Iron binary alloys

Figure 5.26. Iron binary alloys. Examples of the effects produced by the addition of different metals on the stability of the yFe (cF4-Cu type) field are shown. In the Fe-Ge and Fe-Cr systems the 7 field forms a closed loop surrounded by the a-j two-phase field and, around it, by the a field. Notice in the Fe-Cr diagram a minimum in the a-7 transformation temperature. The iron-rich region of the Fe-Ru diagram shows a different behaviour the 7 field is bounded by several, mutually intersecting, two (and three) phase equilibria. The Fe-Ir alloys are characterized, in certain temperature ranges, by the formation of a continuous fee solid solution between Ir and yFe. Compare with Fig. 5.27 where an indication is given of the effects produced by the different elements of the Periodic Table on the stability and extension of the yFe field.

The synthetic approach developed for the synthesis of platinum-iron binary alloy nanopartides was subsequently adopted for the preparation of several other binary alloy nanopartides, such as FePd [90] or MnPt [91]. However, these alloys required further structural characterization, as well as further developments of the methods for controlling the partide size, shape, and composition. 

Notwithstanding the large amount of work on pure iron and binary alloys, it remains difficult to translate the results to commercially useful steels. It is believed, on the one hand, that effusion of carbon monoxide can cause non-healing Assures in the scale , and on the other, that silicon creates self-healing layers at the metal interface . ... 

Dilute binary alloys of nickel with elements such as aluminium, beryllium and manganese which form more stable sulphides than does nickel, are more resistant to attack by sulphur than nickel itself. Pfeiffer measured the rate of attack in sulphur vapour (13 Pa) at 620°C. Values around 0- 15gm s were reported for Ni and Ni-0-5Fe, compared with about 0-07-0-1 gm s for dilute alloys with 0-05% Be, 0-5% Al or 1-5% Mn. In such alloys a parabolic rate law is obeyed the rate-determining factor is most probably the diffusion of nickel ions, which is impeded by the formation of very thin surface layers of the more stable sulphides of the solute elements. Iron additions have little effect on the resistance to attack of nickel as both metals have similar affinities for sulphur. Alloying with other elements, of which silver is an example, produced decreased resistance to sulphur attack. In the case of dilute chromium additions Mrowec reported that at low levels (<2%) rates of attack were increased, whereas at a level of 4% a reduction in the parabolic rate constant was observed. The increased rates were attributed to Wagner doping effects, while the reduction was believed to result from the... 

With industry proving to be so conservative about binary alloys it is hardly surprising that ternary alloys receive little attention. Nevertheless, two ternary alloys at least have become commercially available iron-chromium-nickel (so-called stainless steel) for both functional and domestic markets and an electronic connector and solderable alloy based on copper-zinc-tin. 

Dowden and Reynolds (49,50) in further experimental work on the hydrogenation of benzene and styrene with nickel-copper alloys as catalysts, found a similar dependence. The specific activities of the nickel-copper alloy catalysts decreased with increasing copper content to a negligible value at 60% copper and 30-40% copper for benzene and styrene, respectively. Low-temperature specific heat data indicated a sharp fall (1) in the energy density of electron levels N(E) at the Fermi surface, where the d-band of nickel becomes filled at 60 % copper, and (2) from nickel to the binary alloy 80 nickel -)- 20 iron. Further work by these authors (50) on styrene hydrogenation with nickel-iron alloy... 

T. Miyazaki, S. Takagishi, H. Mori, and T. Kozakai. The phase decomposition of iron-molybdenum binary alloys by spinodal mechanism. Acta Metall.. 28(8) 1143-1153, 1980. 

CARBIDES. A binary solid compound of carbon and another element. The most familiar carbides are those of calcium, tungsten, silicon, boron, and iron (cemcntitc) Two factors have an important bearing on the properties of carbides (1) the difference in electronegativity between carbon and the second elemenl. and (2) whether the second element is a transition metal. Saltlike carbides of alkali metals are obtained by reaction with acetylene. Those ohlained from silver, copper, and mercury sails are explosive. See also Carbon and Iron Metals, Alloys, and Steels. 

In binary alloy systems, a eutectoid alloy is a mechanical mixture of two phases which form simultaneously from a solid solution when it cools through Ihe eutectoid temperature. Alloys leaner or richer in one of the metals undergo transformation from the solid solution phase over a range of temperatures beginning above and ending al the eutectoid temperature. The structure of such alloys will consist of primary particles of one of the stable phases in addition to ihe eutectoid. lor example ferrite and pearlite in low-carbon steel. See also Iron Metals, Alloys, and Steels. 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

Metal organic chemical vapor deposition (MOCVD) is a well-established, practical technique for forming simple as well as complex solid state films (130). For binary systems the conventional approach is to use mixtures of the most readily available molecules containing the elements of interest. This approach has been employed to prepare borides of several types. For example, iron-boron alloys have been pre-... 

A special type of catalyst which is typified by Raney Nickel is prepared by leaching out one component from a binary alloy leaving a skeletal structure of the desired catalyst. Raney Nickel itself is made by leaching out aluminium from an aluminium-nickel alloy with sodium hydroxide. Cobalt and iron catalysts have also been prepared in this manner. 

The model based on metal-hydroxide ions ([MOH]+) was further developed by Grande and Talbot [71]. Sasaki and Talbot [72] demonstrated the extendibility of this model to the electrodeposition of Co—Fe and Ni—Co alloys. They found that there is a slight inhibition of the more positive metal deposition and a promotion (acceleration) of the less positive metal deposition for all binary iron-group alloys. 

Table 2 summarizes the best data obtained in three groups of alloys namely binary, ternary and complex alloys with combined strengthening with borides and silicides. The binary alloys is practically quasi-binary ones because contain enough content of iron, which transforms these formally alpha-alloys into practical pseudo-alpha ones containing small but important amount of beta-phase. 

Iron-Carbon Alloys.—Of all the different binary alloys, probably the most important are those formed by iron and carbon alloys consisting not of two metals, but of a metal and a non-metal. On account of the importance of these alloys, an attempt will be made to describe in brief some of the most important relationships met with. 

P. King, H. Uhhg, Passivity in the iron-chrominm binary alloys, J. Phys. Chem. 63 (1959) 2026—2032. S. Fujimoto, R.C. Newman, S.P. Kaye, H. Kheyrandish, J.S. Colligon, Passivation thresholds in iron-chromium alloys prepared by ion-beam spnttering, Corros. Sci. 35 (1993) 51-55. 

FIGURE 10.4 Iron-aluminum system. (From M. Hansen and K. Anderko, Constitution of Binary Alloys y... 

Ngi] Ngia, N., Yavoyskiy, V.I., Kosterev, L.B., Afanas yev, M.I., Hydrogen Solubility in Binary Iron-Base Alloys , Russ. Metall., (4), 11-15 (1972), translated fium Izv. Akad. Nauk SSSR, Met., (4),18-22, (1972) (Experimental, Phase Relations, Thermodyn., 19)... 

Because the binary nickel-molybdenum alloys have poor physical properties (low ductility, poor workability), other elements, for example, iron, are added to form ternary or multicomponent alloys. These are also difficult to work, but they mark an improvement over the binary alloys. Resistance of such alloys to hydrochloric and sulfuric acids is better than that of nickel, but it is not improved with respect to oxidizing media (e.g., HNO3). Since the Ni-Mo-Fe alloys have active corrosion potentials and do not, therefore, establish passive-active cells, they do not pit in the strong acid media to which they are usually exposed in practice. 

---