Coatings for electrodes in electric arc furnaces

Abstract

A graphite-containing electrode is described that includes a zirconium-based coating that retards loss of material from the electrode when used at elevated temperatures, e.g., when used in an arc furnace at 1000-2000°C. The zirconium-based coating may be disposed on the graphite-containing surface of the electrode or on a pre-coating that is disposed on the surface of the electrode. The zirconium-based coating includes one or more zirconium compounds, such as zirconia. Compositions and methods for coating the graphite-containing electrode with the zirconium-based coating composition are also described.

Description

[Technical field]

[0001] This application relates to protective coatings for electrodes, and more particularly to zirconium-containing coatings provided on graphite-containing electrodes. [Background technology]

[0002] Carbon-based (e.g., graphite) electrodes used in furnaces for steel production (e.g., electric arc furnaces) are subjected to harsh operating conditions including high temperatures, the crushing of molten steel or other metals, and the passage of large currents and charges through the electrodes. Exemplary electrodes used for these purposes vary in diameter from 15 to 30 inches (38 to 76 cm) and can even be 2 feet (0.61 meters) or longer. Such electrodes may have lengths as long as 10 feet (3 meters) or longer.

[0003] These electrodes, when used in electric arc furnaces, eventually wear out or otherwise deteriorate due to oxidation and / or high temperatures. Temperatures in industrial electric arc furnaces can reach 1,800°C or even higher. Spraying the arc furnace electrodes with water is often used to cool the electrodes during operation, and such cooling can mitigate the deterioration to some extent, but nevertheless, up to 70 weight percent of the electrodes can oxidize and / or otherwise deteriorate. Such losses are costly, since electrode costs are a significant part of the electric arc steelmaking process. Summary of the Invention [Problem to be solved by the invention]

[0004] It would be highly desirable to provide electrodes that have a longer service life and are better protected from degradation and loss at harsh temperatures and other environmental conditions such as those experienced by graphite-containing electrodes operating in electric arc furnaces. [Means for solving the problem]

[0005] Described herein are zirconium-based compositions and methods for coating and protecting graphite-containing electrodes, such as those used in electric arc furnaces, protected graphite-containing electrodes including zirconium-based coatings, and arc furnaces incorporating such protected electrodes.

[0006] Applicants have discovered that a zirconium-based coating composition can be applied to a graphite-containing electrode to extend its useful life. Upon curing (e.g., drying in some embodiments), the coating composition forms a protective coating on the electrode. Applicants have discovered that a protected graphite-containing electrode so coated exhibits a slower rate of mass loss under conditions such as those experienced by the electrode in an operating electric arc furnace than a similar electrode without the coating. Furthermore, such coated (protected) electrodes exhibit a higher cooling rate when cooled by water spray than a similar electrode without the zirconium-based coating. Thus, applying a zirconium-based coating composition to a graphite-containing electrode in accordance with the disclosed method is expected to provide the electrode with a longer useful life. When used in an electric arc furnace, the protected electrodes last longer, thereby reducing the operating costs of the arc furnace incorporating them.

[0007] In one aspect, a method of protecting a graphite electrode includes applying a zirconium-based coating composition onto the graphite electrode and curing the coating composition to form a protective coating on the graphite electrode.

[0008] In a further aspect, a protected graphite-containing electrode is provided that includes a graphite-containing electrode and a zirconium-based coating disposed on a surface of the graphite-containing electrode. In some such embodiments, the protected graphite-containing electrode may further include a pre-coating disposed on a surface of the underlying graphite-containing electrode to increase adhesion of the overlying zirconium-based coating to the graphite-containing electrode. Thus, in such embodiments, the pre-coating is disposed between the electrode (also referred to herein as a "member") and the zirconium-based coating. In practical effect, the pre-coating functions as a primer layer between the electrode and the zirconium-based coating. In other embodiments, the graphite-containing electrode does not include a pre-coating, and the zirconium-based coating may be disposed directly on the surface of the graphite-containing member (electrode).

[0009] In a further aspect, an arc furnace is provided with at least one protected graphite-containing electrode, the at least one protected graphite-containing electrode comprising a graphite-containing electrode and at least one zirconium-based coating disposed on the electrode.

[0010] The disclosed compositions and methods reduce electrode degradation and wear, while improving heat transfer and increasing the cooling rate of the electrode. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an electric arc furnace according to certain embodiments of the present invention;

[0012] [Diagram 2] FIG. 2 is a schematic diagram of a guard electrode according to certain embodiments of the present invention.

[0013] [Diagram 3] FIG. 2 is a schematic diagram of a guard electrode according to certain embodiments of the present invention.

[0014] [Figure 4]FIG. 1 is a graph showing coating benefits over thermal cycling at 1000° C.

[0015] [Diagram 5] FIG. 13 is a graph showing results without phytic acid pre-coating.

[0016] [Figure 6] FIG. 1 is a graph showing coating benefits over thermal cycling at 1500° C.

[0017] [Figure 7] FIG. 1 is a graph showing coating benefits for thermal cycling at 1100° C., 1300° C. and 1500° C.

[0018] [Figure 8] FIG. 1 is a graph showing heat flux of a coated graphite electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Although the present disclosure provides reference to various embodiments, those skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present application. Various embodiments are described in detail with reference to the drawings. Reference to various embodiments is not intended to limit the scope of the claims appended hereto. Moreover, any examples described in this application are illustrative and not intended to be limiting, merely describing some of the many possible embodiments of the appended claims.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. In case of conflict, the present document, including definitions, will prevail. Although methods and materials similar or equivalent to those described herein may be used in the practice or testing of this application, the methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety and for all purposes.

[0021] As used herein, the terms "comprise(s)", "include(s)", "having", "has", "can", "contain(s)", and variations thereof are intended to be open-ended transitional phrases, terms, or words that do not exclude the possibility of additional acts or structures. The singular forms "a", "and", and "the" include plural referents unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments that "comprise", "consist of", and "consist essentially of" the embodiments or elements presented herein, whether or not expressly stated.

[0022] As used herein, the terms "optional" or "optionally" mean that the subsequently described event or circumstance may occur but need not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not occur.

[0023] As used herein, the term "about" to modify amounts, concentrations, volumes, process temperatures, process times, yields, flow rates, pressures, and similar values ​​and ranges of ingredients in a composition, for example, when describing embodiments of the present disclosure, refers to variations in numerical quantities that may occur, for example, due to typical measuring and handling procedures used to make a compound, composition, concentrate, or use formulation; due to accidental errors in these procedures; due to differences in the manufacture, source, or purity of starting materials or ingredients used to carry out the method, and due to similar approximation considerations. The term "about" also encompasses amounts that differ due to degradation of a formulation having a particular initial concentration or mixture, and amounts that differ due to mixing or processing a formulation having a particular initial concentration or mixture. When modified by the term "about", the appended claims include equivalents of these amounts. Furthermore, when "about" is used to describe a range of values, for example, "about 1 to 5" means "1 to 5" and "about 1 to about 5" and "1 to about 5" and "about 1 to 5" unless otherwise limited by the context.

[0024] As used herein, the term "substantially" means "for the most part."

[0025] As used herein, the term "substantially free" of a material means "to a significant extent free" of that material, or to such an extent that the amount of material present only negligibly affects the properties of the composition. For example, a composition that is "substantially free" of a particular compound or material may not contain that compound or material, or may have a small amount of that compound or material present due to unintended contamination, side reactions, incomplete purification, or the like. A "small amount" may be a trace amount, an immeasurable amount, an amount that does not interfere with value or properties, or some other amount as the context provides. A composition that has "substantially only" a list of provided ingredients may consist of only those ingredients, or may have trace amounts of some other ingredients present, or may have one or more additional ingredients that do not materially affect the properties of the composition. Additionally, for example, "substantially" as used to modify the type or amount, property, measurable amount, manner, value, or range of a compounded ingredient in a composition in describing an embodiment of the present disclosure refers to a variation that does not affect the recited composition, property, amount, manner, value, or range as a whole in a manner that invalidates the intended composition, property, amount, manner, value, or range. When modified with the term "substantially," the claims appended hereto include equivalents according to this definition.

[0026] As used herein, "consisting essentially of" and "consisting of" are to be interpreted in accordance with U.S. patent law.

[0027] As used herein, any recited range of values ​​should be construed as supporting a claim reciting any subrange having endpoints that are real values ​​within the recited range, contemplating all values ​​within that range. By way of example, the disclosure herein of a range of 1 to 5 is intended to support a claim of any of the following ranges: 1 to 5, 1 to 4, 1 to 3, 1 to 2, 2 to 5, 2 to 4, 2 to 3, 3 to 5, 3 to 4, and 4 to 5, as well as fractions thereof, e.g., 1.5 to 3.5, 1.7 to 4.8, etc.

[0028] A protective coating system is described for protecting electrodes, more particularly graphite-containing electrodes, especially those operating in electric arc furnaces, from degradation. A protected electrode suitable for use in an electric arc furnace is described. An arc furnace including the protected electrode is also described. Additionally, compositions and methods for coating electrodes in electric arc furnaces are described. In some embodiments, the electric arc furnace is used in steelmaking. The disclosed coatings improve electrode life and improve heat flux, thereby increasing the cooling rate of the electrode. Thus, one aspect of the invention is an arc furnace comprising one or more protected electrodes as further described herein.

[0029] The protection strategy of the present invention can be implemented with a wide range of electrodes. For illustrative purposes, the principles of the present invention will be described in the context of an electric arc furnace. FIG. 1 shows an electric arc furnace ("EAF") 10 incorporating a plurality of protective electrodes 14 of the present invention. The walls of the furnace define an interior 12. In implementations where the electric arc furnace 10 is used for steelmaking, the furnace 10 may consist of a refractory-lined vessel that is typically larger in size, water-cooled, and covered with a retractable roof.

[0030] In some embodiments, each of the electrodes 14 is clamped by an electrode holder or clamp for insertion of the electrodes 14 into the furnace 10. The electrodes 14 may enter the furnace through one or more openings, such as an opening through the roof. However, in other embodiments, one or more electrodes 14 may be inserted into the furnace interior 12 through one or more walls or floors of the furnace 10. In still other embodiments, each electrode 14 may be disposed entirely within the interior 12.

[0031] The electrode is automatically raised and lowered by a suitable positioning system, which may use either an electric winch hoist or a hydraulic cylinder. The furnace 10 desirably includes a regulating system. In some implementations, the regulating system helps to maintain a nearly constant current and power input during melting of the charge, even though scrap may move under the electrode 14 as the charge melts.

[0032] The electric arc furnace 10 is a furnace in which charge material is heated by an electric arc. An electric arc is struck between the tip of the electrode 14 and the material in the furnace, causing the material to heat and, if necessary, melt. When an arc is formed between the charge material and the electrode, the charge is heated both by the current passing through the charge and by the radiant energy emitted by the arc. An embodiment of the electric arc furnace 10 may be, for example, an electric arc furnace as described in detail by J. A. T. Jones, B. Bowman, P. A. Lefrank, "Electric Furnace Steelmaking", The Making, Shaping and Treating of Steel, R. J. Fruehan, Editor. 1998, The AISE Steel Foundation: Pittsburgh, but such an embodiment is modified to incorporate the protected electrode 14 of the present invention. The cited documents are incorporated herein by reference in their entirety.

[0033] The graphite-containing electrode 14 can operate in high temperature environments of 400° C. to 3000° C. In a conventional electric arc furnace, a typical electrode will oxidize and / or otherwise degrade and thus wear away in the high temperature atmosphere of a conventional furnace. As a result of such degradation, the shape of the electrode may change (e.g., to the shape of a pencil tip) and the diameter of the base of the electrode may decrease by approximately 50-70% compared to the original electrode diameter.

[0034] Degradation reduces electrode performance and necessitates maintenance, inspection, or replacement of the degraded electrodes. A significant advantage of the present invention is that the protected electrode(s) 14 in the furnace 10 are more resistant to degradation than conventional unprotected electrodes and therefore last longer before requiring maintenance, inspection, or replacement.

[0035] An electric arc furnace 10 may include one or more guarded electrodes 14 of the present invention. For purposes of illustration, the arc furnace 10 is shown as being powered by a three-phase power supply and thus includes three guarded electrodes 14. However, in other embodiments, the arc furnace includes one, two, four, five, six, seven, eight, nine, ten, or more than ten electrodes and / or is supplied with other types of power, such as a two-phase power supply, or a DC power supply.

[0036] Each electrode 14 may comprise a single segment or may be assembled from multiple segments. An electrode 14 formed from multiple segments is referred to herein as a combination electrode. A combination electrode may be provided in segments that are assembled with a threaded connection. The threaded connection allows the segments to be disassembled so that new segments can be added when the electrode segments wear out. In some embodiments, a combination electrode has an upper metal section to which a lower section including a carbon material such as graphite is attached by a threaded connection or threaded nipple or the like.

[0037] The types of graphite-containing electrodes that may include and be protected by any of the zirconium-based coatings described herein are not particularly limited, but for purposes of illustration, protected electrode 14 is shown with particular reference to Figures 2-3, which show electrode 14 that is cylindrical in shape and thus circular in cross section, however, alternative embodiments of electrode 14 are described herein.

[0038] FIG. 2 illustrates in more detail an embodiment of a cylindrical shielded electrode 14 in cross section. The shielded electrode 14 includes a graphite-containing member 16 having a surface 17. A protective zirconium-based coating 18 of the present invention is provided on at least a portion of the surface 17. The graphite-containing member 16 may be a graphite-containing electrode or any portion thereof, such as a graphite-containing segment of a combination electrode. The protective zirconium-based coating 18 is preferably present around the entire circumference of the electrode 14, as shown in FIG. 2. However, partial coverage of the surface 17 is also expected to have a significant beneficial effect in retarding loss and / or deterioration of the member 16.

[0039] 2-3 show an embodiment of a cylindrical protected electrode 14 for illustrative purposes, the shape and size of the graphite-containing electrode member 16 protected by the coating of the present invention are not particularly limited, and in shape, the graphite-containing electrode may be cylindrical, cubic, rectangular, conical, frustoconical, polygonal cylindrical, irregular, and combinations thereof. For example, the electrode member 16 may be cylindrical having a long axis but terminating in a tapered end, a rounded end, a conical end that narrows toward a tip, a frustoconical end that tapers toward a tip, and the like. For illustrative purposes, each of the electrodes 14 is shown as having a blunt tip. However, as discussed above, use of the electrodes 14 in the furnace 10 will cause the electrodes 14 to deteriorate and change in shape. Thus, one or more tips of the electrodes 14 may be tapered or other shapes before, during, and / or after use.

[0040] The graphite-containing electrode member 16 may be of any size. The electrode member 16, being cylindrical, has a length along the longitudinal axis and a circular cross section with a diameter in a plane perpendicular to the axis. In certain embodiments, the diameter of the electrode member 16 (or an electrode segment in a combined electrode) is between about 1 inch and 40 inches (0.0254 inches and 1.016 meters), between about 3 inches and about 30 inches (0.0762 meters and 0.762 meters), or between about 7 inches and about 30 inches (0.1778 meters and 0.762 meters).

[0041] In exemplary embodiments, the length of the electrode member 16 is between about 1 foot and 40 feet (0.3048 meters and 12.192 meters), between about 3 feet and about 30 feet (0.9144 meters and 9.144 meters), between about 3 feet and about 20 feet (0.9144 meters and 6.096 meters), between about 10 feet and 30 feet (3 meters and 9.1 meters), between about 10 feet and 20 feet (3 meters and 6.1 meters), or between about 12 feet and about 18 feet (3.7 meters and 5.5 meters). However, the electrode may vary in length due to loss of material from the electrode member 16, particularly from the tip (the portion of the electrode proximate the furnace charge to be melted). In combination electrodes, the length may be altered or restored by adding or replacing segments of the electrode member 16, such as at the end distal to the tip, to compensate for loss of electrode material from the tip proximal to the material to be melted in the furnace. The length of each segment may be approximately 5 feet to 15 feet (1.524 meters to 4.572 meters).

[0042] The graphite-containing electrode member 16 may include one or more of petroleum coke, needle coke, and graphite. The graphite-containing electrode may further include coal pitch to bind the coke as a binder. Thus, in embodiments, the electrode 16 includes, consists of, or consists essentially of one or more of petroleum coke, needle coke, and graphite, and coal pitch (coal tar). In some embodiments, the electrode 14 used in the electric arc furnace is a carbon-based electrode. In some embodiments, the electrode used in the electric arc furnace is a graphite-containing electrode.

[0043] In certain embodiments of the combination electrode, the segments comprise, consist of, or consist essentially of graphite or a graphite-containing material, include a cylindrical or generally cylindrical shape, and have an axis and a length along the axis.

[0044] The graphite-containing electrode member 16 may include 0-100 parts by weight petroleum coke to 0-100 parts by weight needle coke, or other weight ratios of petroleum coke to needle coke may be used, such as 90 parts by weight to 10 parts by weight, or 80 parts by weight to 20 parts by weight, or 70 parts by weight to 30 parts by weight, or 60 parts by weight to 40 parts by weight, or 50 parts by weight to 50 parts by weight, or 40 parts by weight to 60 parts by weight, or 30 parts by weight to 70 parts by weight, or 20 parts by weight to 80 parts by weight, or 10 parts by weight to 90 parts by weight, or 0 parts by weight to 100 parts by weight petroleum coke to needle coke. When petroleum coke is present, low sulfur petroleum coke is preferred over high sulfur petroleum coke. For high temperature applications, a higher percentage of needle coke than petroleum coke is preferred. However, the disclosed protective coating 18 is useful for a variety of electrode materials, including a variety of graphite types.

[0045] Any of the protective coating compositions 18 disclosed herein may be applied to one or more surfaces of a graphite-containing electrode member 16 of any size or shape to provide a resulting protected electrode 14 protected by the protective coating 18.

[0046] 3 illustrates in cross-section a further embodiment of the cylindrical protected electrode 14, where the protected electrode 14 of FIG. 2 has been modified in FIG. 3 to further include a pre-coating 20 having a surface 22. The protected graphite-containing electrode 14 includes a graphite-containing electrode (graphite-containing member 16 and pre-coating 20) and a zirconium-based coating 18. The pre-coating 20 is disposed on at least a portion of the surface 17 of the graphite member 16, and the zirconium-based coating 18 is disposed on at least a portion of the surface 22 of the pre-coating 20. Preferably, all or a majority of the outer peripheral surface of the electrode 14 includes the zirconium-based coating 18 adjacent the pre-coating 20, as shown in FIG. 3. In other words, the pre-coating 20 may coat substantially all of the surface 17 of the member 16, and the protective coating 18 may coat the entire surface 22 underlying the pre-coating 20. However, partial coverage of surface 17 with pre-coating 20 and / or partial coverage of the pre-coating with protective coating 18 is expected to provide benefits in extending the life of component 16 .

[0047] Pre-coating 20 promotes adhesion of zirconium-based protective coating 18 to graphite-containing component 16. However, in embodiments lacking a separate pre-coating 20, such as the embodiment shown in FIG. 2, zirconium-based coating 18 may include one or more components of pre-coating 20 to promote adhesion of protective coating 18 to surface 17 without the use of a separate primer layer, such as pre-coating 20. In embodiments, one or more components that may be incorporated into pre-coating 20 and / or protective coating 18 include, consist of, or consist essentially of phytic acid (PA).

[0048] In some embodiments, the zirconium-based coating composition 18 of Figures 2 and 3 not only acts as a thermal barrier coating having low thermal conductivity, but also serves to provide oxidation protection, improved heat flux, or a combination thereof. In some embodiments, the zirconium-based coating has a melting point of at least about 2000°F. (1093°C), at least about 2200°F. (1204°C), or in the range of about 2200°F to about 3500°F (about 1204°C to about 1927°C).

[0049] 2 and 3 are useful for extending the life of the electrode 14. In some embodiments, the coating composition 18 and, if used, the pre-coating 20 are applied as a thermal barrier coating to protect graphite electrodes used in electric arc furnaces used in steel production.

[0050] How to make a protected electrode

[0051] Any of the zirconium-based coating compositions and embodiments thereof described herein may be used in any of the methods and embodiments of making the protected electrode 14 described herein.

[0052] Referring to FIG. 2, the zirconium-based coating composition may be applied directly to at least the surface 17 of the graphite-containing member 16. The graphite-containing member 16 may be a graphite-containing electrode or a portion thereof, such as a segment of a graphite-containing electrode. In some such embodiments, the zirconium-based coating composition is liquid (i.e., is typically liquid at 1 atmosphere and 20° C. or is heated to a suitable temperature to become liquid). The liquid may be single-phase or multi-phase, such as a liquid or solid phase dispersed in a liquid carrier. The zirconium-based coating composition may be applied continuously or in batches, any number of times, with or without a curing process between applications.

[0053] In embodiments including a precoating, such as precoating 20 as shown in FIG. 3, a liquid precoating composition (i.e., a precoating composition that is liquid at 1 atmosphere and 20° C. or heated to a suitable temperature so as to be liquid) is applied to surface 17 of graphite-containing member 16 and optionally cured to form precoating 20 on surface 17 to form a precoated, unprotected electrode having surface 22. A zirconium-based coating composition is applied to surface 22 of cured precoating 20 or to uncured precoating composition. The precoating composition and zirconium-based coating composition may be applied multiple times, with or without curing between any of the applications. The single or multiple applications of the precoating composition and zirconium-based coating composition may optionally be applied in any order, provided that, for the embodiment of FIG. 3, at least one application of the precoating composition precedes or is applied simultaneously with the first application of the zirconium-based coating composition. This condition is desirable when electrode member 16 has not been previously treated with a protective coating of the present invention. In other implementations, the previously protected electrode member 16 may have its protection refreshed or regenerated by reapplication of one or more additional pre-coatings 20 and / or one or more additional protective coatings 18. In some implementations, multiple pre-coatings 20 are applied, followed by one or more protective coatings 18. In some implementations, alternating coatings of pre-coatings 20 and protective coatings 18 are applied until two or more coatings of each type are provided on the member 16. The pre-coating compositions and zirconium-based coating compositions are cured on the surface of the electrode member 16.

[0054] Any of the zirconium-based coating compositions and / or pre-coating compositions described herein may be applied and cured on the graphite-containing electrode 14, portion thereof, or graphite-containing member 16 before the electrode, part, or member is installed in the arc furnace 10. Alternatively, the coating composition may be applied to the electrode 14, part, or member 16 after installation of the electrode 14, part, or member 16 as part of a furnace assembly. In the latter case, one or both types of coating compositions may be applied to the electrode 14, part, or member 16 during operation of the furnace 10.

[0055] Graphite-containing electrodes used in arc furnaces often include cylindrical or substantially cylindrical segments that are fixed such that the electrode is shaped like an elongated cylinder. Each graphite-containing electrode is supported by a clamp and mounted substantially vertically so as to project downwardly from the clamp into the arc furnace, whereby a portion of the electrode is disposed between the clamp and the top of the furnace outside the arc furnace, and a portion of the electrode often passes through an opening in the top of the arc furnace and projects downwardly into the interior of the arc furnace. The lower end of the electrode (the end portion closest to the bottom of the arc furnace) is particularly susceptible to losses, so that over time the end portion becomes tapered, i.e. narrower, than the substantially cylindrical portion further from the bottom of the furnace, eventually causing graphite to be lost from the lower end of the electrode, thereby shortening the electrode. To compensate for the shortening of the electrode, a new substantially cylindrical portion of graphite is fixed to the upper portion of the electrode (the end portion of the electrode furthest from the arc furnace) and the tip of the electrode is lowered. This method can be used with the protected electrode 14 of the present invention. In this way, the graphite-containing electrode is maintained despite the process of graphite loss from the lower end of the electrode.

[0056] The graphite-containing electrode 14 of Figures 1-3 may be cooled by water sprayed from nozzles disposed about the long axis of the electrode. In other words, the nozzles are disposed circumferentially around the electrode 14 and spray cooling water radially inward toward the electrode 14. The graphite-containing electrode 14 may be cooled by spraying water around the electrode, for example, on a curved surface of the graphite-containing electrode 14, the curved surface being disposed between the clamp and the arc furnace 10. Thus, many conventional arc furnaces already include a means for applying a liquid, such as water, to a major surface of the electrode between the clamp and the top of the arc furnace, above the furnace itself. The cooling water evaporates, thereby cooling the electrode.

[0057] Such application strategies can be used in the practice of the present invention not only to provide a cooling liquid, but also to apply the coating of the present invention to the electrode 14 while the electrode 14 is installed in the furnace 10. Advantageously, the zirconium-based coating composition described herein may be a liquid that can be sprayed in addition to or instead of water using existing sprayer equipment associated with the arc furnace. The zirconium-based coating composition may be sprayed onto the graphite-containing electrode member 16 outside the arc furnace internal cavity, but the liquid composition may flow down the electrode under the influence of gravity, thereby coating at least a portion of the electrode's major surface. Even if the liquid composition does not reach the bottom end of the electrode before all of the composition's water has evaporated, the coated graphite-containing electrode will include a coating layer of the zirconium-based coating over a portion of the electrode's major surface, preferably around the electrode's periphery. As the lower portion of the electrode adjacent the furnace charge is continuously lost, the electrode is lowered, a new segment is added to the top, and a coating is added to the portion of the electrode located adjacent the atomizer, and finally, the bottom end of the electrode includes a zirconium-based coating that slows the rate of graphite loss as described herein.

[0058] Thus, in some embodiments, the zirconium-based coating composition is applied to the graphite-containing electrode member 16 or pre-coated graphite-containing electrode member 16 by spraying the zirconium-based coating composition on the graphite-containing electrode member 16 in situ, i.e., while the graphite-containing electrode member 16 is disposed or partially disposed in the arc furnace 10. In some such embodiments, the zirconium-based coating composition may be sprayed onto the surface of the graphite-containing electrode member 16 located between the clamp and the top of the arc furnace. Some or all of the zirconium-based coating composition may adhere to the graphite-containing electrode member 16 (or the pre-coated portion thereof) and, in some cases, may run down the graphite-containing electrode member 16 under the influence of gravity. The moisture evaporates, leaving a zirconium-based coating on the surface of the graphite-containing electrode member 16 and / or the pre-coated surface of the graphite-containing electrode member 16, for example, between the clamp and the top of the arc furnace 10, or even as far down as the portion of the graphite-containing electrode disposed in the arc furnace. The coating left on the graphite-containing electrode retards the loss of the graphite on which it is disposed.

[0059] Each of the coating compositions used to provide protective coating 18 or pre-coating 20 may be applied at a wet thickness of 0.1 to 5 microns, for example, about 0.1 to about 5 microns, about 0.2 to about 4 microns, about 0.1 to about 3 microns, about 0.2 to about 2 microns, or about 1 micron.

[0060] In some embodiments, the coating composition used to provide the protective coating 18 or pre-coating 20 may be applied as an aqueous solution. In some embodiments, the coating composition is applied by any suitable method, such as brushing, painting, spraying, dipping, or the like, and any combination thereof. The coating composition used to provide the protective coating 18 or pre-coating 20 may be applied as many times as necessary.

[0061] In some embodiments, spraying of the coating composition used to provide the protective coating 18 or pre-coating 20 is by a spray ring. In some embodiments, the spray ring is reported in U.S. Pat. No. 4,852,120, which is incorporated herein by reference in its entirety. In some embodiments, the spray ring is located below the electrode clamp and the coating composition is sprayed below the electrode clamp. In some embodiments, the spray ring is used for localized in-situ application during electrode operation. In some embodiments, the spray ring configuration is as shown in FIG. 3 of U.S. Pat. No. 4,852,120.

[0062] Curing is a physical or chemical process by which a material liquid becomes solid by chemical changes such as crosslinking, physical actions such as cooling and solidifying, physical actions such as loss of liquid solvent from the material (e.g., by evaporation), physical crosslinking, or a combination thereof. In embodiments where the zirconium-based coating composition includes a liquid carrier such as water, curing may include, consist of, or consist essentially of drying the zirconium-based coating composition by evaporation of the liquid carrier at ambient conditions, or by application of heat, optionally under vacuum, in air, or in an artificial atmosphere such as one containing nitrogen, carbon dioxide, argon, reduced oxygen content, and the like.

[0063] Coatings 18 and 20 may be applied to electrode member 16 while electrode member 16 is installed or removed from furnace 10 (FIG. 1). For example, coatings may be applied onto electrode member 16 while installed in furnace 10. When protected electrode 14 is in operation, electrode 14 and surroundings are exposed to heat from an arc between the electrode tip and the charge of furnace 10, which may cause evaporation of any liquid carrier in the zirconium-based coating composition, thereby curing (drying) the composition into a zirconium-based coating and providing any necessary curing. However, curing of the coating composition may also be assisted. Thus, in some such embodiments, drying includes, consists of, or consists essentially of passing a gas stream over the wet-coated graphite-containing electrode, heating the coated graphite-containing electrode at a temperature between 30° C. and 2000° C., or a combination of passing and heating. In some such embodiments, the gas is air or nitrogen. In embodiments, drying includes, consists of, or consists essentially of heating the wet-coated graphite-containing electrode at a temperature of from about 60°C to about 2000°C, in embodiments, from 100°C to 2000°C, in embodiments, from 150°C to 1600°C, in embodiments, from about 150°C to about 1600°C, in embodiments, from about 100°C to about 1000°C, or in embodiments, from about 200°C to about 1000°C.

[0064] Curing of the zirconium-based coating composition and / or pre-coating may occur at the location of application of the coating composition on the electrode, or (if a liquid) the coating composition may flow down the surface of the electrode under the influence of gravity and harden (e.g., dry) at a location different from where it was originally applied.

[0065]

[0066] In some embodiments, a pre-coating 20, also referred to as a bond coating 20 for its ability to help bond the protective coating 18 to the member 16, is applied before the zirconium-based coating composition. The bond coating 20 helps the protective coating 18 (e.g., a zirconium-based coating) to adhere better. In some embodiments, the bond coating or pre-coating 20 is applied simultaneously with the coating composition used to form the protective coating 18, or can be applied before the protective coating composition, optionally followed by application of additional bond coating material simultaneously with the protective coating composition. In some embodiments, the bond coating or pre-coating 20 includes phytic acid (also referred to as inositol hexaphosphate (IP6) or inositol polyphosphate). In some embodiments, the bond coating 20 is pre-applied at a concentration of 40 ppm to 10,000 ppm of phytic acid in a liquid carrier such as water. In some embodiments, when the coating compositions used to provide the protective coating 18 or pre-coating 20 are applied simultaneously, the weight ratio of the pre-coating composition to the protective coating composition is 1:1 or 2:1. In some embodiments, when the coating compositions used to provide protective coating 18 or pre-coating 20 are applied simultaneously, the bond coating and coating compositions are each applied at a concentration ranging from 1.5 ppm to 1500 ppm by weight.

[0067] Zirconium-based coating composition

[0068] Embodiments of the zirconium-based coating compositions may be used in any of the methods and embodiments disclosed herein to make a protected graphite-containing electrode 14.

[0069] In embodiments useful for making the protected electrode 14, the zirconium-based coating composition comprises, consists of, or consists essentially of one or more zirconium compounds and a carrier liquid, such as water or other aqueous carrier. Optionally, the zirconium-based coating composition may include one or more yttrium compounds, phytic acid, and / or other ingredients. Preferably, the carrier liquid is aqueous and includes water and at least one other solvent. In certain embodiments, the liquid carrier may comprise, consist of, or consist essentially of water.

[0070] In some embodiments, at least one of the one or more zirconium compounds, and in some embodiments, each zirconium compound, is a compound that pyrolyzes, hydrolyzes, and / or otherwise reacts to form zirconia at temperatures between 60° C. and 2,000° C., in some embodiments, between 100° C. and 1500° C. in the presence of water (water vapor and / or steam), and / or in some embodiments, between 100° C. and 1500° C. in the absence of water.

[0071] The one or more zirconium compounds may include, consist of, or consist essentially of one or more of zirconium oxychloride, zirconium(IV) acetylacetonate, and zirconia. In some embodiments, the one or more zirconium compounds in the zirconium-based coating composition may include, consist of, or consist essentially of one or more of zirconium oxychloride and zirconium(IV) acetylacetonate.

[0072] The one or more yttrium compounds are optional in the zirconium-based coating composition and may comprise, consist of, or consist essentially of one or more of yttrium acetate, yttrium nitrate, yttrium sulfamate, yttrium lactate, yttrium formate, yttrium (III) chloride, yttrium sulfate, and any combination thereof. In some embodiments, when present, the one or more yttrium compounds may comprise, consist of, or consist essentially of yttrium acetate, yttrium sulfamate, yttrium lactate, yttrium formate, and any combination thereof. Without wishing to be bound by theory, it is speculated that the yttrium compounds help prevent mass loss from the electrode in the operating conditions of the arc furnace. Furthermore, without being bound by theory, it is speculated that yttrium nitrate may have oxidizing properties that are beneficial in helping to further extend the life of the electrode, but nevertheless shorten the life of the electrode compared to other yttrium compounds. Additionally, other nitrates, including nitric acid, are suspected to have oxidizing properties that shorten electrode life. Therefore, yttrium nitrate compounds are not the preferred yttrium compounds. Preferably, when one or more yttrium compounds are present, yttrium nitrate compounds are excluded.

[0073] The zirconium-based coating composition may contain one or more zirconium compounds in an amount of about 0.01 mg to about 10 mg, or about 0.5 mg / mL to about 10 mg / mL, or about 0.1 mg / mL to about 10 mg / mL, or about 0.1 mg / mL to about 5 mg / mL, or about 0.3 mg / mL to about 3 mg / mL, or about 1.0 mg / mL to about 2.0 mg / mL, or about 1.0 mg / mL to about 1.4 mg / mL, or about 1.2 mg / mL, or about 1.5 mg / mL, or about 0.1 mg / mL to about 0.8 mg / mL, or about 0.5 mg / mL to about 10 mg / mL, or about 0.5 mg / mL to about 0.8 mg / mL, or about 0.75 mg / mL per mL of the zirconium-based coating composition.

[0074] The zirconium-based coating composition may contain from about 0 mg to about 0.5 mg, or from about 0 mg / mL to about 1.5 mg / mL, or from about 0.1 mg / mL to about 0.7 mg / mL, or from about 0.2 mg / mL to about 0.3 mg / mL, or about 0.3 mg / mL of one or more yttrium compounds per mL of zirconium-based coating composition.

[0075] The zirconium-based coating composition may comprise one or more zirconium compounds and one or more yttrium compounds in a weight ratio of from about 15:1 to about 1:1, or from about 10:1 to about 5:1, or from about 9:1 to about 6:1, or from about 9:1 to about 7:1, or from about 8:1 of the one or more zirconium compounds to the one or more yttrium compounds.

[0076] The zirconium-based coating composition may contain about 0.01 mg to about 10 mg of phytic acid per mL of zirconium-based coating composition, or about 0.1 mg / mL to about 5 mg / mL, or about 0.3 mg / mL to about 3 mg / mL, or about 0.1 mg / mL to about 0.8 mg / mL, or about 0.5 mg / mL to about 10 mg / mL, or about 0.5 mg / mL to about 0.8 mg / mL, or about 0.75 mg / mL of phytic acid.

[0077] In some embodiments where the zirconium-based coating composition includes phytic acid, the weight ratio of the one or more zirconium compounds to phytic acid is about 2:1 to 1:2, in some embodiments, about 3:2 to 2:3, or in some embodiments, about 1:1.

[0078] The zirconium-based coating may be applied to the graphite-containing electrode as an aqueous composition, which may be a solution, an aqueous dispersion, an aqueous slurry, or any combination thereof, i.e., some or all of the materials in the zirconium-based coating may be dissolved and / or dispersed in water.

[0079] The zirconium-based coating composition may be about 99-75% zirconium (based on the total weight of zirconia and other additives in the coating composition), or about 90-80% zirconium. In one particular such embodiment, the zirconium-based coating composition comprises, consists of, or consists essentially of an aqueous solution of zirconium (IV) acetylacetonate at a concentration of 1.5 mg / mL by volume of solution. In a further particular embodiment, the zirconium-based coating composition comprises, consists of, or consists essentially of an aqueous solution of zirconyl chloride (zirconium oxychloride) at a concentration of 1.5 mg / mL by volume of solution.

[0080] Pre-coating Composition

[0081] The pre-coating composition may comprise, consist of, or consist essentially of phytic acid in a carrier liquid. In preferred such embodiments, the carrier liquid is a solvent, preferably comprising, consisting of, or consisting essentially of water. The phytic acid may be dissolved, dispersed, or both dissolved and dispersed in the carrier liquid. The carrier liquid may comprise, consist of, or consist essentially of water. The concentration of phytic acid in the pre-coating composition may be from about 1 mg to about 100 mg of phytic acid per mL of pre-coating composition, or from about 5 mg / mL to about 80 mg / mL, or from about 10 mg / mL to about 60 mg / mL, or from about 20 mg / mL to about 60 mg / mL, or from about 30 mg / mL to about 50 mg / mL, or from about 40 mg of phytic acid per mL of pre-coating solution. The concentration of phytic acid in the pre-coating composition may be from about 1 mg to about 100 mg of phytic acid per mL of solvent, or from about 5 mg / mL to about 80 mg / mL, from about 10 mg / mL to about 60 mg / mL, from about 20 mg / mL to about 60 mg / mL, from about 30 mg / mL to about 50 mg / mL, or about 40 mg of phytic acid per mL of carrier liquid. In certain embodiments, the pre-coating may include one or more zirconium compounds and / or one or more yttrium compounds as described herein with respect to zirconium-based coating compositions.

[0082] After curing (e.g., drying), any of the zirconium-based coating compositions disclosed herein become a zirconium-based coating 18 (FIGS. 2 and 3). After curing (e.g., drying), any of the pre-coating compositions become a pre-coating 20 (FIG. 3). In some implementations, the composition of the resulting coating is expected to be similar or the same as the composition of the coating composition minus the liquid carrier lost during curing. However, without being bound by theory, it is believed that at least a portion of the zirconium compound(s) and / or yttrium compound(s) decompose under the high temperature conditions experienced in an arc furnace, possibly forming one or more zirconium oxide compounds and / or one or more yttrium oxide compounds, respectively. For example, zirconium acetylacetonate and / or zirconium oxychloride may decompose into materials including zirconium and oxide species. Thus, the composition of the zirconium-based coating may change with time and / or proximity to the tip of the electrode. However, regardless of whether any of the one or more zirconium and / or yttrium compounds decompose, Applicants have discovered that after application of the zirconium-based coating composition and drying thereof, the protected electrode 14 has an extended life and reduced mass loss.

[0083] In some embodiments, the zirconium-based coating 18 includes one or more chemically stabilized zirconias (i.e., various metal oxides, such as yttrium oxide blended with zirconia), such as yttria-stabilized zirconia, ceria-stabilized zirconia, calcia-stabilized zirconia, scandia-stabilized zirconia, magnesia-stabilized zirconia, india-stabilized zirconia, ytterbia-stabilized zirconia, as well as mixtures of such stabilized zirconias. See, for example, Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd Ed., Vol. 24, pp. 882-883 (1984) for a description of suitable zirconias.

[0084] In some embodiments, the zirconium-based coating 18 comprises, consists of, or consists essentially of chemically stabilized zirconia, which comprises, consists of, or consists essentially of zirconia and a stabilizing metal oxide, which is selected from the group consisting of yttria, calcium oxide, scandia, india, ytterbia, and any combination thereof.

[0085] In some embodiments, the chemically stabilized zirconia comprises, consists of, or consists essentially of zirconia, a stabilizing metal oxide, and one or more thermal conductivity adjusting metal compounds. In embodiments, the one or more thermal conductivity adjusting metal compounds comprise, consist of, or consist essentially of one or more lanthanide oxides, one or more actinide oxides, or combinations thereof. In embodiments, the one or more thermal conductivity adjusting metal compounds comprise, consist of, or consist essentially of a compound selected from the group consisting of dysprosia, erbia, europia, gadolinia, neodymia, praseodymia, urania, hafnia, one or more pyrochlores, and any combination thereof to further reduce the thermal conductivity of the thermal barrier coating.

[0086] Each of the one or more pyrochlores has the general formula A2B2O7, where A is a metal having a valence of 3+ or 2+ (e.g., gadolinium, aluminum, cerium, lanthanum, or yttrium), B is a metal having a valence of 4+ or 5+ (e.g., hafnium, titanium, cerium, or zirconium), and the sum of the valences of A and B is 7. In embodiments, A is selected from the group consisting of gadolinium, aluminum, cerium, lanthanum, and yttrium. In embodiments, B is selected from the group consisting of hafnium, titanium, cerium, and zirconium. In embodiments, the one or more pyrochlores are selected from the group consisting of gadolinium zirconate, lanthanum titanate, lanthanum zirconate, yttrium zirconate, lanthanum hafnate, cerium zirconate, aluminum cerate, cerium hafnate, aluminum hafnate, lanthanum cerate, and any combination thereof.

[0087] In some embodiments, the protected electrode 18 exhibits less oxidation and better heat flux when exposed to high temperatures compared to a similar but unprotected electrode. In some embodiments, the weight loss of the protected electrode is reduced by about 2%-95%, 5%-75%, 5%-50%, 5%-25%, 2%-10%, 5%-15%, 50%-95%, 50%-20%, or 50%-75% when the unprotected and protected electrodes are subjected to the same degradation conditions.

[0088] After curing, the dry thickness of the zirconium-based coating may be from 0.01 to 100 nm, or from 0.05 to 10 nm, or from 0.05 nm to 7 nm, or from 0.1 to 5 nm.

[0089] Thus, a protected graphite-containing electrode 18 is provided that comprises, consists of, or consists essentially of a graphite-containing electrode member 16 and a zirconium-based coating 18 disposed on at least a portion of a surface 17 of the graphite-containing electrode member 16.

[0090] In another aspect, a coated graphite-containing electrode 18 is disclosed that comprises, consists of, or consists essentially of a graphite-containing member 16 including a surface 17, and a pre-coating 20 disposed on at least a portion of the surface 17 of the graphite-containing member 16, the pre-coating 20 including a surface 22, and a zirconium-based coating 18 disposed on at least a portion of the surface 22 of the pre-coating 20. The pre-coating 20 functions, at least in part, as a bond coating designed and adapted to promote adhesion of the zirconium-based coating 18 to the graphite-containing electrode member 16, the bond coating being disposed between the graphite-containing member 16 and the zirconium-based coating 18.

[0091] The pre-coating 20 may include, consist of, or consist essentially of phytic acid.

[0092] The zirconium-based coating 18 may comprise, consist of, or consist essentially of zirconium oxychloride, zirconium acetylacetonate, zirconia, or any combination thereof.

[0093] The zirconium-based coating 18 may include, consist of, or consist essentially of one or more zirconium compounds.

[0094] The zirconium-based coating 18 may include, consist of, or consist essentially of one or more zirconium compounds and one or more yttrium compounds.

[0095] The zirconium-based coating 18 may include, consist of, or consist essentially of one or more zirconium compounds and phytic acid and / or salts of phytic acid.

[0096] The zirconium-based coating 18 may include one or more zirconium compounds, one or more yttrium compounds, and phytic acid and / or salts of phytic acid.

[0097] The one or more zirconium compounds may include, consist of, or consist essentially of one or more of zirconium oxychloride, zirconium(IV) acetylacetonate, and zirconia. The one or more yttrium compounds may include, consist of, or consist essentially of yttrium acetate, yttrium sulfamate, yttrium lactate, yttrium formate, yttrium, yttrium(III) chloride, yttrium(III) sulfate.

[0098] The zirconium-based coating 18 may include one or more zirconium compounds in an amount between about 10% and 100% by weight, or between about 40 weight percent (wt%) and 100% by weight, or between about 70% and 100% by weight, or between about 60% and 100% by weight, or between about 80% and about 90% by weight, or between about 80% and 100% by weight, or between about 30% and about 60% by weight, or between about 30% and about 70% by weight, or between about 40% and about 60% by weight, or between about 50% by weight, or between about 40% and about 30% and about 50% by weight, or between about 20% and about 60% by weight, or 100% by weight of the zirconium-based coating.

[0099] The zirconium-based coating may comprise phytic acid in an amount of about 10% to about 80% by weight based on the weight of the zirconium-based coating, or about 10% to about 90% by weight based on the weight of the zirconium-based coating, or about 20% to about 70% by weight, or about 30% to about 60% by weight, or about 40% to about 60% by weight, or about 50% by weight.

[0100] The zirconium-based coating 18 may include one or more yttrium compounds in an amount of from about 1% to about 20% by weight of the one or more yttrium compounds, or from about 2% to about 20% by weight, or from about 1% to about 15% by weight, or from about 2% to about 12% by weight, or from about 6% to about 16% by weight, or from about 8% to about 11% by weight, or from about 9% to about 11% by weight, or from about 8% to about 10% by weight, or about 10% by weight of the one or more yttrium compounds, based on the weight of the zirconium-based coating.

[0101] When the zirconium-based coating 18 includes one or more yttrium compounds, the weight ratio of the one or more zirconium compounds to the one or more yttrium compounds can be from about 15:1 to about 1:1, or from about 10:1 to about 5:1, or from about 9:1 to about 6:1, or from about 9:1 to about 7:1, or about 8:1.

[0102] In some embodiments in which the zirconium-based coating 18 comprises phytic acid, the weight ratio of the one or more zirconium compounds to phytic acid is about 2:1 to 1:2, in some embodiments, about 3:2 to 2:3, or in some embodiments, about 1:1. EXAMPLES

[0103] The following examples are intended to illustrate different aspects and embodiments of the present invention and should not be considered as limiting the scope of the invention. It will be appreciated that various modifications and variations can be made without departing from the scope of the claims.

[0104] Example 1. Evaluation of coating

[0105] The various coatings were evaluated under electric arc-like conditions. Graphite electrode material was used to obtain circular graphite disks. The disks weighed approximately 22-26 grams, had a diameter of 3.5 cm, and a thickness of approximately 1.5 cm. Before use, the disks were washed with deionized water, acetone, and isopropanol, and then dried under nitrogen. The clean, dry graphite disks were immersed in a solution of phytic acid (PA) at a concentration of 40 mg / mL for 5 minutes, and after removal from the PA solution, the disks were immersed at room temperature for 5 minutes in different solutions obtained by mixing an equal volume solution of phytic acid (1.5 mg / mL) with 1.5 mg / mL of various sample additive solutions. The various sample additives are listed in Table 1. After removing the disks from the various sample solutions, the coated graphite disks were dried under nitrogen and placed in a 65 °C oven for approximately 30 minutes. The coated disks were weighed and then placed in a high-temperature oven at 1000 °C for 1 hour. After 1 hour at high temperature, the graphite disks were cooled to room temperature. The graphite disks cooled to room temperature were weighed to record the final weight of the graphite disks after heat treatment and the weight percent remaining was recorded. A gravimetric analysis was performed to determine the weight percent remaining based on the initial and final weights of the graphite disks. The various sample additives are shown in Table 1. [Table 1]

[0106] ZrOCl2 = zirconium oxychloride (zirconyl chloride) CAS#7699-43-6.

[0107] Zr(acac)4 = zirconium acetylacetonate CAS#17501-44-9.

[0108] Phytic Acid (Inositol Hexaphosphate) CAS#83-86-3.

[0109] FeCl3 = Iron(III) chloride (ferric chloride) CAS#7705-08-0.

[0110] Yttrium acetate (Y(OAc)3·4H2O) CAS#85949-60-6.

[0111] Y(NO3)3 = Yttrium nitrate (Y(NO3)3·6H2O) CAS#13494-98-9.

[0112] The data in Table 1 are presented as the weight percent remaining for the coated graphite disks as compared to control untreated graphite disks each subjected to a single heat treatment at 1000° C. for 1 hour.

[0113] Example 2. Coatings evaluated over multiple thermal cycles

[0114] The graphite disks and the various treatments are as described in Example 1 and Table 2. The various treated disks were subjected to three different thermal cycles. Each thermal cycle was at 1000° C. for 1 hour. After the disks were subjected to the first cycle at 1000° C., the disks were cooled and the same disks were subjected to another round of heating at 1000° C. After cooling the disks, the same disks are subjected to a third round of heating at 1000° C. The data is shown in FIG. 4 as the weight percent remaining for the coated graphite disks as compared to a control untreated graphite disk that was subjected to multiple heat treatments at 1000° C. for 1 hour each. The control uncoated graphite is completely decomposed with 0 weight percent remaining at the end of the third thermal cycle at 1000° C. for 1 hour. [Table 2]

[0115] Example 3. Evaluation of discs without pre-coating

[0116] The graphite disks and various treatments were as described in Example 1 and Table 3. However, unlike Example 1, the disks were not subjected to a phytic acid pre-coating. The data is presented in FIG. 5 as the weight percent remaining for the coated graphite disks as compared to control untreated graphite disks that were each subjected to a heat treatment at 1000° C. for 1 hour without the phytic acid pre-coating step. The data shows that the control uncoated graphite disks are similar to the coated graphite disk samples that do not include an initial pre-coating with phytic acid. [Table 3]

[0117] Example 4. Evaluation of disks at high temperatures

[0118] The graphite disks and various treatments were as described in Example 1 and Table 4. However, unlike Example 1, the disks were subjected to a temperature of 1500° C. for 1 hour. The data is presented in FIG. 6 as the weight percent remaining for the coated graphite disks as compared to the control untreated graphite disks, each of which was subjected to a heat treatment at 1500° C. for 1 hour. The results show that higher temperatures result in greater loss of graphite disks. However, the coated graphite disk samples show a higher weight percent remaining as compared to the untreated control. [Table 4]

[0119] Example 5. Evaluation of disks at different temperatures The graphite disks and various treatments were as described in Example 1 and Table 5. However, unlike Example 1, the disks were subjected to temperatures of 1100° C., 1300° C., and 1500° C. for 1 hour. The data is presented in FIG. 7 as the weight percent remaining of the coated graphite disks compared to the control untreated graphite disks subjected to different heat treatments. The data shows that the coated disks have a higher weight percent remaining compared to the untreated control. However, the coated disks showed a decrease in protection with increasing temperature. [Table 5]

[0120] Example 6. Evaluation of heat flux

[0121] The graphite electrode was machined into a cylindrical shape with dimensions of 2 inches height and 1 inch diameter. A small cavity with dimensions of 0.033 inches diameter and 0.5 inches height was machined in the center of the top of the cylinder. Another cavity with dimensions of 0.25 inches diameter and 0.75 inches height was machined in the bottom of the cylinder. The cavity was created to accommodate the location of a thermocouple to monitor the temperature of the electrode during heating and cooling.

[0122] The graphite cylinder was coated in the same manner as the graphite disk described in Example 1 and Table 6. [Table 6]

[0123] The graphite cylinder specimen was heated to 900°F (482.2°C) in a heating chamber with a gold plated copper core and held in place with the aid of an electromagnet. Once the graphite cylinder specimen reached 900°F, it was dropped between a sprayer that sprayed water at ambient conditions onto the graphite cylinder and the temperature drop of the graphite specimen was monitored using thermocouples attached to the top and bottom of the specimen. Data was recorded in real time on a computer and a cooling curve for the graphite cylinder specimen was plotted. The cooling curve was used to calculate heat flux data.

[0124] The higher heat flux for the coated graphite disks indicated a better cooling capability of the coated graphite samples when compared to the uncoated control. The higher heat flux is a measure of the improved heat transfer of the coated graphite samples. The data is shown in Figure 8.

Claims

1. 1. A method for protecting an arc furnace electrode, said method comprising: applying a coating composition onto at least a portion of a surface of the graphite-containing electrode, the coating composition comprising one or more zirconium compounds and a liquid carrier, the one or more zirconium compounds reacting to form zirconia as the coating composition cures; and curing the applied coating composition such that the one or more zirconium compounds react to form a zirconium-based coating on the surface, the zirconium-based coating comprising zirconia.

2. The method of claim 1 , wherein the liquid carrier comprises water.

3. 3. The method of claim 1 or 2, wherein the graphite-containing electrode comprises a curved surface and the applying comprises spraying the coating composition onto at least a portion of the curved surface.

4. The method of any one of claims 1 to 3, wherein the method further comprises inserting at least a portion of the electrode into an electric arc furnace after or before the coating.

5. The method of any one of claims 1 to 4, wherein the coating composition comprises one or more of zirconium oxychloride and zirconium acetylacetonate.

6. The method of any one of claims 1 to 5, wherein the coating composition comprises zirconium acetylacetonate.

7. The method of any one of claims 1 to 6, wherein the coating composition further comprises one or more yttrium compounds.

8. The method of any one of claims 1 to 7, comprising applying a bonding coating composition onto the surface of at least a portion of the graphite-containing electrode prior to applying the coating composition onto the surface, the bonding coating composition comprising phytic acid.

9. The method of any one of claims 1 to 8, wherein the coating composition further comprises phytic acid.

10. 1. A coated graphite-containing electrode, comprising: a graphite-containing electrode including a surface; a zirconium-based coating disposed on at least a portion of the surface; A coated graphite-containing electrode, wherein the zirconium-based coating comprises zirconia, and the coated graphite-containing electrode is obtainable by the method according to any one of claims 1 to 9.

11. 11. The coated graphite-containing electrode of claim 10, wherein the coating further comprises one or more yttrium compounds.

12. 12. The coated graphite-containing electrode of claim 10 or 11, wherein the surface of the graphite-containing electrode is primed with a composition comprising phytic acid.

13. An electric arc furnace comprising a coated graphite-containing electrode according to any one of claims 10 to 12.

14. A method for protecting an arc furnace electrode, the method comprising:

1. A method comprising: applying a coating composition onto at least a portion of a surface of a graphite-containing electrode, the coating composition comprising one or more zirconium compounds and a liquid carrier, the one or more zirconium compounds reacting on the graphite-containing electrode to form zirconia.

15. The method of claim 14, wherein the coating composition further comprises phytic acid.

16. The method of claim 14 or 15, wherein the one or more zirconium compounds include one or more of zirconium oxychloride and zirconium acetylacetonate.

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