Chemical elements
  Tungsten
    Isotopes
    Energy
    Production
    Preparation
    Application
    Physical Properties
    Chemical Properties
    Compounds
      Tungsten Hexafluoride
      Tungsten Oxyfluorides
      Tungsten Dichloride
      Double Chlorides of Trivalent Tungsten
      Tungsten Tetrachloride
      Tungsten Pentachloride
      Tungsten Hexachloride
      Tungsten Oxychlorides
      Tungsten Dibromide
      Tungsten Pentabromide
      Tungsten Hexabromide
      Tungsten Chlorobromides
      Tungsten Oxybromides
      Tungsten Di-iodide
      Tungsten Tetra-iodide
      Tungsten Dioxide
      Ditungsten Pentoxide
      Tungsten Trioxide
      Tungstic Acid
      Aluminium Tungstates
      Ammonium Tungstates
      Antimony Tungstates
      Barium Tungstates
      Normal Bismuth Tungstate
      Cadmium Tungstates
      Calcium Tungstates
      Cerium Tungstate
      Chromium Tungstates
      Cobalt Tungstates
      Copper Tungstates
      Indium Tungstate
      Iron Tungstates
      Lanthanum Tungstate
      Lead Tungstates
      Lithium Tungstates
      Magnesium Tungstates
      Manganese Tungstates
      Mercury Tungstates
      Neodymium Tungstate
      Nickel Tungstates
      Platinum Tungstates
      Potassium Tungstates
      Praseodymium Tungstate
      Rubidium Tungstates
      Samarium Tungstate
      Silver Tungstates
      Sodium Tungstates
      Strontium Tungstates
      Thallium Tungstates
      Tin Tungstates
      Uranium Tungstate
      Ytterbium Tungstates
      Yttrium Tungstate
      Zinc Tungstates
      Metatungstic Acid
      Ammonium Metatungstate
      Barium Metatungstate
      Cadmium Metatungstate
      Calcium Metatungstate
      Cerium Metatungstate
      Cobalt Metatungstate
      Lead Metatungstate
      Magnesium Metatungstate
      Mercurous Metatungstate
      Nickel Metatungstate
      Potassium Metatungstate
      Rubidium Metatungstate
      Samarium Metatungstate
      Silver Metatungstate
      Sodium Metatungstate
      Strontium Metatungstate
      Thallous Metatungstate
      Zinc Metatungstate
      Pertungstic Acid
      Tungsten Bronzes
      Potassium Tungsten Bronze
      Lithium Tungsten Bronze
      Lithium Potassium Tungsten Bronze
      Sodium tungsten bronzes
      Tungsten Disulphide
      Tungsten Trisulphide
      Thiotungstates
      Tungsten Diselenide
      Tungsten Triselenide
      Tungsten Phosphides
      Tungsten Diphosphide
      Tritungsten Tetraphosphide
      Tungsten Monophosphide
      Tungsten Subphosphide
      Phosphotungstic Acids
      12-Tungstophosphoric Acid
      11-Tungstophosphates
      21:2-Tungstophosphoric Acid
      10-Tungstophosphoric Acid
      9-Tungstophosphoric Acid
      17:2-Tungstophosphates
      3-Tungstophosphates
      Hypophosphotungstates
      Tungsten Diarsenide
      Tungsten Chloro-arsenide
      12-Tungsto-arsenates
      11-Tungsto-arsenates
      9-Tungsto-arsenic Acid
      17:2-Tungsto-arsenates
      Tungsto-arsenites
      Tritungsten Carbide
      Ditungsten Carbide
      Tungsten Monocarbide
      Tungsten Iron Carbides
      Tungstocyanic Acid
      Ammonium Tungstocyanide
      Calcium Tungstocyanide
      Cadmium Tungstocyanide
      Caesium Tungstocyanide
      Lead Tungstocyanide
      Magnesium Tungstocyanide
      Manganese Tungstocyanide
      Potassium Tungstocyanide
      Rubidium Tungstocyanide
      Silver Tungstocyanide
      Sodium Tungstocyanide
      Strontium Tungstocyanide
      Thallium Tungstocyanide
      Zinc Tungstocyanide
      Tungsticyanic Acid
      Tungsten Sesquisilicide
      Tungsten Disilicide
      Tungsten Trisilicide
      12-Tungstosilicic Acid
      Iso-12-tungstosilicic Acid
      10-Tungstosilicates
      Tungsten Boride
      12-Tungstoboric Acid
      Iso-12-tungstoboric Acid
    Alloys
    PDB 1aor-2rav
    PDB 2rb5-6fit

Tungsten Dioxide, WO2






Tungsten Dioxide, WO2, may be obtained as a brown amorphous powder by heating the trioxide to dull redness in a current of hydrogen. The residue remains in a stable condition, if allowed to cool in contact with hydrogen, for about twenty-four hours, but it is difficult to obtain the pure dioxide by this means, as reduction is liable to proceed further unless the temperature is carefully regulated. It may also be produced by heating tungsten di-iodide to 500° C. in a current of carbon dioxide, by acting on the tetrachloride with water, or by heating a mixture of ammonium chloride and normal potassium tungstate, the residue being well washed with water. In the wet way it is obtained as copper-red spangles by the addition of moderately strong hydrochloric acid and zinc to tungsten trioxide, to one of its hydrates, or to sodium met atungst ate.

The crystalline form has been obtained by heating lithium para-tungstate in a current of hydrogen at about the melting-point of glass for forty-five minutes. The product, after cooling, was treated successively with boiling water, concentrated hydrochloric acid, and lithium hydroxide solution, and then very carefully washed with warm water; it remains as an opaque, brown, micro-crystalline powder, with a metallic lustre.

The density of tungsten dioxide, according to Karsten, is 12.1109. It is stable in the air but is readily oxidised. Heated in oxygen, it yields the trioxide; at 500° C. in nitrous oxide or nitric oxide, the blue oxide, W2O5, results, while nitrogen peroxide yields the trioxide. The following thermal values have been determined:

W + O2 = WO2 + 127,900 calories.
4WO2 + O2 = 2W2O5 + 125,200 calories.
2W2O5 + O2 = 4WO3 + 140,400 calories.

Heated in chlorine, the yellow oxychloride, WO2Cl2, is obtained. Tungsten dioxide thus acts as a powerful reducer, and will convert mercuric and cupric salts to the mercurous and cuprous condition, and precipitate the metal from ammoniacal silver solutions. The amorphous variety is soluble in hydrochloric and sulphuric acids, yielding red solutions which on standing undergo partial oxidation with loss of colour; the crystalline dioxide is unacted upon, even by the hot concentrated acids. Nitric acid has a slow oxidising action. Concentrated alkali solutions dissolve the amorphous oxide, with formation of the tungstate and liberation of hydrogen, but have no action on the crystalline variety.

Tungsten dioxide is reduced to the metal by heating with carbon to about 1020° C.

The corresponding hydroxide, W(OH)4, has been prepared by the electrolytic reduction of solutions of tungsten trioxide in hydrochloric or hydrofluoric acid. It is a brown powder, insoluble in sodium hydroxide, sulphuric acid, or acetic acid, but soluble in concentrated hydrochloric acid, yielding a greenish solution which rapidly becomes blue owing to oxidation of tetravalent tungsten to the pentavalent condition.


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