Chemical elements
  Uranium
    Isotopes
    Energy
    Production
    Application
    Physical Properties
    Chemical Properties
    Compounds
      Uranium Difluoride
      Uranium Tetrafluoride
      Uranous Oxyfluoride
      Uranium Hexafluoride
      Uranyl Fluoride
      Uranium Trichloride
      Uranium Tetrachloride
      Uranium Pentachloride
      Uranyl Chloride
      Uranyl Chlorate
      Uranyl Perchlorate
      Uranium Tetrabromide
      Uranyl Bromide
      Uranium Tetra-iodide
      Uranyl Iodide
      Uranyl Iodate
      Uranous Oxide
      Uranous Hydroxide
      Uranium Pentoxide
      Urano-uranic Oxide
      Uranium Trioxide
      Ammonium Diuranate
      Ammonium Hexa-uranate
      Hydroxylamine Uranate
      Hydroxylamine Potassio-uranate
      Barium Uranate
      Barium Diuranate
      Bismuth Uranate
      Iron Uranate
      Lithium Uranate
      Potassium Uranate
      Potassium Diuranate
      Potassium Tetra-uranate
      Potassium Hexa-uranate
      Rubidium Uranate
      Silver Diuranate
      Sodium Uranate
      Sodium Diuranate
      Sodium Triuranate
      Sodium Penta-uranate
      Strontium Uranate
      Zinc Uranate
      Peruranic acid
      Ammonium Peruranate
      Barium Peruranates
      Lithium Peruranate
      Nickel Peruranate
      Potassium Peruranate
      Sodium Peruranates
      Uranium Monosulphide
      Uranium Sesquisulphide
      Uranium Disulphide
      Uranium Oxysulphide
      Uranyl Sulphide
      Uranium Sulphite
      Uranyl Sulphite
      Complex Uranyl Sulphites
      Uranium Sulphate
      Uranium Dithionates
      Uranyl Sulphate
      Uranyl Pyrosulphate
      Uranyl Thiosulphate
      Uranyl Dithionate
      Uranium Sesquiselenide
      Uranium Diselenide
      Uranyl Selenide
      Uranyl Selenite
      Uranyl Selenate
      Uranium Telluride
      Uranium Nitrides
      Uranous Nitrate
      Uranyl Nitrate
      Uranium Monophosphide
      Uranous Phosphide
      Uranyl Hypophosphite
      Uranyl Phosphite
      Uranous Phosphates
      Uranyl Phosphates
      Complex Uranyl Phosphates
      Uranyl Aminophosphates
      Uranous Arsenide
      Uranyl Metarsenite
      Uranous Arsenate
      Uranyl Arsenates
      Complex Uranyl Arsenates
      Uranous Antimonide
      Uranous Antimonate
      Uranium Carbide
      Complex Uranyl Carbonates
      Ammonium Uranyl Carbonate
      Calcium Uranyl Carbonate
      Potassium Uranyl Carbonate
      Sodium Uranyl Carbonate
      Thallium Uranyl Carbonate
      Potassium Uranyl Ferrocyanide
      Uranyl Platinocyanide
      Uranyl Cyanate
      Uranyl Thiocyanate
      Uranium Silicide
      Uranium Boride
      Uranyl Perborate
    PDB 1anv-3pu4

Uranous Oxide, UO2






Uranous Oxide, Uranium Dioxide, UO2, owing to its stability and metallic appearance, was until 1842 thought to be the element. It may be obtained as a brown amorphous powder, usually pyrophoric, by reducing the green oxide, U3O8, or uranyl oxalate, by heating in a current of hydrogen; by igniting the higher oxides in an indifferent atmosphere, such as carbon dioxide or nitrogen; or by heating urano-uranic oxide with ammonium chloride, ammonium chloride and sulphur, or anhydrous oxalic acid. It is also produced by reducing uranyl sulphate or nitrate in hydrogen; or by heating together uranyl phosphate, potassium carbonate, and potassium cyanide; or by electrolysis of a solution of uranyl nitrate. It is obtained as a black powder by reducing an aqueous solution of uranyl chloride by means of powdered aluminium or magnesium.

Uranous oxide is also obtained in the form of black microscopic crystals when urano-uranic oxide is reduced with carbon or heated with a little hydrofluoric acid; when crystallised uranic hydroxide is heated in hydrogen; when uranyl chloride is heated with potassium in a current of hydrogen, or with a mixture of ammonium and sodium chlorides; or when the double chloride, Na2UCl6, is heated to redness in a moisture-laden stream of carbon dioxide. Especially fine black cubic crystals are obtained by fusing together 1 part of sodium diuranate and 4 parts of magnesium chloride. The amorphous form may be readily converted into the crystalline variety by fusion with borax, the product being washed with dilute hydrochloric acid, when jet-black octahedra are obtained.

A brick-red variety of uranous oxide has been obtained by calcining uranyl bromide in the air. It is very stable at high temperatures, and is converted to the black modification by heating in hydrogen without any appreciable loss of oxygen.

On a commercial scale uranous oxide is prepared by fusing at red heat a mixture of 35 parts of common salt and 20 parts of sodium uranate with 1 part of powdered charcoal, the heating being continued until the escape of gas ceases. After cooling, the mass is lixiviated with water, and the residue of uranous oxide is washed by decantation. By washing with 5 per cent, hydrochloric acid, any iron, aluminium, or vanadium compounds may be removed, and a commercial product of purity equivalent to 97 per cent. U3O8 is obtained. If the uranous oxide is required for the production of ferro-uranium, the complete removal of iron is not necessary.

Uranous oxide exists in various forms, depending, as indicated above, on the mode of formation. The crystals are usually regular in form, of density 10.95 to 11.0 at 4° C., and are isomorphous with those of cerium and thorium dioxides. The specific heat, according to Regnault, is 0.0619. The magnetisability of uranous oxide is greater than that of the metal or of the higher oxides, the magnetic susceptibility being +7.51×10-6. When heated in an atmosphere of nitrogen, the oxide melts at 2176° C. It is the most stable of the oxides of uranium at high temperatures, and in many respects behaves like an element. It cannot be reduced by heating in a current of hydrogen, but it is reduced by carbon at about 1500° C. It combines directly with chlorine and bromine at red heat, uranyl compounds being produced. When heated in oxygen, it is readily oxidised, the action commencing at about 185° C., and the only product is urano-uranic oxide. The heat of the reaction is as follows:

3UO2 + 2O = U3O8 + 75,300 calories.

Uranous oxide is only difficultly soluble in hydrochloric and sulphuric acids, even when concentrated. With the latter acid, insoluble uranium sulphate is formed. It readily dissolves, however, in dilute nitric acid forming uranyl nitrate; it is also soluble in aqua regia. The amounts of the oxide dissolving in these acids in a given time vary widely with the mode of preparation of the oxide.

It resembles the dioxide of molybdenum in being able to reduce salts of silver in ammoniacal solution, with precipitation of silver, thus:

UO2 + 2Ag + 2OH' → UO3 + 2Ag + H2O.


Colloidal Uranous Oxide

During the electrolysis of a solution of uranyl chloride a black reduction product is precipitated at the cathode. This precipitate dissolves in water, forming a dark-coloured colloidal solution, which by titration with potassium permanganate, before and after reduction with zinc, has been shown to contain uranous oxide. A similar solution may be obtained by the reduction of uranyl chloride by zinc or copper in dilute acid solution. When very dilute, the solution has a yellow tinge. In an electric field it becomes decolorised at the anode and precipitation takes place at the cathode. It behaves as a typical positive colloid with coagulating agents.
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