Gold costs were about $317 per troy ounce in 2007, but these can vary widely depending on mining type and ore quality; global mine production amounted to 2,471.1 tonnes. After initial production, gold is often subsequently refined industrially by the Wohlwill process which is based on electrolysis or by the Miller process, that is chlorination in the melt. The Wohlwill process results in higher purity, but is more complex and is only applied in small-scale installations. Other methods of assaying and purifying smaller amounts of gold include parting and inquartation as well as cupellation, or refining methods based on the dissolution
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