Based on the finding that blowing of NH₃ gas onto molten pure copper at atmospheric pressure causes its evaporation of enormously high rate, attempts have been made on elimination of copper dissolved in molten steel by NH₃ gas blowing under reduced pressure. Typical behaviors of molten steel by NH₃ gas are boiling, splashing and in a violent case slopping from the crucible.
Evaporation from liquid pure copper by top-blowing of NH₃ was observed by the laser-light sheet method and it was confirmed that a large amount of copper smoke takes off from the molten surface attacked by NH₃ gas. The condensates of the smoke were fine copper particles.
The decuprization experiments have been conducted to measure the rate at which the copper level in the molten steel is reduced by using a vacuum induction furnace and blowing NH₃ gas through a vertical water-cooled copper nozzle. For comparison, the rate of copper elimination from a small molten steel droplet has also been determined. From these experiments the rate constant for copper elimination from a flat and smooth surface of molten steel was the order of 2 × 10^-3m·min^-1 at 1900 K and the pressure range of 10010000Pa.
Because the boiling phenomena are accompanied by an immense increase in the surface area from which volatile species are able to evaporate, NH₃ gas blowing may be useful to reduce the decuprization time. Nitrogen concentration in the molten steel increases with increasing the flow rate of NH₃ gas. It was reduced down to the initial level by vacuum degassing after stopping NH₃ gas blowing.