Rhodium mechanical properties

Alloys with rhodium Rhodium alloys readily with platinum in all proportions, although the workability of the resulting alloy decreases rapidly with increasing rhodium content. Alloys containing up to about 40% rhodium, however, are workable and find numerous applications. The principal physical and mechanical properties of rhodium-platinum alloys are listed in Table 6.3. 

Table 6.3 Physical and mechanical properties of rhodium-platinum alloys...

Hardness of the aimealed metals covers a wide range. Rhodium (up to 40%), iridium (up to 30%), and mthenium (up to 10%) are often used to harden platinum and palladium whose intrinsic hardness and tensile strength are too low for many intended appHcations. Many of the properties of rhodium and indium. Group 9 metals, are intermediate between those of Group 8 and Group 10. The mechanical and many other properties of the PGMs depend on the physical form, history, and purity of a particular metal sample. For example, electrodeposited platinum is much harder than wrought metal. 

Platinum, palladium, and rhodium are the major materials used industrially for the catalytic oxidation of CO. This initiated a variety of studies on single crystals, on supported particles, as well as on real catalysts in order to obtain important details about this catalytic process. In this section, an overview over the reactive properties of free Pt and Pd clusters will be presented and the catalytic CO combustion reaction on clusters of these metals will be discussed. Subsequently, the activity of deposited mass-selected Pt and Pd clusters in this reaction will be analyzed in order gain insight into the details of the catalytic reaction mechanisms on these materials. 

A free-radical polymerization mechanism can be excluded on the basis of the polymer microstructure and experiments with radical inhibitors. Rhodium(I)-spe-cies, formed by reduction of Rh " salts used as catalyst precursors by butadiene monomer, have been suggested as the active species. The catalyst is stable during the aqueous polymerization for over 30 h [23]. Catalyst activities are moderate with up to ca. 2x10 TO h [24, 25]. By contrast to industrially important free-radical copolymerization, styrene is not incorporated in the rhodium-catalyzed butadiene polymerization [26]. Only scarce data is available regarding the stability and other properties of the polymer dispersions obtained. Precipitation of considerable portions of the polymer has been mentioned at high conversions in butadiene polymerization [23, 27]. 

Rh(TTP) reacts with alkyl halides, acyl halides, aroyl halides, and sulfonyl halides, but it shows no evidence of reaction with molecular hydrogen. These observations further emphasize the fact that Rh(TTP) is essentially a nucleophile and it therefore reacts with those reagents RX that can oxidatively add by nucleophilic attack (34). Rh(TTP) does not react with H2, and H2 seems always to add to (P complexes via a concerted mechanism (35). It appears that Rh(TTP) has very little diradical character, i.e. it is not a good analog of a carbene (35). It is possible that this unreactivity may be associated with the stereochemistry of chelation by the macrocyclic ligand. Earlier studies on the oxidative addition reactions of Rh(I) complex with a tetraaza macrocycle revealed that the Rh(I) had strong nucleophilic properties but the activation of molecular H2 was not reported (36, 37). This possibility is supported by reports that dialkyl sulfide complexes of rhodium chloride catalyze the hydrogenation of olefins (38). 

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