Columbium, or Niobium (symbol Cb or Nb, atomic weight 94), one of the metallic elements of the nitrogen group, first detected in 1801 by C. Hatchett in a specimen of columbite (niobite) from Massachusetts (Phil. Trans. 1802, 49). It is usually found associated with tantalum, the chief minerals containing these two elements being tantalite, columbite, fergusonite and yttrotantalite; it is also a constituent of pyrochlor, euxenite and samarskite. Columbium compounds are usually prepared by fusing columbite with an excess of acid potassium sulphate, boiling out the fused mass with much water, and removing tin and tungsten from the residue by digestion with ammonium sulphide, any iron present being simultaneously converted into ferrous sulphide. The residue is washed, extracted by dilute hydrochloric acid, and again well washed with boiling water. It is then dissolved in hydrofluoric acid and heated in order to expel silicon fluoride; finally the columbium, tantalum and titanium fluorides are separated by the different solubilities of their double fluorides (C. Marignac, Ann. chim. et phys. 1866 [4], 8, p. 63; 1868, 13, p. 28; see also W. Gibbs, Jahresb. 1864, p. 685; R. D. Hall and E. F. Smith, Proc. Amer. Philos. Soc. 1905, 44, p. 177).
The metal was first obtained by C. W. Blomstrand (Journ. prak. Chem. 1866, 97, p. 37) by reducing the chloride with hydrogen; it has more recently been prepared by H. Moissan by reducing the oxide with carbon in the electric furnace (the product obtained always contains from 2-3% of combined carbon), and by H. Goldschmidt and C. Vautin (Journ. Soc. Chem. Industry, 1898, 19, p. 543) by reducing the oxide with aluminium powder. As obtained by the reduction of the chloride, it is a steel grey powder of specific gravity 7.06. It burns on heating in air; and is scarcely attacked by hydrochloric or nitric acids, or by aqua regia; it is soluble in warm concentrated sulphuric acid.
Columbium hydride, CbH, is obtained as a greyish metallic powder, when the double fluoride, CbF5, 2KF, is reduced with sodium. It burns when heated in air, and is soluble in warm concentrated sulphuric acid. Three oxides of columbium are certainly known, namely the dioxide, Cb2O2, the tetroxide, Cb2O4, and the pentoxide, Cb2O5, whilst a fourth oxide, columbium trioxide, Cb2O3, has been described by E. F. Smith and P. Maas (Zeit. f. anorg. Chem. 1894, 7, p. 97). Columbium dioxide, Cb2O2, is formed when dry potassium columbium oxyfluoride is reduced by sodium (H. Rose, Pogg. Ann. 1858, 104, p. 312). It burns readily in air, and is converted into the pentoxide when fused with acid potassium sulphate. Columbium tetroxide, Cb2O4 is obtained as a black powder when the pentoxide is heated to a high temperature in a current of hydrogen. It is unattacked by acids. Columbium pentoxide (columbic acid), Cb2O5, is obtained from columbite, after the removal of tantalum (see above). The mother liquors are concentrated, and the double salt of composition 2KF·CbOF3·H2O, which separates, is decomposed by sulphuric acid, or by continued boiling with water (C. Marignac; see also G. Krüss and L. F. Nilson, Ber. 1887, 20, p. 1676). It is a white amorphous infusible powder, which when strongly heated in sulphuretted hydrogen, yields an oxysulphide. Several hydrated forms are known, yielding salts known as columbates. A percolumbic acid, HCbO4·nH2O, has been prepared by P. Melikoff and L. Pissarjewsky (Zeit. f. anorg. Chem. 1899, 20, p. 341), as a yellow amorphous powder by the action of dilute sulphuric acid on the potassium salt, which is formed when columbic acid is fused in a silver crucible with eight times its weight of caustic potash (loc. cit.). Salts of the acid H3CbO8 have been described by C. W. Balke and E. F. Smith (Jour. Amer. Chem. Soc. 1908, 30, p. 1637).
Columbium trichloride, CbCl3, is obtained in needles or crystalline crusts, when the vapour of the pentachloride is slowly passed through a red-hot tube. When heated in a current of carbon dioxide it forms the oxychloride CbOCl3, and carbon monoxide. Columbium pentachloride, CbCl5, is obtained in yellow needles when a mixture of the pentoxide and sugar charcoal is heated in a current of air-free chlorine. It melts at 194° C. (H. Deville) and boils at 240.5° C. It is decomposed by water, and dissolves in hydrochloric acid. Columbium oxychloride, CbOCl3, is formed when carbon tetrachloride, and columbic acid are heated together at 440° C.: 3CCl4 + Cb2O5 = 2CbOCl3 + 3COCl2, and also by distilling the pentachloride, in a current of carbon dioxide, over ignited columbic acid. It forms a white silky mass which volatilizes at about 400° C. It deliquesces in moist air, and is decomposed violently by water. Columbium pentafluoride, CbF5, is obtained when the pentoxide is dissolved in hydrofluoric acid. It is only known in solution; evaporation of the solution yields the pentoxide. The oxyfluoride, CbOF3, results when a mixture of the pentoxide and fluorspar is heated in a current of hydrochloric acid. It forms many double salts with other metallic fluorides.
Columbium oxysulphide, CbOS3, is obtained as a dark bronze coloured powder when the pentoxide is heated to a white heat in a current of carbon bisulphide vapour; or by gently heating the oxychloride in a current of sulphuretted hydrogen. It burns when heated in air, forming the pentoxide and sulphur dioxide.
Columbium nitride, Cb3N5 (?), is formed when dry ammonia gas is passed into an ethereal solution of the chloride. A heavy white precipitate, consisting of ammonium chloride and columbium nitride, is thrown down, and the ammonium chloride is removed by washing it out with hot water, when the columbium nitride remains as an amorphous residue (Hall and Smith, loc. cit.).
Potassium fluoxy percolumbate, K2CbO2F5·H2O, is prepared by dissolving potassium columbium oxyfluoride in a 3% solution of hydrogen peroxide. The solution turns yellow in colour, and, when saturated, deposits a pasty mass of crystals. The salt separates from solutions containing hydrofluoric acid in large plates, which are greenish yellow in colour.
The atomic weight was determined by C. Marignac (Ann. chim. et phys. 1866 (4), 8, p. 16) to be 94 from the analysis of potassium columbium oxyfluoride, and the same value has been obtained by T. W. Richards (Journ. Amer. Chem. Soc. 1898, 20, p. 543).
