A high-performance integral graphite sagger and its preparation method

Abstract

The present invention discloses a high-performance monolithic graphite sagger and its preparation method. The preparation method comprises the following steps: S1. Mixing flake graphite, a pre-burned material, a mixed liquid, amorphous alumina fine powder, and carbon nanofibers to obtain a mixed material; S2. Placing the mixed material in a mold and maintaining pressure for a certain period of time, and then demolding the mold to obtain a green sagger; S3. Heat-treating the green sagger and then cooling it in a furnace to obtain a high-performance monolithic graphite sagger. The pre-burned material is prepared by ball-milling borax, carbon black, silicon powder, and zirconium oxychloride to obtain a pre-mixed material, which is then heat-treated in an inert gas atmosphere, cooled, and ground to obtain a pre-burned material; and the mixed liquid is a mixture of thermosetting phenolic resin, industrial alcohol, and lanthanum nitrate. The high-performance monolithic graphite sagger prepared by the present invention exhibits high strength, good density, and a high degree of graphitization.

Description

Technical Field

[0001] The present invention relates to the technical field of saggers, and in particular to a high-performance integral graphite sagger and a preparation method thereof. Background Art

[0002] Graphite crucible is the key carrier for holding battery negative electrode materials for heat treatment (it is not excluded that it can be used for heat treatment of battery positive electrode materials such as lithium iron phosphate). It has excellent thermal shock stability and non-wetting properties, and has a long service life and stable overall performance.

[0003] At present, the commonly used graphite saggers mainly include the following three categories:

[0004] (1) Assembled graphite sagger: This type of sagger is a typical assembly / combination processing sagger, that is, first select the graphite block material for cutting and grinding, and process it into a graphite plate with a mortise and tenon structure, and then assemble it ( A spliced ​​graphite sagger, CN202222900311.6 ). On this basis, graphite screws can also be installed for reinforcement ( An assembled graphite sagger, CN202320081392.3 The assembled graphite sagger is based on the characteristics of the graphite block being soft and easy to process. It makes full use of the size of the raw materials to perform cutting and other process operations to prepare the graphite sagger. Its advantage is that the preparation cost of the sagger is low, but its disadvantage is that it has low strength and is easy to deform and damage. In particular, it faces the risk of structural failure at the splicing point, which may lead to the scrapping of the entire sagger.

[0005] (2) Internally hollowed graphite saggers: This type of sagger is essentially still a processed sagger, that is, first select the graphite block material, then hollow it out, cut it and grind it, and then hollow out the entire graphite block to prepare the graphite sagger. However, from a structural point of view, the internally hollowed graphite sagger is an integral sagger. Although it is processed, there are no assembly joints, the sagger structure is complete, and no high-temperature treatment or other processes are required. The main disadvantage of this type of sagger is that due to the overall hollowing of the graphite block, a large amount of raw materials are wasted, resulting in high prices.

[0006] (3) Molded graphite saggers: This type of sagger is structurally an integral sagger, where the graphite raw material and binder are placed in a mold and pressed into shape as a whole, and then heat treated at high temperature. Molded graphite saggers have good integrity and are significantly cheaper to produce than hollowed-out graphite saggers, making them the main trend in the development of graphite saggers.

[0007] At present, there are few reports on molded integral graphite saggers, and the product performance and process technology still need to be further improved. The main shortcomings of molded integral graphite saggers are: first, the graphite material itself is relatively soft, resulting in low strength of the graphite sagger; second, the raw materials and binders used in the graphite sagger contain amorphous carbon, which further affects the strength of the graphite sagger; third, the graphite sagger is difficult to sinter. By increasing the amount of binder, the mechanical properties of the graphite sagger can be improved, but the increase in the amount of binder is also likely to increase the porosity of the sagger and reduce the density of the sagger body.

[0008] Patented technology, "A Method for Preparing Graphite Saggars (CN202310863367.5)," reports a method for increasing the density of graphite saggars, primarily addressing the problems of low density and strength. The technical solution specifies that ammonium dihydrogen phosphate and cerium nitrate are deposited onto the graphite surface via hydrothermal precipitation to increase its roughness, thereby enhancing the strength of the formed graphite saggar body. Furthermore, reducing the use of binders can reduce the saggar's porosity. It should be noted that while surface modification of the graphite has a positive effect, the basic cerium phosphate on the surface will also dehydrate and escape from the saggar at high temperatures, leaving pores as gases escape, which in turn increases the graphite saggar's porosity. Furthermore, the technology also suggests that granulation and rapid drying can prevent agglomeration of mixed particles. However, rapid granulation and rapid drying results in rapid drying of the surface of the granulated spheres, while components such as the binder remain within the granules. This surface drying, in turn, hinders the volatilization and escape of the binder within the granules. This can also lead to the escape of the binder at higher heat treatment temperatures, leaving pores. Summary of the Invention

[0009] The purpose of the present invention is to address the above-mentioned deficiencies in the prior art and provide a high-performance monolithic graphite sagger and a method for preparing the same. The high-performance monolithic graphite sagger prepared by the present invention has high strength, good density and high degree of graphitization.

[0010] The preparation method of a high-performance integral graphite sagger of the present invention comprises the following specific steps:

[0011] S1. mixing flake graphite, pre-sintered material, mixed solution, amorphous alumina fine powder and carbon nanofiber to obtain a mixture;

[0012] S2, placing the mixture in a mold and holding it under pressure for a certain period of time, and then demoulding it to obtain a sagger green body;

[0013] S3, heat-treating the green sagger and then cooling it with the furnace to obtain a high-performance integral graphite sagger;

[0014] The pre-burned material is prepared by the following method: borax, carbon black, silicon powder and zirconium oxychloride are mixed and ball-milled to obtain a pre-mixed material, and then the pre-mixed material is placed in an inert gas atmosphere for heat treatment, cooled and then ground to obtain a pre-burned material;

[0015] The mixed liquid is prepared by mixing thermosetting phenolic resin, industrial alcohol and lanthanum nitrate.

[0016] Furthermore, the mass ratio of borax: carbon black: silicon powder: zirconium oxychloride is 100: (80-85): (15-25): (6-12).

[0017] Furthermore, during the preparation of the pre-sintered material, the premixed material is placed in an argon atmosphere furnace, kept warm at 1400-1420° C. for 3-5 hours, cooled with the furnace, and ground to a particle size of ≤45 μm to obtain the pre-sintered material.

[0018] Furthermore, the mass ratio of thermosetting phenolic resin: industrial alcohol: lanthanum nitrate is 100: (25-30): (0.6-0.8).

[0019] Furthermore, the mass ratio of flake graphite: pre-sintered material: mixed solution: amorphous alumina fine powder: carbon nanofiber is 100: (70-75): (8-10): (1.2-1.8): (2.6-3.3).

[0020] Furthermore, in step S2, the mixture is placed in a mold, maintained at a pressure of 5-8 MPa for 30-40 seconds, then increased to 20-30 MPa, maintained for 20-30 seconds, and then further increased to 120-140 MPa, maintained for 10-15 seconds, and demolded to obtain a sagger green body.

[0021] Furthermore, in step S3, the sagger green body is heat treated at 300-350° C. for 20-25 hours, then placed in a nitrogen atmosphere furnace at 1470-1530° C. for 8-10 hours, and cooled with the furnace to obtain a high-performance integral graphite sagger.

[0022] Furthermore, the Si content of the silicon powder is ≥99.5wt%; and\or

[0023] The C content of the flake graphite is ≥98wt%; the particle size of the flake graphite is 45μm~1.2mm, wherein the mass ratio of [45μm~80μm]:[0.1mm~0.5mm]:[0.8~1.2mm] is (30~35):(35~40):(25~30).

[0024] Furthermore, the amorphous aluminum oxide is amorphous, has a particle size of 5 to 12 μm, and an Al2O3 content of ≥99.9 wt%;

[0025] The carbon nanofiber has a length of 5 to 8 μm and a diameter of 25 to 40 nm.

[0026] A high-performance integral graphite sagger prepared by the above-mentioned preparation method.

[0027] The beneficial effects of the present invention are:

[0028] (1) The present invention uses carbon black as a carbon source, silicon powder as a silicon source, and zirconium oxychloride as a zirconium source. Under the conditions of a high-temperature liquid medium created by borax, a silicon carbide-zirconium boride non-oxide ceramic bond is formed in situ through argon protection, and then the bond is introduced as a whole into the graphite crucible ingredients, which is beneficial to the overall dispersion of the components and can improve the strength of the graphite crucible.

[0029] (2) The present invention adopts non-aqueous bonding (no water is introduced into the bonding system), which further avoids the escape of gas from the raw material components during high-temperature firing and leaves pores, thereby improving the density of the sagger.

[0030] (3) The present invention uses lanthanum nitrate as a catalyst and utilizes the ionic coordination of rare earth components and nitrate groups to promote the nucleophilic effect, which is beneficial to the graphitization of phenolic resin without damaging the mechanical strength of the graphite crucible.

[0031] (4) The present invention utilizes the amorphous properties of amorphous aluminum oxide to reduce the activation energy of the sintering reaction, thereby reducing the temperature of the heat treatment reaction, achieving low-temperature rapid sintering and saving energy.

[0032] (5) The present invention utilizes the grading adjustment of flake graphite and the introduction of carbon nanofibers to improve the interlocking and cross-linking of material components, further enhancing the bonding strength of the graphite crucible. In addition, the in-situ nitridation reaction of the bonding system forms aluminum nitride whiskers in the high-carbon system, thereby enhancing the oxide-non-oxide bonding and improving the mechanical strength and density of the crucible.

[0033] The high-performance integral graphite sagger prepared by the present invention has been tested:

[0034] Bulk density: 2.14~2.28g / cm 3 ;

[0035] Apparent porosity: 4.4-5.2%;

[0036] Flexural strength: 22.2~24.6MPa;

[0037] Thermal conductivity: 38.2~46.2W / (m·K). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a cross-sectional SEM image of the high-performance monolithic graphite sagger prepared in Example 1. DETAILED DESCRIPTION

[0039] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0040] Example 1

[0041] 1. A method for preparing a high-performance integral graphite sagger, characterized in that the specific steps are as follows:

[0042] 1) preparing borax:carbon black:silica powder:zirconium oxychloride in a mass ratio of 100:80:25:6, adding the mixture to a high-energy planetary ball mill and mixing for 60-90 minutes to obtain a premix;

[0043] 2) placing the premix in an argon atmosphere furnace, keeping the temperature at 1400° C. for 3 hours, cooling with the furnace, and grinding to a particle size of ≤45 μm to obtain a pre-sintered material;

[0044] 3) preparing a mixture of thermosetting phenolic resin, industrial alcohol, and lanthanum nitrate in a mass ratio of 100:25:0.8 and mixing for 3-5 minutes to obtain a mixed solution;

[0045] 4) adding the flake graphite: the pre-calcined material: the mixed solution: amorphous alumina fine powder: carbon nanofiber in a mass ratio of 100:75:8:1.8:3.3, adding the ingredients to a high-speed blender and mixing for 25-30 minutes to obtain a mixture;

[0046] 5) placing the mixture in a mold, maintaining the pressure at 5-8 MPa for 30-40 seconds, then increasing the pressure to 20 MPa, maintaining the pressure for 20 seconds, and then increasing the pressure to 140 MPa, maintaining the pressure for 15 seconds, and demolding to obtain a sagger green body;

[0047] 6) The sagger green body was heat treated at 300° C. for 20 h, then placed in a nitrogen atmosphere furnace at 1530° C. for 8 h, and cooled with the furnace to obtain a high-performance integral graphite sagger.

[0048] The Si content of the silicon powder is ≥99.5wt%.

[0049] The C content of the flake graphite is ≥98wt%; the particle size of the flake graphite is 45μm-1.2mm, wherein the mass ratio of [45μm-80μm]:[0.1mm-0.5mm]:[0.8-1.2mm] is 30:35:25.

[0050] The amorphous aluminum oxide is in an amorphous state, has a particle size of 5 to 12 μm, and has an Al2O3 content of ≥99.9 wt%.

[0051] The length of carbon nanofibers is 5 to 8 μm and the diameter is 25 to 40 nm.

[0052] Figure 1The cross-sectional SEM image of the high-performance integral graphite saggar prepared in Example 1 shows that the cross-section of the saggar sample is in a typical transgranular fracture state, indicating that the saggar sample has high mechanical strength; a clear graphitized layered structure can be observed in the fault, and velvety whisker protrusions can be seen in the matrix, indicating that the aggregate-matrix bond is tight and firm.

[0053] The high-performance integral graphite sagger prepared in this embodiment was tested:

[0054] Bulk density: 2.14g / cm 3 ;

[0055] Apparent porosity: 5.2%;

[0056] Flexural strength: 22.2MPa;

[0057] Thermal conductivity: 46.2W / (m·K).

[0058] Example 2

[0059] 1. A method for preparing a high-performance integral graphite sagger, characterized in that the specific steps are as follows:

[0060] 1) preparing borax:carbon black:silica powder:zirconium oxychloride in a mass ratio of 100:82:22:9, adding the mixture to a high-energy planetary ball mill and mixing for 60-90 minutes to obtain a premix;

[0061] 2) placing the premix in an argon atmosphere furnace, keeping the temperature at 1415° C. for 5 hours, cooling the furnace, and grinding the premix to a particle size of ≤45 μm to obtain a pre-sintered material;

[0062] 3) preparing a thermosetting phenolic resin, industrial alcohol, and lanthanum nitrate in a mass ratio of 100:27:0.7 and mixing for 3-5 minutes to obtain a mixed solution;

[0063] 4) adding the flake graphite: the pre-calcined material: the mixed solution: amorphous alumina fine powder: carbon nanofiber in a mass ratio of 100:73:9:1.6:3.1, adding the ingredients to a high-speed blender and mixing for 25-30 minutes to obtain a mixture;

[0064] 5) placing the mixture in a mold, maintaining the pressure at 5-8 MPa for 30-40 seconds, then increasing the pressure to 25 MPa, maintaining the pressure for 30 seconds, and then increasing the pressure to 130 MPa, maintaining the pressure for 12 seconds, and demolding to obtain a sagger green body;

[0065] 6) The sagger green body was heat treated at 320° C. for 24 h, then placed in a nitrogen atmosphere furnace and kept at 1480° C. for 9 h, and cooled with the furnace to obtain a high-performance integral graphite sagger.

[0066] The Si content of the silicon powder is ≥99.5wt%.

[0067] The C content of the flake graphite is ≥98wt%; the particle size of the flake graphite is 45μm to 1.2mm, wherein the mass ratio of [45μm to 80μm]:[0.1mm to 0.5mm]:[0.8 to 1.2mm] is 33:38:26.

[0068] The amorphous aluminum oxide is in an amorphous state, has a particle size of 5 to 12 μm, and has an Al2O3 content of ≥99.9 wt%.

[0069] The length of carbon nanofibers is 5 to 8 μm and the diameter is 25 to 40 nm.

[0070] The high-performance integral graphite sagger prepared in this embodiment was tested:

[0071] Bulk density: 2.21g / cm 3 ;

[0072] Apparent porosity: 4.6%;

[0073] Flexural strength: 23.4MPa;

[0074] Thermal conductivity: 41.5W / (m·K).

[0075] Example 3

[0076] 1. A method for preparing a high-performance integral graphite sagger, characterized in that the specific steps are as follows:

[0077] 1) preparing borax:carbon black:silica powder:zirconium oxychloride in a mass ratio of 100:85:15:12, adding the mixture to a high-energy planetary ball mill and mixing for 60-90 minutes to obtain a premix;

[0078] 2) placing the premix in an argon atmosphere furnace, keeping the temperature at 1420° C. for 4 hours, cooling the furnace, and grinding the premix to a particle size of ≤45 μm to obtain a pre-sintered material;

[0079] 3) preparing a mixture of thermosetting phenolic resin, industrial alcohol, and lanthanum nitrate in a mass ratio of 100:30:0.6 and mixing for 3-5 minutes to obtain a mixed solution;

[0080] 4) adding the flake graphite: the pre-calcined material: the mixed solution: amorphous alumina fine powder: carbon nanofiber in a mass ratio of 100:70:10:1.2:2.6 to a high-speed blender and mixing for 25-30 minutes to obtain a mixture;

[0081] 5) placing the mixture in a mold, maintaining the pressure at 5-8 MPa for 30-40 seconds, then increasing the pressure to 30 MPa, maintaining the pressure for 30 seconds, and then increasing the pressure to 120 MPa, maintaining the pressure for 10 seconds, and demolding to obtain a sagger green body;

[0082] 6) The sagger green body was heat treated at 350° C. for 25 h, then placed in a nitrogen atmosphere furnace and kept at 1470° C. for 10 h, and cooled with the furnace to obtain a high-performance integral graphite sagger.

[0083] The Si content of the silicon powder is ≥99.5wt%.

[0084] The C content of the flake graphite is ≥98wt%; the particle size of the flake graphite is 45μm to 1.2mm, wherein the mass ratio of [45μm to 80μm]:[0.1mm to 0.5mm]:[0.8 to 1.2mm] is 35:40:30.

[0085] The amorphous aluminum oxide is in an amorphous state, has a particle size of 5 to 12 μm, and has an Al2O3 content of ≥99.9 wt%.

[0086] The length of carbon nanofibers is 5 to 8 μm and the diameter is 25 to 40 nm.

[0087] The high-performance integral graphite sagger prepared in this embodiment was tested:

[0088] Bulk density: 2.28g / cm 3 ;

[0089] Apparent porosity: 4.4%;

[0090] Flexural strength: 24.6MPa;

[0091] Thermal conductivity: 38.2W / (m·K).

[0092] Comparative Example 1

[0093] 1. A method for preparing a monolithic graphite sagger, characterized in that the specific steps are as follows:

[0094] 1) preparing borax, carbon black, silicon powder, and zirconium oxychloride in a mass ratio of 60:82:22:9, adding the mixture to a high-energy planetary ball mill and mixing for 60 to 90 minutes to obtain a premix;

[0095] 2) placing the premix in an argon atmosphere furnace, keeping the temperature at 1415° C. for 5 hours, cooling the furnace, and grinding the premix to a particle size of ≤45 μm to obtain a pre-sintered material;

[0096] 3) preparing a thermosetting phenolic resin, industrial alcohol, and lanthanum nitrate in a mass ratio of 100:27:0.7, and mixing for 3-5 minutes to obtain a mixed solution;

[0097] 4) adding the flake graphite: the pre-calcined material: the mixed solution: amorphous alumina fine powder: carbon nanofiber in a mass ratio of 100:73:9:1.6:3.1, adding the ingredients to a high-speed blender and mixing for 25-30 minutes to obtain a mixture;

[0098] 5) placing the mixture in a mold, pressing and molding at 130 MPa, and demolding to obtain a sagger green body;

[0099] 6) The sagger green body was heat treated at 320° C. for 24 h, then placed in a nitrogen atmosphere furnace and kept at 1480° C. for 9 h, and cooled with the furnace to obtain a high-performance integral graphite sagger.

[0100] The Si content of the silicon powder is ≥99.5wt%.

[0101] The C content of the flake graphite is ≥98wt%; the particle size of the flake graphite is 45μm to 1.2mm, wherein the mass ratio of [45μm to 80μm]:[0.1mm to 0.5mm]:[0.8 to 1.2mm] is 33:38:26.

[0102] The amorphous aluminum oxide is in an amorphous state, has a particle size of 5 to 12 μm, and has an Al2O3 content of ≥99.9 wt%.

[0103] The length of carbon nanofibers is 5 to 8 μm and the diameter is 25 to 40 nm.

[0104] The high-performance integral graphite sagger prepared in this comparative example was tested:

[0105] Bulk density: 1.86g / cm 3 ;

[0106] Apparent porosity: 10.4%;

[0107] Flexural strength: 11.7MPa;

[0108] Thermal conductivity: 20.3W / (m·K).

[0109] Compared with Example 2, it can be seen that reducing the amount of borax added leads to a decrease in the degree of bonding between the pre-fired material and the non-oxide ceramics in the sagger due to the decrease in the liquid phase amount and the diffusion mass transfer rate during the high-temperature sintering process. At the same time, due to the change in the pressing molding process, the degree of bonding between the sagger components is reduced under the action of the elastic aftereffect, thereby increasing the porosity of the sagger and weakening the mechanical strength and thermal conductivity of the sagger.

[0110] Any matters not mentioned above shall be subject to the existing technology.

[0111] Although some specific embodiments of the present invention have been described in detail through examples, those skilled in the art should understand that the above examples are for illustration only and are not intended to limit the scope of the present invention. Those skilled in the art of the present invention may make various modifications or additions to the described specific embodiments or replace them in similar ways, but they will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent replacements, improvements, etc. made to the above embodiments based on the technical essence of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high-performance integral graphite sagger, characterized in that: The specific steps are as follows: S1. mixing flake graphite, pre-sintered material, mixed solution, amorphous alumina fine powder and carbon nanofiber to obtain a mixture; S2, placing the mixture in a mold and holding it under pressure for a certain period of time, and then demoulding it to obtain a sagger green body; S3, heat-treating the green sagger and then cooling it with the furnace to obtain a high-performance integral graphite sagger; The pre-burned material is prepared by the following method: borax, carbon black, silicon powder and zirconium oxychloride are mixed and ball-milled to obtain a pre-mixed material, and then the pre-mixed material is placed in an inert gas atmosphere for heat treatment, cooled and then ground to obtain a pre-burned material; The mixed liquid is prepared by mixing thermosetting phenolic resin, industrial alcohol and lanthanum nitrate; The mass ratio of borax: carbon black: silica fume: zirconium oxychloride is 100: (80-85): (15-25): (6-12); During the preparation of the pre-sintered material, the premixed material is placed in an argon atmosphere furnace, kept at 1400-1420° C. for 3-5 hours, cooled with the furnace, and ground to a particle size of ≤45 μm to obtain the pre-sintered material; The mass ratio of flake graphite: pre-calcined material: mixed solution: amorphous alumina fine powder: carbon nanofiber is 100: (70-75): (8-10): (1.2-1.8): (2.6-3.3); The particle size of the flake graphite is 45 μm to 1.2 mm, wherein the mass ratio of [45 μm to 80 μm]: [0.1 mm to 0.5 mm]: [0.8 mm to 1.2 mm] is (30 to 35): (35 to 40): (25 to 30); The amorphous aluminum oxide is in a non-crystalline state.

2. The method for preparing a high-performance integral graphite sagger according to claim 1, wherein: The mass ratio of thermosetting phenolic resin: industrial alcohol: lanthanum nitrate is 100: (25~30): (0.6~0.8).

3. The method for preparing a high-performance integral graphite sagger according to claim 1, wherein: In step S2, the mixture is placed in a mold, maintained at a pressure of 5-8 MPa for 30-40 seconds, then increased to 20-30 MPa, maintained for 20-30 seconds, and then further increased to 120-140 MPa, maintained for 10-15 seconds, and demolded to obtain a sagger green body.

4. A method for preparing a high-performance integral graphite sagger according to any one of claims 1 to 3, characterized in that: In step S3, the sagger green body is heat treated at 300-350° C. for 20-25 hours, then placed in a nitrogen atmosphere furnace at 1470-1530° C. for 8-10 hours, and cooled with the furnace to obtain a high-performance integral graphite sagger.

5. The method for preparing a high-performance integral graphite crucible according to any one of claims 1 to 3, characterized in that: The Si content of the silicon powder is ≥99.5wt%; and\or The carbon content of the flake graphite is ≥98 wt %.

6. A method for preparing a high-performance integral graphite crucible according to any one of claims 1 to 3, characterized in that: The particle size of amorphous alumina is 5~12μm, and the Al2O3 content is ≥99.9wt%; The carbon nanofibers have a length of 5-8 μm and a diameter of 25-40 nm.

7. A high-performance monolithic graphite sagger prepared by the preparation method according to any one of claims 1 to 6.

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