Alloys transition metals

Metallic Glasses. Under highly speciali2ed conditions, the crystalline stmcture of some metals and alloys can be suppressed and they form glasses. These amorphous metals can be made from transition-metal alloys, eg, nickel—2irconium, or transition or noble metals ia combination with metalloid elements, eg, alloys of palladium and siUcon or alloys of iron, phosphoms, and carbon. 

F. R. de Boer, R. Boom, W.C.M. Mattens, A.R. Miedema and A.K. Niessen. Cohesion in Metals (Transition metal alloys). North-Holland, Amsterdam (1988). 

More effort has probably been devoted to study of the corrosion and passivation properties of Fe-Cr-Ni alloys, e.g. stainless steel and other transition-metal alloys, than to any other metallic system [2.42, 2.44, 2.55, 2.56]. The type of spectral information obtainable from an Fe-Cr alloy of technical origin, carrying an oxide and contaminant film after corrosion, is shown schematically in Fig. 2.13 [2.57]. 

INVESTIGATION OF GALVANO-MAGNETIC PROPERTIES OF TRANSITION METAL ALLOY SYSTEMS USING THE KUBO-GREENWOOD EQUATION... 

Such calculations have also been performed for isolated impurities of late transition metals alloyed into the surface of other transition metals, and the trends are the same. The accuracy of the numbers in Fig. 6.33 is limited since many approximations had to be made to calculate them. Nevertheless, they reflect trends very well and give useful insight into reactivity trends that have actually been measured for a number of pseudomorfic overlayers [J.A. Rodriquez and D.W. Goodman, Science 257 (1992) 897]. 

Select a suitable pool of transition metal alloys and, using DPT techniques, evaluate the values of the catalytic descriptors on these alloys. A more approximate, but still very useful, alternative is to estimate the descriptors by some form of linear interpolation [Andersson et al., 2006 Jacobsen et al., 2001]. 

Medvedev IG. 2004. To a theory of electrocatalysis for the hydrogen evolution reaction The hydrogen chemisorption energy on the transition metal alloys within the Anderson-Newns model. Russ J Electrochem 40 1123-1131. 

Stamenkovic V, Mun BS, Blizanac BB, Mayrhofer KJJ, Ross PN Jr, Markovic NM. 2006a. The effect of surface composition on electronic structure, stability and electrocehmical properties of Pt-transition metal alloys Pt-skin vs. Pt-skeleton surfaces. J Am Chem Soc 137 1. 

Lee K, Savadogo O, Ishihara A, Mitsushima S, Kamiya N, Ota K-I. 2006. Methanol-tolerant oxygen reduction electrocatalysts based on Pd-3D transition metal alloys for direct methanol fuel cells. J Electrochem Soc 153 A20-A24. 

Ruban AV, Skriver HE, Nprskov JK. 1999. Surface segregation energies in transition-metal alloys. Phys Rev B 59 15990-16000. 

Van der Woude and Miedema [335] have proposed a model for the interpretation of the isomer shift of Ru, lr, Pt, and Au in transition metal alloys. The proposed isomer shift is that derived from a change in boundary conditions for the atomic (Wigner-Seitz) cell and is correlated with the cell boundary electron density and with the electronegativity of the alloying partner element. It was also suggested that the electron density mismatch at the cell boundaries shared by dissimilar atoms is primarily compensated by s —> electron conversion, in agreement with results of self-consistent band structure calculations. 

Manninen, S., Honkimaki, V., Hamalainen, K., Laukkanen, J., Blaas. C., Redinger, J., McCarthy, J. and Suortti, P. (1996) Compton-scattering study of the electronic properties of the transition-metal alloys FeAI, CoAI, and NiAl, Phys. Rev., B53,7714-7720. 

See LANTHANIDE-TRANSITION METAL ALLOY HYDRIDES See Poly(tetralluoroethylene) Metal hydrides... 

Steels and other structural transition-metal alloys are hardened by various extrinsic factors. The compositions and internal micro-structures of these materials are very complex. Therefore, simple descriptions and/or interpretations of their behaviors cannot be given, so they will not be discussed here. 

Relatively little attention has been devoted to the direct electrodeposition of transition metal-aluminum alloys in spite of the fact that isothermal electrodeposition leads to coatings with very uniform composition and structure and that the deposition current gives a direct measure of the deposition rate. Unfortunately, neither aluminum nor its alloys can be electrodeposited from aqueous solutions because hydrogen is evolved before aluminum is plated. Thus, it is necessary to employ nonaqueous solvents (both molecular and ionic) for this purpose. Among the solvents that have been used successfully to electrodeposit aluminum and its transition metal alloys are the chloroaluminate molten salts, which consist of inorganic or organic chloride salts combined with anhydrous aluminum chloride. An introduction to the chemical, electrochemical, and physical properties of the most commonly used chloroaluminate melts is given below. 

The Hume-Rothery phases constitute an interesting and ubiquitous group of binary and complex intermetallic substances it was indeed Hume-Rothery who, already in the twenties, observed that one of the relevant parameters in rationalizing compositions and structures of a number of phases is the average number of valence electrons per atom (nJnM). An illustration of this fact may be found in Table 4.6, where a number of the Hume-Rothery structure types have been collected, together with a few more major structure types relevant to transition metal alloys. For each phase the corresponding VEC has been reported as njnai ratio, both calculated on the basis of the s and p electrons and of s, p and d electrons. 

Sodium-antimony alloy, 4797 Sodium germanide, 4418 Sodium-zinc alloy, 4798 Titanium-zirconium alloys, 4921 See also LANTHANIDE-TRANSITION METAL ALLOY HYDRIDES... 

Several lanthanide-transition metal alloys (LaNi5, PrCo5, SmCo5) readily absorb large volumes of hydrogen under mild conditions, and some of these alloy hydrides function as active hydrogenation catalysts e.g., the title structures, which are pyrophoric in air. Analogous hydrides may be expected to behave similarly. 

The heats of formation of equiatomic AB transition-metal alloys may be predicted by generalizing the rectangular d band model for the elements to the case of disordered binary systems, as illustrated in the lower panel of Fig. 7.13. Assuming that the A and transition elements are characterized by bands of width WA and WB, respectively, then they will mix together in the disordered AB alloy to create a common band with some new width, WAB. The alloy bandwidth, WAB may be related to the elemental bond integrals, hAA and , and the atomic energy level mismatch, AE — EB — EAt by evaluating the second moment of the total alloy density of states per atom ab( ), namely... 

We see that the simple rectangular d band model reproduces the behaviour found by experiment and predicted by Miedema s semi-empirical scheme. However, we must stress that the model does not give credence to any theory that bases the heat of formation of transition-metal alloys on ionic Madelung contributions that arise from electronegativity differences between the constituent atoms because in the metallic state the atoms are perfectly screened and, hence, locally charge neutral. Instead, the model supports... 

Fig. 7.15 The contributions to the normalized heats of formation, AH/(AN)2, for the case of 4d transition metal alloys. The experimental and semi-empirical values of Miedema eta/. (1980) for A/V = 1 and 2 are given by the solid dots and crosses respectively. (From Pettifor (1987).)...

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