Non-ferrous metal cover gases

Abstract

Disclosed are cover gas compositions comprising fluoroolefins for impeding the oxidation of molten nonferrous metals and alloys, such as magnesium. The cover gas compositions can include at least one fluoroolefin and a carrier gas.

1 . A method for impeding the oxidation of a molten nonferrous metal exposed to air, comprising:
 (a) providing molten nonferrous metal having a surface; and   (b) exposing said surface to a cover gas composition that includes at least one fluoroolefin.   
     
     
         2 . The method of  claim 1  further comprising the step of:
 (c) forming a protective film on said surface.   
     
     
         3 . The method of  claim 1  wherein said at least one fluoroolefin comprises a C2-C6 fluoroolefin including one or more compounds having Formula I:
   XCF z R 3−z   (I)   where X is a C 1 , C 2 , C 3 , C 4 , or C 5  radical, each R is independently Cl, F, Br, I or H, and z is 1 to 3.   
     
     
         4 . The method of  claim 1  wherein said fluoroolefin is selected from the group consisting of CF 3 CF═CH 2 , CF 3 CH═CHF, and CF 3 CF═CHF. 
     
     
         5 . The method of  claim 1  wherein said metal is selected from the group consisting of magnesium, aluminum, lithium, and alloys thereof 
     
     
         6 . The method of  claim 5  wherein said metal is magnesium. 
     
     
         7 . The method of  claim 1  wherein said fluoroolefin composition further comprises at least one carrier gas. 
     
     
         8 . The method of  claim 7  wherein the carrier gas selected from the group consisting of nitrogen, carbon dioxide, air, noble gas, and mixtures thereof. 
     
     
         9 . The method of  claim 8 , wherein the fluoroolefin is present in the cover gas composition in an amount that avoids flammable mixtures of the fluoroolefin and the carrier gas. 
     
     
         10 . The method of  claim 1 , wherein the fluoroolefin comprises HFO-1234ze, and the HFO-1234ze is present in the cover gas composition in an amount of less than about 6% by volume of the cover gas composition. 
     
     
         11 . The method of  claim 10 , wherein the fluoroolefin comprises trans-HFO-1234ze. 
     
     
         12 . A cover gas composition comprising:
 at least one fluoroolefin comprising trans-HFO-1234ze in an amount of less than about 6% by volume of the cover gas composition; and   at least one carrier gas;   wherein the cover gas composition is effective to impede oxidation of the molten nonferrous metals and alloys.   
     
     
         13 . The cover gas composition of  claim 12 , wherein the carrier gas is present in an amount of greater than about 94% by volume of the cover gas composition. 
     
     
         14 . The cover gas composition of  claim 12 , wherein the carrier gas selected from the group consisting of nitrogen, carbon dioxide, air, noble gas, and mixtures thereof 
     
     
         15 . The cover gas composition of  claim 12 , wherein said metal is selected from the group consisting of magnesium, aluminum, lithium, and alloys thereof 
     
     
         16 . The cover gas composition of  claim 15 , wherein said metal is magnesium. 
     
     
         17 . A molten metal composition comprising a nonferrous reactive metal having a protective film on its surface, wherein said film is formed by a reaction between the metal and a fluoroolefin composition and said film impedes the oxidation of said metal. 
     
     
         18 . The molten metal composition of  claim 17  wherein said metal is selected from the group consisting of magnesium, aluminum, lithium, and alloys of at least one these. 
     
     
         19 . The molten metal composition of  claim 18  wherein said metal is magnesium or a magnesium alloy.