Degassing:
While it is not possible to prevent gas absorption the hazards of dissolved gases might be reduced by
(a) Eliminating the gas or gases or
(b) Eliminating or isolating one or more of the components of the gas.
Hydrogen is fully removed from the atmosphere about a melt; any hydrogen gas dissolved shall tend to escape. Therefore pouring and melting under a vacuum is one method however it is very costly. Vacuum degassing is another try to join the advantages of vacuum, considering with the economy of air melting. In this technique metal is placed in an evacuated chamber (for degassing) previous to pouring; pouring occurs in the open atmosphere. Flushing along an inert gas as argon is the most common method of eliminating gas. In this method the inert gas is bubbled through the metal directly. The pressure of the dissolved gas in every inert gas bubble is zero. Thus any dissolved gas migrates eagerly to the bubble where it gathers and is flushed from the metal baths.
Inert gases such like nitrogen, chlorine or argon are utilized in practice for degassing metals especially magnesium and aluminium alloys. Simply the gases are piped from storage tanks through graphite tubes into the metal baths directly. Sometimes solid degassers are also utilized like a source of the inert gas. Here a solid compound held beneath the melt surface decomposes to provide the flushing action. In steel building practice the CO from the carbon boil behaves as an inert gas to flush hydrogen from the metal .Gas porosity is also minimized by eliminating or isolating one of the components of the gas. Therefore in steel making after the carbon boil has progressed to the wished point it is blocked by adding aluminum or silicon to the bath to tie up one of the reagents of the CO gas. Another instance is the addition of phosphor-copper to copper base alloys to tie up dissolved oxygen. The phosphorus joint with dissolved oxygen to make a solid P2O5 that floats out of the bath and prevents the oxygen from joining with any dissolved hydrogen to make water vapour.