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Physical & Chemical properties

Water solubility

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Gallium arsenide is a metallic compound and as other metallic compounds practically not soluble in water. In an oxygen-free atmosphere a solubility of 13 µg As/l (total As concentration) was observed. Under these conditions all dissolved As was found as As(III). Therefore one can assume that not GaAs itself was dissolved but the oxidized surface layer of the particles.

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Gallium arsenide is a metallic compound and as other metallic compounds practically not soluble in water. In an oxygen-free atmosphere a solubility of 13 µg GaAs/l (total As concentration) was observed. Under these conditions all dissolved As was found as As(III). Therefore one can assume that not GaAs itself was dissolved but the oxidized surface layer of the particles. The solubility in ultra-pure water and in an argon atmosphere may not be seen representative for environment or physiological conditions.

In the presence of oxygen and after a longer period of time, i.e. several days, higher solubilities seem to occur. These higher amounts of Gallium and Arsenic in the medium are nearest a consequence of an oxidizing process. Therefore, the standard concept of an equilibrium/saturation water solubility is not applicable to this substance.

Gallium arsenide is usually produced by crystallisation in the form of a massive block, from which wafers (disks) are then produced. Only for experimental testing of intrinsic physico-chemical, toxicological and ecotoxicological properties, a GaAs powder sample has been prepared by the REACH registrant. This powder, which is not marketed, was produced by breaking/crushing and grinding of wafers and its particle size is characterised by the following parameters: D10 = 41.1 µm, D50 = 299.4 µm and D90 = 816 µm. This material has been used in a standard water solubility test (OECD 105), as well as in ecotoxicological tests (OECD 201,202,203).