Chemical elements
    Physical properties
    Chemical properties
      Boron Hydrides
      Boron trihydride
      Boron halogen
      Boron trifluoride
      Hydrofluoboric acid
      Potassium borofluoride
      Fluoboric acid
      Perfluoboric acid
      Boron subchloride
      Boron trichloride
      Boron tribromide
      Boron tri-iodide
      Oxides of Boron
      Tetraboron trioxide
      Boron dioxide
      Tetraboron pentoxide
      Boron sesqui-oxide
      Boron trioxide
      Boric anhydride
      Boric Acids
      Orthoboric acid
      Boric acid
      Boracic acid
      Complex Boric Acids
      Perboric Acid and Perborates
      Sodium perborate
      Sodium hyperborate
      Potassium perborate
      Rubidium perborate
      Ammonium perborate
      Barium perborate
      Boron sesquisulphide
      Boron trisulphide
      Boron pentasulphide
      Boron selenide
      Boron nitride
      Boron amide
      Boron imide
      Boron phosphide
      Boron phospho-iodides
      Boron carbide
      Boron thiocyanate
      Boron Alkyls
      Boron trimethyl
      Boron Silicides and

Boron Silicides, B2Si and B6Si

Boron Silicides, B2Si and B6Si are produced when a mixture of crystalline silicon (5 pts.) and amorphous boron (1 pt.), packed in a refractory earthenware tube, is heated for 40 to 60 seconds by means of an electric current of 600 amperes at 45 volts. The outer portions of the product and those portions which were in proximity to the carbon electrodes are discarded, and the remainder treated with a cold mixture of nitric and hydrofluoric acids to eliminate free silicon. The residue is purified by heating for half an hour with commercial potassium hydroxide, which is just melted but not dehydrated. After washing with water, dilute nitric acid, and boiling water, and drying at 130°, a mixture of the two silicides is obtained.

The silicide B3Si is left when the mixture is heated with an excess of boiling nitric acid, the other compound being completely decomposed. It forms black, rhombic plates which are transparent and yellow or browji in very thin layers. The density is 2.52. It easily scratches quartz and ruby, but is softer than boron carbide. Fluorine, chlorine, and bromine attack it in increasing order of difficulty, and it is only superficially oxidised by air or oxygen at a red heat. It is rapidly oxidised by fused anhydrous potassium hydroxide, less rapidly by fused alkali carbonates, and not at all by fused alkali nitrates. Boiling concentrated sulphuric acid slowly oxidises it.

The silicide B6Si is isolated from a mixture of the silicides, in which it is more abundant than the other, by heating with fused anhydrous potassium hydroxide. It forms thick, opaque crystals of density 2.47. In chemical properties it resembles the other silicide, except in its behaviour towards fused potassium hydroxide and boiling nitric acid.

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