Alumina / graphene oxide composite sol with long-term dispersion stability, preparation method thereof and application of alumina / graphene oxide composite sol in wear-resistant anticorrosive coating

Abstract

The invention belongs to the technical field of surface engineering, and relates to aluminum oxide and graphene oxide composite sol with long-term dispersion stability, a preparation method of the aluminum oxide and graphene oxide composite sol and application of the aluminum oxide and graphene oxide composite sol in a wear-resistant anticorrosive coating. The preparation method comprises the following steps: S1, preparing alumina sol; s2, preparing a graphene oxide aqueous dispersion; s3, preparing aluminum oxide / graphene oxide composite sol: mixing the aluminum oxide sol with the graphene oxide aqueous dispersion, and performing ultrasonic dispersion to obtain the aluminum oxide / graphene oxide composite sol. Graphene oxide is selected as a lubricating additive phase to be compounded with aluminum oxide sol, and long-term dispersion stability is achieved; the friction coefficient can be obviously reduced, the tribological performance of the coating can be improved, the microcosmic filling effect can be achieved, the porosity of the coating can be reduced, invasion of a corrosion medium to a metal implant can be prevented, and the corrosion resistance of the coating can be improved.

Description

Technical Field

[0001] This invention belongs to the field of surface engineering technology, and relates to an alumina-graphene oxide composite sol with long-term dispersion stability, its preparation method, and its application in wear-resistant and corrosion-resistant coatings. Background Technology

[0002] Orthopedic hand reconstruction utilizes artificial biomaterials to repair or replace damaged or diseased musculoskeletal tissues. Its main purpose is to alleviate patient pain and restore normal physiological function to bones and joints. Currently, the risk of joint dysfunction or bone damage due to degeneration and injury is increasing year by year, leading to a growing demand for biomedical materials used in surgical implants or interventions.

[0003] After joint prosthesis implantation, on the one hand, the interaction between the implant and the articular cartilage or joint inevitably causes friction and wear. The wear debris generated during this process can induce inflammatory reactions in surrounding tissues, potentially leading to infection in the surgical site and ultimately surgical failure. On the other hand, prolonged exposure of the joint prosthesis to the human body fluid environment containing different ions can trigger electrochemical reactions at the interface between the implant and body tissues, leading to corrosion phenomena such as pitting corrosion, crevice corrosion, and fretting corrosion. Surface coating technology can improve the surface properties of the implant without affecting its mechanical properties. However, considering the long-term service life of the implant and human safety, improving the wear resistance, corrosion resistance, and biocompatibility of the implant coating has become a key research direction in this field.

[0004] Alumina has high hardness and excellent wear resistance, which greatly reduces the generation of wear debris. In addition, alumina has excellent bioinertness and chemical stability. It can not only remain stable in the human body fluid environment, but also form a protective barrier between metal implants and human tissues, reducing the release of soluble metal ions. It has great advantages as an implant coating. At present, there are many methods for preparing alumina coatings, mainly including chemical vapor deposition, magnetron sputtering, plasma spraying, atomic layer deposition and sol-gel method. Among them, the sol-gel method has the following technical advantages compared with other methods: (1) simple equipment and process, easy to promote and implement; (2) low reaction temperature, simple and easy to control the composition formula; (3) high uniformity of the prepared coating; (4) high chemical purity. The precursor used to prepare the coating is inorganic salt or alkoxide, which is easy to purify and can be used to prepare materials with high purity requirements. However, this method also has the disadvantages of the presence of micro voids and cracks in the coating affecting corrosion resistance, large friction coefficient of the prepared coating, and thin coating in a single application.

[0005] Graphene, a two-dimensional nanomaterial composed of a single layer of carbon atoms, possesses a honeycomb lattice structure formed by sp² hybridization. This structure not only boasts the lowest theoretical density (2.26 g / cm³) at the atomic level but also exhibits a high electron cloud density. Furthermore, the layers of graphene are bound together by van der Waals forces, facilitating interlayer slippage under external forces and significantly reducing the friction coefficient of the composite material. Dispersing graphene in coatings can improve coating density, reduce porosity, and enhance the coating's tribological corrosion resistance. In summary, the following problems exist in the modification of two-dimensional graphene during the preparation of alumina coatings using the sol-gel method:

[0006] (1) Graphene materials have extremely high specific surface area (about 2600 m² / g), which makes their surface energy high and thermodynamically unstable. In order to achieve a more stable state, graphene materials tend to reduce surface energy by agglomerating with each other. In the sol-gel method of graphene-modified coating, ultrasonic or stirring treatment is usually performed before coating preparation to achieve short-term dispersion. This will require a dispersion step before each coating preparation, which increases the difficulty of the process. It may even be impossible to disperse and use the coating because of the agglomeration of nanomaterials during the coating preparation process, which will result in uneven coating quality in the same batch.

[0007] (2) The alumina coating prepared by the sol-gel method has poor friction properties and a high coefficient of friction (usually 0.6-0.9), which may cause mechanical tissue damage, local inflammation and other risks.

[0008] (3) During the heat treatment film formation process, the coating prepared by the present method will develop micropores and microcracks as organic matter and water in the sol evaporate, which is not conducive to blocking the invasion of corrosive media into the metal implant.

[0009] In summary, maintaining the long-term dispersion stability of composite sols, significantly reducing the coefficient of friction of the coating, and facilitating the prevention of corrosive media from penetrating metal implants are major issues that need to be addressed. Summary of the Invention

[0010] In view of the technical problems described in the background art above, such as the poor long-term dispersion stability of existing graphene composites dissolved in coatings, the high coefficient of friction, and the inability to prevent the intrusion of corrosive media into metal implants, the present invention provides an alumina-graphene oxide composite sol with long-term dispersion stability, its preparation method, and its application in wear-resistant and anti-corrosion coatings.

[0011] The concept of this invention is:

[0012] Compared to existing two-dimensional graphene materials, this invention uses graphene oxide as a lubricating additive phase combined with alumina sol. On one hand, the uniformly dispersed graphene oxide nanosheets in the coating undergo interlayer slippage under external force, significantly reducing the coefficient of friction and improving the tribological properties of the coating. Simultaneously, the two-dimensional nanosheet structure of graphene oxide not only acts as a micro-filler, reducing the porosity of the coating and thus facilitating the barrier against corrosive media intrusion into metal implants, but its high aspect ratio also provides a "physical barrier" effect, thereby enhancing the coating's corrosion resistance. On the other hand, unlike graphene, graphene oxide contains abundant oxygen-containing functional groups on its surface. These functional groups endow graphene oxide with significant hydrophilicity, allowing it to be stably dispersed in water. Therefore, water is used as a medium to mix the stable graphene oxide aqueous dispersion with the alumina sol phase to obtain a stable alumina / graphene oxide sol. Furthermore, graphene oxide possesses unique in-plane wrinkles, which enhance its antibacterial properties and exhibits good biocompatibility in in vitro experiments. Furthermore, the present invention optimizes and adjusts process parameters (e.g., the amount of graphene oxide added, the amount of graphene oxide dispersant, and the heat treatment calcination temperature) to obtain a composite sol with long-term dispersion stability, thereby forming a wear-resistant, corrosion-resistant, and highly biocompatible coating.

[0013] Based on the above inventive concept, and to achieve the above objectives, the technical solution provided by this invention is as follows:

[0014] A method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability includes the following steps:

[0015] S1: Preparation of alumina sol

[0016] Alumina sol was prepared by sol-gel method using aluminum isopropoxide as a precursor.

[0017] S2: Preparation of graphene oxide aqueous dispersion

[0018] Graphene oxide sheets were added to water and ultrasonically dispersed to obtain an aqueous dispersion of graphene oxide.

[0019] S3: Preparation of alumina / graphene oxide composite sol

[0020] The alumina sol from step S1 is mixed with the graphene oxide aqueous dispersion from step S2, and then ultrasonically dispersed to obtain an alumina / graphene oxide composite sol.

[0021] Further specifying, the specific process of preparing alumina sol using the sol-gel method in step S1 is to add aluminum isopropoxide to water, hydrolyze it, and then add a catalyst to obtain alumina sol.

[0022] Further specified, the hydrolysis temperature is 75 ℃-95 ℃, the hydrolysis time is 40 min-80 min; the molar ratio of aluminum isopropoxide, nitric acid and water is 1:(0.2-0.3):(70-80).

[0023] Further specifying, the dimensions of the graphene oxide sheet in step S2 are: a sheet diameter of 0.5 µm - 5 µm and a thickness of 1 nm - 3 nm.

[0024] Further specifying, in step S3, the mass ratio of alumina sol to graphene oxide aqueous dispersion is 2:3 to 3:2; and in the alumina / graphene oxide composite sol, the mass fraction of graphene oxide is 0.005%-0.020%.

[0025] An alumina / graphene oxide composite sol is prepared by any of the preparation methods.

[0026] Application of alumina / graphene oxide composite sol in wear-resistant and corrosion-resistant coatings.

[0027] Further specifying, in application, the alumina / graphene oxide composite sol is uniformly coated onto a pretreated substrate using a dip-coating method, followed by heat treatment, heat preservation, and cooling.

[0028] Further specifying, the dip-coating method involves immersing a pretreated substrate in an alumina / graphene oxide composite sol, pulling it up at a rate of 0.5 mm / s-5 mm / s, and drying it in air for 10 min-30 min; repeating the pulling operation multiple times.

[0029] Further specifying the conditions for the heat treatment, the heating rate is 4 ℃ / min - 10 ℃ / min, the heat treatment temperature is 500 ℃, and the holding time is 30 min - 60 min.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. This invention prepares an alumina / graphene oxide composite sol by mixing an aqueous dispersion of graphene oxide sheets with alumina sol. No significant sedimentation was observed after 30 days of standing. This confirms that the alumina / graphene oxide composite sol prepared by this invention has long-term dispersion stability. When applied to wear-resistant and anti-corrosion coatings, no additional dispersion is required, reducing process difficulty, minimizing process steps and avoiding resource waste, ensuring the uniformity of coating quality within the same batch, improving the anti-corrosion performance of the coating, and facilitating its widespread application in wear-resistant and anti-corrosion coatings.

[0032] 2. In this invention, graphene oxide sheets are uniformly and stably dispersed in the coating. Graphene oxide sheets are two-dimensional nanomaterials, and their interlayer sliding is easy, which can play a good lubricating role. This allows the coating to form a transfer film through shear deformation during friction, which significantly reduces the coefficient of friction and wear volume, and enhances the friction resistance of the coating. In addition, the high aspect ratio of graphene oxide sheets has a "physical barrier" effect, which makes the coating less prone to micropores and microcracks, which helps to block the intrusion of corrosive media into metal implants, thereby improving the corrosion resistance of the coating.

[0033] 3. The present invention uses graphene oxide sheets, which are two-dimensional nanomaterials with unique in-plane wrinkles. These wrinkles not only enhance the antibacterial properties of the alumina / graphene oxide composite sol, but also exhibit good biocompatibility in in vitro experiments. This makes the alumina / graphene oxide composite sol a promising candidate for the modification of coatings for medical implants.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0036] Figure 1 A comparison of friction coefficients (left) and wear volume (right) of the substrate (316-L stainless steel, denoted as Substrate), the coating of Example 1 (Al2O3 / GO), and the coating of Comparative Example 1 (Al2O3).

[0037] Figure 2 Digital photographs of alumina / graphene oxide sol (left) and its 24-hour storage after Examples 1, 5, 6, and 7 (right);

[0038] Figure 3 Digital photographs of the alumina / graphene oxide sol in Example 1 after different number of days, from left to right: preparation completed, 1 day, 7 days, 14 days, and 30 days;

[0039] Figure 4 A comparison of the friction coefficient and wear volume of coatings prepared from alumina / graphene oxide sol after different number of days of storage in Example 1;

[0040] Figure 5 Biocompatibility of the substrate (316-L stainless steel, denoted as Substrate), the coating of Example 1 (Al2O3 / GO), and the coating of Comparative Example 1 (Al2O3).

[0041] Figure 6 The corrosion resistance of the substrate (316-L stainless steel, denoted as Substrate), the coating of Example 1 (Al2O3 / GO), and the coating of Comparative Example 1 (Al2O3) are shown in the figure. The left figure is the Tafel curve, and the right figure is the self-corrosion current density calculated by the Tafel extrapolation method. Detailed Implementation

[0042] The present invention and the resulting technology will be clearly and completely described below with reference to embodiments, so as to fully understand the purpose and effects of the present invention. The embodiments described in detail below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0043] This invention provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability, comprising the following steps:

[0044] S1: Preparation of alumina sol

[0045] Alumina sol was prepared by sol-gel method using aluminum isopropoxide as a precursor.

[0046] The specific process of preparing alumina sol using the sol-gel method in step S1 is as follows: aluminum isopropoxide is added to water, hydrolyzed, and then a catalyst is added to obtain alumina sol.

[0047] Preferably, the hydrolysis temperature is 75 ℃-95 ℃, and the hydrolysis time is 40 min-80 min;

[0048] Preferably, the molar ratio of aluminum isopropoxide, nitric acid, and water is 1:(0.2-0.3):(70-80). For example, the molar ratios of aluminum isopropoxide, nitric acid, and water are 1:0.2:70, 1:0.25:75, and 1:0.3:80.

[0049] S2: Preparation of graphene oxide aqueous dispersion

[0050] Graphene oxide sheets were added to water and ultrasonically dispersed to obtain an aqueous dispersion of graphene oxide.

[0051] The dimensions of the graphene oxide sheet in step S2 are: a diameter of 0.5 µm - 5 µm and a thickness of 1 nm - 3 nm.

[0052] S3: Preparation of alumina / graphene oxide composite sol

[0053] The alumina sol from step S1 is mixed with the graphene oxide aqueous dispersion from step S2, and then ultrasonically dispersed to obtain an alumina / graphene oxide composite sol.

[0054] In step S3, the mass ratio of alumina sol to graphene oxide aqueous dispersion is 2:3 to 3:2; in the alumina / graphene oxide composite sol, the mass fraction of graphene oxide is 0.005%-0.020%.

[0055] The present invention also provides an alumina / graphene oxide composite sol, which is prepared by any of the above preparation methods. The alumina / graphene oxide composite sol prepared by the present invention has long-term dispersion stability and can improve the wear resistance and corrosion resistance of the coating.

[0056] This invention also provides an application of alumina / graphene oxide composite sol in wear-resistant and corrosion-resistant coatings. In application, the alumina / graphene oxide composite sol is uniformly coated onto a pre-treated substrate using a dip-coating method, followed by heat treatment, heat preservation, and cooling.

[0057] Preferably, the method for pre-treating the substrate is to sequentially grind, ultrasonically clean, and dry the substrate.

[0058] Preferably, the substrate is stainless steel, titanium alloy, or cobalt alloy, but other metal alloys are also acceptable. Ultrasonic cleaning involves alternating ultrasonic cleaning with three organic solvents: ethanol, acetone, and ethanol.

[0059] Preferably, the dip-coating method involves immersing the pretreated substrate in an alumina / graphene oxide composite sol, pulling it up at a rate of 0.5 mm / s-5 mm / s, and drying it in air for 10 min-30 min; repeating the pulling operation multiple times to uniformly coat the alumina / graphene oxide composite sol onto the pretreated substrate.

[0060] Preferably, the heat treatment conditions are: a heating rate of 4 ℃ / min - 10 ℃ / min, a temperature of 500 ℃, and a holding time of 30 min - 60 min.

[0061] It should be noted that in the above preparation method, there is no obvious order between steps S1 and S2, and the order can be adjusted.

[0062] The preparation and application of the invented alumina / graphene oxide composite sol are described in detail below with specific embodiments, and the technical effects of the invention are verified through performance testing.

[0063] It should be noted that, unless otherwise specified, the chemicals and reagents used in the following embodiments are all commercially available products commonly used in the field.

[0064] It should be noted that, unless otherwise specified, the operations and testing methods used in the following embodiments are conventional operations and existing standard testing methods in the art.

[0065] Example 1

[0066] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability, including the following steps:

[0067] S1: Preparation of alumina sol

[0068] Aluminum isopropoxide was used as a precursor, deionized water as a solvent, and nitric acid as a catalyst. The molar ratio of aluminum isopropoxide:nitric acid:water was 1:0.25:75. After hydrolyzing aluminum isopropoxide at 90°C for 1 hour, nitric acid was added to obtain a transparent and stable alumina sol.

[0069] S2: Preparation of graphene oxide aqueous dispersion

[0070] Graphene oxide was dispersed in deionized water and then sonicated for 20 minutes before use. The added graphene oxide sheets had a diameter of 0.5-5 µm and a thickness of 1-3 nm.

[0071] S3: Preparation of alumina / graphene oxide composite sol

[0072] After the alumina sol is formed by adding the catalyst, an alumina sol and a graphene oxide aqueous dispersion with a mass ratio of 1:1 are added to the alumina sol, and the mixture is stirred at 90°C for 3 hours to obtain an alumina / graphene oxide composite sol with long-term dispersion stability, referred to as alumina / graphene oxide composite sol.

[0073] In the alumina / graphene oxide composite sol prepared in this embodiment, the mass fraction of graphene oxide is 0.010%, that is, the mass of graphene oxide accounts for 0.010% of the mass of the alumina / graphene oxide sol.

[0074] Furthermore, this embodiment also utilizes the alumina / graphene oxide composite sol with long-term dispersion stability prepared above to obtain an alumina / graphene oxide composite coating, namely a wear-resistant and corrosion-resistant coating. Specifically, it includes:

[0075] S4: Substrate Pretreatment

[0076] The substrate (commercial 316L stainless steel, 25mm×25mm×2mm) was sequentially sanded with 400#, 800#, 1200#, 1500#, and 2000# sandpaper, then ultrasonically cleaned alternately for 5 minutes in three organic solvents (ethanol, acetone, and ethanol), and finally dried with a nitrogen gun for later use. The substrate can be replaced with titanium alloy or cobalt alloy.

[0077] S5: Uniform coating by dip coating method

[0078] The treated substrate was immersed in the prepared alumina / graphene oxide composite sol for 1 minute, then pulled up at a speed of 1 mm / s, and dried in air for 10 minutes. The above pulling operation was repeated three times.

[0079] S6: Heat treatment for film formation

[0080] The coated substrate was heat-treated in air at a heating rate of 4℃ / min to 500℃ and held for 30 min. It was then cooled to room temperature in the furnace to obtain an alumina / graphene oxide composite coating.

[0081] Example 2

[0082] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability. In step S3, the mass fraction of graphene oxide in the alumina / graphene oxide composite sol is 0.005%, and the other conditions are the same as in Example 1.

[0083] This embodiment utilizes the prepared alumina / graphene oxide composite sol with long-term dispersion stability to obtain an alumina / graphene oxide composite coating (wear-resistant and corrosion-resistant coating), referring to Example 1.

[0084] Example 3

[0085] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability. In step S3, the mass fraction of graphene oxide in the alumina / graphene oxide composite sol is 0.015%, and the other conditions are the same as in Example 1.

[0086] This embodiment utilizes the prepared alumina / graphene oxide composite sol with long-term dispersion stability to obtain an alumina / graphene oxide composite coating (wear-resistant and corrosion-resistant coating), referring to Example 1.

[0087] Example 4

[0088] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability. In step S3, the mass fraction of graphene oxide in the alumina / graphene oxide composite sol is 0.020%, and the other conditions are the same as in Example 1.

[0089] This embodiment utilizes the prepared alumina / graphene oxide composite sol with long-term dispersion stability to obtain an alumina / graphene oxide composite coating (wear-resistant and corrosion-resistant coating), referring to Example 1.

[0090] Example 5

[0091] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability. In step S3, the mass ratio of alumina sol to graphene oxide aqueous dispersion is 9:1, and the other conditions are the same as in Example 1.

[0092] This embodiment utilizes the prepared alumina / graphene oxide composite sol with long-term dispersion stability to obtain an alumina / graphene oxide composite coating (wear-resistant and corrosion-resistant coating), referring to Example 1.

[0093] Example 6

[0094] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability. In step S3, the mass ratio of alumina sol to graphene oxide aqueous dispersion is 7:3, and the remaining conditions are the same as in Example 1.

[0095] This embodiment utilizes the prepared alumina / graphene oxide composite sol with long-term dispersion stability to obtain an alumina / graphene oxide composite coating (wear-resistant and corrosion-resistant coating), referring to Example 1.

[0096] Example 7

[0097] This embodiment provides a method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability. In step S3, the mass ratio of alumina sol to graphene oxide aqueous dispersion is 3:7, and the remaining conditions are the same as in Example 1.

[0098] This embodiment utilizes the prepared alumina / graphene oxide composite sol with long-term dispersion stability to obtain an alumina / graphene oxide composite coating (wear-resistant and corrosion-resistant coating), referring to Example 1.

[0099] Example 8

[0100] The method for preparing the wear-resistant and corrosion-resistant coating provided in this embodiment involves a heat treatment temperature of 300°C, with the remaining conditions being the same as in Example 1.

[0101] Example 9

[0102] The method for preparing the wear-resistant and corrosion-resistant coating provided in this embodiment involves a heat treatment temperature of 700°C, with the remaining conditions being the same as in Example 1.

[0103] The performance of the alumina / graphene oxide composite sol and the wear-resistant and corrosion-resistant coating prepared in the examples was further tested through the following experiments. Meanwhile, to demonstrate the technical advantages of the present invention, the following comparative examples were designed.

[0104] Comparative Example 1

[0105] In this comparative example, no graphene oxide was added in S2, and the graphene oxide aqueous dispersion added in S3 was replaced with deionized water. The other conditions were the same as in Example 1.

[0106] Comparative Example 2

[0107] In this comparative example, no graphene oxide was added in S2, and the graphene oxide aqueous dispersion added in S3 was replaced with deionized water. The other conditions were the same as in Example 5.

[0108] Comparative Example 3

[0109] In this comparative example, no graphene oxide was added in S2, and the graphene oxide aqueous dispersion added in S3 was replaced with deionized water. The other conditions were the same as in Example 6.

[0110] Comparative Example 4

[0111] In this comparative example, no graphene oxide was added in S2, and the graphene oxide aqueous dispersion added in S3 was replaced with deionized water. The other conditions were the same as in Example 7.

[0112] Comparative Example 5

[0113] In this comparative example, no graphene oxide was added in S2, and the graphene oxide aqueous dispersion added in S3 was replaced with deionized water. The other conditions were the same as in Example 8.

[0114] Comparative Example 6

[0115] In this comparative example, no graphene oxide was added in S2, and the graphene oxide aqueous dispersion added in S3 was replaced with deionized water. The other conditions were the same as in Example 9.

[0116] The performance of the embodiments and comparative examples of this invention is as follows.

[0117] Test 1

[0118] The tribological properties of the wear-resistant and corrosion-resistant coatings (hereinafter referred to as coatings) obtained under different treatment processes in Examples 1-9 and Comparative Examples 1-6 were tested respectively. The test results are shown in Table 1 below. Figure 1 .

[0119] Table 1. Tribological properties of coatings with different treatment processes

[0120]

[0121] As shown in Table 1, the tribological properties of the alumina / graphene oxide composite coatings formed after modification with graphene oxide in Examples 1, 2, 3, and 4 were significantly improved. Among them, the parameters used in Example 1 showed the best tribological properties, with a friction coefficient reduced by 67% and wear volume reduced by 91% compared to the pure alumina coating in Comparative Example 1. This indicates that the graphene oxide dispersed in the coating plays a lubricating role. This is mainly attributed to the fact that graphene oxide, as a two-dimensional material, is prone to sliding between its layers. During friction, it forms a transfer film through shear deformation, thereby reducing the friction coefficient.

[0122] To determine the effect of the content of the aqueous dispersion of graphene oxide on the coating, the mixing ratios of alumina sol and aqueous graphene oxide dispersion were designed. Specifically, data from Examples 1 and 5-7 show that when the mass ratio of alumina sol to aqueous graphene oxide dispersion varied between 9:1, 7:3, 1:1, and 3:7, the tribological properties initially increased and then decreased with increasing water content. Based on this trend, it was deduced that the alumina / graphene oxide composite coating exhibited good tribological properties when the mass ratio of alumina sol to aqueous graphene oxide dispersion was below 7:3 and above 3:7, specifically between 6:4 and 4:6. Furthermore, the tribological properties were optimal when the mass ratio of alumina sol to aqueous graphene oxide dispersion was 1:1. Meanwhile, Comparative Examples 1, 2, 3, and 4 in Table 1 show the effect of adding different amounts of deionized water on the coating without adding graphene oxide. It can be observed that when the water content is low, it has almost no effect on the coating, but when the water content is too high, i.e., the ratio is 3:7, the coating is also damaged during the friction process, with a large wear volume.

[0123] Table 1 shows that the composite coatings prepared by heat treatment at 300℃ and 700℃ have poorer performance compared to a heat treatment temperature of 500℃. This is mainly because at lower heat treatment temperatures, the alumina sol cannot form alumina and exists in the coating as AlOOH, resulting in poor tribological properties. Conversely, at excessively high heat treatment temperatures, graphene oxide decomposes, affecting the graphene oxide content in the coating and consequently reducing tribological properties. Comparative Examples 1, 5, and 6 show similar results; the pure alumina coating treated at 300℃ exhibits even worse tribological properties, while the coefficient of friction and wear volume are not significantly different between those treated at 500℃ and 700℃. Therefore, considering all factors, the suitable heat treatment temperature is 500℃.

[0124] Test 2

[0125] Figure 2Digital photographs of the alumina / graphene oxide composite sol with different water contents in Examples 1 and 5-7 before and after 24 hours of natural sedimentation are shown. The figures show that at mass ratios of 9:1 and 7:3, the alumina / graphene oxide composite sol exhibited relatively significant sedimentation. This indicates that when the water content is low, the graphene oxide sheets tend to agglomerate in the alumina sol, resulting in incomplete dispersion and thus failing to achieve optimal performance in the coating. This is consistent with the tribological data in Table 1. At a mass ratio of 3:7, organic matter and moisture in the coating evaporate during subsequent heat treatment, making the coating prone to defects and more susceptible to damage during friction. This is consistent with the changes in friction and wear data in Example 7 of Table 1. The sedimentation data further demonstrates that when the mass ratio of alumina sol to graphene oxide aqueous dispersion is 1:1, the graphene oxide sheets can be stably dispersed in the alumina sol for a long period, and the prepared coating does not form defects that affect its tribological properties.

[0126] Test 3

[0127] Figure 3 The sedimentation of the alumina / graphene oxide composite sol in Example 1 after 30 days of storage is shown. It can be seen that no significant sedimentation occurred in the alumina / graphene oxide composite sol during the 30-day storage period, indicating that it has long-term dispersion stability.

[0128] Figure 4 The tribological properties of the coatings prepared from the alumina / graphene oxide sol of Example 1 after 1, 7, 14, and 30 days of storage are shown. The results indicate that although the tribological properties decreased during the 30-day settling process, the decrease was relatively small, demonstrating that excellent tribological properties are maintained even after long-term storage. The average coefficient of friction of the coating prepared after 30 days of settling was 0.36, a 44% decrease compared to Comparative Example 1; the wear volume of the coating prepared after 30 days of settling was 3.8 × 10⁻⁶. 3 μm 3 Compared to Comparative Example 1, the coefficient of friction decreased by 82%. This indicates that the coating has a lower coefficient of friction, which can improve its friction resistance.

[0129] The above results indicate that this invention utilizes the characteristic that the polar groups (hydroxyl, carboxyl, and epoxy groups, etc.) contained on the surface of graphene oxide sheets are easily and stably dispersed in water, and the characteristic that the water solvent can be removed during heat treatment without affecting the overall composition of the coating. Water was selected as the dispersion liquid for graphene oxide, and the optimal content of the added graphene oxide aqueous dispersion was studied and discovered. While improving the tribological properties, it also maintained long-term stable dispersion.

[0130] Test 4

[0131] Figure 5The biocompatibility of Example 1, Comparative Example 1, and the substrate with L929 cells was shown. According to national standards, Grade 0 (RGR ≥ 100%) and Grade 1 (75% ≤ RGR < 100%) are considered non-toxic. Figure 5 As shown, the toxicity level is 1, indicating that it is safe in the human body.

[0132] Test 5

[0133] Figure 6 The corrosion resistance of Example 1, Comparative Example 1, and the substrate in a simulated body fluid environment at 37°C is shown. The Tafel curve is a curve that represents the relationship between overpotential and logarithmic current density. The x and y axes of the curve represent corrosion potential (Ecorr) and corrosion current density (Icorr), respectively. The self-corrosion current density was obtained by Tafel extrapolation. The results show that the corrosion resistance of the alumina coating is superior to that of the stainless steel substrate, and the alumina coating containing graphene oxide has the lowest self-corrosion current density, i.e., the best corrosion resistance, which is consistent with the inferences drawn above.

[0134] In summary, this invention achieves the preparation of an alumina / graphene oxide composite sol with long-term dispersion stability by adjusting the graphene oxide content and the content of the graphene oxide aqueous dispersion; furthermore, it achieves the preparation of a wear-resistant and corrosion-resistant coating by adjusting the heat treatment temperature during the coating of the alumina / graphene oxide composite sol and the base layer. The alumina / graphene oxide composite sol and its wear-resistant and corrosion-resistant coating provided by this invention significantly improve the tribological properties of the coating. Simultaneously, the prepared alumina / graphene oxide composite sol exhibits ultra-long-term dispersion stability, maintaining excellent tribological properties even after one month of storage. This provides an efficient and reliable technical approach for the modification of coatings for medical implants and has significant engineering application value.

[0135] The above are preferred embodiments of the present invention and should not be construed as limiting the technical solutions of the present invention. Any changes, modifications, substitutions and variations made by those skilled in the art to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing an alumina / graphene oxide composite sol with long-term dispersion stability, characterized in that, Includes the following steps: S1: Preparation of alumina sol Alumina sol was prepared by sol-gel method using aluminum isopropoxide as a precursor. S2: Preparation of graphene oxide aqueous dispersion Graphene oxide sheets were added to water and ultrasonically dispersed to obtain an aqueous dispersion of graphene oxide. S3: Preparation of alumina / graphene oxide composite sol The alumina sol from step S1 is mixed with the graphene oxide aqueous dispersion from step S2 and then ultrasonically dispersed to obtain the final product.

2. The method for preparing the alumina / graphene oxide composite sol with long-term dispersion stability according to claim 1, characterized in that, The specific process of preparing alumina sol using the sol-gel method in step S1 is as follows: aluminum isopropoxide is added to water, hydrolyzed, and then a catalyst is added to obtain alumina sol.

3. The method for preparing the alumina / graphene oxide composite sol with long-term dispersion stability according to claim 2, characterized in that, The hydrolysis temperature is 75 ℃-95 ℃, and the hydrolysis time is 40 min-80 min; the molar ratio of aluminum isopropoxide, nitric acid and water is 1:(0.2-0.3):(70-80).

4. The method for preparing the alumina / graphene oxide composite sol with long-term dispersion stability according to claim 2, characterized in that, The dimensions of the graphene oxide sheet in step S2 are: a diameter of 0.5 µm-5 µm and a thickness of 1 nm-3 nm.

5. The method for preparing the alumina / graphene oxide composite sol with long-term dispersion stability according to claim 1, characterized in that, In step S3, the mass ratio of alumina sol to graphene oxide aqueous dispersion is 2:3 to 3:2; in the alumina / graphene oxide composite sol, the mass fraction of graphene oxide is 0.005%-0.020%.

6. An alumina / graphene oxide composite sol, characterized in that, It is prepared by any one of the preparation methods of claims 1-5.

7. The application of the alumina / graphene oxide composite sol according to claim 6 in wear-resistant and corrosion-resistant coatings.

8. The application according to claim 7, characterized in that, In application, the alumina / graphene oxide composite sol is uniformly coated onto a pretreated substrate using a dip-coating method, followed by heat treatment, heat preservation, and cooling.

9. The application according to claim 8, characterized in that, The dip-coating method involves immersing a pre-treated substrate in an alumina / graphene oxide composite sol, pulling it up at a rate of 0.5 mm / s-5 mm / s, and drying it in air for 10 min-30 min; the pulling operation is repeated multiple times.

10. The application according to claim 8, characterized in that, The heat treatment conditions are: a heating rate of 4 ℃ / min - 10 ℃ / min, a temperature of 500 ℃, and a holding time of 30 min - 60 min.

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