Tungsten wire, deposition

Boron filaments are formed by the chemical vapor deposition of boron trichloride on tungsten wire. High performance reinforcing boron fibers are available from 10—20 mm in diameter. These are used mainly in epoxy resins and aluminum and titanium. Commercial uses include golf club shafts, tennis and squash racquets, and fishing rods. The primary use is in the aerospace industry. 

Figure 3.1. Multichamber deposition system for organic light emitting diodes (S sample, RF 02 plasma generator, P vacuum pump, Sh shutter, Q quartz microbalance, C crucibles, M mask for electrode patterning, T tungsten wires for metal deposition).

Alternatives to activated tungsten wire emitters are also known, but less widespread in use. Cobalt and nickel [44,47] as well as silver [48] can be electrochemi-cally deposited on wires to produce activated FD emitters. Mechanically strong and efficient emitters can be made by growing fine silicon whiskers from silane gas on gold-coated tungsten or tantalum wires of 60 pm diameter. [45] Finally, on the fracture-surface of graphite rods fine microcrystallites are exposed, the sharpness of which provides field strengths sufficient for ionization. [49]... 

Using Pyrex ampoules with resistively heated tungsten wire or strip filaments, protactinium metal has been prepared on the milligram scale (9,13,15). An improved technique is to use a quartz van Arkel-De Boer bulb with an inductively heated W sphere which solves the previous problem of filament breaking and considerably improves the deposition rate of Pa metal (109). 

Boron, which is used to make composites, is deposited on a tungsten wire when the wire is heated electrically in the presence of boron trichloride vapor and gaseous hydrogen. Write a balanced equation for the reaction. 

The boron is deposited on a tungsten wire, the substate. In a similar way SiC vapour is deposited on C fibres. 

The van Arkel or Iodide Process was first used in The Netherlands in 1925 to make especially pure nitrides1. This process can make several metal nitrides (TiN, ZrN, HfN, VN, NbN, BN and AIN) by passing a mixture of the metal halide with nitrogen and hydrogen over a hot tungsten wire. The metal halide decomposes and the resulting nitride deposits on the wire. The process is described in U.S. Patent 1,671,213. 

Compared to conventional (macroscopic) electrodes discussed hitherto, microelectrodes are known to possess several unique properties, including reduced IR drop, high mass transport rates and the ability to achieve steady-state conditions. Diamond microelectrodes were first described recently diamond was deposited on a tip of electrochemically etched tungsten wire. The wire is further sealed into glass capillary. The microelectrode has a radius of few pm [150]. Because of a nearly spherical diffusion mode, voltammograms for the microelectrodes in Ru(NHy)63 and Fe(CN)64- solutions are S-shaped, with a limiting current plateau (Fig. 33a), unlike those for macroscopic plane-plate electrodes that exhibit linear diffusion (see e.g. Fig. 18). The electrode function is linear over the micro- and submicromolar concentration ranges (Fig. 33b) [151]. 

Boron in high modulus and strength properties is available with this type of fiber. A vapor deposition process is the principal method to produce boron filaments, using /2 mil tungsten wire as a plating substrate. 

HMDE (hanging mercury drop electrode) [71, 72], gold-foil [73], copper-wire [74], tungsten-wire [75, 76] and pyrolytic graphite-coated tube [78] have been used as the electrodes for electrochemical deposition, and successfully applied to the determination of Cu, Cd, Pb, Zn, Hg and so forth. In atomic absorption analysis the electrodes are usually heated directly for atomization of metals. 

Copper and nickel were deposited from metal foil wrapped around a hot tungsten filament. Chromium was evaporated from a chrome plated tungsten wire. XPS measurements were made to determine the metal coverage as well as the electronic structure at the interface. The metal coverage was determined by substituting the experimentally measured areas under the XPS curves, core hole cross sections ( ), and electron mean free path in both the metal and the polymer and an instrument response... 

Boron Trichloride. Boron trichloride is prepared commercially by the chlorination of boron carbide (equation 15). Direct chlorination of boric acid or a sodium borate in the presence of carbon is an alternative method. Most of the boron trichloride produced is converted to filaments of elemental boron by chemical vapor deposition (CVD) on tungsten wire in a hydrogen atmosphere. Numerous laboratory preparations of boron trichloride have been reported. One of the most convenient is the halogen exchange reaction of aluminum chloride with boron trifluoride or a metal fluoroborate. 

Diamond-coated metallic microprobes of cylindrical geometry, fabricated by chemical vapor diamond deposition on tungsten wires, using selective growth techniques have also been quoted[82]. The tungsten wires (130 pm diameter, 5.5 cm long) were electrochemically sharpened to a tip diameter of approximately 0.5 pm. The chemical vapor diamond deposition... 

Diamond deposition by the hot filament method consists of a carbon containing gas and hydrogen, which undergo dissociation by passing through a hot filament usually made of tungsten wire. The dissociated molecules then deposit on a substrate (at approximately 900°C) where a carbon matrix grows in the form of diamond. Deposition dynamics is described by the CVD process. 

PR Formation during direct heating of tungsten wire in pure nitrogen at 2500 °C. Evaporating tungsten combines with nitrogen. The nitride deposits on the enclosure wall. 

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