ALUMINUM ELECTROLYZER ELECTRODE (VARIANTS)

Abstract

The invention relates to vertical or inclined electrodes of an electrolyzer for electrolytically producing aluminum from aluminum oxide. An electrode contains an electrode base and a surface coating based on refractory ceramics. According to a first variant of the invention, the electrode base is made of a composite material containing between 5% and 90% by mass of refractory ceramics, and of at least one metal having a melting temperature exceeding 1000 C., which forms refractory intermetallic compounds upon interaction with aluminum, and/or containing at least one alloy of such a metal. According to a second variant of the invention, the electrode base is made of a metal alloy, for example structural steel or another alloy, and the surface of the electrode base has applied thereto an intermediary layer consisting of a composite material having the composition described above.

Claims

1. An electrolyzer electrode for electrolytically producing aluminum from the aluminum oxide dissolved in molten electrolyte, including an electrode base and a surface coating applied to the base and based on or made from refractory ceramics, wherein the electrode base is made of a composite material containing between 5% and 90% by mass of refractory ceramics and at least one metal having a melting temperature exceeding 1000 C, which forms refractory intermetallic compounds upon interaction with aluminum, and optionally containing at least one alloy of such metal.

2. The electrode according to claim 1, wherein as the metal having a melting temperature exceeding 1000 C included into the composite material is used at least one of the following metals: iron, nickel, manganese, titanium, tantalum, zirconium, chromium, niobium, cobalt, vanadium, and optionally at least one alloy thereof.

3. The electrode according to claim 1, wherein as refractory ceramics included into the composite material of the electrode base and into the composite material of the surface coating borides and carbides of titanium, zirconium, niobium, tantalum, tungsten, molybdenum, boron carbides and optionally mixtures thereof are used.

4. The electrode according to claim 3, wherein borides and carbides are formed in the composite material of the electrode base during the electrode production process by adding boron and carbon into a metal and optionally an alloy included into the composite material.

5. The electrode according to claim 3, wherein refractory ceramics in the composite material is uniformly distributed throughout the material volume in the form of particles of 1-1000 m.

6. The electrode according to claim 1, wherein the composite material containing more than 90% by mass of refractory ceramics is applied to the electrode base as a surface coating.

7. The electrode according to claim 1, wherein the electrode base surface of the composite material which is placed underneath the surface coating of refractory ceramics is saturated with carbon.

8. The electrode according to claim 1, wherein it is a cathode or a cathode part of a bipolar electrode.

9. An electrolyzer electrode for electrolytically producing aluminum from the aluminum oxide dissolved in molten electrolyte, comprising an electrode base and a surface coating applied to the base and based on or made of refractory ceramics, wherein the electrode base is made of steel or metal alloy having an intermediate layer applied to the electrode base surface, wherein said intermediate layer is made of a composite material containing between 5% and 90% by mass of refractory ceramics and at least one metal having a melting temperature exceeding 1000 C., which forms refractory intermetallic compounds upon interaction with aluminum, and optionally containing at least one alloy of such metal.

10. The electrode according to claim 9, wherein the material for the metal alloy base is structural carbon steel.

11. The electrode according to claim 10, wherein heat-resistant and fire-resistant steel or heat-resistant and fire-resistant metal alloy is used as a base material.

12. The electrode according to claim 9, wherein as the metal having a melting temperature exceeding 1000 C. included into the composite material is used at least one of the following metals: iron, nickel, manganese, titanium, tantalum, zirconium, chromium, niobium, cobalt, vanadium, and optionally at least one alloy thereof.

13. The electrode according to claim 9, wherein as refractory ceramics in the composite material borides and carbides of titanium, zirconium, niobium, tantalum, tungsten, molybdenum, boron carbides and optionally mixtures thereof are used.

14. The electrode according to claim 13, wherein borides and carbides in the composite material of the electrode base are formed during the electrode production process by adding boron and carbon into metal or alloy included into the composite material.

15. The electrode according to claim 13, wherein the refractory ceramics is presented in the form of particles of 1-1000 m, wherein the particles are uniformly distributed throughout the material.

16. The electrode according to claim 9, wherein the intermediate layer is produced of the composite material the content of refractory ceramics of which increases across the layer thickness from the electrode base towards the surface coating from between 5 and 90% by mass near the base surface and up to more than 90% near the surface coating.

17. The electrode according to claim 9, wherein the electrode base surface coated with the intermediate layer of the composite material containing between 5 and 90% by mass of ceramics is covered with an additional layer containing more than 90% by mass of ceramics.

18. The electrode according to claim 9, wherein the cumulative thickness of the intermediate layer and surface coating is 0.5-10 mm.

19. The electrode according to claim 9, wherein the intermediate or additional layer surface saturated with carbon is arranged underneath the aluminum-wetted surface coating made of or based on the refractory ceramics.

20. The electrode according to claim 9, wherein it is a cathode or a cathode part of a bipolar electrode.

21. The electrode according to claim 17, wherein the intermediate or additional layer surface saturated with carbon is arranged underneath the aluminum-wetted surface coating made of or based on the refractory ceramics.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The essence of the inventive technical solution will be further described with the reference to the schematic representations of parts of aluminum-wetted electrodes cross-sections of the embodiments of the invention (FIG. 1 and FIG. 2). The drawings are illustrations of a part of the electrode cross-section adjacent to the surface since the shape and dimensions of electrodes can be randomly selected.

[0048] FIG. 1 is a representation of the first embodiment of electrodes comprising a base 2 of a composite material containing between 5 and 90% by mass of refractory ceramics.

[0049] FIG. 1 (A) is a representation of an electrode comprising a base 2 of a composite material containing between 5 and 90% of ceramics and a coating 3 based on refractory ceramics.

[0050] FIG. 1 (B) is a representation of an electrode comprising a base 2 of a composite material containing between 5 and 90% by mass of refractory ceramics, the surface 4 of which is carbon saturated and has a coating 3 based on refractory ceramics applied thereto.

[0051] FIG. 2 is a representation of the second embodiment of electrodes comprising a base of a metal alloy 1 and an intermediate layer of a composite material 2.

[0052] FIG. 2 (A) is a representation of an electrode comprising a base of a structural steel or a metal alloy 1 having a layer of a composite material 2 containing between 5 and 90% by mass of refractory ceramics and a coating based on the refractory ceramics 3 applied thereto.

[0053] FIG. 2 (B) is a representation of an electrode comprising a base 1 of a structural steel or a metal alloy, a surface 4 of which is carbon saturated and has a coating 3 based on the refractory ceramics applied thereto. In this case, the carbon saturated steel or alloy surface plays the role of an intermediate layer between the base and the coating.

[0054] FIG. 2 (C) is a representation of an electrode comprising a base 1 of a structural steel or a metal alloy with applied an intermediate layer 2 of a composite material containing between 5 and 90% by mass of refractory ceramics, the surface 4 of which is carbon saturated and has a coating 3 based on the refractory ceramics applied thereto.

EMBODIMENTS OF THE INVENTION

[0055] Example 1 illustrates the first embodiment of the invention. To produce an aluminum-wetted electrode, a plate of the composite material 80% by mass Fe20% by mass TiB.sub.2, having dimensions of 94*77*10 mm were used as a workpiece for a base 2. A stainless steel rod served as a current collector was arc-welded to the plate. Next, the workpiece surface of the wetted electrode was covered with a suspension of ceramic particles TiB.sub.2 in a solution of phenol-formaldehyde resin to create a surface coating. The covered coating was dried for 1 hour at room temperature, then for 1 hour at 150 C. In such a way, a surface coating layer 3 having a thickness of 1.5 mm and consisted of titanium diboride (93% by mass) and phenol formaldehyde resin (7% by mass) was formed on the aluminum-wetted electrode surface.

[0056] FIG. 1(A) schematically illustrates a cross-section of the electrode produced according to the Example 1.

[0057] Produced by this method sample was tested as a vertical cathode at electrolysis with two vertical electrodes in a corundum container having a diameter 110 mm and a height 220 mm and placed inside a safety graphite crucible. A copper plate having dimensions of 115*80*5 mm was used as an anode. The cathode was immersed in the melt so that a welded contact with a current collector was above the electrolyte level. The anode was fully immersed into the melt. The current densities of the anode and cathode were 0.5 A/cm.sup.2, the electrolysis temperature was 850 C.

[0058] In a few minutes after the start, the voltage was set in the range of 4.634.65V, and then its changes were insignificant. The test duration was 24 hours. Based on the test results, it was found that the surface of the electrode-cathode produced according to the invention was well aluminum-wetted and didn't have any signs of destructions. The cathode preserved its geometry. The cathode aluminum mass was 350.2 g. The current output as per the pure aluminum basis was 70%. Metal contamination with ironthe main component of the cathode metal basewas less than 0.1% by mass.

[0059] Example 2 illustrates the second embodiment of the invention. To produce an aluminum-wetted electrode, a metal base of the structural steel St3 having dimensions of 100*70*5 mm was used. The metal (steel) base had a shank for welding a metal current collector thereto. At the first step, foam ferronickel plates having a thickness of 3 mm were brazed to a base 1 to form an intermediate layer. The specific porosity of the foam ferronickel was 60 PPI. The porous metal base on the base surface was impregnated with a suspension of ceramic particles TiB.sub.2 in a solution of phenol-formaldehyde resin to produce a composite material intermediate layer. At the next step, a layer of that suspension of about 1 mm in thickness was applied to form the surface coating. Further, an electrode workpiece having the surface coating applied thereto was dried for 1 hour at room temperature, than for 1 hour at 150 C. For coat sintering, samples were fired for 3 hours at 800 C. in the activated carbon filling. Thus, the layer of composite material consisted of a ferronickel matrix and titanium diboride particles distributed therein, and the surface coating layer 3 based on the refractory ceramics were formed on the surface of the metal (steel) base. The refractory ceramics content in the composite material of the intermediate layer was about 80% by mass.

[0060] FIG. 2(A) schematically illustrates a cross-section of the electrode produced according to the Example 1.

[0061] Produced by this method sample was tested as a vertical cathode at electrolysis with two vertical electrodes in a corundum container having a diameter 110 mm and a height 220 mm and placed inside a safety graphite crucible. A copper plate having dimensions of 100*70*3 mm was used as an anode. The anode and cathode were immersed into the melt so that the electrolyte level above them was about 1 cm. The current densities of the anode and cathode were 0.5 A/cm.sup.2, the electrolysis temperature was 850 C.

[0062] In a few minutes after the start, the voltage was set in the range of 5.365.41V, then changed insignificantly. The test duration was 24 hours. Based on the test results it was found that the surface of the cathode was well aluminum-wetted and didn't have any signs of destructions. The cathode preserved its geometry. The cathode aluminum mass was 365.3 g. The current output as per the pure aluminum basis was 75%. Metal contamination with ironthe main component of the cathode metal basewas less than 0.1% by mass. The other electrodes produced with the use of the metal base of the structural steel St3 according to the embodiments of the invention of FIGS. 2B and 2C have shown similar results.

[0063] Example 3 is an illustration of a specific variant of the invention according to the first embodiment with the carburization of a composite material base surface. To produce an aluminum-wetted electrode, a plate of the composite material containing 80% by mass Fe20% by mass TiB.sub.2, having dimensions of 96*81*10 mm was used as a workpiece for a base 2. The plate was solid-phase carburized in order to diffusely saturate a surface layer 4 of the sample with carbon. As a carburizing agent, the mixture consisting of 80% of charcoal and 20% of sodium carbonate was used. The carburizing process continued for 10 hours in the sealed corundum container at 900 C. Then, a stainless steel rod served as a current collector was arc-welded to the composite material plate. Next, the workpiece surface of the wetted element was covered with a suspension of ceramic particles TiB.sub.2 in a solution of phenol-formaldehyde resin. The electrode base 2 was dried for 1 hour at room temperature, then for 1 hour at 150 C. In such a way, a surface coating layer 3 having a thickness of 2 mm and consisted of titanium diboride (93% by mass) and phenol formaldehyde resin (7% by mass) was formed.

[0064] FIG. 1(B) schematically illustrates a cross-section of the electrode produced according to the Example 3.

[0065] Produced by this method sample was tested as a vertical cathode at electrolysis with two vertical electrodes in a corundum container having a diameter 110 mm and a height 220 mm and placed inside a safety graphite crucible. A copper plate having dimensions of 114*79*4.4 mm was used as an anode. The cathode was immersed in the melt so that a welded contact with a current collector was above the electrolyte level. The anode was fully immersed into the melt. The current densities of the anode and cathode were 0.5 A/cm.sup.2, the electrolysis temperature was 850 C.

[0066] In a few minutes after the start, the voltage was set in the range of 5.956.05V, then changed insignificantly. The test duration was 24 hours. Based on the test results it was found that the surface of the cathode was well aluminum-wetted and didn't have any signs of destructions. The cathode preserved its geometry. The cathode aluminum mass was 360 g. The current output as per the pure aluminum basis was 65%. Metal contamination with ironthe main component of the cathode metal basewas less than 0.1% by mass.

[0067] Obtained results have confirmed that the inventive aluminum-wetted electrode is resistant to oxidation, aluminum, and electrolyte, has the high electrical conductivity, ensures a reliable electrical contact between an aluminum-wetted element and a current collector.