Method for preparing high-end purified graphite electrode by electric arc method

Abstract

The invention discloses a method for preparing a high-end purified graphite electrode by an electric arc method. The preparation method for preparing the high-end purified graphite electrode through the electric arc method comprises the steps that S1, raw materials are prepared, the raw materials of the graphite electrode comprise needle coke, carbon fibers and modified pitch, and the needle coke is pretreated; s2, carbon fibers, modified pitch and the pretreated needle coke are mixed and kneaded according to the proportion and subjected to compression molding, and an electrode is obtained; s3, carrying out primary roasting, dipping and secondary roasting on the pressed and molded electrode; s4, performing graphitization and purification treatment on the electrode subjected to secondary roasting to obtain a graphite electrode; and S5, carrying out post-treatment on the prepared graphite electrode. According to the preparation method for preparing the high-end purified graphite electrode through the electric arc method, the problem that the graphite electrode prepared in the prior art is poor in performance at least can be solved.

Description

[0001] The present application claims priority to the Chinese patent application No. 202510997415.9, filed on July 18, 2025, and entitled "Preparation method of graphite electrode and quartz crucible", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of graphite electrode preparation, in particular, to a preparation method of high-end purified graphite electrode prepared by arc method. BACKGROUND

[0003] The quartz crucible is a core container for preparing single crystal silicon, polycrystalline silicon and other materials in the semiconductor industry, and its purity, high temperature resistance and stability directly affect the quality of crystal growth. In the preparation process of the quartz crucible, the graphite electrode, as a resistance heating element or a conductive carrier in a molten environment, plays a key role in conducting current and generating high temperature. The high-end purified graphite electrode, due to its excellent electrical conductivity, corrosion resistance, high temperature stability and low impurity content, becomes a necessary material for preparing high-purity quartz crucibles and is widely used in the field of precision manufacturing such as semiconductor wafers.

[0004] In the prior art, the graphite electrode is usually prepared from ordinary graphite raw materials (such as petroleum coke, pitch coke, etc.) through mixing, molding, baking, graphitization and other processes. The graphite electrode prepared from the aforementioned graphite raw materials has the problems of high impurity content, insufficient structural uniformity and limited high temperature resistance. Moreover, the existing graphite electrode has the problems of high energy consumption, slag dropping and polluting the quartz crucible, and insufficient current resistance when used to prepare high-purity quartz crucibles by arc method. SUMMARY

[0005] The main purpose of the present application is to provide a preparation method of high-end purified graphite electrode prepared by arc method, which at least solves the problem of poor performance of the graphite electrode prepared by the prior art.

[0006] According to one aspect of the present application, there is provided a preparation method of high-end purified graphite electrode prepared by arc method, which comprises: Step S1: preparing raw materials, the raw materials of the graphite electrode including needle coke, carbon fiber and modified pitch, and pretreating the needle coke; Step S2: mixing and molding the carbon fiber, the modified pitch and the pretreated needle coke in proportion to obtain an electrode; Step S3: performing primary baking, impregnation and secondary baking on the molded electrode; Step S4: performing graphitization and purification treatment on the electrode after secondary baking to obtain a graphite electrode; Step S5: post-processing the prepared graphite electrode.

[0007] Further, in the step S1, the mass percentage of the needle coke is 65%-75%, the mass percentage of the carbon fiber is 5%-6%, and the mass percentage of the modified pitch is 19%-30%.

[0008] Further, the needle coke comprises sulfur and ash, wherein the mass percentage of the sulfur is less than or equal to 0.5%, and the mass percentage of the ash is less than or equal to 0.1%; and / or, The softening point of the modified pitch is less than or equal to 110℃, and the mass percentage of quinoline insoluble in the modified pitch is 10%-12%.

[0009] Further, in the step S1, the pretreatment comprises crushing, grinding treatment and purification treatment; wherein, After the crushing and grinding treatment, the needle coke comprises fine powder, medium particles and coarse particles, wherein the particle size of the fine powder is 0μm-80μm, the particle size of the medium particles is 80μm-200μm, and the particle size of the coarse particles is 200μm-400μm; and / or, The ash content of the needle coke after the purification treatment is less than or equal to 10μg / g.

[0010] Further, the mass percentage of the fine powder is 20%-30%, the mass percentage of the medium particles is 20%-30%, and the mass percentage of the coarse particles is 40%-60%.

[0011] Further, in the step S2, the volume density of the electrode obtained after the compression molding treatment is greater than or equal to 1.70g / cm 3 .

[0012] Further, in the step S3, after the first baking, the mass percentage of the volatile matter of the electrode is less than or equal to 8%; and / or, After the impregnation, the weight gain rate of the electrode is greater than or equal to 14%; and / or, After the second baking, the volume density of the electrode is greater than or equal to 1.69g / cm 3 .

[0013] Further, in the step S4, the graphitization rate of the electrode is greater than or equal to 96%, and / or, The resistivity of the electrode is less than or equal to 5.5μΩ·m.

[0014] Further, in the step S5, the post-processing mode comprises mechanical processing and / or chemical cleaning.

[0015] In the present application, the graphite electrode is prepared by using needle coke, carbon fiber and modified pitch as raw materials, crushing, grinding and purifying the needle coke, and then using mixing and extrusion molding, one-time baking, impregnation and two-time baking, graphitization and purification treatment, and post-treatment of the graphite electrode. The graphite electrode prepared by the above preparation method has extremely low content of heteroatoms, high strength, strong oxidation resistance, low unit consumption, strong current resistance, and significantly improved performance of the graphite electrode. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate exemplary embodiments of the present application and together with the description serve to explain the application. In the drawings: Figure 1 The flow chart of the preparation method for preparing high-end purified graphite electrode by arc method disclosed in the embodiments of the present application. DETAILED DESCRIPTION

[0017] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0018] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise, and it should also be understood that the terms "comprise" and / or "include" as used in the specification indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0019] Unless specifically stated otherwise, the relative arrangements of the components and steps illustrated in these embodiments and the numerical expressions and values set forth in the examples are not meant to limit the scope of the present application. It should also be understood that the size of the various parts shown in the figures can not be to scale for ease of illustration. Techniques, methods, and devices known to those of ordinary skill in the art can not be discussed in detail, but should be considered as part of the description of the present application. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments can have different values. It should be noted that similar reference numbers and letters in the following drawings represent similar items, and therefore, once an item is defined in one drawing, it need not be further discussed in subsequent drawings.

[0020] As mentioned in the background section, in the prior art, graphite electrodes are typically prepared from common graphite raw materials (such as petroleum coke, pitch coke, etc.) through processes such as kneading, molding, calcination, and graphitization. Graphite electrodes prepared using the aforementioned raw materials suffer from high impurity content, insufficient structural uniformity, and limited high-temperature resistance. Furthermore, existing graphite electrodes exhibit high energy consumption, slag shedding and damage to the quartz crucible, and insufficient current tolerance when using the electric arc method to prepare high-purity quartz crucibles. Therefore, this application provides a method for preparing high-end purified graphite electrodes using the electric arc method. The graphite electrodes prepared by this method have extremely low heteroatom content, high strength, strong oxidation resistance, low energy consumption per unit, and strong current resistance. The following will provide a detailed description of this application with reference to the accompanying drawings. Figure 1 As shown in the embodiments of this application, a method for preparing high-end purified graphite electrodes by electric arc method is provided.

[0021] Specifically, the preparation method of this arc method for high-end purified graphite electrodes includes: Step S1: Prepare raw materials. In this application, the raw materials for the graphite electrode include needle coke, carbon fiber and modified pitch, and the needle coke is pretreated.

[0022] In this application, needle coke refers to high-end petroleum-based needle coke, a high-quality carbon material. Needle coke is obtained from heavy distillates (such as catalytic cracking clarified oil, ethylene tar, and vacuum residue) produced during petroleum refining through deep processing and high-temperature pyrolysis. Petroleum-based needle coke is produced from ethylene tar, vacuum and thermal cracking residue, and catalytic cracking slurry as raw materials, undergoing high-temperature carbonization under specific conditions. Petroleum-based needle coke possesses characteristics such as low thermal expansion coefficient, low sulfur content, low ash content, low volatile matter content, high density, high electrical conductivity, and easy graphitization. This needle coke is primarily used in the manufacture of ultra-high power graphite electrodes.

[0023] Carbon fiber is a high-performance inorganic fiber material with characteristics such as high strength, lightweight, corrosion resistance, and excellent electrical and thermal conductivity. It is widely used in aerospace, automotive, sporting goods, energy, composite materials and other fields.

[0024] Modified asphalt is a product of coal tar pitch modified through special processes (such as oxidation, polymerization, and heat treatment). It is an important chemical raw material widely used in metallurgy, carbon, and refractory materials. Modified asphalt can typically be produced through processes such as oxidative modification, blending modification, and heat treatment modification.

[0025] In this application, when preparing the graphite electrode, the mass percentage of needle coke is 65%-75%. For example, the mass percentage of needle coke can be 65%, 68%, 70%, 75%, etc., and the specific value can be adapted according to actual production.

[0026] Furthermore, this application uses needle coke as the main solid raw material, and the needle coke contains sulfur and ash. Specifically, sulfur refers to elemental sulfur existing in the form of organic sulfur (such as thiols, thioethers, thiophenes, etc.) and inorganic sulfur (such as sulfides, sulfates), and is a key harmful impurity indicator for measuring the purity and quality of needle coke. Its sources are mainly related to raw materials (such as petroleum residue oil, coal tar) and production processes. Ash refers to the mass fraction of inorganic impurities (such as metal oxides, salts, etc.) remaining after the material is burned at high temperature, usually expressed as a percentage or ppm (μg / g). Sulfur is a key indicator for measuring the purity of materials, especially crucial in high-end industrial raw materials (such as graphite, carbon fiber, semiconductor materials).

[0027] In this application, the mass percentage of sulfur in the needle coke is less than or equal to 0.5%. For example, the mass percentage of sulfur can be 0.45%, 0.3%, 0.2%, etc. Furthermore, in this application, the mass percentage of ash in the needle coke is less than or equal to 0.1%. For example, the mass percentage of ash can be 0.09%, 0.07%, 0.01%, etc. In this application, strictly controlling the mass percentage of sulfur in the needle coke to be less than or equal to 0.5% and the mass percentage of ash to be less than or equal to 0.1% is key to improving the performance of needle coke as a high-quality raw material.

[0028] Specifically, controlling the mass percentage of sulfur can reduce the adverse effects of sulfur compounds generated at high temperatures on the conductivity and chemical stability of graphite electrodes during volatilization; it can also extend the service life of equipment for preparing graphite electrodes; it can also improve the graphitization efficiency and purity of electrodes, and reduce environmental pollution.

[0029] Specifically, in this application, controlling the ash content by a mass percentage of less than or equal to 0.1% can avoid structural defects in metal-catalyzed graphite and ensure that the electrode resistivity meets requirements; it can also improve the electrode's density and mechanical strength. For example, industrial data shows that for every 0.05% reduction in ash content, electrode life can be extended by 10%-15%; for every 0.01% increase in ash content, resistivity may increase by 3 μΩ. •m-5μΩ •m.

[0030] Furthermore, needle coke requires pretreatment before being mixed with modified pitch and carbon fiber. This pretreatment specifically includes crushing, grinding, and purification. Crushing and grinding can be performed using equipment such as a jaw crusher. In this application, the purpose of crushing and grinding is to break the needle coke into fine, medium, and coarse particles. The fine particles have a diameter of 0 μm-80 μm, the medium particles have a diameter of 80 μm-200 μm, and the coarse particles have a diameter of 200 μm-400 μm. The fine particles have a high specific surface area and conductivity, which fills the gaps between large particles, improving the overall conductivity and structural density of the material. The medium particles balance strength and conductivity. The coarse particles act as a high-strength skeleton, significantly improving the material's impact resistance and wear resistance, and reducing the coefficient of thermal expansion.

[0031] In actual production, the mass percentage of fine powder in the added needle coke is 20%-30%, for example, it can be 20%, 25%, 30%, etc.; the mass percentage of medium particles is 20%-30%, for example, it can be 20%, 25%, 30%, etc.; and the mass percentage of coarse particles is 40%-60%, for example, it can be 40%, 50%, 60%, etc. Of course, in other embodiments of this application, the mass percentage of the three particle sizes can be adjusted according to actual process requirements, as long as it is within the scope of protection of this application.

[0032] Furthermore, purification treatment refers to removing metallic impurities from needle coke of different particle sizes by high-temperature chlorination roasting at 1200℃-1400℃, so that the ash content in the needle coke meets the requirement of less than or equal to 10μg / g.

[0033] Furthermore, the mass percentage of carbon fiber is 5%-6%, for example, it can be 5%, 5.5%, 5.8%, and 6%. Carbon fiber can optimize electrode performance through its unique physicochemical properties, overcoming the limitations of traditional graphite materials in terms of conductivity, mechanical strength, and thermal shock resistance. In this application, carbon fiber exhibits extremely high conductivity (resistivity as low as 5 μΩ). •cm-10μΩ •cm), and has a large aspect ratio (length / diameter can reach 10). 3 -10 4 Carbon fibers can form a three-dimensional, interconnected conductive framework within a graphite matrix, reducing interparticle contact resistance. Traditional graphite electrodes rely on physical contact between particles for conductivity, resulting in localized weak points in conductivity. The addition of carbon fibers can fill these gaps, with particularly significant effects in ultra-high power graphite electrodes requiring low resistivity.

[0034] Carbon fiber boasts a tensile strength of 2000MPa-7000MPa and an elastic modulus of 200GPa-400GPa, significantly higher than graphite (tensile strength approximately 10MPa-30MPa). This enhances the mechanical strength and fracture resistance of graphite electrodes. Furthermore, carbon fiber exhibits a low axial thermal expansion coefficient (-1×10⁻⁶⁻). 6 / ℃-1×-610⁻ 6 / ℃), and graphite (approximately -61×10⁻ 6 / -6℃-2×10⁻ 6 The carbon fiber concentration (°C) is close to that of the graphite matrix, which can alleviate the stress caused by thermal expansion mismatch during rapid heating and cooling cycles (such as electric furnace start-up and shutdown), thereby improving the thermal shock resistance and high-temperature stability of the graphite electrode. Furthermore, the addition of carbon fiber can improve the plasticity of the preform. The flexibility and entanglement ability of carbon fiber can enhance the plasticity and formability of the paste (needle coke + binder), especially in extrusion or vibration molding, reducing mold wear and improving the uniformity of preform density. Adding carbon fiber can also reduce the amount of binder used: the surface-active groups of carbon fiber can form a chemical bond with the binder, reducing the amount of binder added by 5%-10% while ensuring the strength of the preform. This reduces the release of volatiles during subsequent heat treatment, reduces porosity formation, and carbon fiber can also inhibit the carbonization shrinkage of modified pitch during calcination.

[0035] Furthermore, the mass percentage of modified asphalt is 19%-30%. For example, the mass percentage of modified asphalt can be 19%, 20%, 25%, 30%, etc., and the specific value is selected adaptively according to actual production. In the process of preparing graphite electrodes, modified asphalt is used as a binder. Of course, in other embodiments of this application, the binder can also be phenolic resin, petroleum asphalt, etc. In this application, modified asphalt is preferred as a binder for preparing high-end purified graphite electrodes. The unique advantages of modified asphalt as a binder are: modified asphalt (softening point 80℃-100℃) is in a low-viscosity fluid state at the kneading temperature (100℃-220℃), which can fully wet the surface of needle coke and carbon fibers, fill the gaps between particles, and form a uniform paste. In addition, it has a high coking value (55%-65%), and after calcination, it is converted into glassy carbon, forming a strong bonding interface with the graphitization products of needle coke. Moreover, the thermal stability of modified asphalt is compatible with graphitization, reducing porosity, reducing environmental pollution, and reducing electrode oxidation loss.

[0036] Furthermore, in this application, the softening point of the modified asphalt is less than or equal to 110°C. A low softening point means that the asphalt can melt at a lower temperature, allowing it to more uniformly wet the surface of solid raw material particles and form a good physical bonding network. The paste formed after kneading asphalt with a low softening point has better plasticity and ductility, making it easier to produce high-density, low-porosity green bodies through processes such as extrusion, and reducing cracks or delamination defects. Low-temperature melting also allows the asphalt to fill the spaces between raw material particles more fully. The coke (binder phase) produced during carbonization (high-temperature heat treatment) can uniformly coat the aggregate particles, enhancing the bonding force between aggregates and improving the mechanical strength (such as flexural strength and compressive strength) and electrical continuity of the finished electrode.

[0037] Furthermore, the mass percentage of quinoline-insoluble matter in the modified asphalt is 10%-12%. For example, the mass percentage of quinoline-insoluble matter can be 10%, 11%, 12%, etc. When the content of quinoline-insoluble matter is controlled at 10%-12%, it can form sufficient skeletal support while avoiding a surge in asphalt viscosity due to excessive quinoline-insoluble matter, which would reduce fluidity and affect the uniformity of mixing. Quinoline-insoluble matter particles can act as graphitization nuclei in the coke formed after carbonization, promoting the transformation of surrounding asphalt-based carbon into an ordered graphite structure, thereby improving the conductivity and oxidation resistance of the finished electrode (wherein, the higher the degree of graphitization, the stronger the oxidation resistance).

[0038] Step S2: Mix carbon fiber, modified pitch and pretreated needle coke in a certain proportion and press them into shape to obtain an electrode.

[0039] Specifically, the mass percentage of needle coke is 65%-75%, the mass percentage of carbon fiber is 5%-6%, and the mass percentage of modified bitumen is 19%-30%. In actual production, the appropriate proportions are selected based on actual needs, and the mixture is kneaded in a vacuum mixer at 100℃-220℃ for 40-55 minutes. The vacuum degree of the vacuum mixer is less than or equal to -0.08MPa, and the temperature of the vacuum mixer is between 160℃ and 180℃. This setup ensures sufficient contact and uniform distribution of the binder (modified bitumen) with the solid raw materials (needle coke and carbon fiber), forming a high-quality paste that provides a good foundation for subsequent molding and carbonization. Furthermore, kneading in a vacuum mixer removes air, increases the density of the paste, promotes interfacial bonding between the modified bitumen and the solid raw materials, and inhibits bitumen oxidation and deterioration.

[0040] The electrode forming process can include extrusion molding, compression molding, vibration molding, and isostatic pressing. In this application, extrusion molding is preferred due to its high production efficiency. In this application, the working pressure of the extrusion equipment is set to be greater than or equal to 30 MPa, and the bulk density of the green preform is ensured to be greater than or equal to 1.70 g / cm³. 3High pressure forces the removal of pores and air, increasing the green density and reducing the risk of cracking or collapse due to excessive porosity during subsequent firing. High pressure also enhances interparticle mechanical meshing and bonding, promotes uniform binder distribution, and strengthens interfacial adhesion. During the extrusion molding process, ensure the green density is greater than or equal to 1.70 g / cm³. 3 This can balance molding feasibility and subsequent performance; if the density is too low (e.g., less than 1.65 g / cm³), it will affect the final product. 3 The electrode has high internal porosity, leading to rapid escape of volatiles during calcination, which can easily cause cracking and deformation of the green body. Furthermore, insufficient residual carbon after carbonization results in low electrode strength and conductivity. Excessive density (e.g., greater than 1.80 g / cm³) is also problematic. ³ ): Higher extrusion pressure (e.g., greater than 50 MPa) is required, which increases equipment load and energy consumption, and may cause carbon fiber breakage or asphalt extrusion ("sweating") due to excessive extrusion, thus damaging the uniformity of the structure.

[0041] Step S3: The pressed electrode is subjected to a first firing, impregnation, and a second firing.

[0042] Specifically, the first firing involves a stepped heating to 1200℃, followed by a holding period of 22-30 days, resulting in a volatile matter content of ≤8%. The stepped heating rate is less than or equal to 50℃ / h. This stepped heating prevents electrode cracking due to thermal stress, promotes full carbonization, and stabilizes the microstructure, which is beneficial for subsequent impregnation and secondary firing. The 22-30 day holding period ensures sufficient volatile matter removal and improves firing uniformity, preventing incomplete internal carbonization. Controlling the volatile matter content to ≤8% reduces the risk of subsequent processes and guarantees the binder carbonization rate.

[0043] Furthermore, a special impregnation bitumen with a coking value of ≥50% is used for impregnation, which improves the density and conductivity of the electrode, and the impregnation bitumen has good compatibility with the calcined body. Impregnation is carried out under pressure at 180℃-200℃ for 3-4 hours. This setting, within the aforementioned temperature range, improves impregnation efficiency and avoids overheating and decomposition of the bitumen. Pressurized impregnation for 3-4 hours, with an impregnation pressure ≥1.5MPa, forces the bitumen into the fine pores of the electrode, increasing the impregnation depth and filling rate, resulting in a significantly higher weight gain compared to atmospheric pressure impregnation. This setting also ensures impregnation uniformity: sufficient impregnation time ensures that the bitumen fully penetrates the interior of the blank, avoiding sufficient surface impregnation while leaving voids inside. In this application, the bitumen impregnation penetration rate is ≥95%. The weight gain rate directly reflects the amount of asphalt penetration. A weight gain rate of 14% or more for the electrode means that the pores of the green body are effectively filled, laying the foundation for the generation of more carbonaceous material during subsequent firing, and ultimately improving the density and strength of the electrode (e.g., a bulk density target of 1.69 g / cm³). 3 ).

[0044] Furthermore, the secondary calcination is carried out at 700℃-800℃ for 5-20 days, resulting in an electrode bulk density greater than or equal to 1.69 g / cm³. 3 700℃-800℃ is the key stage for asphalt carbonization (2000℃-3000℃ below the graphitization temperature), causing the impregnated asphalt to decompose and generate new coke, filling the original pores and further increasing the density. This setting also avoids excessive sintering. Temperatures below 800℃ prevent excessive aggregation of aggregate particles, which could lead to increased brittleness, while retaining a certain degree of structural toughness, facilitating subsequent processing (such as machining and graphitization). Holding at this temperature for 5-20 days ensures complete carbonization. The electrode's bulk density is greater than or equal to 1.69 g / cm³. 3 It can directly improve electrode performance, reduce resistivity and improve conductivity, and enhance thermal shock resistance and corrosion resistance.

[0045] Step S4: The electrode after secondary calcination is graphitized and purified to obtain a graphite electrode.

[0046] Specifically, chlorine and Freon gases are introduced into an Atchison furnace at 2800℃-3000℃ to chemically react with metallic impurities (such as oxides of Fe, Si, and Al) in the electrode, thus removing impurities. Furthermore, impurity atoms (such as metal ions) can embed between graphite layers or replace carbon atoms, forming defects and hindering electron conduction. Gas treatment can reduce the impurity content to the ppm level, ensuring the purity of the graphitized structure. High-temperature graphitization promotes the orderly arrangement of carbon atoms, increasing the graphitization rate of the electrode. In this application, after graphitization and purification treatment of the electrode following secondary calcination, the graphitization rate of the electrode is greater than or equal to 96%, at which point the resistivity of the electrode can be reduced to 10. -6 Ω·m-10 -5 With conductivity at the Ω·m level, approaching that of ideal graphite, it effectively reduces energy loss during current transmission. Furthermore, after graphitization and purification of the motor, the carbon atom interlayer bonding is tighter, defects (such as vacancies and edge groups) are reduced, and the electrode volume density increases to a certain extent, meeting relevant industry standards (e.g., greater than or equal to 1.7 g / cm³). 3 ).

[0047] Through graphitization, the electrodes' electrical and thermal conductivity are closer to their theoretical maximum values, making them suitable for ultra-high power electric arc furnaces. The resistivity is less than or equal to 5.5 μΩ·m, meeting the highest industry standards.

[0048] Step S5: Post-process the prepared graphite electrode.

[0049] Specifically, post-processing includes machining and chemical cleaning. Machining involves removing the surface oxide layer through CNC grinding, achieving a surface roughness Ra ≤ 0.4 μm for the graphite electrode. This setup removes the surface oxide layer, improving appearance precision. Lowering surface roughness reduces contact resistance, resulting in more uniform current distribution, reduced heat loss, and inhibits electrochemical corrosion of the electrode surface. Furthermore, in this application, a mixture of hydrofluoric acid and nitric acid can be used to remove metal residues, followed by rinsing with pure water until the resistivity is less than or equal to 16.5 MΩ·cm. It is noteworthy that after each batch of graphite electrodes is prepared, XRD phase analysis is performed on each batch to ensure that the graphite phase occupies at least 99.9% of the electrode, and SEM (scanning electron microscopy) is used for microstructural examination.

[0050] The physicochemical properties of the graphite electrode prepared in this application are as follows: To verify the technical effects of this application, the following specific embodiments and comparative examples are provided: Example 1 In this embodiment, the total mass of raw materials is 0.5 t / kg, of which needle coke accounts for 65% by mass, carbon fiber accounts for 5% by mass, and modified pitch accounts for 30% by mass. The needle coke is crushed and ground into fine, medium, and coarse particles. After purification using a high-temperature chlorination roasting method, it is mixed in a vacuum mixer at 180°C and then extruded at 30 MPa. The formed electrodes are placed in a ring furnace heated to 1200°C and held for 30 days. Afterward, they are placed in special impregnation pitch and impregnated at 200°C and 1.5 MPa for 3-4 hours. They are then placed in a ring furnace at 750°C for a second roasting and held for 15 days. The electrodes are then placed in an Atchison furnace at 2900°C and subjected to graphitization treatment using chlorine and Freon gases. After graphitization, the graphite electrodes are post-treated by machining and chemical cleaning. The measured physicochemical properties of the product are as follows: Example 2 The total mass of raw materials in Example 2 is basically the same as that in Example 1. The difference is that in this example, the mass percentage of needle coke is 70%, the mass percentage of carbon fiber is 5%, and the mass percentage of modified pitch is 25%.

[0051] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Example 3 The total mass of raw materials in Example 3 is basically the same as that in Example 1. The difference is that in this example, the mass percentage of needle coke is 75%, the mass percentage of carbon fiber is 5%, and the mass percentage of modified pitch is 20%.

[0052] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Example 4 The total mass of raw materials in Example 4 is basically the same as that in Example 1. The difference is that in this example, the mass percentage of needle coke is 75%, the mass percentage of carbon fiber is 6%, and the mass percentage of modified pitch is 19%.

[0053] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Comparative Example 1 The total mass of raw materials in Comparative Example 1 is basically the same as that in Example 1. The difference is that in this example, the mass percentage of needle coke is 70% and the mass percentage of modified bitumen is 30%.

[0054] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Comparative Example 2 The total mass of raw materials in Comparative Example 2 is basically the same as that in Example 1. The difference is that in this example, the needle coke is not purified before mixing.

[0055] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Comparative Example 3 The total mass of raw materials in Comparative Example 3 is basically the same as that in Example 1. The difference is that in this example, the mass percentage of needle coke is 80%, the mass percentage of carbon fiber is 5%, and the mass percentage of modified pitch is 15%.

[0056] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Comparative Example 4 The total mass of raw materials in Comparative Example 4 is basically the same as that in Example 1. The difference is that in this example, the mass percentage of needle coke is 55%, the mass percentage of carbon fiber is 5%, and the mass percentage of modified pitch is 40%.

[0057] When the raw materials in this embodiment are used to produce graphite electrodes, the physicochemical properties of the product are as follows: Table 1: According to Table 1, by comparing the standard values ​​with those of Examples 1, 2, and 3, it can be seen that when the amount of needle coke added to the raw materials for electrode preparation increases, all the indicators of the prepared electrode meet the industry standard values. Specifically, the bulk density and compressive strength of the electrode show a trend of increasing with increasing needle coke addition and increasing with decreasing modified pitch addition; resistivity and coefficient of thermal expansion show a trend of decreasing with increasing needle coke addition and decreasing with decreasing modified pitch addition; ash content shows a trend of decreasing with increasing needle coke addition and then remaining unchanged, and decreasing with decreasing modified pitch and then remaining unchanged. By comparing Examples 3 and 4, it can be seen that when the amount of needle coke added remains constant, the bulk density and compressive strength of the electrode show a trend of increasing with increasing carbon fiber addition and increasing with decreasing modified pitch addition; resistivity, ash content, and coefficient of thermal expansion show a trend of decreasing with increasing carbon fiber addition and decreasing with decreasing modified pitch addition.

[0058] By comparing Example 1, Example 2 and Comparative Example 1, it can be seen that when the amount of needle coke added remains unchanged, the bulk density and resistivity of the electrode remain unchanged after the addition of carbon fiber to the removal of carbon fiber, while the compressive strength and ash content decrease, but the coefficient of thermal expansion increases. When the amount of modified asphalt added remains unchanged, the bulk density of the electrode increases after the addition of carbon fiber to the removal of carbon fiber, while the resistivity, compressive strength and ash content decrease, and the coefficient of thermal expansion remains unchanged.

[0059] Comparative examples and Comparative Example 2 show that when the needle coke is not purified before mixing, the bulk density of the electrode increases, the resistivity, compressive strength and ash content decrease, while the coefficient of thermal expansion remains unchanged.

[0060] By comparing Example 1 and Comparative Example 3, it can be seen that when the amount of carbon fiber added remains unchanged, the amount of needle coke added exceeds its maximum value, and the amount of modified pitch added is less than the minimum value, the bulk density of the electrode prepared increases, while the resistivity, compressive strength, ash content and coefficient of thermal expansion all decrease.

[0061] By comparing Examples 1 and 4, it can be seen that when the amount of carbon fiber added remains unchanged, the amount of needle coke added is less than its minimum value, and the amount of modified pitch added is greater than its maximum value, the bulk density, resistivity, ash content and thermal expansion coefficient of the prepared electrode all increase. Among them, the resistivity exceeds the industry standard value, while the compressive strength decreases.

[0062] Specifically, the above situation mainly occurs because needle coke has a fibrous or needle-like textured structure, high particle regularity, and high packing density. As the amount added increases, the particles can pack more tightly, reducing porosity and thus increasing the electrode's bulk density. Furthermore, as the main skeleton material of the electrode, the high crystallinity and ordered graphitized structure of needle coke provide stronger mechanical support; the more added, the better the continuity and density of the skeleton, and the higher the compressive strength. Simultaneously, the high degree of graphitization of needle coke also gives it good electrical conductivity; increasing the amount added can shorten the conductive path, reduce electron transport resistance, and thus lower resistivity. Because needle coke has a low coefficient of thermal expansion and its ordered crystal structure results in small atomic vibration amplitudes when heated, increasing the amount added enhances the overall thermal stability of the electrode, thus reducing the coefficient of thermal expansion. The reason for the initial decrease in ash content followed by no change may be that needle coke undergoes high-temperature calcination during production, resulting in extremely low impurity content (such as metal oxides and inorganic salts). Initially increasing the amount added can dilute the ash impurities in the electrode, causing a decrease in ash content. When the amount of needle coke added reaches a certain proportion, the impurity content in the electrode is close to the minimum value of the raw material itself. Further increasing the amount added will no longer have a significant effect on the ash content, so the ash content tends to stabilize.

[0063] Modified bitumen, as a binder, can fill the pores between needle coke and carbon fibers after melting at high temperatures. However, excessive addition can lead to the formation of pores from the volatiles produced by bitumen decomposition. Reducing the amount added can decrease the residual volatiles, making the electrode structure denser and improving its bulk density and compressive strength. In this application, reducing the amount of modified bitumen is equivalent to increasing the relative proportion of skeleton materials such as needle coke, thereby strengthening the supporting role of the skeleton and further improving the compressive strength. The coke structure formed after the carbonization of modified bitumen is disordered and has lower conductivity than needle coke. Reducing the amount of bitumen can reduce the proportion of disordered carbon, making the overall conductivity of the electrode more dependent on the ordered structure of needle coke, thus reducing the resistivity. Moreover, the coefficient of thermal expansion of bitumen after carbonization is higher than that of needle coke. Reducing the amount of bitumen can reduce the overall thermal expansion trend of the electrode, thereby reducing the coefficient of thermal expansion. Modified bitumen contains a certain amount of ash impurities (such as metal compounds). Reducing the amount added can directly reduce the impurity content in the electrode, thus reducing the ash content. When the amount of asphalt added is reduced to a certain extent, its contribution to ash content is reduced to the minimum. At this point, the electrode ash content is mainly determined by other raw materials such as needle coke. Further reducing the amount of asphalt will not significantly change the ash content, so it tends to stabilize.

[0064] Carbon fiber possesses a high-strength, high-modulus one-dimensional linear structure. When added, it can interweave between needle-like coke particles, forming a "skeleton-fiber" interlocking structure, significantly improving the compressive strength of the electrode. Furthermore, due to its high aspect ratio, carbon fiber can fill the pores between needle-like coke particles, reducing porosity and making the electrode structure denser, thus increasing its bulk density. In addition, carbon fiber has excellent electrical conductivity; when added, it can form a three-dimensional conductive network with the needle-like coke, shortening the electron transport path and reducing the overall resistivity. Moreover, carbon fiber has a negative coefficient of thermal expansion (approximately -1 × 10⁻⁻ axially). 6 The addition of carbon fiber (at a temperature of 0.5°C) can counteract the positive expansion of needle coke and pitch carbonization phases, thus reducing the overall thermal expansion coefficient of the electrode. During the high-temperature carbonization process in carbon fiber production, the impurity content is extremely low (ash content is typically <0.5%). Increasing the amount added can dilute the ash impurities in the electrode, reducing the ash content.

[0065] When the amount of needle coke added is fixed, the effect of adding carbon fiber during the preparation process on the electrode performance may be due to the following: Adding carbon fiber can fill the gaps between needle coke particles, but modified pitch, acting as a binder, will melt and fill the remaining pores. Without carbon fiber, the gaps between needle coke particles may be filled by more pitch (or pitch carbonization), and the overall bulk density does not change significantly. Furthermore, without carbon fiber, only the needle coke and the modified pitch carbonization phase are bonded, lacking the mechanical interlocking formed by fiber penetration, leading to a decrease in compressive strength. Moreover, the interfacial bonding force between carbon fiber and needle coke is stronger than that between pitch carbonization and needle coke; without carbon fiber, particle slippage easily occurs, reducing strength. In addition, needle coke itself has high graphitization and conductivity. When carbon fiber is missing, needle coke particles are connected through the pitch carbonization phase (disordered carbon). Although the continuity of the conductive network decreases slightly, the high conductivity of needle coke still dominates the overall resistivity. Furthermore, the pitch carbonization phase filling the gaps between needle coke particles may increase the particle contact area, partially offsetting the reduction in conductive pathways caused by the lack of carbon fiber, resulting in no significant change in resistivity. However, carbon fiber production may leave residual catalysts (such as metal salts) or surface treatment agents, introducing additional ash upon addition. Without carbon fiber, electrode ash comes only from needle coke and modified pitch, reducing the total amount of impurities. Furthermore, the axial thermal expansion coefficient of carbon fiber is negative (-1×10⁻⁶). 6 / ℃), -6 can offset needle coke (approximately 1×10⁻ 6 / ℃) and the positive expansion of the pitch carbonization phase; without the addition of carbon fibers, the electrode thermal expansion is dominated by the positive expansion phase, the coefficient increases, and the penetration of carbon fibers can also restrict the thermal deformation of needle-shaped coke particles. Without carbon fibers, the degree of freedom of particle thermal motion increases, and the thermal expansion effect is more significant.

[0066] When the amount of modified bitumen added is fixed, the impact of adding carbon fiber on electrode performance may be due to the following reasons: Carbon fiber itself has a lower density than needle coke. Without carbon fiber, the overall electrode density increases due to the increased proportion of the high-density phase (needle coke). While carbon fiber has high conductivity, its contact points with needle coke may create localized resistance. Without carbon fiber, the conductive network relies on direct contact between the needle coke and the bitumen carbonized phase. If the needle coke particles are in closer contact, the resistivity decreases. The reduced compressive strength of the electrode may be due to the fact that the mechanical reinforcement of carbon fiber is crucial for compressive strength. Without carbon fiber, the needle coke is only bonded by the bitumen carbonized phase, resulting in a significant decrease in strength. Furthermore, the dispersion of carbon fiber improves the uniformity of the electrode structure. After removal, needle coke particles may form weak areas due to differences in packing, leading to a decrease in strength. Additionally, carbon fiber has a higher ash content than both needle coke and modified bitumen. Without carbon fiber, the impurity content is further reduced, thus reducing ash content. When the modified pitch is fixed, the negative expansion effect of the carbon fiber and the positive expansion effect of the needle coke and pitch carbonization phase may just cancel each other out. After the carbon fiber is removed, the proportion of the positive expansion phase (needle coke + pitch carbonization phase) remains unchanged, and the coefficient of thermal expansion remains stable.

[0067] Unpurified needle coke may contain a significant amount of inorganic minerals (such as compounds of silicon, iron, and calcium). These impurities may fill the pores between needle coke particles in a molten or solid state during mixing and sintering, reducing the internal void volume of the electrode and thus increasing its bulk density. Furthermore, some metallic impurities in the unpurified needle coke (such as iron and nickel) possess electrical conductivity. These impurities, distributed within the graphitized structure of the needle coke, may form additional conductive pathways, reducing the overall resistivity. In addition, inorganic impurities (especially amorphous minerals) have poor compatibility with the graphite crystal structure of needle coke. After electrode sintering, these impurities may exist as brittle phases at grain boundaries, forming stress concentration points that make the material more prone to fracture under external forces, resulting in decreased compressive strength. In other words, although the bulk density increases, the impurities filling the pores may disrupt the original continuous graphite skeleton of the needle coke, reducing structural uniformity and ultimately weakening its strength. If certain organic impurities in needle coke are more likely to decompose and volatilize at high temperatures when unpurified (such as incompletely pyrolyzed organic matter), while the content of inorganic impurities is relatively low, a temporary decrease in ash content may occur. The reason why the thermal expansion coefficient of the electrode remains unchanged may be that the thermal expansion coefficient of needle coke is mainly determined by the anisotropy of graphite crystals. If the thermal expansion characteristics of impurities are similar to those of graphite, or if their content is low and uniformly distributed, their impact on the overall thermal expansion coefficient may be insignificant.

[0068] When needle coke is added in excess, the particles can form a denser packing structure through an "interlocking effect," reducing porosity and increasing the overall bulk density. Needle coke is a highly graphitized conductive phase; excessive addition directly increases the contact area of ​​conductive particles in the electrode, forming a more continuous electron transport pathway, and the resistivity decreases significantly with the increase in the proportion of the conductive phase. Furthermore, excessive addition of needle coke also results in insufficient asphalt binder phase between particles (insufficient asphalt content), leading to weakened interfacial bonding between skeletal particles. Under stress, particles are prone to slippage or breakage due to insufficient bonding, and the compressive strength decreases with the lack of binder phase. Moreover, when needle coke is added in excess and asphalt content is reduced, the proportion of low-ash phase increases significantly, and the overall ash content of the electrode decreases with the reduction of high-ash phase (asphalt). In addition, needle coke has a low coefficient of thermal expansion (approximately zero expansion along the crystal axis). Excessive addition significantly increases the proportion of low-expansion phase in the electrode, dominating the overall thermal expansion characteristics and thus reducing the coefficient of thermal expansion.

[0069] When modified asphalt is added in excess, it fills the pores between particles, initially causing an increase in the apparent density of the green body due to "liquid phase filling." However, insufficient needle coke leads to an increase in the proportion of low-density phases (high porosity after asphalt carbonization) in the overall structure, creating the illusion of excessive asphalt filling rather than true skeleton compaction. Needle coke is a highly conductive phase; when its dosage is below the minimum, the conductive pathways (needle coke particle contact network) in the electrode are significantly reduced, and the resistivity rises sharply due to the lack of conductive phase, even exceeding industry standards. Furthermore, as a major aggregate, insufficient needle coke cannot form a rigid skeleton, and the electrode relies primarily on the binder phase after asphalt carbonization for support under stress. However, excessive asphalt carbonization easily produces brittle structures (such as glassy carbon phase), and the interfacial bonding force between the binder phase and aggregate weakens due to the imbalance in proportion, resulting in a decrease in overall strength. In addition, reducing needle coke dosage and increasing asphalt dosage, with the high ash content of modified asphalt dominating, effectively increases the concentration of ash impurities per unit volume. Even if the needle coke itself has low ash content, it cannot offset the increased impurities brought by the asphalt. Furthermore, excessive asphalt significantly increases the proportion of high-expansion phases in the electrode, leading to an increase in the overall coefficient of thermal expansion.

[0070] As can be seen from the above embodiments, this application uses needle coke, carbon fiber and modified pitch as raw materials and the addition amount of each raw material meets the addition requirements. The graphite electrode is prepared by the above method. The graphite electrode has extremely low heteroatom content, high strength, strong oxidation resistance, low single consumption and strong current resistance, which significantly improves the performance of the graphite electrode.

[0071] Combined again Figure 1 As shown, on the other hand, this application also provides a quartz crucible, which is prepared from a graphite electrode prepared by the above-described method for preparing high-end purified graphite electrodes by electric arc method.

[0072] Specifically, the prepared graphite electrode needs to maintain stability during arc melting at 1700℃. After the melting process, the electrode is removed and the oxide layer on its surface is removed using an air blowing device. The inner layer of the crucible, made with the graphite electrode, is prepared using synthetic quartz sand (purity ≥4N8, i.e., purity greater than or equal to 99.998%) via chemical vapor deposition (CVD). This results in a metal impurity content of less than 20 ppm and enhances resistance to melt erosion, thus extending the crucible's service life. The outer layer uses natural sand (purity ≥4N, i.e., purity greater than or equal to 99.99%). Natural sand is only 1 / 3 to 1 / 2 the price of synthetic sand, reducing material costs and providing mechanical support (compressive strength ≥80 MPa) to prevent deformation of the crucible (e.g., bulging ≤2 mm) due to softening of the inner layer at high temperatures.

[0073] Furthermore, natural sand contains small amounts of impurities (such as Al₂O₃ and TiO₂), whose thermal conductivity is slightly higher than that of synthetic sand. These impurities form outer heat dissipation channels, controlling the temperature difference between the inner and outer walls of the crucible within 200℃-300℃ and reducing internal thermal stress concentration. During crucible preparation, the bubble layer thickness must be controlled to ≤0.5mm. Excessive bubble layer thickness (greater than 0.5mm) leads to uneven heat conduction in the quartz crucible, causing melt composition segregation; it also reduces the structural strength of the quartz crucible, making it prone to cracking during actual use.

[0074] In summary, the graphite electrodes prepared using the aforementioned arc method for high-end purified graphite electrodes, when used in the production of quartz crucibles, exhibit superior uniform heat conduction and low impurity release characteristics. This results in more ordered crystallization of the quartz melt during solidification, reducing defects such as porosity and improving the density and transparency of the crucible walls. Furthermore, the low-ash content of the electrodes prevents chemical reactions between quartz and impurities (such as the formation of low-melting-point silicates), enhancing the crucible's resistance to erosion during repeated high-temperature use and extending its service life. In addition, the high-density, low-ash graphite electrodes exhibit better oxidation resistance at high temperatures, reducing the graphite electrode wear rate during melting and decreasing replacement frequency, thus lowering material costs and energy consumption in quartz crucible production; it also improves the production efficiency of quartz crucibles.

[0075] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0076] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0077] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high-end purified graphite electrodes using an electric arc method, characterized in that, The method for preparing high-end purified graphite electrodes using the electric arc method includes: Step S1: Prepare raw materials. The raw materials for the graphite electrode include needle coke, carbon fiber and modified pitch, and pretreat the needle coke. Step S2: Mix carbon fiber, modified pitch and pretreated needle coke in a certain proportion and press them into shape to obtain an electrode. Step S3: The pressed electrode is subjected to a first firing, impregnation, and a second firing. Step S4: The electrode after secondary calcination is graphitized and purified to obtain a graphite electrode; Step S5: Post-process the prepared graphite electrode.

2. The method for preparing high-end purified graphite electrodes by arc method according to claim 1, characterized in that, In step S1, the mass percentage of needle coke is 65%-75%, the mass percentage of carbon fiber is 5%-6%, and the mass percentage of modified pitch is 19%-30%.

3. The method for preparing high-end purified graphite electrodes by arc method according to claim 2, characterized in that, The needle coke comprises sulfur and ash, wherein the mass percentage of sulfur is less than or equal to 0.5%, and the mass percentage of ash is less than or equal to 0.1%; and / or, The modified asphalt has a softening point of less than or equal to 110°C, and the mass percentage of quinoline insolubles in the modified asphalt is 10%-12%.

4. The method for preparing high-end purified graphite electrodes by arc method according to claim 1, characterized in that, In step S1, the pretreatment includes crushing, grinding, and purification; wherein, After the crushing and grinding process, the needle-shaped coke comprises fine powder, medium particles, and coarse particles, wherein the fine powder has a particle size of 0μm-80μm, the medium particles have a particle size of 80μm-200μm, and the coarse particles have a particle size of 200μm-400μm; and / or, The ash content of the needle coke after purification is less than or equal to 10 μg / g.

5. The method for preparing high-end purified graphite electrodes by arc method according to claim 4, characterized in that, The fine powder has a mass percentage of 20%-30%, the medium particles have a mass percentage of 20%-30%, and the coarse particles have a mass percentage of 40%-60%.

6. The method for preparing high-end purified graphite electrodes by arc method according to claim 1, characterized in that, In step S2, the electrode obtained by compression molding has a bulk density greater than or equal to 1.70 g / cm³. 3 .

7. The method for preparing high-end purified graphite electrodes by arc method according to claim 1, characterized in that, In step S3, after the first calcination, the mass percentage of volatile matter in the electrode is less than or equal to 8%; and / or, After the impregnation, the weight gain of the electrode is greater than or equal to 14%; and / or, After the secondary calcination, the bulk density of the electrode is greater than or equal to 1.69 g / cm³. 3 .

8. The method for preparing high-end purified graphite electrodes by arc method according to claim 1, characterized in that, In step S4, the graphitization rate of the electrode is greater than or equal to 96%, and / or, The resistivity of the electrode is less than or equal to 5.5 μΩ·m.

9. The method for preparing high-end purified graphite electrodes by arc method according to claim 1, characterized in that, In step S5, the post-processing method includes machining and / or chemical cleaning.

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