A method of multiple impregnation for making high density graphite crucibles

Abstract

The application discloses a method for preparing high-density graphite crucible through multiple impregnation, which uses graphite and petroleum coke as powder materials, and uses pitch material I and pitch material II with different temperature viscosity characteristics as impregnation materials. The method comprises the following steps: firstly, using pitch material I and graphite and petroleum coke as raw materials to prepare a primary green body; then, performing secondary impregnation of pitch material II on the primary green body through an impregnation tank after roasting the primary green body to obtain a secondary green body; performing third impregnation of pitch material I on the secondary green body through the impregnation tank after roasting the secondary green body to obtain a third green body; finally, directly feeding the third green body into a graphitization furnace to perform high-temperature graphitization treatment, and graphitizing the carbonized pitch component in the third green body to obtain the graphite crucible. The method can effectively improve the structural density of the graphite crucible and reduce the porosity of the graphite crucible, thereby prolonging the service life of the graphite crucible on the basis of ensuring the service performance of the graphite crucible.

Description

Technical Field

[0001] This invention relates to the field of graphite crucible preparation technology, specifically a method for preparing high-density graphite crucibles through multiple impregnations. Background Technology

[0002] Graphite crucibles possess excellent thermal conductivity and high-temperature resistance. During high-temperature use, they exhibit a low coefficient of thermal expansion and a certain degree of resistance to rapid heating and cooling. They also demonstrate excellent chemical stability and good resistance to acidic and alkaline solutions. In industries such as metallurgy, casting, machinery, and chemicals, they are widely used in metal smelting, lithium battery anode material purification, polycrystalline silicon material smelting, and ingot casting. Their lifespan has a significant impact on productivity and economic benefits.

[0003] In the preparation of graphite crucibles, crystalline natural graphite or artificial graphite is first used as the main raw material and pitch is mixed and kneaded as a binder. After kneading, the mixture is pressed into a green blank using a static pressing process. Then, the green blank is calcined under vacuum conditions.

[0004] The differences in quality and performance of finished graphite crucibles mainly stem from variations in raw materials, processing conditions, and other factors. Crucibles produced under different technical conditions exhibit inconsistent performance and lifespan. The impact of asphalt in the raw materials on the quality of finished graphite crucibles is primarily evident during the calcination stage. During heat treatment, asphalt, acting as a binder, is transformed into coke and encapsulated in the transition layer between carbon particles. After being converted to coke at high temperatures, asphalt forms an interfacial carbon mesh layer in the semi-finished product, acting as a bridge and reinforcement. The performance of the calcined product largely depends on the uniformity of the asphalt within the green body after molding and the changes in the asphalt during calcination. The uniformity of the asphalt within the green body directly affects the internal structural uniformity of the formed graphite crucible material. Furthermore, softened asphalt exhibits rheological properties; the softened asphalt components flow and accumulate towards the gravity side within the green body due to gravity, leading to defects in the internal uniformity of the formed graphite rod during subsequent graphitization, thus affecting the quality of the finished graphite rod.

[0005] For the reasons mentioned above, the graphite crucible products sintered from green blanks formed after a single impregnation in traditional technology have a large porosity and a low structural density, which leads to a much higher demand for their performance. Therefore, in order to improve the various performance indicators of isostatic graphite products, it is necessary to repeatedly re-fire and re-impregnate the impregnated products several times. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a method for preparing high-density graphite crucibles by multiple impregnation, so as to overcome the defects in the above-mentioned technical background.

[0007] The technical problem solved by this invention is achieved by the following technical solution:

[0008] A method for preparing a high-density graphite crucible through multiple impregnations specifically includes the following steps:

[0009] S1 screens graphite, petroleum coke, and asphalt as raw materials, wherein the graphite is natural or artificial graphite, with a true specific gravity greater than 2.15 and a carbon content greater than 99%; the petroleum coke has a true specific gravity greater than 2.10 and a carbon content greater than 98%; the asphalt includes: asphalt I with an asphaltene content exceeding 15wt%, a softening point of 50–70℃, and a viscosity of 15–80 mPa·s at 150–200℃; and asphalt II with an asphaltene content of 10–13.5wt%, a softening point of 50–70℃, and a viscosity of less than 100 mPa·s at 150–200℃.

[0010] S2 crushes graphite and petroleum coke, which are used as raw materials, into powder. The crushed graphite powder and petroleum coke powder are dry-mixed. After the dry mixing is completed, asphalt material I is added and heated for wet mixing, so that the asphalt impregnates the graphite and petroleum coke particles to obtain the mixture.

[0011] S3 involves pressing the mixture obtained in step S2 into a mold to form a green blank;

[0012] S4 feeds the green billet into the baking furnace for the first baking operation, controlling the vacuum degree of the baking furnace at 0.08MPa~0.09MPa. The baking temperature profile during the baking operation is as follows:

[0013] During the process from room temperature to 200℃, the heating rate is 20-35℃ / h, and after heating to 200℃, the temperature is maintained for 36-48h.

[0014] After the heat preservation is completed, the temperature continues to rise. During the process of 200 to 500℃, the heating rate is 5 to 8℃ / h. Then, the temperature is maintained at 500℃, so that the total duration of this stage is controlled within 150 to 200h.

[0015] After the heat preservation is completed, the temperature is reduced from 500 to 100℃ at a rate of 20 to 35℃ / h. After reaching 100℃, the furnace naturally cools down to room temperature, which is the first green blank after the first firing operation.

[0016] S5 takes out the primary green body obtained through step S4 and performs secondary impregnation of asphalt material II in an impregnation tank. The secondary impregnation is vacuum impregnation, and during the impregnation process, an ultrasonic reactor is inserted into the impregnation tank for ultrasonic assistance to improve the fluidity of asphalt material II. The secondary green body is then removed from the tank.

[0017] S6 feeds the secondary green billet into the baking furnace for a second baking operation. During the second baking operation, the temperature curve of the first baking is used as a reference to carry out the second baking operation, and the secondary green billet after the second baking operation is completed is obtained.

[0018] S7 takes out the secondary green body obtained through step S6 and uses an impregnation tank to impregnate asphalt material I for the third time. The third impregnation is vacuum pressure impregnation. After the impregnation is completed, the green body is taken out of the tank to obtain the third green body.

[0019] S8 directly feeds the three-stage green blanks into a graphitization furnace for high-temperature graphitization treatment, and graphitizes the carbonized asphalt components to obtain a graphite crucible.

[0020] As a further limitation, when the raw materials graphite and petroleum coke are crushed, the particle size of the crushed graphite powder is controlled to be 50-80 μm, and the particle size of the petroleum coke is ≤2 mm.

[0021] As a further limitation, the mass ratio of graphite powder to petroleum coke used to prepare primary green bodies is 3:1 to 1:1; and the mass ratio of the mixture of graphite powder and petroleum coke to asphalt is 2:1 to 5:2.

[0022] As a further limitation, during the heating and wet mixing in step S2, the wet mixing temperature is controlled at 150–200°C, and the wet mixing time is 1–3 hours.

[0023] As a further limitation, when the mixture is pressed and molded in step S3, a vibration pressure molding machine is used for vacuum dry pressing. During molding, the vacuum degree is controlled to be 0.075-0.085 MPa and the molding pressure is 1.5-3.0 MPa.

[0024] As a further limitation, when the mixture is pressed and molded in step S3, an isostatic pressing machine is used for cold isostatic pressing, and the molding pressure of the isostatic pressing machine is controlled to be 150-300 MPa during molding.

[0025] As a further limitation, during the secondary impregnation in step S5, the vacuum degree inside the impregnation tank is controlled to be 0.080–0.095 MPa, and the temperature is 120–150 °C; when the ultrasonic generator is controlled to provide ultrasonic assistance, the ultrasonic power is 600–800 W, the ultrasonic frequency is 40–60 kHz, and the processing time is 70–90 min.

[0026] As a further limitation, when performing three impregnations in step S7, a vacuum is first drawn in the impregnation tank with a vacuum degree of 0.075 to 0.090 MPa and a temperature of 120 to 150°C. Then, softened liquid asphalt is added to the impregnation tank, and pressure is applied to the auxiliary tank of the impregnation tank with a pressure greater than 1.5 MPa. The processing time is 50 to 60 minutes.

[0027] As a further limitation, after the three green blanks are subjected to high-temperature graphitization treatment in step S7, the three green blanks can be coated with a coating with a thickness of 0.6 to 0.8 mm and a coating type of SiC coating, Y2O3 coating, or a composite coating of both.

[0028] Beneficial Effects: The present invention provides a method for preparing high-density graphite crucibles through multiple impregnation. This method involves mixing graphite, petroleum coke, and asphalt in a certain proportion, repeatedly impregnating the mixture with different types of asphalt, and then using a roasting process to fully carbonize the repeatedly impregnated asphalt material to prepare a graphite crucible green body. The green body is then graphitized to produce a graphite crucible. Through the adjustment and optimization of the roasting and multiple impregnation processes, this method significantly improves the bulk density and apparent porosity of the finished graphite crucible. It effectively prevents and inhibits the development of surface defects such as cracking and oxidation during the roasting of the finished graphite crucible, thus extending the service life of the finished graphite crucible by 20-30%. Detailed Implementation

[0029] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0030] In this invention, unused and damaged graphite crucibles are used as raw materials. These graphite crucibles are graphite crucibles that failed to be repaired during manufacturing or were bumped or dropped during transportation and storage. Before recycling, the surface of the graphite crucibles is cleaned, and then the graphite crucibles are put into a jaw crusher for crushing. The crushed material is then pulverized multiple times by a pulverizer and ground to obtain recycled graphite powder for later use.

[0031] In Example 1:

[0032] Graphite, petroleum coke, and asphalt were selected as raw materials, among which:

[0033] Graphite: Artificial graphite, with a true specific gravity greater than 2.15 and a carbon content of 99.4% (Hebei Runhuabang New Material Technology Co., Ltd.);

[0034] Petroleum coke: True specific gravity greater than 2.10 and carbon content greater than 98.6% (Shijiazhuang Chongjun Mineral Products Co., Ltd.);

[0035] Asphalt Material I: Asphaltene content is 15.5–17.3 wt%, softening point is 58–64℃, and viscosity is 15–80 mPa·s at 150–200℃ (imported product, produced in the Athabasca oil sands region of Alberta, Canada).

[0036] Asphalt Component II: Asphaltene content is 12.1–13.2 wt%, softening point is 62–65℃, and viscosity is 97 mPa·s at 150–200℃ (Hebei Fengtaiyuan Energy Technology Co., Ltd.)

[0037] Graphite and petroleum coke, used as raw materials, are crushed into powder. The particle size of the crushed graphite powder is 50–80 μm, and the particle size of the petroleum coke is 0.6–1.2 mm. The crushed graphite powder and petroleum coke powder are added to a kneader at a mass ratio of 2:1 and dry-mixed for 50 minutes to obtain a mixed powder.

[0038] The powder mixture is added to asphalt mix I and heated for wet mixing. The mass ratio of powder mixture to asphalt is controlled at 5:2. The wet mixing temperature is controlled at 160℃, and the wet mixing treatment lasts for 2 hours. During the wet mixing process, the coal tar pitch is first melted in an asphalt melting tank. Half of the powder mixture is added and wet-mixed using physical stirring. After stirring for 1 hour, the remaining powder mixture is added, and physical stirring continues for 15 minutes. Then, ultrasonic equipment is used to assist dispersion, using the energy generated by ultrasound to break down the asphalt polymer and reduce the asphalt viscosity. During this process, the ultrasonic power is controlled at 800W and the ultrasonic frequency at 40kHz. Ultrasonic-assisted treatment continues until the wet mixing is completed, resulting in the wet mixture. In another embodiment, wet mixing can be performed directly without ultrasonic assistance, achieving a similar effect. However, this method requires heat preservation conditions, extending the wet mixing treatment time to 80–120 hours.

[0039] The wet mixture is used as raw material and is put into a mold for forming by a vibration pressure molding machine. During forming, the vacuum degree is controlled at 0.080MPa and the forming pressure is 2.6MPa to obtain a green body.

[0040] The green blanks are fed into the firing furnace for the first firing operation. Before firing, the firing furnace is evacuated (vacuum degree 0.09MPa) and filled with auxiliary materials to ensure that the green blanks in the crucible do not deform during the firing process. The firing temperature profile is controlled as follows during the firing operation:

[0041] During the process from room temperature to 200℃, the heating rate was 25℃ / h, and the temperature was maintained at 200℃ for 48 hours.

[0042] After the heat preservation is completed, the temperature continues to rise. During the process of 200 to 500℃, the heating rate is 6℃ / h. Then, the temperature is maintained at 500℃ for 120h, so that the total duration of this stage is controlled within 170h.

[0043] After the heat preservation is completed, the temperature is reduced from 500 to 100℃ at a rate of 20℃ / h. After reaching 100℃, the furnace naturally cools down to room temperature, which is the first green blank after the first firing operation.

[0044] The primary green body obtained from heat treatment is taken out and subjected to secondary impregnation of asphalt material II using a conventional impregnation tank. The vacuum degree inside the impregnation tank is controlled at 0.09 MPa and the temperature at 135℃. During this process, an ultrasonic generator is connected to the impregnation tank to perform ultrasonic-assisted treatment with a power of 800W and a frequency of 40KHz. The impregnation treatment lasts for 90 minutes, and the secondary green body is obtained after being removed from the tank.

[0045] The second batch of green billets is fed into a baking furnace for a second baking operation. The process of the first baking operation is repeated during the second baking to ensure consistent asphalt carbonization. Specifically, the baking furnace is evacuated (vacuum degree 0.09 MPa) and filled with auxiliary materials before baking to ensure the crucible green billets do not deform during the baking process. The baking temperature profile is controlled as follows during the baking operation:

[0046] During the process from room temperature to 200℃, the heating rate was 25℃ / h, and the temperature was maintained at 200℃ for 48 hours.

[0047] After the heat preservation is completed, the temperature continues to rise. During the process of 200 to 500℃, the heating rate is 6℃ / h. Then, the temperature is maintained at 500℃ for 120h, so that the total duration of this stage is controlled within 170h.

[0048] After the heat preservation is completed, the temperature is lowered from 500 to 100℃ at a rate of 20℃ / h. After reaching 100℃, the furnace is allowed to cool naturally to room temperature, thus completing the second firing process for the secondary green body.

[0049] The secondary green body obtained in the aforementioned steps is taken out and impregnated with asphalt material I for the third time using a pressure impregnation tank. During impregnation, a vacuum is first drawn in the impregnation tank, and the vacuum degree is controlled at 0.082 MPa and the temperature is 135°C. Then, softened liquid asphalt is added to the impregnation tank, and pressure is added to the pressure boosting auxiliary tank of the impregnation tank, and the pressure boosting pressure is controlled at 1.75 MPa. The impregnation process is carried out for 60 minutes. After the impregnation is completed, the tertiary green body is obtained by removing it from the tank.

[0050] The three green blanks are subjected to high-temperature graphitization in a graphitization furnace. During the high-temperature graphitization process, the three green blanks are loaded into the Atchison graphitization furnace and lining is used with expanded graphite sheets. The graphitization process is carried out at a high temperature of 2800℃ for 200 hours, which yields a finished graphite crucible with a highly graphitized interior.

[0051] In Example 2:

[0052] In Example 2, all raw material selection, component ratios and operating steps are the same as in Example 1. The only difference between Example 2 and Example 1 is that when using the mixed wet material as raw material to make a green body, the reference document 2 uses an isostatic pressing machine for cold isostatic pressing, and the molding pressure set on the isostatic pressing machine is 200 MPa.

[0053] Thirty graphite crucibles (round, outer diameter 1600±5mm, inner diameter 1320±5mm, height 2100±5mm) were prepared for Examples 1 and 2 using the above technical solution. After removing individuals with obvious parameter differences and replenishing the quantity, the physical parameters were measured.

[0054] The average density of Example 1 is 2.16 g / cm³. 3 The maximum density is 2.23 g / cm³. 3 The average porosity was 12.1%, with a minimum of 9.6%. The graphite crucibles prepared using this method had a relatively dense internal structure, significantly lower than that of similar domestic products (machine-pressed graphite crucibles) which have a porosity of 1.6–1.8 g / cm³. 3 It has a density value of 17-22% and a porosity value of 17-22%. At the same time, its service life is 17-20 cycles when a complete polycrystalline melting and casting cycle is performed without coating the inner protective layer, which is significantly better than the 13-15 cycles of similar domestic products (isostatic graphite crucibles).

[0055] The average density of Example 2 is 2.41 g / cm³. 3 The maximum density is 2.47 g / cm³. 3 The average porosity is 8.6%, and the minimum is 8.1%. The internal structure of the graphite crucibles prepared using this method is very dense, significantly higher than the 2.0–2.2 g / cm³ porosity of similar domestic products (isostatic graphite crucibles). 3 Its density value and porosity value are 9-11%, and its service life after a complete polycrystalline melting and casting cycle without coating the inner protective layer is 21-25 times, which is significantly better than the 16-18 times of similar domestic products (isostatic graphite crucibles).

[0056] The main reason why the graphite crucible in this embodiment can achieve the above-mentioned density enhancement effect is that it uses asphalt material with different viscosities and asphaltene content as impregnating material to make the blank and to perform multiple impregnation treatments on the green blank.

[0057] Generally, asphalt contains two different types of chemical structures: asphaltenes and asphalene. The proportion of asphaltenes and asphalene in asphalt varies greatly depending on the origin and processing technology. The viscosity of asphalt at external temperature is determined by the macroscopic and microscopic properties of the spatial structure of asphaltenes and asphalene. The viscosity increases with the increase of asphalene content. The high viscosity of Athabasca asphalt (asphalt material I used in this example) is also a result of high asphalene content (>15wt%, weight percentage).

[0058] It is generally believed that the lower the viscosity of asphalt, the better its fluidity, which is more conducive to impregnation. However, the drawback is that asphalt with better fluidity has a lower asphaltene content and a smaller molecular weight of asphaltene, which is not conducive to the formation of high-density polymers. In this embodiment, the high asphaltene content and high molecular weight of Athabasca asphalt make it easier to form polymers. During the preparation process, this type of asphalt can be used to impregnate the mixture powder to form a dense structural reinforcement inside the green body. In order to compensate for the fluidity defects in the green body preparation process, this embodiment extends the wet mixing time or uses heating and ultrasound to disperse the structure of the asphaltene polymer to temporarily inhibit the regeneration of the polymer and produce a wet mixture that can be used to prepare high-density graphite crucible green bodies.

[0059] The crucible green body prepared by the above-mentioned wet mixture has a dense basic structure, which is equivalent to providing a stable coarse aggregate skeleton for the crucible green body. Moreover, the proportion of internal volatiles during the heat treatment process is lower, resulting in fewer pores caused by the vaporization of volatiles during the heat treatment process, which is more conducive to the densification of the finished graphite crucible.

[0060] The subsequent secondary impregnation is used to further fill the internal gaps of the crucible green blank. It takes advantage of the good fluidity of the asphalt material II, and uses an ultrasonic generator to further optimize its fluidity. Through this fluidity advantage, the impregnation effect and impregnation ratio of the crucible green blank in the impregnation tank are improved, ensuring its impregnation weight gain.

[0061] The three-stage impregnation of asphalt material I using a pressure impregnation tank is used to create a dense impregnation layer on the surface of the crucible green blank.

[0062] The aforementioned three impregnation processes can improve the density of the finished graphite crucible. Correspondingly, each impregnation process is followed by a high-temperature treatment (corresponding to primary firing, secondary firing, and high-temperature graphitization). During these high-temperature treatments, the asphalt undergoes carbonization and graphitization. The primary and secondary firings only involve carbonization, which can be considered as targeting only the asphalt. The impregnating asphalt only needs basic carbonization during secondary or higher firings, and this temperature does not need to be very high. The firing curve can be obtained by optimizing the firing curve through thermal analysis of the impregnated asphalt, thus ensuring the carbonization rate and carbon content of the green body. On the basis of improving efficiency, we can improve work efficiency and reduce equipment operating costs. During the carbonization of asphalt, a series of volatiles such as nitrogen oxides, sulfur oxides, and carbon monoxide are generated. The release of these volatiles will reduce the weight of the green body and create pores inside the green body. The multiple impregnation and firing process can effectively reduce the porosity (the second impregnation will fill the pores generated during the first firing, and the third impregnation will fill the pores generated during the second firing). Then, the surface of the green body with high asphaltene content and high viscosity is impregnated with asphalt material I after the second firing to form a dense structural reinforcement, thereby increasing the overall density of the graphite crucible after final graphitization and molding.

[0063] Furthermore, in the above embodiments of the present invention, after the three-stage green body undergoes high-temperature graphitization treatment, a coating treatment is applied to the green body to form a coating structure, thereby further improving its performance. For example, a SiC coating can be prepared on the graphite surface using chemical vapor deposition; a SiC coating can be prepared on the graphite surface using liquid phase impregnation; or a composite coating can be obtained by preparing a SiC coating on the graphite surface using chemical vapor deposition followed by liquid phase impregnation on the SiC coating surface. These coating structures can effectively block oxidation to prevent the crucible from prematurely oxidizing and failing, further significantly improving its performance. The performance of graphite crucibles is important, as they can protect the contents during sintering. To ensure optimal performance, the coating thickness needs to be controlled between 0.6 and 0.8 mm. Too thin a coating will result in poor performance, while too thick a coating will easily peel off. The reason for coating treatment after high-temperature graphitization is that the impregnation asphalt on the surface of the three green bodies during the three impregnation processes contains asphalt oil, which will prevent the coating from adhering. The high temperature during graphitization will cause the asphalt oil in the asphalt component to volatilize. At the same time, after the asphalt is carbonized and graphitized, the surface has a certain number of pores, which is suitable for coating structure adhesion.

[0064] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-density graphite crucible through multiple impregnations, characterized in that, The following steps are included: S1 screens graphite, petroleum coke, and asphalt as raw materials, wherein the graphite is natural or artificial graphite, with a true specific gravity greater than 2.15 and a carbon content greater than 99%; the petroleum coke has a true specific gravity greater than 2.10 and a carbon content greater than 98%; the asphalt includes: asphalt I with an asphaltene content exceeding 15wt%, a softening point of 50–70℃, and a viscosity of 15–80 mPa·s at 150–200℃; and asphalt II with an asphaltene content of 10–13.5wt%, a softening point of 50–70℃, and a viscosity of less than 100 mPa·s at 150–200℃. S2 crushes graphite and petroleum coke, which are used as raw materials, into powder. The crushed graphite powder and petroleum coke powder are dry-mixed. After the dry mixing is completed, asphalt material I is added and heated for wet mixing, so that the asphalt impregnates the graphite and petroleum coke particles to obtain the mixture. S3 involves pressing the mixture obtained in step S2 into a mold to form a green blank; S4 feeds the green billet into the baking furnace for the first baking operation, controlling the vacuum degree of the baking furnace at 0.08MPa~0.09MPa. The baking temperature profile during the baking operation is as follows: During the process from room temperature to 200℃, the heating rate is 20-35℃ / h, and after heating to 200℃, the temperature is maintained for 36-48h. After the heat preservation is completed, the temperature continues to rise. During the process of 200 to 500℃, the heating rate is 5 to 8℃ / h. Then, the temperature is maintained at 500℃, so that the total duration of this stage is controlled within 150 to 200h. After the heat preservation is completed, the temperature is reduced from 500 to 100℃ at a rate of 20 to 35℃ / h. After reaching 100℃, the furnace naturally cools down to room temperature, which is the first green blank after the first firing operation. S5 takes out the primary green body obtained through step S4 and performs secondary impregnation of asphalt material II in an impregnation tank. The secondary impregnation is vacuum impregnation, and during the impregnation process, an ultrasonic reactor is inserted into the impregnation tank for ultrasonic assistance to improve the fluidity of asphalt material II. The secondary green body is then removed from the tank. During the secondary impregnation, the vacuum degree inside the impregnation tank is controlled at 0.080–0.095 MPa, and the temperature is controlled at 120–150 °C; when the ultrasonic reactor is used for ultrasonic assistance, the ultrasonic power is 600–800 W, the ultrasonic frequency is 40–60 kHz, and the processing time is 70–90 min. S6 feeds the secondary green billet into the baking furnace for a second baking operation. During the second baking operation, the temperature curve of the first baking is used as a reference to carry out the second baking operation, and the secondary green billet after the second baking operation is completed is obtained. S7 takes out the secondary green body obtained through step S6 and uses an impregnation tank to impregnate asphalt material I for the third time. The third impregnation is vacuum pressure impregnation. After the impregnation is completed, the green body is taken out of the tank to obtain the third green body. When performing three impregnations, first, a vacuum is drawn in the impregnation tank with a vacuum degree of 0.075 to 0.090 MPa and a temperature of 120 to 150°C. Then, softened liquid asphalt is added to the impregnation tank, and pressure is applied to the auxiliary tank of the impregnation tank with a pressure greater than 1.5 MPa. The treatment time is 50 to 60 minutes. S8 directly feeds the three-stage green blanks into a graphitization furnace for high-temperature graphitization treatment, and graphitizes the carbonized asphalt components to obtain a graphite crucible.

2. The method for preparing a high-density graphite crucible through multiple impregnations according to claim 1, characterized in that, When the raw materials, graphite and petroleum coke, are crushed, the particle size of the crushed graphite powder is controlled to be 50-80 μm, and the particle size of the petroleum coke is ≤2 mm.

3. The method for preparing a high-density graphite crucible through multiple impregnations according to claim 1, characterized in that, The mass ratio of graphite powder to petroleum coke used to prepare primary green bodies is 3:1 to 1:1; and the mass ratio of the graphite powder, petroleum coke mixture to asphalt is 2:1 to 5:

2.

4. The method for preparing a high-density graphite crucible through multiple impregnations according to claim 1, characterized in that, In step S2, the wet mixing temperature is controlled at 150-200°C and the wet mixing time is 1-3 hours.

5. The method for preparing a high-density graphite crucible through multiple impregnations according to claim 1, characterized in that, In step S3, when the mixture is pressed and molded, a vibration pressure molding machine is used for vacuum dry pressing. During molding, the vacuum degree is controlled to be 0.075-0.085 MPa and the molding pressure is 1.5-3.0 MPa.

6. The method for preparing a high-density graphite crucible through multiple impregnations according to claim 1, characterized in that, When the mixture is pressed and molded in step S3, an isostatic pressing machine is used for cold isostatic pressing, and the molding pressure of the isostatic pressing machine is controlled to be 150-300 MPa during molding.

7. The method for preparing a high-density graphite crucible through multiple impregnations according to claim 1, characterized in that, After the three green blanks are subjected to high-temperature graphitization in step S7, a coating treatment can be applied to the three green blanks. The corresponding coating thickness is 0.6 to 0.8 mm, and the coating type is SiC coating, Y2O3 coating, or a composite coating of both.