A method for preparing an antioxidant coating on the surface of a graphite product and a graphite crucible containing the coating.

Abstract

This invention discloses a method for preparing an anti-oxidation coating on the surface of graphite products and a graphite crucible containing the coating. The method for preparing the anti-oxidation coating includes the following steps: mixing an ethanol solution of an alcohol-soluble resin with an ethanol solution of boric acid; adding an acid catalyst to adjust the pH value, and then aging to form a boric acid-resin gel impregnation solution; placing the graphite crucible in an impregnation container, drawing a vacuum, and completely immersing the graphite crucible in the boric acid-resin gel impregnation solution; introducing a protective atmosphere and adjusting the pressure to continue impregnation; separating the graphite crucible from the boric acid-resin gel impregnation solution and performing vacuum sintering, thereby obtaining an anti-oxidation coating on the surface and surface pores of the graphite crucible. The graphite crucible prepared by this invention has a thermal shock resistance time of up to 72 hours. After 72 hours, the graphite crucible can still basically remain intact, which is significantly better than the graphite crucibles of the prior art, significantly increasing the service life of the graphite crucible and reducing the cost for vacuum high-temperature evaporation aluminum film manufacturers.

Description

Technical Field

[0001] This invention belongs to the field of graphite material surface treatment technology, specifically relating to a method for preparing an antioxidant coating for graphite products (especially graphite crucibles) and a graphite crucible containing the coating. Background Technology

[0002] Graphite materials are widely used in high-temperature vacuum evaporation equipment, such as graphite crucibles, due to their excellent high-temperature stability, thermal conductivity, and thermal shock resistance. However, two major problems exist in actual production (such as vacuum high-temperature aluminum film evaporation): First, during vacuum high-temperature aluminum film evaporation, molten aluminum easily seeps into the micropores and gaps of the graphite crucible. Due to the difference in thermal expansion coefficients between aluminum and graphite, the crucible is prone to cracking upon cooling. Second, because the production process requires repeated opening and closing of the vacuum chamber to add aluminum, the hot graphite crucible is repeatedly exposed to air, resulting in severe thermal shock and high-temperature oxidation, causing the oxide layer on the crucible surface to peel off, ultimately leading to failure.

[0003] To address the aforementioned issues, Chinese Patent Publication No. CN200410049150.8 discloses a process involving resin and aluminum salt impregnation and sintering. In this process, resin containing a specific metal salt is deeply filled into the pores of graphite. Ammonia is used for curing, causing the metal salt to convert into hydroxides that precipitate within the pores. Finally, high-temperature treatment decomposes the hydroxides into high-melting-point metal oxide ceramics, which, together with the carbonized carbon matrix of the resin, form a dense composite sealing layer, effectively preventing the penetration and corrosion of high-temperature molten aluminum. This method allows graphite crucibles to withstand 22 thermal shocks before failure, extending their service life to some extent. However, with increasing industrial demands for continuous production efficiency and cost control, the thermal shock resistance of this technology is no longer sufficient to meet higher usage requirements, leading to frequent graphite crucible replacements and increased production costs for enterprises. Figure 1 As shown, the graphite crucible cracked after 22 thermal shocks, and its integrity could not be guaranteed. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a new method for preparing an anti-oxidation coating on the surface of graphite products and a graphite crucible containing the coating. The graphite crucible prepared by this invention has good thermal shock resistance and anti-oxidation ability, and a long service life.

[0005] The objective of this invention is achieved by the following method: a method for preparing an antioxidant coating on the surface of a graphite product, comprising the following steps: (1) Mix the ethanol solution of the alcohol-soluble resin with the ethanol solution of boric acid until homogeneous; (2) Add an acid catalyst to the mixed solution in step (1), adjust the pH value to 2~4, and then age it at 40~60℃ for 36~60 hours to form a boric acid resin gel impregnation solution; (3) Place the cleaned and dried graphite crucible in an impregnation container, evacuate to a vacuum degree of less than 10 Pa, and completely immerse the graphite crucible in the boric acid resin gel impregnation solution for 0.5 h to 2 h. (4) Introduce a protective atmosphere and adjust the pressure to 0.1~0.6 MPa, and maintain the immersion at this pressure for 0.5h~2h; (5) Separate the graphite crucible from the boric acid resin gel impregnation liquid and perform vacuum sintering. Under a protective atmosphere, heat the crucible at a rate of 1~5℃ / min, first heat it to 800℃ and hold it for 1~2h, then heat it to 1200℃ and hold it for 1~2h, and finally heat it to 1600℃ and hold it for 1~2h. Then cool it naturally to obtain an anti-oxidation coating on the surface of the graphite crucible and in the surface pores.

[0006] The ethanol solution of the alcohol-soluble resin in step (1) is prepared by mixing the alcohol-soluble resin and ethanol at a mass-volume ratio of 1g:50mL~100mL and heating to dissolve in a water bath at 50℃~80℃; the ethanol solution of the boric acid is prepared by mixing the boric acid and ethanol at a mass-volume ratio of 1g:10mL~50mL and heating to dissolve in a water bath at 50℃~70℃.

[0007] The alcohol-soluble resin mentioned in step (1) is a phenolic resin, a modified phenolic resin, an alkyd resin, or a polyester resin. The main function of the above-mentioned alcohol-soluble resin is to provide a carbon source. Phenolic resin, modified phenolic resin, alkyd resin, or polyester resin can easily form a gel with boric acid. Other unlisted resins can also be used.

[0008] The acid catalyst in step (2) is one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid or acetic acid.

[0009] The protective atmosphere in step (4) and / or step (5) is nitrogen, argon or clean air.

[0010] The vacuum impregnation and vacuum sintering in steps (3) to (5) are carried out in an integrated vacuum impregnation and sintering equipment.

[0011] An antioxidant and corrosion-resistant graphite crucible is prepared using the above method.

[0012] Compared with the prior art, the present invention has the following advantages: Excellent antioxidant protection: By combining the sol-gel method with vacuum pressure impregnation, boric acid resin gel is fully filled into the pores of graphite. After high-temperature sintering, a composite structure of dense boron carbide ceramic layer and borate glass phase is formed. Boron carbide has extremely high hardness and resistance to aluminum liquid corrosion, while the glass phase effectively seals the surface micropores and prevents oxygen from penetrating. The two work synergistically to significantly improve antioxidant and anti-permeability capabilities.

[0013] Significantly improved thermal shock resistance: The anti-oxidation coated graphite crucible prepared by the method described in this invention can withstand thermal shock failure for up to 72 hours, approximately 62 cycles, which is far higher than the 22 cycles of the prior art. This significantly enhances the thermal shock resistance stability of the graphite matrix, extends the service life of the crucible, and significantly reduces the production costs of enterprises. Attached Figure Description

[0014] Figure 1 It is a graphite crucible that has been subjected to 22 thermal shocks in the existing technology (and has been broken).

[0015] Figure 2 This is a photograph (remaining intact) of the graphite crucible prepared according to the present invention after 72 hours of thermal shock resistance.

[0016] Figure 3 This is a schematic diagram of the integrated vacuum impregnation and sintering equipment.

[0017] Figure 4 This is a structural schematic diagram of an integrated vacuum impregnation and sintering equipment from one angle.

[0018] Figure 5 This is a structural schematic diagram of an integrated vacuum impregnation and sintering equipment from another angle.

[0019] Figure 6 This is a cross-sectional view of an integrated vacuum impregnation and sintering equipment.

[0020] Figure 7 This is a cross-sectional SEM image (from right to left) of the graphite crucible prepared according to the present invention.

[0021] Figure 8 This is an EDS scan line position diagram of the cross section of the graphite crucible prepared by this invention (the right side of the sample is the sample surface, and the data is observed from right to left).

[0022] Figure 9 This is a distribution diagram of the secondary photon counts in the energy spectrum of each element.

[0023] Figure 10 These are the energy spectra of each element scanned.

[0024] Figure 11 This is a graph showing the weight loss rate-time curves of different graphite crucible samples in an air atmosphere at 800℃. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading the contents of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by this invention. Example 1

[0026] An antioxidant and corrosion-resistant graphite crucible, the preparation method includes the following steps: (1) Weigh 10g of phenolic resin, dissolve it in 500mL of ethanol, and stir in an 80℃ water bath until completely dissolved; weigh 10g of boric acid, dissolve it in 200mL of ethanol, and stir in a 70℃ water bath until completely dissolved.

[0027] (2) Mix the two solutions above, add acetic acid to adjust the pH value to 3.0, and let it stand at 50°C for 48 hours to obtain boric acid resin gel impregnation solution.

[0028] (3) Place the pretreated and dried graphite crucible in a container such as... Figures 3-6 In the vacuum impregnation and sintering integrated equipment shown, the vacuum is drawn to 5 Pa, the impregnation liquid is injected, and vacuum impregnation is carried out for 1 hour.

[0029] (4) Fill the vacuum impregnation and sintering integrated equipment with high-purity argon gas, adjust the pressure to 0.3 MPa, and impregnate for 1 hour.

[0030] (5) Drain the impregnation solution.

[0031] (6) Under argon protection, the temperature is increased to 800℃ at 2℃ / min and held for 1 hour; the temperature is increased to 1200℃ at 2℃ / min and held for 1 hour; the temperature is increased to 1600℃ at 2℃ / min and held for 1 hour; the furnace is cooled naturally to obtain an anti-oxidation and anti-corrosion graphite crucible with an anti-oxidation coating.

[0032] like Figures 3-6As shown, the integrated vacuum impregnation and sintering equipment includes an impregnation and sintering tank 1. An upper cover 13 is provided on the upper part of the impregnation and sintering tank 1, forming a good seal when the upper cover 13 is closed. Preferably, the upper cover 13 adopts a double-layer water-jacketed end cap structure, with the upper cover jacket sealingly connected to a cooling water circulation pipeline to achieve furnace cooling. The impregnation and sintering tank 1 has an inner furnace body 3 that accommodates a crucible 2. The crucible 2 is preferably placed upside down inside the inner furnace body 3 to facilitate the smooth discharge of the impregnation liquid from the inner furnace body 3 after impregnation. The side wall has an exhaust port 4 and an inlet port 5. The exhaust port 4 is connected to a vacuum system, and the inlet port 5 is connected to a gas source supplying nitrogen, argon, or clean air. An impregnation liquid conduit 6 is installed at the top of the impregnation and roasting tank 1. One end of the impregnation liquid conduit 6 is connected to the impregnation liquid storage tank 14, and the outlet of the other end extends into the bottom of the inner furnace body 3. The impregnation and roasting tank 1 is equipped with a heating assembly for heating the crucible 2. The heating assembly includes a heater 7, a graphite electrode 8, and a water-cooled electrode 9. The heater 7 is located inside the inner furnace body 3. The graphite electrode 8 is installed at the bottom of the heater 7. The water-cooled electrode 9 is installed at the bottom of the graphite electrode 8. The other end of the water-cooled electrode 9 passes through the bottom of the inner furnace body 3 and extends downward. A graphite insulation layer is provided on the outside of the inner furnace body and the heating assembly. The system also includes a control system 10 to control the operation of the vacuum system, the heating assembly, the inlet port, and the impregnation liquid conduit 6.

[0033] The graphite insulation layer includes a graphite insulation cylinder 31 installed outside the furnace body and a graphite felt 32 installed outside the heating components. Furthermore, a graphite felt is also installed on the upper part of the inner furnace body to enclose the inner furnace body 3 as much as possible, reducing heat loss. The graphite felt 32 and the graphite insulation cylinder 31 are not completely sealed; there is a certain gap. This gap ensures pressure balance between the inner furnace body 3 and the impregnation and roasting tank 1, preventing pressure differences from affecting process stability. Simultaneously, the tight insulation layer reduces heat loss, resulting in significant energy savings. The reasonable structural design is conducive to pressure balance and temperature uniformity.

[0034] The impregnation and calcination tank 1 adopts a double-layer water-cooled structure. An inlet and an outlet are provided on the outer wall of the tank. Furthermore, a refrigeration system is installed between the inlet and outlet to provide a low-temperature water source for the water-cooling system. The double-layer water-cooled structure of the impregnation and calcination tank 1 and the double-layer water-jacketed end cap structure of the top cover effectively reduce the temperature of the outer wall of the equipment, protect the seals and the safety of operators, and extend the service life of the equipment.

[0035] A pressure gauge 11 and a pressure relief valve 12 are connected to the side wall of the impregnation and calcination tank 1. The vacuum level inside the impregnation and calcination tank 1 is displayed by the pressure gauge, and the impregnation and calcination tank 1 can withstand a pressure range of 10. ~4 Pa~1 MPa, and the pressure is quickly released through the pressure relief valve after calcination.

[0036] A thermocouple (not shown in the figure) is installed on the inner furnace body 3 to monitor the temperature. The inner furnace body contains the core area of ​​the crucible, where the temperature can reach up to 1700℃. The temperature inside the inner furnace body can be adjusted as needed. The core area of ​​the inner furnace body can reach a maximum temperature of 1700℃. Combined with graphite heaters, graphite electrodes, and water-cooled electrodes, along with an insulation layer composed of graphite insulation cylinders and graphite felt, the temperature rise is stable and the insulation effect is good, meeting the requirements of high-temperature sintering.

[0037] The impregnation solution storage tank 14 is a constant-temperature tank, maintaining a constant temperature of 30℃. The tank's volume is matched to the solvent in the inner furnace. A solenoid valve 15 is installed on the impregnation solution conduit 6, which is controlled by a controller in the electrical control cabinet to achieve automatic liquid feeding. Maintaining the impregnation solution storage tank temperature at 30℃ ensures the fluidity and wetting properties of the impregnation solution. Combined with the inverted crucible design, it facilitates the smooth discharge of residual liquid after impregnation, reducing waste and improving impregnation uniformity.

[0038] The specific steps for vacuum impregnation and vacuum sintering of graphite crucibles in an integrated vacuum impregnation and sintering equipment are as follows: Open the top cover of the impregnation calcination tank 1, place the crucible 2 upside down inside the inner furnace body 3, and close the top cover 13 to form a sealed space in the impregnation calcination tank 1; evacuate the impregnation calcination tank 1 using the vacuum system to achieve the required vacuum level, such as 10 Pa; open the solenoid valve on the impregnation liquid conduit 6 to allow the impregnation liquid to enter the inner furnace body 3, ensuring the impregnation liquid level is sufficient to submerge the crucible and exceed the upper edge of the crucible by at least 10 mm, and impregnate for a certain period of time; introduce nitrogen (argon, clean air, etc.) into the impregnation calcination tank 1 through the air inlet 5 until the pressure reaches the required level, such as 0.1~0.6 MPa, and continue impregnating for a certain period of time; adjust the pressure inside the impregnation calcination tank 1 to discharge the impregnation liquid from the impregnation calcination tank 1; then heat the tank according to a specific heating program, heating the crucible 2 inside the inner furnace body 3 using the heating components, and protecting and cooling the impregnation calcination tank 1 using the water cooling system.

[0039] Vacuum impregnation and vacuum sintering of graphite crucibles can be carried out in an integrated vacuum impregnation and sintering equipment or in a separate equipment, while maintaining the same process parameters as the above steps, such as impregnation pressure, impregnation time, sintering pressure, and sintering heating rate.

[0040] The cross-section of the antioxidant and erosion-resistant graphite crucible prepared in Example 1 was scanned using SEM, as shown below. Figure 7 As shown. From Figure 7 It can be seen that the coating is tightly bonded to the graphite substrate, with no obvious interface cracks or peeling, and the coating thickness is uniform. Figure 7 EDS line scan analysis was performed on the white scan line area, such as... Figure 8 As shown, the secondary photon count distribution of each element is as follows: Figure 9 As shown, the corresponding energy spectrum is as follows: Figure 10As shown. EDS analysis results indicate that from the surface of the graphite crucible to its interior ( Figure 8 (From right to left) Besides carbon (C), boron (B) is the main penetrating element. The count intensity of boron increases significantly in the coating area and remains at a high level within about 1 mm from the surface, indicating that boron has successfully penetrated into the pores of the graphite surface. Energy dispersive spectroscopy (EDS) Figure 10 Further investigation confirmed that the coating contained elements such as B, C, and O. Based on the process conditions, it was determined that boron carbide (B4C) and a small amount of borate glass phase were generated in the coating.

[0041] Table 1 shows the EDS quantitative analysis data. Due to the low content of elements such as Al, Si, and S, Table 2 only retains two decimal places, resulting in the content of elements such as Al, Si, and S being 0.00. This does not mean that Al, Si, and S are not present.

[0042] Table 1 Example 2

[0043] The basic steps are the same as in Example 1, except that: in step (1), 10g of boron-modified phenolic resin is dissolved in 1000mL of ethanol and 10g of boric acid is dissolved in 500mL of ethanol; in step (2), the pH value is adjusted to 2.0 and aged at 40℃ for 60h; in step (3), the vacuum is drawn to 7Pa and vacuum impregnated for 2 hours; in step (4), clean air is introduced to a pressure of 0.1MPa and impregnated for 2h. Example 3

[0044] The basic steps are the same as in Example 1, except that: in step (1), the ratio of epoxy modified phenolic resin to ethanol is 1g:80mL, and the ratio of boric acid to ethanol is 1g:10mL; in step (2), the pH value is adjusted to 4.0 and aged at 40℃ for 36h; in step (3), the vacuum is drawn to 6Pa and vacuum impregnated for 0.5h; in step (4), nitrogen is introduced to a pressure of 0.6MPa and impregnated for 0.5h.

[0045] To further verify the protective effect of the antioxidant coating prepared in this invention under high-temperature oxidation conditions, isothermal oxidation weight loss tests were conducted on the coated graphite crucibles prepared in Examples 1-3. Three samples were provided for each of Examples 1-3, namely samples 5-7, 8-10, and 11-13. All samples were placed in a muffle furnace at 1100℃ and subjected to a room temperature-1100℃ thermal shock oxidation cycle under atmospheric pressure. Samples were weighed every 15 minutes, and the weight loss rate was calculated. The results are as follows: Figure 11 As shown.

[0046] from Figure 11It can be seen that the weight loss rate of the coated graphite crucibles prepared using Examples 1-3 of the present invention is always less than 10% within 150 minutes of oxidation, indicating that the coating can effectively isolate oxygen and significantly inhibit the high-temperature oxidation of the graphite substrate, making it suitable for harsh working conditions such as vacuum high-temperature evaporation where repeated contact with air occurs.

[0047] The graphite crucibles prepared in Examples 1-3 were used on an aluminum vapor deposition production line. One roll of aluminum film was vapor-deposited per hour. Then, aluminum material was added after opening the cavity, with the addition time being approximately 10 minutes. Aluminum film deposition was then continued. This process was repeated. The results are shown in Table 2 below. Table 2

[0048] The test results show that the graphite crucible prepared by this invention can withstand thermal shock failure for up to 72 hours. Figure 2 As shown, after 72 hours, the graphite crucible remained largely intact, significantly superior to existing graphite crucibles, significantly increasing the service life of the graphite crucible and reducing the cost for vacuum high-temperature aluminum film deposition companies.

[0049] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several changes and improvements without departing from the overall concept of the present invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an antioxidant coating on the surface of a graphite product, characterized in that: Includes the following steps, (1) Mix the ethanol solution of the alcohol-soluble resin with the ethanol solution of boric acid until homogeneous; (2) Add an acid catalyst to the mixed solution in step (1), adjust the pH value to 2~4, and then age it at 40~60℃ for 36~60 hours to form a boric acid resin gel impregnation solution; (3) Place the cleaned and dried graphite crucible in an impregnation container, evacuate to a vacuum degree of less than 10 Pa, and completely immerse the graphite crucible in the boric acid resin gel impregnation solution for 0.5 h to 2 h. (4) Introduce a protective atmosphere and adjust the pressure to 0.1~0.6 MPa, and maintain the immersion at this pressure for 0.5h~2h; (5) Separate the graphite crucible from the boric acid resin gel impregnation liquid and perform vacuum sintering. Under a protective atmosphere, heat the crucible at a rate of 1~5℃ / min, first heat it to 800℃ and hold it for 1~2h, then heat it to 1200℃ and hold it for 1~2h, and finally heat it to 1600℃ and hold it for 1~2h. Then cool it naturally to obtain an anti-oxidation coating on the surface of the graphite crucible and in the surface pores.

2. The method for preparing an antioxidant coating on the surface of a graphite product according to claim 1, characterized in that: The ethanol solution of the alcohol-soluble resin in step (1) is prepared by mixing the alcohol-soluble resin and ethanol at a mass-volume ratio of 1g:50mL~100mL and heating to dissolve in a water bath at 50℃~80℃; the ethanol solution of the boric acid is prepared by mixing the boric acid and ethanol at a mass-volume ratio of 1g:10mL~50mL and heating to dissolve in a water bath at 50℃~70℃.

3. The method for preparing an antioxidant coating on the surface of a graphite product according to claim 1, characterized in that: The alcohol-soluble resin mentioned in step (1) is a phenolic resin, a modified phenolic resin, an alkyd resin, or a polyester resin.

4. The method for preparing an antioxidant coating on the surface of a graphite product according to claim 1, characterized in that: The acid catalyst in step (2) is one of dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid or acetic acid.

5. The method for preparing an antioxidant coating on the surface of a graphite product according to claim 1, characterized in that: The protective atmosphere in step (4) and / or step (5) is nitrogen, argon or clean air.

6. The method for preparing an antioxidant coating on the surface of a graphite product according to claim 1, characterized in that: The vacuum impregnation and vacuum sintering in steps (3) to (5) are carried out in an integrated vacuum impregnation and sintering equipment.

7. An antioxidant and corrosion-resistant graphite crucible, characterized in that, It is prepared by the method described in any one of claims 1 to 6.

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