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AssigneeAluminum Company of America
InventorsPerry A. Foster, Jr., Subodh K. Das, Aaron J. Becker
Estimating the term…
A metal such as aluminum is produced by electrolysis of a compound of the metal in a solvent such as a molten salt. Electrolysis is carried out by passing a current from an anode to a cathode between which the solvent bath is situated. The cathode or cathode member is composed of a graphite substrate coated with a refractory hard metal such as titanium diboride. The coating adhesion of the TiB.sub.2 is improved through control of the manufacture and structure of the graphite substrate to favor a higher coefficient of thermal expansion and to have the density of the graphite fall within a range of 1.6 to 1.85 grams per cubic centimeter. The steps in producing the graphite may include working it so as to provide a grain direction. One embodiment includes aligning the refractory hard metal coated graphite in the electrolytic cell with the graphite grain direction parallel to the direction of current flow from anode to cathode. The refractory hard metal coating can be imparted by chemical vapor deposition and should exhibit a dense columnar structure which reduces penetration of the coating by molten aluminum.
A method for the production of metal in an electrolytic cell comprising electrolyzing a bath comprising a compound of the metal dissolved in a molten solvent by passing electric current between one or more anodic and one or more cathodic surfaces to produce said metal which collects upon a base cathode surface, wherein the improvement comprises providing one or more cathode surfaces extending outwardly from said base cathode surface toward each anode, said cathode surfaces comprising a refractory hard metal coating on a graphite substrate, said graphite substrate being provided by graphitizing carbonaceous material to produce a substantially unitary and continuous graphite structure having a density of 1.6 to 1.85 grams per cubic centimeter and a coefficient of thermal expansion ranging from 0.7 to 1.4 times that of the refractory hard metal coating, said graphite exhibiting a directional grain pattern which is substantially aligned parallel to the overall direction of current flow in said electrolytic cell, said refractory hard metal coating being deposited upon said graphite substrate by chemical vapor deposition effected to provide a dense columnar structure describing a substantially continuous band within said refractory hard metal coating.
A method for the production of aluminum in an electrolytic cell comprising electrolyzing a molten fluoroaluminate salt bath containing aluminum oxide dissolved therein by passing electric current between one or more anodic and one or more cathodic surfaces to electrolyze said bath therebetween to produce molten aluminum which collects beneath said salt bath as a molten aluminum pool wherein the improvement comprises providing one or more cathode surfaces protruding from a cathode base beneath said molten aluminum pool and through said pool and into the overlying salt bath for electrolyzing said salt bath between said anodic and said protruding cathode surfaces, said protruding cathode surfaces comprising a boride coating selected from the borides of titanium and zirconium on a graphite substrate, said graphite substrate being provided by working and graphitizing carbonaceous material to produce a graphite having a density of 1.6 to 1.85 grams per cubic centimeter and a directional grain orientation which is aligned with the direction of overall anode-cathode current movement in said electrolytic cell, said graphite having a coefficient of thermal expansion ranging from 5.9 to 8.3 in/in/.degree.C. and from 0.9 to 1.1 times that of said boride coating, said graphite exhibiting a directional grain pattern which is substantially aligned with the direction of current flow in said electrolytic cell, said boride coating having a thickness of 0.01 to 0.05 inch and exhibiting a dense columnar structure through at least 0.01 inch of thickness substantially describing a substantially closed band within said coating.
Dependencies are inferred from the claim text.