Gold parting in 1860's Australia. It is able to refine gold up to 99.5% purity. The process involves blowing a stream of chlorine gas over and through a crucible filled with molten impure gold. Impurities in the gold form chlorides before the gold does and these insoluble salts are removed from the melt by skimming the surface. Invented by Emil Wohlwill in 1874, this produces the highest purity gold (99.999%). It is an electrolytic process using pure gold for the cathode (or titanium as a starter cathode) and chloroauric acid (gold chloride-hydrochloric acid) as the electrolyte; this is made by dissolving gold
Ultra-high-purity steam for oxidation and annealing and is both less expensive and safer. An effective passivation of the rear surface of industrial solar cells is a prerequisite to considerably improve the conversion efficiency. An excellent level of surface passivation on lowly doped p-type surfaces is provided by thermal grown silicon oxides. However, dry thermal oxidation processes require relatively high temperatures (>1000 °C) and, due to the low growth rate, long process times. To decrease both oxidation temperature and process time the dry oxidation process can be replaced by a wet oxidation followed by nitrogen annealing. Best cell performance requires a forming gas anneal after firing. Ultra-high-purity