Metals volatilization

The general characteristics of all these elements generally preclude their extraction by any method involving aqueous solution. For the lighter, less volatile metals (Li, Na, Be, Mg, Ca) electrolysis of a fused salt (usually the chloride), or of a mixture of salts, is used. The heavier, more volatile metals in each group can all be similarly obtained by electrolysis, but it is usually more convenient to take advantage of their volatility and obtain them from their oxides or chlorides by displacement, i.e. by general reactions such as... 

Polonium-210 is a low-melting, fairly volatile metal, 50% of which is vaporized in air in 45 hours at 55C. It is an alpha emitter with a half-life of 138.39 days. A milligram emits as many alpha particles as 5 g of radium. 

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,... 

Reduction to Gaseous Metal. Volatile metals can be reduced and easily and completely separated from the residue before being condensed to a hquid or a soHd product in a container physically separated from the reduction reactor. Reduction to gaseous metal is possible for 2inc, mercury, cadmium, and the alkah and aLkaline-earth metals, but industrial practice is significant only for 2inc, mercury, magnesium, and calcium. 

Selective solution of the aluminum from the ahoy using a volatile metal, such as mercury, lead, bismuth, cadmium, magnesium, or zinc, has been investigated. After extracting the aluminum from the original ahoy into the volatile metal, the volatile metal is distilled, leaving pure aluminum. Neither electrolysis nor volatile metal extraction can extract aluminum from iron aluniinide [12004-62-3J, EeAl, titanium aluniinide [12004-78-3] TiAl, or Al C. ... 

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. 

Easily decomposed, volatile metal carbonyls have been used in metal deposition reactions where heating forms the metal and carbon monoxide. Other products such as metal carbides and carbon may also form, depending on the conditions. The commercially important Mond process depends on the thermal decomposition of Ni(CO)4 to form high purity nickel. In a typical vapor deposition process, a purified inert carrier gas is passed over a metal carbonyl containing the metal to be deposited. The carbonyl is volatilized, with or without heat, and carried over a heated substrate. The carbonyl is decomposed and the metal deposited on the substrate. A number of papers have appeared concerning vapor deposition techniques and uses (170—179). 

Some catalysts are ha2ardous materials, or they react to form ha2ardous substances. For example, catalysts used for hydrogenation of carbon monoxide form volatile metal carbonyl compounds such as nickel carbonyl, which are highly toxic. Many catalysts contain heavy metals and other ha2ardous components, and environmentally safe disposal has become an increasing concern and expense. 

In conventional treating systems using cold-gas cleanup, the small fraction of metals released to the gas phase is captured effectively in the gas cooling and gas treating steps. The combination of gas cooling and multistage gas—Hquid contacting reduces very substantially the potential for airborne emissions of volatile metals such as lead, beryUium, mercury, or arsenic. 

Although Tm is classified into the group of volatile metals, it has the lowest vapor pressure within this group and is next to the non-volatile group. This intermediary property of Tm in volatility may be responsible for the observation of trace amount of TmC2. The vapor pressure of Tm suggests the upper limit of volatility of metals that can be encapsulated. 

Other routes include the high-temperature halogenation of metal oxides, sometimes in the presence of carbon, to assist removal of oxygen the source of halogen can be X2, a volatile metal halide CX4 or another organic halide. A few examples of the many reactions that have been used industrially or for laboratory scale preparations are ... 

Another problem in high-temperature corrosion can be the effect of the formation of volatile metallic halides which can, in turn, disrupt the integrity of a protective surface oxide. Figure 7.73 shows that in the Ti-O-Cl system at very low oxygen potentials, volatile TiClj can be formed directly from TiO and Ti, whereas from Fig. 7.74 it is clear that in the system U-O-Cl at 450°C the volatile chloride cannot be formed directly from the oxides. 

Casting Skull Recycle. After ingot casting, a residue containing up to 5% of the plutonium feed remains behind. Usually the metal buttons fed to the casting operations retain some of the calcium used in the reduction operation, as well as other volatile metals and oxides. 

The volatile metal is separated by distillation and condensed. Mercury is the only metallic element that is liquid at room temperature (gallium and cesium are liquids on warm days). It has a long liquid range, from its melting point of — 39°C to its boiling point of 357°C, and so it is well suited for its use in thermometers, silent electrical switches, and high-vacuum pumps. 

Several patents dealing with the use of volatile metal amidinate complexes in MOCVD or ALD processes have appeared in the literature.The use of volatile amidinato complexes of Al, Ga, and In in the chemical vapor deposition of the respective nitrides has been reported. For example, [PhC(NPh)2]2GaMe was prepared in 68% yield from GaMes and N,N -diphenylbenzamidine in toluene. Various samples of this and related complexes could be heated to 600 °C in N2 to give GaN. A series of homoleptic metal amidinates of the general type [MIRCfNROilnl (R = Me, Bu R = Pr, BuO has been prepared for the transition metals Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La. The types of products are summarized in Scheme 226. The new compounds were found to have properties well-suited for use as precursors for atomic layer deposition (ALD) of thin films. 

Volatilization is also a dominant transport mode for mercury, which is the most volatile metal in its elemental state. As with lead, a key reaction that can increase the volatility of mercury is formation of an organometallic compound. In this case, the reactions take place in water and are primarily biological, being mediated by bacteria commonly found in the upper levels of sediments. These reactions and their importance in the global mercury cycle are discussed in some detail later in the chapter. 

There are several environmentally significant mercury species. In the lithosphere, mercury is present primarily in the +II oxidation state as the very insoluble mineral cirmabar (HgS), as a minor constituent in other sulfide ores, bound to the surfaces of other minerals such as oxides, or bound to organic matter. In soil, biological reduction apparently is primarily responsible for the formation of mercury metal, which can then be volatilized. Metallic mercury is also thought to be the primary form emitted in high-temperature industrial processes. The insolubility of cinnabar probably limits the direct mobilization of mercury where this mineral occurs, but oxidation of the sulfide in oxygenated water can allow mercury to become available and participate in other reactions, including bacterial transformations. 

For a given volume of the unit cell, the most stable hexaborides are those of the least volatile metals LaB is then more stable than CaBg, in spite of their identical parameters. 

Vapor fed aerosol flame synthesis (VAFS) the precursor is in gas phase by using volatile metal precursors such as chlorides. 

At the Department of Chemical Engineering new catalytically active materials have been produced by burning volatile metal compounds in a flame. This produces an aerosol of very small particles that can be collected on a filter. Especially if the particles are cooled very fast, it is possible to obtain a large area per gram of material. In the following, AI2O3 is produced by this method. 

Spycher, N. and Reed, M. (1989) Evolution of a Broadlands-type epithermal ore fluids along alternative P-T paths Implications for the transport and deposition ofba.se precious and volatile metals. Econ. Geol, 84, 328-359. 

Hazardous waste burning incinerators, cement kilns, and LWAKs do not follow a tiered approach to regulate the release of toxic metals into the atmosphere. The MACT rule finalized numerical emission standards for three categories of metals mercury, low-volatile metals (arsenic, beryllium, and chromium), and semivolatile metals (lead and cadmium). Units must meet emission standards for the amount of metals emitted. For example, a new cement kiln must meet an emission limit of 120pg/m3 of mercury, 54pg/m3 of low-volatile metals, and 180 pg/m3 of semivolatile metals. 

The rule proposes emission standards for dioxins, furans, mercury, cadmium, lead, PM, hydrochloric acid, chlorine, carbon monoxide, hydrocarbons, and several low-volatile metals. It also proposes a new comparable fuels exclusion and makes significant changes to the existing combustion regulations. 

Low-volatile metals (arsenic + beryllium + chromium) 92 pg/dscm 2.1 E-5 lb/MMBtu and 56 flg/dscm 9.5 E-5 lb/MMBtu and llOpg/dscm 380 pg/dscm 1.26 E-4 lb/MMBtu or 370pg/dscm depending on Btu content of hazardous TCI standard as surrogate... 

Most of the work initially was with the more volatile transition metals, i.e. the first row metals plus palladium, silver and gold, because these were easy to evaporate in reasonable quantities in simple apparatus. However, efforts to use the less volatile metals of the second and third rows gained momentum. Skell used sublimation of resistively heated wires of molybdenum and tungsten to make the remarkably stable [Mo(rj4-C4H6)3] and [W(1j4-C4H6)3] (42). Green... 

Previously, intense beams of metal clusters could only be produced for the most volatile metals. The limitation arose from significant materials problems involved in the construction of high temperature ovens. The development of a source that utilizes laser vaporization and subsequent condensation in a rapidly flowing gas eliminated the materials problem and has enabled just about any material to be studi ed(la,8). 

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