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 Bronzes






The compounds known as tungsten bronzes are reduction products of the tungstates of the alkali and alkaline earth metals. Their exact constitution is not known, but it is generally recognised that the molecule contains several hexavalent tungsten atoms and one tetravalent tungsten atom, and may be represented by the formula R2O.(WO3)x.WO2. The empirical formula accordingly becomes R2.(WO3)x+1.

The substances have been designated as tungsten bronzes because, owing to their remarkable properties, they may be used as substitutes for bronze powders. They all possess extremely vivid colours and are quite insoluble in water. Strong acids, including hydrofluoric acid, do not attack them; even hot aqua regia has only slight action. They are decomposed, however, by fusion with alkali, sulphur, ammonium persulphate, or ammonium hydrogen sulphate.

The bronzes may be obtained by the following methods:
  1. Reduction of an acid tungstate by heating in hydrogen4 or coal gas, or by fusion with metallic tin, zinc, or iron.
  2. Electrolytic reduction of a fused acid tungstate; or of a fused mixture of tungstic acid with the requisite quantity of a metallic carbonate; or of a solution of tungstic acid in a fused mixture of alkali chlorides, the ratio of tungstic acid to chloride being greater than 1:2.
  3. Synthesis by fusing together a metallic tungstate, either acid or normal, with tungsten dioxide, in absence of air.
The bronzes are obtained in the crystalline form, generally as cubes or needles, and exhibit colours ranging from golden yellow to violet and dark blue, a metallic lustre also being sometimes evident. The colour sometimes varies according to whether the bronze is dry or moist, and suspensions of a finely powdered bronze often show by transmitted light the colour which is complementary to its usual colour. The bronzes show metallic properties in being of high density, 6.5 to 7.5, and excellent conductors of electricity. The difficulties which are encountered in the analysis of the tungstates are enhanced in the case of the bronzes by their insolubility and resistance to ordinary reagents. The difficulty of determining whether a product is homogeneous or not, and the fact that the same method of preparation will sometimes give totally different products when repeated, lead to doubt as to whether many of the bronzes described in the literature are definite compounds. For example, von Knorre, by fusing together equal molecular proportions of sodium and potassium paratungstates, and heating the mass to redness in hydrogen, obtained on one occasion a purple- red sodium-potassium bronze to which he ascribed the composition 2Na4W5O15.5K2W4O12, and on another occasion a darker red bronze of composition 2Na2W3O9.3K2W4O12.

The bronzes are generally analysed by first oxidising completely to tungstate and then determining the amount of metal and tungstic acid in the product. It is therefore necessary that the oxidation should be really complete and not merely superficial as when the bronze is heated in the air - a method which has sometimes been employed. Wohler suggested heating the bronze with sulphur, decomposing the mass with aqua regia, and estimating the alkali metal and tungstic acid in separate portions of the liquid. A more satisfactory method is due to Philipp.2 The finely powdered bronze is boiled with a large excess of ammoniacal silver nitrate solution, and silver is precipitated which is ignited and weighed. The silver always contains a little tungstic acid, which is left as a residue on treating with nitric acid and can be weighed. The tungsten and sodium are estimated in the filtrate from the silver. In this reaction the quantity of silver precipitated is always proportional to the amount of oxygen necessary for the complete oxidation of the bronze, so that the ratio WO2:WO3 is accurately obtained. If the bronze is rich in tungsten it is necessary to heat the mixture to about 120° C. in order to obtain complete decomposition. This reduction of silver nitrate by bronzes is remarkable in view of their stability towards ordinary oxidising agents.


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