Highly dense isotropic graphite powder and method for producing the same

Abstract

The application belongs to the field of isotropic graphite powder preparation, in particular to high-density isotropic graphite powder and a preparation method thereof. The raw material components of the graphite powder include modified mesophase pitch coke micro powder, needle coke micro powder, a composite binder and nano silicon carbide dispersant. The weight percentage of each raw material component is as follows: modified mesophase pitch coke micro powder 55-75%, needle coke micro powder 10-20%, composite binder 15-25% and nano silicon carbide dispersant 0.5-3%. The application combines the dispersion and skeleton enhancement of nano silicon carbide to make the green body obtain excellent compactness under a medium static pressure of 180-200 MPa, and high compactness can be achieved without high-pressure forming. After calcination and graphitization, the volume density of the product can reach 1.88-1.95 g / cm3, and the bending strength is 45-60 MPa, solving the problems of insufficient compactness and low strength of graphite products in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of isotropic graphite powder preparation, specifically a high-density isotropic graphite powder and its preparation method. Background Technology

[0002] The production process of isostatic graphite generally involves grinding, batching, mixing, secondary grinding, and molding of the raw coke, followed by calcination in a furnace to remove volatiles, and then graphitization. The flexural and compressive strength of graphite is influenced by various factors, including raw material selection, blending, and production process control.

[0003] There are still many problems to be solved in the manufacturing process of isostatic graphite: First, in the aggregate configuration stage, the existing process generally uses traditional coke powder as the aggregate, which results in the limited bulk density and bonding performance of the aggregate itself, resulting in insufficient compactness of the green body after subsequent molding. After calcination and graphitization treatment, the bulk density and flexural strength of the product are low.

[0004] Secondly, uneven mixing of materials is prone to occur during the batching and kneading process. This not only affects the flowability and filling density of the pressed powder, leading to uneven pressure transmission during molding and making the green body prone to defects, but also causes uneven microstructure and significant anisotropy in subsequent products.

[0005] Therefore, the present invention provides a high-density isotropic graphite powder and its preparation method. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by the present invention to solve its technical problem is as follows: The present invention provides a high-density isotropic graphite powder, wherein the raw material components of the graphite powder include modified mesophase pitch coke micro powder, needle coke micro powder, composite binder and nano silicon carbide dispersant, wherein the weight percentage of each raw material component is: modified mesophase pitch coke micro powder 55%~75%, needle coke micro powder 10%~20%, composite binder 15%~25%, and nano silicon carbide dispersant 0.5%~3%.

[0008] Furthermore, the particle size distribution of the modified mesophase pitch coke micro powder is: D50 = 15~25μm, with particles <5μm accounting for <10% and particles >50μm accounting for <5%.

[0009] Furthermore, the particle size D50 of the needle-shaped coke powder is 5~10μm.

[0010] Furthermore, the composite binder is made by compounding coal tar pitch and furan resin in a weight ratio of 7:3 to 8:2.

[0011] Furthermore, the average particle size of the nano-silicon carbide dispersant is 40~80nm.

[0012] A method for preparing highly dense isotropic graphite powder, the method comprising the following steps:

[0013] S1. Aggregate pretreatment and gradation: The modified mesophase asphalt coke powder and needle coke powder by weight percentage are placed in a high-speed mixer and dry-mixed at 60~80℃ for 30~60 minutes to obtain graded aggregate.

[0014] S2. Initial mixing: Heat the graded aggregate to 120~140℃, add the composite binder by weight percentage, and knead in a kneader at a speed of 20~40rpm for 90~120 minutes to obtain the initial mixture.

[0015] S3. Dispersion and fine mixing: Cool the initial mixture to 80~100℃, add the weight percentage of nano silicon carbide dispersant, and continue to knead at a speed of 40~60rpm for 60~90 minutes to obtain a uniform paste.

[0016] S4. Cooling and pulverizing: The paste is cooled to room temperature, crushed by a roller crusher, and then pulverized by an air jet mill to obtain pressed powder with a particle size D50 of 20~35μm.

[0017] The beneficial effects of this invention are as follows:

[0018] This invention discloses a high-density isotropic graphite powder and its preparation method. Through the compounding of modified mesophase pitch coke and needle coke, combined with the dispersion and skeletal reinforcement of nano-silicon carbide, excellent density can be achieved in the green body under a moderate static pressure of 180-200 MPa, achieving high density without high-pressure molding. After calcination and graphitization, the bulk density of the product can reach 1.88-1.95 g / cm³, and the flexural strength reaches 45-60 MPa, solving the problems of insufficient density and low strength of graphite products in existing technologies.

[0019] By using particle size distribution design and combining it with the dispersing effect of nano-silicon carbide, the flowability and molding uniformity of the pressed powder are effectively improved. At the same time, the composite binder (coal tar pitch and furan resin compound) forms a stable coking bridging structure after carbonization, which reduces the anisotropy ratio (the ratio of resistivity in the Z direction to that in the X direction) of the final product to 1.05~1.25, meeting the requirements for material uniformity in high-end single crystal furnace hot zones, semiconductor epitaxial disks and other fields.

[0020] The graphite powder prepared by this invention has good flowability and high filling density, and the pressure is uniformly transmitted during isostatic pressing, resulting in fewer green defects. The synergistic effect of coal tar pitch and furan resin in the composite binder can reduce the rapid volatilization of components during high-temperature calcination, significantly reduce the calcination crack rate, and increase the product yield from the industry average of about 75% to more than 85%. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0022] An embodiment of the present invention provides a high-density isotropic graphite powder. The raw material components of the graphite powder include modified mesophase pitch coke micro powder, needle coke micro powder, composite binder, and nano-silicon carbide dispersant. The weight percentages of each raw material component are as follows: modified mesophase pitch coke micro powder 55%~75%, needle coke micro powder 10%~20%, composite binder 15%~25%, and nano-silicon carbide dispersant 0.5%~3%.

[0023] The particle size distribution of the modified mesophase pitch coke micro powder is: D50 = 15~25μm, with particles <5μm accounting for <10% and particles >50μm accounting for <5%.

[0024] The particle size D50 of needle-shaped coke powder is 5~10μm.

[0025] The composite binder is made by mixing coal tar pitch and furan resin in a weight ratio of 7:3 to 8:2.

[0026] The average particle size of the nano-silicon carbide dispersant is 40~80nm.

[0027] A method for preparing highly dense isotropic graphite powder, the method comprising the following steps:

[0028] S1. Aggregate pretreatment and gradation: The modified mesophase asphalt coke powder and needle coke powder by weight percentage are placed in a high-speed mixer and dry-mixed at 60~80℃ for 30~60 minutes to obtain graded aggregate.

[0029] S2. Initial mixing: Heat the graded aggregate to 120~140℃, add the composite binder by weight percentage, and knead in a kneader at a speed of 20~40rpm for 90~120 minutes to obtain the initial mixture.

[0030] S3. Dispersion and fine mixing: Cool the initial mixture to 80~100℃, add the weight percentage of nano silicon carbide dispersant, and continue to knead at a speed of 40~60rpm for 60~90 minutes to obtain a uniform paste.

[0031] S4. Cooling and pulverizing: The paste is cooled to room temperature, crushed by a roller crusher, and then pulverized by an air jet mill to obtain pressed powder with a particle size D50 of 20~35μm.

[0032] Example 1

[0033] 1. Raw material formula (percentage by mass)

[0034] Modified mesophase pitch coke micro powder (D50=20μm) 65%, needle-shaped coke micro powder (D50=8μm) 15%, composite binder (coal tar pitch: furan resin=7.5:2.5) 18.5%, and nano-silicon carbide (average particle size 50nm) 1.5%.

[0035] 2. Powder preparation

[0036] (1) According to the above proportions, put the modified mesophase asphalt coke powder and needle coke powder into the mixing equipment and dry mix at 70°C for 45 minutes to ensure that the two aggregates are mixed evenly.

[0037] (2) Heat the temperature inside the mixing equipment to 130°C, add the preset amount of composite binder, adjust the speed to 30 rpm, and continue mixing for 105 minutes to ensure that the composite binder fully coats the aggregate particles.

[0038] (3) Cool the temperature inside the kneading equipment to 90°C, add nano silicon carbide, adjust the speed to 50 rpm, and continue kneading for 75 minutes to make the nano silicon carbide evenly dispersed in the mixture.

[0039] (4) Cool the kneaded mixture to room temperature, crush it with rollers, and then send it into an air jet mill for pulverization. Control the D50 of the pulverized material to 28μm to obtain pressed powder A.

[0040] 3. Molding and Sintering

[0041] (1) Load the pressed powder A into the rubber mold, place it in the cold isostatic pressing equipment, and hold it under pressure of 190MPa for 5 minutes to obtain the green body;

[0042] (2) Place the green blanks into the baking furnace and bake them under an inert atmosphere according to a specific heating curve (1℃ / min to 600℃, and 3℃ / min to 1100℃). After baking, cool them to room temperature.

[0043] (3) The calcined blank is sent into a graphitization furnace and graphitized at 2600℃. After the treatment, graphite product A1 is obtained.

[0044] Example 2

[0045] 1. Raw material formula (percentage by mass)

[0046] Modified mesophase pitch coke micro powder (D50=20μm) 70%, needle-shaped coke micro powder (D50=8μm) 12%, composite binder (coal tar pitch: furan resin=7.5:2.5) 16.5%, and nano-silicon carbide (average particle size 50nm) 1.5%.

[0047] 2. Powder preparation and subsequent processes

[0048] The powder preparation, molding and sintering processes were exactly the same as in Example 1, resulting in powder B and the final graphite product B1.

[0049] Comparative Example 1

[0050] 1. Raw material formula (percentage by mass)

[0051] It uses 72% ordinary petroleum coke (D50=22μm) as aggregate and 28% pure coal tar pitch as binder, without adding nano silicon carbide or other components.

[0052] 2. Preparation process

[0053] The preparation process is similar to that in Example 1, and pressed powder C and final product C1 are obtained.

[0054] Comparative Example 2

[0055] 1. Raw material formula (percentage by mass)

[0056] The aggregate type and proportion are exactly the same as in Example 1, namely 65% ​​modified mesophase pitch coke micro powder (D50=20μm) and 15% needle coke micro powder (D50=8μm); the composite binder in Example 1 is replaced with an equal amount of pure coal tar pitch (18.5%) and nano silicon carbide (average particle size 50nm) 1.5%, and the remaining components remain unchanged.

[0057] 2. Preparation process

[0058] The preparation process is exactly the same as in Example 1, and pressed powder D and final graphite product D1 are obtained.

[0059] Performance Testing and Comparison

[0060] The above-mentioned products were subjected to performance testing, and the results are shown in Table 1 below;

[0061] Table 1 shows:

[0062]

[0063] Data Analysis:

[0064] As shown in Table 1, under the same molding pressure of 190 MPa, the graphite products A1 and B1 prepared in Examples 1-2 of this invention exhibit superior density, strength, isotropy, and yield compared to the graphite products C1 and D1 prepared in Comparative Examples 1-2. In particular, the C1 sample prepared in Comparative Example 1, using a conventional formulation, shows significant differences in performance indicators compared to the example samples. Although the aggregate ratio of the D1 sample prepared in Comparative Example 2 is consistent with that of Example 1 and its bulk density is acceptable, the absence of a composite binder and the use of only pure coal tar pitch demonstrates that the introduction of furan resin in the composite binder plays a crucial role in improving the carbonization structure and enhancing the uniformity of performance of the product.

[0065] 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 the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-density isotropic graphite powder, characterized in that, The raw material components of this graphite powder include modified mesophase pitch coke micro powder, needle coke micro powder, composite binder and nano silicon carbide dispersant. The weight percentages of each raw material component are as follows: modified mesophase pitch coke micro powder 55%~75%, needle coke micro powder 10%~20%, composite binder 15%~25%, and nano silicon carbide dispersant 0.5%~3%.

2. The high-density isotropic graphite powder according to claim 1, characterized in that: The particle size distribution of the modified mesophase pitch coke micro powder is: D50 = 15~25μm, and the proportion of particles with a particle size <5μm is <10%, and the proportion of particles with a particle size >50μm is <5%.

3. The high-density isotropic graphite powder according to claim 1, characterized in that: The particle size D50 of the needle-shaped coke powder is 5~10μm.

4. The high-density isotropic graphite powder according to claim 1, characterized in that: The composite binder is made by mixing coal tar pitch and furan resin in a weight ratio of 7:3 to 8:

2.

5. The high-density isotropic graphite powder according to claim 1, characterized in that: The average particle size of the nano-silicon carbide dispersant is 40~80nm.

6. A method for preparing highly dense isotropic graphite powder, used in any one of claims 1-5, characterized in that, The preparation method includes the following steps: S1. Aggregate pretreatment and gradation: The modified mesophase pitch coke powder and needle coke powder of the specified weight percentage are placed in a high-speed mixer and dry-mixed at 60~80℃ for 30~60 minutes to obtain graded aggregate. S2. Initial mixing: The graded aggregate is heated to 120~140℃, the composite binder of the specified weight percentage is added, and the aggregate is kneaded in a kneader at a speed of 20~40 rpm for 90~120 minutes to obtain the initial mixture. S3. Dispersion and fine mixing: Cool the initial mixture to 80~100℃, add the nano silicon carbide dispersant by weight percentage, and continue to knead at a speed of 40~60rpm for 60~90 minutes to obtain a uniform paste. S4. Cooling and pulverizing: The paste is cooled to room temperature, crushed by a roller crusher, and then pulverized by an air jet mill to obtain pressed powder with a particle size D50 of 20~35μm.

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