Platinum applications

Cp(CO)2Fe-C=CR (R = H, Ph, Bu, C=CH) and Cp (CO)2Fe-C=CH concluded that alkynyl-to-metal n donation is significant and destabilises the metal d levels due to filled-filled interactions, while metal-to-ligand 7i backdonation is very weak." " The same overall picture obviously applies to bis(alkynyl) complexes C=CR)2(PR3)2 of palladium and platinum. Application of... 

CARBON - CARBON AND ARTIFICIALGRAPHITE - APPLICATIONS OF BAKED AND GRAPHITIZED CARBON] (Vol 4) -With osmium tetroxide catalyst [PLATINUM-GROUP METALS, COMPOUNDS] (Vol 19)... 

The principal applications of the PGMs are summarized in Table 17. Table 17. Applications of the Platinum-Group Metals... 

An interesting field of application is the protection of tantalum against hydrogen embrittlement by electrical connection to platinum metals. The reduction in hydrogen overvoltage and the shift of the free corrosion potential to more positive values apparently leads to a reduced coverage by adsorbed hydrogen and thereby lower absorption [43] (see Sections 2.1 and 2.3.4). 

The selection of the cure system in these applications is directed by constraints such as location of the adhesive in terms of confined space, speed and depth of cure, etc. The volumes of silicones typically applied are relatively small. In general, the uncured adhesive needs to be dispensed in a well-defined and limited area, and needs to stay in place without flowing during cure. No by-products of the cure reaction are acceptable as they may contaminate other sensitive areas of the devices. These constraints often direct the choice to the platinum-catalyzed hydrosilylation cure system that is relatively expensive. 

In many applications tantalum can be substituted for platinum and gold, and there are some environments in which tantalum is more corrosion resistant than platinum. Table 3.37 lists the main chemicals for which tantalum is not a suitable substitute for platinum and, conversely, those for wliich tantalum is better than platinum. Tantalum is rapidly embrittled by nascent hydrogen even at room temperature. Therefore, it is very important to avoid the formation of galvanic couples between tantalum and other metals. 

Gold can be used only in very small portions or very thin coatings because of its cost. Most of the applications for wliich it was used in the past have now been accomplished with tantalum at a much lower cost. A gold/ platinum/rhodium alloy is used in the manufacture of rayon-spinning jets in the production of rayon fibers. This alloy presents the combination of strength, corrosion resistance and abrasion resistance necessary to prevent changes in hole dimensions. 

Powerforming is a version of the platinum reforming process. Basically there are two types of unit semi-regenerative and cyclic. The choice of unit and the exact process conditions used will depend to a large extent on the particular application. However, certain generalizations regarding each of the two types can be made. 

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

Barnard, K. N., Christie, G. L. and Gage, D. G. Service Experience with Lead Silver Alloy Anodes in Cathodic Protection of Ships , Corrosion, 15, 11, 581-586 (1959) Peplow, D. B. and Shreir, L. L. Lead/Platinum Electrodes for Marine Applications , Corr. Tech. Apr. (1984)... 

Niobium like tantalum relies for its corrosion resistance on a highly adherent passive oxide film it is however not as resistant as tantalum in the more aggressive media. In no case reported in the literature is niobium inert to corrosives that attack tantalum. Niobium has not therefore been used extensively for corrosion resistant applications and little information is available on its performance in service conditions. It is more susceptible than tantalum to embrittlement by hydrogen and to corrosion by many aqueous corrodants. Although it is possible to prevent hydrogen embrittlement of niobium under some conditions by contacting it with platinum the method does not seem to be broadly effective. Niobium is attacked at room temperature by hydrofluoric acid and at 100°C by concentrated hydrochloric, sulphuric and phosphoric acids. It is embrittled by sodium hydroxide presumably as the result of hydrogen absorption and it is not suited for use with sodium sulphide. 

Cathodic protection applications in fresh water include use of ferrite-coated niobium , and the more usual platinum-coated niobium . Platinised niobium anodes have been used in seawater, underground and in deep wells " and niobium connectors have been used for joining current leads Excellent service has been reported in open-seawater, where anodic potentials of up to 120V are not deleterious, but crevice corrosion can occur at 20 to 40V due to local surface damage, impurities such as copper and iron, and under deposits or in mud ... 

The deliberate raising of the electrical potential of titanium, either by the attachment of discrete particles of a noble metal, such as platinum or palladium, at the surface, or by the application of positive direct current to force the formation of a protective film, is dealt with at a later point. The electrochemical aspect of the corrosion of titanium is comprehensively treated in a number of papers ... 

By a mechanism similar to that discussed in relation to platinum coating, titanium can function as a conducting jig to support aluminium components and assemblies in conventional anodising baths. In this application the exposed titanium acquires the insulating film, but allows current to pass to the aluminium at the points of contact . 

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. 

The excellent resistance of platinum, rhodium and iridium to oxidation at high temperatures finds numerous applications in technology, in particular in the form of platinum-based alloys. Osmium and ruthenium form volatile oxides which may be isolated (OSO4 and RujOj), and they are not widely used. 

Platinum and rhodium-platinum and iridium-platinum alloys are frequently employed to line and sheath autoclaves, reactor vessels and tubes, and a wide range of equipment. Linings are generally 0-13 mm to 0- 38 mm thick, and for certain applications co-extruded platinum-lined Inconel or other metal reactor or cooling tubes are fabricated. In such cases the platinum is bonded to the base metal, but in all other instances platinum linings are of the loose type. 

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