Inert anode designs for reduced operating voltage of aluminum production cells

Abstract

Inert anodes useful in electrolytic aluminum production cells are disclosed. The inert anodes have sloped bottom surfaces with controlled bubble release angles. In one embodiment, the bottom surface is substantially conical with a bubble release angle of up to 30 degrees. The cross-sectional size of the inert anodes is also controlled in order to maximize efficiency of the cells. The inert anodes may be provided in arrays in aluminum production cells in order to achieve commercial cell currents.

What is claimed is:  
     
         1 . An inert anode for use in an electrolytic aluminum production cell, the inert anode comprising a bottom surface including a region that is upwardly sloped from an interior portion to an exterior portion of the inert anode, wherein the upwardly sloped region has a bubble release angle of up to about 30 degrees.  
     
     
         2 . The inert anode of  claim 1 , wherein the bubble release angle is from about 2 to about 20 degrees.  
     
     
         3 . The inert anode of  claim 1 , wherein the bubble release angle is from about 5 to about 15 degrees.  
     
     
         4 . The inert anode of  claim 1 , wherein the bubble release angle is from about 8 to about 12 degrees.  
     
     
         5 . The inert anode of  claim 1 , wherein the bubble release angle is about 10 degrees.  
     
     
         6 . The inert anode of  claim 1 , wherein the inert anode includes a cross sectional dimension of from about 2 to about 6 inches.  
     
     
         7 . The inert anode of  claim 1 , wherein the inert anode is substantially cylindrical and has a cross sectional diameter of less than 10 inches.  
     
     
         8 . The inert anode of  claim 1 , wherein the inert anode is substantially cylindrical and has a cross sectional diameter of from about 2 to about 6 inches.  
     
     
         9 . The inert anode of  claim 1 , wherein the bottom surface is substantially symmetrical about an axis of rotation defined by a central longitudinal axis of the inert anode.  
     
     
         10 . The inert anode of  claim 1 , wherein the bottom surface is non-symmetrical about an axis of rotation defined by a central longitudinal axis of the inert anode.  
     
     
         11 . The inert anode of  claim 10 , wherein the bottom surface defines a minimum bubble release angle and a maximum bubble release angle, the minimum bubble release angle is from zero to about 20 degrees, and the maximum bubble release angle is from about 2 to about 30 degrees.  
     
     
         12 . The inert anode of  claim 11 , wherein the minimum bubble release angle is from about 1 to about 15 degrees, and the maximum bubble release angle is from about 5 to about 20 degrees.  
     
     
         13 . The inert anode of  claim 1 , wherein the bottom surface includes a substantially straight portion defined by a longitudinal section of the inert anode.  
     
     
         14 . The inert anode of  claim 13 , wherein the bubble release angle is measured from the substantially straight portion.  
     
     
         15 . The inert anode of  claim 1 , wherein the bottom surface is substantially conical.  
     
     
         16 . The inert anode of  claim 1 , wherein the bottom surface has a lowermost tip.  
     
     
         17 . The inert anode of  claim 16 , wherein the lowermost tip is located at an axial center of the inert anode.  
     
     
         18 . The inert anode of  claim 16 , wherein the lowermost tip is rounded.  
     
     
         19 . The inert anode of  claim 18 , wherein the rounded tip has a radius of curvature of from about 0.5 to about 2 inches.  
     
     
         20 . The inert anode of  claim 1 , wherein the bottom surface comprises a curved shoulder at an intersection of the bottom surface and a sidewall of the inert anode.  
     
     
         21 . The inert anode of  claim 20 , wherein the curved shoulder has a substantially elliptical shape.  
     
     
         22 . The inert anode of  claim 20 , wherein the curved shoulder has a substantially circular shape.  
     
     
         23 . The inert anode of  claim 1 , wherein the inert anode has an elongated cross section having a length to width aspect ratio of from about 1.1:1 to about 50:1.  
     
     
         24 . The inert anode of  claim 1 , wherein the inert anode has a substantially rectangular cross section.  
     
     
         25 . The inert anode of  claim 1 , wherein the inert anode has a substantially elliptical cross section.  
     
     
         26 . The inert anode of  claim 1 , wherein the inert anode has a substantially ovular cross section.  
     
     
         27 . The inert anode of  claim 1 , wherein the inert anode comprises a ceramic phase including an oxide of at least one metal selected from Fe, Ni, Zn, Co and Al.  
     
     
         28 . An inert anode for use in an electrolytic aluminum production cell, the inert anode comprising a substantially conical bottom surface having a bubble release angle of from about 5 to about 30 degrees.  
     
     
         29 . The inert anode of  claim 28 , wherein the bubble release angle is from about 8 to about 12 degrees.  
     
     
         30 . The inert anode of  claim 28 , wherein the bubble release angle is about 10 degrees.  
     
     
         31 . The inert anode of  claim 28 , wherein the inert anode includes a cross sectional dimension of from about 2 to about 6 inches.  
     
     
         32 . The inert anode of  claim 28 , wherein the bottom surface has a rounded lowermost tip.  
     
     
         33 . The inert anode of  claim 28 , wherein the bottom surface comprises a curved shoulder at an intersection of the bottom surface and a sidewall of the inert anode.  
     
     
         34 . The inert anode of  claim 33 , wherein the curved shoulder has a substantially elliptical shape.  
     
     
         35 . The inert anode of  claim 33 , wherein the curved shoulder has a substantially circular shape.  
     
     
         36 . An array of inert anodes for use in an electrolytic aluminum production cell, the array comprising a plurality of inert anodes comprising a bottom surface including a region that is upwardly sloped from an interior portion to an exterior portion of the inert anode, wherein the upwardly sloped region has a bubble release angle of up to about 30 degrees.  
     
     
         37 . The array of  claim 36 , wherein the inert anodes are spaced apart by a distance of from zero to about 5 inches.  
     
     
         38 . The array of  claim 36 , wherein the inert anodes are provided in a substantially square pattern.  
     
     
         39 . The array of  claim 36 , wherein the inert anodes are provided in a substantially hexagonal pattern.  
     
     
         40 . The array of  claim 36 , wherein the inert anodes have cross sectional dimensions of from about 2 to about 6 inches.  
     
     
         41 . An electrolytic aluminum production cell comprising: 
 a molten salt bath comprising an electrolyte and aluminum oxide;    a cathode; and    an inert anode comprising a bottom surface including a region that is upwardly sloped from an interior portion to an exterior portion of the inert anode, wherein the upwardly sloped region has a bubble release angle of up to about 30 degrees.    
     
     
         42 . The electrolytic aluminum production cell of  claim 41 , wherein the cell comprises an array including a plurality of the inert anodes.  
     
     
         43 . A method of producing aluminum comprising: 
 passing current between an inert anode and a cathode through a molten salt bath comprising an electrolyte and aluminum oxide; and    controlling flow of oxygen bubbles generated at a surface of the inert anode by providing the inert anode with a bottom surface including a region that is upwardly sloped from an interior portion to an exterior portion of the inert anode, wherein the upwardly sloped region has a bubble release angle of up to about 30 degrees.    
     
     
         44 . The method of  claim 43 , wherein the bubble release angle is from about 5 to about 15 degrees.  
     
     
         45 . The method of  claim 43 , wherein the inert anode has a cross sectional diameter of from about 2 to about 6 inches.  
     
     
         46 . The method of  claim 43 , wherein the cell is operated at a voltage of less than about 6 volts.  
     
     
         47 . The method of  claim 43 , wherein the cell is operated at a voltage of less than about 5.5 volts.  
     
     
         48 . The method of  claim 43 , wherein the cell is operated at a voltage of less than about 5 volts.  
     
     
         49 . The method of  claim 43 , wherein the cell is operated at a current density of from about 0.5 to about 1.5 Amps/cm 2 .