Roasting and graphitizing toughness optimization method of graphite electrode for industrial silicon

Abstract

The invention relates to the technical field of graphite electrode material preparation, and discloses a roasting and graphitizing toughness optimization method of a graphite electrode for industrial silicon, which comprises the following steps: step 1, raw material pretreatment and formula optimization; step 2, forming treatment; step 3, roasting by stages; step 4, dipping treatment; and step 5, graphitization treatment. The breaking strength of the prepared high-toughness graphite electrode is larger than or equal to 15 MPa, and the elastic modulus is smaller than or equal to 10 GPa. Compared with the prior art, the method has the advantage that the roasting and graphitizing toughness optimization method of the graphite electrode for industrial silicon is provided. According to the method, through the synergistic effect of specific raw material proportioning, staged slow roasting, vacuum pressure impregnation and a multi-stage accurate temperature control graphitization process, the compactness and microstructure of the electrode are effectively improved, the breaking strength and thermal shock resistance of the graphite electrode are remarkably improved, and the service life of the graphite electrode in an industrial silicon furnace is prolonged.

Description

Technical Field

[0001] This invention relates to the field of graphite electrode material preparation technology, specifically to a method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness. Background Technology

[0002] Graphite electrodes are key components in electric furnaces for industrial silicon smelting, serving to conduct current and generate an electric arc to melt the furnace charge. The industrial silicon production environment is extreme, and the electrodes are subjected to extremely high thermal loads, mechanical stresses, and thermal shocks, making them prone to cracking, peeling, and even breakage. This leads to rapid electrode consumption, increased production costs, and affects the stability and continuity of the smelting process.

[0003] The performance of graphite electrodes, especially their thermal shock resistance, depends primarily on their toughness, typically exhibiting high flexural strength and low elastic modulus. The electrode fabrication process, particularly the calcination and graphitization processes, has a decisive impact on the microstructure and mechanical properties of the final product. Traditional graphite electrode manufacturing processes suffer from problems such as excessively rapid calcination heating rates and inaccurate temperature control during graphitization, leading to numerous microcracks, uneven pore distribution, insufficient density and strength, and poor toughness, making it difficult to meet the stringent requirements of industrial silicon smelting.

[0004] Therefore, developing a dedicated preparation method for graphite electrodes used in industrial silicon smelting, which optimizes the electrode's microstructure by precisely controlling the calcination and graphitization processes, thereby significantly improving its toughness, has important industrial application value. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the above-mentioned technical difficulties and provide a method for optimizing the toughness of graphite electrodes for industrial silicon through calcination and graphitization. This method, through the synergistic effect of specific raw material ratios, staged slow calcination, vacuum pressure impregnation, and multi-stage precise temperature-controlled graphitization processes, effectively improves the density and microstructure of the electrodes, significantly enhances the flexural strength and thermal shock resistance (i.e., toughness) of the graphite electrodes, and extends their service life in industrial silicon furnaces.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] A method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness includes the following steps:

[0008] Step 1: Raw material pretreatment and formula optimization: Petroleum coke and pitch coke are mixed at a weight ratio of 75-85:20-30 to obtain aggregate; 10-12% of the mass of the modified binder is added to the aggregate, and after stirring evenly, it is kept at 100-120℃ for 1.5-2 hours to obtain paste.

[0009] Step 2, Molding process: Place the paste obtained in Step 1 into a mold and mold it under a pressure of 20-30 MPa for 4-5 minutes to obtain the electrode green blank;

[0010] Step 3: Staged Calcination: The electrode green blank is placed in a calcination furnace and calcined in stages under a protective atmosphere.

[0011] First stage: Increase the temperature from room temperature to 300℃ at a rate of 3-5℃ / h and hold for 13-20 hours;

[0012] Second stage: Increase the temperature from 300℃ to 600℃ at a rate of 4-6℃ / h and hold for 15-25 hours;

[0013] The third stage: the temperature is increased from 600℃ to 900℃ at a rate of 6-10℃ / h, and held at that temperature for 20-30 hours;

[0014] Fourth stage: Naturally cool to room temperature to obtain the calcined electrode;

[0015] Step 4, Impregnation treatment: Place the calcined electrode obtained in step 3 into an impregnation tank, evacuate to a vacuum degree ≤5kPa, maintain for 1-2 hours, then introduce impregnation agent, impregnate at a pressure of 0.5-1MPa for 4-5 hours, then take out the electrode and dry it at 150-200℃ for 2-3 hours.

[0016] Step 5, graphitization treatment: The electrode that has undergone impregnation treatment in step 4 is placed in a graphitization furnace. First, an inert gas is introduced for protection, and then the temperature is increased to 1000-1200℃ at a rate of 60-80℃ / h and held for 2-3 hours. Next, the temperature is increased to 2500-2800℃ at a rate of 100-150℃ / h and held for 5-6 hours. Finally, the temperature is decreased to 800-1000℃ at a rate of 30-50℃ / h and then allowed to cool naturally to room temperature to obtain the high-toughness graphite electrode.

[0017] Furthermore, in step one, the modified binder is a mixture of coal tar pitch, carbon black, and furan resin in a mass ratio of (5-7):(2-3):(1-2).

[0018] Furthermore, in step one, the particle size of both the petroleum coke and the pitch coke is independently 100–500 μm.

[0019] Furthermore, in step three, the protective atmosphere is nitrogen or argon, and the furnace pressure is maintained at a slightly positive pressure during the staged heating and roasting process.

[0020] Furthermore, in step four, the impregnating agent is liquid asphalt or resin.

[0021] Furthermore, in step five, the inert gas is argon.

[0022] Furthermore, in step five, during the process of heating to 2500-2800℃ at a rate of 100-150℃ / h, when the temperature reaches 2000-2200℃, it is held for 0.5-1h.

[0023] Furthermore, the prepared high-toughness graphite electrode has a flexural strength ≥15MPa and an elastic modulus ≤10GPa.

[0024] Furthermore, the prepared high-toughness graphite electrodes are used in industrial silicon smelting.

[0025] The advantages of this invention compared to the prior art are:

[0026] 1. The specific aggregate ratio and modified binder formulation of this invention improve the plasticity and coking value of the paste, laying the foundation for high-strength embryos.

[0027] 2. The ultra-slow heating and long-term heat preservation of this invention ensure the smooth progress of the binder coking process, effectively reducing internal defects and crack sources, and improving the strength of the green body.

[0028] 3. This invention significantly improves the density of the electrode and reduces the porosity, thus ensuring the production of graphite electrodes with high volume density and high strength.

[0029] 4. This invention promotes the full growth and orderly arrangement of graphite microcrystals through precisely controlled heating, holding and cooling processes. While achieving high conductivity, it reduces the elastic modulus and significantly enhances the toughness (thermal shock resistance) of the electrode. Detailed Implementation

[0030] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. Furthermore, the term "comprising" and any variations thereof are intended to cover non-exclusive inclusion.

[0031] The present invention will now be described in further detail with reference to the embodiments.

[0032] Example 1

[0033] A method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness includes the following steps:

[0034] Step 1: Raw Material Pretreatment and Formulation Optimization: Petroleum coke and pitch coke are mixed at a weight ratio of 75:20 to obtain aggregate; a modified binder accounting for 10% of its mass is added to the aggregate, stirred evenly, and kept at 100℃ for 1.5 hours to obtain a paste. The modified binder is a mixture of coal tar pitch, carbon black, and furan resin at a mass ratio of 5:2:1. The particle size of both petroleum coke and pitch coke is 100 μm.

[0035] Step 2, Molding process: The paste obtained in Step 1 is placed into a mold and molded under a pressure of 20MPa for 4 minutes to obtain the electrode green blank;

[0036] Step 3: Staged Calcination: The electrode green blank is placed in a calcination furnace and calcined in stages under a protective atmosphere.

[0037] First stage: Increase the temperature from room temperature to 300℃ at a rate of 3℃ / h and hold for 13 hours;

[0038] Second stage: Increase the temperature from 300℃ to 600℃ at a rate of 4℃ / h and hold for 15 hours;

[0039] The third stage: the temperature is increased from 600℃ to 900℃ at a rate of 6℃ / h and held for 20 hours;

[0040] Fourth stage: Naturally cool to room temperature to obtain the calcined electrode;

[0041] The protective atmosphere is nitrogen or argon, and the furnace pressure is maintained at a slightly positive pressure during the staged heating and roasting process.

[0042] Step 4, Impregnation treatment: Place the calcined electrode obtained in Step 3 into an impregnation tank, evacuate to a vacuum degree ≤5kPa, maintain for 1 hour, then introduce an impregnating agent and impregnate at a pressure of 0.5MPa for 4 hours. Then remove the electrode and dry it at 150℃ for 2 hours; the impregnating agent is liquid asphalt or resin.

[0043] Step 5, Graphitization Treatment: The electrode treated with impregnation in Step 4 is placed in a graphitization furnace. First, an inert gas is introduced for protection. Then, the temperature is increased to 1000℃ at a rate of 60℃ / h and held for 2 hours. Next, the temperature is increased to 2500℃ at a rate of 100℃ / h and held for 5 hours. Finally, the temperature is decreased to 800℃ at a rate of 30℃ / h and then allowed to cool naturally to room temperature to obtain the high-toughness graphite electrode. The inert gas is argon. During the process of increasing the temperature to 2500℃ at a rate of 100℃ / h, when the temperature reaches 2000℃, it is held for 0.5 hours.

[0044] The high-toughness graphite electrode prepared has a flexural strength ≥15MPa and an elastic modulus ≤10GPa.

[0045] The prepared high-toughness graphite electrode is used in industrial silicon smelting.

[0046] Example 2

[0047] A method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness includes the following steps:

[0048] Step 1: Raw Material Pretreatment and Formulation Optimization: Petroleum coke and pitch coke are mixed at a weight ratio of 85:30 to obtain aggregate; a modified binder accounting for 12% of its mass is added to the aggregate, stirred evenly, and kept at 120℃ for 2 hours to obtain a paste. The modified binder is a mixture of coal tar pitch, carbon black, and furan resin at a mass ratio of 7:3:2. The particle size of both petroleum coke and pitch coke is independently 500μm.

[0049] Step 2, Molding process: The paste obtained in Step 1 is placed into a mold and molded under a pressure of 30MPa for 5 minutes to obtain the electrode green blank;

[0050] Step 3: Staged Calcination: The electrode green blank is placed in a calcination furnace and calcined in stages under a protective atmosphere.

[0051] Phase 1: Increase the temperature from room temperature to 300℃ at a rate of 5℃ / h and hold for 20 hours;

[0052] Second stage: Increase the temperature from 300℃ to 600℃ at a rate of 6℃ / h and hold for 25 hours;

[0053] The third stage: the temperature is increased from 600℃ to 900℃ at a rate of 10℃ / h and held for 30 hours;

[0054] Fourth stage: Naturally cool to room temperature to obtain the calcined electrode;

[0055] The protective atmosphere is nitrogen or argon, and the furnace pressure is maintained at a slightly positive pressure during the staged heating and roasting process.

[0056] Step 4, Impregnation treatment: Place the calcined electrode obtained in Step 3 into an impregnation tank, evacuate to a vacuum degree ≤ 5 kPa, maintain for 2 hours, then introduce an impregnation agent and impregnate at a pressure of 1 MPa for 5 hours. Then remove the electrode and dry it at 200°C for 3 hours. The impregnation agent is liquid asphalt or resin.

[0057] Step 5, Graphitization Treatment: The electrode treated in Step 4 is placed in a graphitization furnace. First, an inert gas is introduced for protection. Then, the temperature is increased to 1200℃ at a rate of 80℃ / h and held for 3 hours. Next, the temperature is increased to 2800℃ at a rate of 150℃ / h and held for 6 hours. Finally, the temperature is decreased to 1000℃ at a rate of 50℃ / h and then allowed to cool naturally to room temperature to obtain the high-toughness graphite electrode. The inert gas is argon. During the heating process from 150℃ / h to 2800℃, when the temperature reaches 2200℃, it is held for 1 hour.

[0058] The high-toughness graphite electrode prepared has a flexural strength ≥15MPa and an elastic modulus ≤10GPa.

[0059] The prepared high-toughness graphite electrode is used in industrial silicon smelting.

[0060] The present invention and its embodiments have been described above, and this description is not restrictive. If those skilled in the art are inspired by this description and design similar embodiments without departing from the spirit of the invention, such embodiments should fall within the protection scope of the present invention.

Claims

1. A method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness, characterized in that, Includes the following steps: Step 1: Raw material pretreatment and formula optimization: Petroleum coke and pitch coke are mixed at a weight ratio of 75-85:20-30 to obtain aggregate; 10-12% of the mass of the modified binder is added to the aggregate, and after stirring evenly, it is kept at 100-120℃ for 1.5-2 hours to obtain paste. Step 2, Molding process: Place the paste obtained in Step 1 into a mold and mold it under a pressure of 20-30 MPa for 4-5 minutes to obtain the electrode green blank; Step 3: Staged Calcination: The electrode green blank is placed in a calcination furnace and calcined in stages under a protective atmosphere. First stage: Increase the temperature from room temperature to 300℃ at a rate of 3-5℃ / h and hold for 13-20 hours; Second stage: Increase the temperature from 300℃ to 600℃ at a rate of 4-6℃ / h and hold for 15-25 hours; The third stage: the temperature is increased from 600℃ to 900℃ at a rate of 6-10℃ / h, and held at that temperature for 20-30 hours; Fourth stage: Naturally cool to room temperature to obtain the calcined electrode; Step 4, Impregnation treatment: Place the calcined electrode obtained in step 3 into an impregnation tank, evacuate to a vacuum degree ≤5kPa, maintain for 1-2 hours, then introduce impregnation agent, impregnate at a pressure of 0.5-1MPa for 4-5 hours, then take out the electrode and dry it at 150-200℃ for 2-3 hours. Step 5, graphitization treatment: The electrode that has undergone impregnation treatment in step 4 is placed in a graphitization furnace. First, an inert gas is introduced for protection, and then the temperature is increased to 1000-1200℃ at a rate of 60-80℃ / h and held for 2-3 hours. Next, the temperature is increased to 2500-2800℃ at a rate of 100-150℃ / h and held for 5-6 hours. Finally, the temperature is decreased to 800-1000℃ at a rate of 30-50℃ / h and then allowed to cool naturally to room temperature to obtain the high-toughness graphite electrode.

2. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 1, characterized in that: In step one, the modified binder is a mixture of coal tar pitch, carbon black and furan resin in a mass ratio of (5-7):(2-3):(1-2).

3. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 1, characterized in that: In step one, the particle size of both the petroleum coke and the pitch coke is independently 100–500 μm.

4. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 1, characterized in that: In step three, the protective atmosphere is nitrogen or argon, and the furnace pressure is maintained at a slightly positive pressure during the staged heating and roasting process.

5. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 1, characterized in that: In step four, the impregnating agent is liquid asphalt or resin.

6. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 1, characterized in that: In step five, the inert gas is argon.

7. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 1, characterized in that: In step five, during the process of raising the temperature to 2500-2800℃ at a rate of 100-150℃ / h, when the temperature reaches 2000-2200℃, it is held for 0.5-1h.

8. A method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to any one of claims 1 to 7, characterized in that: The high-toughness graphite electrode prepared has a flexural strength ≥15MPa and an elastic modulus ≤10GPa.

9. The method for calcining and graphitizing graphite electrodes for industrial silicon to optimize toughness according to claim 8, characterized in that: The prepared high-toughness graphite electrode is used in industrial silicon smelting.