A graphite crucible and a preparation method thereof

Abstract

The present invention relates to the technical field of graphite crucibles, and specifically relates to a graphite crucible and a preparation method thereof. The preparation method dissolves a conventional binder in asphalt to prepare a liquid-phase binder, thereby increasing the mixing uniformity between the binder, graphite, and carbon powder. Further, by means of the tumbling and shearing function of the fusion machine, the apparent porosity of the crucible can be comprehensively reduced and its flexural strength can be enhanced on the premise of a lower mass percentage of the binder. Specifically, the apparent porosity of the crucible product can be reduced from more than 15% in the conventional process to about 10%; the flexural strength of the crucible product can be stably increased from the conventional 15-20 MPa to 20-23 MPa; the density of the crucible product can be increased from the traditional 1.65 g / cm3 to 1.8 g / cm 3 above; the binder dosage can be reduced from 10%-15% in the traditional process to less than 10% to meet the bonding requirements.

Description

Technical Field

[0001] The present invention relates to the technical field of graphite crucibles, and more specifically, it relates to a graphite crucible and a preparation method thereof. Background Art

[0002] Graphite crucibles are used as graphitization sintering containers for lithium battery anode materials due to their high carbon content (up to 99.9%), high temperature resistance, and oxidation resistance. Graphitization is an important process for graphite anode materials, and the quality of the graphite crucible is particularly important. In the traditional preparation process of graphite crucibles, graphite powder is generally bonded simply with a solid-phase binder. The mixing uniformity of the solid-phase binder and graphite powder is slightly poor, and the bonding effect is also poor. To achieve a better bonding effect, the dosage needs to be increased, but increasing the dosage of the binder will reduce the density of the graphite crucible. In addition, the solid-phase binder is a resin type, and after carbonization, it belongs to hard carbon. Although the strength of the graphite crucible increases, due to the high degree of disorder in its internal structure caused by the difficulty of graphitization of hard carbon, the porosity of the crucible increases, resulting in a decrease in its density and consistency. Summary of the Invention

[0003] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a preparation method of a graphite crucible, which can solve the technical problems of high porosity, low strength, and low density during the pressing process of the product.

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A preparation method of a graphite crucible, which includes the following steps:

[0006] S1: Take a binder and dissolve it in heavy oil to prepare a liquid-phase binder solution with a mass fraction of 20 - 40%;

[0007] S2: Put graphite, carbon powder, and the liquid-phase binder solution into a mixer in sequence according to the mass ratio and mix them evenly to obtain a semi-liquid mixture;

[0008] S3: Put the semi-liquid mixture into a crucible mold and press out a crucible blank;

[0009] S4: Transfer the crucible blank to a carbonization furnace. Under an inert gas atmosphere, heat it at a heating rate of 2 - 5 °C / min to 600 - 900 °C and keep it warm for 10 - 20 h. After the heat preservation ends, heat it at a heating rate of 3 - 6 °C / min to 1200 - 1600 °C and keep it warm for 20 - 30 h, and then cool it naturally to room temperature to obtain a semi-finished crucible;

[0010] S5: Transfer the semi-finished crucible to a CVD furnace. Under the protection of an inert gas, introduce acetylene to react for 1 - 5 h at 700 - 900 °C. After the reaction ends, cool it naturally to obtain a graphite crucible.

[0011] Preferably, the binder in step S1 is one or a combination of two of medium-temperature pitch and high-temperature pitch.

[0012] Preferably, the mass ratio of graphite, carbon powder, and liquid-phase binder in step S2 is 87-94%:2-5%:4-8%.

[0013] Preferably, the molding pressure in step S3 is 5-20 Mpa, the pressure holding time is 5-20 min, and the mold temperature is 150-250 °C.

[0014] Preferably, the inert gas in step S4 is nitrogen or argon.

[0015] Preferably, the volume ratio of nitrogen to acetylene introduced in step S4 is 1.5-3:1.

[0016] Another object of the present invention is to provide a graphite crucible prepared by the above preparation method.

[0017] The present invention has the following advantages over the prior art:

[0018] (1) The present invention uses heavy oil as the solvent for dissolving the binder. Due to its own viscosity, it synergistically acts as a binder during the subsequent molding process with the binder. Moreover, the addition of the binder is in a liquid form and is fused with graphite and carbon powder, and its mixing effect is more uniform and the binding effect is better. The combined use of the two significantly reduces the amount of binder used, from 10%-15% binder usage in the traditional process to less than 10% to meet the binding requirements. Less binder usage is of great benefit to improving the density and flexural strength of the crucible products, and can increase the density of the crucible products from the traditional 1.65 g / cm 3 to 1.8 g / cm 3 or above. In addition, heavy oil contains some carbon elements, and during the subsequent carbonization process, it can form hard carbon coating on the surface of graphite and carbon powder, which can also improve the overall strength of the graphite crucible, and the final flexural strength can be further increased to more than 22 MPa.

[0019] (2) In the present invention, a fusion machine is used to replace the conventional kneader. Compared with the conventional kneader that realizes mixing through the flipping and collision of materials, the fusion machine not only has the collision between materials, but also has the shearing effect of the cutter on the materials, which greatly improves the consistency of the materials compared with kneading. Finally, the apparent porosity of the sagger products can be reduced from more than 15% in the conventional process to about 10%; during the subsequent molding and carbonization processes, the risk of product cracking can be significantly reduced, and the risk of product cracking is reduced from one-thousandth in the conventional process to one-ten-thousandth, greatly reducing the production cost; at the same time, the improvement of consistency also helps to increase the pressure that the sagger products can withstand during the molding process, further improving the flexural strength of the sagger products. This process can stably increase the flexural strength of the sagger products from the conventional 15 - 20 MPa to 22 - 25 MPa. Detailed Embodiments

[0020] The present invention will be further described below in conjunction with embodiments, but the scope of protection required by the present invention is not limited to the scope described in the embodiments.

[0021] Embodiment 1

[0022] A method for preparing a graphite sagger, which comprises the following steps:

[0023] S1: Take a certain weight of heavy oil, add it to a container, start a high-speed disperser, stir at a speed of 500 rpm / min, after stirring for 20 min, slowly add high-temperature pitch as a binder to the high-speed stirred heavy oil solution, and continue to stir for 60 min after the high-temperature pitch is added to prepare a liquid-phase binder solution with a mass fraction of 20%.

[0024] S2: Put graphite, carbon powder, and the liquid-phase binder solution into the fusion machine in sequence according to the mass ratio of 87%:5%:8%, stir at a speed of 1000 rpm / min for 120 min to obtain a semi-liquid mixture.

[0025] S3: Put the semi-liquid mixture into a sagger mold, and mold out the sagger blank under a molding pressure of 15 ± 1 Mpa, a holding pressure time of 10 min, and a mold temperature of 160 ± 5 °C.

[0026] S4: Transfer the sagger blank to a carbonization furnace, under an inert gas atmosphere, heat it at a heating rate of 5 °C / min to 600 °C and hold for 20 h, after the holding is completed, heat it at a heating rate of 6 °C / min to 1600 °C and hold for 20 h, and then naturally cool it to room temperature to obtain a sagger semi-finished product.

[0027] S5: Transfer the sagger semi-finished product to a CVD furnace, under nitrogen protection, when heating to 700 °C, introduce acetylene for reaction for 4 h according to the volume ratio of nitrogen:acetylene = 1.5:1, and after the reaction is completed, naturally cool it to obtain the graphite sagger.

[0028] Example 2

[0029] A preparation method of a graphite crucible, which comprises the following steps:

[0030] S1: Take a certain weight of heavy oil, add it to a container, start a high-speed disperser, with a stirring speed of 500 rpm / min. After stirring for 20 min, slowly add high-temperature pitch as a binder to the high-speed stirred heavy oil solution. After the high-temperature pitch is added, continue stirring for 60 min to prepare a liquid-phase binder solution with a mass fraction of 20%;

[0031] S2: Put graphite, carbon powder, and the liquid-phase binder solution into a mixer in sequence according to the mass ratio of 90%:4%:6%, and stir at a speed of 1000 rpm / min for 120 min to obtain a semi-liquid mixture;

[0032] S3: Put the semi-liquid mixture into a crucible mold, with a molding pressure of 20±1 Mpa, a pressure holding time of 10 min, and a mold temperature of 200±5°C to mold a crucible blank;

[0033] S4: Transfer the crucible blank to a carbonization furnace. Under an inert gas atmosphere, heat it up to 600°C at a heating rate of 5°C / min and hold for 20 h. After the holding is completed, heat it up to 1600°C at a heating rate of 6°C / min and hold for 20 h, and then naturally cool it to room temperature to obtain a semi-finished crucible;

[0034] S5: Transfer the semi-finished crucible to a CVD furnace. Under nitrogen protection, when heating up to 700°C, introduce acetylene according to the volume ratio of nitrogen:acetylene = 2:1 and react for 5 h. After the reaction is completed, naturally cool it down to obtain a graphite crucible.

[0035] Example 3

[0036] A preparation method of a graphite crucible, which comprises the following steps:

[0037] S1: Take a certain weight of heavy oil, add it to a container, start a high-speed disperser, with a stirring speed of 500 rpm / min. After stirring for 20 min, slowly add high-temperature pitch as a binder to the high-speed stirred heavy oil solution. After the high-temperature pitch is added, continue stirring for 90 min to prepare a liquid-phase binder solution with a mass fraction of 40%;

[0038] S2: Put graphite, carbon powder, and the liquid-phase binder solution into a mixer in sequence according to the mass ratio of 92%:4%:4%, and stir at a speed of 1000 rpm / min for 120 min to obtain a semi-liquid mixture;

[0039] S3: Load the semi - liquid mixture into the sagger mold, and press - mold it at a molding pressure of 20 ± 1 Mpa, a holding pressure time of 10 min, and a mold temperature of 200 ± 5 °C to obtain a sagger blank;

[0040] S4: Transfer the sagger blank to a carbonization furnace. Under an inert gas atmosphere, heat it at a heating rate of 5 °C / min to 600 °C and hold for 20 h. After the holding is completed, heat it at a heating rate of 6 °C / min to 1600 °C and hold for 20 h, and then naturally cool it to room temperature to obtain a semi - finished sagger;

[0041] S5: Transfer the semi - finished sagger to a CVD furnace. Under nitrogen protection, when heating to 700 °C, introduce acetylene for reaction at a volume ratio of nitrogen:acetylene = 2:1 for 5 h. After the reaction is completed, naturally cool it to obtain a graphite sagger.

[0042] Comparative Example 1

[0043] A graphite sagger, compared with Example 3 in its preparation method, is characterized in that step S1 is omitted, and graphite, carbon powder, and high - temperature pitch are successively put into a mixer according to a mass ratio of 92%:4%:4% for mixing, and then produced by the same method subsequently.

[0044] Comparative Example 2

[0045] A graphite sagger, compared with Example 3 in its preparation method, is characterized in that step S1 is omitted, and graphite, carbon powder, and high - temperature pitch are successively put into a mixer according to a mass ratio of 86%:4%:10% for mixing, and then produced by the same method subsequently.

[0046] Comparative Example 3

[0047] A graphite sagger, compared with Example 3 in its preparation method, is characterized in that step S1 is omitted, and graphite, carbon powder, and high - temperature pitch are successively put into a mixer according to a mass ratio of 81%:4%:15% for mixing, and then produced by the same method subsequently.

[0048] Comparative Example 4

[0049] A graphite sagger, compared with Example 3 in its preparation method, is characterized in that step S1 is omitted, and graphite, carbon powder, and high - temperature pitch are successively put into a mixer according to a mass ratio of 77%:5%:18% for mixing, and then produced by the same method subsequently.

[0050] Comparative Example 5

[0051] A graphite sagger, compared with Example 3 in its preparation method, is characterized in that step S1 is omitted, and graphite, carbon powder, and phenolic resin are successively put into a mixer according to a mass ratio of 86%:4%:10% for mixing, and then produced by the same method subsequently.

[0052] Comparative Example 6

[0053] A graphite crucible, compared with the preparation method of Example 3, is different in that step S1 is omitted, and graphite, carbon powder, and phenolic resin are sequentially put into a fusion machine for mixing according to a mass ratio of 81%:4%:15%, and then produced in the same method.

[0054] Comparative Example 7

[0055] A graphite crucible, compared with the preparation method of Example 3, is different in that step S1 is omitted, and graphite, carbon powder, and phenolic resin are sequentially put into a fusion machine for mixing according to a mass ratio of 77%:5%:18%, and then produced in the same method.

[0056] Comparative Example 8

[0057] A graphite crucible, compared with the preparation method of Example 3, is different in that in step S2, a kneading machine is used to mix graphite, carbon powder, and a liquid binder, and then produced in the same method.

[0058] Performance tests were carried out on the graphite crucibles and their semi-finished products prepared in Examples 1-3 and Comparative Examples 1-8. Specifically, density, apparent porosity, and flexural strength tests were carried out successively according to the standards of GB / T 24528-2009, GB / T2997-2015, and GB / T 3074.1-2021. The relevant results are shown in Table 1:

[0059] Table 1 Performance data of examples and comparative examples

[0060]

[0061]

[0062] As can be seen from the above table: (1) In the present invention, heavy oil is used as the solvent for dissolving the binder. Because it has a certain viscosity itself, it plays a bonding role in cooperation with the binder in the subsequent forming process. Moreover, the addition of the binder is fused with graphite and carbon powder in a liquid form, and its mixing effect is more uniform and the bonding effect is better. The combined use of the two significantly reduces the amount of the binder, from 10%-15% of the binder amount in the traditional process to less than 10% to meet the bonding requirements. Less binder amount is beneficial to improving the density and flexural strength of the crucible products. It can increase the density of the crucible products from the traditional 1.65 g / cm 3 to 1.8 g / cm 3 or more. In addition, heavy oil contains some carbon elements. In the subsequent carbonization process, it can form hard carbon to coat the surface of graphite and carbon powder, and can also improve the overall strength of the graphite crucible body. The final flexural strength can be further increased to more than 22 MPa.

[0063] (2) The present invention uses a fusion machine to replace the conventional kneading machine. Compared with the conventional kneading machine that realizes mixing through the flipping and collision of materials, the fusion machine not only has the collision between materials, but also has the shearing effect of the tool on the materials, which makes the consistency of the materials greatly improved compared with kneading. Finally, the apparent porosity of the sagger products can be reduced from more than 15% in the conventional process to about 10%; during the subsequent molding and carbonization processes, the risk of product cracking can be greatly reduced, and the risk of product cracking is reduced from one-thousandth in the conventional process to one-ten-thousandth, greatly reducing the production cost; at the same time, the improvement of consistency also helps to increase the pressure that the sagger products can withstand during the molding process, further improving the flexural strength of the sagger products. This process can stably increase the flexural strength of the sagger products from the conventional 15-20 MPa to 22-25 MPa.

[0064] The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions falling within the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the raw materials of the present invention, several improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a graphite sagger, characterized in that: The following steps are involved: S1: dissolving the binder in heavy oil to prepare a liquid binder solution with a mass fraction of 20-40%; S2: Put graphite, carbon powder and liquid binder solution into a fusion machine in order according to the mass ratio and mix them evenly to obtain a semi-liquid mixture; S3: putting the semi-liquid mixture into a sagger mold to mold out a sagger body; S4: Transfer the sagger body to a carbonization furnace, and heat it to 600-900°C at a heating rate of 2-5°C / min and keep it at that temperature for 10-20h under an inert gas atmosphere. After the heat preservation, heat it to 1200-1600°C at a heating rate of 3-6°C / min and keep it at that temperature for 20-30h, and then cool it naturally to room temperature to obtain a sagger body semi-finished product; S5: Transfer the semi-finished sagger to a CVD furnace, and introduce acetylene at 700-900°C for reaction for 1-5h under the protection of inert gas. After the reaction, cool down naturally to obtain a graphite sagger. The binder in step S1 is one or a combination of medium-temperature asphalt and high-temperature asphalt; The mass ratio of graphite, carbon powder and liquid binder in step S2 is 87-94%:2-5%:4-8%.

2. The preparation method according to claim 1, characterized in that: In step S3, the molding pressure is 5-20 MPa, the holding time is 5-20 min, and the mold temperature is 150-250°C.

3. The preparation method according to claim 1, characterized in that: The inert gas in step S4 is nitrogen or argon.

4. The preparation method according to claim 1, characterized in that: The inert gas in step S5 is nitrogen, and the volume ratio of the nitrogen to acetylene is 1.5-3:

1.

5. A graphite sagger, characterized in that: Prepared by the preparation method according to any one of claims 1 to 4.

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