Platinum metals Properties

The second form consists of Pt metal but the iridium is present as iridium dioxide. Iridium metal may or may not be present, depending on the baking temperature (14). Titanium dioxide is present in amounts of only a few weight percent. The analysis of these coatings suggests that the platinum metal acts as a binder for the iridium oxide, which in turn acts as the electrocatalyst for chlorine discharge (14). In the case of thermally deposited platinum—iridium metal coatings, these may actually form an intermetallic. Both the electrocatalytic properties and wear rates are expected to differ for these two forms of platinum—iridium-coated anodes. 

Attempts to classify carbides according to structure or bond type meet the same difficulties as were encountered with hydrides (p. 64) and borides (p. 145) and for the same reasons. The general trends in properties of the three groups of compounds are, however, broadly similar, being most polar (ionic) for the electropositive metals, most covalent (molecular) for the electronegative non-metals and somewhat complex (interstitial) for the elements in the centre of the d block. There are also several elements with poorly characterized, unstable, or non-existent carbides, namely the later transition elements (Groups 11 and 12), the platinum metals, and the post transition-metal elements in Group 13. 

As noted above, the roasting of most metal sulfides yields either the oxide or sulfate. However, a few metals can be obtained directly by oxidation of their sulfides, and these all have the characteristic property that their oxides are much less stable than SO2. Examples are Cu, Ag, Hg and the platinum metals. In addition, metallic Pb can be extracted by partial oxidation of galena to form a sulfate (the Scotch hearth or Newnham process, p. 370). The oversimplified reaction is ... 

Corrosion (spontaneous dissolution) of the catalyticaUy active material, and hence a decrease in the quantity present. Experience shows that contrary to widespread belief, marked corrosion occurs even with the platinum metals. For smooth platinum in sulfuric acid solutions at potentials of 0.9 to 1.0 V (RHE), the steady rate of self-dissolution corresponds to a current density of about 10 A/cm. Also, because of enhanced dissolution of ruthenium from the surface layer of platinum-ruthenium catalysts, their exceptional properties are gradually lost, and they are converted to ordinary, less active platinum catalysts. 

Much of the Pt Mossbauer work performed so far has been devoted to studies of platinum metal and alloys in regard to nuclear properties (magnetic moments and lifetimes) of the excited Mossbauer states of Pt, lattice dynamics, electron density, and internal magnetic field at the nuclei of Pt atoms placed in various magnetic hosts. The observed changes in the latter two quantities, li/ (o)P and within a series of platinum alloys are particularly informative about the conduction electron delocalization and polarization. 

Direct Cg cyclization of alkanes into cyclohexane-type rings. The occurrence of this process is claimed under the effect of unreduced surface platinum complexes which have no metallic properties (24). 

Elemental composition Pt 85.91%, O 14.09%. The oxide may be characterized by its physical properties and by x-ray diffraction. The compound may be thermally decomposed at elevated temperatures or reduced by hydrogen to form platinum metal which may be digested with aqua regia and HCl, diluted, and analyzed by flame AA, ICP/AES or ICP/MS. 

Similar to (SN)t in their one-dimenston.il conductivity properties arc the stacked columnar complexes typified by [Pl(CN)j i. These square planar ions adopt a closely spaced parallel arrangement, allowing for considerable interaction among the d i orbitals of the platinum atoms. These orbitals are normally filled with electrons, so in order to get a conduction band some oxidation (removal of electrons) must take place. This may be readily accomplished by adding a little elemental chlorine or bromine to the pure tetracyanoplatinate salt to get stoichiometries such as K-.[Pt(CN)jBr0, in which the platinum has an average oxidation state of +2.3. The oxidation may also be accomplished electrolytically. as in the preparation of Rbj(Pt(CN)4J(FHF)04 (Fig. 16.8). which has a short Pt—Pi separation. The Pt—Pt distance is only 280 pm. almost as short as that (bund in platinum metal itself (277 pm) and in oxidized platinum "pop complexes (270 to 278 pm see Chapter l5).4- Cold-bronze materials of this type were discovered as early as 1842. though they have been little understood until recent times. The complexes behave not only as one-dimensional conductors, but... 

Platinum is one member of a family of six elements, called the platinum metals, which almost always occur together, Before the discovery of the sister elements, the term platinum was applied to an alloy with Pt as the dominant metal, a practice that persists to some degree even today. The major properties of the platinum metals are given in Table 1 See also Iridium Osmium Palladium Rhodium and Ruthenium. 

Because of their unique properties and in spite of their high initial cost, the platinum metals find many applications in industry. Since used platinum metals retain a large portion of their initial value, many scrap materials arc a major source of recoverable platinum metals. Practically every application of platinum generates scrap in some form, which is eventually returned to the platinum refiner for recycling. Although there are ample mine reserves, they soon would be depleted without constant scrap recycling. 

A.5 State whether the following are extensive or intensive properties (a) the color of copper sulfate (b) the temperature of boiling liquid oxygen (LOX) (c) the cost of platinum metal (d) the energy content of a beaker of water. 

Cooper, B. J. Platinum-Carbon Catalysts with Molecular Sieve Properties. Shape Selectivity in Hydrogenation Catalysis. Platinum Metals Rev, 14, 133 (1970). 

Mestroni G, Alessio E, Calligaris M, Attia WM, Quadrifoglio F, Cauci S, Sava G, Zorzet S, Pacor S (1989) Chemical, biological and antitumor properties of mthenium(II) complexes with dimethyl sulfoxide. In Alessio E, Clarke MJ (eds) Ruthenium and other non-platinum metal complexes in cancer chemotherapy. Springer-Verlag, Berlin, New York, pp 71-87... 

Magnetic Properties of the Platinum Metals and Their Alloys... 

Using this local moment model, and using band theory or its variations, a number of workers have been able to formulate expressions which represent the measured magnetic data reasonably well, at least for the case where well-localized moments are developed on the solute atoms (II, 18). However, considerably more data has become available on other properties of dilute alloys, including data on resistivity and specific heat, neutron scattering, various magnetic resonance experiments, Moss-bauer measurements, Kondo effect, and the like. Measurements have been extended also to alloys of many other systems besides those involving the platinum metals. 

It will not be possible, in this paper, to deal with all of the platinum metal chalcogenides. Instead, a number of examples will be chosen and their electrical as well as magnetic properties correlated with the atomic positions in the various structures formed. The first group of compounds to be discussed crystallize with the pyrite structure, which is shown in Figure 1. This structure is similar to the NaCl structure if we replace Na by Fe and each Cl by an S2 group. However, the S-S distance within... 

Aromatic compounds are reduced over the six platinum metal group catalysts at widely different rates, as expected, but additionally the products of reduction frequently vary with the metal used. Many of these results may be correlated in terms of two parameters not obviously connected to aromatic properties the relative tendencies of these catalysts to promote double bond migration in olefins and to promote hydro-genolysis of vinylic and allylic functions. 

The crystal structures adopted by the binary carbides and nitrides are similar to those found in noble metals. The resemblance is not coincidental, and has been explained using Engel-Brewer valence bond theory [5]. Briefly, the main group elements C and N increase the metal s effective s-p electron count, so that structures and chemical properties of the early transition metals resemble those of the Group 8 metals. This idea was first introduced by Levy and Boudart [6] who noted that tungsten carbide had platinum-like properties. 

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