High purity gallium made from gallium arsenide scrap - obtd. in semiconductor mfr., where scrap is decomposed to obtain gallium, which is purified by hydrogenation and fractional crystallisation

摘要

The scrap is decomposed by heating in a vacuum of 0.1-0.01 torr from 25-1150 deg.C. using varying heating speeds of 0.5-20 deg.C./ minute; this operation causes the As to sublime and the sublimate is condensed. The molten Ga left is cooled at 0.05-15 deg.C./minute to 50-100 deg.C., and is filtered. The molten filtrate is hydrogenated, and is subjected to multistage fractional crystallisation, with 60-95% crystallisation of the Ga in each stage; the metal residue enriched with impurities in each stage is recycled to the preceding stage. Heating in vacuo is pref. at 5-20 deg.C./minute up to 900 deg.C., and then from 900-1,100 deg.C. at 0.5-10 deg.C./minute, and next to 1,150 deg.C. at 5-20 deg.C./minute. Gallium with a purity of 99.99999 wt.% can be obtd. by a simple process.