynamics of iron-aluminum alloys at 1573K. Metallurgical Transactions, 24B, 481-486. 

R. J. Hawkins and M. W. Davies, "Thermodynamics of iron oxide-bearing, calcium fluoride-based slags," J. Iron Steel Inst., London, 209(3) (1971), 226-30. 

Lemire, R.J., Berner, U., Musikas, C., Palmer, D.A., Taylor, P., and Tochiyama, O. (2013) Chemical Thermodynamics of Iron. Part 1, vol. 13a, OECD Publishing, Paris, 1082 pp. Lengweiler, H., Buser, W., and Feitknecht, W. (1961) Die ermittlung der loslichkeit von eisen(III)-hydroxiden mit 59Fe. I. Fallungs-und auflbsungsversuche. Helv. Chim. Acta, 44, 796-805. 

Hexa.cya.no Complexes. Ferrocyanide [13408-63 ] (hexakiscyanoferrate-(4—)), (Fe(CN) ) , is formed by reaction of iron(II) salts with excess aqueous cyanide. The reaction results in the release of 360 kJ/mol (86 kcal/mol) of heat. The thermodynamic stabiUty of the anion accounts for the success of the original method of synthesis, fusing nitrogenous animal residues (blood, horn, hides, etc) with iron and potassium carbonate. Chemical or electrolytic oxidation of the complex ion affords ferricyanide [13408-62-3] (hexakiscyanoferrate(3—)), [Fe(CN)g] , which has a formation constant that is larger by a factor of 10. However, hexakiscyanoferrate(3—) caimot be prepared by direct reaction of iron(III) and cyanide because significant amounts of iron(III) hydroxide also form. Hexacyanoferrate(4—) is quite inert and is nontoxic. In contrast, hexacyanoferrate(3—) is toxic because it is more labile and cyanide dissociates readily. Both complexes Hberate HCN upon addition of acids. 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Eig. 2. The thermodynamic regions of corrosion, immunity, and passivation of iron in an iron—water system assuming passivation by a film of Ee202 (H)-... 

The hrst successful study which clarihed the mechanism of roasting, was a study of the oxidation of pyrite, FeSa, which is not a typical industrial process because of the availability of oxide iron ores. The experiment does, however, show die main features of roasting reactions in a simplihed way which is well supported by the necessaty thermodynamic data. The Gibbs energy data for the two sulphides of iron are,... 

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. 

Fluid Iron Ore Reduction (FIOR) is a process for reducing ore to iron with a reducing gas in a fluid bed. For thermodynamic efficiency, iron ore reduction requires counter current flow of ore and reducing gas. This is achieved in FIOR in a multiple bed reactor. Precautions are necessary to prevent significant back mixing of solids between beds, since this would destroy counter current staging. 

All the anhydrous - -3 and +2 halides of iron are readily obtained, except for iron(III) iodide, where the oxidizing properties of Fe and the reducing properties of 1 lead to thermodynamic instability. It has, however, been prepared in mg quantities by the following reaction, with air and moisture rigorously excluded,... 

The region of immunity [Fig. 1.15 (bottom)] illustrates how corrosion may be controlled by lowering the potential of the metal, and this zone provides the thermodynamic explanation of the important practical method of cathodic protection (Section 11.1). In the case of iron in near-neutral solutions the potential E = —0-62 V for immunity corresponds approximately with the practical criterion adopted for cathodically protecting the metal in most environments, i.e. —0-52 to —0-62V (vs. S.H.E.). It should be observed, however, that the diagram provides no information on the rate of charge transfer (the current) required to depress the potential into the region of immunity, which is the same (< —0-62 V) at all values of pH below 9-8. Consideration of curve//for the Hj/HjO equilibrium shows that as the pH... 

It must be emphasised that although, the rate of anodic dissolution of iron increases with,increase in. pH this will not necessarily apply to the corrosion rate which will be dependent On a number of other. factors, e.g. the thermodynamics and kinetics of the cathodic reaction, film formation, etc. 

The steel will be considered to be an ideal ternary solution, and therefore at all temperatures a, = 0-18, Ani = 0-08 and flpc = 0-74. Owing to the Y-phase stabilisation of iron by the nickel addition it will be assumed that the steel, at equilibrium, is austenitic at all temperatures, and the thermodynamics of dilute solutions of carbon in y iron only are considered. 

Before considering the principles of this method, it is useful to distinguish between anodic protection and cathodic protection (when the latter is produced by an external e.m.f.). Both these techniques, which may be used to reduce the corrosion of metals in contact with electrolytes, depend upon the electrochemical mechanisms that result from changing the potential of a metal. The appropriate potential-pH diagram for the Fe-H20 system (Section 1.4) indicates the magnitude and direction of the changes in the potential of iron immersed in water (pH about 7) necessary to make it either passive or immune in the former case the stability of the metal depends on the formation of a protective film of metal oxide (passivation), whereas in the latter the metal itself is thermodynamically stable and egress of metal ions from the lattice into the solution is thus prevented. 

The decomposition process can be significantly intensified by the mechanical activation of the material prior to chemical decomposition. Based on a thermodynamic analysis of the system, Akimov and Chernyak [452] showed that the mechanical activation initiates dislocations mostly on the surface of the grains, and that heterogeneities in the surface cause the predominant migration of iron and manganese to the grain boundaries. It is noted that this phenomenon is more pronounced for manganese than it is for iron. 

Richardson, F.D. and Jeffes, J.H.E. (1952) The thermodynamics of substances of interest in iron and steel making. III. Sulfides Iron Steal Inst. J., 171, 165-175. 

Mathematical models have been developed [1144—1146,1623]. The scale formation of iron carbonate and iron monosulfide has been simulated by thermodynamic and electrochemical models [49,1144,1154,1893]. 

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