Chemical elements
  Arsenic
      Occurrence
      Ubiquity
      History
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
      Aluminium Arsenide
      Antimony Arsenides
      Barium Arsenide
      Bismuth Arsenides
      Cadmium Arsenides
      Calcium Arsenide
      Cerium Arsenide
      Chromium Arsenides
      Cobalt Arsenides
      Copper Arsenides
      Gold Arsenides
      Iridium Arsenide
      Iron Arsenides
      Lead Arsenides
      Lithium Arsenide
      Magnesium Arsenide
      Manganese Arsenides
      Mercury Arsenides
      Molybdenum Arsenide
      Nickel Arsenides
      Niobium Arsenide
      Palladium Di-arsenide
      Platinum Arsenides
      Potassium Arsenides
      Rhodium Arsenide
      Ruthenium Arsenide
      Silver Arsenides
      Sodium Arsenide
      Strontium Arsenide
      Thallium Arsenide
      Tin Arsenides
      Tungsten Arsenide
      Uranium Arsenide
      Zinc Arsenides
      Arsenic Subhydride
      Arsenic Monohydride
      Arsenic Trihydride
      Arsenic Trifluoride
      Arsenic Pentafluoride
      Arsenic Nitrosyl Hexafluoride
      Arsenic Trichloride
      Arsenic Oxychloride
      Arsenic Pentachloride
      Arsenic Tribromide
      Arsenic Oxybromide
      Arsenic Moniodide
      Arsenic Diiodide
      Arsenic Triiodide
      Arsenic Pentiodide
      Arsenic Suboxide
      Arsenious Oxide
      Aluminium Arsenite
      Ammonium Arsenites
      Antimony Arsenite
      Barium Arsenites
      Beryllium Arsenite
      Bismuth Arsenite
      Cadmium Arsenites
      Calcium Arsenites
      Chromic Arsenite
      Cobalt Arsenites
      Copper Arsenites
      Gold Arsenites
      Iron Arsenites
      Lead Arsenites
      Lithium Arsenite
      Magnesium Arsenites
      Manganese Arsenites
      Mercury Arsenites
      Nickel Arsenites
      Palladium Pyroarsenite
      Platinum Arsenites
      Potassium Arsenites
      Arsenites of Rare Earth Metals
      Rubidium Metarsenite
      Silver Arsenites
      Sodium Arsenites
      Strontium Arsenites
      Thallous Orthoarsenite
      Tin Arsenites
      Titanyl Tetrarsenite
      Tungsto-arsenites
      Uranyl Metarsenite
      Zinc Arsenites
      Zirconium Arsenite
      Arsenic Tetroxide
      Arsenic Pentoxide
      Aluminium Arsenates
      Ammonium Arsenates
      Barium Arsenates
      Beryllium Arsenates
      Bismuth Arsenates
      Cadmium Arsenates
      Caesium Arsenate
      Calcium Arsenates
      Chromium Arsenates
      Cobalt Arsenates
      Copper Arsenates
      Hydroxylamine Orthoarsenate
      Iron Arsenates
      Lead Arsenates
      Lithium Arsenates
      Magnesium Arsenates
      Manganese Arsenates
      Mercury Arsenates
      Molybdenum Arsenates
      Nickel Arsenates
      Palladium Arsenate
      Platinic Arsenate
      Potassium Arsenates
      Rare Earth Metals Arsenates
      Rhodium Arsenate
      Rubidium Arsenates
      Silver Arsenates
      Sodium Arsenates
      Strontium Arsenates
      Thallium Arsenates
      Thorium Arsenates
      Tin Arsenates
      Titanyl Arsenate
      Tungsto-arsenic Acids
      Uranium Arsenates
      Vanado-arsenates
      Zinc Arsenates
      Zirconium Arsenates
      Perarsenates
      Arsenic and Sulphur
      Arsenic Subsulphide
      Tetrarsenic Trisulphide
      Arsenic Disulphide
      Arsenic Trisulphide
      Arsenic Pentasulphide
      Thioarsenates
      Ammonium Thioarsenates
      Antimony Thioarsenate
      Barium Thioarsenates
      Beryllium Thioarsenate
      Bismuth Thioarsenate
      Cadmium Thioarsenates
      Calcium Thioarsenates
      Cerium Thioarsenates
      Chromium Thioarsenate
      Cobalt Thioarsenate
      Copper Thioarsenates
      Gold Thioarsenates
      Iron Thioarsenates
      Lead Thioarsenates
      Lithium Thioarsenates
      Magnesium Thioarsenates
      Manganese Thioarsenates
      Mercury Thioarsenates
      Molybdenum Thioarsenates
      Nickel Thioarsenates
      Platinic Thioarsenate
      Potassium Thioarsenates
      Silver Thioarsenates
      Sodium Thioarsenates
      Strontium Thioarsenates
      Thallium Orthothioarsenate
      Tin Thioarsenates
      Uranyl Thioarsenate
      Yttrium Thioarsenate
      Zinc Thioarsenates
      Zirconium Thioarsenate
      Trioxythioarsenic Acid
      Dioxydithioarsenic Acid
      Oxytrithioarsenic Acid
      Arsenic Monosulphatotrioxide
      Arsenic Disulphatotrioxide
      Arsenic Trisulphatotrioxide
      Arsenic Tetrasulphatotrioxide
      Arsenic Hexasulphatotrioxide
      Arsenic Octasulphatotrioxide
      Complex salts of Sulphato-compounds of Arsenic
      Arsenic Nitride
      Arsenic Imide
      Arsenic Amide
      Arsenic Phosphides
      Arsenic oxyphosphides
      Arsenic Phosphate
      Arsenic Thiophosphate
      Arsenic Tricarbide
      Arsenic Pentasilicide
      Boron Arsenate
    Detection of Arsenic
    Estimation of Arsenic
    Physiological Properties
    PDB 1b92-1ihu
    PDB 1ii0-1tnd
    PDB 1tql-2hmh
    PDB 2hx2-2xnq
    PDB 2xod-3htw
    PDB 3hzf-3od5
    PDB 3ouu-9nse

Iron Arsenides






The system Fe-As has been investigated by Friedrich, alloys containing up to 56 per cent. As having been examined. The following compounds are indicated on the freezing point curve: Fe2As, Fe3As2, FeAs, and possibly Fe5As4. Thus the curve falls from the freezing point of iron (1535° C.) to a eutectic point at 30 per cent. As and 835° C., and rises to a maximum at 40.1 per cent. (Fe2As) and 919° C. Less distinct maxima occur at 51.7 per cent. As (i.e. Fe5As4) and 964° C., and at 57.3 per cent. As (i.e. FeAs) and 1031° C., the latter point being obtained by extrapolation of the curve of solidification times. A reaction between the solid products occurs at 800° C. in all alloys containing 40 to 56 per cent. As, the maximum development of heat taking place with 47.2 per cent., corresponding with the formation of Fe3As2.

The above conclusions were confirmed by micrographic examination of the alloys, which were etched by means of a hot solution of iodine in potassium iodide. Alloys containing more than 40 per cent. As were non-magnetic. Those formed in the neighbourhood of a maximum were brittle. A study of the E.M.F. diagram of Fe-As alloys containing 6 to 56 per cent. As indicated the formation of Fe2As and Fe5As4. The effect of adding small quantities of arsenic (up to 8 per cent.) to iron was examined by Oberhoffer and Gallaschik, who observed that on cooling the change point of the δ mixed crystals with liquid to y mixed crystals (which they recorded as 1440° C.) was depressed 80° by the presence of 0.5 per cent. As and remained constant with further addition. The change point on heating was not affected. With more than 3 per cent. As no change point could be detected. The maximum solubility of arsenic in δ-iron is 0.9 per cent, and in γ-iron 6.8 per cent. Micro-examination confirmed the thermal data and revealed homogeneous mixed crystals up to 6.67 per cent. As. The alloy with 7.29 per cent. As showed traces of eutectic.

A comprehensive X-ray investigation has been made of Fe-As alloys containing up to 56.9 per cent. As, the highest content obtainable. The alloys were prepared by dropping pellets of arsenic into molten pure iron contained in a magnesia crucible in an atmosphere of nitrogen. The displacement of Fe lines indicated that α-iron will hold approximately 5 per cent, of arsenic in solution at room temperature. With increasing arsenic the first compound indicated, Fe2As, has a simple tetragonal lattice with a = 3.627 A. and c = 5.973 A., two molecules forming the unit cell. The As atom is surrounded by 4Fe at 2.40 A., 4Fe at 2.60 A. and 1Fe at 2.41 A. The Fe-As distances are less than those calculated from the normal atomic radii. The arsenide Fe3As2 could not be found in slowly cooled alloys, but quenched alloys of the proper composition, when examined microscopically, presented an appearance suggesting high-temperature stability (above 795° C.) for Fe3As2, the compound breaking down at lower temperatures into Fe2As and FeAs. The arsenide FeAs has a simple orthorhombic lattice with a = 3.366 A., b = 6.016 A. and c = 5.428 A., each unit cell containing four molecules. The lattice structure resembles that of the corresponding cobalt arsenide. The crystal structure of various minerals containing iron arsenide, for example, lollingite, FeAs2, safflorite (Co, Fe)As2, rammelsbergite (Ni, Co, Fe)As2, and certain arseno-sulphides, including arsenopyrite, has been investigated. The conclusions as regards lollingite are not in agreement, and further study is desirable. Buerger gives the following structure: space group, Vh12; two molecules in unit cell, with dimensions a = 2.85, b = 5.25 and c = 5.92 A.; the effective As radius 1.23 A.; Fe-As = 2.35 and Fe radius 1.12 A., as in marcasite, with which mineral lollingite is isomorphous.

A metallographic and analytical examination of the ternary system Ni-Fe-As shows the formation of the crystalline double arsenides 2Fe2As.Ni5As2 and 4Fe2As.Ni5As2.


Iron Subarsenide, Fe2As

Iron Subarsenide, Fe2As, is formed by melting a mixture of the two elements in the requisite proportions. It melts at 919° C. A product of the same composition is obtained when a mixture of borax and arsenopyrite is heated in a carbon crucible and the product digested with hydrochloric acid.

The conditions under which the formation of the arsenides Fe3As2 and Fe5As4 may occur. The former was obtained by Brukl as a black precipitate by the action of arsine on an alcoholic solution of ferrous ammonium sulphate. The product was only slightly attacked by concentrated hydrochloric or sulphuric acid but was soluble in nitric acid, aqua regia and bromine water.

Iron Monarsenide, FeAs

Iron Monarsenide, FeAs, may be obtained by heating iron in a current of arsenic vapour at 835° to 380° C.; by heating a mixture of the elements in a bomb tube at 680° C., or a mixture of iron, arsenious oxide and carbon in an electric arc furnace; by the action of fused potassium cyanide on iron arsenate; by reduction of the di-arsenide at 680° C. in a current of hydrogen; or by dropping a solution of a ferrous salt into an atmosphere of arsine.

It forms silver-white, rhombic crystals, of density 7.83, and melting point 1020° C. according to Hilpert and Dieckmann or 1031° C. according to Friedrich. It is non-magnetic. Steel-grey crystals of the arsenide of density 7.94 have been found associated with tin sulphide in the hearth of an old tin smelting furnace in Cornwall.

The product, of density 7.22, which results when iron is heated in arsenic vapour at 395° to 415° C. agrees in composition with the formula Fe2As3. The existence of such an arsenide has not been confirmed, however, although some forms of lollingite approach this composition.

Iron Di-arsenide, FeAs2

Iron Di-arsenide, FeAs2, occurs as the minerals lollingite and arsenoferrite, and may be made artificially by heating iron in arsenic vapour at 480° to 618° C., or by heating a finely powdered mixture of the elements in a bomb tube at 700° to 750° C. After treatment with dilute hydrochloric acid the pure di-arsenide is obtained as a silver-grey microcrystalline powder of density 7.38. It melts at 980° to 1040° C. It is insoluble in hydrochloric acid, whether dilute or concentrated, but is slowly oxidised by nitric acid, yielding arsenic acid. Heated with concentrated sulphuric acid, sulphur dioxide is evolved. When heated in air it burns, yielding arsenious oxide and ferric oxide. It is non-magnetic.

When the mineral lollingite is heated in vacuo it loses 23.8 per cent, of arsenic, the residue containing two unidentified constituents. Arsenopyrite, treated similarly, decomposes at 675° to 685° C.
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