Complex alloys

The modification shows that the transition temperature may vary significantly from those stated above and in general shift to higher temperatures as the gas pressure in the synthesis process increases. The transition from one zone to the next is not abmpt, but smooth. Hence, the transition temperatures should not be considered as absolute but as guidelines. Furthermore, not all zones are found in all types of deposit. For example. Zone T (see Fig. 7) is not prominent in pure metals, but becomes more pronounced in complex alloys, compounds, or in deposits produced at higher gas pressures. Zone 3 is not often seen in materials with high melting points. 

Komplex-erz, n. complex ore, -ion, n. complex ion. -salz, n. complex salt. -stahli m. complex alloy steel, -verbindung, /. complex compound. 

Cast irons, although common, are in fact quite complex alloys. The iron-carbon phase diagram exhibits a eutectic reaction at 1 420 K and 4-3 wt.<7oC see Fig. 20.44). One product of this eutectic reaction is always austenite however, depending on the cooling rate and the composition of the alloy, the other product may be cementite or graphite. The graphite may be in the form of flakes which are all interconnected (although they appear separate on a... 

Rowlands, J. C., Electrochemical Aspects of Preferential Phase Corrosion in Complex Alloys , Corros. Sci., 2, 89 (1962)... 

Other more complex alloys based on the nickel-chromium system are the... 

For quaternary and more complex alloys a suggestion of Chipman and Sherman might be used. Chipman s school have made use of the symbol c for the rate of change of In y of the dilute solute, C, with small additions of alloying elements, X. Thus for the solution of carbon in iron ... 

For the more complex alloys anodic polarisation offers a vital extra variable in the use of selective etchants and has been widely exploited for alloys for which simple chemical etchants have proved inadequate. Besides many types of alloys steelthis technique has been applied to copper and the Cu-Be-Ni-Zr alloys " , uranium-base alloys " , Ni-Al alloys , tin-bearing invar and many others. 

A hot-dipped tin coating on steel has a layer of FeSnj at the interface between the tin and the steel. This alloy grows very slowly in comparison with the more complex alloy layers formed in galvanising and in aluminising. It usually comprises 10-20% of the total coating thickness. 

Detailed consideration of the structure of many of the advanced and complex alloys which are of considerable technological importance (high-strength titanium alloys, nickel-base superalloys, etc.) is beyond the scope of this section, other than to point out that no new principles are involved. Certain titanium alloys, for example, exhibit a martensitic transformation, while many nickel-base superalloys are age hardening. Similarly, cast irons, although by no means advanced materials, are relatively complex they are considered in Section 1.3 where graphitisation is discussed. 

Manganese is also present in most commercial electrodes. In a series of experiments examining the cycle lives of the homologous alloys LaNi M (M= Mn, Cu, Al, and Co) Sakai et al. [50] noted that Mn was the least effective. In more complex alloys examined by Adzic et al. 

The metal in a nickel metal hydride battery is usually a complex alloy of several metals, such as Cr. Ni, Co, V, Ti, Fe, and Zr. 

F. C. Frank, J. S. Kasper, Complex alloy structures regarded as sphere packings. I Definitions and basic principles, Acta Crystallogr. 11 (1958) 184. II Analysis and classification of representative structures, Acta Crystallogr. 12 (1959) 483. 

F. C. Frank and J. S. Kasper, Complex Alloy Structures Regarded as Sphere Packings. II. Analysis and Classification of Representative Structures, Acta Cryst., 12, 483 (1959). 

Massalski TB, Turchi PEA eds (2005) The science of complex alloy phases. The Minerals, Metals Materials Society, Warrendale, PA... 

A quantum-mechanical interpretation of Miedema s parameters has already been proposed by Chelikowsky and Phillips (1978). Extensions of the model to complex alloy systems have been considered. As an interesting application we may mention the discussion on the stabilities of ternary compounds presented by de Boer et al. (1988). In the case of the Heusler-type alloys XY2Z, for instance, the stability conditions with respect to mechanical mixtures of the same nominal composition (XY2+Z, X+Y2Z, XY+YZ, etc.) have been systematically examined and presented by means of diagrams. The Miedema s parameters, A t>, A ws1/3, moreover, have been used as variables for the construction of structural maps of intermetallic phases (Zunger 1981, Rajasekharan and Girgis 1983). 

A different, more complex, alloying behaviour is illustrated in a number of figures (Figs. 2.18-2.21) where several examples of alloy diagrams are presented which are typically characterized by the formation, through a range of different mechanisms, of intermediate phases. 

According to the brazing design, the metals to be joined, etc., several filler materials can be used ranging from pure metals (Cu, Ag, Au) to complex alloys (of Co, Ni, Ag, Au, Mg, Al, etc.). There are several basic brazing processes in torch brazing for... 

Ternary and more complex alloys are now the subjects of investigations that seek further improvements in oxygen reduction activity. Struc-... 

Table 2 records some examples of this phenomenon in which oxygen arrays in oxides are the same as metal atom arrays in alloys. Recognition of this fact has been exploited to simplify the description of complex alloys (see especially Andersson ), which is essentially the reverse of what we propose to do here, namely to simplify the description of oxide structures by giving them in terms of known alloy structures. Nevertheless Tables 1 and 2 provide striking evidence of Nature s parsimony in the use of patterns in crystal structures. 

Pt-Rh/AROs catalysts are widely used in automotive-exhaust emission control. In these systems, Pt is generally used for the oxidation of CO and hydrocarbons and Rh is active for the reduction of nitric oxide to N2. HRTEM and AEM show two discrete particle morphologies and Pt-Rh alloy particles (Lakis et al 1995). EM studies aimed at understanding the factors leading to deactivation, surface segregation of one metal over the other and SMSI are limited. There are great opportunities for EM studies, in particular, of surface enrichment, and defects and dislocations in the complex alloy catalysts as sites for SMSI. 

A study on neohexane reactions revealed (167, 168) that the inactive additives suppress hydrogenolysis of neohexane in a way similar to that which suppresses hydrogenolysis of hexane. It can be further seen (see Fig. 16) that these additives do not substantially alter the regularly observed preference of Pt for the reactions induced by 3Cay complexes, as opposed to those which are induced by 2Ca/J complexes. Alloying with Au or Ag only strengthens this preference. Rather surprisingly, the addition of Cu has quite different consequences (see below). 

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