Metal and soft carbon double-layer impregnated graphite sagger and preparation method thereof

Abstract

The invention relates to the technical field of graphite saggers, in particular to a metal and soft carbon double-layer impregnated graphite sagger and a preparation method thereof. According to the preparation method, a pore-forming agent and a graded semi-graphitized material are mixed and carbonized at a low temperature, so that the porosity of a matrix raw material is improved, a metal / alloy layer framework is immersed, and the hardness and strength of the sagger are improved; and a soft carbon layer is further filled between the metal framework and the graphite layer, so that the porosity of the product can be reduced, the density can be increased, and the service life of the graphite sagger can be greatly prolonged. Specifically, the apparent porosity of the sagger product can be reduced from 15% or above of a conventional process to 10% or below; the breaking strength of a sagger product is stably improved to 40 Mpa or above from conventional 15-20 Mpa; the compressive strength can be stably improved to 70 Mpa or above from conventional 40-50 Mpa, and the density of a sagger product is improved to 1.8 g / cm < 3 > or above from traditional 1.65 g / cm < 3 >.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of graphite ladle, more particularly, it relates to a metal and soft carbon double-layer impregnated graphite ladle and a preparation method thereof. BACKGROUND

[0002] The graphite ladle is widely used in high-precision fields such as lithium batteries, chemical metallurgy, electronic semiconductors and aerospace due to its high carbon content (up to 99.9%), high temperature resistance, rapid heat conduction and oxidation resistance. The metal impregnated graphite ladle is an upgraded product of the conventional graphite ladle process, which not only has various advantages of the graphite ladle, but also greatly improves the hardness and heat conductivity of the graphite ladle, and widens the application scenarios of the graphite ladle.

[0003] Currently, the metal impregnated graphite ladle process is relatively less studied, mainly because the metal molecules are relatively larger than the graphite pores, and the conventional high-pressure impregnation process can only penetrate a small amount of metal solution into the graphite pores. If too much metal is impregnated, the metal layer will expand and contract with the graphite layer due to the frequent changes in high and low temperatures (temperature difference of more than 1000 DEG C) in the application scenarios of the ladle, resulting in cracking and damage of the ladle, which greatly affects the service life of the ladle, and there is also a "sandwich layer" of incomplete impregnation, which greatly reduces the strength and service life of the ladle. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of a metal and soft carbon double-layer impregnated graphite ladle, which solves the technical problems of low strength, easy cracking and damage, and low service life of the metal impregnated graphite ladle.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A preparation method of a metal and soft carbon double-layer impregnated graphite ladle, comprising the following steps: S1: taking the semi-graphitized material after grading and the pore former according to a mass ratio of 80-85:15-20, and mixing them in a VC mixing device; S2: loading the mixed material into a stainless steel crucible, transferring it into a carbonization furnace, and heating it to 300-400 DEG C at a heating rate of 2-5 DEG C / min and maintaining it for 2-5 h, then heating it to 800-900 DEG C at a heating rate of 1-4 DEG C / min and maintaining it for 2-5 h, and throughout the process, inert gas is introduced at a flow rate of 2-5 L / min, and the material is discharged after the temperature drops to 100 DEG C; S3: taking out the material in the crucible, and crushing it into powder by a universal crusher for multiple times; S4: washing the crushed material with water until the pH is neutral, and then drying it in a 100 DEG C oven to obtain the base material; S5: Place the matrix material into the mold and compact it with an isostatic pressing device to obtain the graphite sagger blank; S6: Add solid metal into the metal melting chamber, purge the air in the chamber with inert gas to prevent oxidation, and then heat up to melt the solid metal into molten metal. S7: Place the graphite sagger blank into the impregnation chamber, heat the product to preheat it, draw a vacuum to make the impregnation chamber negative pressure, open the connecting valve between the metal melting chamber and the impregnation chamber, ensure that the molten metal melt immerses the graphite sagger blank, close the connecting valve, quickly pressurize the impregnation chamber and hold the pressure for a certain time, after the pressure holding is completed, drain the molten metal melt from the impregnation chamber, and after cooling to room temperature, take out the graphite sagger blank to complete the metal impregnation; S8: Place the graphite sagger blank that has been impregnated with metal into the asphalt impregnation equipment. First, evacuate the impregnation chamber to -50 to -300 Pa. Then, let the liquid asphalt flow into the chamber. Then, pressurize it to 5-10 MPa and hold the pressure for 3-5 hours. After the pressure holding is completed, the liquid asphalt is returned to the asphalt storage tank. Cool down, depressurize and take out the graphite sagger blank. S9: Transfer the graphite sagger blank after the second impregnation to the carbonization furnace. Under an inert gas atmosphere, heat it to 600-900℃ at a heating rate of 3-10℃ / min and hold it for 10-20h. After holding, heat it to 1200-1600℃ at a heating rate of 2-5℃ / min and hold it for 20-30h. Then cool it naturally to room temperature to obtain the sagger semi-finished product. S10: Transfer the semi-finished box body to the CVD furnace. Under the protection of inert gas, acetylene is introduced at 700-900℃ for 1-5 hours. After the reaction is completed, the temperature is naturally lowered. After cleaning the surface burrs and dust, the finished graphite box body is obtained.

[0006] Preferably, the semi-graphitized material after gradation in step S1 is a mixture of 100-mesh crucible material, 200-mesh electrode recycled material, and graphitized depolymerization tail powder in a mass ratio of 6:3:1; the pore-forming agent in step S1 includes at least one of sodium chloride, potassium chloride, sodium hydroxide, and potassium hydroxide.

[0007] Preferably, the mixing speed in step S1 is 200-1000 rpm and the mixing time is 60-120 min.

[0008] Preferably, the number of pulverization times in step S3 is 2-5 times, and the powder particle size D50 = 20-100 μm.

[0009] Preferably, the molding pressure in step S5 is 5-20 MPa, the holding time is 5-20 min, and the mold temperature is 150-250℃.

[0010] Preferably, the solid metal in step S6 is an alloy made of at least one of copper, aluminum, iron, and titanium; the melting temperature is 500-1500℃, and the heating rate is 2-10℃ / min. Preferably, in step S7, the preheating temperature is 200-800℃, the heating rate is 2-10℃ / min, the preheating time is 30-120min, and the vacuum is evacuated to -50--300pa; the pressure applied to the impregnation chamber is 20-50MPa, and the pressure holding time is 30-60min.

[0011] Preferably, the asphalt in step S8 is either coal tar pitch or petroleum asphalt; Another object of the present invention is to provide a graphite sagger prepared by the aforementioned preparation method.

[0012] The present invention has the following advantages over the prior art: (1) In this invention, a pore-forming agent is first used to expand the pores of the semi-graphitized material so that the metal / alloy layer skeleton can be immersed, thereby improving the hardness and strength of the sagger. At the same time, since the pore-forming agent itself is alkaline or becomes alkaline after combining with water, if the alkaline material is directly made into a sagger, it will have an adverse effect on the life of the sagger and the material loaded in the sagger. Therefore, before using the pore-forming material as a matrix material, the material needs to be washed with water until it is neutral.

[0013] (2) By filling a soft carbon layer between the metal layer and the graphite layer, the present invention alleviates the technical problem that the sagger is prone to cracking and damage due to the compression of the metal layer and the graphite layer caused by the back-and-forth thermal expansion and contraction of the metal layer and the graphite layer in application scenarios with frequent changes in high and low temperatures (temperature difference of more than 1000℃); at the same time, it improves the service life of the sagger, reduces the porosity of the product, increases the density, and effectively avoids the phenomenon of "sandwich layer" during the metal impregnation process.

[0014] (3) In the end, the present invention uses CVD furnace calcination as the final process. Acetylene is cracked at high temperature to produce carbon, which further fills the pores in the graphite sagger caused by the overflow of gas due to the carbonization of the soft carbon layer, further improving the bulk density of the product and improving the strength of the graphite sagger.

[0015] (4) The preparation method provided by the present invention can reduce the apparent porosity of the sagger product from more than 15% to less than 10%; stably increase the flexural strength of the sagger product from 15-20 MPa to more than 40 MPa; stably increase the compressive strength from 40-50 MPa to more than 70 MPa; and reduce the density of the sagger product from the traditional 1.65 g / cm³. 3 Increased to 1.8 g / cm³ 3 above. Attached Figure Description

[0016] Figure 1This is a process flow diagram of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to embodiments, but the scope of protection of the present invention is not limited to the scope described in the embodiments. Example 1

[0018] A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, comprising the following steps: S1: Take 100-mesh crucible material, 200-mesh electrode waste material and graphitized depolymerization tail powder at a mass ratio of 6:3:1, mix at 400 rpm for 60 min to obtain graded semi-graphitized material; take the graded semi-graphitized material and potassium hydroxide at a mass ratio of 80:20 and add them to the VC mixing equipment for mixing at 600 rpm for 90 min to mix evenly; S2: Load the mixed material into a stainless steel crucible, transfer it into a carbonization furnace, heat it to 400℃ at a heating rate of 5℃ / min and hold it for 2 hours. After holding, heat it to 900℃ at a heating rate of 3℃ / min and hold it for 4 hours. Nitrogen gas is introduced throughout the process at a flow rate of 3L / min. After cooling to 100℃, discharge the material. S3: Remove the material from the crucible and crush it multiple times with a universal pulverizer until the material is crushed to D50=85um; S4: Wash the pulverized material with Wahaha purified water until the pH is neutral, and then dry it in a 100℃ oven to obtain the matrix raw material; S5: Place the matrix material into the mold and compact it with an isostatic pressing device to obtain a graphite sagger blank. The molding pressure is 15 MPa, the holding time is 20 min, and the mold temperature is 200℃. S6: Add a solid copper-aluminum-iron alloy (50% copper, 30% aluminum, 20% iron) into the metal melting chamber, purge the air in the chamber with nitrogen to prevent oxidation, and then heat the solid alloy to 800°C at a heating rate of 5°C / min to melt it into a molten metal. S7: Place the graphite sagger blank into the impregnation chamber, preheat the product to 500℃ at a heating rate of 10℃ / min for 60min, and then evacuate to -150pa; open the connecting valve between the metal melting chamber and the impregnation chamber to ensure that the molten metal submerges the graphite blank, then close the connecting valve, rapidly pressurize the impregnation chamber to 30MPa, and maintain the pressure for 40min. After the pressure is maintained, drain the molten metal from the impregnation chamber (e.g., drain the molten metal to the molten metal recovery chamber, or drain the molten metal back to the metal melting chamber), and after cooling to room temperature, remove the graphite sagger blank to complete the metal impregnation. S8: Place the graphite crucible blank that has been impregnated with metal into the asphalt impregnation equipment. First, evacuate the impregnation chamber to -80pa, then let the liquid coal tar pitch flow into the chamber, then pressurize to 8MPa and hold the pressure for 3 hours. After the pressure holding is completed, the liquid asphalt is returned to the asphalt storage tank, cooled, depressurized and removed from the graphite blank. S9: The graphite sagger blank after the second impregnation is transferred to a carbonization furnace and fired under a nitrogen atmosphere. The firing curve is as follows: the temperature is raised to 900℃ in 200 min at room temperature (with an average heating rate of about 4.38℃ / min), held for 15 h, then raised to 1300℃ in 120 min (with an average heating rate of about 3.33℃ / min), held for 30 h, and finally cooled naturally to room temperature before being removed from the furnace to obtain the sagger semi-finished product. S10: Transfer the semi-finished box body to the CVD furnace. Under nitrogen protection, acetylene is introduced at 700-800℃ for 4 hours. After the reaction is completed, the temperature is naturally lowered. After cleaning the surface burrs and dust, the finished graphite box body is obtained. Example 2

[0019] A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that sodium chloride is used as a pore-forming agent in step S1 and all subsequent steps are the same as those for the graded semi-graphitized material. Example 3

[0020] A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that in step S1, the graded semi-graphitized material is mixed with potassium hydroxide at a mass ratio of 85:15 in a VC mixing device, and then all subsequent identical steps are performed.

[0021] Comparative Example 1 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that a pore-forming agent is not used in step S1, and all subsequent identical steps are performed using only the graded semi-graphitized material.

[0022] Comparative Example 2 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that the metal impregnation process in steps S6 and S7 is omitted, while other production process steps are carried out in the same way.

[0023] Comparative Example 3 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that the water washing process in step S4 is omitted, while other production steps are carried out in the same way.

[0024] Comparative Example 4 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that the bitumen impregnation process in steps S8 and S9 is omitted, and the graphite sagger blank after metal impregnation is transferred to the CVD furnace, while other production steps are carried out in the same way.

[0025] Comparative Example 5 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that the acetylene filling step S10 is omitted, while other production steps are carried out in the same way.

[0026] Comparative Example 6 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that in step S1, the graded semi-graphitized material is mixed with potassium hydroxide at a mass ratio of 90:10 in a VC mixing device, and then all subsequent identical steps are performed.

[0027] Comparative Example 7 A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, which differs from Example 1 in that in step S1, the graded semi-graphitized material is mixed with potassium hydroxide at a mass ratio of 75:25 in a VC mixing device, and then all subsequent identical steps are performed.

[0028] The physical properties of the graphite saggers prepared in Examples 1-3 and Comparative Examples 1-7 were tested. Specifically, the density, apparent porosity, and flexural strength were tested according to GB / T 24528-2009, GB / T2997-2015, and GB / T 3074.1-2021 standards, respectively. The relevant results are shown in Table 1. Table 1 Physical performance data of the embodiments and comparative examples

[0029] In addition, thermal shock stability tests were conducted on the graphite crucibles prepared in Examples 1-3 and Comparative Examples 1-7 to simulate the actual use conditions of the graphite crucibles. The thermal shock stability test method is as follows: The specimen (the graphite crucible was processed into a 50mm*10mm*5mm strip) was placed in a high-temperature furnace at 1250℃ and kept at that temperature for 10 minutes. Then, it was removed and forced to cool to room temperature in air at 25℃. This process was recorded as one cycle. After every 10 cycles, the residual flexural strength of the specimen was measured, and the surface crack propagation was observed. The test was terminated when the strength retention rate was less than 50% or macroscopic cracks appeared. The thermal shock stability was evaluated by the number of cycles and the strength retention rate. The data are shown in Table 2. Among them, the strength retention rate (%) = (strength after thermal shock / initial strength) * 100%.

[0030] Table 2 Thermal shock stability data of the embodiments

[0031] Table 3 Comparative thermal shock stability data

[0032] Note: In Table 3, “(-)” indicates that macroscopic cracks were observed after the specified number of cycles; “ / ” indicates that the test was stopped because the sample group had failed due to cracking.

[0033] Based on the data in Table 1-3, the following conclusions can be drawn: The entire process designed in this invention, consisting of "pore-forming agent expansion - water washing and alkali removal - metal impregnation - asphalt impregnation and carbonization - CVD acetylene sealing," is an organic whole, with significant synergistic effects between each step. Examples 1-3, representing a complete implementation of this invention, demonstrate that their physical properties (high density, low porosity, high strength) and thermal stability (strength retention rate >68% after 100 thermal cycles) have reached optimal and stable levels, proving the effectiveness and repeatability of the preparation method of this invention.

[0034] Comparative Example 1 (without pore-forming agent) showed the worst performance, indicating that pore-forming agent is a prerequisite for achieving high metal impregnation and thus fundamentally improving material strength. Comparative Examples 6 (90:10) and 7 (75:25) showed that neither too low nor too high a proportion of pore-forming agent could achieve the best results; a ratio of 15-20% was necessary to achieve the expected performance.

[0035] The strength, especially thermal shock stability, of Comparative Example 3 (unwashed) was significantly worse than that of the Example, demonstrating that alkaline residues severely degrade the high-temperature performance and service life of materials. The washing step is crucial for ensuring the long-term reliability of the product, and its role cannot be ignored.

[0036] Comparative Example 4 (without bitumen impregnation) failed after only 40 cycles of thermal shock resistance, a stark contrast to Example 1's 100 cycles. This strongly suggests that the primary function of the soft carbon layer is not simply to increase strength, but rather to act as a buffer layer, effectively addressing the cracking problem caused by the difference in thermal expansion coefficients between metal and graphite, thus significantly extending product lifespan.

[0037] Comparative Example 5 (without CVD) showed better physical properties and thermal shock stability than Comparative Example 4, but significantly worse than Example 1. This indicates that CVD treatment, by further sealing surface micropores through carbon pyrolysis, can further improve the density, strength, and high-temperature stability of the product, and is an important step in optimizing the final performance.

[0038] In summary, the preparation method provided by this invention solves a key technical contradiction in the field of metal-impregnated graphite saggers: the difficulty of simultaneously achieving "high metal impregnation amount" and "high thermal shock resistance." By introducing a specific proportion of pore-forming agent to ensure the impregnation amount, and innovatively using a soft carbon layer as a stress buffer layer, a balance between high strength and long service life is ultimately achieved.

[0039] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the original intent of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a metal and soft carbon double-layer impregnated graphite sagger, characterized in that, Includes the following steps: S1: Take the graded semi-graphitized material and the pore-forming agent and mix them in a VC mixing equipment at a mass fraction of 80-85:15-20; S2: Load the mixed material into a stainless steel crucible, transfer it into a carbonization furnace, heat it to 300-400℃ at a heating rate of 2-5℃ / min and hold it for 2-5 hours. After holding, heat it to 800-900℃ at a heating rate of 1-4℃ / min and hold it for 2-5 hours. Inert gas is introduced throughout the process at a flow rate of 2-5L / min. After cooling to 100℃, discharge the material. S3: Remove the material from the crucible and crush it into powder using a universal pulverizer multiple times. S4: Wash the pulverized material with water until the pH is neutral, and then dry it in a 100℃ oven to obtain the matrix raw material; S5: Place the matrix material into the mold and compact it with an isostatic pressing device to obtain the graphite sagger blank; S6: Add solid metal into the metal melting chamber, purge the air in the chamber with inert gas to prevent oxidation, and then heat up to melt the solid metal into molten metal. S7: Place the graphite sagger blank into the impregnation chamber, preheat the product by heating, and create a vacuum to make the impregnation chamber negative pressure. Open the connecting valve between the metal melting chamber and the impregnation chamber to ensure that the molten metal submerges the graphite sagger blank, and then close the connecting valve. Quickly pressurize the impregnation chamber and maintain the pressure for a certain period of time. After the pressure is maintained, drain the molten metal from the impregnation chamber. After cooling to room temperature, remove the graphite sagger blank to complete the metal impregnation. S8: Place the graphite sagger blank that has been impregnated with metal into the asphalt impregnation equipment. First, evacuate the impregnation chamber to -50 to -300 Pa. Then, let the liquid asphalt flow into the chamber. Then, pressurize it to 5-10 MPa and hold the pressure for 3-5 hours. After the pressure holding is completed, the liquid asphalt is returned to the asphalt storage tank. Cool down, depressurize and take out the graphite sagger blank. S9: Transfer the graphite sagger blank after the second impregnation to the carbonization furnace. Under an inert gas atmosphere, heat it to 600-900℃ at a heating rate of 3-10℃ / min and hold it for 10-20h. After holding, heat it to 1200-1600℃ at a heating rate of 2-5℃ / min and hold it for 20-30h. Then cool it naturally to room temperature to obtain the sagger semi-finished product. S10: Transfer the semi-finished box body to the CVD furnace. Under the protection of inert gas, acetylene is introduced at 700-900℃ for 1-5 hours. After the reaction is completed, the temperature is naturally lowered. After cleaning the surface burrs and dust, the finished graphite box body is obtained.

2. The preparation method according to claim 1, characterized in that, The semi-graphitized material after gradation in step S1 is a mixture of 100-mesh crucible material, 200-mesh electrode recycled material, and graphitized depolymerization tail powder in a mass ratio of 6:3:1; the pore-forming agent in step S1 includes at least one of sodium chloride, potassium chloride, sodium hydroxide, and potassium hydroxide.

3. The preparation method according to claim 1, characterized in that, The mixing speed in step S1 is 200-1000 rpm, and the mixing time is 60-120 min.

4. The preparation method according to claim 1, characterized in that, The number of pulverization times in step S3 is 2-5 times, and the powder particle size D50 = 20-100um.

5. The preparation method according to claim 1, characterized in that, In step S5, the molding pressure is 5-20 MPa, the holding time is 5-20 min, and the mold temperature is 150-250℃.

6. The preparation method according to claim 1, characterized in that, The solid metal in step S6 is an alloy made of at least one of copper, aluminum, iron, and titanium; the melting temperature is 500-1500℃, and the heating rate is 2-10℃ / min.

7. The preparation method according to claim 1, characterized in that, In step S7, the preheating temperature is 200-800℃, the heating rate is 2-10℃ / min, the preheating time is 30-120min, and the vacuum is evacuated to -50--300pa; the pressure applied to the impregnation chamber is 20-50MPa, and the pressure holding time is 30-60min.

8. The preparation method according to claim 1, characterized in that, The asphalt in step S8 is either coal tar pitch or petroleum asphalt.

9. A metal and soft carbon double-layer impregnated graphite sagger, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

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