Abstract:
In the electrolytic production of aluminum, in a cell having a side wall including a layer of carbon electrically insulated from a jacket of metal, the improvement including interposing a layer of tile (27) between the carbon layer (23,24) and the metal jacket (28).

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the lining of a cell for the electrolytic production of aluminum. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a new and improved process and cell for the electrolytic production of aluminum. 
     This as well as other objects which will become apparent in the discussion that follows are achieved according to the present invention by providing, in the electrolytic production of aluminum, in a cell having a side wall including a layer of carbon electrically insulated from a jacket of metal, the improvement comprising interposing a layer of tile between the carbon layer and the metal jacket. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The sole FIGURE of the drawing is an elevational, cross-sectional view of a side wall portion of a cell for the electrolytic production of aluminum, the cutting plane for the cross section being along an edge of the illustrated graphite block. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now in detail to the sole FIGURE of the drawing, it will be seen that a preferred cell for use in an embodiment of the present invention is similar to the Hall-Heroult-type cell shown in FIG. 1 of U.S. Pat. No. 3,852,173 in that graphite block 23 is used here as carbon block as was done in FIG. 1 of U.S. Pat. No. 3,852,173. In the present embodiment, another type of carbon block, anthracite block 24, is placed on top of the graphite. Anthracite block is cheaper than graphite block, and it is used in the upper part of the side wall, where the greater thermal conductivity and erosion resistance of graphite block is not needed. 
     Interposed between the top of the anthracite block 24 and the underside of the metal, e.g. steel, deck plate 25 is a layer of quarry tile 26. 
     According to an embodiment of the present invention, an upwardly extending layer of quarry tile 27 is interposed between the carbon block and the metal, e.g. steel, jacket 28 of the cell. This quarry tile is held in place by a cement, e.g. silicon carbide mortar (not shown), at its joints 29a, 29b and at its interfaces 31a, 31b with jacket 28 and the carbon blocks. 
     It has been found that presence of tile 27 in a Hall-Heroult cell can permit electrolysis using a voltage across the cell at an average of at least 0.1 volts less than the average voltage for electrolysis in a cell without the tile. 
     EXAMPLE 
     Quarry tile 27 of the American Olean Tile Company, Lewisport, Ky., was installed in three cells in the manner shown in the FIGURE, using silicon carbide cement at the joints and at the interfaces. The average voltage across the three cells was 4.313 volts. This is to be compared with an average voltage of 4.448 volts for three similar cells in the same plant. Thus, an average savings of 0.135 volts per cell was realized. 
     The tile was referred to by the supplier as its standard grade quarry tile. The individual pieces measured 6×6×1/2 inches thick. In a water absorption test according to ASTM C-20-70, such tile gives a percent water adsorption percentage between 0.5 and 0.6. In compression testing according to ASTM C-67-50, the tile shows a compressive crushing strength of between 25,000 and 30,000 psi. In thermal expansion testing according to ASTM C-372, a coefficient of linear thermal expansion is measured at a value of between 2.5×10 -6  and 3×10 -6  inches per inch per degree Fahrenheit. In thermal conductivity testing according to ASTM C-177, a &#34;K&#34; factor is recorded between 3 and 5. 
     The silicon carbide cement was that of the Carborundum Company, Refractories Division, of Keasby, N.J., sold under the designation of Carbofrax No. 4 silicon carbide mortar/patch. Typically, this product will analyze 86.0% silicon carbide. The silicon carbide particle size is 36 mesh and finer. Maximum use temperature is around 3200° F. 
     The carbon blocks measured 4 inches in thickness and were provided at their joints 30 with C-38 cement (not shown) of the Union Carbide Corporation, Carbon Products Division, of Niagara Falls, N.Y. This product is conductive approximately to the extent of the carbon blocks, resists oxidation, and can maintain bonding at service temperatures to 1400° C. and above. 
     While the invention has been described in terms of preferred embodiments, the claims appended hereto are intended to encompass all embodiments which fall within the spirit of the invention.