High-strength flexible graphite sheet and method of making same

Abstract

The application discloses a high-strength flexible graphite sheet and a preparation method thereof. The method comprises the following steps: preparing expanded graphite, blending the expanded graphite with a trace amount of high-temperature-resistant fiber, spraying a surfactant solution, and then compressing. In the blending process, the expanded graphite maintains a worm shape through suitable mixing conditions, and the distance between adjacent graphite micro-pieces is increased without peeling off the graphite micro-pieces in the worm. Through the surfactant, the interaction force between the graphite micro-pieces is reduced, the graphite micro-pieces of different graphite worms can be intercalated to a certain extent, and the surface area of the interaction between the graphite micro-pieces is increased. The method adopted by the application enables the flexible graphite to maintain excellent anti-creep property, and the mechanical property is greatly improved, so that the flexible graphite is not easy to be damaged in use as a high-temperature sealing material, and the service life is increased.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of high-temperature sealing materials, and particularly relates to a high-strength flexible graphite sheet and a preparation method thereof. BACKGROUND

[0002] With the vigorous development of global chemical industry, sealing materials under high temperature are needed. At present, the materials of high-temperature sealing materials mainly include metal and flexible graphite. Compared with metal, the flexible graphite has better anti-creep property, but has poor mechanical property.

[0003] The flexible graphite has poor mechanical property and is easily damaged in use, and the mechanical property of the flexible graphite needs to be enhanced to improve the situation. The existing method is to use the inner and outer rings made of steel as a support frame, or to paste the flexible graphite gasket on a metal plate (Fluid Machinery, 2013, 41(06): 37-41+78). In these methods, the flexible graphite gasket itself is still easy to wear.

[0004] Therefore, it is necessary to establish a low-cost and simple method to improve the mechanical property of the flexible graphite gasket itself while maintaining the anti-creep property of the flexible graphite, so as to improve the service life. SUMMARY

[0005] An object of the present application is to provide a preparation method of a high-strength flexible graphite sheet to overcome the deficiencies of the prior art.

[0006] The technical scheme for achieving the above object of the present application is as follows:

[0007] Step (1), placing graphite in a mixed solvent of acid and oxidizing agent, standing for intercalation at room temperature, then taking out the graphite, washing with water until the pH value is 6-7, and drying to obtain intercalated, washed and dried graphite;

[0008] Preferably, the mass ratio of the graphite, the acid and the oxidizing agent is 1:(1-10):(0.2-1), the acid is concentrated sulfuric acid or concentrated nitric acid, and the oxidizing agent is potassium permanganate or perchloric acid;

[0009] Step (2), heating the intercalated, washed and dried graphite obtained in step (1) at 700-1000℃ for 7-30s to obtain expanded graphite;

[0010] Preferably, the heating temperature is 800-950℃, and the heating time is 10-15s;

[0011] Step (3), blending the expanded graphite and high-temperature resistant fiber, spraying a surfactant solution and drying; the mass ratio of the high-temperature resistant fiber to the expanded graphite is (0.05-3):100;

[0012] The surface active agent is one of aqueous solutions of polysorbate, polyethylene oxide or polyethylene glycol; the mass concentration of the surface active agent is 0.5-2%;

[0013] The high-temperature-resistant fiber is one or more of basalt fiber, aluminum silicate fiber, boron nitride fiber and glass fiber;

[0014] As preferred, the surface active agent is polysorbate;

[0015] As preferred, the high-temperature-resistant fiber is one or both of basalt fiber and boron nitride fiber;

[0016] As preferred, the mass ratio of the high-temperature-resistant fiber to the expanded graphite is (1-2):100;

[0017] As preferred, the high-temperature-resistant fiber is a dispersed single fiber with a length of 1-3 mm;

[0018] As preferred, the blending method is dry mixing by a ball mill or wet mixing by high-speed stirring in a liquid; when the dry mixing is used, the mixing is performed in the ball mill for 1-3 h, and when the wet mixing is used, the mixing is performed in a dispersion liquid (glycol or dimethylformamide) at 60-120 DEG C and 200-1000 rpm for 1-3 h, and finally filtered and dried; more preferably, the blending method is the wet mixing, the dispersion liquid is glycol, the temperature is 80-110 DEG C, the stirring speed is 400-800 rpm, and the stirring time is 1-2 h;

[0019] Step (4), preparing the flexible graphite sheet

[0020] (4-1) repeatedly compressing the expanded graphite and the high-temperature-resistant fiber after the blending and drying in step (3) at 0.5-5 MPa for 2-8 times, each time for 2-10 min;

[0021] (4-2) then repeatedly compressing at 5-30 MPa for 2-8 times, each time for 2-10 min, to obtain the flexible graphite sheet.

[0022] As preferred, the compression pressure in step (4-1) is 1-3 MPa, the compression times are 3-6, and each time for 4-8 min; the compression pressure in step (4-2) is 8-20 MPa, the compression times are 3-6, and each time for 4-8 min.

[0023] Another object of the present application is to provide a high-strength flexible graphite sheet prepared by the above method.

[0024] The present application has the following advantages:

[0025] 1. The present application adopts expanded graphite and a trace amount of high-temperature-resistant fiber to be blended, then is sprayed with a surfactant solution, and then is compressed. The expanded graphite is in the form of a worm, and the graphite microsheets in the same graphite worm are not completely separated, and are partially connected with adjacent graphite microsheets. The present method maintains the worm shape of the expanded graphite through appropriate mixing conditions, and increases the distance between adjacent graphite microsheets without peeling the graphite microsheets in the worm. The adjacent graphite microsheets in the same graphite worm adhere to each other during compression, and the present method reduces the interaction force between the graphite microsheets through the surfactant, so that the degree of complete adhesion of the graphite microsheets during compression is reduced, so that the graphite microsheets of different graphite worms can be intercalated to a certain extent, and the surface area of the interaction of the graphite microsheets is increased. The main force providing tensile strength in the flexible graphite generated after compression is the wrinkles on the surface of the graphite microsheets due to compression, so that the increase in the surface area of the interaction of the graphite microsheets can increase the number of wrinkles and thus the tensile strength, and also increase the contact area with the high-temperature-resistant fiber, so that the fiber fully toughens the flexible graphite. The method adopted by the present application greatly improves the mechanical properties of the flexible graphite, so that it is not easy to be damaged in actual use, and the service life is increased.

[0026] 2. Since the present application adopts high-temperature-resistant fiber, the fiber will not reduce the strength due to melting at high temperature, so that the toughened composite flexible graphite can be used at high temperature. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The present application is a schematic diagram, wherein (a) is the graphite microsheet in the graphite worm under normal conditions, and (b) is the graphite microsheet in the graphite worm during compression. DETAILED DESCRIPTION

[0028] The present application will be more fully understood from the following detailed description. Detailed embodiments of the present application are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the present application and can be embodied in various forms. Therefore, specific functional details disclosed herein are not to be interpreted as limiting, but only as a representative basis for teaching one skilled in the art to employ the present application in virtually any appropriate detailed embodiment. The present application is a schematic diagram, wherein (a) is the graphite microsheet in the graphite worm under normal conditions, and (b) is the graphite microsheet in the graphite worm during compression.

[0029] The present application provides a method of using a trace amount of high-temperature-resistant fiber and expanded graphite to be compressed through a specific process to realize toughened flexible graphite. The schematic diagram of the present application is shown in Figure 1 . Figure 1 In (a), the expanded graphite is in the form of a worm, and the graphite microsheets therein are perpendicular to the length direction of the graphite worm, and adjacent graphite microsheets are partially connected. Figure 1In (b), adjacent graphite microsheets of the same graphite worm adhere to each other during compression, and the method of the present application reduces the degree of adhesion of adjacent graphite microsheets, allowing intercalation with microsheets of other graphite worms.

[0030] Example 1:

[0031] The graphite and concentrated sulfuric acid, perchloric acid were left to stand at room temperature for 30 min, and the mass ratio of the graphite, concentrated sulfuric acid, and perchloric acid was 1:3:0.5. The graphite was washed with water until the pH value was 6-7, and then dried. The graphite was heated in a muffle furnace at 950°C for 10 s to become expanded graphite.

[0032] The expanded graphite was blended with 2.5% by mass of boron nitride single fibers 3 mm long in ethylene glycol at 120°C with high-speed stirring at 200 rpm for 2 h, and then the dispersion was suction filtered. The filtered residue was washed with water and dried, and then the mixture was sprayed with 0.5% polyethylene oxide aqueous solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 2 MPa for 8 times, each time for 2 min, and then repeatedly compressed at 5 MPa for 5 times, each time for 10 min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 12.3 MPa, an elongation at break of 0.71%, and a creep rate of 0.09%. A flexible graphite sheet without filler under the same conditions had a tensile strength of 7.4 MPa, an elongation at break of 0.42%, and a creep rate of 0.15%.

[0033] Example 2:

[0034] The graphite and concentrated sulfuric acid, perchloric acid were left to stand at room temperature for 30 min, and the mass ratio of the graphite, concentrated sulfuric acid, and perchloric acid was 1:3:0.5. The graphite was washed with water until the pH value was 6-7, and then dried. The graphite was heated in a muffle furnace at 950°C for 10 s to become expanded graphite.

[0035] The expanded graphite was blended with 2.5% by mass of boron nitride single fibers 3 mm long in ethylene glycol at 120°C with high-speed stirring at 200 rpm for 2 h, and then the dispersion was suction filtered. The filtered residue was washed with water and dried, and then the mixture was sprayed with 0.5% polyethylene oxide aqueous solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 2 MPa for 8 times, each time for 2 min, and then repeatedly compressed at 5 MPa for 5 times, each time for 10 min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 12.3 MPa, an elongation at break of 0.71%, and a creep rate of 0.09%. A flexible graphite sheet without filler under the same conditions had a tensile strength of 7.4 MPa, an elongation at break of 0.42%, and a creep rate of 0.15%.

[0036] Example 3:

[0037] The graphite and concentrated sulfuric acid, potassium permanganate were left at room temperature for 30 min, the mass ratio of graphite, concentrated sulfuric acid and potassium permanganate was 1:1:0.2. The graphite was washed with water, and dried after the pH value was 6-7. The graphite was heated at 1000℃ in a muffle furnace for 7s to become expanded graphite.

[0038] The expanded graphite was blended with 0.1% mass fraction of basalt single fiber with a length of 1mm by a ball mill for 1h, and then the mixture was sprayed with 0.5% polysorbate aqueous solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 0.5MPa for 2 times, each time for 10min, and then repeatedly compressed at 5MPa for 8 times, each time for 8min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 8.8MPa, an elongation at break of 1.12%, and a creep rate of 0.21%. Under the same conditions, the flexible graphite sheet without filler had a tensile strength of 7.2MPa, an elongation at break of 0.40%, and a creep rate of 0.25%.

[0039] Example 4:

[0040] The graphite and concentrated sulfuric acid, potassium permanganate were left at room temperature for 30 min, the mass ratio of graphite, concentrated sulfuric acid and potassium permanganate was 1:1:0.2. The graphite was washed with water, and dried after the pH value was 6-7. The graphite was heated at 1000℃ in a muffle furnace for 7s to become expanded graphite.

[0041] The expanded graphite was blended with 3% mass fraction of glass fiber single fiber with a length of 3mm in dimethylformamide at 80℃ with high-speed stirring at 800rpm for 3h, and then the dispersion was suction filtered. The filtered residue was washed with water and dried, and then the mixture was sprayed with 0.5% polyethylene glycol aqueous solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 1MPa for 6 times, each time for 4min, and then repeatedly compressed at 20MPa for 4 times, each time for 8min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 11.4MPa, an elongation at break of 1.28%, and a creep rate of 0.11%. Under the same conditions, the flexible graphite sheet without filler had a tensile strength of 8.0MPa, an elongation at break of 0.42%, and a creep rate of 0.19%.

[0042] Example 5:

[0043] The graphite and concentrated sulfuric acid, potassium permanganate were left at room temperature for 30 min, the mass ratio of graphite, concentrated sulfuric acid and potassium permanganate was 1:1:0.2. The graphite was washed with water, and dried after the pH value was 6-7. The graphite was heated at 1000℃ in a muffle furnace for 7s to become expanded graphite.

[0044] The expanded graphite was blended with 1% by mass of basalt single fiber of 3 mm in length in ethylene glycol at 80°C under high-speed stirring at 500 rpm for 1 h, and then the dispersion was suction-filtered. The mixture remaining after filtration was washed with water and dried, and the mixture was sprayed with 2% aqueous polyethylene oxide solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 3 MPa for 3 times, each time for 4 min, and then repeatedly compressed at 10 MPa for 2 times, each time for 5 min, to produce a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 11.5 MPa, an elongation at break of 1.31%, and a creep rate of 0.13%. A flexible graphite sheet without filler under the same conditions had a tensile strength of 7.9 MPa, an elongation at break of 0.45%, and a creep rate of 0.21%.

[0045] Example 6:

[0046] The graphite was left to stand at room temperature for 30 min with concentrated sulfuric acid and potassium permanganate at a mass ratio of 1:2:0.3. The graphite was washed with water so that the pH was 6-7 and then dried. The graphite was heated in a muffle furnace at 800°C for 10 s to become expanded graphite.

[0047] The expanded graphite was blended with 2% by mass of aluminum silicate single fiber of 3 mm in length in dimethylformamide at 90°C under high-speed stirring at 1000 rpm for 3 h, and then the dispersion was suction-filtered. The mixture remaining after filtration was washed with water and dried, and the mixture was sprayed with 2% aqueous polyethylene glycol solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 4 MPa for 3 times, each time for 4 min, and then repeatedly compressed at 15 MPa for 5 times, each time for 2 min, to produce a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 10.8 MPa, an elongation at break of 1.16%, and a creep rate of 0.12%. A flexible graphite sheet without filler under the same conditions had a tensile strength of 8.3 MPa, an elongation at break of 0.47%, and a creep rate of 0.16%.

[0048] Example 7:

[0049] The graphite was left to stand at room temperature for 30 min with concentrated nitric acid and perchloric acid at a mass ratio of 1:7:0.3. The graphite was washed with water so that the pH was 6-7 and then dried. The graphite was heated in a muffle furnace at 850°C for 13 s to become expanded graphite.

[0050] The expanded graphite was blended with 0.05% mass fraction of boron nitride single fiber with length of 1 mm by a ball mill for 1 h, and the mixture was sprayed with 1% polyethylene oxide aqueous solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 2 MPa for 5 times, each time for 3 min, and then repeatedly compressed at 10 MPa for 4 times, each time for 6 min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 9.0 MPa, an elongation at break of 0.83%, and a creep rate of 0.15%. The flexible graphite sheet without filler had a tensile strength of 8.0 MPa, an elongation at break of 0.45%, and a creep rate of 0.21% under the same conditions.

[0051] Example 8:

[0052] The graphite was left to stand at room temperature for 30 min with concentrated sulfuric acid and potassium permanganate, and the mass ratio of the graphite, the concentrated sulfuric acid, and the potassium permanganate was 1:5:0.5. The graphite was washed with water to have a pH value of 6-7 and then dried. The graphite was heated in a muffle furnace at 900°C for 12 s to become expanded graphite.

[0053] The expanded graphite was blended with 1% mass fraction of glass fiber single fiber with length of 1 mm by a ball mill for 2 h, and the mixture was sprayed with 2% polysorbate aqueous solution and dried. The uniformly blended expanded graphite was repeatedly compressed at 1 MPa for 4 times, each time for 7 min, and then repeatedly compressed at 12 MPa for 3 times, each time for 8 min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 10.6 MPa, an elongation at break of 1.23%, and a creep rate of 0.14%. The flexible graphite sheet without filler had a tensile strength of 7.7 MPa, an elongation at break of 0.41%, and a creep rate of 0.22% under the same conditions.

[0054] Example 9:

[0055] The graphite was left to stand at room temperature for 30 min with concentrated sulfuric acid and perchloric acid, and the mass ratio of the graphite, the concentrated sulfuric acid, and the perchloric acid was 1:4:0.5. The graphite was washed with water to have a pH value of 6-7 and then dried. The graphite was heated in a muffle furnace at 900°C for 10 s to become expanded graphite.

[0056] The expanded graphite was blended with 2% by mass of basalt single fiber with a length of 2 mm in ethylene glycol at 100°C under high-speed stirring at 600 rpm for 2 h. The dispersion was then suction filtered, and the remaining mixture was washed with water and dried. The mixture was then sprayed with 0.5% aqueous polysorbate and dried. The blended expanded graphite was repeatedly compressed at 2 MPa for 5 times, each time for 3 min, and then repeatedly compressed at 20 MPa for 3 times, each time for 6 min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 14.3 MPa, an elongation at break of 0.82%, and a creep rate of 0.08%. A flexible graphite sheet without filler had a tensile strength of 8.0 MPa, an elongation at break of 0.43%, and a creep rate of 0.17% under the same conditions.

[0057] Example 10:

[0058] The graphite was left to stand at room temperature for 30 min with concentrated sulfuric acid and potassium permanganate at a mass ratio of 1:5:0.5. The graphite was washed with water until the pH value was 6-7, and then dried. The graphite was heated in a muffle furnace at 900°C for 12 s to obtain expanded graphite.

[0059] The expanded graphite was blended with 1.5% by mass of boron nitride single fiber with a length of 3 mm in dimethylformamide at 120°C under high-speed stirring at 800 rpm for 1.5 h. The dispersion was then suction filtered, and the remaining mixture was washed with water and dried. The mixture was then sprayed with 1% aqueous polysorbate and dried. The blended expanded graphite was repeatedly compressed at 3 MPa for 4 times, each time for 4 min, and then repeatedly compressed at 15 MPa for 4 times, each time for 5 min, to obtain a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 13.2 MPa, an elongation at break of 0.73%, and a creep rate of 0.09%. A flexible graphite sheet without filler had a tensile strength of 7.8 MPa, an elongation at break of 0.44%, and a creep rate of 0.16% under the same conditions.

[0060] Comparative Example 1:

[0061] The graphite was left to stand at room temperature for 30 min with concentrated sulfuric acid and potassium permanganate at a mass ratio of 1:5:0.5. The graphite was washed with water until the pH value was 6-7, and then dried. The graphite was heated in a muffle furnace at 900°C for 12 s to obtain expanded graphite.

[0062] The expanded graphite was blended with 1% by mass of glass fiber monofilament of 1 mm in length using a ball mill for 2 h. The uniformly blended expanded graphite was repeatedly compressed at 1 MPa for 4 times, each time for 1 min, to produce a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 5.5 MPa, an elongation at break of 1.37%, and a creep rate of 0.84%. A flexible graphite sheet without filler had a tensile strength of 3.7 MPa, an elongation at break of 0.47%, and a creep rate of 1.22% under the same conditions.

[0063] Comparative Example 2:

[0064] The graphite was left to stand at room temperature for 30 min in concentrated sulfuric acid and perchloric acid at a mass ratio of 1:3:0.5. The graphite was washed with water to a pH of 6-7 and then dried. The graphite was heated in a muffle furnace at 950°C for 10 s to become expanded graphite.

[0065] The expanded graphite was blended with 2.5% by mass of boron nitride monofilament of 3 mm in length in ethylene glycol under high-speed stirring at 8000 rpm for 2 h. The dispersion was then suction filtered, and the filtered residue was washed with water and dried. The mixture was then sprayed with 0.5% polyethylene oxide aqueous solution and dried. The expanded graphite microsheets were exfoliated and were no longer graphite worms. The uniformly blended expanded graphite was first repeatedly compressed at 2 MPa for 8 times, each time for 2 min, and then repeatedly compressed at 5 MPa for 5 times, each time for 10 min, to produce a flexible graphite sheet. The final flexible graphite sheet had a tensile strength of 4.7 MPa, an elongation at break of 0.76%, and a creep rate of 2.4%.

Claims

1. A method for preparing a high-strength flexible graphite sheet, characterized in that... The preparation method includes the following steps: Step (1): Place the graphite in a mixed solvent of acid and oxidant and let it stand at room temperature for 30 minutes. Then take out the graphite and wash it with water until the pH value reaches 6-7. Then dry it to obtain intercalated, washed and dried graphite. Step (2): Heat the graphite from step (1) after intercalation, washing and drying in a muffle furnace at 700-1000℃ for 7-30s to obtain expanded graphite; Step (3): Blend expanded graphite and high-temperature resistant fiber, spray with surfactant solution, and then dry; wherein the mass ratio of high-temperature resistant fiber to expanded graphite is (0.05-3):100; the blending method is wet mixing; the wet mixing is to stir in the dispersion at a speed of 200-1000 rpm and a temperature of 60-120℃ for 1-3 hours, and finally filter and dry; the dispersion is ethylene glycol or dimethylformamide; The surfactant is one of polysorbate, polyethylene oxide, or polyethylene glycol aqueous solution; the mass concentration of the surfactant is 0.5-2%; the surfactant reduces the interaction force between expanded graphite microsheets, thereby reducing the degree of complete adhesion of the expanded graphite during compression. The high-temperature resistant fiber is one or more of basalt fiber, aluminosilicate fiber, boron nitride fiber, and glass fiber; Step (4): Preparation of flexible graphite sheets (4-1) The expanded graphite and high-temperature resistant fiber after being blended and dried in step (3) are repeatedly compressed at 0.5-5MPa 2-8 times, with each compression lasting 2-10 minutes; (4-2) Compress the graphite sheet repeatedly at 5-30 MPa 2-8 times, with each compression time being 2-10 min, to obtain a flexible graphite sheet.

2. The method as described in claim 1, characterized in that... The mass ratio of graphite, acid, and oxidant in step (1) is 1:(1-10):(0.2-1).

3. The method as described in claim 1 or 2, characterized in that... The acid in step (1) is concentrated sulfuric acid or concentrated nitric acid, and the oxidant is potassium permanganate or perchloric acid.

4. The method as described in claim 1, characterized in that... Step (2) The heating temperature in the muffle furnace is 800-950℃ and the heating time is 10-15s.

5. The method as described in claim 1, characterized in that... The high-temperature resistant fiber mentioned in step (3) is a single fiber with a length of 1-3 mm.

6. The method as described in claim 1, characterized in that... The high-temperature resistant fiber in step (3) is one or both of basalt fiber and boron nitride fiber; the mass ratio of the high-temperature resistant fiber to expanded graphite is (1-2):

100.

7. The method as described in claim 1, characterized in that... The dispersion in step (3) is ethylene glycol, the stirring temperature is 80-110℃, the stirring speed is 400-800rpm, and the stirring time is 1-2h.

8. The method as described in claim 1, characterized in that... In step (4-1), the compression pressure is 1-3 MPa, the compression is performed 3-6 times, and the compression time is 4-8 min each time; in step (4-2), the compression pressure is 8-20 MPa, the compression is performed 3-6 times, and the compression time is 4-8 min each time.

9. A high-strength flexible graphite sheet, prepared by any one of the methods described in claims 1-8.

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