Gallium, Therapeutic Effects
نویسنده
چکیده
Metallic gallium dissolves slowly in dilute mineral acids but rapidly in aqua regia and concentrated sodium hydroxide. In its compounds, the valency is +3. Its oxygen compounds resemble those of aluminum in that there are highand lowtemperature forms of Ga2O3 and two hydroxides, Ga(OH)3 and GaO·OH. Substances which lower the hydrogen ion concentration throw down a white gelatinous precipitate from Ga(III) salt solutions. This precipitate is amorphous to x-rays and has a variable water content (gallium oxide hydrate, Ga2O3·xH2O). It dissolves both in acids and in strong bases and differs from aluminum oxide hydrate in being soluble in ammonia solutions. As the precipitate ages, its solubility in caustic alkalis diminishes. Gallium halides have covalent character and therefore have good solubility in many nonpolar solvents in which they exist in dimeric form. Like aluminum, gallium is precipitated as the white oxide hydrate from solutions of its salts by reducing the hydrogen ion concentration. Gallium sulfate, Ga2(SO4)3, crystallizes from aqueous solutions as an 18-hydrate similar to Al2(SO4)3·18H2O. It can be dehydrated by heating and decomposes above 520 C with loss of SO3. With ammonium sulfate, it forms the double salt (NH4)Ga(SO4)2·12H2O, ammonium gallium alum. The crude metal contains 99–99.9% gallium. The material for semiconductor manufacture is used in purities from 99.9999% (6 N) to 99.999999% (8 N). The binary compounds, GaP and GaAs, are of great industrial importance. They may be prepared by direct combination of the elements at high temperature.
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