Metal-substrate alloy

In the applications just mentioned, rare earths impart their beneficial influence either when they are introduced into the high-temperature material as an alloy addition or finely dispersed oxide, or when they are applied to a metal substrate alloy as a coating. A third possibility, which has not been widely exploited to date, is to introduce the rare-earth element into the environment. These three application classifications are shown schematically in fig. 5. 

Reactive Evaporation. In reactive evaporation (RE), metal or alloy vapors are produced in the presence of a partial pressure of reactive gas to form a compound either in the gas phase or on the substrate as a result of a reaction between the metal vapor and the gas atoms ... 

Although metals and alloy substrates account for much of the volume ia electroplating, there is a large and growing amount of plastic surfaces being plated, both for decorative trim and for electronic shielding appHcations. On a smaller scale, other materials that ate plated iaclude wood (qv), plaster, fibers (qv) and cloth materials, and plant and animal tissue, such as leaves, leather (qv), paper (qv), and seasheUs. 

Electroplating—the process of electrodeposition onto a metallic substrate of a thin adherent layer of a metal or alloy having desirable chemical, physical and/or mechanical properties. 

In general, many metals and alloys (e.g. of Al, Ta and Mo) can be deposited on metallic and some non-metallic substrates. M may also be a metal compound having special useful properties (e.g. borides, nitrides, oxides, silicides and carbides), or even a non-metal such as Si (as in Ihrigising ). 

Electrodeposition deposition of a metal or alloy onto a substrate by electrochemical reduction of its ions from an electrolyte under the application of a cathodic overpotential. 

Incorporation of Metal In certain cases, metal atoms, after their discharge, can penetrate into the substrate metal, forming alloys or intermetallic compounds in the surface layer and down to a certain depth. This effect has been known for a long time in the discharge of metals at liquid mercury, where liquid or solid amalgams are formed. In 1968 B. Kabanov showed that an analogous effect is present in metal ion discharge at many solid metals. 

Figure 3.17 Computational high throughput screening for 736 pure metals and surface alloys. The rows indicate the identity of the pure metal substrates, and the columns indicate the identity of the solute embedded in the surface layer of the substrate. The solute coverage is (a) ilVIL, (b) ML, and (c) 1 ML, and the adsorbed hydrogen coverage is also jML. The diagonals of the plots correspond to the hydrogen adsorption free energy on the pure metals. Adapted from [Greeley et al., 2006] see this reference for more details.

Traditional alloy design emphasizes surface and structural stability, but not the electrical conductivity of the scale formed during oxidation. In SOFC interconnect applications, the oxidation scale is part of the electrical circuit, so its conductivity is important. Thus, alloying practices used in the past may not be fully compatible with high-scale electrical conductivity. For example, Si, often a residual element in alloy substrates, leads to formation of a silica sublayer between scale and metal substrate. Immiscible with chromia and electrically insulating [112], the silica sublayer would increase electrical resistance, in particular if the subscale is continuous. 

There are several ways to prepare thin films for use as model catalyst supports.30-31 For the purposes of this review, we will point the reader toward other sources that discuss two of these methods direct oxidation of a parent metal and selective oxidation of one component of a binary alloy. 32 34 The remaining method consists of the deposition and oxidation of a metal on a refractory metal substrate. This method has been used extensively in our group323131 11 and by others33-52-68 and will be the focus of the discussion here. The choice of the metal substrate is important, as lattice mismatch between the film and the substrate will determine the level of crystallinity achieved during film growth. 

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