Adding a small amount of fluorine salts such as NaF,Na3AlF6,CaF2 to the chloride salts, mainly for refining such as absorption melting Al2O3, fluoride salts can also effectively remove the oxide film on the surface of the melt, improving the effect of degassing, the reasons are follows:
1. Fluoride can be separated from aluminium melt and chemically react to form gaseous AlF,SiF4,BF3 etc, they promote the separation of oxide film from aluminium melt by mechanical action, squeeze the oxide film and push it into the solvent.
2. The current generated at the interface where the above reaction occurs also causes the oxide film to be “washed out” and broken. Therefore, the presence of fluorine salts accelerates the destruction process of the oxide film on the surface of the aluminium melt, and the hydrogen in the melt can more escape conveniently.
3. Chloride salts, especially CaF2 can increase the surface tension of the mixed molten salts, make the molten salt of the adsorbed oxide spheroidized, facilitate separation from the melt, reduce the loss caused by solid slag enclosing aluminium, and the increase of the surface tension of the body accelerates the process of flux adsorption and inclusion