Ch. 14: Synthetic Man Made Diamonds

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	HOW TO MAKE SYNTHETIC DIAMONDS solves carbon, and on cooling, liberates it in the form of graphite. Moissan discovered that several other metals, especially silver, have similar properties. The quantity of carbon entering into solution increases with the temperature. For the manufacturing of artificial diamonds the first necessity is to select pure iron free from sulphur, silicon, phosphorus, etc., and to pack it in a carbon crucible with the pure charcoal of some organic substance such as sugar and starch. Moissan used such a mixture in a furnace with 700 amperes and 40 volts. Beside graphite and diamonds there may be formed black opaque carbon particles of a density from 3.0 to 3.5 and the hardness of diamonds. These are black diamonds or carbonado. In fact comparatively few diamonds are transparent and colorless and show crystalline structure. Besides these may be carbide of silicon and corundum, arising from impurities in the material employed. Graphite dissolves in hydrofluoric acid. Graphitic oxide may be left. Crookes says Sir James Dewar placed a few small diamonds in a carbon tube, and, maintaining a current of hydrogen to prevent oxidation, raised the temperature of the tube in an electric furnace to that of the arc. In a few minutes the diamond was transformed into graphite. To remove graphite after it is well washed allow it to soak in strong hydrofluoric acid in the cold for two days, then in boiling acid. After this treatment, hot sulfuric acid is again applied to remove the fluorides. The residue is well washed and again treated with nitric acid and potassium 129

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