Preparation method of expandable graphite with low initial expansion temperature

Abstract

The invention relates to the field of graphite materials, and particularly discloses expandable graphite with a low initial expansion temperature. A preparation method of expandable graphite with a low initial expansion temperature comprises the following steps that crystalline flake graphite and an intercalator solution with the concentration of (76 + / -0.2)% are stirred to react for 8-10 min at the temperature of 30-50 DEG C, and the mass ratio of the crystalline flake graphite to the intercalator solution is 1: (5.1-5.3); an oxidizing agent is added, a reaction is conducted for 25-30 min at the temperature of 30-50 DEG C, and the mass ratio of the crystalline flake graphite to the oxidizing agent is 1: (0.26-0.28); adding a decolorizing agent for decolorizing, and reacting for 25-30 minutes at the temperature of 30-35 DEG C; performing vacuum filtration; washing with deionized water, washing, and carrying out vacuum filtration to obtain a filter cake; and drying the filter cake to obtain the expandable graphite. The expandable graphite can be used for low-temperature flame-retardant materials and has the advantages of being low in initial expansion temperature, large in expansion rate and good in expansion stability.

Description

Technical Field

[0001] This application relates to the field of graphite materials technology, and more specifically, it relates to a method for preparing expandable graphite with a low initial expansion temperature. Background Technology

[0002] Expandable graphite is a functional material formed by embedding intercalating agents (such as sulfuric acid, nitric acid, organic acids, etc.) between graphite layers through chemical or electrochemical methods. It can expand rapidly under high temperature or microwave radiation, with a volume expansion rate of tens to hundreds of times, forming a worm-like porous structure; this expandable graphite is thus called expanded graphite. This property makes it widely used in the following fields: flame retardant materials—the dense carbon layer formed after expansion can insulate heat and oxygen, and is used as a flame retardant additive in polymers, building materials, cables, etc.; sealing materials—its high-temperature expansion ability fills sealing gaps; energy and environment—used as battery electrodes, adsorbents (such as oil stain treatment), or phase change material carriers.

[0003] In the prior art, Chinese invention patent application CN101327926A discloses a method for preparing low-temperature expandable graphite. The main steps are: immersing flake graphite in a solution mainly composed of an oxidant and an intercalating agent to carry out an intercalation reaction; filtering; displacing the intercalating material between the graphite layers in the resulting solid phase using a water exchange method; and drying the resulting solid phase, which is the target material. The initial expansion temperature of the expandable graphite produced by this method is 160℃, making it difficult to meet the requirements of certain low-temperature applications, such as low-temperature flame-retardant polymer processing or low-temperature sealing. Summary of the Invention

[0004] In order to achieve a low initial expansion temperature for expandable graphite, this application provides a method for preparing expandable graphite with a low initial expansion temperature.

[0005] In a first aspect, this application provides a method for preparing expandable graphite with a low initial expansion temperature, employing the following technical solution: A method for preparing expandable graphite with a low initial expansion temperature includes the following steps: (1) Stir the flake graphite and the intercalating agent solution with a concentration of (76±0.2)% at 30-50℃ for 8-10 min. The mass ratio of flake graphite to intercalating agent solution is 1:5.1-5.3. (2) Add an oxidant to the product obtained in step (1) and react at 30-50℃ for 25-30 min. The mass ratio of flake graphite to oxidant is 1:0.26-0.28. (3) Add a decolorizing agent to the product obtained in step (2) and react at 30-35℃ for 25-30 min; (4) Vacuum filter the product obtained in step (3); (5) Wash the product obtained in step (4) with deionized water until pH = 6-7, then vacuum filter to obtain filter cake; (6) Dry the filter cake at 60-70℃ until the moisture content is less than 1% to obtain expandable graphite.

[0006] By employing the above technical solution, a specific amount of intercalating agent is first inserted into the interlayer of flake graphite to form an intercalation compound. This specific amount of intercalating agent increases the interlayer spacing of graphite, weakens the interlayer forces, and makes the graphite structure more loose. Moreover, the intercalating agent interacts with the carbon atoms between the graphite layers to form a stable intercalation complex. This complex is more easily decomposed when heated, generating gas, thereby promoting the expansion of graphite. Then, an oxidizing agent is used for oxidation reaction and surface modification. The oxidizing agent can react with the carbon atoms on the graphite surface to generate oxygen-containing functional groups such as hydroxyl and carboxyl groups, changing the chemical properties of the graphite surface, weakening the interlayer interactions, and introducing hydrophilic groups, which improves the dispersibility of graphite in water, which is beneficial for subsequent decolorization, filtration, and drying. At the same time, the presence of these hydrophilic groups can also generate gas when decomposed by heat, promoting the expansion of graphite. Next, a decolorizing agent is used for decolorization, which can remove impurities and colored substances generated during the reaction process, improving the purity of expandable graphite. The pressure change of vacuum filtration may also have a certain impact on the graphite structure, which is beneficial for lowering the initial expansion temperature.

[0007] Optionally, the intercalating agent is ammonium bicarbonate and acetic acid, with a mass ratio of acetic acid to ammonium bicarbonate of 1:1.2-1.5.

[0008] By employing the above technical solution, ammonium bicarbonate and acetic acid are used as intercalating agents. Both have low decomposition temperatures and can provide an acidic environment and gases, thereby rapidly promoting expansion. After ammonium bicarbonate intercalates into flake graphite, ammonium and carbonate ions enter the graphite interlayer, increasing the interlayer spacing. Under heating or certain conditions, ammonium bicarbonate decomposes to produce carbon dioxide, ammonia, and water, which helps the flake graphite expand. Acetic acid is a weak acid with small molecules that can enter the graphite interlayer. During heating, acetic acid will also volatilize or partially decompose, producing acetic acid vapor and other gases. These gases will expand the graphite layers, reducing interlayer forces. Moreover, after entering the interlayer, acetic acid may interact with carbon atoms on the graphite surface, changing the electron cloud distribution between layers and further weakening the interlayer forces, which is beneficial for lowering the initial expansion temperature. After intercalation with ammonium bicarbonate and acetic acid, the interlayer spacing of flake graphite increases and the interlayer forces weaken, providing favorable conditions for subsequent oxidation reactions and expansion.

[0009] The carbon dioxide, ammonia, and water produced by the decomposition of ammonium bicarbonate, together with the gases produced by the volatilization or decomposition of acetic acid, create greater pressure between the graphite layers, making it easier to separate the graphite layers and thus synergistically reducing the initial expansion temperature. The two intercalating agents enter the graphite interlayer, complementing each other and improving the intercalation efficiency. Ammonium bicarbonate may more easily enter the larger gaps between the layers, while acetic acid molecules may enter some smaller areas, making the entire interlayer structure more uniformly expanded, thereby improving the expansion stability of the same batch of expandable graphite.

[0010] During the intercalation process, the compounds of ammonium bicarbonate and acetic acid are thoroughly mixed with the flake graphite. Acetic acid may first partially dissolve or penetrate into the interlayer of graphite, changing the surface properties of the interlayer and making it easier for ammonium bicarbonate to enter. Subsequently, the gas produced by the decomposition of ammonium bicarbonate further expands the interlayer. When heated, acetic acid continues to volatilize or decompose, and together with the gas produced by the decomposition of ammonium bicarbonate, it forms a strong interlayer pressure, which promotes the rapid separation of graphite layers. Therefore, ammonium bicarbonate and acetic acid can achieve a good synergistic effect, thereby reducing the initial expansion temperature.

[0011] Optionally, the oxidant comprises sodium nitrite and hydrogen peroxide in a mass ratio of 1:2.5-3.

[0012] By adopting the above technical solution, sodium nitrite itself has a certain oxidizing property and can undergo a disproportionation reaction under acidic conditions. Hydrogen peroxide can decompose at low temperatures (<60℃) to produce active oxygen, promoting intercalation. When sodium nitrite and hydrogen peroxide are mixed, in the acidic environment provided by acetic acid in the intercalating agent, the nitric acid produced by sodium nitrite and the hydroxyl radicals produced by the decomposition of hydrogen peroxide can work synergistically to enhance the oxidizing ability, thereby introducing more oxygen-containing functional groups into the graphite interlayer, further destroying the interlayer structure of graphite, further increasing the interlayer spacing, and further weakening the interlayer force. When heated, the gas is more likely to escape from the interlayer, thereby promoting the generation of expansion and lowering the initial expansion temperature. Moreover, sodium nitrite can react with ammonium salts, producing gas expansion at around 80℃. Ammonium bicarbonate decomposes at low temperatures to produce ammonia and carbon dioxide gas, providing initial gas to drive the interlayer expansion of graphite. Carbon dioxide will dissolve in water to form carbonic acid, making the solution acidic. Sodium nitrite can react in acidic or ammonium salt environments, thus participating in the following reaction: NaNO2 + NH4 + →N₂↑+2H₂O+Na + This promotes graphite expansion, making the expansion more uniform, reducing the difference in expansion ratio, and making the expansion ratio more stable, with the difference within the same batch being less than 5%.

[0013] Optionally, potassium persulfate is also added to the oxidant, with the mass ratio of sodium nitrite to potassium persulfate being 1:0.5-0.6.

[0014] By employing the above technical solution, potassium persulfate is added to the oxidant. Potassium persulfate has oxidizing and acidifying effects; its hydrolysis produces potassium bisulfate, further lowering the pH of the system and providing a more suitable acidic environment for the reaction of sodium nitrite and ammonium ions. Furthermore, its strong oxidizing properties can oxidize the graphite edges, enhancing the penetration of the intercalating agent. Under acidic conditions, sodium nitrite reacts with ammonium ions to generate nitrogen gas, supplementing the nitrogen supply and synergistically with carbon dioxide to achieve uniform expansion, reducing the difference in expansion ratio and increasing the stability of the expansion ratio. If the amount of potassium persulfate is too small, the oxidation effect is weak, the graphite layers are not fully opened, leading to an increased expansion initiation temperature and a loose expansion structure. If the amount of potassium persulfate is excessive, the overly strong acidity may corrode the graphite sheets, causing damage to the carbon skeleton, reducing the strength of the expanded graphite worm-like structure, potentially decreasing the expansion ratio, and causing excessive oxidation leading to an increased expansion temperature.

[0015] Optionally, the mass ratio of ammonium bicarbonate, sodium nitrite, and potassium persulfate is 53.9-55.7:1:0.6.

[0016] By adopting the above technical solution, the above amounts of ammonium bicarbonate, sodium nitrite and potassium persulfate can better expand the gas in flake graphite, achieving a lower initial expansion temperature and a higher expansion ratio.

[0017] Optionally, the decolorizing agent is selected from at least one of oxalic acid, formic acid, hydrogen peroxide, sodium nitrite, and perboric acid.

[0018] By adopting the above technical solution, impurities and colored substances may be introduced during the intercalation and oxidation process. However, oxalic acid and formic acid have strong reducing and complexing abilities and can react with colored substances to reduce or complex them into colorless or light-colored substances, thereby achieving the purpose of decolorization. This not only removes the color but also removes some impurities and improves the purity of expandable graphite.

[0019] Optionally, the mass ratio of the flake graphite to the decolorizing agent is 1:0.6-0.66.

[0020] By adopting the above technical solution, the above amount of decolorizing agent will not damage the structure of expandable graphite. The decolorized expandable graphite remains structurally stable and can expand uniformly when heated. If the amount of decolorizing agent is too large, it may cause damage to the graphite structure or leave too much acid, affecting subsequent applications.

[0021] Optionally, the particle size of the flake graphite is 50-80 mesh.

[0022] By adopting the above technical solution, the flake graphite in this particle size range has a large specific surface area, high intercalation efficiency, low gas escape resistance, and low initial expansion temperature.

[0023] Optionally, the pressure during vacuum filtration is -(0.08~0.1)MPa.

[0024] In summary, this application has the following beneficial effects: 1. Because this application uses specific amounts of intercalating agent and oxidizing agent to treat flake graphite, and then decolorizes it to produce expandable graphite, the intercalating agent and oxidizing agent work synergistically during the reaction process, acting together on the graphite interlayer and surface to form an intercalation complex with specific structure and properties. This complex is more likely to decompose and generate gas when heated, promoting the uniform expansion of graphite. Moreover, through intercalation, oxidation and other steps, the structure of graphite is significantly changed, such as increased interlayer spacing, weakened interlayer forces, and changed surface properties. These changes work together to improve the expansion performance of expandable graphite, resulting in a lower initial expansion temperature.

[0025] 2. In this application, ammonium bicarbonate and acetic acid are preferably used as intercalating agents, and sodium nitrite and hydrogen peroxide are used as oxidants. Under the acidic environment provided by acetic acid, ammonium bicarbonate and sodium nitrite can react at low temperature to produce nitrogen gas, which increases the amount of expansion gas produced, thereby promoting the expansion of graphite at low temperature, increasing the expansion ratio, and making the graphite expansion more uniform.

[0026] 3. In this application, potassium persulfate is preferably added to the oxidant to provide a more suitable acidic environment for the reaction of sodium nitrite and ammonium bicarbonate, so that the two react fully and the expansion ratio is improved. Detailed Implementation

[0027] The following embodiments provide a further detailed description of this application. Example

[0028] Example 1: A method for preparing expandable graphite with a low initial expansion temperature, comprising the following steps: (1) Mix 50g of flake graphite with a particle size of 50 mesh and 260g of intercalating agent solution with a concentration of 76% and react at 30°C for 35min. The intercalating agent includes acetic acid and ammonium bicarbonate in a mass ratio of 1:1.5. (2) Add 13g of oxidant to the product obtained in step (1) and react at 30°C for 25min. The oxidant contains sodium nitrite and hydrogen peroxide in a mass ratio of 1:3. (3) Add a decolorizing agent to step (2) for decolorization, and react at 30°C for 30 min. The decolorizing agent is formic acid solution, and the mass ratio of the decolorizing agent to flake graphite is 1:0.6. (4) The product obtained in step (3) is subjected to vacuum filtration at a pressure of -0.1 MPa. (5) Wash the product obtained in step (4) with deionized water until the pH is 7, then vacuum filter to obtain filter cake. The vacuum filtration pressure is -0.1 MPa. (6) The filter cake is dried at 70°C until the moisture content is less than 1% to obtain expandable graphite.

[0029] Example 2: A method for preparing expandable graphite with a low initial expansion temperature, comprising the following steps: (1) Mix 50g of flake graphite with a particle size of 50 mesh and 255g of intercalating agent solution with a concentration of 75.8%, and react at 80℃ for 30min. The intercalating agent includes acetic acid and ammonium bicarbonate with a mass ratio of 1:1.2. (2) Add 14g of oxidant to the product obtained in step (1) and react at 50°C for 25min. The oxidant contains sodium nitrite and hydrogen peroxide in a mass ratio of 1:2.5. (3) Add a decolorizing agent to step (2) for decolorization, and react at 30°C for 25 min. The decolorizing agent is formic acid solution, and the mass ratio of the decolorizing agent to flake graphite is 1:0.65. (4) The product obtained in step (3) is subjected to vacuum filtration at a pressure of -0.08 MPa. (5) Wash the product obtained in step (4) with deionized water until the pH is 7, then vacuum filter to obtain filter cake. The vacuum filtration pressure is -0.08 MPa. (6) The filter cake is dried at 60°C until the moisture content is less than 1% to obtain expandable graphite.

[0030] Example 3: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that (1) 50g of flake graphite with a particle size of 50 mesh and 265g of intercalating agent solution with a concentration of 76.2% are mixed and reacted at 30°C for 35min. The intercalating agent includes acetic acid and ammonium bicarbonate with a mass ratio of 1:1.3. (2) Add 13.5g of oxidant to the product obtained in step (1) and react at 30°C for 25min. The oxidant contains sodium nitrite and hydrogen peroxide in a mass ratio of 1:2.8. (3) Add a decolorizing agent to step (2) for decolorization, and react at 35°C for 30 min. The decolorizing agent is formic acid solution, and the mass ratio of the decolorizing agent to flake graphite is 1:0.6. (4) The product obtained in step (3) is subjected to vacuum filtration at a pressure of -0.1 MPa. (5) Wash the product obtained in step (4) with deionized water until the pH is 7, then vacuum filter to obtain filter cake. The vacuum filtration pressure is -0.1 MPa. (6) The filter cake is dried at 70°C until the moisture content is less than 1% to obtain expandable graphite.

[0031] Example 4: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that potassium permanganate is used in equal amounts to replace ammonium bicarbonate and ammonium formate as an intercalating agent.

[0032] Example 5: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that an equal amount of ammonium bicarbonate is used instead of acetic acid.

[0033] Example 6: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that an equal amount of hydrogen peroxide is used instead of sodium nitrite.

[0034] Example 7: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the oxidant contains sodium nitrite, hydrogen peroxide and potassium persulfate in a mass ratio of 1:3:0.6.

[0035] Example 8: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the oxidant contains sodium nitrite, hydrogen peroxide and potassium persulfate in a mass ratio of 1:3:0.5.

[0036] Example 9: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 7 in that the oxidant contains sodium nitrite, hydrogen peroxide and potassium persulfate in a mass ratio of 1:3:0.1.

[0037] Example 10: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 7 in that the oxidant contains sodium nitrite, hydrogen peroxide and potassium persulfate in a mass ratio of 1:3:1.

[0038] Comparative Example Comparative Example 1: A method for preparing expandable graphite with a low initial expansion temperature, which differs from Example 1 in that the mass of the intercalating agent solution is 180g.

[0039] Comparative Example 2: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the mass of the intercalating agent solution is 200g.

[0040] Comparative Example 3: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the mass of the intercalating agent solution is 300g.

[0041] Comparative Example 4: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the amount of oxidant used is 6g.

[0042] Comparative Example 5: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the amount of oxidant used is 8g.

[0043] Comparative Example 6: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the amount of oxidant used is 10g.

[0044] Comparative Example 7: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the amount of oxidant used is 12g.

[0045] Comparative Example 8: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the amount of oxidant used is 18g.

[0046] Comparative Example 9: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the amount of oxidant used is 19g.

[0047] Comparative Example 10: A method for preparing expandable graphite with a low initial expansion temperature, which differs from Example 1 in that the concentration of the intercalating agent solution is 70%.

[0048] Comparative Example 11: A method for preparing expandable graphite with a low initial expansion temperature, which differs from Example 1 in that the concentration of the intercalating agent solution is 75%.

[0049] Comparative Example 12: A method for preparing expandable graphite with a low initial expansion temperature, which differs from Example 1 in that the concentration of the intercalating agent solution is 78%.

[0050] Comparative Example 13: A method for preparing expandable graphite with a low initial expansion temperature, which differs from Example 1 in that the concentration of the intercalating agent solution is 80%.

[0051] Comparative Example 14: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the particle size of the flake graphite is 100 mesh.

[0052] Comparative Example 15: A method for preparing expandable graphite with low initial expansion temperature, which differs from Example 1 in that the particle size of the flake graphite is 30 mesh.

[0053] Performance testing I. Expansion Initiation Temperature Detection: Expandable graphite was prepared according to the methods in the Examples and Comparative Examples, and the initial expansion temperature was detected according to the following methods. The detection results of Examples 1-10 and Comparative Examples 1-3 are recorded in Table 1, the detection results of Examples 1 and Comparative Examples 4-9 are recorded in Table 2, the detection results of Examples 1 and Comparative Examples 10-13 are recorded in Table 3, and the detection results of Examples 1 and Comparative Examples 14-15 are recorded in Table 4.

[0054] Method for detecting expansion initiation temperature: Accurately weigh 2 mL of expandable graphite using a graduated cylinder, place it in a preheated initiation temperature meter and heat for 10 minutes. Take it out and read its expansion height. Take expansion of 2 divisions as the standard. If it does not expand or expands less than 2 divisions, increase the initiation temperature meter by 1℃ and resample until expansion reaches 2 divisions.

[0055] Table 1 As can be seen from the data in Table 1, in Examples 1-3, specific ratios of flake graphite, intercalating agent solution and oxidant were used, and specific proportions of acetic acid and ammonium bicarbonate were used as intercalating agents, and sodium nitrite and hydrogen peroxide were used as oxidants. After intercalation, oxidation and decolorization, expandable graphite with ultra-low initial expansion temperature was obtained, which can be used as a low-temperature flame retardant material.

[0056] In Example 4, potassium permanganate was used as an intercalating agent. Compared with Example 1, its initial expansion temperature increased, indicating that using potassium permanganate alone as an intercalating agent could not effectively reduce the initial expansion temperature. In Example 5, ammonium bicarbonate was used as an intercalating agent. Compared with Example 1, the initial expansion temperature of the expandable graphite increased. In Example 6, hydrogen peroxide was used instead of sodium nitrite. The initial expansion temperature of the resulting expandable graphite increased compared with Example 1. This shows that using acetic acid and ammonium bicarbonate as intercalating agents and sodium nitrite and hydrogen peroxide as oxidants can achieve a better low-temperature expansion effect.

[0057] Compared with Example 1, Examples 7 and 8 also added a certain amount of potassium persulfate to the oxidant to provide an acidic environment and increase the oxidizing capacity, thereby further reducing the initial expansion temperature.

[0058] Compared with Example 7, Examples 9 and 10 respectively reduced and increased the amount of potassium persulfate. The data in Table 1 show that the initial expansion temperature of the expandable graphite prepared in Examples 9 and 10 is lower than that in Example 7, but better than that in Example 1, indicating that the amount of potassium persulfate added affects the initial expansion temperature of the expandable graphite.

[0059] Table 2 As can be seen from the data in Table 2, compared with Example 1, the amount of oxidant used in Comparative Examples 4-7 was reduced, which shows that the initial expansion temperature of the prepared expandable graphite increased significantly. Moreover, the smaller the amount of oxidant used, the higher the expansion initiation temperature. In Examples 8-9, the amount of oxidant was increased, which shows that the larger the amount of oxidant used, the higher the expansion initiation temperature.

[0060] Table 3 As can be seen from the data in Table 3, the appropriate concentration of intercalating agent solution in Examples 1-3 can effectively reduce the initial expansion temperature of expandable graphite. In Comparative Examples 10 and 11, the concentration of intercalating agent solution is lower than that in Example 1, but the expansion initiation temperature is increased. In Examples 12 and 13, the concentration of intercalating agent is increased, but the expansion initiation temperature is also increased. This indicates that an appropriate concentration of intercalating agent can yield expandable graphite with a lower expansion initiation temperature.

[0061] Table 4 project Flake graphite particle size Expansion initiation temperature / °C Example 1 50 mesh 90 Comparative Example 14 30 mesh 120 Comparative Example 15 100 mesh 150 As shown in Table 4, using flake graphite with a particle size of 50 mesh can produce expandable graphite with a lower initial expansion temperature. However, changing the particle size of the flake graphite will have a significant impact on the initial expansion temperature.

[0062] II. Testing of expansion volume and expansion stability: Expandable graphite prepared in the examples and comparative examples was tested according to the following methods, and the test results were recorded in Table 5.

[0063] 1. Expansion volume test method: The expansion volume is determined according to the national standard GB10698-1989. A certain mass of expandable graphite is weighed and placed in a quartz beaker that has been preheated at 300℃ for 5 minutes. The beaker is then immediately placed in a 300℃ high-temperature resistance furnace without closing the furnace door until it stops expanding. The sample is then immediately removed, and the volume after expansion is read. The expansion volume is calculated according to the formula: expansion volume = expanded volume / sample mass.

[0064] 2. Expansion stability test method: Five samples of the same mass (1±0.001g) are randomly weighed from the same batch of expandable graphite. The expansion volume of the five samples is tested according to the expansion volume test method. The average expansion volume and relative standard deviation of the five samples are calculated. The same batch is considered uniform if the relative standard deviation is ≤5%.

[0065] Table 5 As can be seen from the data in Table 5, the expandable graphite prepared in Examples 1-3 has a high expansion volume, and the relative standard deviation of the expansion volume of the same batch is small, indicating good stability of the expansion volume.

[0066] Compared with Example 1, Example 4 used potassium permanganate as an intercalating agent and Example 5 used ammonium bicarbonate as an intercalating agent. It can be seen that the expansion volume of the expandable graphite prepared in Example 4 and Example 5 is reduced, and the expansion stability is decreased.

[0067] In Example 6, hydrogen peroxide was used instead of sodium nitrite. Compared with Example 1, the expansion volume decreased significantly, indicating that using hydrogen peroxide alone as an oxidant did not significantly improve the expansion volume of expandable graphite.

[0068] In Examples 7 and 8, potassium persulfate was also added to the oxidant, and the expansion stability of the expandable graphite prepared in Examples 7 and 8 was further increased compared with Example 1.

[0069] Compared with Example 7, Examples 9 and 10 used reduced and increased amounts of potassium persulfate, respectively. As can be seen, the expansion volume of the prepared expandable graphite changed slightly, and the relative standard deviation decreased. The expansion performance of the same batch was more stable.

[0070] In Comparative Examples 1-3, the amount of intercalating agent solution was changed. Compared with Example 1, it can be seen that the expansion volume decreased in Comparative Examples 1 and 2, and although the expansion volume was larger in Comparative Example 3, its expansion stability was poor.

[0071] Compared with Example 1, the amount of oxidant was changed in Comparative Examples 4-9. It can be seen that the expansion volume of Comparative Examples 4-7 was reduced and the expansion stability was not as good as that of Example 1, while the expansion stability of Comparative Examples 8-9 also decreased significantly.

[0072] Compared with Example 1, Comparative Examples 10-13 showed that the expansion volume decreased in Comparative Examples 10-11, while the expansion volume was larger in Examples 12-13, but the expansion stability decreased.

[0073] In Comparative Examples 14 and 15, changing the particle size of flake graphite resulted in changes in the expansion volume of the prepared expandable graphite, and the expansion stability was not as good as in Example 1.

[0074] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing expandable graphite with a low initial expansion temperature, characterized in that, Includes the following steps: (1) Stir the flake graphite and the intercalating agent solution with a concentration of (76±0.2)% at 30-50℃ for 8-10 min. The mass ratio of flake graphite to intercalating agent solution is 1:5.1-5.

3. (2) Add an oxidant to the product obtained in step (1) and react at 30-50℃ for 25-30 min. The mass ratio of flake graphite to oxidant is 1:0.26-0.

28. (3) Add a decolorizing agent to the product obtained in step (2) and react at 30-35℃ for 25-30 min; (4) Vacuum filter the product obtained in step (3); (5) Wash the product obtained in step (4) with deionized water until pH=6-7, then vacuum filter to obtain filter cake; (6) Dry the filter cake at 60-70℃ until the moisture content is less than 1% to obtain expandable graphite.

2. The method for preparing expandable graphite with low initial expansion temperature according to claim 1, characterized in that: The intercalating agent is ammonium bicarbonate and acetic acid, with a mass ratio of acetic acid to ammonium bicarbonate of 1:1.2-1.

5.

3. The method for preparing expandable graphite with low initial expansion temperature according to claim 2, characterized in that: The oxidant comprises sodium nitrite and hydrogen peroxide in a mass ratio of 1:2.5-3.

4. The method for preparing expandable graphite with low initial expansion temperature according to claim 3, characterized in that: The oxidant also contains potassium persulfate, and the mass ratio of sodium nitrite to potassium persulfate is 1:0.5-0.

6.

5. The method for preparing expandable graphite with low initial expansion temperature according to claim 4, characterized in that: The mass ratio of ammonium bicarbonate, sodium nitrite, and potassium persulfate is 53.9-55.7:1:0.

6.

6. The method for preparing expandable graphite with low initial expansion temperature according to claim 1, characterized in that: The decolorizing agent is selected from at least one of oxalic acid, formic acid, hydrogen peroxide, sodium nitrite, and perboric acid.

7. The method for preparing expandable graphite with low initial expansion temperature according to claim 1, characterized in that: The mass ratio of the flake graphite to the decolorizing agent is 1:0.6-0.

66.

8. The method for preparing expandable graphite with low initial expansion temperature according to claim 1, characterized in that: The particle size of the flake graphite is 50-80 mesh.

9. The method for preparing expandable graphite with low initial expansion temperature according to claim 1, characterized in that: The pressure during vacuum filtration is -(0.08~0.1)MPa.

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