Graphite electrode additive and use method thereof

Abstract

The invention discloses a graphite electrode additive and a use method thereof, the additive is added into a graphite electrode raw material, and the graphite electrode raw material comprises petroleum coke and coal pitch; the additive comprises a material A and a material B, the material B is prepared from a furan oligomer, saturated fatty acid, ferritic acid, light-burned magnesia and a phosphorus compound; and the material C comprises mixed resin, an aromatic nitro compound, a metal oxide, a boride and methyl hydroxyethyl cellulose. A graphite electrode additive is used, and a using method comprises the following steps: using a material A: adding calcium cyanamide into petroleum coke in the form of powder, and calcining the calcium cyanamide and the petroleum coke together; using the material B: stirring coal pitch according to a heating curve, and respectively adding saturated fatty acid, light-burned magnesia and a phosphorus compound at a low temperature of 160-250 DEG C; adding the furan oligomer and the glutaric acid at the medium temperature of 250-400 DEG C; and a material C is used: the material C is stirred into a mixture of particles formed by petroleum coke and coal pitch. The product quality and performance of the graphite electrode are improved, and the process difficulty is weakened.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite electrode production, in particular to a graphite electrode additive and its usage method. Background Art

[0002] Graphite electrodes are mainly made from petroleum coke and needle coke as raw materials, with coal tar pitch as the binder. They are manufactured through calcination, batching, kneading, molding, baking, graphitization, and machining. They are conductors that release electrical energy in the form of an electric arc in an electric arc furnace to heat and melt the furnace charge. According to their quality index levels, they can be divided into ordinary power, high power, and ultra-high power.

[0003] Currently, in the production of graphite products, the mixing of petroleum coke and coal tar pitch is crucial for the quality of the graphite product blanks and finished products. In actual production, on the one hand, the rheology of coal tar pitch is not good, and extremely high temperatures are required to achieve fluidity, which places great pressure on heating equipment and stirring equipment. The mixing effect of graphite matrix raw materials is poor, and kneading is difficult. During the graphitization process of the blanks, swelling often occurs, resulting in cracking and scrapping of the blanks. Therefore, most graphite products on the market have uneven and dense textures, poor strength, low resistance, and poor high-temperature resistance. Summary of the Invention

[0004] The purpose of the present invention is to provide a graphite electrode additive and its usage method to solve the problems that most graphite products on the market have uneven and dense textures, poor strength, low resistance, and poor high-temperature resistance.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions: A graphite electrode additive, the mass percentage of the additive to the graphite electrode raw materials is 10% - 15%, and the graphite electrode raw materials include petroleum coke and coal tar pitch; among them.

[0006] The additive includes: Material A is: 8% - 12% calcium cyanamide; Material B is: 15% - 18% furan oligomer, 12% - 16% saturated fatty acid, 8% - 10% ferrous oxalate, 5% - 8% light burned magnesia, and 0.8% - 1.2% phosphorus compound; Material C is: 16% - 20% mixed resin, 4% - 9% aromatic nitro compound, 5% - 8% metal oxide, 3% - 6% boride, and 1.5% - 2% methylhydroxyethyl cellulose.

[0007] A further technical solution is: The phosphorus compound is composed of ammonium phosphate, phosphoric acid, and triphenyl phosphate in a mass ratio of 1 - 2:1:1.

[0008] A further technical solution is that the boride is boron carbide and boron oxide in a mass ratio of 1:1.

[0009] A further technical solution is that the mixed resin is linear phenolic resin and furfural resin in a mass ratio of 1 - 1.2:2.

[0010] A further technical solution is that the aromatic nitro compound is dinitrobenzene.

[0011] A further technical solution is that the metal oxide is at least one of titanium oxide or zirconium oxide.

[0012] A method for using a graphite electrode additive, using the graphite electrode additive, the method is as follows: Use of material A: Calcium cyanamide is added to petroleum coke in powder form, and the two are calcined together; Use of material B: Stir in coal tar pitch according to the heating curve, and add saturated fatty acid, light-burned magnesia and phosphorus compound at a low temperature of 160°C - 250°C respectively; add furan oligomer and ferrous oxalate at a medium temperature of 250°C - 400°C; Use of material C: Stir into the mixture of particulate matter formed by petroleum coke and coal tar pitch.

[0013] A further technical solution is that the aromatic nitro compound is pre-mixed with the mixed resin.

[0014] A further technical solution is that a curing agent in a mass ratio of 0.5 - 0.8:100 is added to the mixture of petroleum coke particulate matter and coal tar pitch, and the curing agent is an acidic halide or a metal halide.

[0015] Compared with the prior art, at least one of the following beneficial effects can be achieved by the present invention: The present invention provides a graphite electrode additive and a method for using the same. The additive of the present invention can prevent the blank from expanding during the graphitization process, and the blank will not crack and be scrapped. First, it reduces the sulfur content of petroleum coke, and second, it improves the rheology of coal tar pitch, improves the mixing effect of graphite matrix raw materials and the kneading and forming effect. The density, flexural strength and lattice layer spacing of the graphite electrode are improved, with good strength, high resistance and high temperature resistance.

[0016] Moreover, the method adds the additive along with each processing step of the raw materials. First, it promotes the processing efficiency of each step, reduces the working pressure of each processing equipment, saves energy and reduces consumption, saves time, improves the processing effect of each raw material, prepares for the forming and graphitization of the blank, and weakens the existing difficulty of the graphite processing technology. Specific embodiments

[0017] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0018] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0019] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments may be combined with each other.

[0020] Example 1: A graphite electrode additive, the mass percentage of the additive to the graphite electrode raw material is 10% - 15%, and the graphite electrode raw material includes petroleum coke and coal tar pitch; among them.

[0021] The additive includes: Material A is: 8% - 12% calcium cyanamide; Material B is: 15% - 18% furan oligomer, 12% - 16% saturated fatty acid, 8% - 10% ferrous oxalate, 5% - 8% light burned magnesia, and 0.8% - 1.2% phosphorus compound; Material C is: 16% - 20% mixed resin, 4% - 9% aromatic nitro compound, 5% - 8% metal oxide, 3% - 6% boride, and 1.5% - 2% methylhydroxyethyl cellulose.

[0022] The phosphorus compound is composed of ammonium phosphate, phosphoric acid, and triphenyl phosphate in a mass ratio of 1 - 2:1:1.

[0023] The boride is boron carbide and boron oxide in a mass ratio of 1:1.

[0024] The mixed resin is linear phenolic resin and furfural resin in a mass ratio of 1 - 1.2:2.

[0025] The aromatic nitro compound is dinitrobenzene.

[0026] The metal oxide is at least one of titanium oxide or zirconium oxide.

[0027] Table 1.

[0028] Table 1 description: Control tests were carried out on different usage situations of the graphite electrode additive in graphite production. Experimental group 1 means no additive was added. Table 2. Experimental Results For the graphite electrode products produced according to Table 1, strength, resistance tests and microscopic observations were carried out. It can be seen that under the additive components in Experimental Group 2, Experimental Group 5 and Experimental Group 6, the density, flexural strength and lattice layer spacing of the graphite electrodes are the best, and statistical errors are of course not excluded.

[0029] As is well known, in graphite production, sulfur and sulfides will increase the fluidity and molding performance (also called plasticity) of coal tar pitch, another raw material for graphite electrodes. After the sulfur in petroleum coke is chelated, the plasticity of the green body is reduced. One of the raw materials for graphite electrode raw materials is petroleum coke, which will undergo irreversible expansion during graphitization. Generally, between 1500 - 1900 °C of graphitization, it will damage the internal structure of the green body (the green body before graphitization of the graphite electrode) during graphitization, resulting in the scrapping of the green body. When calcining petroleum coke (petroleum coke is calcined and crushed into particles, such as long-grain coke), calcium cyanamide (as a sulfur chelating agent and anti-expansion agent, is added to the petroleum coke in powder form during calcination), and carbon-graphite products are produced using the calcined petroleum coke added with calcium cyanamide, the green body can avoid expansion during the graphitization process, and the green body will not crack and be scrapped.

[0030] Using ferrous oxalate as a chemically active additive and adding it to coal tar pitch can play an oxidation or catalytic oxidation role to improve the coking rate and strength of the pitch, and at the same time can reduce the reactivity of the coke to the lowest level.

[0031] Light burned magnesia is used as an oil additive, which plays an anti-corrosion and desulfurization role. At the same time, it is an excellent flame retardant for rubber and resin products. When using substances such as mixed resins and furan oligomers as additives and adding them to the graphite electrode formulation, the plasticity of the green body and the high-temperature resistance of the graphite product can be further improved.

[0032] Adding a phosphorus compound composed of ammonium phosphate, phosphoric acid and triphenyl phosphate to coal tar pitch with a quinoline insoluble content slightly greater than 5%. This phosphorus compound can generate hydroxy acids between the softening point and coking temperature of the pitch, and the maximum addition amount shall not exceed 1.2%. Usually, the addition is 0.8%. The phosphorus compound is added to the pitch at a temperature that reduces the viscosity of the pitch, so that it is easy to stir the mixture. The characteristic of phosphorus-modified pitch is a high coking rate. Graphite products prepared with phosphorus-modified pitch binder have excellent oxidation resistance.

[0033] Saturated fatty acids are added to the pitch to improve the rheology necessary for electrode paste, reduce the internal and external friction coefficients of the electrode paste, enhance the adhesion between the pitch and carbon materials, and infiltrate the molten pitch into the carbon aggregate particles. Saturated fatty acids have an activating property on the pitch, which not only improves the mixing and pressing conditions but also improves the coking process of the green body during roasting. Saturated fatty acids are fatty acids containing saturated bonds, with a large number of carbon-carbon bonds and hydrogen bonds. When heated together with the pitch, the activated double bonds of saturated fatty acids polymerize and condense with the macromolecular groups in the pitch, achieving an activating and dispersing effect, increasing the coking rate, increasing the γ component, improving the mechanical strength of graphite products, and further preventing cracking.

[0034] Adding an appropriate amount of furan oligomer to medium-temperature pitch can significantly improve the product performance. When adding 15 - 18% (by weight) of furan oligomer, the strength of the product obtained is 72 MPa, while for the product made only with medium-temperature pitch, its flexural strength is only 60 MPa. When the addition amount of furan oligomer is higher than 18%, the flexural strength of the product decreases. The asphalt-furan oligomer component undergoes a chemical reaction before 400 °C, accelerating the escape of volatile substances and forming a condensed structure. When the temperature continues to rise, the thermal decomposition of the condensed structure is relatively stable, and the coking rate increases, thus obtaining a product with high mechanical strength. Adding furan oligomer to medium-temperature pitch, this oligomer is polymerized from hydroxy and bisfurfurylideneacetone, and it has a high coking rate. Its components contain active hydroxyl groups and vinyl groups, forming a dense three-dimensional network structure under certain conditions. The bisfurfurylideneacetone oligomer is heat-treated at 160 °C, and the double bonds of its hydroxyl groups and vinyl groups unfold. During the unfolding of the unsaturated bonds, the furan oligomer changes from a liquid state to a solid state. Medium-temperature pitch remains liquid at 160 - 250 °C. At this temperature, the asphalt-polymer mixture is a two-phase system, and the suture macromolecules of the polymer are in a free state. The curing of the polymer has an obvious effect on the molecular distribution characteristics within the volume of the pitch. The asphalt-polymer binder significantly increases the coke density of the mixture in the 160 - 175 °C region. The optimal ratio of the asphalt-polymer component depends on the type of polymer and its formation of a dense three-dimensional network structure. The stronger the formation of the suture structure of the polymer, the less the dosage required to achieve the best effect. Adding 16% bisfurfurylideneacetone to medium-temperature pitch can achieve the best effect, obtaining a product with the highest compressive and flexural strengths, and at the same time significantly reducing the oxidability of the asphalt coke. The oxidative weight loss of the sample decreases from 62% to 42%.

[0035] Aromatic nitro compounds, such as dinitronaphthalene or dinitrobenzene, are added to the coal tar pitch binder to increase the coking yield of the binder by means of their dehydrogenation reaction. However, during the mixing process, these aromatic nitro compounds will cause extreme polymerization of the coal tar pitch, resulting in a significant decrease in the flow viscosity of the mixture and making it difficult to extrude qualified blanks. An appropriate amount of furan oligomer can be added simultaneously to increase the flow viscosity of the mixture and enable the extrusion of blanks with a uniform structure. Polystyrene and polyacrylonitrile are thermoplastic high-molecular substances, which not only have a high coking yield but are also easily graphitized. During the carbonization process, due to the dehydrogenation effect of the aromatic nitro compounds, the coking yield of the binder is increased, accompanied by the shrinkage of the blank, resulting in a dense structure of the blank and obtaining a high-density graphite product.

[0036] Aromatic nitro compounds are added to furfuryl alcohol monomers or sugar alcohol mixed resins, or phenolic resins and their mixed resins to make them mix and dissolve, and then cured, carbonized and graphitized to obtain impervious graphite products with a certain thickness. The method is to add an appropriate amount of dinitrobenzene to the mixture based on furfuryl alcohol and furfural, mix and cure, cut the cured product into the required thickness, and then roast and graphitize to obtain impervious carbon products with a large thickness. It should be noted that considering the rapid curing to prepare blanks, in addition, an appropriate amount of methylhydroxyethyl cellulose is added as a plasticizer to the furfuryl alcohol-modified coal tar pitch binder, and a hydrolyzed acidic halide or metal halide at 20-25°C is used as the curing agent. 0-0.25mm coke powder with a particle size of 28.6-33.7% and 0.4-0.2mm coke powder with a particle size of 71.4-66.3% are used as the base materials respectively. The mixed powder is molded at room temperature, the blank is cured at 60-520°C, and then carbonized and graphitized to obtain a high-density and high-strength graphite product with a uniform structure.

[0037] Add metal oxides below 100 mesh, such as titanium dioxide or zirconium oxide, to the coke powder and binder mixture. After mixing, pressing, roasting, and graphitization, an antioxidant carbon-graphite product is obtained. The additive forms a high-melting-point oxidation-resistant solid substance (TiCWC) in the green body. The product containing this additive has excellent oxidation resistance, thermal shock resistance, and high thermal conductivity when used under high-temperature conditions, and is a product with wide applications. After graphitization at 2200 °C, there is a part of silicon in the sample. The graphitization temperature is higher than the decomposition temperature of silicon carbide (2700 °C). With the loss of silicon, the titanium content in the sample decreases insignificantly. Due to the loss of silicon and part of titanium, the density of the graphite material decreases. After graphitization at 2800 °C, the obvious boundary between the coke and the binder no longer exists, and the material structure becomes more uniform, which is related to the rapid decomposition of silicon carbide. Thus, a graphite electrode material with a resistivity of 2 - 3 Ω·mm / M and a thermal conductivity as high as 1200 K·Ca1 / M·h·d can be obtained. Adding zirconium oxide to the graphite matrix material formulation has a relatively obvious effect on the magnetoresistance and conductivity of the product. In calcined petroleum coke powder with a particle size of 1 - 2 mm and medium-temperature pitch, add electrolytic zirconium and crystalline silicon. The powder is pre-mixed, mixed and pulverized, then heated to 100 °C in a mixer and mixed for 15 minutes, pressed into shape, roasted to 900 °C, and subjected to thermomechanical treatment (2500 °C). As the additive dosage increases, the resistivity of the product decreases, but its magnetoresistance increases. The growth of the graphite lattice formed by silicon and zirconium during thermomechanical treatment plays a catalytic role. The change in the electronic properties of the graphite product depends on the silicon content. Increasing the silicon content at 2200 - 2500 °C will improve the graphite crystal structure.

[0038] The problem with high-sulfur coke calcined at 100 °C or higher temperature is that sulfur will cause irreversible crystal swelling of the roasting green body during the graphitization process, and sometimes the green body will crack. Adding iron or calcium compounds to the formulated powder can prevent the graphitization green body from swelling. Usually, the addition amount is 0.5% - 5.0% (by weight) to prevent crystal swelling. Generally, the crystal swelling of petroleum coke occurs in the range of 1400 - 2500 °C. Adding additives can delay the crystal swelling to 2600 - 2800 °C. To eliminate the delayed swelling of the green body added with iron or calcium compounds, titanium or zirconium oxides can be added to the powder again. Under the combined action of titanium and iron or calcium oxides, the swelling of the roasting green body caused by sulfur precipitation during graphitization can be basically eliminated. This move aims to overcome the problems existing in the prior art, with the publication number CN109665852A and the name of a roasting additive applicable to graphite electrodes and its preparation process. In this technical solution, 0.9 - 1.2 parts of ferric oxide, 0.5 - 0.8 parts of polyethylene glycol, 0.4 - 0.7 parts of phthalate, and 0.8 - 1.1 parts of calcium carbonate are used.

[0039] Adding borides, boron oxide and boron carbide to the asphalt-coke base material can increase the coking rate of the blank by 10%. When boron is present during the diffusion of solid carbon, boron-containing graphite is formed. In the temperature range of 1600 - 2100 °C, under the influence of surface diffusion of carbon materials, the three-dimensional ordering of the carbon structure is accelerated. In the temperature range of 2100 - 2400 °C, internal diffusion of boron crystals occurs, and boron atoms effectively replace carbon atoms in the graphite lattice, thus obtaining graphite with antioxidant properties and resistance to sulfuric and nitric acid corrosion. Adding boron oxide as a sintering catalyst to the mixture of graphite base and asphalt binder, and using magnetic field orientation, the C direction of graphite crystals is arranged in a certain direction, and the interlayer spacing of the graphite lattice is uniform and reduced. Adding boron compounds to the base material can improve the sliding performance of the product at high temperatures, and the wear of carbon products and the metal materials matched with them is significantly reduced, such as the brush structure products prepared from graphite electrodes. When there is carbon contact between metal materials, an electric field is formed on their surface, and the electric field strength mainly depends on the electron affinity and the density of states of the contacting materials. When the temperature is high, the mobility of metal ions in the oxide layer is correspondingly high. At the beginning, the wear of both the metal matching material and the carbon product is relatively high, and adding boron reduces the density of states. The diffusion of carbon into the metal electric field in the metal oxide layer increases, accelerating the corrosion of the metal, and the adhesion between copper and carbon increases. The ground carbon powder first adheres to the depressions on the metal surface, forming carbon-carbon contact. In this way, the wear of both is reduced.

[0040] The effect of adding boron on the growth of the carbide layer formed at the interface between molten silicon carburization and graphite melt. The thickness of the carbide layer increases with the increase of the boron content in the melt. Adding boron to the melt will cause a sharp increase in the carbon content, and the hardness of the carbide crystals formed at the graphite-melt interface reaches 5000 kg / (m) 2 , which is significantly higher than the hardness of the crystals formed by pure molten silicon. The diffusion rate of carbon through boron-added silicon carbide is higher than that of pure silicon carbide. The activation energy for carbon diffusion through pure SiC is 43 k·Cal / mol, and through boron-added SiC it is 53 k·Cal / mol. Adding borides to the base material of graphite products can affect the physical properties of the products. The covalent radii of carbon atoms and boron atoms are not very different. Boron atoms can replace carbon atoms in the graphite lattice. Containing 1% boron in artificial graphite can reduce its thermal conductivity and resistivity. The graphitization degree of boron-containing graphite treated at 2400 °C is equivalent to that of boron-free graphite treated at 3000 °C.

[0041] Example 2: A method for using a graphite electrode additive. When using a graphite electrode additive, the method is as follows: Use of Material A: Add calcium cyanamide in powder form to petroleum coke and calcine them together; Use of Material B: Stir in coal tar pitch according to the heating curve, and add saturated fatty acid, light burned magnesia and phosphorus compounds at low temperatures of 160°C to 250°C respectively; add furan oligomers and ferrous oxalate at medium temperatures of 250°C to 400°C. Use of Material C: Stir into the mixture of particulate matter formed from petroleum coke and coal tar pitch.

[0042] Preferably, the aromatic nitro compound is premixed with the mixed resin.

[0043] The aromatic nitro compound, such as dinitrobenzene, is premixed with the mixed resin in advance, which can ensure the homogeneous mixing of the two and prepare for the later carbonization of the resin. In addition, methylhydroxyethyl cellulose as a plasticizer can promote the fusion of the two.

[0044] Preferably, a curing agent is added to the mixture of petroleum coke particulate matter and coal tar pitch at a mass ratio of 0.5 to 0.8:100, and the curing agent is an acidic halide or a metal halide.

[0045] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A graphite electrode additive, characterized in that, The mass percentage of the additive to the graphite electrode raw material is 10% - 15%, and the graphite electrode raw material includes petroleum coke and coal tar pitch; wherein, The additive includes: Material A is: calcium cyanamide 8% - 12%; Material B is: furan oligomer 15% - 18%, saturated fatty acid 12% - 16%, ferrooxalic acid 8% - 10%, lightly burned magnesia 5% - 8% and phosphorus compound 0.8% - 1.2%; Material C is: mixed resin 16% - 20%, aromatic nitro compound 4% - 9%, metal oxide 5% - 8%, boride 3% - 6% and methylhydroxyethyl cellulose 1.5% - 2%.

2. The graphite electrode additive according to claim 1, wherein: The phosphorus compound is composed of ammonium phosphate, phosphoric acid and triphenyl phosphate in a mass ratio of 1 - 2:1:

1.

3. The graphite electrode additive according to claim 1, wherein: The boride is boron carbide and boron oxide in a mass ratio of 1:

1.

4. The graphite electrode additive according to claim 1, wherein: The mixed resin is linear phenolic resin and furfural resin in a mass ratio of 1 - 1.2:

2.

5. The graphite electrode additive according to claim 1, characterized in that: The aromatic nitro compound is dinitrobenzene.

6. The graphite electrode additive according to claim 1, characterized in that: The metal oxide is at least one of titanium oxide or zirconium oxide.

7. A method for using a graphite electrode additive, characterized in that, Using the graphite electrode additive as described in any one of claims 1 - 6, the using method is as follows: Use of Material A: Add calcium cyanamide in powder form to petroleum coke and calcine them together; Use of Material B: Stir it into coal tar pitch according to the heating curve, and add saturated fatty acid, lightly burned magnesia and phosphorus compound at a low temperature of 160°C - 250°C respectively; add furan oligomer and ferrooxalic acid at a medium temperature of 250°C - 400°C; Use of Material C: Stir it into the mixture of particulate matter formed by petroleum coke and coal tar pitch.

8. The method for using the graphite electrode additive according to claim 7, characterized in that: The aromatic nitro compound and the mixed resin are pre - mixed.

9. The method for using the graphite electrode additive according to claim 7, characterized in that: An accelerator with a mass ratio of 0.5 - 0.8:100 is added to the mixture of petroleum coke particulate matter and coal tar pitch, and the accelerator is an acidic halide or a metal halide.

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