CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. provisional application No.

62/353,246, filed June 22, 2016, which is herein incorporated by reference in its entirety.

FIELD

[0002] Embodiments of the present disclosure generally relate to electrodes useful for the electrolytic production of metal.

BACKGROUND

[0003] Hall-Heroult electrolytic cells are utilized to produce aluminum metal in the commercial production of aluminums form alumina that is dissolved in molten electrolyte and reduced by a DC electric current using electrodes.

SUMMARY

[0004] In some embodiments, an electrode includes: a core; an outer shell; and an intermediate layer disposed between the core and the outer shell, wherein the intermediate layer covers at least a portion of the core, wherein the intermediate layer comprises an inner boundary and an outer boundary, wherein the intermediate layer electrically contacts the core at the inner boundary and electrically contacts the outer shell at the outer boundary, wherein the intermediate layer at the inner boundary has a first coefficient of thermal expansion that is substantially similar to a coefficient of thermal expansion of the core, and wherein the intermediate layer at the outer boundary has a second coefficient of thermal expansion that is substantially similar to a coefficient of thermal expansion of the outer shell. [0005] In some embodiments, the core comprises one or more electrically conductive materials.

[0006] In some embodiments, the core comprises at least one metal or metal alloy.

[0007] In some embodiments, the at least one metal comprises at least one of: copper, nickel, iron, manganese, aluminum, cobalt, titanium, zinc or combinations thereof.

[0008] In some embodiments, the at least one metal of the core is in the form of at least one of: a solid material, a metal foam, a metal powder, a metal wire, or combinations thereof.

[0009] In some embodiments, the core comprises a cermet material having a continuous metal phase.

[00010] In some embodiments, the cermet material comprises a structure of alternating metal fibers and ceramic fibers.

[00011] In some embodiments, the cermet material comprises an interwoven microstructure.

[00012] In some embodiments, the outer shell comprises one or more ceramic materials.

[00013] In some embodiments, the ceramic material of the outer shell comprises at least one of oxides of iron, oxides of titanium, oxides of aluminum, oxides of chromium, oxides of zinc, oxides of vanadium, oxides of nickel, oxides of copper, oxides of ruthenium, oxides of tin, oxides of cobalt, nickel ferrites, copper ferrites, zinc ferrites, magnetite and combinations thereof.

[00014] In some embodiments, the intermediate layer comprises one or more cermet materials and wherein the one or more cermet materials comprise a metallic phase and a ceramic phase. [00015] In some embodiments, the metallic phase of the cermet material is continuous and the ceramic phase of the cermet material is discontinuous.

[00016] In some embodiments, the cermet material comprises 20 to 90 wt. % metal phase and the balance ceramic phase.

[00017] In some embodiments, the cermet material of the intermediate layer has a first ceramic concentration proximal the inner boundary of the intermediate layer and a second ceramic concentration proximal the outer boundary of the intermediate layer, and wherein the second ceramic concentration is greater than the first ceramic concentration.

[00018] In some embodiments, the coefficient of thermal expansion of the core is greater than the coefficient of thermal expansion of the outer shell.

[00019] In some embodiments, the core has a first electrical conductivity and the outer shell has a second electrical conductivity, and wherein the intermediate layer has a third electrical conductivity between the first electrical conductivity and second electrical conductivity.

[00020] In some embodiments, the intermediate layer comprises one or more sub-layers.

[00021] In some embodiments, a method of forming a multi-layer electrode, includes: coating a core material with a first cermet material via at least one of spray coating, dip coating, and slip casting to form a first coated core, wherein the first cermet material has a first coefficient of thermal expansion at an inner boundary electrically contacting the core, that is substantially similar to a coefficient of thermal expansion of the core material; coating the coated core with a second cermet material via at least one of spray coating, dip coating, and slip casting, to form a second coated core; and coating the second coated core with a ceramic material via at least one of spray coating, dip coating, and slip casting, wherein the second cermet material has a second coefficient of thermal expansion at an outer boundary electrically contacting the ceramic material, that is substantially similar to a coefficient of thermal expansion of the ceramic material.

[00022] In some embodiments, coating the core with the cermet material further comprises: pressing a cermet powder on the core; and sintering the cermet powder.

[00023] In some embodiments, coating the core with the cermet material further comprises: forming a slurry comprising sub-micron size oxide powders and polymer binders; spray drying the slurry to form aggregated oxide granules; mixing the aggregated oxide granules with metal powder to produce a cermet powder blend; spray drying the slurry to form cerment granules; isostatically pressing the cermet granules onto the core to form a green intermediate layer; sintering the electrode to a temperature of 1000 to 1350 degrees Celsius in an inert gas atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

[00024] Embodiments of the present invention, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the invention depicted in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[00025] Figures 1A-1B depict a cross section of one embodiment of an electrode in accordance with some embodiments of the present invention.

[00026] Figures 2A-2E depict plan views of different embodiments of an electrode in accordance with some embodiments of the present invention. [00027] Figures 3A-3B are micrographs of electrodes in accordance with some embodiments of the present invention.

[00028] Figures 4A-4B depict a core of an electrode in accordance with some embodiments of the present invention.

[00029] Figures 5 A-5B depict the cermet material of the intermediate layer of an electrode in accordance with some embodiments of the present invention.

[00030] Figures 6A-6B depict a core of an electrode in accordance with some embodiments of the present invention.

[00031] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DESCRIPTION

[00032] The present invention will be further explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Further, some features may be exaggerated to show details of particular components.

[00033] The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. In addition, any measurements, specifications and the like shown in the figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[00034] Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention which are intended to be illustrative, and not restrictive.

[00035] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases "in one embodiment" and "in some embodiments" as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases "in another embodiment" and "in some other embodiments" as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

[00036] In addition, as used herein, the term "or" is an inclusive "or" operator, and is equivalent to the term "and/or," unless the context clearly dictates otherwise. The term "based on" is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of "a," "an," and "the" include plural references. The meaning of "in" includes "in" and "on. [00037] As used herein, "cermet material" is a composite material comprising a ceramic phase and a metallic phase. In some embodiments, the ceramic phase is a continuous phase and the metal phase is a discontinuous phase in the cermet material. In some embodiments, the metal phase is a continuous phase and the ceramic phase is a discontinuous phase in the cermet material.

[00038] As used herein, a "discontinuous phase" is a phase of a cermet material that is present in the cermet material as dispersed particles surrounded by the continuous phase of the cermet material.

[00039] As used herein, a "continuous phase" is a phase of a cermet material that surrounds the dispersed particles of the discontinuous phase.

[00040] As used herein, a "metallic phase" is a phase of a cermet material that comprises at least one alloy and/or elemental metal. In some embodiments, the metallic phase may comprise at least one of copper, nickel, iron, cobalt, titanium, aluminum, zinc, and/or alloys thereof.

[00041] As used herein, a "ceramic phase" is a phase of a cermet material that comprises at least one metal oxide. In some embodiments, the ceramic phase may comprise at least one ceramic material such as: a copper oxide, a nickel oxide, an iron oxide, a cobalt oxide, a titanium oxide, an aluminum oxide, a zinc oxide, and/or combinations thereof.

[00042] As used herein, a "ceramic concentration" is an amount of ceramic material per unit volume of cermet material.

[00043] As used herein, a "ceramic concentration gradient" is a difference in ceramic concentration along a direction within a cermet material. [00044] Figures 1A and IB depict an electrode 1 in accordance with some embodiments of the present disclosure. In some embodiments, the electrode 1 is suitable for use in an aluminum electrolysis cell. In some embodiments the electrode 1 is suitable for use as an anode in an aluminum electrolysis cell. In some embodiments, the electrode comprises a core 100, an outer shell 300; and an intermediate layer 200 disposed between the core 100 and the outer shell 300.

[00045] In some embodiments, the core 100 comprises one or more electrically conductive materials. In some embodiments, the core 100 comprises at least one metal. In some embodiments, the metal of the core 100 may comprise at least one of: copper, nickel, iron, manganese, aluminum, cobalt, titanium, aluminum, zinc and combinations thereof. In some embodiments, the core 100 comprises at least one metal alloy, including but not limited to: corrosion protected steel, carbon steel, nickel -chromium alloy (e.g. Inconel®), or nickel- chromium -molybdenum alloy (e.g. Hastelloy®). In some embodiments, the core 100 comprises at least one of: a solid material, a metal foam, a metal powder, a metal wire; and cermet having a continuous metal phase and a discontinuous ceramic phase. In some embodiments, the core 100 comprises a continuous metal phase and a continuous ceramic phase.

[00046] In some embodiments, as illustrated in Figure 4A, the core 100 comprises cermet having a layered metal 400/ceramic 402 structure. In some embodiments, the core 100 comprises a cermet having an alternating metal 400/ceramic 402 structure as illustrated in Figure 4B. In some embodiments, as illustrated in Figures 6A and 6B, the core 100 may comprise a cermet having an interwoven metal 400/ceramic 402 microstructure.

[00047] In some embodiments, the core 100 is cylindrical and has a diameter of 1/8 inch to 6 inches. In some embodiments, the core is cylindrical and has a diameter of 1/4 inch to 5 inches. In some embodiments, the core is cylindrical and has a diameter of 1/2 inch to 4 inches. In some embodiments, the core is cylindrical and has a diameter of 1 inch to 3 inches. In some embodiments, the core is cylindrical and has a diameter of about 2 inches.

[00048] In some embodiments, the core is non-cylindrically shaped and has a thickness of

1/8 inch to 4 inches and width of 1/2 inch to 12 inches. In some embodiments, the core is non- cylindrical shaped and has a thickness of 1/4 inch to 3 inches. In some embodiments, the core is non-cylindrical shaped and has a thickness of 1/2 inch to 2 inches. In some embodiments, the core is non-cylindrical shaped and has a thickness of about 1 inch. In some embodiments, the core is non-cylindrical shaped and has a width of 1 inch to 11 inches. In some embodiments, the core is non-cylindrical shaped and has a width of 2 inches to 10 inches. In some embodiments, the core is non-cylindrical shaped and has a width of 3 inches to 9 inches. In some embodiments, the core is non-cylindrical shaped and has a width of 4 inches to 8 inches. In some embodiments, the core is non-cylindrical shaped and has a width of 5 inches to 7 inches. In some embodiments, the core is non-cylindrical shaped and has a width of about 6 inches.

[00049] In some embodiments, the core has a height of 2 to 48 inches. In some embodiments, the core has a height of 4 to 46 inches. In some embodiments, the core has a height of 6 to 44 inches. In some embodiments, the core has a height of 8 to 42 inches. In some embodiments, the core has a height of 10 to 40 inches. In some embodiments, the core has a height of 12 to 36 inches. In some embodiments, the core has a height of 14 to 32 inches. In some embodiments, the core has a height of 16 to 28 inches. In some embodiments, the core has a height of 18 to 24 inches.

[00050] In some embodiments, the outer shell 300 comprises one or more ceramic materials. In some embodiments, the ceramic materials of the outer shell 300 comprise at least one of oxides of iron, oxides of titanium, oxides of aluminum, oxides of chromium, oxides of zinc, oxides of vanadium, oxides of nickel, oxides of copper, oxides of ruthenium, oxides of tin, oxides of cobalt, nickel ferrites, copper ferrites, zinc ferrites, magnetite and combinations thereof.

[00051] In some embodiments, the outer shell 300 has a thickness of 1/4 inch to 3 inches.

In some embodiments, the outer shell 300 has a thickness of 1/2 inch to 2 inches. In some embodiments, the outer shell 300 has a thickness of about 1 inch.

[00052] In some embodiments, the coefficient of thermal expansion of the core 100 is greater than the coefficient of thermal expansion of the outer shell 300. For example, Table 1 depicts non-limiting examples of materials suitable for use as the core, along with electrical conductivity and CTE values of the of the core material. Table 2 depicts non-limiting examples of materials suitable for use as the outer shell along with electrical conductivity and CTE values of the outer shell material. Thermal stresses arising from thermal expansion mismatch between the core 100 and the outer shell 300 can lead to cracking of the outer shell 300 during use of the electrode 1 in an aluminum electrolysis cell. Cracking of the outer shell can lead to corrosion of the core 100 from exposure to electrolytic bath chemicals in the aluminum electrolysis cell.

Table 1

Table 2

Ni Ferrite 0.03 5.1 14.2

[00053] In some embodiments, the intermediate layer 200 may have coefficient of thermal expansion (CTE) that is between the coefficients of thermal expansion of the core 100 and the outer shell 300. Thus, in some embodiments, the intermediate layer 200 may serve to at least partially compensate for this difference in thermal expansion. Therefore, in some embodiments, the intermediate layer 200 may serve to prevent the outer shell 300 from cracking during use of the electrode 1 in an aluminum electrolysis cell. Furthermore, the intermediate layer 200 may add corrosion protection to the core 100.

[00054] In some embodiments, as depicted in Figure 1A-1B, the intermediate layer 200 has an inner boundary 202 and an outer boundary 204. The inner boundary 202 of the intermediate layer 200 contacts the core 100. The outer boundary 204 of the intermediate layer contacts the outer shell 300. In some embodiments, the intermediate layer 200 at the inner boundary 202 has a coefficient of thermal expansion that is substantially similar to a coefficient of thermal expansion of the core 100 and the intermediate layer 200 at the outer boundary 202 has a coefficient of thermal expansion that is substantially similar to a coefficient of thermal expansion of the outer shell 300. In some embodiments, the intermediate layer 200 may have an electrical conductivity that is between the electrical conductivities of the core 100 and the outer shell 300.

[00055] In some embodiments, the intermediate layer covers at least a portion of the core 100. In some embodiments, the intermediate layer covers at least 5% of the core. In some embodiments, the intermediate layer covers at least 10% of the core. In some embodiments, the intermediate layer covers at least 15% of the core. In some embodiments, the intermediate layer covers at least 20% of the core. In some embodiments, the intermediate layer covers at least 25% of the core. In some embodiments, the intermediate layer covers at least 30% of the core. In some embodiments, the intermediate layer covers at least 35% of the core. In some embodiments, the intermediate layer covers at least 40% of the core. In some embodiments, the intermediate layer covers at least 45% of the core. In some embodiments, the intermediate layer covers at least 50% of the core. In some embodiments, the intermediate layer covers at least 60% of the core. In some embodiments, the intermediate layer covers at least 70% of the core. In some embodiments, the intermediate layer covers at least 80% of the core. In some embodiments, the intermediate layer covers at least 90% of the core. In some embodiments, the intermediate layer covers at least 95% of the core.

[00056] In some embodiments, the intermediate layer 200 comprises one or more cermet materials. In some embodiments, the cermet material of the intermediate layer 200 comprises a metallic phase and a ceramic phase. In some embodiments, the cermet material of the intermediate layer is 20 to 90 wt% metal phase and the balance ceramic phase. In some embodiments, the cermet material of the intermediate layer is 40 to 90 wt% metal phase and the balance ceramic phase. In some embodiments, the cermet material of the intermediate layer is 60 to 90 wt% metal phase and the balance ceramic phase. In some embodiments, the cermet material of the intermediate layer is 80 to 90 wt% metal phase and the balance ceramic phase. In some embodiments, as shown in Figures 5A and 5B, the metallic phase 502 of the cermet material 500 is continuous and the ceramic phase 504 of the cermet material 500 is discontinuous. In some embodiments, the cermet material of the intermediate layer 200 has a first ceramic concentration proximal the inner boundary 202 of the intermediate layer 200 and a second ceramic concentration proximal the outer boundary 204 of the intermediate layer 200. In some embodiments, the second ceramic concentration is higher than the first. In some embodiments, the cermet material of the intermediate layer 200 has a ceramic concentration gradient from the inner boundary to the outer boundary of the intermediate layer. In some embodiments, the ceramic concentration gradient increases from the inner boundary of the intermediate layer to the outer boundary of the intermediate layer.

[00057] Graph 1 shows the coefficient of thermal expansion (CTE) as a function of percent of metal phase in nickel ferrite cermet. The circular data points represent cermet of nickel ferrite and Cu and the square data point represent the cermet of nickel ferrite and Ni30Cu. As shown in Graph 1, when the metallic phase (Cu or Ni30Cu) is less than about 30 weight percentage, the CTEs of the cermet material is substantially constant. When the metallic phase (Cu or Ni30Cu) is higher than 30 weight percentage, the CTEs of the cermet material increases proportionally with metallic phase percentage, indicating metallic phases becomes the continuous phase after reaching 30 wt.%.

Graph 1 :

0 20 40 60 80 100

Metal percentage (wt%)

[00058] In some embodiments, the intermediate layer 200 may comprise one or more sublayers of cermet material. In some embodiments, as depicted in Figure IB, the intermediate layer 200 comprises, a first sub-layer 220 located proximal the inner boundary 202 of the intermediate layer 200, a third sub-layer 230 located proximal the outer boundary 204 of the intermediate layer 200, and a second sub-layer 210 located between the first sub-layer 220 and third sub-layer 230. In some embodiments, the first sub-layer 220 comprises a first cermet material, the second sub-layer 210 comprises a second cermet material, and the third sub-layer 230 comprises a third cermet material. In some embodiments, the first cermet material has a continuous metal phase and a discontinuous ceramic phase. In some embodiments, the third cermet material has a continuous ceramic phase and a discontinuous metal phase. [00059] In some embodiments, the first cermet material comprises 70 to 90 wt. % metal phase. In some embodiments, the first cermet material comprises 72 to 88 wt. % metal phase. In some embodiments, the first cermet material comprises 75 to 85 wt. % metal phase. In some embodiments, the first cermet material comprises 77 to 83 wt. % metal phase. In some embodiments, the first cermet material comprises about 80 wt. % metal phase.

[00060] In some embodiments, the first cermet material comprises 10 to 30 wt. % ceramic phase. In some embodiments, the first cermet material comprises 12 to 28 wt. % ceramic phase. In some embodiments, the first cermet material comprises 15 to 25 wt. % ceramic phase. In some embodiments, the first cermet material comprises 17 to 23 wt. % ceramic phase. In some embodiments, the first cermet material comprises about 20 wt. % ceramic phase.

[00061] In some embodiments, the second cermet material comprises 40 to 60 wt. % metal phase. In some embodiments, the second cermet material comprises 42 to 58 wt. % metal phase. In some embodiments, the second cermet material comprises 45 to 55 wt. % metal phase. In some embodiments, the second cermet material comprises 47 to 53 wt. % metal phase. In some embodiments, the second cermet material comprises about 50 wt. % metal phase.

[00062] In some embodiments, the second cermet material comprises 40 to 60 wt. % ceramic phase. In some embodiments, the second cermet material comprises 42 to 58 wt. % ceramic phase. In some embodiments, the second cermet material comprises 45 to 55 wt. % ceramic phase. In some embodiments, the second cermet material comprises 47 to 53 wt. % ceramic phase. In some embodiments, the second cermet material comprises about 50 wt. % ceramic phase.

[00063] In some embodiments, the third cermet material comprises 70 to 90 wt. % ceramic phase. In some embodiments, the third cermet material comprises 72 to 88 wt. % ceramic phase. In some embodiments, the third cermet material comprises 75 to 85 wt. % ceramic phase. In some embodiments, the third cermet material comprises 77 to 83 wt. % ceramic phase. In some embodiments, the third cermet material comprises about 80 wt. % ceramic phase.

[00064] In some embodiments, the third cermet material comprises 10 to 30 wt. % metal phase. In some embodiments, the third cermet material comprises 12 to 28 wt. % metal phase. In some embodiments, the third cermet material comprises 15 to 25 wt. % metal phase. In some embodiments, the third cermet material comprises 17 to 23 wt. % metal phase. In some embodiments, the third cermet material comprises about 20 wt. % metal phase.

[00065] In some embodiments, the intermediate layer has a thickness of 1/16 to 1 inch. In some embodiments, the intermediate layer has a thickness of 1/8 to 1/2 inch. In some embodiments, the intermediate layer has a thickness of about 1/4 inch.

[00066] In some embodiments, the first sub-layer has a thickness of 1/8 inch to 4 inches.

In some embodiments, the first sub-layer has a thickness of 1/4 inch to 3 inches. In some embodiments, the first sub-layer has a thickness of 1/2 inch to 2 inches. In some embodiments, the first sub-layer has a thickness of about 1 inch.

[00067] In some embodiments, the second sub-layer has a thickness of 1/4 inch to 2 inches. In some embodiments, the second sub-layer has a thickness of 1/2 inch to 1.5 inches. In some embodiments, the second sub-layer has a thickness of about 1 inch.

[00068] In some embodiments, the third sub-layer has a thickness of 1/4 to 1 inch. In some embodiments, the third sub-layer has a thickness of 3/8 to 7/8 inch. In some embodiments, the third sub-layer has a thickness of 1/2 to 3/4 inch. In some embodiments, the third sub-layer has a thickness of about 5/8 inch.

[00069] The electrode may be formed in a variety of shapes. Non-limiting examples of the shape of the electrode include cylindrical or non-cylindrical. For example, in some embodiments as shown in Figure 2A, the electrode may have a rectangular shape when viewed from the top. In some embodiments, as shown in Figure 2B, the electrode may have a rounded rectangular shape when viewed from the top. In some embodiments, as shown in Figure 2C, the electrode may be pill shaped when viewed from the top. In some embodiments, as shown in Figure 2D, the electrode may be elliptical when viewed from the top. In some embodiments, as shown in Figure 2E, the electrode may have a circular shape when viewed from the top.

[00070] Figure 3 A is a micrograph of one embodiment of an electrode in accordance with the present invention. As shown in Figure 3A, the electrode includes a core comprised of wires 110, an outer shell 310 comprised of ceramic material, and an intermediate layer 210 comprised of cermet material having a continuous metal phase and a discontinuous ceramic phase.

[00071] Figure 3B is a micrograph of another embodiment of an electrode in accordance with the present invention. As shown in Figure 3B, the electrode includes a core comprised of solid metal material 120, an outer shell 320 comprised of ceramic material, and an intermediate layer 220 comprised of cermet material. The embodiment of Figure 3B depicts an intermediate layer 220 having an increasing ceramic concentration gradient from the solid metal material 120 of the core to the outer shell 320 of ceramic material.

[00072] In some embodiments, a method of forming a multi-layer electrode, includes coating a core material with a first cermet material via at least one of spray coating, dip coating, and slip casting to form a first coated core, wherein the first cermet material has a first coefficient of thermal expansion at an inner boundary electrically contacting the core, that is substantially similar to a coefficient of thermal expansion of the core material; coating the coated core with a second cermet material via at least one of spray coating, dip coating, and slip casting, to form a second coated core; and coating the second coated core with a ceramic material via at least one of spray coating, dip coating, and slip casting, wherein the second cermet material has a second coefficient of thermal expansion at an outer boundary electrically contacting the ceramic material, that is substantially similar to a coefficient of thermal expansion of the ceramic material.

[00073] In some embodiments, the coating with the cermet material (e.g. first cermet material or second cermet material) comprises pressing a cermet powder onto the underlying material (e.g. electrode core) and sintering the cermet powder.

[00074] In some embodiments, coating the core with cermet material comprises producing a cermet powder blend. In some embodiments, the step of producing a cermet powder blend includes mixing aggregated oxide granules with metal powder. In some embodiments, the aggregated oxide granules may be produced, for example, by forming a slurry of sub-micron size oxide powders and polymer binders or a slurry of sub-micron size oxide powders, polymer binders, and metal powders, and then spray drying the slurry to form aggregated oxide granules that flow and deform readily during forming. In some embodiments, the cermet powder blend may be mixed into a slurry and spray dried to from cermet granules. In some embodiments, the cermet granules may be pressed isostatically onto the core at an isostatic pressure to form a green intermediate layer. In some embodiments, the isostatic pressure is 5 to 35 kpsi (thousand pounds per square inch). In some embodiments, the green intermediate layer may be heated in an inert atmosphere. In some embodiments the inert atmosphere comprises Ar and/or N2 with oxygen concentration below lOOppm. In some embodiments, the core with green intermediate layer is placed in a furnace and exposed to a first temperature of 400 to 600 degrees C to burn out the polymer binder. In some embodiments, the heating rate is from 10 to 180 degrees C/hr. In some embodiments, the electrode with green intermediate layer is exposed to a second temperature of 1000 to 1350 degrees Celsius to sinter the cermet granules and form a cermet intermediate layer.

[00075] While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. Further still, the various steps may be carried out in any desired order (and any desired steps may be added and/or any desired steps may be eliminated).