Transport platinum group metals

The hydrogen reduction of the metal halides, described in Sec. 1.2, is generally the favored reaction for metal deposition but is not suitable for the platinum-group metals since the volatilization and decomposition temperatures of their halides are too close to provide efficient vapor transport. 1 1 For that reason, the decomposition of the carbonyl halide is preferred. The exception is palladium which is much more readily deposited by hydrogen reduction than by the carbonyl-halide decomposition. 

CVD Reactions. The rhodium halides, like those of the other platinum group metal s, are volatile with a decomposition pointtoo close to the vaporization point to make them usable for CVD transport. The metal is commonly produced by the decomposition of metallo-organic precur-... 

Weathering, washing and transport of primary deposits formed alluvial deposits of platinum group metals. Platinum and other heavy metals and minerals were concentrated in clay and sand. Secondary deposits occur in the Urals and Colombia. Os-miridium, originally found in Russia, is nowadays mainly obtained along with secondary deposits of gold in Alaska and in Witwatersrand in South Africa. 

This direct reduction gave very poor dispersion because the neutral hydride is very mobile and favors transport processes leading to metal agglomeration in large particles. A calcination step, preferably in pure oxygen, must be conducted to decompose the complex prior to H2-reduction to obtain well-dispersed platinum clusters [74]. This requirement is valid for all other ammino cations of platinum group metals (see Sect. 3 for case studies). The only exception is ru-... 

Wiseman CLS, Zereini F (2009) AirbOTne particulate matter, platinum group elements and human health a review of recent evidence. Sci Total Environ 407 2493-2500 Wood SA (1996) The role of humic substances in the transport and fixation of metals of economic interest (Au, Pt, Pd, U, V). Ore Geol Rev 11 1-31 Zelikoff JT, Schermerhom KR, Fang K, Cohen MD, Schlesinger RB (2002) A role for associated transition metals in the immunotoxicity of inhaled ambient particulate matter. Environ Health Perspect 110 871-875... 

The solvent-catEdysts are the transition metals such as iron, cobalt, chromium, nickel, platinum, and palladium. These metal-solvents dissolve carbon extensively, break the bonds between groups of carbon atoms and between individual atoms, and transport the carbon to the growing diamond surface. 

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