Rhenium deposits

The hydrogenation catalyst consists of a mixture of palladium and rhenium deposited on a carbon substrate. It provides 100% conversion and about 90% selectivity to THF. Reactor operating temperature is approximately 200°C (400 F) and pressure is approximately 2500 psig [6,7]. 

Fluorination of tungsten and rhenium produces tungsten hexafluoride, WF, and rhenium hexafluoride [10049-17-9J, ReF, respectively. These volatile metal fluorides are used in the chemical vapor deposition industry to produce metal coatings and intricately shaped components (see Thin films,... 

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Rhenium hexafluoride is used for the deposition of rhenium metal films for electronic, semiconductor, laser parts (6—8), and in chemical vapor deposition (CVD) processes which involve the reduction of ReF by hydrogen at elevated (550—750°C) temperatures and reduced (<101.3 kPa (1 atm)) pressures (9,10). 

Aqueous Electrodeposition. The theory of electro deposition is well known (see Electroplating). Of the numerous metals used in electro deposition, only 10 have been reduced to large-scale commercial practice. The most commonly plated metals are chromium, nickel, copper, zinc, rhodium, silver, cadmium, tin, and gold, followed by the less frequendy plated metals iron, cesium, platinum, and palladium, and the infrequendy plated metals indium, mthenium, and rhenium. Of these, only platinum, rhodium, iddium, and rhenium are refractory. 

The Chilean deposits have an average grade of rhenium ranging from 230 to 570 ppm. The El Teniente mine is said to hold the world s largest reserves of rhenium, an estimated 680 metric tons. This ore also contains 1.5 wt % Cu and 0.04 wt % Mo. 

Rhenium exhibits a greater resistance than tungsten to the water cycle effect, in which lamps and electron tubes become blackened by deposition of metal. This phenomenon involves catalysis by small quantities of water that react with the metal in a hot filament to produce a volatile metal oxide and hydrogen. The oxide condenses on the surface of the bulb and is reduced back to the metal by hydrogen. 

Rhenium may be electroplated from solutions of ReO in sulfuric acid. To obtain a durable rhenium plate it is desirable to deposit the metal in thin layers, annealing at high temperature after each layer is appHed. 

Ethylene oxide (qv) was once produced by the chlorohydrin process, but this process was slowly abandoned starting in 1937 when Union Carbide Corp. developed and commercialized the silver-catalyzed air oxidation of ethylene process patented in 1931 (67). Union Carbide Corp. is stiU. the world s largest ethylene oxide producer, but most other manufacturers Hcense either the Shell or Scientific Design process. Shell has the dominant patent position in ethylene oxide catalysts, which is the result of the development of highly effective methods of silver deposition on alumina (29), and the discovery of the importance of estabUshing precise parts per million levels of the higher alkaU metal elements on the catalyst surface (68). The most recent patents describe the addition of trace amounts of rhenium and various Group (VI) elements (69). 

Solid catalysts for the metathesis reaction are mainly transition metal oxides, carbonyls, or sulfides deposited on high surface area supports (oxides and phosphates). After activation, a wide variety of solid catalysts is effective, for the metathesis of alkenes. Table I (1, 34 38) gives a survey of the more efficient catalysts which have been reported to convert propene into ethene and linear butenes. The most active ones contain rhenium, molybdenum, or tungsten. An outstanding catalyst is rhenium oxide on alumina, which is active under very mild conditions, viz. room temperature and atmospheric pressure, yielding exclusively the primary metathesis products. 

The acetylacetonates are stable in air and readily soluble in organic solvents. From this standpoint, they have the advantage over the alkyls and other alkoxides, which, with the exception of the iron alkoxides, are not as easily soluble. They can be readily synthesized in the laboratory. Many are used extensively as catalysts and are readily available. They are also used in CVD in the deposition of metals such as iridium, scandium and rhenium and of compounds, such as the yttrium-barium-copper oxide complexes, used as superconductors. 1 1 PI Commercially available acetyl-acetonates are shown in Table 4.2. 

Deposition temperature range is 400-600°C at a pressure of 200 Torr. Rhenium carbonyl is a solid at room temperature and must be vaporized at a temperature > 117°C. It decomposes at 250°C. This reach on is used for the coating of spheres in a fluidized bed. 

Coating for targets for x-ray cathodes (co-deposition with rhenium). 

Donaldson, J. G., APreliminary Study ofthe Vapor Deposition of Rhenium and Rhenium-Tungsten, V. ofthe Less CommonMetals, 14 93-101(1968)... 

The nozzle of original design was fabricated from a niobium alloy coated with niobium silicide and could not operate above 1320°C. This was replaced by a thin shell of rhenium protected on the inside by a thin layer of iridium. The iridium was deposited first on a disposable mandrel, from iridium acetylacetonate (pentadionate) (see Ch. 6). The rhenium was then deposited over the iridium by hydrogen reduction of the chloride. The mandrel was then chemically removed. Iridium has a high melting point (2410°C) and provides good corrosion protection for the rhenium. The nozzle was tested at 2000°C and survived 400 cycles in a high oxidizer to fuel ratio with no measurable corrosion.O l... 

The refractory metals for which CVD is commonly used to produce free-standing shapes are tungsten, niobium, rhenium, tantalum, molybdenum, and nickelb lb lb l (see Ch. 6). Shapes presently produced include rods, tubes, crucibles, manifolds, ordnance items, nozzles, and thrust chambers. They are usually deposited on a disposable mandrel of copper, molybdenum, or graphite which is subsequently machined off or removed chemically by etching. 

Most published work has focused on the deposition of Ni, Co, and NiCo alloys from hypophosphite electrolytes [14], and this part of the review will deal primarily with these alloys. Other Co alloys studied include CoZnP [15, 16], the recording characteristics of which were described by Soraya [17] CoSnP [18], which is reported to have enhanced corrosion resistance and the rhenium and manganese alloys used for vertical recording, discussed below. Other reductants, such as hydrazine [19], dimethylamine borane [20-22], pyridine borane [23], and borohydride [24, 25], can be used for the chemical deposition of nickel and cobalt, but to date there has been no significant application of these to the technology of magnetic media. 

The tube is positioned in a tube furnace so that the boat is near the center of the furnace, a thermocouple is introduced in the open end, and the open end of the furnace is plugged with Pyrex wool. The tube is evacuated and the temperature raised to 450° at about 3° per minute. A transitory blue deposit is formed in the cool portion of the tube at 200° at 300°, a green ring forms in the tube just inside the furnace at 300 to 350°, a blue-black deposit, presumably a mixture of rhenium (V) bromide and rhenium (VI) oxide tetrabromide,2 forms in the portion of the tube just outside the furnace at 350 to 370°, a blue-black... 

Holmen and coworkers15-17 also observed a loss in activity when water was introduced to un-promoted and Re-promoted cobalt deposited on >-Al203. In a recent paper similar results were reported for Co Re supported on both narrow-pore and wide-pore y-Al203,18 and permanent deactivation was observed when the inlet ratio H20 H2 was 0.7. The same group reported that the rhenium-promoted catalysts lost activity more rapidly than their un-promoted counterparts.14-1619... 

Kim43,49 utilized the effect of water on the activity in FTS patents using un-promoted and promoted cobalt deposited on Ti02 (rutile). For a wide range of external H20 addition levels, beneficial effects of increased productivity could be realised. However, when more than 28% water was added to the feed of the rhenium based version, the CO conversion was affected negatively. More recent experimental investigations of the effect of added water on the rate of the FTS over titania-supported Co are summarized in Table 4. 

A partial separation of technetium from molybdenum and rhenium may be obtained at a controlled cathode potential of — 1.1 V vs. SCE. However, deposition only takes place at technetium concentrations of lO M or greater . 

The main sources of rhenium are the molybdenite and coliunbite ores. Some rhenium is recovered as a by-product of the smelting of copper sulfide (CuS) ores. Molybdenum sulfide (MoSj) is the main ore and is usually associated with igneous rocks and, at times, metaUic-like deposits. Molybdenite is found in Chile, as well as in the states of New Mexico, Utah, and Colorado in the United States. 

Figure 11.28 shows the rhenium and osmium isotopic compositions of black shales and sulfide ores from the Yukon Territory (Horan et al., 1994). The black shale and sulfide layers are approximately isochronous. The superimposed reference isochrons bracket the depositional age of the enclosing shales. One reference line represents the minimum age (367 Ma) with an initial ( Os/ Os)q ratio of one, consistent with the mantle isotopic composition at that age (see later). The other reference isochron is drawn for a maximum age of 380 Ma, with ( 870s/ 860s)o = 12 (the maximum value measured in terrigenous sediments). Further examples of application of Re-Os dating of sediments can be found in Ravizza and Turekian (1989). 

Keywords molybdenite, rhenium, granite, ore deposit, fractionation... 

Newberry, R.J.J. 1979a. Polytypism in molybdenite (II) relationship between pol ypism, ore deposition, alteration stages and rhenium contents. American Mineralogist, 64, 768-775. 

Rhenium in Canadian minerai deposits W. David Sinclair Ian R. Jonasson Rod V. Kirkham, Art E. Soregaroli ... 

Rhenium abundance in most rocks is measured in parts per billion or less and minerals in which it is a major constituent are rare. It is similar geochemically to molybdenum, which it commonly accompanies through magmatic and related hydrothermal stages, and is concentrated in molybdenite associated with various types of granite-related deposits. Molybdenites with some of the highest concentrations of rhenium are associated with porphyry Cu and Cu-Au deposits, which are the primary industrial source of rhenium. Rhenium can also be concentrated by low-temperature... 

Rhenium in molybdenite has been studied by various authors (e.g., Giles Schilling 1972 Stein et al. 2001 Berzina et al. 2005). Rhenium data in this paper are from a study of more than 150 Canadian and some foreign deposits (Jonasson etal. in prep.). 

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