Impregnation liquid for graphite impregnation, application of impregnation liquid and obtained high-performance graphite material

Abstract

The invention relates to impregnation liquid for graphite impregnation, application of the impregnation liquid and an obtained high-performance graphite material, and belongs to the technical field of graphite surface treatment. According to the impregnation liquid, a synergistic system is formed by phosphoric acid, aluminum dihydrogen phosphate, aluminum hydroxide, hydrochloric acid and other components according to a specific ratio, and after pressure impregnation and curing, a compact aluminum phosphate ceramic protection layer can be formed on the surface of graphite and in internal pores. The protective layer can effectively block oxygen permeation, so that the oxidation resistance of the graphite product is remarkably improved; and meanwhile, graphite pores are fully filled with the impregnation liquid, so that the compactness, hardness and breaking strength of the material are synchronously improved, and the service life of the material in a severe environment is remarkably prolonged. The service life of the treated graphite rotor in molten aluminum degassing is prolonged from 3-4 days to 7-10 days, and the core problems that the rotor is prone to loss and frequent in replacement are effectively solved. The comprehensive performance of the graphite product treated by the impregnation liquid is remarkably improved, and the harsh application requirements in the fields of aluminum processing and the like can be better met.

Description

Technical Field

[0001] This invention relates to the field of graphite surface treatment technology, and in particular to an impregnation solution for graphite impregnation, its application, and the resulting high-performance graphite material. Background Technology

[0002] Graphite products are widely used due to their high temperature resistance, self-lubrication, and good thermal conductivity. In the aluminum processing industry, this material is used in the core components of online refining and degassing equipment—rotors and rotors. These rotors need to rotate at high speeds in molten aluminum at a high temperature of approximately 750°C, making the working environment extremely harsh.

[0003] Under these harsh operating conditions, the inherent shortcomings of graphite materials become the primary technical problem: firstly, it is highly susceptible to oxidation and ablation under high-temperature and oxygen-rich conditions; secondly, the material has numerous internal pores, resulting in insufficient hardness and low flexural strength. This directly leads to short service life and frequent replacement of rotor components. The industry typically requires a rotor service life of ≥700 ladles of molten aluminum, while the actual service life of unreinforced ordinary graphite rotors is only about 3-4 days (processing an average of 140 ladles of molten aluminum per day, equivalent to approximately 420-560 ladles), making it difficult to reliably meet the demands of continuous production. Common methods such as resin impregnation or simple coatings suffer from problems such as easy peeling at high temperatures and short-lived protective effects, failing to simultaneously and significantly improve the material's oxidation resistance and mechanical properties.

[0004] Therefore, developing a surface modification technology that can deeply penetrate the graphite matrix and form a stable reinforcing phase at high temperatures, thereby significantly extending the service life of rotors in high-temperature molten aluminum, has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art, namely, to address the problems of easy oxidation and burn-off and short lifespan of graphite rotors used in aluminum refining, by providing an impregnation solution for graphite impregnation, its application, and the resulting high-performance graphite material. This impregnation solution can form a dense aluminum phosphate ceramic protective layer inside the graphite, significantly improving its oxidation resistance, hardness, and flexural strength, thus making it particularly suitable for preparing long-life graphite rotors / rotors for aluminum degassing equipment.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides an impregnation solution for graphite impregnation, comprising an aluminum source, a phosphorus source, an acid modifier, and a solvent.

[0007] In a preferred embodiment of the impregnation solution of the present invention, the aluminum source includes aluminum hydroxide and / or aluminum dihydrogen phosphate, the phosphorus source includes phosphoric acid and / or aluminum dihydrogen phosphate, the acidity regulator includes hydrochloric acid, and the solvent includes water.

[0008] In a preferred embodiment of the impregnation solution of the present invention, the aluminum source is aluminum hydroxide and aluminum dihydrogen phosphate; the phosphorus source is phosphoric acid and aluminum dihydrogen phosphate; the acidity regulator is hydrochloric acid; and the solvent is water.

[0009] Preferably, the water is deionized water.

[0010] As a preferred embodiment of the impregnation solution of the present invention, the impregnation solution is composed of aluminum hydroxide, aluminum dihydrogen phosphate, phosphoric acid, hydrochloric acid and water.

[0011] As a preferred embodiment of the impregnation solution of the present invention, the impregnation solution is composed of the following components by weight: 70-90 parts aluminum hydroxide, 300-320 parts aluminum dihydrogen phosphate, 110-140 parts phosphoric acid, 65-85 parts hydrochloric acid, and the balance being water.

[0012] Secondly, the present invention provides a high-performance graphite material, which is obtained by impregnating a graphite substrate with the above-mentioned impregnation solution.

[0013] Thirdly, the present invention provides a method for preparing the above-mentioned high-performance graphite material, comprising the following steps: S1. Pre-treat the graphite substrate; S2. Prepare the impregnation solution; S3. Place the pretreated graphite substrate in the impregnation solution and perform pressure impregnation treatment; S4. Curing treatment is performed on the impregnated graphite substrate.

[0014] In a preferred embodiment of the preparation method of the high-performance graphite material of the present invention, step S1 includes pretreatment with organic solvent cleaning and drying. Specifically, the graphite product (such as graphite block, sealing ring, etc.) is first cleaned of surface oil stains and dust with acetone or alcohol, and then dried to remove internal moisture and prevent moisture from affecting the penetration of the subsequent impregnation solution.

[0015] In a preferred embodiment of the preparation method of the high-performance graphite material of the present invention, in step S3, the pressure of the pressurized impregnation treatment is 0.5-1.2 MPa, and the holding time is 24-72 hours; and / or, in step S4, the curing treatment includes a first curing at 60-100°C for 18-30 hours; after the first curing, a second curing is performed at 150-200°C for 36-72 hours. During the second curing, i.e., the high-temperature curing stage, the active components in the impregnation solution react inside and on the surface of the graphite pores, generating a continuous and dense aluminum phosphate-based ceramic protective layer in situ. This ceramic phase is firmly bonded to the graphite matrix, thereby endowing the material with excellent hardness, strength, and oxidation resistance.

[0016] Fourthly, the present invention provides the application of the above-mentioned impregnation solution in the preparation of high-performance graphite materials.

[0017] Fifthly, the present invention provides a graphite rotor, which is processed from the high-performance graphite material described in the present invention.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides an impregnation solution for graphite impregnation, its application, and the resulting high-performance graphite material. The impregnation solution, composed of phosphoric acid, aluminum dihydrogen phosphate, aluminum hydroxide, and hydrochloric acid in a specific ratio, forms a synergistic system. After pressure impregnation and curing, it forms a dense aluminum phosphate ceramic protective layer on the graphite surface and within its internal pores. This protective layer effectively blocks oxygen penetration, significantly improving the oxidation resistance of graphite products. Simultaneously, by fully filling the graphite pores with the impregnation solution, the density, hardness, and flexural strength of the material are simultaneously improved, thus significantly extending its service life in harsh environments. The service life of the treated graphite rotor in aluminum degassing is extended from 3-4 days (420-560 packs) to 7-10 days (980-1400 packs), achieving a doubling and consistently exceeding the industry quality assurance requirement of ≥700 packs, effectively solving the core problem of rotor wear and frequent replacement. Graphite products treated with this impregnation solution exhibit significantly improved overall performance, better meeting the demanding application requirements in fields such as aluminum processing. Detailed Implementation

[0019] To better illustrate the purpose, technical solution, and advantages of this invention, the invention will be further described below with reference to specific embodiments. The embodiments described below are some, but not all, embodiments of this invention. The embodiments of this invention are used to illustrate the invention, not to limit it. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Unless otherwise specified, experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. The raw materials and reagents used are commercially available conventional products or products that conform to relevant national / industry standards and are all commercially available.

[0020] Example 1 A method for preparing a high-performance graphite material specifically includes the following steps: S1. Pretreatment of graphite substrate: First, the graphite substrate surface is ultrasonically cleaned with acetone for 10 minutes to thoroughly remove oil stains and dust. Then, the cleaned graphite substrate is placed in an oven at 110°C and dried for 3 hours to ensure that the moisture in its internal pores is fully removed, so as to avoid affecting the penetration and reaction of the impregnation solution during subsequent impregnation.

[0021] S2. Preparation of impregnation solution: Weigh the following raw materials based on a total mass of 1000 kg: 80 kg aluminum hydroxide, 310 kg aluminum dihydrogen phosphate, 125 kg phosphoric acid (mass fraction 85%), 75 kg hydrochloric acid (mass fraction 31%), and 410 kg deionized water. Under stirring conditions, add the above raw materials sequentially to the reaction vessel and continue stirring and mixing at 50°C for 4 hours until a uniform, stable, and transparent solution is formed, which is the impregnation solution.

[0022] S3. Pressure Impregnation Treatment: The pretreated graphite substrate from step S1 is completely immersed in the impregnation solution prepared in step S2, and both are placed together in a pressure tank impregnation furnace and sealed. A pressure of 0.8 MPa is applied to the tank and maintained at this pressure for 48 hours, allowing the impregnation solution to fully penetrate and fill the pores inside the graphite substrate under pressure.

[0023] S4. Post-treatment curing: After impregnation, remove the graphite substrate and allow it to drip off excess impregnation solution. Place the drip-dried graphite substrate in an oven for curing. First curing (drying): Dry at 80°C for 24 hours to remove most of the free solvent and moisture, forming a preliminary adhesion layer; Second curing (high-temperature curing): To obtain better performance, the graphite substrate after the first curing is transferred to another oven and cured at 180°C for another 48 hours. At this high temperature, the components in the impregnation solution react further to form a dense aluminum phosphate ceramic phase, which is firmly bonded to the inner wall and surface of the graphite pores.

[0024] Example 2 This embodiment provides a method for preparing high-performance graphite materials, the steps of which are basically the same as those in Example 1, the only difference being the formulation of the impregnation solution. The impregnation solution is prepared by mixing the following components: 70 kg of aluminum hydroxide, 300 kg of aluminum dihydrogen phosphate, 110 kg of phosphoric acid (mass fraction of 85%), 65 kg of hydrochloric acid (mass fraction of 31%), and 455 kg of deionized water.

[0025] Example 3 This embodiment provides a method for preparing high-performance graphite materials, the steps of which are basically the same as those in Example 1, the only difference being the formulation of the impregnation solution. The impregnation solution is prepared by mixing the following components: 90 kg of aluminum hydroxide, 320 kg of aluminum dihydrogen phosphate, 140 kg of phosphoric acid (mass fraction of 85%), 85 kg of hydrochloric acid (mass fraction of 31%), and 365 kg of deionized water.

[0026] Example 4 This embodiment provides a method for preparing a high-performance graphite material, with steps S1, S2, and S3 being exactly the same as in Example 1. Step S4 is as follows: After impregnation, the graphite substrate is removed and allowed to drip naturally to remove excess impregnation liquid from the surface. The drip-dried graphite substrate is then placed in an oven for a first curing (drying): it is dried at 80°C for 24 hours to remove most of the free solvent and moisture, thus initially fixing the impregnation liquid components, thereby obtaining the graphite material.

[0027] Comparative Example 1 This comparative example uses untreated raw graphite substrate.

[0028] Comparative Example This comparative example provides a treatment scheme for graphite material, and its preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of impregnation solution) is as follows: Take 1000 kg of deionized water and stir it at 50°C for 4 hours to prepare the impregnation solution.

[0029] Comparative Example 3 This comparative example provides a treatment scheme for graphite materials, and its preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of the impregnation solution) is as follows: Weigh the following raw materials based on a total mass of 1000 kg: 75 kg of hydrochloric acid (mass fraction 31%) and 925 kg of deionized water. Under stirring conditions, add the above raw materials sequentially to the reaction vessel and continuously stir and mix at 50°C for 4 hours until a homogeneous solution is formed, thus obtaining the impregnation solution.

[0030] Comparative Example 4 This comparative example provides a graphite material processing scheme, whose preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of the impregnation solution) is as follows: Based on a total mass of 1000 kg, the following raw materials are weighed: 80 kg of aluminum hydroxide, 310 kg of aluminum dihydrogen phosphate, 125 kg of phosphoric acid (mass fraction 85%), and 485 kg of deionized water. Under stirring conditions, the above raw materials are added sequentially to a reaction vessel and continuously stirred and mixed at 50°C for 4 hours until a homogeneous solution is formed, thus obtaining the impregnation solution.

[0031] Comparative Example 5 This comparative example provides a graphite material processing scheme, whose preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of the impregnation solution) is as follows: Weigh the following raw materials based on a total mass of 1000 kg: 80 kg aluminum hydroxide, 125 kg phosphoric acid (mass fraction 85%), 75 kg hydrochloric acid (mass fraction 31%), and 720 kg deionized water. Under stirring conditions, add the above raw materials sequentially to a reaction vessel and continuously stir and mix at 50°C for 4 hours until a homogeneous solution is formed, thus obtaining the impregnation solution.

[0032] Comparative Example 6 This comparative example provides a graphite material processing scheme, whose preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of the impregnation solution) is as follows: Weigh the following raw materials based on a total mass of 1000 kg: 310 kg of aluminum dihydrogen phosphate, 125 kg of phosphoric acid (mass fraction 85%), 75 kg of hydrochloric acid (mass fraction 31%), and 490 kg of deionized water. Under stirring conditions, add the above raw materials sequentially to the reaction vessel and continuously stir and mix at 50°C for 4 hours until a homogeneous solution is formed, thus obtaining the impregnation solution.

[0033] Comparative Example 7 This comparative example provides a graphite material processing scheme, whose preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of the impregnation solution) is as follows: Based on a total mass of 1000 kg, the following raw materials are weighed: 80 kg of aluminum hydroxide, 310 kg of aluminum dihydrogen phosphate, 125 kg of phosphoric acid (mass fraction 85%), 61 kg of nitric acid (mass fraction 65%), and 424 kg of deionized water. Under stirring conditions, the above raw materials are added sequentially to a reaction vessel and continuously stirred and mixed at 50°C for 4 hours until a homogeneous solution is formed, thus obtaining the impregnation solution.

[0034] Comparative Example 8 This comparative example provides a graphite material processing scheme, whose preparation steps S1, S3, and S4 are exactly the same as those in Example 1. Step S2 (preparation of the impregnation solution) is as follows: Weigh the following raw materials based on a total mass of 1000 kg: 50 kg aluminum hydroxide, 250 kg aluminum dihydrogen phosphate, 180 kg phosphoric acid (85% by mass), 75 kg nitric acid (65% by mass), and 445 kg deionized water. Under stirring conditions, add the above raw materials sequentially to the reaction vessel and continuously stir and mix at 50°C for 4 hours until a homogeneous solution is formed, thus obtaining the impregnation solution.

[0035] The components and contents of Examples 1-4 and Comparative Examples 1-8 are shown in Table 1 below.

[0036] Table 1

[0037] Performance testing The graphite products of Examples 1-4 and Comparative Examples 1-8 were subjected to performance tests for density, high-temperature oxidation resistance, flexural strength, and Vickers hardness, respectively. The test results are shown in Table 2 below. Bulk density: The Archimedes displacement method was used to determine the bulk density, apparent porosity and true porosity of dense shaped refractory products according to GB / T2997-2000. High-temperature oxidation resistance: The graphite sample to be tested was dried in a 105℃ oven for 2 hours to remove adsorbed water. After cooling, its initial mass (m1) was accurately weighed. Subsequently, the sample was placed in a muffle furnace and heated to 1200℃ at a rate of 5℃ / min under static air atmosphere, and held at this temperature for 2 hours. After the program was completed, the sample was allowed to cool naturally to room temperature with the furnace, and its mass (m2) was accurately weighed again. The oxidation weight loss rate was calculated according to the following formula: Oxidation weight loss rate (%) = [(m1- m2) / m1] × 100%.

[0038] Flexural strength: Tested in accordance with GB / T13465.1-2002 "General Rules for Test Methods of Mechanical Properties of Impermeable Graphite Materials"; Vickers hardness: Referring to GB / T 4340.1-2009 "Metallic materials - Vickers hardness test - Part 1: Test method", a Vickers hardness tester was used to test the polished surface of the graphite product sample. The test force was 1 kgf, and the holding time was 15 seconds. At least 5 points were evenly selected on the surface of each graphite product sample for testing, and the average value was taken as the Vickers hardness value of the sample, reported in HV1 units.

[0039] Table 2

[0040] As shown in Table 2, the graphite materials treated with the impregnation solution of the present invention (Examples 1-4) exhibited significantly improved density, oxidation resistance, and mechanical properties compared to the untreated graphite substrate in Comparative Example 1. This is attributed to the synergistic effect of the components in the formulation, as detailed below: First, all components together constitute a complete reaction system, and none can be omitted. As can be seen from Comparative Examples 4-6, the absence of any one of hydrochloric acid, aluminum dihydrogen phosphate, or aluminum hydroxide will lead to a significant decrease in the key properties of the graphite product, proving that the three do not simply coexist, but rather constitute a synergistic system with complementary functions.

[0041] Secondly, hydrochloric acid is irreplaceable in the system. In Comparative Example 7, although the performance of the graphite material was better than that of the acid-free system after replacing hydrochloric acid with nitric acid of equal hydrogen ion concentration, it was still significantly lower than that of the example containing hydrochloric acid. This indicates that hydrochloric acid is crucial to the final effect of the impregnation system, and its role is not solely provided by the acidic environment.

[0042] Finally, the proportions of each component significantly affect performance. Comparative Example 8 is a high-phosphorus, low-aluminum formulation. Even though all components are present, the imbalance in proportions means that the final performance cannot reach the level of the preferred formulations of this invention (Examples 1-3). This demonstrates that the optimal synergistic enhancement effect can only be achieved within the proportion range described in this invention. In summary, the impregnation solution of this invention is a highly efficient synergistic system based on specific components and ratios, which can significantly improve the overall performance of graphite products. At the same time, this system also offers process flexibility: a first curing step (Example 4) is sufficient for conventional use; if combined with a second curing process (Examples 1-3), key indicators such as high-temperature oxidation resistance can be further optimized.

[0043] Application effect verification To verify the performance improvement effect of graphite materials treated with the impregnation solution of this invention under typical harsh working conditions, this invention also conducted comparative industrial application tests: A graphite rotor for an online refining and degassing machine for molten aluminum, processed with the same formula and process as in Example 1, was used as the test sample, and an untreated original graphite rotor from the same batch was used as the control sample. The rotors were installed in a box-type degassing machine of an aluminum alloy casting company. The widely used A356 cast aluminum alloy melt was used as the processing object. The continuous operation was compared under the standard working conditions simulating actual production (aluminum melt temperature 740-760℃, rotor speed 300-500 rpm, and high-purity nitrogen gas). The test adopted an operating system of continuously processing about 140 bags of molten aluminum per day until the rotor failed due to oxidation, ablation, diameter reduction, or insufficient strength.

[0044] The test results show that the average service life of the control rotor without impregnation treatment is 3-4 days, and the cumulative treatment of molten aluminum is about 420-560 bags. The average service life of the test rotor treated with the impregnation solution of this invention is extended to 7-10 days, and the cumulative treatment of molten aluminum is about 980-1400 bags.

[0045] Therefore, it is evident that the graphite rotor treated with the impregnation solution of this invention, under actual working conditions such as the refining of high-silicon aluminum alloys represented by A356, has a service life more than twice that of the untreated rotor, and can consistently exceed the industry warranty requirement of ≥700 packages. This significant extension of service life is directly due to the high oxidation resistance and high mechanical strength obtained by the material after treatment, effectively solving the core problem of easy wear and frequent replacement of graphite rotors in aluminum processing applications.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An impregnation solution for graphite impregnation, characterized in that, It contains aluminum source, phosphorus source, acid regulator and solvent.

2. The impregnation solution as described in claim 1, characterized in that, The aluminum source includes aluminum hydroxide and / or aluminum dihydrogen phosphate, the phosphorus source includes phosphoric acid and / or aluminum dihydrogen phosphate, the acid regulator includes hydrochloric acid, and the solvent includes water.

3. The dip solution of claim 2, wherein, The aluminum source is aluminum hydroxide and aluminum dihydrogen phosphate; the phosphorus source is phosphoric acid and aluminum dihydrogen phosphate; the acidity regulator is hydrochloric acid; and the solvent is water.

4. The dip solution of claim 3, wherein, The impregnation solution is composed of aluminum hydroxide, aluminum dihydrogen phosphate, phosphoric acid, hydrochloric acid and water.

5. The dip solution of claim 4, wherein, The impregnation solution, by weight, comprises the following components: 70-90 parts aluminum hydroxide, 300-320 parts aluminum dihydrogen phosphate, 110-140 parts phosphoric acid, 65-85 parts hydrochloric acid, with the balance being water.

6. A high performance graphite material, characterized by, It is obtained by impregnation treatment of a graphite substrate with the impregnation solution described in any one of claims 1-5.

7. A method of producing a high performance graphite material as claimed in claim 6, characterized by, Includes the following steps: S1. Pre-treat the graphite substrate; S2. Prepare the impregnation solution; S3. Place the pretreated graphite substrate in the impregnation solution and perform pressure impregnation treatment; S4. Curing treatment is performed on the impregnated graphite substrate.

8. The method of claim 7, wherein the high performance graphite material is prepared by the steps of: In step S3, the pressure of the pressurized impregnation treatment is 0.5-1.2 MPa, and the holding time is 24-72 hours; and / or, in step S4, the curing treatment includes a first curing at 60-100°C for 18-30 hours; after the first curing, a second curing is performed at 150-200°C for 36-72 hours. ​ 9. The application of the impregnation solution according to any one of claims 1-5 in the preparation of high-performance graphite materials.

10. A graphite rotor characterized in that, It is processed from the high-performance graphite material described in claim 6.

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