METHOD AND SYSTEM OF PROTECTING EASILY OXIDIZED METALS MELTS LIKE MOLTEN MAGNESIUM BY IN SITU GENERATION OF BORON TRIFLUORIDE GAS

摘要

A method and system are provided for preventing oxidation of an easily oxidizable, molten metal having a surface exposed to an oxygen-containing atmosphere. The method comprises placing a quantity of a solid metal fluoroborate salt (12) in an enclosed chamber (16) heated to a temperature sufficient to cause the solid metal fluoroborate salt to decompose to produce boron trifluoride gas and a metal fluoride, which is discharged from the decomposition chamber through outlet (18). The boron trifluoride gas is then mixed in the chamber with an oxygen-containing gas (20) to produce a boron trifluoride-containing gas mixture, which is transferred to an enclosed vessel (40) containing the molten metal. When the boron trifluoride gas contacts the surface of the molten metal (42) it causes the formation of a thin, highly elastic protective film (44) on the surface of the metal, thereby preventing oxidation of the molten metal. Where the metal is magnesium or a magnesium based alloy, the preferred metal fluoroborate salts are potassium fluoroborate and sodium fluoroborate.