Preparation method of high-strength, high-density and high-coking-value isostatic pressing graphite

Abstract

A preparation method of high-strength and high-density isostatic pressing graphite comprises the following steps: firstly, starting from raw materials, modifying aggregate to increase the specific surface area of the aggregate; secondly, starting from a core process mixing and kneading technical mechanism, asphalt with a higher softening point is adopted as a binder to ensure that the binder asphalt is in contact with the aggregate in a molten state, so that the binder asphalt can be more and more uniformly combined with the aggregate, and therefore, the volume density of the isostatic pressing graphite is improved, the resistivity is reduced, and the strength is improved; the volume density of the obtained isostatic pressing graphite is larger than or equal to 1.5 g / cm < 3 >, the compressive strength is larger than or equal to 80 MPa, the breaking strength is larger than or equal to 40 MPa, and the resistivity is 25-46 omega.m. Compared with the traditional process, the process provided by the invention has the advantages that multiple dipping and roasting processes are reduced, the production period is shortened, and the production efficiency is higher.

Description

Technical Field

[0001] The invention belongs to the field of isostatic graphite preparation, and specifically relates to a method for preparing high-strength, high-density and high-coking value isostatic graphite. Background Art

[0002] Isostatic graphite is a new type of graphite material developed in the 1960s. It has the advantages of large molding specifications, uniform blank structure, high density, high strength, and its characteristics are independent of size, shape, and sampling direction. It is also called "isotropic" graphite. Isostatic graphite is an irreplaceable material for manufacturing single crystal silicon furnaces, metal continuous casting graphite crystallizers, and graphite electrodes for electrospark machining. It is also an excellent material for manufacturing rocket ignition poles, excitation poles, nozzles and rudders, and graphite nuclear reactor deceleration materials and reflective materials.

[0003] Its conventional production process includes: fine grinding, screening, batching, kneading, molding, roasting, impregnation, graphitization and purification, etc. Among them, kneading technology is the core technology that determines the quality of the final product, ensuring that the binder is evenly coated on the surface of the aggregate, and can be evenly penetrated and adsorbed by the pores of the aggregate, especially the micropores, to finally form a uniform spherical viscous paste.

[0004] Chinese patent CN102060293A discloses "a method for preparing binderless graphite products". It is possible to form isostatic graphite green bodies and isostatic graphite calcined products with certain mechanical strength by relying solely on the self-adhesiveness and self-sintering properties of raw petroleum coke powder and coal tar pitch mesophase small ball powder. The isostatic graphite calcined products are then further graphitized to obtain binderless graphite products. The method used in the invention to improve the yield of isostatic graphite calcined products is to use the self-adhesiveness and self-sintering properties of raw petroleum coke powder and the self-sintering properties of coal tar pitch mesophase small ball powder without using binder pitch, and to form a mixture of the two, while increasing the particle size of the raw materials, so that the volatile matter removal channel is unobstructed, reducing crack waste in the calcination stage, and improving the yield of the product.

[0005] Chinese patent CN102241397A discloses a "method for manufacturing cold isostatic graphite". The invention uses raw coke treated at a relatively low temperature, which is initially crushed and lifted to a stock bin by a hoist. A mill is used for grinding. The particles are screened and enter a stock bin. They are then mixed with 120°C high-temperature asphalt. After the mixture is qualified, they are pressed. The pressed product is roasted once. After the roasting is completed, it is impregnated once in a horizontal impregnation tank. After the impregnation is completed, the final product is obtained by graphitization. The production cycle is greatly shortened and the strength, density and other physical and chemical properties of the product are improved.

[0006] Chinese patent CN102992766A discloses "a production process for high-density isotropic isostatically pressed graphite circular hollow core billets", with diversified production specifications and varieties. According to user needs, different specifications of hydraulic press special hollow core molds can be used to produce diversified graphite circular hollow core billets. The outer diameter, inner diameter and height of the billet can be arbitrarily designed according to product requirements.

[0007] Chinese patent CN102910912A discloses "a high-hardness isostatic graphite and its preparation method". The invention omits the steps of kneading, repeated impregnation and roasting, simplifies the manufacturing process, and while utilizing the characteristics of the mesophase carbon microspheres themselves, it incorporates some cheap traditional materials such as petroleum coke or asphalt coke, significantly reducing the manufacturing cost.

[0008] Chinese patent CN107522196A discloses "a superhard isostatic graphite and its preparation method", which is made of petroleum coke or asphalt coke, with a certain proportion of natural gas semi-reinforced nano carbon black and graphite powder added. The binder is coal tar produced by an ordinary coking plant with a softening point of 85-120°C and a coking value of 48-65%. The kneading adopts a high-powered kneading machine system designed and modified independently to ensure uniform distribution of the aggregate mixed powder, and to fully infiltrate and coat the binder asphalt, so that the uniformity and plasticity of the mixture are improved, the inclusion of powder and asphalt is reduced, and it is directly graphitized after roasting, which eliminates the repeated impregnation and roasting of the traditional process, shortens the production cycle, and reduces the production cost.

[0009] The improvement of mechanical properties such as density and strength and electrochemical properties of existing isostatic graphite is mostly achieved by changing the amount of binder, mixing multiple types of aggregates, changing the heating rate, increasing the graphitization temperature, etc. The overall production cost is high, the production cycle is long, and the yield is difficult to guarantee. Summary of the invention

[0010] The present invention aims to provide a method for preparing high-strength, high-density and high-coking value isostatic graphite, which can improve the strength and bulk density of isostatic graphite and reduce the resistivity. The obtained isostatic graphite has a bulk density of ≥1.5g / cm 3 , compressive strength ≥80MPa, flexural strength ≥40MPa, resistivity is 25-46Ω·m; compared with the traditional process, the present invention does not require multiple impregnation and roasting, thus shortening the production cycle.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] A method for preparing high-strength, high-density and high-coking value isostatic graphite comprises the following steps:

[0013] 1) Mix and grind one or more of petroleum coke, asphalt coke, needle coke, isotropic coke and cooked coke as aggregate for later use;

[0014] 2) The obtained aggregate is mixed evenly with isotropic asphalt having a softening point of 250-260°C, and then subjected to coating treatment, wherein the coating treatment temperature is controlled to be 30-50°C above the softening point of the isotropic asphalt, and the coating treatment time is 2-5h; then, under the protection of inert gas, the temperature is raised to 600-700°C for heat treatment for 1-2h, and the heating rate is controlled to be ≥8°C / min. After the heat treatment, the aggregate is cooled to below 200°C in the furnace to obtain a modified aggregate with a core-shell structure; the addition amount of the isotropic asphalt is 3-8%wt of the total weight of the aggregate;

[0015] 3) Put the modified aggregate into a kneading device, exhaust and remove water for 30 to 60 minutes at 160 to 180° C., naturally cool to room temperature, release pressure to normal pressure, then add binder asphalt thereto, knead under vacuum to obtain a kneaded paste; the kneading temperature is 30 to 90° C. above the softening point of the binder asphalt, the kneading time is 60 to 90 minutes, the mass ratio of the modified aggregate to the binder asphalt is 2:0.3 to 1; the binder asphalt is an isotropic asphalt with a softening point of 200 to 280° C. or an anisotropic asphalt with a softening point of 150 to 160° C. and an anisotropic size of ≤5 μm;

[0016] 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

[0017] Preferably, the median diameter D of the aggregate 50 8~25μm.

[0018] Preferably, the median diameter D of the binder asphalt is 50 6~8μm.

[0019] Furthermore, the specific surface area of ​​the modified aggregate is ≥20m 2 / g.

[0020] Preferably, in step 3), the anisotropic size of the anisotropic asphalt is ≤5 μm.

[0021] The volume density of isostatic graphite obtained by the present invention is ≥1.5g / cm 3 , compressive strength ≥80MPa, flexural strength ≥40MPa, resistivity is 25~46Ω·m.

[0022] The present invention uses isotropic asphalt at 250-260°C to modify aggregates, obtains modified aggregates with a core-shell structure, increases the specific surface area of ​​the aggregates, ensures that the binder asphalt can be evenly adsorbed into the pores on the surface of the aggregates during the subsequent kneading process, and penetrates into the micropores of the aggregates as the temperature rises during roasting, further strengthening the bonding force between the aggregates and gradually forming bonding coke. Since the pores and micropores of the aggregates are completely filled with asphalt, the volume density of the product is increased, the resistivity is reduced, the binder asphalt is converted into bonding coke, and the strength of the product is increased.

[0023] The binder asphalt of the present invention adopts isotropic asphalt with a softening point of 200-280°C or anisotropic asphalt with a softening point of 150-160°C. The kneading temperature is controlled at 60-90°C above the softening point of the binder asphalt, so that the binder asphalt is in a molten state, which can make the binder asphalt more and more evenly coated on the surface of the aggregate. Subsequent molding, roasting and graphitization treatment can make the binder asphalt penetrate into the pores and micropores of the aggregate. The traditional method uses asphalt with a softening point of ≤120℃ as a binder and adopts high-temperature kneading. The asphalt needs to be boiled in a boiling kettle for a period of time. The asphalt is mixed with the aggregate in a liquid state, and the mixing is uneven. Particles will agglomerate during the kneading process. In the later stage, the asphalt must be allowed to enter the pores of the aggregate through the sheeting process. Secondary grinding can ensure the molding particle size requirements, and the cost is high. At the same time, the asphalt coking value is low, and the cooked embryo has many pores after roasting. Multiple impregnation and roasting are required in the future to make the binder asphalt more combined with the aggregate to improve the volume density, strength, etc. The production cycle is long, and the asphalt volatiles overflow a lot, which is not environmentally friendly.

[0024] Because the present invention uses asphalt with a higher softening point as the binder, a higher kneading temperature is required to ensure that the binder asphalt is in a molten state during the kneading process. In order to prevent the aggregate from being denatured due to excessively high temperature during the kneading process, the aggregate is degassed and dehydrated at 160-180°C for 30-60 minutes before kneading to reduce the boiling point of the modified aggregate and prevent the modified aggregate from being denatured at high temperature.

[0025] The use of anisotropic asphalt with anisotropic size ≤5μm can make the asphalt penetrate into the micropores of the aggregate better, making the bonding force stronger during molding and the green body denser; the binder asphalt has a high coking value, and the final green body has a high coking value of more than 85%, which improves the strength of isostatic graphite.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] In the process of preparing isostatic graphite, the present invention firstly starts from the raw materials, modifies the aggregates and increases the specific surface area of ​​the aggregates; secondly, starting from the core process kneading technology mechanism, asphalt with a higher softening point is used as a binder to ensure that the binder asphalt contacts the aggregates in a molten state, so that the binder asphalt can be more and more evenly combined with the aggregates. Moreover, due to the increase in the specific surface area of ​​the aggregates, after subsequent molding and roasting treatment, the binder asphalt can enter the pores and micropores of the aggregates, reduce the pores of the isostatic graphite, increase the volume density of the product, reduce the resistivity, and improve the strength. The obtained isostatic graphite has a volume density of ≥1.5g / cm 3 , compressive strength ≥ 80MPa, flexural strength ≥ 40MPa, resistivity 25~46Ω·m. Conventional isostatic graphite has a compressive strength of 70~80Mpa and a bulk density of ≤1.4g / cm 3 , the resistivity is about 50Ω·m.

[0028] The present invention directly forms, roasts and graphitizes after kneading to obtain the high-strength, high-density and high-coking value isostatic graphite; however, the traditional method uses a low softening point of the binder asphalt and a small specific surface area of ​​the aggregate, which will leave pores after forming, and subsequent impregnation and roasting are required multiple times to allow the binder asphalt to enter the pores to increase the volume density of the product. Therefore, compared with the traditional process, the present invention reduces the multiple impregnation and roasting processes, shortens the roasting time by nearly half of the traditional process, and has higher production efficiency. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific implementation modes.

[0030] Example 1

[0031] A method for preparing high-strength, high-density and high-coking value isostatic graphite comprises the following steps:

[0032] 1) Grind 7kg of petroleum coke and use it as aggregate. The median diameter of the aggregate is D 50 12.351μm;

[0033] 2) The obtained aggregate was mixed with 0.216 kg of a 0.216 kg 50 The isotropic asphalt with a particle size of 6.123 μm is mixed evenly, and then coated at a temperature of 300° C. for 3 hours; then, under nitrogen protection, the temperature is raised to 700° C. for heat treatment for 1 hour, and the heating rate is controlled at 10° C. / min. After the heat treatment, the furnace is cooled to below 200° C. to obtain a modified aggregate with a core-shell structure; the amount of the isotropic asphalt added is 5.2%wt of the total weight of the aggregate;

[0034] 3) The modified aggregate is placed in a kneading device, and the air is exhausted and dehydrated for 30 minutes at 165°C, and the temperature is naturally reduced to room temperature and the pressure is released to normal pressure. Then, 2.36 kg of binder asphalt is added thereto, and kneaded in a vacuum state at a kneading temperature of 295°C and a kneading time of 60 minutes to obtain a kneaded paste; the mass ratio of the modified aggregate to the binder asphalt is 2:1; the binder asphalt has a softening point of 205°C and a median diameter D 50 isotropic asphalt with a thickness of 6.214 μm;

[0035] 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

[0036] The specific surface area of ​​the aggregate and the properties of isostatic graphite obtained are shown in Table 1.

[0037] Comparative Example 1 uses the same aggregate as the present invention, and the properties of the isostatic graphite obtained by the traditional process are shown in Table 1.

[0038] Traditional process flow: aggregate toner powder - kneading - sheeting - grinding - molding - roasting - impregnation - roasting, roasting and impregnation times 3-5 times.

[0039] Example 2

[0040] A method for preparing high-strength, high-density and high-coking value isostatic graphite comprises the following steps:

[0041] 1) Grind 7kg of asphalt coke and use it as aggregate. The median diameter of the aggregate is D 50 13.213μm;

[0042] 2) The obtained aggregate was mixed with 0.356 kg of a 0.5-kg 50 The isotropic asphalt with a particle size of 6.033 μm is evenly mixed, and then coated at a temperature of 290°C for 2 hours. Then, the temperature is raised to 600°C for heat treatment for 1.7 hours under nitrogen protection, and the heating rate is controlled at 8°C / min. After the heat treatment, the aggregate is cooled to below 200°C in the furnace to obtain a modified aggregate with a core-shell structure.

[0043] 3) The modified aggregate was placed in a kneading device, and the mixture was degassed and dehydrated for 45 minutes at 170°C, and the mixture was naturally cooled to room temperature and depressurized to normal pressure. Then, 3.40 kg of binder asphalt was added thereto, and the mixture was kneaded under vacuum at a kneading temperature of 271°C and a kneading time of 90 minutes to obtain a kneaded paste; the binder asphalt had a softening point of 220°C and a median diameter of D 50 isotropic asphalt with a thickness of 7.045 μm;

[0044] 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

[0045] The specific surface area of ​​the aggregate and the properties of isostatic graphite obtained are shown in Table 1.

[0046] Comparative Example 2 and Example 2 of the present invention use the same aggregate, and the properties of the isostatic graphite obtained by the traditional process are shown in Table 1.

[0047] Example 3

[0048] A method for preparing high-strength, high-density and high-coking value isostatic graphite comprises the following steps:

[0049] 1) 7 kg of needle coke, asphalt coke, petroleum coke and isotropic coke were mixed and ground and used as aggregate. The median diameter of the aggregate was D 50 24.512μm;

[0050] 2) The obtained aggregate is mixed with 0.412 kg of a 0.412 kg 50 The isotropic asphalt with a particle size of 6.001 μm is evenly mixed, and then coated at a temperature of 290°C for 5 hours. Then, under the protection of nitrogen, the temperature is raised to 650°C for heat treatment for 1.5 hours, and the heating rate is controlled at 15°C / min. After the heat treatment, the aggregate is cooled to below 200°C in the furnace to obtain a modified aggregate with a core-shell structure.

[0051] 3) The modified aggregate was placed in a kneading device, and the mixture was degassed and dehydrated for 40 minutes at 160°C, and the mixture was naturally cooled to room temperature and depressurized to normal pressure. Then, 2.08 kg of binder asphalt was added thereto, and the mixture was kneaded under vacuum at a kneading temperature of 340°C and a kneading time of 85 minutes to obtain a kneaded paste; the binder asphalt had a softening point of 265.3°C and a median diameter of D 50 isotropic asphalt with a thickness of 7.337 μm;

[0052] 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

[0053] The specific surface area of ​​the aggregate and the properties of isostatic graphite obtained are shown in Table 1.

[0054] Comparative Example 3 and Example 3 of the present invention use the same aggregate, and the properties of the isostatic graphite obtained by the traditional process are shown in Table 1.

[0055] Example 4

[0056] A method for preparing high-strength, high-density and high-coking value isostatic graphite comprises the following steps:

[0057] 1) 7 kg of needle coke, asphalt coke, petroleum coke and isotropic coke were mixed and ground and used as aggregate. The median diameter of the aggregate was D 50 15.003μm;

[0058] 2) The obtained aggregate was mixed with 0.532 kg of a 0.532 kg aggregate having a softening point of 255.7 °C and a median diameter of D 50 The isotropic asphalt with a particle size of 6.412 μm is evenly mixed, and then coated at a temperature of 305°C for 4 hours. Then, the temperature is raised to 680°C for heat treatment for 1.2 hours under nitrogen protection, and the heating rate is controlled at 12°C / min. After the heat treatment, the aggregate is cooled to below 200°C in the furnace to obtain a modified aggregate with a core-shell structure.

[0059] 3) The modified aggregate was placed in a kneading device, and the mixture was degassed and dehydrated for 60 minutes at 180°C, and the mixture was naturally cooled to room temperature and depressurized to normal pressure. Then, 1.05 kg of binder asphalt was added thereto, and the mixture was kneaded under vacuum at a kneading temperature of 220°C and a kneading time of 75 minutes to obtain a kneaded paste; the binder asphalt had a softening point of 155°C and a median diameter of D 50 Anisotropic asphalt of 6.009 μm;

[0060] 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

[0061] The specific surface area of ​​the aggregate and the properties of isostatic graphite obtained are shown in Table 1.

[0062] Comparative Example 4 and Example 4 of the present invention use the same aggregate, and the properties of the isostatic graphite obtained by the traditional process are shown in Table 1.

[0063] Example 5

[0064] A method for preparing high-strength, high-density and high-coking value isostatic graphite comprises the following steps:

[0065] 1) 7 kg of needle coke and asphalt coke were mixed and ground and used as aggregate. The median diameter of the aggregate was D 50 8.091μm;

[0066] 2) The obtained aggregate was mixed with 0.372 kg of a 0.5-kg 50 The isotropic asphalt with a particle size of 6.051 μm is evenly mixed, and then coated at a temperature of 290°C for 3 hours. Then, the temperature is raised to 630°C for heat treatment for 2 hours under nitrogen protection, and the heating rate is controlled at 20°C / min. After the heat treatment, the aggregate is cooled to below 200°C in the furnace to obtain a modified aggregate with a core-shell structure.

[0067] 3) The modified aggregate was placed in a kneading device, and the mixture was degassed and dehydrated for 50 minutes at 170°C, and the mixture was naturally cooled to room temperature and depressurized to normal pressure. Then, 1.08 kg of binder asphalt was added thereto, and the mixture was kneaded under vacuum at a kneading temperature of 250°C and a kneading time of 80 minutes to obtain a kneaded paste; the binder asphalt had a softening point of 160°C and a median diameter of D 50 Anisotropic asphalt of 7.121 μm;

[0068] 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

[0069] The specific surface area of ​​the aggregate and the properties of isostatic graphite obtained are shown in Table 1.

[0070] Comparative Example 5 and Example 5 of the present invention use the same aggregate, and the properties of the isostatic graphite obtained by the traditional process are shown in Table 1.

[0071] It can be seen from Table 1 that the isostatic graphite prepared by the method of the present invention has higher volume density, compressive strength, flexural strength and lower resistivity than the isostatic graphite obtained by the traditional process.

[0072] Table 1

[0073]

[0074]

Claims

1. A method for preparing high-strength and high-density isostatic graphite, It is characterized in that The following steps are involved: 1) Mix and grind one or more of petroleum coke, asphalt coke, needle coke, isotropic coke and cooked coke as aggregate for later use; 2) The obtained aggregate is uniformly mixed with isotropic asphalt having a softening point of 250-260° C., wherein the addition amount of the isotropic asphalt is 3-8%wt of the total weight of the aggregate; then a coating treatment is performed, wherein the coating treatment temperature is controlled to be 30-50° C. above the softening point of the isotropic asphalt, and the coating treatment time is 2-5 hours; then, under the protection of an inert gas, the temperature is raised to 600-700° C. for heat treatment for 1-2 hours, and the heating rate is controlled to be ≥8° C. / min. After the heat treatment is completed, the aggregate is cooled to below 200° C. with the furnace to obtain a modified aggregate with a core-shell structure; 3) Put the modified aggregate into a kneading device, exhaust and remove water for 30 to 60 minutes at 160 to 180° C., naturally cool to room temperature, release pressure to normal pressure, then add binder asphalt thereto, knead under vacuum to obtain a kneaded paste; the kneading temperature is 30 to 90° C. above the softening point of the binder asphalt, the kneading time is 60 to 90 minutes, the mass ratio of the modified aggregate to the binder asphalt is 2:0.3 to 1; the binder asphalt is an isotropic asphalt with a softening point of 200 to 280° C. or an anisotropic asphalt with a softening point of 150 to 160° C.; 4) The kneaded paste is molded and / or isostatically pressed, and then calcined and graphitized to obtain isostatic graphite.

2. The method for preparing high-strength, high-density and high-coking value isostatic graphite according to claim 1, It is characterized in that The median diameter D of the aggregate 50 8~25μm.

3. The method for preparing high-strength, high-density and high-coking value isostatic graphite according to claim 1, It is characterized in that The median diameter D of the binder asphalt 50 6~8μm.

4. The method for preparing high-strength, high-density and high-coking value isostatic graphite according to claim 1, It is characterized in that The specific surface area of ​​the modified aggregate is ≥20m 2 / g.

5. The method for preparing high-strength, high-density and high-coking value isostatic graphite according to claim 1, It is characterized in that In step 3), the anisotropic size of the anisotropic asphalt is ≤5 μm.

6. The method for preparing high-strength, high-density and high-coking value isostatic graphite according to claim 1, It is characterized in that The obtained isostatic graphite volume density is ≥1.5g / cm 3 , compressive strength ≥80MPa, flexural strength ≥40MPa, resistivity is 25~46Ω·m.

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