Gallium oxides and hydroxides

Gallium Oxides. The preparation conditions of gallium oxides and hydroxides are Hsted iu Table 6. 

There is a paucity of available data for the solubility of indium oxide and hydroxide phases. As the first hydrolysis constant of indium has a stability that lies between those of aluminium and gallium, it is expected that the solid hydroxide phase would also exhibit this behaviour. However, a number of studies (Heyrovsky, 1925 Oka, 1938 Moeller, 1941 Lacroix, 1949) have indicated a solubility that was larger than that seen for aluminium(III). It is believed that this would be unlikely and, as such, these data are not retained. AkseTrud and Spivakovskii (1959) obtained a solubility that was nearly four orders of magnitude smaller than... 

Unlike boron, aluminum, gallium, and indium, thallium exists in both stable univalent (thaHous) and trivalent (thaUic) forms. There are numerous thaHous compounds, which are usually more stable than the corresponding thaUic compounds. The thaUium(I) ion resembles the alkaU metal ions and the silver ion in properties. In this respect, it forms a soluble, strongly basic hydroxide and a soluble carbonate, oxide, and cyanide like the alkaU metal ions. However, like the silver ion, it forms a very soluble fluoride, but the other haUdes are insoluble. Thallium (ITT) ion resembles aluminum, gallium, and indium ions in properties. 

Aluminum is the commonest metallic element on Earth, occurring widely in aluminosilicate minerals and in deposits of the hydroxide bauxite. It is very electropositive and potentially very reactive, but forms a stable oxide film. Gallium, indium and thallium are rarer and less electropositive. 

The stable oxide is Ga Oj, gallic oxide. This is soluble in HCl, H SO, and aqueous alkali hydroxide and ammonia, but if it has been previously strongly heated, it dissolves in these media only extremely slowly. Barium carbonate precipitates the hydroxide from aqueous solutions of gallium salts. The hydroxide dissolves is aqueous acids and alkalis. 

A sample placed behind a 25 jum copper beam intensity monitor is irradiated for 15-20 min with a 2 mA beam of 25 MeV He. By chemical etching in 6 M nitric acid a 25-50 Asurface layer is removed. The sample is dissolved in 14 M nitric acid to which some sodium fluoride, zinc nitrate and gallium oxide carrier are added. After addition of phosphoric acid, the temperature is raised to 125° and 150 ml of distillate are collected. Gallium oxide is added to the distillate and gallium hydroxide is precipitated and filtered off. Finally, fluorine is precipitated as lead chlorofluoride The precipitate is repeatedly measured with a Ge(Li) detector during a 10 h period to allow the control of the half-life. Afterwards the yield of the chemical separation is determined by activation with an Ac-Be isotopic neutron source using the F(n,a) N reaction. 

Gallium hydrolyses to a greater extent than aluminium, with the onset of hydrolysis reactions occurring just above a pH of 1. In fact, even though aluminium has the smallest ionic radius of this series of metals, it has the weakest hydrolysis species and oxide/hydroxide phases. This is due to the presence of stabilising d-orbitals in the heavier metals, gallium, indium and thallium(III). 

The dark brown, diamagnetic powder is stable in dry air and may be purified by vacuum sublimation at 500 °C, but undergoes surface oxidation at higher temperatures. Above 800 °C it disproportionates according to the reverse of equation (3). The hydrous oxides Ga(0)OH and Ga(OH)3 are similar to their aluminum analogs. Thus gallium hydroxide... 

Gallium (Ga, at. mass 69.72) forms colourless Ga " ions. It occurs in solution exclusively in the III oxidation state. Gallium resembles aluminium and zinc in its properties. The hydroxide, Ga(OH)3, precipitates at pH 3, but dissolves in weakly alkaline media (pH 8-9). Gallium forms halide, oxalate, tartrate, acetate, and EDTA complexes. 

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