Surface intermetallic phases

A monolayer of Sm is formed on Ru(OOl) surface which transforms into surface intermetallic phase at higher doses of Sm. It is possible to produce SmRu intermetallic phases of different composition using this method. Alloy formation is confirmed from Ru 3d low binding energy feature at 279 eV. Molecular CO adsorption occurs on open Ru sites as evidenced by twin TPD peaks. The partly oxidized Sm20x species attracts CO molecules for... 

Tin will protect copper from corrosion by neutral water. Pure tin is anodic to copper, and protects discontinuities by sacrificial corrosion. Both intermetallic phases are strongly cathodic to copper, and corrosion is stimulated at gaps in wholly alloyed coatings. An adequate thickness of tin is needed for long service, e.g. 25-50 xm. Another diffusion problem occurs with tin-plated brass. Zinc passes very quickly to the tin surface, where under conditions of damp storage zinc corrosion products produce a film... 

The precursor alloy is quenched to form small grains readily attacked by the caustic solution [31], Quenching can also enable specific intermetallic phases to be obtained, although this is less common. Yamauchi et al. [32-34] have employed a very fast quench to obtain a supersaturation of promoter species in the alloy. It is even possible to obtain an amorphous metal glass of an alloy, and Deng et al. [35] provide a review of this area, particularly with Ni, Ni-P, Ni-B, Ni-Co, and Ni-Co-B systems. The increased catalytic activity observed with these leached amorphous alloy systems can be attributed to either chemical promotion of the catalyzed reaction or an increased surface area of the leached catalyst, depending on the components present in the original alloy. Promotion with additives is considered in more detail later. 

Table 4.9 summarises our findings for the growth of metal particles on the two major type of ceria surfaces, (111) and (001). Results are identical for Rh and Pt catalysts. Moreover, the orientation relationships described in this table do hold for reduction temperatures in the range 473 K - 1173 K, whenever the supported particles remain metallic type and monocrystalline. As we will describe further, in the case of platinum catalysts, a transformation of the metallic particles into an intermetallic phase takes place at 1173 K. Though in this case specific orientation relationships have also been observed with respect to the support, their characteristics differ from those related in Table 4.9. 

The reaction of silicon and chloromethane proceeds phenomenologically in a way that the copper catalyst forms precipitates on the most activated areas of the silicon surface, which are the areas around intermetallic phases, grain boundaries or defects. In these areas one observes the fastet consumption of the silicon particle, also the general surface reacts, but much slower [5]. 

Very little is known about the mechanism of corrosion protection by alloys. For some alloys, the depletion of the passive layer of the alloy by the less stable metal can be assumed, producing a thin surface film of improved corrosion protection (e.g. Fe-Cr-Ni). Recently, it was proposed that the corrosion protection of Zn-Ni alloys might be cormected with the formation of an intermetallic phase [11]. 

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