Chloride metal, volatile

Trimethylchlorosilane TCS 14 readily transforms metal oxides such as ZnO, MgO, MnO, BeO, AI2O3, or Ti02 and oxides of transition metals such as SmO or Iu203 into the corresponding reactive anhydrous chlorides and volatile HMDSO 7 (b.p. 100°C) (Scheme 13.6). 

Demet X procedure simply consists of an oxidation at elevated temperature, both the New Demet and the Demet III process has a sulfiding step which transforms the metal oxides to insoluble sulfides. In Demet III the sulfiding step is followed by a partial oxidation step. This oxidation is carefully controlled to produce metal sulfates and sulfides which can be directly removed by washing or be transferred into soluble compounds by the reductive and oxidative washes used in this procedure. In the New Demet process the sulfiding step is followed by chlorination which results in a transformation of the sulfides into washable chlorides. Since vanadium chlorides are volatile, most of the vanadium removal using this procedure occurs in the gas phase. In the Demet X procedure, the vanadium oxides formed are water soluble or can be transformed into water soluble forms by aqueous treatments. In contrast the nickel oxides are insoluble in water. 

Treatment of impure gold is largely via the Miller process (30) in which chlorine is bubbled through the molten metal and converts the base metals to chlorides, which volatilize. Silver is converted to the chloride, which is molten and can be poured. The remaining gold is less pure (99.6%) than that produced by the Wohlwill process and may require additional treatment such as electrolysis. If platinum-group metals (qv) are present, the chlorine process is unsuitable. 

Methylene chloride, a volatile chlorinated hydrocarbon, is used as a paint remover, metal degreaser, and aerosol propellant. The odor threshold for methylene chloride in the air is 100 ppm. According to Shelton (1989), it has been shown to induce tumors in mice. 

This "outlandish creature was Mendeleeff, the Russian prophet to whom the world listened. Men went in search of the missing elements he described. In the bowels of the earth, in the flue dust of factories, in the waters of the oceans, and in every conceivable corner they hunted. Summers and winters rolled by while Mendeleeff kept preaching the truth of his visions. Then, in 1875, the first of the new elements he foretold was discovered. In a zinc ore mined in the Pyrenees, Lecoq de Roisbaudran came upon the hidden eka-aluminum. This Frenchman analyzed and reanalyzed the mineral and studied the new element m every possible way to make sure there was no error. Mendeleeff must indeed be a prophet For here was a metal exactly similar to his eka-aluminum. It yielded its secret of two new lines to the spectroscope, it was easily fusible, it could form alums, its chloride was volatile. Every one of these characteristics had been accurately foretold by the Russian. Lecoq named it gallium after the ancient name of his native country. 

Magnesium metal is produced primarily by either thermal or electrochemical processes. The thermal process operates at temperatures over 1200°C and utilizes a metallothermic reduction in which magnesium metal volatilizes from MgO and is condensed to recover the metal. The electrochemical process is based on the electrolysis of fused anhydrous magnesium chloride. 

Andrews found that dry chlorine has no action at the ordinary temperature on zinc, iron filings, or reduced copper, but combines at once with arsenic, antimony, and phosphorus, and slowly with mercury. He points out that arsenic, antimony, and phosphorus chlorides are volatile, and mercury is a liquid. Gore found that dry liquid hydrogen chloride has no action on marble and many metals. Wanklyn found that sodium can be fused and shaken with chlorine gas (which must have been dry, although he does not say so) without reaction occurring. R. Cowper, o was unaware of Andrews or Wanklyn s work, found that dry chlorine did not react with sodium, Dutch metal, zinc, or magnesium, and with silver only slowly, but it tarnished bismuth, attacked tin readily, and at once combined with arsenic and antimony. U. Kreusler, who was unaware of previous work, confirmed these results. Parnell s experiments were confirmed and extended by R. E. Hughes, who was also unaware of earlier work. 

The higher chlorides are volatile and reduce directly in hydrogen, depositing both niobium metal and niobium trichloride on the walls of the furnace tube, away from the reaction trays. Besides the inconvenience of this mass transfer effect, the niobium metal powder deposited from reduction of the gaseous higher chlorides tends to be very finely divided and therefore pyrophoric on exposure to air. Nevertheless, the product of the trichloride reduction reaction, has been handled satisfactorily, and has given ductile massive metal on sintering. 

A century ago, Mendeltef used his new periodic table to predict the properties of ekasilicon , later identified as germanium. Some of the predicted properties were metallic character and high m.p. for the element formation of an oxide MOj and of a volatile chloride MCI4. 

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... 

Reaction with Meta/ Oxides. The reaction of hydrogen chloride with the transition-metal oxides at elevated temperatures has been studied extensively. Fe202 reacts readily at temperatures as low as 300°C to produce FeCl and water. The heavier transition-metal oxides require a higher reaction temperature, and the primary reaction product is usually the corresponding oxychlorides. Similar reactions are reported for many other metal oxides, such as Sb202, BeO, AI2O2, andTi02, which lead to the formation of relatively volatile chlorides or oxychlorides. 

The iodides of the alkaU metals and those of the heavier alkaline earths are resistant to oxygen on heating, but most others can be roasted to oxide in air and oxygen. The vapors of the most volatile iodides, such as those of aluminum and titanium(II) actually bum in air. The iodides resemble the sulfides in this respect, with the important difference that the iodine is volatilized, not as an oxide, but as the free element, which can be recovered as such. Chlorine and bromine readily displace iodine from the iodides, converting them to the corresponding chlorides and bromides. 

Many mercury compounds are labile and easily decomposed by light, heat, and reducing agents. In the presence of organic compounds of weak reducing activity, such as amines (qv), aldehydes (qv), and ketones (qv), compounds of lower oxidation state and mercury metal are often formed. Only a few mercury compounds, eg, mercuric bromide/77< 5 7-/7, mercurous chloride, mercuric s A ide[1344-48-5] and mercurous iodide [15385-57-6] are volatile and capable of purification by sublimation. This innate lack of stabiUty in mercury compounds makes the recovery of mercury from various wastes that accumulate with the production of compounds of economic and commercial importance relatively easy (see Recycling). 

Miscellaneous. Electron beams can be used to decompose a gas such as silver chloride and simultaneously deposit silver metal. An older technique is the thermal decomposition of volatile and extremely toxic gases such as nickel carbonyl [13463-39-3] Ni(CO)4, to form dense deposits or dendritic coatings by modification of coating parameters. 

Chlorination. In some instances, the extraction of a pure metal is more easily achieved from the chloride than from the oxide. Oxide ores and concentrates react at high temperature with chlorine gas to produce volatile chlorides of the metal. This reaction can be used for common nonferrous metals, but it is particularly useful for refractory metals like titanium (see Titanium and titanium alloys) and 2irconium (see Zirconium and zirconium compounds), and for reactive metals like aluminum. 

The reaction of chlorine gas with a mixture of ore and carbon at 500—1000°C yields volatile chlorides of niobium and other metals. These can be separated by fractional condensation (21—23). This method, used on columbites, is less suited to the chlorination of pyrochlore because of the formation of nonvolatile alkaU and alkaline-earth chlorides which remain in the reaction 2one as a residue. The chlorination of ferroniobium, however, is used commercially. The product mixture of niobium pentachloride, iron chlorides, and chlorides of other impurities is passed through a heated column of sodium chloride pellets at 400°C to remove iron and aluminum by formation of a low melting eutectic compound which drains from the bottom of the column. The niobium pentachloride passes through the column and is selectively condensed the more volatile chlorides pass through the condenser in the off-gas. The niobium pentachloride then can be processed further. 

The residue, which contains Ir, Ru, and Os, is fused with sodium peroxide at 500°C, forming soluble sodium mthenate and sodium osmate. Reaction of these salts with chlorine produces volatile tetroxides, which are separated from the reaction medium by distillation and absorbed into hydrochloric acid. The osmium can then be separated from the mthenium by boiling the chloride solution with nitric acid. Osmium forms volatile osmium tetroxide mthenium remains in solution. Ruthenium and osmium can thus be separately purified and reduced to give the metals. 

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