Passivation of gallium

Figure 8. Theoretical conditions of corrosion, immunity, and passivation of gallium, at 25°C, assuming passivation by a film of a-Ga203 (16)...

J. S. Herman, E. L. Terry, Hydrogen Sulfide Plasma Passivation of Gallium Arsenide, Appl. Phys. Lett. 1992, 60,716-717. 

M. Tabib-Azar, A. S. Dewa, W. H. Ko, Langmuir-Blodgett Film Passivation of Unpinned -Type Gallium Arsenide Surfaces, Appl. Phys. Lett. 1988, 52, 206-208. 

Al, Ga, In and T1 differ sharply from boron. They have greater chemical reactivity at lower temperatures, well-defined cationic chemistry in aqueous solutions they do not form numerous volatile hydrides and cluster compounds as boron. Aluminium readily oxidizes in air, but bulk samples of the metal form a coherent protective oxide film preventing appreciable reaction aluminium dissolves in dilute mineral acids, but it is passivated by concentrated HN03. It reacts with aqueous NaOH, while gallium, indium and thallium dissolve in most acids. 

Gallium (10 % of the earth s crust) is present in zinc blende, which may contain up to 0.5%, and in certain e.g. British) coal ash. The metal, which is deposited by electrolysis from alkaline solutions of its salts, is silvery-white, hard and brittle. The orthorhombic crystal has a complex lattice. The co-ordination is strictly one-fold, a given gallium atom having one atom situated at 2.43 A and six others at distances varying from 2.70 to 2.79 A. This co-ordination is denoted by 1 + 6 the notation applies only if the six atoms are separated from the reference atom by a distance not greater than 1.2 times that of the nearest one. The metal is stable in dry air and does not decompose water. It dissolves in caustic alkalis and in mineral acids, other than nitric which renders it passive. Its chemistry (Fig. 151) is, in fact, very similar to that of aluminium. 

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