Tungsten vaporization

For the synthesis of materials, the reactants are placed in the copper crucible. An arc is struck by allowing the cathode to touch the anode. The current is raised slowly while the cathode is simultaneously withdrawn so as to maintain the arc. The arc is then positioned so that it bathes the sample in the crucible. The current is increased until the reactants melt When the arc is turned off, the product solidifies in the form of a button. Because of the enormous temperature gradient between the melt and the water-cooled crucible, a thin solid layer of the sample usually separates the melt from the copper hearth in this sense, the sample forms its own crucible and hence contamination with copper does not take place. Contamination of the sample by tungsten vaporizing from the cathode can be avoided by using water-cooled cathodes. The arc method has been successfully used for the synthesis of various oxides of Ti, V and Nb. A number of lower-valence rare-earth oxides, LnO, 5 have been prepared by arc fusion of LnjOj... 

Methyl benzoate, anisole, and diphenyl ether each give sandwich compounds with chromium vapor, although in rather low yield (32, 55, 110). Chromium appears to attack alkyl ethers and this deoxygenation probably competes with complexation with the aromatic oxygen compounds. No simple product has been isolated from chromium atoms and aniline, but bis(7V,7V-dimethylaniline)chromium has been prepared (32). The behavior of molybdenum and tungsten vapors closely resembles that of chromium in reactions with oxygen- and nitrogen-substituted arenes (113). 

Halogen lamps use bromine or other halogen molecules to capture tungsten vapor and return tungsten atoms to the filament. 

Mercaptoundecanoic acid (11-MUA), 1-octanethiol (1-OT), anti-biotin, 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC), streptavidin, 10 mM and 20 mM phosphate buffered saline (PBS), pH = 7.4, (+)-biotinyl-3,6-dioxaoctanediamine (biotin), hexanes, methanol, ethanol, Ag wire (99.99%, 0.5 mm diameter), borosilicate glass substrates, tungsten vapor deposition boats, polystyrene nanospheres with diameters of 400 7 nm were received as a suspension in water and were used without further treatment. All materials were used without further purification. 

It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides by von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tungsten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). 

Since detailed chemical structure information is not usually required from isotope ratio measurements, it is possible to vaporize samples by simply pyrolyzing them. For this purpose, the sample can be placed on a tungsten, rhenium, or platinum wire and heated strongly in vacuum by passing an electric current through the wire. This is thermal or surface ionization (TI). Alternatively, a small electric furnace can be used when removal of solvent from a dilute solution is desirable before vaporization of residual solute. Again, a wide variety of mass analyzers can be used to measure m/z values of atomic ions and their relative abundances. 

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. 

Tungsten hexafluoride is shipped as a Hquid under its own vapor pressure in nickel or steel cylinders in quantities of 45 kilograms per cylinder or less however, it has been shown that the purity of WF packaged in steel cylinders can degrade over time (21). It is classified as a corrosive Hquid by the... 

J. E. J. Schmit2, Chemical Vapor Deposition of Tungsten andTungsten Silicidesfor VESI FJESI Applications, Noyes PubHcations, Park Ridge, N.J., 1992. 

Another important function of metallic coatings is to provide wear resistance. Hard chromium, electroless nickel, composites of nickel and diamond, or diffusion or vapor-phase deposits of sUicon carbide [409-21-2], SiC , SiC tungsten carbide [56780-56-4], WC and boron carbide [12069-32-8], B4C, are examples. Chemical resistance at high temperatures is provided by aUoys of aluminum and platinum [7440-06-4] or other precious metals (10—14). 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Ultraviolet light sources are based on the mercury vapor arc. The mercury is enclosed ia a quart2 tube and a potential is appHed to electrodes at either end of the tube. The electrodes can be of iron, tungsten, or other metals and the pressure ia a mercury vapor lamp may range from less than 0.1 to >1 MPa (<1 to >10 atm). As the mercury pressure and lamp operating temperatures are iacreased, the radiation becomes more iatense and the width of the emission lines iacreases (17). 

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