Preparation method of porous graphite, porous graphite and application thereof

Abstract

The present invention discloses a method for preparing porous graphite, porous graphite, and applications thereof. A method for preparing porous graphite comprises the following steps: S1, mixing graphite, copper powder, and a pore-forming agent, or mixing copper-coated graphite and a pore-forming agent to obtain a mixed powder; S2, pressing the mixed powder into a blank; S3, placing the blank in a roasting furnace and roasting it at 1100-1300°C to obtain porous graphite. In this application, the porosity and pore size of the porous graphite can be controlled by adjusting the proportion of the pore-forming agent. Fewer temperature nodes need to be controlled, and the preparation method is convenient and simple. The prepared porous graphite not only has a controllable porosity and a uniform pore size distribution, but also improves the tensile strength of the porous graphite, thereby ensuring the stability of the porous bearing during operation.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon materials, and in particular to a preparation method of porous graphite, porous graphite and applications thereof. Background Art

[0002] In aerostatic bearings, the air supply and throttle are used in conjunction, and throttle design is a key design step. Common throttle types include hole-type, slot-type, and porous-type. Compared to hole-type and slot-type throttles, porous bearings produce a more uniform distribution of air film pressure, leading to their increasing use in precision machinery. The properties of porous materials have a significant impact on the performance and lifespan of porous bearings. The porous materials used to manufacture bearings primarily include metallic, ceramic, and graphite porous materials. From a machining perspective, metallic porous materials are easy to machine, but due to the metal's good plasticity, machining can easily clog the pores of the surface material. Ceramic porous materials can shed particles during use, potentially scratching the shaft surface or clogging the bearing's air gap. Graphite porous materials offer excellent machining, lubrication, and operating properties.

[0003] Porous graphite possesses the self-lubricating properties of graphite, reducing friction between the spindle and bearings caused by unexpected contact. Currently, porous graphite is typically prepared by mixing graphite with a binder. Low-viscosity asphalt is then pressed into the mixture using cold isostatic pressing to form a compact. The resulting mixture is then calcined, and the porosity and pore size of the porous graphite material are controlled through asphalt infiltration and liquid-phase carbonization.

[0004] During the research process, the applicant found that the above preparation method requires controlling many temperature nodes, and needs to consider the influence of the softening temperature and carbonization temperature of asphalt on the pressing step, which makes the process complicated, and the asphalt infiltration-liquid phase carbonization method is difficult to control the uniformity of the pore distribution of porous graphite and the size of the pores. Summary of the Invention

[0005] In order to easily control the uniformity of pore distribution and the size of pores in porous graphite, the present application provides a method for preparing porous graphite, porous graphite and applications thereof.

[0006] In a first aspect, the present application provides a method for preparing porous graphite, which is implemented using the following technical solution:

[0007] A method for preparing porous graphite comprises the following steps:

[0008] S1. Mixing graphite, copper powder and a pore-forming agent or mixing copper-coated graphite and a pore-forming agent to obtain a mixed powder; in terms of volume percentage, the content of copper powder in the mixed powder is 5-20%, the content of the pore-forming agent is 1%-6%, and the balance is graphite; or the content of the pore-forming agent in the mixed powder is 1%-6%, and the balance is copper-coated graphite;

[0009] S2, pressing the mixed powder into a blank;

[0010] S3. Place the graphite in a calcination furnace and calcine at 1100-1300°C to obtain porous graphite.

[0011] The raw materials of the present application, graphite and copper powder or copper-coated graphite, and the pore-forming agent themselves have a certain shape. When stacked, the space cannot be completely occupied, resulting in partial pores. At the same time, the porosity of the porous graphite is increased by adding the pore-forming agent during the preparation process of the present application. This is because the particles of the pore-forming agent itself occupy a part of the space before sintering. During the roasting process, the pore-forming agent is decomposed by high temperature, which will produce gaseous substances and discharge. After sintering is completed, the volume of the system will become smaller, resulting in partial pores, thereby increasing the porosity of the porous graphite.

[0012] Because the gas generated by the pore-forming agent used in this application needs to be exhausted to the outside of the material, the pores generated during the sintering process are mostly open pores, rather than blind holes or internal voids. This increases the effective porosity of the porous graphite and allows it to flow from one surface of the material to another, significantly improving the throttling effect of the porous bearing. The porous graphite has a large number of pores distributed on its surface and inside, and it has both good processing properties and excellent lubrication and running properties. When used in porous bearings, the air film pressure distribution generated by porous graphite is more uniform than that of hole-type bearings and slit-type throttles. At the same time, because porous graphite has a larger flow resistance and a smaller air volume, it is less likely to cause air hammer instability, thereby improving the performance and life of the porous bearing.

[0013] This application controls the porosity and pore size of porous graphite by adjusting the proportion of a pore-forming agent, thereby controlling the throttling ratio of the porous bearing. The addition of a pore-forming agent replaces the asphalt infiltration-liquid phase carbonization method. This application requires fewer temperature nodes to be controlled, resulting in a convenient and simple preparation method. The application controls the volume percentage of the pore-forming agent to 1% to 6%, increasing the porosity of the porous graphite while maintaining its tensile strength and self-lubricating properties.

[0014] In the preparation method using graphite, copper powder, and a pore-forming agent, copper has a melting point of 800°C and can bond graphite without excessively high temperatures. The addition of copper powder, a non-ferrous metal, can, to a certain extent, overcome the hard and brittle defects of graphite, giving the porous graphite better tensile strength, thereby improving the operational stability of the porous bearing. Furthermore, copper powder has high electrical and thermal conductivity, which can give the porous graphite better heat dissipation capabilities and reduce the temperature rise of the bearing spindle. The present application further controls the volume percentage of copper powder to 5-20%, so that the prepared porous graphite has excellent tensile strength without reducing the porosity.

[0015] In the preparation method using copper-coated graphite and pore-forming agent, copper-coated graphite is a graphite powder surface evenly coated with a layer of copper to form a "core-shell" structure, which increases the contact area and bonding strength between copper and graphite, thereby improving the uniformity and stability of the bonding between graphite particles, and further improving the tensile strength and pore distribution uniformity of porous graphite.

[0016] Preferably, by volume percentage, the content of copper powder in the mixed powder is 12%, the content of pore-forming agent is 3%, and the content of graphite is 85%; or the content of pore-forming agent in the mixed powder is 3% and the content of copper-coated graphite is 97%.

[0017] Preferably, the particle size of the graphite is 800-1600 mesh, and the particle size of the copper powder is 2000-3000 mesh.

[0018] More preferably, the particle size of the graphite is 1200 mesh, and the particle size of the copper powder is 2500 mesh.

[0019] The present invention controls the particle size of graphite to 800-1600 mesh and the particle size of copper powder to 2000-3000 mesh, thereby increasing the pores between graphite and copper powder particles, thereby increasing the porosity of porous graphite; at the same time, it can increase the number of bonding points between graphite particles, thereby increasing the tensile strength of porous graphite.

[0020] Preferably, the particle size of the copper-clad graphite is 200-800 mesh.

[0021] More preferably, the particle size of the copper-clad graphite is 800 mesh.

[0022] Preferably, the copper content in the copper-clad graphite is 50-70 wt%.

[0023] More preferably, the copper content in the copper-clad graphite is 60 wt%.

[0024] Preferably, the pore-forming agent is selected from a combination of one or more of NaHCO3, KHCO3, NH4HCO3, Ca(HCO3)2, and Ba(HCO3)2; more preferably, the pore-forming agent is NaHCO3 or KHCO3.

[0025] The applicant has found that when the pore-forming agent is NaHCO 3 , the pore quality of the porous graphite is better.

[0026] In a second aspect, the present application provides a porous graphite, which is implemented using the following technical solution:

[0027] A porous graphite prepared by the above preparation method.

[0028] Preferably, the porous graphite has a pore size distribution of 1.2 to 1.7 μm and a porosity of 24% to 28%.

[0029] Preferably, the tensile strength of the porous graphite is 80-90 MPa.

[0030] In a third aspect, the present application provides an application of porous graphite, which is achieved by the following technical solution:

[0031] The invention discloses an application of porous graphite, wherein the porous graphite is applied to a gas static pressure bearing or a static pressure air floating guide rail.

[0032] In summary, this application has the following beneficial effects:

[0033] 1. The present invention can control the porosity and pore size of porous graphite by adjusting the proportion of the pore-forming agent, requires fewer temperature nodes to be controlled, and the preparation method is convenient and simple.

[0034] 2. In the preparation method of the present application using graphite, copper powder and a pore-forming agent, the copper powder is used as a binder to improve the tensile properties of the graphite material and ensure the stability of the porous bearing during operation.

[0035] 3. In the preparation method of copper-coated graphite and pore-forming agent adopted in this application, copper-coated graphite is a graphite powder surface uniformly coated with a layer of copper to form a "core-shell" structure, which increases the contact area and bonding strength between copper and graphite, thereby improving the uniformity and stability of the bonding between graphite particles, and further improving the tensile strength and pore distribution uniformity of porous graphite. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a SEM image of the porous graphite prepared in Example 14 of the present application. DETAILED DESCRIPTION

[0037] The present application is further described in detail below with reference to the embodiments.

[0038] Example

[0039] Examples 1-13 provide a method for preparing porous graphite, which will be described below using Example 1 as an example.

[0040] Example 1 provides a method for preparing porous graphite, the steps of which are as follows:

[0041] S1. First, use a particle size analyzer to obtain graphite and copper powder with particle sizes of 800 mesh and 2000 mesh, respectively, and then mix the graphite, copper powder and NaHCO3 according to the contents in Table 1 to obtain a mixed powder;

[0042] S2, using isostatic pressing technology to press the mixed powder into a blank;

[0043] S3. Place the pressed blank in a roasting furnace, control the heating rate to be 5℃ / min from room temperature to 600℃, keep it at 600℃ for 30min, then continue to heat it to 1100℃ at 3℃ / min, and sinter it at 1100℃ for 120min to obtain porous graphite.

[0044] Table 1 Contents of graphite, copper powder and NaHCO3 in the mixed powders of Examples 1-7

[0045]

[0046] Among them, graphite was purchased from Shenzhen Hanhui Graphite Co., Ltd.

[0047] The only difference between Examples 2-7 and Example 1 is that the contents of graphite, copper powder and pore-forming agent are different, as shown in Table 1.

[0048] The only difference between Examples 8-11 and Example 7 is that the particle sizes of graphite and copper powder obtained by the particle size analyzer are different, as shown in Table 2.

[0049] Table 2 Particle size of graphite and copper powder in Examples 7-11

[0050]

[0051] Example 12 is different from Example 11 only in that the heating rate is controlled to be 5°C / min from room temperature to 600°C, kept at 600°C for 30 minutes, then continued to be heated to 1300°C at 3°C / min, and sintered at 1300°C for 120 minutes.

[0052] Example 13 is different from Example 11 only in that an equal volume of NaHCO3 is replaced by NH4HCO3.

[0053] Example 14 provides a method for preparing porous graphite, the steps of which are as follows:

[0054] S1. Mix copper-coated graphite and NaHCO3 in a volume percentage of 97% and 3% respectively to obtain a mixed powder;

[0055] S2, using isostatic pressing technology to press the mixed powder into a blank;

[0056] S3. Place the pressed blank in a roasting furnace, control the heating rate to be 5℃ / min from room temperature to 600℃, keep it at 600℃ for 30min, then continue to heat it to 1100℃ at 3℃ / min, and sinter it at 1100℃ for 120min to obtain porous graphite.

[0057] Among them, copper-clad graphite with a particle size of 800 mesh and a copper content of 60 wt%, brand Cu / C6040, was purchased from Nangong Jinnuo Welding Materials Co., Ltd.

[0058] The only difference between Examples 15-16 and Example 14 is that the contents of copper-coated graphite and NaHCO3 are different, as shown in Table 3.

[0059] Table 3 Content of copper-coated graphite and NaHCO3 in Examples 14-16

[0060]

[0061] The only difference between Examples 17-19 and Example 14 is that the contents and parameters of copper-coated graphite and NaHCO3 are different, as shown in Table 4.

[0062] Table 4 Parameters of copper-clad graphite in Examples 14, 17-19

[0063]

[0064] Comparative Example

[0065] Comparative Example 1 is different from Example 1 only in that no NaHCO3 is added.

[0066] Comparative Example 2 is different from Example 1 only in that the copper powder is replaced by silver powder in equal volume.

[0067] Performance testing

[0068] The following performance tests were performed on the porous graphites prepared in Examples 1-18 and Comparative Examples 1-2 of the present application.

[0069] 1. Pore size distribution: The pore size distribution of porous graphite was tested by the bubble method. The test results are shown in Table 5.

[0070] 2. Porosity: The porosity of porous graphite was tested by weighing method. The test results are shown in Table 5.

[0071] 3. Tensile strength: GB / T 8721-2009 was used to test the tensile strength of porous graphite. The test results are shown in Table 5.

[0072] Table 5 Performance test results

[0073]

[0074]

[0075] The following describes this application in detail with respect to the test data in Table 5.

[0076] The test data of Example 1 and Comparative Example 1 show that the addition of the pore-forming agent increases the porosity of the porous graphite. The test data of Example 1 and Comparative Example 2 show that copper powder can increase the tensile strength of the porous graphite.

[0077] From the test data of Examples 1, 3, and 5 or Examples 2, 4, and 6, it can be seen that when the copper powder content is constant, the more pore-forming agent there is, the greater the porosity of the porous graphite, but the tensile strength of the porous graphite will be appropriately reduced; from the test data of Examples 1 and 2 or Examples 3 and 4 or Examples 5, 6, and 7, it can be seen that when the pore-forming agent content is constant, the more copper powder there is, the higher the tensile strength of the porous graphite, but the porosity of the porous graphite will be lower.

[0078] The test data from Examples 7, 8, and 9 show that larger graphite particle sizes increase the porosity of the porous graphite, but significantly reduce the tensile strength of the porous graphite. The test data from Examples 8, 10, and 11 show that larger copper powder particle sizes slightly increase the porosity of the porous graphite, but reduce the tensile strength of the porous graphite.

[0079] From the test data of Examples 11 and 13, it can be seen that compared with NH4HCO3, NaHCO3 can not only improve the tensile strength of porous graphite, but also make the pore distribution of porous graphite more uniform.

[0080] The test data from Examples 11 and 14 show that the porous graphite prepared using copper-coated graphite and a pore-forming agent exhibits higher tensile strength and more uniform pore distribution. This is because copper-coated graphite is a graphite powder uniformly coated with a layer of copper, forming a "core-shell" structure. This increases the contact area and bonding strength between the copper and graphite, thereby improving the uniformity and stability of the bond between the graphite particles.

[0081] From the test data of Examples 14, 15, and 16, it can be seen that the more copper-coated graphite there is, the higher the tensile strength of the porous graphite is, but the porosity of the porous graphite is reduced.

[0082] From the test data of Examples 14 and 17, it can be seen that when the copper content in the copper-clad graphite is controlled to be constant, the larger the particle size of the copper-clad graphite, the greater the porosity of the porous graphite, but the tensile strength of the porous graphite remains basically unchanged.

[0083] From the test data of Examples 14, 18, and 19, it can be seen that when the particle size of the copper-clad graphite is controlled to remain unchanged, the higher the copper content in the copper-clad graphite, the greater the tensile strength of the porous graphite, but the porosity of the porous graphite remains basically unchanged.

[0084] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing porous graphite, characterized in that: The steps include: S1. Mixing graphite, copper powder and a pore-forming agent or mixing copper-coated graphite and a pore-forming agent to obtain a mixed powder; in terms of volume percentage, the content of copper powder in the mixed powder is 5% to 20%, the content of the pore-forming agent is 1% to 6%, and the balance is graphite; or the content of the pore-forming agent in the mixed powder is 1% to 6%, and the balance is copper-coated graphite; S2, pressing the mixed powder into a blank; S3, placing in a calcination furnace at 1100-1300°C to obtain porous graphite; In terms of volume percentage, the content of copper powder in the mixed powder is 12%, the content of pore-forming agent is 3%, and the content of graphite is 85%; or the content of pore-forming agent in the mixed powder is 3% and the content of copper-coated graphite is 97%; The particle size of the graphite is 800-1600 mesh, and the particle size of the copper powder is 2000-3000 mesh; The particle size of the copper-clad graphite is 200-800 mesh; The copper content in the copper-clad graphite is 50-70wt%; The pore-forming agent is selected from one or more combinations of NaHCO3, KHCO3, NH4HCO3, Ca(HCO3)2, and Ba(HCO3)2.

2. A porous graphite prepared by the preparation method according to claim 1.

3. The porous graphite according to claim 2, characterized in that: The porous graphite has a pore size distribution of 1.2 to 1.7 μm and a porosity of 24% to 28%.

4. The porous graphite according to claim 2, characterized in that: The tensile strength of the porous graphite is 80-90 MPa.

5. An application of the porous graphite according to claim 2, characterized in that: The porous graphite is applied to gas static pressure bearings or static pressure air floating guide rails.

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