Iron distortion

The higher solubility of carbon in y-iron than in a-iroii is because the face-ceiiued lattice can accommodate carbon atoms in slightly expanded octahedral holes, but the body-centred lattice can only accommodate a much smaller carbon concentration in specially located, distorted tetrahedral holes. It follows that the formation of fenite together with cementite by eutectoid composition of austenite, leads to an increase in volume of the metal with accompanying compressive stresses at die interface between these two phases. 

Fig. 8.8. Martensites are always coherent with the parent lattice. They grow os thin lenses on preferred planes and in preferred directions in order to cause the least distortion of the lattice. The crystallographic relationships shown here ore for pure iron.

Figure 11.9 shows that the hardness of martensite increases rapidly with carbon content. This, again, is what we would expect. We saw in Chapter 8 that martensite is a supersaturated solid solution of C in Fe. Pure iron at room temperature would be b.c.c., but the supersaturated carbon distorts the lattice. 

Figure 25.9 Some non-haem iron proteins (a) rubredoxin in which the single Fe is coordinated, almost tetra-hedrally, to 4 cysteine-sulfurs, (b) plant ferredoxin, [Fe2S2(S-Cys)4], (c) [Fe4S4(S-Cys)4] cube of bacterial ferredoxins. (This is in fact distorted, the Fe4 and S4 making up the two interpenetrating tetrahedra, of which the latter is larger than the former).

Other non-haem proteins, distinct from the above iron-sulfur proteins are involved in the roles of iron transport and storage. Iron is absorbed as Fe" in the human duodenum and passes into the blood as the Fe protein, transferrin, The Fe is in a distorted octahedral environment consisting of 1 x N, 3x0 and a chelating carbonate ion which... 

The treatment of iron carbonyls with aqueous or alcoholic alkali can, by varying the conditions, be used to produce a series of interconvertible carbonylate anions [HFe(CO)4] , [Fe(CO)4] ", [Fe2(CO)g]2-, [HFe3(CO) ]- and [Fe4(CO)i3]"". Of these the first has a distorted trigonal bipyrarmdal stracture with axial H, the second... 

Martensitic phase transformations are discussed for the last hundred years without loss of actuality. A concise definition of these structural phase transformations has been given by G.B. Olson stating that martensite is a diffusionless, lattice distortive, shear dominant transformation by nucleation and growth . In this work we present ab initio zero temperature calculations for two model systems, FeaNi and CuZn close in concentration to the martensitic region. Iron-nickel is a typical representative of the ferrous alloys with fee bet transition whereas the copper-zink alloy undergoes a transformation from the open to close packed structure. ... 

When cast iron is exposed to high temperatures under oxidising conditions, oxidation of the metal results, with the formation of a surface scale. In addition, the dimensions of the component become distorted. Although such dimensional changes can occur also in inert atmospheres or in vacuum, the evidence available suggests that this growth is frequently associated with oxidation, and accordingly it is appropriate to consider it as an aspect of the corrosion of the iron. 

Analysis of the volumetric effects indicates that as a result of such mechanical activation, iron and manganese are concentrated in the extended part of the crystal, while tantalum and niobium are predominantly collected in the compressed part of the distorted crystal structure. It is interesting to note that this effect is more pronounced in the case of tantalite than it is for columbite, due to the higher rigidity of the former. Akimov and Chernyak [452] concluded that the effect of redistribution of the ions might cause the selective predominant dissolution of iron and manganese during the interaction with sulfuric acid and other acids. 

Phosphonates exhibit all the properties of polyphosphates, such as threshold effect, crystal distortion, and sequestration, but are superior in their effectiveness. They provide good chelates for calcium, magnesium, iron, and copper and are commonly used where iron fouling is a problem. Their sequestering properties are generally superior to other common chelants, such as EDTA and NTA. 

NOTE Denting is a phenomenon affecting tubes and tube supports. It is caused by the buildup of voluminous metallic oxides (such as copper oxide from FW heaters and iron oxide from carbon steel components), plus chloride ions. The deposit buildup distorts equipment and causes dents. 

Molecular oxygen is transported throughout the body by attaching to the iron(ll) atom in the heme group of hemoglobin. The iron(ll) atom lies at the center of a square planar complex formed by nitrogen atoms. When the O, molecule attaches to the iron, the plane of the heme group becomes distorted. 

The data for the 1,2-diaminoethane complexes now parallels the trends in ionic radius and LFSE rather closely, except for the iron case, to which we return shortly. What is happening Copper(ii) ions possess a configuration, and you will recall that we expect such a configuration to exhibit a Jahn-Teller distortion - the six metal-ligand bonds in octahedral copper(ii) complexes are not all of equal strength. The typical pattern of Jahn-Teller distortions observed in copper(ii) complexes involves the formation of four short and two long metal-ligand bonds. 

Other paramagnetic bis(amidinate) iron(II) complexes of the type [But(NR)2]2Fe (R = Cy, Pr ) have been prepared analogously from the lithium amidinate salts and FeCl2- The coordination geometry around Fe is distorted tetrahedral (Scheme 137). 

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