A porous graphite material with adjustable porosity and its preparation method

Abstract

The present invention provides a porous graphite material with adjustable pores and a preparation method thereof, belonging to the technical field of porous graphite materials; the preparation method includes steps of pore-forming agent treatment, mixing, molding, roasting, pore formation and graphitization; the pore-forming agent treatment step is to mix metal powder and graphite powder, then put them into a ball mill, carry out ball milling treatment under an argon atmosphere, then evacuate, raise the temperature to 400 - 900 °C and treat for 0.5 - 5.0 h, and remove excess graphite powder by vibrating screening to obtain pore-forming agent powder; the porous graphite material prepared by the present invention has adjustable porosity and pore size, high strength and excellent stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of porous graphite materials, and particularly relates to a porous graphite material with adjustable pores and a preparation method thereof. Background Art

[0002] In recent years, with the development of new energy, environmental protection, and high-efficiency energy storage technologies, the demand for high-performance porous materials has been increasing day by day; due to their unique physical and chemical properties, porous materials have shown broad application prospects in the fields of catalysis, adsorption, energy storage, filtration, etc.

[0003] Porous graphite materials are a type of porous materials with a carbon element skeleton and different pore diameters and porosities; porous graphite materials have excellent properties such as a large specific surface area, high-temperature stability, and high corrosion resistance, and are widely used in important fields such as semiconductors, aerospace, new energy, and the nuclear industry.

[0004] The large specific surface area of porous graphite materials enables them to be used in the field of sewage treatment to adsorb heavy metal ions, organic pollutants, etc. in water, providing strong support for environmental protection; their excellent high-temperature stability enables them to play an important role in electronic devices, industrial fields, etc., effectively withstanding high temperatures and better ensuring the stable operation of equipment; their high corrosion resistance makes them irreplaceable in strongly corrosive environments.

[0005] Currently, the pore-forming agent method is used to prepare porous graphite materials. The production process mainly includes steps such as raw material mixing, molding, roasting, and graphitization. During the high-temperature roasting process, the pore-forming agent will decompose and volatilize, leaving pores inside the green body, thereby obtaining porous graphite materials; porous graphite materials with different porosities, pore sizes, and pore size distributions can be prepared by adjusting parameters such as the type, particle size, and addition amount of the pore-forming agent, and they have the advantage of low cost in terms of raw material composition and equipment.

[0006] The types of pore-forming agents in the prior art include organic pore-forming agents and inorganic pore-forming agents;

[0007] Organic pore-forming agents mainly include starch, cellulose, polyvinyl alcohol, plastic particles, synthetic resins, etc. They have a wide source and relatively low price. However, a large amount of gas will be generated during the decomposition of organic pore-forming agents, resulting in unstable pore structures, problems such as pore collapse and poor connectivity, thereby affecting the strength performance of porous graphite materials;

[0008] Inorganic pore-forming agents mainly include various salts, metal oxides, etc. Inorganic pore-forming agents have relatively stable properties and are conducive to uniform mixing with other components. However, some impurities will remain after roasting of inorganic pore-forming agents and are difficult to remove completely, ultimately affecting the strength and other properties of porous graphite materials as well.

[0009] As can be seen from the above, on the one hand, regardless of the type of pore former, the pores are generated during the roasting process, and it is difficult to control their shape and size. The pore size distribution is wide, and the skeleton structure formed by the aggregate is easily damaged by the pore former, resulting in low strength of the graphite material. On the other hand, a series of changes occur in the aggregate and binder components during the roasting process, which also affect the pore shape and pore size distribution, making it difficult to customize the pore specifications.

[0010] CN117700254A discloses a preparation method and system for three-dimensional reticulated through-hole graphite. Specifically, a three-dimensional reticulated metal skeleton template is first prepared, and then the aggregate and binder are kneaded and filled into the reticulated metal skeleton and pressed into shape to obtain a green graphite product. The green graphite product is subjected to electrolytic treatment to remove the pore template formed by the reticulated metal skeleton, and then through roasting treatment and graphitization treatment, a graphite product is obtained.

[0011] This patent mainly produces three-dimensional reticulated through-hole graphite. During the preparation process, the size of the reticulated metal skeleton is large, and the contact area with the aggregate and binder is small. This ensures that during the subsequent electrolysis process, it can fully contact the electrolyte and effectively remove the three-dimensional reticulated metal skeleton, so that the graphite product has good and large-size reticulated through-holes. However, limited by the ductility of the metal, the diameter of the fabricated metal skeleton is large, and the corresponding pore diameter of the prepared graphite product is limited. When the aggregate and binder fill the reticulated metal skeleton, the shapes of other pores generated by the accumulation are random and cannot be finely regulated.

[0012] In order to regulate the pores, researchers found that metal powder can be used as a pore former. However, when using metal powder as a pore former, during the mixing process, the contact area with the aggregate and binder is large, and the contact area between the pore former and the electrolyte during electrolysis is small, making it difficult to ensure the efficient removal of the pore former during the electrolysis process, which in turn affects the porosity and pore size. Moreover, when using metal powder as a pore former, the strength of the prepared graphite material is relatively low.

[0013] Therefore, developing a porous graphite material with adjustable pores and its preparation method, adopting the pore former method to control specific porosity and pore size, and making the prepared porous graphite material have high strength and high consistency, is an urgent problem to be solved in the existing technology. Summary of the Invention

[0014] To solve the existing technical problems, the present invention provides a porous graphite material with adjustable pores and its preparation method. By adopting the metal pore former method, specific porosity and pore size can be controlled, and the porous graphite material prepared thereby has high strength and excellent stability.

[0015] In view of the above technical problems, the present invention adopts the following technical solutions:

[0016] A preparation method of a porous graphite material with adjustable pores, including steps of pore-forming agent treatment, mixing, forming, roasting, pore-forming, and graphitization. The specific operations are as follows:

[0017] 1. Pore-forming agent treatment

[0018] Mix the metal powder and graphite powder, then put them into a ball mill and conduct ball milling treatment under an argon atmosphere. The ball milling time is 15 - 60 min. After the ball milling is completed, evacuate to -0.10 to -0.20 MPa, raise the temperature to 400 - 900 °C, and keep it warm for 0.5 - 5.0 h. After the heat preservation treatment is completed, cool it, and remove the excess graphite powder by vibrating screening to obtain the pore-forming agent powder;

[0019] The volume ratio of the metal powder to the graphite powder is 1:1 - 3;

[0020] The metal powder is one or more of iron powder, nickel powder, copper powder, and aluminum powder, and the particle size of the metal powder is 10 - 100 μm;

[0021] The particle size of the graphite powder is 1 - 100 μm.

[0022] 2. Mixing

[0023] Put the pitch, aggregate, and pore-forming agent powder into a kneading device, heat it to the melting state of the pitch, and mix evenly to obtain the mixture;

[0024] The softening point of the pitch is 70 - 100 °C, and the particle size is 10 - 100 μm;

[0025] The volume ratio of the aggregate, pitch, and pore-forming agent powder is 10:2 - 5:2.0 - 4.5;

[0026] The aggregate is one or more of artificial graphite, pitch coke, carbon black, and natural graphite, and the particle size of the aggregate is 10 - 100 μm.

[0027] 3. Forming

[0028] Perform dry pressing, hot pressing, or isostatic pressing on the mixture, and the forming pressure is 20 - 200 MPa to obtain the green body.

[0029] 4. Roasting

[0030] Place the green body in a roasting furnace for roasting. The roasting atmosphere is argon, the roasting temperature is 600 - 1200 °C, the heating rate is 6 - 12 °C / min, the roasting time is 15 - 22 h. After the roasting is completed, cool it to room temperature to obtain the roasted product.

[0031] 5. Pore-forming

[0032] Connect the calcined product to the positive electrode of the power supply and the carbon rod to the negative electrode of the power supply. Immerse the positive and negative electrodes completely into the mixed solution of the electrolyte and the additive. Apply current to the DC power supply and control the voltage of the DC power supply to be 2.0 - 10.0 V until no metal is deposited on the negative electrode, thus obtaining the pore-forming product.

[0033] The mass ratio of the electrolyte to the additive is 100:0.5 - 3.0.

[0034] The electrolyte is one of ferrous sulfate solution, sodium nitrate solution or the metal salt solution of the metal used, and the mass concentration of the electrolyte is 10 - 65%.

[0035] The additive is one of polyethylene glycol, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate.

[0036] 6. Graphitization

[0037] Put the pore-forming product into a graphitization furnace after drying, and conduct graphitization treatment under an argon atmosphere. The graphitization temperature is 2400 - 2900 °C, and the graphitization time is 8 - 20 h. Wait for it to naturally return to room temperature to obtain the porous graphite material.

[0038] A porous graphite material with adjustable pores is prepared by the aforementioned preparation method.

[0039] In the present invention, pitch coke, petroleum coke, artificial graphite powder, etc. are used as aggregates, pitch is used as a binder, and treated metal powder is used as a pore-forming agent. The porous graphite matrix raw material is prepared by mixing in a certain proportion, and then through processes of mixing, molding, roasting, pore-forming, and graphitization, a porous graphite product is obtained. The treated metal powder exists stably as a pore-forming agent powder, which can be completely fixed and retained in the green body during the roasting process, and its volume, shape, and particle size will not change. The pore-forming agent powder can have a good contact surface with the aggregate and the binder, ensuring a good current path during subsequent electrolysis and improving the electrolysis efficiency. The pore size, shape, and size of the pores formed after the removal of the pore-forming agent are consistent with the particle size of the pore-forming agent, forming a pore structure with a specific porosity and pore size. That is, the size and shape of the pores of the final product can be controlled by adjusting the particle size of the metal powder, avoiding the change of the pore structure caused by the drastic temperature change during the roasting process. During the electrolytic pore-forming process, the additive improves the wettability between the graphite and the electrolyte, ensuring the high efficiency and complete removal of the subsequent electrolytic removal of the pore-forming agent. Finally, while the porosity and pore size of the porous graphite material are adjustable, the strength performance of the porous graphite material is improved.

[0040] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0041] The method for preparing the porous graphite material of the present invention has adjustable porosity and pore size. The volume ratio of the pore-forming agent powder to the aggregate is 20-45%, the particle size of the metal powder is 10-100 μm, the porosity of the obtained product is 30-50%, the pore size is 10-100 μm, the flexural strength is 15-45 MPa, and the compressive strength is 31-110 MPa. Detailed implementation manners

[0042] For a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed implementation manners of the present invention will now be described.

[0043] Example 1

[0044] 1. Treatment of pore-forming agent

[0045] Mix the metal powder and graphite powder, and then put them into a ball mill for ball milling treatment under an argon atmosphere. The ball milling time is 60 min. After the ball milling is completed, evacuate to -0.15 MPa, raise the temperature to 900 °C, and keep it warm for 5.0 h. After the heat preservation treatment is completed, cool it, and remove the excess graphite powder by vibrating screening to obtain the pore-forming agent powder;

[0046] The volume ratio of the metal powder to the graphite powder is 1:1;

[0047] The metal powder is a mixed powder of iron powder and nickel powder, and the mass ratio of the iron powder to the nickel powder is 1:1;

[0048] The particle size of the metal powder is 10 μm;

[0049] The particle size of the graphite powder is 50 μm.

[0050] 2. Mixing

[0051] Put the pitch, aggregate, and pore-forming agent powder into a kneading device, heat it to the melting state of the pitch, and mix evenly to obtain a mixture;

[0052] The softening point of the pitch is 75 °C, and the particle size is 50 μm;

[0053] The volume ratio of the aggregate to the pitch and the pore-forming agent powder is 10:3:2.0;

[0054] The aggregate is artificial graphite powder with a particle size of 40 μm.

[0055] 3. Molding

[0056] Dry press the mixture for molding, and the molding pressure is 20 MPa to obtain a green body.

[0057] 4. Baking

[0058] Place the green body in a roasting furnace for roasting. The roasting atmosphere is argon, the roasting temperature is 1200 °C, the heating rate is 10 °C / min, the roasting time is 15 h. After roasting, cool it to room temperature to obtain a roasted product.

[0059] 5. Pore formation

[0060] Connect the roasted product to the positive electrode of the power supply and the carbon rod to the negative electrode of the power supply. Immerse both the positive and negative electrodes completely in the mixed solution of electrolyte and polyethylene glycol 200. Turn on the DC power supply and control the voltage of the DC power supply to 5.0 V until no more metal is deposited on the negative electrode to obtain a pore-formed product;

[0061] The mass ratio of the electrolyte to polyethylene glycol 200 is 100:3.0;

[0062] The electrolyte is a 65 wt% ferrous sulfate solution.

[0063] 6. Graphitization

[0064] Put the pore-formed product into a graphitization furnace after drying and conduct graphitization treatment in an argon atmosphere. The graphitization temperature is 2400 °C and the graphitization time is 8 h. Wait for it to naturally return to room temperature to obtain a porous graphite material.

[0065] Example 2

[0066] 1. Pore former treatment

[0067] Mix the metal powder and graphite powder, then put them into a ball mill and conduct ball milling treatment in an argon atmosphere. The ball milling time is 15 min. After ball milling, evacuate to -0.20 MPa, raise the temperature to 400 °C, hold for 3.0 h. After the holding treatment, cool it and remove the excess graphite powder by vibrating screening to obtain a pore former powder;

[0068] The volume ratio of the metal powder to the graphite powder is 1:3;

[0069] The metal powder is copper powder with a particle size of 100 μm;

[0070] The graphite powder has a particle size of 1 μm.

[0071] 2. Mixing

[0072] Put the pitch, aggregate, and pore former powder into a kneading device, heat it to the melting state of the pitch, and mix evenly to obtain a mixed material;

[0073] The softening point of the pitch is 70 °C and the particle size is 10 μm;

[0074] The volume ratio of the aggregate to the pitch and pore former powder is 10:2:3.5;

[0075] The aggregate is a mixture of carbon black and pitch coke, the mass ratio of carbon black to pitch coke is 1:1, and the particle size of the aggregate is 10 μm.

[0076] 3. Molding

[0077] The mixture is hot-pressed and molded under a molding pressure of 200 MPa to obtain a green body.

[0078] 4. Baking

[0079] The green body is placed in a baking furnace for baking. The baking atmosphere is argon, the baking temperature is 700 °C, the heating rate is 6 °C / min, and the baking time is 22 h. After baking, it is cooled to room temperature to obtain a baked product.

[0080] 5. Pore formation

[0081] The baked product is connected to the positive electrode of the power supply, and the carbon rod is connected to the negative electrode of the power supply. The positive and negative electrodes are completely immersed in the mixed solution of the electrolyte and sodium dodecyl sulfate. The DC power supply is energized, and the voltage of the DC power supply is controlled at 2.0 V until no more metal is deposited at the negative electrode to obtain a pore-formed product;

[0082] The mass ratio of the electrolyte to sodium dodecyl sulfate is 100:1.0;

[0083] The electrolyte is a 10 wt% copper chloride solution.

[0084] 6. Graphitization

[0085] The pore-formed product is dried and then put into a graphitization furnace for graphitization treatment under an argon atmosphere. The graphitization temperature is 2600 °C, and the graphitization time is 20 h. After naturally returning to room temperature, a porous graphite material is obtained.

[0086] Example 3

[0087] 1. Pore former treatment

[0088] The metal powder and graphite powder are mixed and then put into a ball mill for ball milling treatment under an argon atmosphere. The ball milling time is 40 min. After ball milling, the vacuum is pumped to -0.10 MPa, the temperature is raised to 400 °C, and heat preservation treatment is carried out for 0.5 h. After the heat preservation treatment, it is cooled, and the excess graphite powder is removed by vibrating screening to obtain pore former powder;

[0089] The volume ratio of the metal powder to the graphite powder is 1:2;

[0090] The metal powder is aluminum powder with a particle size of 50 μm;

[0091] The particle size of the graphite powder is 100 μm.

[0092] 2. Mixing

[0093] Put asphalt, aggregate, and pore-forming agent powder into a kneading device, heat it to the molten state of asphalt, and mix evenly to obtain a mixture.

[0094] The softening point of the asphalt is 100 °C, and the particle size is 100 μm.

[0095] The volume ratio of the aggregate to asphalt and pore-forming agent powder is 10:5:4.5.

[0096] The aggregate is natural graphite, and the particle size of the aggregate is 100 μm.

[0097] 3. Forming

[0098] Isostatically press the mixture to form a green body under a forming pressure of 130 MPa.

[0099] 4. Baking

[0100] Place the green body in a baking furnace for baking. The baking atmosphere is argon, the baking temperature is 600 °C, the heating rate is 12 °C / min, and the baking time is 20 h. After baking, cool it to room temperature to obtain a baked product.

[0101] 5. Pore formation

[0102] Connect the baked product to the positive electrode of the power supply and the carbon rod to the negative electrode of the power supply. Immerse the positive and negative electrodes completely in the mixed solution of electrolyte and sodium dodecylbenzenesulfonate. Turn on the DC power supply, control the voltage of the DC power supply to 10.0 V until no metal is deposited on the negative electrode to obtain a pore-formed product;

[0103] The mass ratio of the electrolyte to sodium dodecylbenzenesulfonate is 100:0.5.

[0104] The electrolyte is a 30 wt% sodium nitrate solution.

[0105] 6. Graphitization

[0106] Put the pore-formed product into a graphitization furnace after drying, and perform graphitization treatment under an argon atmosphere. The graphitization temperature is 2900 °C, and the graphitization time is 9.0 h. Wait for it to naturally return to room temperature to obtain a porous graphite material.

[0107] Test the porosity, pore size, and strength properties of the porous graphite materials prepared in Examples 1-3, as follows:

[0108]

[0109] Unless otherwise specified, the ratios described in the present invention are all mass ratios, and the percentages are all mass percentages.

[0110] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a porous graphite material with adjustable pores, characterized in that, It includes steps of pore-forming agent treatment, mixing, forming, roasting, pore-forming, and graphitization; The steps of the pore-forming agent treatment are as follows: mix metal powder and graphite powder, then put them into a ball mill, carry out ball milling treatment under an argon atmosphere, the ball milling time is 15 - 60 min. After the ball milling ends, evacuate to -0.10~-0.20 MPa, raise the temperature to 400 - 900 °C, keep the temperature for 0.5 - 5.0 h. After the heat preservation treatment ends, cool it, and remove the excess graphite powder by vibrating screening to obtain the pore-forming agent powder; The volume ratio of the metal powder to the graphite powder is 1:1 - 3; The metal powder is one or more of iron powder, nickel powder, copper powder, and aluminum powder, and the particle size of the metal powder is 10 - 100 μm; The particle size of the graphite powder is 1 - 100 μm; The steps of the mixing are as follows: put asphalt, aggregate, and pore-forming agent powder into a kneading device, heat it to the melting state of asphalt, and mix evenly to obtain a mixture; The softening point of the asphalt is 70 - 100 °C, and the particle size is 10 - 100 μm; The volume ratio of the aggregate, asphalt, and pore-forming agent powder is 10:2 - 5:2.0 - 4.5; The aggregate is one or more of artificial graphite, pitch coke, carbon black, and natural graphite, and the particle size of the aggregate is 10 - 100 μm; Process the pore-forming agent powder through the steps of mixing, forming, and roasting to obtain a roasted product; The steps of the pore-forming are as follows: connect the roasted product to the positive electrode of the power supply, connect the carbon rod to the negative electrode of the power supply, completely immerse the positive electrode and the negative electrode together into the mixed solution of the electrolyte and the additive, turn on the DC power supply, control the voltage of the DC power supply to be 2.0 - 10.0 V until no metal is deposited on the negative electrode to obtain a pore-formed product; The electrolyte is one of ferrous sulfate solution or sodium nitrate solution; The additive is one of polyethylene glycol, sodium dodecyl sulfate, and sodium dodecylbenzenesulfonate.

2. The preparation method of a porous graphite material with adjustable pores according to claim 1, characterized in that, The steps of the forming are as follows: carry out dry pressing, hot pressing or isostatic pressing on the mixture, the forming pressure is 20 - 200 MPa to obtain a green body.

3. The preparation method of a porous graphite material with adjustable pores according to claim 2, characterized in that, The steps of the roasting are as follows: place the green body in a roasting furnace for roasting, the roasting atmosphere is argon, the roasting temperature is 600 - 1200 °C, the heating rate is 6 - 12 °C / min, the roasting time is 15 - 22 h. After the roasting ends, cool it to room temperature to obtain a roasted product.

4. The preparation method of a porous graphite material with adjustable pores according to claim 1, characterized in that, In the steps of the pore-forming, the mass ratio of the electrolyte to the additive is 100:0.5 - 3.0; The mass concentration of the electrolyte is 10 - 65%.

5. The preparation method of a porous graphite material with adjustable pores according to claim 1, characterized in that, The graphitization step is as follows: after drying the pore-forming product, it is placed in a graphitization furnace, and graphitization treatment is carried out under an argon atmosphere. The graphitization temperature is 2400 - 2900 °C, and the graphitization time is 8 - 20 h. Wait for it to naturally return to room temperature to obtain a porous graphite material.

6. A porous graphite material with adjustable pores prepared by the preparation method according to any one of claims 1 - 5.

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