Insulating lid for aluminum production cells

Abstract

An aluminum production cell includes an inert anode and an insulating lid comprising alumina and at least one metal fluoride. The insulating lid preferably comprises about 35-90 wt. % of a mixture of sodium fluoride and aluminum fluoride and about 10-65 wt. % alumina.

What is claimed is:  
     
         1 . An aluminum production cell comprising at least one inert anode, a chamber containing a molten salt bath contacting said inert anode, a cathode spaced from said inert anode, and an insulating lid covering said chamber said insulating lid comprising a preformed refractory block containing about 10-65 wt. % alumina and about 35-90 wt. % of at least one metal fluoride selected from sodium fluoride, aluminum fluoride, and mixtures thereof.  
     
     
         2 . The aluminum production cell of  claim 1 , wherein alumina comprises about 25-50 wt. % of the preformed refractory block.  
     
     
         3 . The aluminum production cell of  claim 1 , wherein said insulating block comprises sodium fluoride and aluminum fluoride.  
     
     
         4 . The aluminum production cell of  claim 1 , wherein said insulating block comprises sodium fluoride and aluminum fluoride in an NaF:AlF 3  weight ratio of about 1:1 to about 2:1.  
     
     
         5 . The aluminum production cell of  claim 4 , wherein the NaF:AlF 3  weight ratio is about 1.5:1.  
     
     
         6 . The aluminum production cell of  claim 1 , wherein said refractory block further comprises at least one metal fluoride selected from calcium fluoride and magnesium fluoride.  
     
     
         7 . The aluminum production cell of  claim 1 , wherein said inert anode comprises a ceramic or cermet material.  
     
     
         8 . The aluminum production cell of  claim 1 , wherein said inert anode comprises nickel oxide and iron oxide.  
     
     
         9 . The aluminum production cell of  claim 1 , further comprising loose insulation around a portion of the preformed insulating block.  
     
     
         10 . The aluminum production cell of  claim 9 , further comprising at least one additional layer of insulating material above the preformed insulating block.  
     
     
         11 . The aluminum production cell of  claim 1 , wherein the preformed insulating block is positioned above at least one anode of said cell.  
     
     
         12 . A process for producing aluminum in a cell comprising at least one inert anode, a chamber containing a molten salt bath containing alumina, a cathode spaced from said inert anode, and an insulating lid covering said chamber, said process comprising 
 (a) passing an electric current between said anode and said cathode, thereby to produce aluminum at the cathode, and    (b) conserving heat in said chamber by providing said insulating lid with a composition comprising about 10-65 wt. % alumina and about 35-90 wt. % of at least one metal fluoride.    
     
     
         13 . The process of  claim 12 , wherein said insulating lid comprises at least one metal fluoride selected from sodium fluoride, aluminum fluoride, magnesium sluoride, calcium fluoride, and mixtures thereof.  
     
     
         14 . The process of  claim 12 , wherein said insulating lid comprises a preformed refractory block comprising about 50-75 wt. % of a mixture of sodium fluoride and aluminum fluoride and about 25-50 wt. % alumina.  
     
     
         15 . The process of  claim 14 , wherein said mixture comprises NaF and AlF 3  in an NaF:AlF 3  weight ratio of about 1:1 to about 2:1.