Iridium high-temperature properties

High Temperature Properties. There are marked differences in the abihty of PGMs to resist high temperature oxidation. Many technological appHcations, particularly in the form of platinum-based alloys, arise from the resistance of platinum, rhodium, and iridium to oxidation at high temperatures. Osmium and mthenium are not used in oxidation-resistant appHcations owing to the formation of volatile oxides. High temperature oxidation behavior is summarized in Table 4. 

Platinum alloys containing from 0 5 to 20 per cent, of tantalum are hard, withstand heat, as well as the action of adds and fused potassium hydrogen sulphate, and are more resistant to the action of aqua-regia than platinum.8 They possess the mechanical properties off platinum-iridium alloys and are less expensive the relative quantities, of tantalum and iridium required to produce the same hardness and mechanical resistance are stated to be 1 5. Platinum-tantalum alloys, hence have been recommended for various purposes in place of platinum or platinum-iridium. Tantalum can also be coated with platinum, andl can then be utilised in high-temperature work. ... 

Description and general properties. Iridium [7439-88-5], chemical symbol Ir, atomic number 77, and relative atomic mass 192.217(3), is a silvery-white, extremely hard and brittle metal that is nonmalleable at room temperature but can be hot worked at high temperature. These properties make iridium most difficult to machine, form, or work. Iridium has a high melting point (2410°C), a high Young s modulus (517 GPa), and the highest density... 

Conduct research on advanced matrix manufacturing of materials with tunable thermal, mechanical, neutronic, and environmental resistance properties at high temperatures, such as electron-beam vapor deposition of rhenium and iridium on graphitized foam. 

Electron-beam physical vapor deposition (EB-PVD) of rhenium on graphite has been demonstrated at The Pennsylvania State University. With EB-PVD technology, two or more materials ean be co-evaporated or deposited in layers to form functionally tailored coatings with improved properties and performance. Because rhenium is compatible not only with carbon but with platinum, palladium, ihodium, ruthenium, osmium, and iridium, it follows that EB-PVD technology can produce coatings with improved rhenium properties. For instance, deposition by electron-beam co-evaporation of rhenium with iridium will most likely provide high-temperature oxidation resistance. (Note that, presently, high-temperature, 2500 K, oxidation resistance is commercially achieved by vapor deposition of 50- to 250-pm-thick iridium films on rhenium.2... 

The ruthenium(II) polypyridyl complexes are also popular but the brightnesses do not exceed 15,000 and thermal quenching is rather significant. This property can be utilized to design temperature-sensitive probes providing that the dyes are effectively shielded from oxygen (e.g., in polyacrylonitrile beads). Despite often very high emission quantum yields the visible absorption of cyclometallated complexes of iridium(III) and platinum(II) is usually poor (e < 10,000 M-1cm-1), thus,... 

An iridium(I) complex with the l,2-bis(tcrt-butylmethylphosphino)ethane (4) and tetrakis(3,5-bis(trifluoromethyl)phenyl)borate as the counter anion catalyzes the hydrogenation of several acyclic aromatic Ai-arylimines under atmospheric hydrogen pressure at room temperature, giving the desired chiral amines with high-to-excellent enantioselectivities (up to 99%, Fig. 6) [19]. The authors also tested (S )-BINAP (Fig. 1) and (/ )-Ph-PHOX (PHOX = 2-[2-(diphenylphosphino) phenyl]-4,5-dihydrooxazole) hgands with lower enantioselectivities [19]. Both steric and electronic properties of the ligand and the combination with the BArF anion are in the base of the efficacy of this catalytic system. On the other hand, attempted hydrogenations of Ai-(2,2,2-trifluoro-l-phenylethylidene)aniline and M-(l,2,2-trimethyl-propylidene)aniline under the same conditions resulted in... 

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