Arsenic and Arsenides

Arsenic and Arsenides.—Appearance potentials for the negative ions As, AsJ, and As3, formed from As by dissociative resonance capture, have been measured, giving values of the standard heats of formation.615 

Deyris, J. Roy-Montreuil, A. Rouault, A. Krumbiigel-Nylund, J.-P. Senateur, R. Fruchart, and A. Michel, Compt. rend., 1974, 278, C, 237. 

A new cationic complex containing Hg—As bonds has been synthesized following equation (21). The products with X = NOj, PFe, or BFI are stable 

Arsenic and Arsenides.—Vapour-pressure and density measurements on the element up to 77 atm and 1400 K have led to the following thermodynamic 

The mixed phosphine-arsine (CF3)2PAsH2 is the product when trimethyl-iodosilane is displaced from a mixture of (CF 3)2PI and Me3SiAsH2. Although the compound decomposes to (CF3)2PH and a polymeric arsenic hydride on standing, it has been characterized and fully investigated. The diarsine analogue (CF3)2AsAsH2 has similarly been prepared but cannot be isolated because of lower stability. 

The compound Sn4As3 has been identified in the SnAs-Sn system. The high-temperature modification of V4AS3, according to powder diffraction data, is isotypic with Cr4As3, while the americium binary compounds AmAs, AmSb, and AmBi have the sodium chloride structure. 

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When arsine is passed over a heated metal, such as the alkali and alkaline earth metals, zinc or tin, the decomposition of the gas is accelerated and the arsenide of the metal is formed. If platinum is used, the removal of arsenic from the gas is complete.3 The action of sodium or potassium on arsine in liquid ammonia yields 4 the dihydrogen arsenide (MHgAs). Heated alkali hydroxides in the solid form quickly decompose the gas, forming arsenites, and at higher temperatures arsenates and arsenides of the metals.5 The aqueous and alcoholic solutions have no appreciable action.6 When the gas is passed over heated calcium oxide the amount of decomposition is not more than that due to the action of heat alone. Heated barium oxide, however, is converted into a dark brown mixture of barium arsenite and arsenate, hydrogen being liberated.7 The gas is absorbed by soda-lime.8... 

Phosphorus dissolves in arsenic trichloride on warming without reaction and is deposited on cooling.8 If the mixture is heated in the presence of aluminium chloride at 130° to 150° C. for 40 minutes, a brownish-red compound of composition A1As3C13 results,9 from which, however, aluminium chloride can readily be removed by water or ammonia, leaving a residue of finely divided black arsenic. If the compound is heated to 190° C. in the absence of air, it turns black as arsenic trichloride and aluminium chloride distil off and a bright grey mixture of arsenic and arsenide remains. It has been suggested that the arsenic is co-ordinatively bound, and that the compound may be /Ass... 

Cobalt is a metallic element (symbol Co atomic no. 27). It is an important constitnent of the cobalamins (vitamin B12) and is fonnd as arsenates and arsenides in natnrally occnrring minerals snch as erythrite, skntterndite, and smaltite. 

If antimony and arsenic are present ia the feed, copper and iron react to form the respective antimonides and arsenides known as speiss (specific gravity 6.0). If it is preferred to remove copper ia a speiss layer, the sulfur ia the siater must be reduced and the addition of scrap iron may be necessary to encourage speiss formation. Matte and speiss are usually sent to a copper smelter for recovery of the metals. 

Arsine is used for the preparation of gallium arsenide [1303-00-0] GaAs, (17), and there are numerous patents covering this subject (see Arsenic and ARSENIC alloys). The conversion of a monomeric arsinogaHane to gallium arsenide has also been described (18). GaUium arsenide has important appHcations in the field of optoelectronic and microwave devices (see Lasers Microwave technology Photodetectors). 

Arsenic and antimony are metalloids. They have been known in the pure state since ancient times because they are easily obtained from their ores (Fig. 15.3). In the elemental state, they are used primarily in the semiconductor industry and in the lead alloys used as electrodes in storage batteries. Gallium arsenide is used in lasers, including the lasers used in CD players. Metallic bismuth, with its large, weakly bonded atoms, has a low melting point and is used in alloys that serve as fire detectors in sprinkler systems the alloy melts when a fire breaks out nearby, and the sprinkler system is activated. Like ice, solid bismuth is less dense than the liquid. As a result, molten bismuth does not shrink when it solidifies in molds, and so it is used to make low-temperature castings. 

The radii in the lowest row of the table were obtained by a number of approximate considerations. For instance, if we assume the bismuth radius to bear the same ratio to the interatomic distance in elementary bismuth as in the case of arsenic and antimony, we obtain (Bi) = 1.16— 1.47 A. A similar conclusion is reached from a study of NiSb and NiBi (with the nickel arsenide structure). Although the structures of the aurous halides have not been determined, it may be pointed out that if they are assumed to be tetrahedral (B3 or Bi) the interatomic distances in the chloride, bromide, and iodide calculated from the observed densities1) are 2.52, 2.66, and 2.75 A, to be compared with 2.19, 2.66, and 2.78 A, respectively, from pur table. 

When colloids of metal sulfides, selenides, phosphides and arsenides are illxuninated in the presence of air, decomposition takes place. Metal ions migrate into solution and sulfate, selenite, phosphate or arsenate are formed. The process was first investigated in the case of colloidal CdS... 

Reactions with phosphorus, arsenic and antimony form phosphide, arsenide, and antimonide of potassium, respectively ... 

In his Elements of the Art of Assaying Metals, Johann Andreas Cramer pointed out the close association of bismuth with arsenic and cobalt. Every ore of Bismuth, said he, as is shewn by the chemical analysis, is reduced to the State of Ore by Arsenide For this goes out of it by Sublimation. You find m the same Ore that Kind of Earth that gives an azure Colour to Glasses, of which we have already spoken in the Article of Cobalt. Whence it is evident that the Ore of Bismuth may widiout Impropriety be called Cobalt of Bismuth The more, because you will find in any ore of Bismuth the same Principles as in Cobalt, only in a different Propoition (55). This close association of bismuth and cobalt m nature made it difficult for eaily chemists to distinguish between them (56). 

The list in Table 7.2 may appear incomplete to the modem chemist utilizing or studying chemical deposition e.g., only thioacetamide is noted as a sulphide source and selenides are not included. However, when we reflect that the vast bulk of the work carried out on CD concerned just sulphides, selenides and oxides, this old table might point the way to a major expansion of the CD technique, both for semiconductors and for other compounds. Further processing may be expected to extend the types of material even further. For example, arsenates and phosphates may be reducible in some cases to the better-known (to the semiconductor community) arsenides and phosphides. 

When heated under ordinary pressure, arsenic does not melt the metallic form volatilises at a dull red heat, while amorphous arsenic does so at a lower temperature. The sublimation temperatures are given on p. 32. Even at ordinary temperature the element possesses an appreciable vapour pressure, as may be shown 8 by enclosing pieces of arsenic and silver in a vessel, but not in contact with each other after some months the silver is found to be coated with a film of arsenide. Vapour pressure measurements of grey metallic arsenic and its liquid at temperatures up to 853° C. have been made the results, expressed in atmospheres, are as follows ... 

Cobalt Arsenides.—Cobalt alloys readily with arsenic and several compounds have been prepared. On the freezing point curve5 there is a eutectic point at 916° C. and 30 per cent. As, and maxima occur at 926° C., 959° C. and 1180° C., corresponding respectively with Co6As2 (33-7 per cent. As), Co2As (38-9 per cent. As) and CoAs (about 55 per... 

The arsenide Cu5As.2 has been prepared by passing a current of carbon dioxide and arsenic vapour over finely divided copper heated to the temperature of boiling sulphur 11 by the action of copper on arsenic trichloride or on arsenic dissolved in hydrochloric acid 12 and by the action of cuprous chloride on arsenic. Lustrous regular crystals of density 7-56 are obtained. These tarnish on exposure to air. When heated it loses arsenic and yields Cu3As, which at a higher temperature also decomposes. Cu5As2 dissolves in nitric acid. It is readily attacked by chlorine or bromine.13... 

Mercuric arsenide forms microscopic mamellated crystals. When dry it oxidises readily in the air to arsenious oxide and mercury. On heating it volatilises without melting, forming a sublimate of arsenic and mercury and a little arsenious oxide. The arsenide is therefore dried under diminished pressure. When heated with an alkyl iodide, a diarsonium mercuriodide of the type As2R6I2.2HgI2 is formed.8... 

The reaction commences at a temperature above 400° C., before the melting temperature is reached, and the fused product therefore always contains some arsenious oxide.1 When heated in hydrogen, the pentoxide is reduced first to arsenious oxide and then to free arsenic. Similar reduction occurs when it is heated with carbon or phosphorus with sulphur, arsenious sulphide is formed. Arsenic and metallic arsenides result when the pentoxide is heated with alkali metals,2 zinc, lead, iron or most other heavy metals mercury and silver react only at high temperature gold and platinum do not react. 

Many metals, including magnesium, aluminium,13 zinc, tin and iron,14 precipitate arsenic and liberate arsine from aqueous arsenic acid. When copper is placed in such a solution containing mineral acid, copper arsenide is formed on the metal 15 this reaction is employed under the... 

When hydrogen is allowed to react with an aqueous solution of an alkali arsenate containing ferric oxide at a temperature of 300° C. and under a pressure greater than 130 atmospheres, green crystals of scoro-dite are formed.1 If the action is prolonged, elementary arsenic and ferric arsenides are produced. 

The Reinsch Test.12 When a strip of polished copper foil is placed in a solution of arsenious acid a grey film is formed on the copper owing to deposition of arsenic and formation of copper arsenide, Cu5As2. The deposition occurs in the cold with concentrated solutions, but only on warming with dilute solutions. It is possible to detect by this means... 

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