Chemical elements
    Physical Properties
      Nickel Fluoride
      Nickel Dichloride
      Double Nickel Chlorides
      Nickel Dibromide
      Nickel Di-iodide
      Nickel Chlorate
      Nickel Perchlorate
      Nickel Bromate
      Nickel Iodate
      Tri-nickel Suboxide
      Nickel Suboxide
      Nickel Monoxide
      Nickel Dihydroxide
      Nickelo-nickelic Oxide
      Nickel Dioxide
      Nickel Subsulphide
      Nickel Monosulphide
      Nickel Sesquisulphide
      Tri-nickel Tetrasulphide
      Nickel Disulphide
      Nickel Tetrasulphide
      Nickel Sulphite
      Nickel Thiosulphate
      Nickel Dithionate
      Nickel Sulphate
      Nickel Subselenide
      Nickel Selenide
      Nickel Sesquiselenide
      Nickel Selenite
      Nickel Sesquitelluride
      Nickel Tellurite
      Nickel Chromate
      Nickel Dichromate
      Double Nickel Chromates
      Nickel Molybdate
      Nickel Nitride
      Nickel Azoimide
      Nickel Nitrite
      Nickel Nitrate
      Di-nickel Phosphide
      Nickel Sesquiphosphide
      Nickel Diphosphide
      Nickel Triphosphide
      Nickel Hypophosphite
      Nickel Phosphite
      Nickel Metaphosphate
      Nickel Orthophosphate
      Nickel Pyrophosphate
      Nickel Thio-orthophosphate
      Nickel Thiopyrophosphite
      Nickel Thiopyrophosphate
      Tri-nickel Diarsenide
      Nickel Arsenide
      Nickel Diarsenide
      Nickel Arsenite
      Nickel Orthoarsenate
      Nickel Antimonide
      Nickel Antimonate
      Nickel Thioantimonite
      Nickel Vanadate
      Nickel Carbide
      Nickel Tetracarbonyl
      Nickel Carbonate
      Nickel Monocyanide
      Nickel Cyanide
      Nickel Thiocyanate
      Nickel Thiocarbonate Hexammoniate
      Nickel Subsilicide
      Nickel Orthosilicate
      Nickel Monoboride
      Nickel Borates
    PDB 1a5n-1g2a
    PDB 1g3v-1mn0
    PDB 1mro-1s9b
    PDB 1scr-1xmk
    PDB 1xu1-2cg5
    PDB 2cqz-2jih
    PDB 2jk8-2v4b
    PDB 2vbq-3c2q
    PDB 3c6c-3h85
    PDB 3hdp-3kvb
    PDB 3l1m-3o00
    PDB 3o01-4ubp
    PDB 8icl-9ant

Nickel Dioxide, NiO2

Presumably the Nickel Dioxide, NiO2 described as nickel sesquioxide and obtained when nickel nitrate or chlorate is gently heated, or when potassium chlorate is fused with nickel chloride, really consists of the dioxide in intimate association with more or less nickel monoxide, according to circumstances (vide supra).

The existence of nickel dioxide was first indicated by Dufau, who prepared barium nickelite, BaO.2NiO2, by igniting nickel oxide and barium carbonate in an electric arc. The nickelite resulted as dark-coloured crystals of density 4.8 at 20° C. and attacked by water.

In the hydrated form, NiO2.xH2O, nickel dioxide is obtained by decomposing an aqueous solution of a nickel salt by warming with sodium or potassium hypochlorite, and by passing chlorine through a suspension of nickelous hydroxide in water. It also results when a neutral solution of nickel sulphate is electrolysed. In the literature it is frequently referred to and described as the hydrated sesqui-oxide.

The hydrated oxide readily dissolves in acids, yielding nickelous salts. It decomposes hydrochloric acid evolving chlorine, and hydrogen peroxide evolving oxygen, being itself reduced to nickel monoxide. With sulphurous acid the sulphite and dithionate are produced. With sulphuric acid oxygen is liberated, nickel sulphate resulting; with aqueous ammonia nitrogen is evolved. Acetic acid gives at first a brownish yellow colour which rapidly turns green.

The oxide is reduced by hydrogen, carbon monoxide, and by carbon. The reduction in an atmosphere of hydrogen begins at about 190° C. The oxide burns in fluorine, and when heated in hydrogen sulphide yields water and the monosulphide, NiS. Pellini (vide infra) ascribes the following graphical formula to the dioxide:

A compound of similar composition has been obtained by the action of hydrogen peroxide upon free nickel hydroxide or upon cooled nickel chloride solution to which potassium hydroxide in alcoholic solution is added. It is a greyish green substance giving all the reactions of hydrogen peroxide, and is quite different from the foregoing isomeride. Pellini suggests that it is a true peroxide, namely:

Numerous other substances described as oxides of nickel have been placed on record, and formulae suggested such as Ni4O7, Ni5O7, Ni3O5, NiO, and Ni3O2.H2O. These are probably not separate chemical entities, but mixtures of nickel, nickelous oxide, and nickel dioxide according to circumstances.

When a dilute solution of a nickel salt is electrolysed at 70° C. in the presence of chromic acid and an alkali pyrophosphate, the tetroxide, NiO4 is obtained.

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