Electrolytic reduction of metal oxides

Abstract

An electrolytic cell and a method of electrolytically reducing a metal oxide, such as titania, in a solid state are disclosed. The electrolytic cell includes (a) a molten electrolyte, (b) a cathode in contact with the electrolyte, the cathode being formed at least in part from the metal oxide, and (c) a molten metal anode (such as silver or copper) in contact with the electrolyte.

1 . An electrolytic cell for electrolytic reduction of a metal oxide in a solid state, which electrolytic cell includes (a) a molten electrolyte, (b) a cathode in contact with the electrolyte, the cathode being formed at least in part from the metal oxide, and (c) a molten metal anode in contact with the electrolyte.  
     
     
         2 . The electrolytic cell defined in  claim 1  wherein the metal of the molten metal anode has a relatively high saturation level for oxygen at the operating temperature of the cell.  
     
     
         3 . The electrolytic cell defined in  claim 1  wherein the metal of the molten metal anode is chosen such that its melting point is within the operating temperature ranges of the electrolyte.  
     
     
         4 . The electrolytic cell defined in  claim 1  wherein the melting point of the metal of the molten metal anode is higher than the melting point of the electrolyte and lower than the vaporisation and/or decomposition temperature of the electrolyte.  
     
     
         5 . The electrolytic cell defined in  claim 1  wherein the metal of the molten metal anode has a very low solubility in the molten electrolyte at the cell operating temperatures,  
     
     
         6 . The electrolytic cell defined in  claim 1  wherein the metal of the molten metal anode is silver or copper.  
     
     
         7 . The electrolytic cell defined in  claim 1  further including a means for removing oxygen that has diffused into the molten metal anode from the cell.  
     
     
         8 . The electrolytic cell defined in  claim 7  wherein the cell oxygen removal means includes a duct that communicates with the molten metal anode and a device to create a partial pressure reduction between the molten metal anode and a head of molten metal within the duct.  
     
     
         9 . A method of electrolytically reducing a metal oxide in a solid state in an electrolytic cell, which electrolytic cell includes (a) a molten electrolyte, (b) a cathode in contact with the electrolyte, the cathode being formed at least in part from the metal oxide, and (c) a molten metal anode in contact with the electrolyte, which method includes applying a cell potential across the anode and the cathode.  
     
     
         10 . The method defined in  claim 9  including maintaining the cell temperature above the melting points of the electrolyte and the metal of the metal anode.  
     
     
         11 . The method defined in  claim 9  including applying a cell potential above a decomposition potential of at least one constituent of the electrolyte so that there are cations of a metal other than that of the cathode metal oxide in the electrolyte.  
     
     
         12 . The method defined in  claim 9  wherein the metal oxide is a titanium oxide.  
     
     
         13 . The method defined in  claim 9  wherein the metal oxide is titania.  
     
     
         14 . The method defined in  claim 9  wherein the electrolyte is a CaCl 2 -based electrolyte that includes CaO as one of the constituents.  
     
     
         15 . The method defined in  claim 14  including maintaining the cell potential above the decomposition potential for CaO.  
     
     
         16 . The method defined in  claim 14  including maintaining the cell potential below the decomposition potential for CaCl 2 .  
     
     
         17 . The method defined in  claim 14  including maintaining the cell potential below 3.0V.  
     
     
         18 . The method defined in  claim 14  including maintaining the cell potential below 2.5V.  
     
     
         19 . The method defined in  claim 14  including maintaining the cell potential below 2.0V.  
     
     
         20 . The method defined in including maintaining the cell potential at least 1.5V.