Titanium-based matrix surface composite coating based on in-situ conversion of titanium peroxide complex and preparation method thereof

Abstract

The application provides a titanium-based matrix surface composite coating based on in-situ conversion of titanium peroxide complex and a preparation method thereof. A titanium peroxide complex solution is prepared by complexing titanium hydroxide precipitate obtained by hydrolysis of tetrabutyl titanate with hydrogen peroxide, and nanometer titanium dioxide particles or nanometer titanium dioxide tubes are dispersed in the solution to obtain a composite slurry. The slurry is coated with a solution of chloroplatinic acid alternately or mixed, dried for multiple times, and then sintered by gradient temperature rising and holding in an air atmosphere, so that the titanium peroxide complex is in-situ converted into a titanium dioxide cement phase and bridges the nanometer titanium dioxide framework, the chloroplatinic acid is converted into di-potassium pentoxide to fill the pores, and a dense composite coating is formed. The prepared coating has strong bonding force, high density, excellent corrosion resistance and stability, and can effectively prolong the service life of a titanium anode.

Description

Technical Field

[0001] This invention relates to the field of metal surface coating technology, and in particular to a composite coating for titanium substrate surface based on in-situ transformation of titanium peroxide complex and its preparation method. Background Technology

[0002] Oxide coatings on titanium substrates have the characteristics of dimensional stability and excellent corrosion resistance, and have important application value in corrosive media environments. The density of the coating, the bonding strength with the titanium substrate, and the stability of the microstructure are the core factors that determine the coating's protective life and operational reliability.

[0003] Existing oxide coatings on titanium substrates are mainly prepared through a metal salt precursor coating-high-temperature thermal oxidation process, or by directly coating and sintering nano-oxide particles. When using metal salt precursors for pyrolysis, the high-temperature decomposition process easily produces large volume shrinkage, leading to the formation of microcracks and interconnected pores within the coating. Corrosive media can penetrate along these pores to the titanium substrate surface, causing substrate passivation and oxidative instability, ultimately resulting in coating blistering and peeling. When using nano-oxide particles for direct sintering, the particles only achieve point contact through the sintering neck, resulting in weak interfacial bonding and low overall mechanical strength of the coating. Furthermore, the large number of pores formed by the natural accumulation of particles cannot be effectively filled, making it difficult to form a continuous and dense protective structure.

[0004] To improve the corrosion resistance of coatings, existing technologies often introduce corrosion-resistant components such as tantalum pentoxide into the coating system. However, these components are usually incorporated into the precursor through simple physical mixing, resulting in poor component dispersion uniformity. This fails to specifically fill the gaps between oxide particle skeletons, limiting the pore sealing effect and failing to optimize the load-bearing skeleton-sealing filling at the microstructural level. Meanwhile, conventional titanium dioxide-based coatings generally suffer from insufficient adhesion to the titanium substrate, high sintering internal stress, and susceptibility to cracking, making it difficult to meet the long-term service requirements under harsh corrosive environments.

[0005] Therefore, developing a method for preparing composite coatings on titanium substrates with high bonding strength, good density, and excellent corrosion resistance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to provide a composite coating on a titanium substrate surface based on the in-situ conversion of titanium peroxide complexes, its preparation method and application. The titanium dioxide cement phase generated by the in-situ conversion of titanium peroxide complexes bridges the nano-titanium dioxide skeleton, and tantalum pentoxide fills the pores, effectively improving the adhesion, density and corrosion resistance of the titanium anode coating.

[0007] This invention provides a method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes, comprising the following steps: The titanium substrate is subjected to degreasing, sandblasting and acid etching to obtain a pretreated titanium substrate; The titanium hydroxide precipitate obtained by hydrolysis of tetrabutyl titanate was washed and then complexed with hydrogen peroxide solution to obtain a titanium peroxide complex solution. Nano-sized titanium dioxide particles or titanium dioxide nanotubes are dispersed in the titanium peroxide complex solution to obtain a composite slurry; Tantalum chloride is dissolved in an organic solvent to obtain a tantalum chloride solution; The composite slurry and the tantalum chloride solution are alternately coated or mixed and then coated onto the surface of the pretreated titanium substrate. The coating and drying steps are repeated multiple times to obtain a coating precursor. The coating precursor is heated to 400℃~550℃ in air at a rate of 3~8℃ / min and then kept at that temperature to convert the titanium peroxide complex of the precursor into a titanium dioxide cemented phase in situ, and the tantalum chloride is converted into a tantalum pentoxide sealing phase. The mixture is then naturally cooled to room temperature in the furnace to obtain a composite coating on the titanium substrate surface.

[0008] Furthermore, in the step of heating the coating precursor to 400℃~550℃ in air at a rate of 3~8℃ / min and then holding it at that temperature, the holding process causes the titanium dioxide cement phase to coat and connect the nano-titanium dioxide particles or titanium dioxide nanotubes, and the tantalum pentoxide sealing phase fills the pores between the nano-titanium dioxide particles or titanium dioxide nanotubes and the titanium dioxide cement phase.

[0009] Furthermore, the step of alternately coating or mixing the composite slurry and the tantalum chloride solution onto the surface of the pretreated titanium substrate, drying, and repeating the coating and drying steps multiple times includes: After each coating, dry the product at 80–120°C. Repeat the coating and drying process 3–10 times. When using a mixed coating method, the molar ratio of titanium in the nano-titanium dioxide to tantalum in tantalum chloride is 1:0.5 to 1:5.

[0010] Furthermore, the step of washing the titanium hydroxide precipitate obtained from the hydrolysis of tetrabutyl titanate and then complexing it with hydrogen peroxide solution includes: Tetrabutyl titanate was added dropwise to deionized water at 0~5℃ and stirred to obtain titanium hydroxide precipitate. The titanium hydroxide precipitate was washed and dispersed in a hydrogen peroxide solution with a mass concentration of 7% to 30%, and ethanol was added as a co-solvent. The mixture was stirred at room temperature until the precipitate dissolved to obtain a titanium peroxide complex solution.

[0011] Furthermore, the step of dispersing nano-titanium dioxide particles or titanium dioxide nanotubes in the titanium peroxide complex solution to obtain a composite slurry includes: Take 0.1~1.0g of nano-titanium dioxide particles or titanium dioxide nanotubes, add them to 5~20mL of the titanium peroxide complex solution, and then add 0~1 times the volume of the titanium peroxide complex solution of ethanol. Disperse the mixture ultrasonically at 200~500W power for 15~30 minutes to obtain a composite slurry.

[0012] Furthermore, the step of dissolving tantalum chloride in an organic solvent to obtain a tantalum chloride solution includes: Tantalum chloride was added to n-butanol under ice-water bath conditions and stirred until completely dissolved to prepare a tantalum chloride n-butanol solution with a tantalum ion concentration of 0.3~0.7 mol / L.

[0013] Furthermore, the nano-titanium dioxide particles are anatase type with a particle size of 20-30 nm.

[0014] The present invention also provides a composite coating on a titanium substrate surface, comprising: The composite coating comprises nano-titanium dioxide particles or titanium dioxide nanotubes, a titanium dioxide cement phase formed by in-situ transformation of titanium peroxide complex, and a tantalum pentoxide sealing phase. The titanium dioxide cementing phase coats and connects the nano-titanium dioxide particles or titanium dioxide nanotubes, and the tantalum pentoxide sealing phase fills the pores between the nano-titanium dioxide particles or titanium dioxide nanotubes and the titanium dioxide cementing phase.

[0015] Furthermore, the composite coating on the titanium substrate surface includes: The composite coating on the titanium substrate surface has a layered structure or a homogeneous composite structure. The stacked structure consists of alternating reinforcing layers and sealing layers. The reinforcing bottom layer is composed of nano-titanium dioxide particles or titanium dioxide nanotubes and a titanium dioxide cement phase, and the sealing surface layer is composed of a tantalum pentoxide sealing phase. In the homogeneous composite structure, nano-titanium dioxide particles or titanium dioxide nanotubes, titanium dioxide cement phase, and tantalum pentoxide sealing phase are uniformly distributed.

[0016] The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes provided in the above embodiments has the following beneficial effects: The titanium dioxide cement phase is formed by high-temperature in-situ conversion of titanium peroxide complex, which uniformly coats and bridges nano-titanium dioxide particles or nanotube skeletons, replacing the traditional point contact sintering bonding mode between particles, and constructing a continuous and stable three-dimensional load-bearing structure. This significantly improves the internal cohesion of the coating and the interfacial bonding strength with the titanium matrix, and alleviates the failure risk of coating blistering and peeling. The tantalum pentoxide sealing phase generated by pyrolysis can effectively fill the pores and gaps between nanoparticle skeletons, block the communication channels for corrosive media to penetrate into the titanium matrix, solve the problem of high porosity and easy to cause passivation corrosion of the matrix in traditional coatings from the microstructure level, and improve the corrosion resistance and long-term stability of the coating. Using liquid titanium peroxide complex precursors for in-situ conversion into films can reduce volume shrinkage and internal stress concentration during heat treatment, alleviate microcrack formation, ensure the structural stability of the coating in harsh corrosive environments, and extend the service life of the coating. The coating can be flexibly controlled to form a multilayer or homogeneous composite structure through two process paths: alternating coating or mixed coating, to match the performance requirements of different service scenarios; the overall process is controllable, requires no complex equipment, and can be widely used for the preparation of protective coatings on titanium substrates. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing a composite coating on a titanium substrate surface based on in-situ conversion of titanium peroxide complexes, as provided in an embodiment of the present invention. Figure 2 This is a SEM image of the composite coating on the surface of the titanium substrate prepared in Example 1 of this invention; Figure 3 This is a SEM image of the composite coating on the titanium substrate surface prepared in Example 2 of the present invention; Figure 4 This is a SEM image of the composite coating on the surface of the titanium substrate prepared in Example 3 of this invention; Figure 5 This is a SEM image of the composite coating on the surface of the titanium substrate prepared in Example 4 of this invention; Figure 6 This is a SEM image of the composite coating on the titanium substrate surface prepared in Comparative Example 1 of this invention; Figure 7 This is a SEM image of the composite coating on the titanium substrate surface prepared in Comparative Example 2 of this invention; Figure 8 These are graphs showing the test results of the composite coating enhancement on the titanium substrate surface in various embodiments and comparative examples of the present invention; The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] Reference Figure 1 This is a schematic flowchart of the method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes proposed in this invention, including the following steps: S1, the titanium substrate is subjected to degreasing, sandblasting and acid etching to obtain a pretreated titanium substrate; S2, the titanium hydroxide precipitate obtained by hydrolysis of tetrabutyl titanate is washed and then complexed with hydrogen peroxide solution to obtain a titanium peroxide complex solution. S3, disperse nano-titanium dioxide particles or titanium dioxide nanotubes in the titanium peroxide complex solution to obtain a composite slurry; S4, dissolve tantalum chloride in an organic solvent to obtain a tantalum chloride solution; S5, the composite slurry and the tantalum chloride solution are alternately coated or mixed and then coated onto the surface of the pretreated titanium substrate, dried, and the coating and drying steps are repeated multiple times to obtain the coating precursor; S6, the coating precursor is heated to 400℃~550℃ in air at a rate of 3~8℃ / min and kept at that temperature to convert the titanium peroxide complex into a titanium dioxide cemented phase in situ and the tantalum chloride into a tantalum pentoxide sealing phase. The mixture is then naturally cooled to room temperature in the furnace to obtain a composite coating on the titanium substrate surface.

[0020] As described in step S1 above, the titanium substrate is processed into a plate shape of 60mm × 170mm × 1mm. The surface of the titanium substrate is ultrasonically cleaned sequentially with acetone and anhydrous ethanol, each cleaning lasting 15 minutes, to remove surface oil and organic residues. After degreasing, the surface of the titanium substrate is sandblasted with 24-mesh black corundum until the surface exhibits a uniformly rough state, in order to remove the original oxide layer and form a mechanical interlocking interface. After sandblasting, the titanium substrate is immersed in a 10% oxalic acid solution heated to boiling for 2 hours for etching. The boiling oxalic acid reacts with the surface of the titanium substrate, further removing the residual oxide scale and contaminant layer after sandblasting, while simultaneously forming dense micro-corrosion pits and a rough structure on the surface. Immediately after etching, the titanium substrate is rinsed repeatedly with deionized water to ensure no oxalic acid residue or reaction byproducts. The rinsed titanium substrate is then dried in a dry environment to obtain a pretreated titanium substrate. After this pretreatment, the surface of the titanium substrate has high cleanliness and uniform roughness, which can effectively enhance the mechanical interlocking between the composite coating and the titanium substrate and reduce the risk of coating cracking due to thermal expansion differences or poor interfacial bonding during sintering.

[0021] As described in step S2 above, under ice-water bath conditions of 0 to 5°C, 40 ml of tetrabutyl titanate is slowly added dropwise to 200 ml of deionized water while stirring vigorously. Tetrabutyl titanate undergoes a hydrolysis reaction with water, generating a white titanium hydroxide precipitate. During the dropwise addition, the system temperature is controlled within the range of 0 to 5°C to avoid localized overheating and potential runaway reaction. After the addition is complete, the titanium hydroxide precipitate is washed by centrifugation with deionized water at low temperature, repeating the washing three to five times to remove hydrolysis byproducts such as butanol and other organic impurities. The washed titanium hydroxide precipitate is redispersed in 200 ml of deionized water, and 60 ml of a 7% hydrogen peroxide solution is added, along with 20 ml of ethanol as a co-solvent. The solution is magnetically stirred at room temperature for 0.5 to 1 hour. The white precipitate gradually dissolves, and the solution changes from a turbid state to an orange-clear state, yielding a titanium peroxide complex solution. The criteria for successful preparation are an orange or orange-red solution that is completely clear and transparent, without any white turbidity or precipitate formation. In this titanium peroxide complex solution, titanium exists in the form of a soluble complex and has good storage stability in air. After high-temperature treatment, it can be decomposed in situ and transformed into a titanium dioxide cemented phase.

[0022] As described in step S3 above, 0.1–1.0 g of nano-titanium dioxide particles or titanium dioxide nanotubes are added to 5–20 ml of titanium peroxide complex solution. The nano-titanium dioxide is preferably anatase type with a particle size of 20–30 nm. Then, 0–1 times the volume of the titanium peroxide complex solution is added as a diluent and co-solvent to reduce the viscosity of the slurry and improve its dispersion. The mixture is placed in an ultrasonic dispersion device and treated at 200–500 W for 15–30 min to ensure that the nano-titanium dioxide particles or titanium dioxide nanotubes are uniformly suspended in the titanium peroxide complex solution, preventing agglomeration and sedimentation, resulting in a uniform and stable composite slurry. The composite slurry is milky white or light yellow in suspension and shows no obvious stratification or precipitation after standing. For example, 1.0 g of anatase nano-titanium dioxide powder is weighed, added to 20 ml of titanium peroxide complex solution, and then 20 ml of ethanol is added. The mixture is ultrasonically dispersed at 300 W for 20 min to obtain a uniform composite slurry. This composite slurry can be used directly in subsequent coating processes. The titanium peroxide complex acts as both a liquid phase carrier and a precursor in the slurry, while the nano-titanium dioxide particles or titanium dioxide nanotubes are uniformly distributed in the slurry system as a framework phase, providing a structural basis for the final formation of a dense cemented composite coating.

[0023] As described in step S4 above, 9.9 g of tantalum chloride powder is weighed in a fume hood and placed in a container under ice-water bath conditions. n-Butanol is slowly added while continuously stirring until the tantalum chloride is completely dissolved. The resulting solution is transferred to a 50 ml volumetric flask and diluted to the mark with n-butanol to obtain a tantalum chloride n-butanol solution with a tantalum ion concentration of 0.5 mol / L. Maintaining an ice-water bath environment during preparation effectively inhibits the violent exothermic reaction when tantalum chloride comes into contact with the solvent, preventing localized overheating that could cause solvent evaporation or solute decomposition. The resulting tantalum chloride n-butanol solution is colorless or pale yellow and transparent with moderate viscosity, suitable for subsequent brushing or mixed coating processes. In actual preparation, the concentration of the tantalum chloride solution can be adjusted within the range of 0.3–0.7 mol / L according to the required tantalum content in the coating. If the concentration is too low, the tantalum content introduced in a single coating is insufficient, resulting in inadequate sealing phase formation; if the concentration is too high, the solution viscosity increases, coating uniformity decreases, and localized crystallization or cracking is prone to occur during drying. The tantalum chloride n-butanol solution is transformed into a tantalum pentoxide sealing phase during subsequent heat treatment, which fills the pores between nano-titanium dioxide particles or titanium dioxide nanotubes and the titanium dioxide cemented phase, blocking the channels for electrolyte to penetrate into the titanium matrix.

[0024] As described in step S5 above, when uniformly coating the composite slurry onto the surface of the pretreated titanium substrate, a soft brush or spraying method can be used. For the multilayer composite process, first brush the composite slurry onto the surface of the titanium substrate and dry it in a 100℃ oven for 10 minutes. After removal, uniformly brush a layer of 0.5 mol / L tantalum chloride n-butanol solution onto the dried surface, and dry it again at 100℃ for 10 minutes. Repeat the above alternating process of composite slurry coating, drying, tantalum chloride solution coating, and drying five times to obtain the multilayer composite precursor. For the mixed coating process, take the composite slurry, add 0.5 mol / L tantalum chloride n-butanol solution at a titanium to tantalum molar ratio of 1:2, and then add an appropriate amount of ethanol as a co-solvent. Sonicate and stir for 20 minutes to homogenize the mixture. Use a soft brush to uniformly brush the mixed coating solution onto the surface of the pretreated titanium substrate and dry it in a 100℃ oven for 10 minutes. Repeat the brushing and drying steps five times to obtain the mixed composite precursor. The drying temperature after each coating can be controlled between 80 and 120°C, and the drying time between 5 and 15 minutes. The number of coating and drying cycles can be adjusted between 3 and 10 times according to the required coating thickness. Both methods can produce precursors that form the desired composite structure during subsequent sintering. The layered composite precursor is beneficial for forming a layered structure with a reinforced bottom skeleton and a tantalum pentoxide sealing layer, while the mixed composite precursor is beneficial for forming a dense coating with a uniform distribution of nano-titanium dioxide, titanium dioxide cementing phase, and tantalum pentoxide sealing phase.

[0025] As described in step S6 above, the coating precursor obtained in step S5 is placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in an air atmosphere, and held for 30 min. During the heating process, the titanium peroxide complex gradually decomposes and transforms in situ into a titanium dioxide cemented phase. This cemented phase coats and connects nano-titanium dioxide particles or titanium dioxide nanotubes, forming a continuous and dense framework. Tantalum chloride is transformed into a tantalum pentoxide sealing phase during the holding stage, filling the pores between the nano-titanium dioxide particles or titanium dioxide nanotubes and the titanium dioxide cemented phase. After the holding period, heating is stopped, and the furnace is allowed to cool naturally to room temperature to obtain a composite coating on the titanium substrate surface. In actual heat treatment, the heating rate can be adjusted within the range of 3 to 8°C / min, and the holding time can be selected within the range of 15 min to 3 h depending on the coating thickness. The heat treatment temperature is controlled at 400 to 550°C to ensure complete decomposition of the titanium peroxide complex and full conversion of tantalum chloride, while avoiding excessive oxidation of the titanium substrate surface that could affect the interfacial bonding.

[0026] The present invention will be specifically described below through examples and comparative examples. Example 1

[0027] A 60mm × 170mm × 1mm titanium plate was ultrasonically cleaned sequentially with acetone and anhydrous ethanol for 15 minutes, then sandblasted with 24-mesh black corundum until the surface was uniformly rough. It was then immersed in a 10% (w / w) boiling oxalic acid solution for etching for 2 hours, rinsed with deionized water, and dried to obtain a pretreated titanium substrate. 40ml of tetrabutyl titanate was added dropwise to 200ml of deionized water in an ice-water bath at 0–5℃, and stirred to obtain titanium hydroxide precipitate. After washing three times by low-temperature centrifugation, the precipitate was dispersed in 200ml of deionized water, and 60ml of 7% (w / w) hydrogen peroxide solution and 20ml of ethanol were added. The mixture was stirred at room temperature for 0.5–1 hour until the precipitate dissolved, yielding an orange-colored transparent titanium peroxide complex solution. 9.9g of tantalum chloride powder was weighed in a fume hood, dissolved in n-butanol in an ice-water bath, and brought to a final volume of 50ml to obtain a tantalum chloride n-butanol solution with a tantalum ion concentration of 0.5mol / L. Weigh 1.0 g of anatase-type nano-titanium dioxide powder with a particle size of 20–30 nm, add 20 ml of titanium peroxide complex solution and 20 ml of ethanol, and ultrasonically disperse at 300 W for 20 min to obtain a uniform composite slurry. Apply the composite slurry evenly to the surface of a pretreated titanium substrate using a soft brush, and dry in a 100 °C oven for 10 min. After removal, evenly brush on a layer of 0.5 mol / L tantalum chloride n-butanol solution, and dry again at 100 °C for 10 min. Repeat the alternating operations of composite slurry coating, drying, tantalum chloride solution coating, and drying five times to obtain a multilayer composite precursor. Place the precursor in a muffle furnace and heat to 500 °C at 5 °C / min under air atmosphere, hold for 30 min. The titanium peroxide complex is converted in situ into a titanium dioxide cemented phase and cements the nano-titanium dioxide particles, while the tantalum chloride is converted into a tantalum pentoxide sealing phase. Then, allow the furnace to cool naturally to room temperature to obtain a composite coating on the titanium substrate surface.

[0028] The coating failure time was verified to be 112.3 hours after enhanced life test.

[0029] Figure 2 This is a scanning electron microscope (SEM) image of the coating prepared in this embodiment. At a 500 nm observation scale, the coating is observed to consist of clusters of uniformly sized nanoparticles. A continuous phase exists between the particles, bridging adjacent particles. No large-scale interconnected pores or penetrating microcracks are observed; only a small number of scattered micropores are present. Based on the preparation process, this continuous phase corresponds to the titanium dioxide cementing phase formed by the in-situ transformation of the corresponding titanium peroxide complex through heat treatment. This phase connects the discrete nano-titanium dioxide particles into a cohesive whole, effectively filling the gaps formed by the natural accumulation of particles. The above morphology indicates that this process can alleviate volume shrinkage and stress cracking during sintering, significantly improving the coating's density and structural continuity. Example 2

[0030] A multilayer composite process was adopted, with titanium dioxide nanotubes as the skeleton reinforcement phase, and the molar ratio of titanium to tantalum in the coating was 1:2.

[0031] The pretreatment steps for the titanium matrix were exactly the same as in Example 1. Take 20 mL of the titanium peroxide complex solution prepared according to the above method, add 1.0 g of titanium dioxide nanotubes, then add 20 mL of ethanol, and ultrasonically disperse at 300 W for 20 minutes to obtain a uniform and stable composite slurry.

[0032] The composite slurry was uniformly brushed onto the pretreated titanium substrate surface using a soft brush and dried in an oven at 100°C for 10 minutes. After removal, a 0.5 mol / L solution of tantalum chloride in n-butanol was uniformly brushed onto the dried coating surface and dried again at 100°C for 10 minutes. The above alternating coating and drying steps were repeated 5 times to obtain the coating precursor.

[0033] A titanium substrate with the coating precursor was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in air atmosphere. The temperature was held for 30 minutes, causing the titanium peroxide complex to transform in situ into a titanium dioxide cemented phase, and tantalum chloride to completely pyrolyze into a tantalum pentoxide sealed phase. After the holding period, heating was stopped, and the substrate was allowed to cool naturally to room temperature, yielding the composite coating on the titanium substrate surface.

[0034] Figure 3 This is a scanning electron microscope (SEM) image of the coating prepared in this embodiment. At a 500 nm observation scale, the coating body forms a continuous, dense phase region with a dendritic diffuse structure at local edges. There are no obvious penetrating microcracks, and the pores are few in number and small in size. Based on the preparation process, this structure is composed of a titanium dioxide nanotube framework, an in-situ transformed titanium dioxide cementing phase, and a tantalum pentoxide sealing phase. One-dimensional framework units are bridged and coated by the cementing phase to form a continuous load-bearing network, while the sealing phase simultaneously fills the gaps in the framework. The overall coating structure is dense and continuous, effectively preventing electrolyte penetration into the titanium substrate. Example 3

[0035] In this embodiment, a composite coating on the surface of a titanium substrate is prepared using a hybrid coating process, with nano-titanium dioxide powder as the skeleton reinforcing phase, and the molar ratio of titanium to tantalum in the coating is 1:2.

[0036] The pretreatment steps for the titanium matrix are the same as in Example 1. Take 20 mL of titanium peroxide complex solution prepared according to the above method, add 1.0 g of anatase nano titanium dioxide powder with a particle size of 20~30 nm, and then add 20 mL of ethanol. Disperse the mixture ultrasonically at 300 W power for 20 minutes to obtain a uniform and stable composite slurry.

[0037] A 0.5 mol / L tantalum chloride n-butanol solution was added to the above composite slurry at a titanium to tantalum molar ratio of 1:2, followed by 8 mL of ethanol as a co-solvent. The mixture was ultrasonically stirred for 20 minutes to ensure homogeneity, yielding a mixed coating solution. The mixed coating solution was then evenly brushed onto the pretreated titanium substrate surface using a soft brush and dried in a 100°C oven for 10 minutes. This brushing and drying process was repeated five times to obtain the coating precursor.

[0038] The titanium substrate with the coating precursor is placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in air atmosphere. The temperature is held for 30 minutes to allow the titanium peroxide complex to be converted in situ into the titanium dioxide cemented phase, and the tantalum chloride to be completely pyrolyzed into the tantalum pentoxide sealed phase. After the holding time is completed, the heating is stopped and the substrate is allowed to cool naturally to room temperature with the furnace to obtain the composite coating on the surface of the titanium substrate.

[0039] Figure 4 This is a scanning electron microscope (SEM) image of the coating prepared in this embodiment. At a 500 nm observation scale, the coating is composed of nanoparticle aggregates with obvious gaps and grooves between them. No layering interface corresponding to the stacking process was observed. A continuous binder phase exists on the surface of the aggregates, without penetrating microcracks. Based on the preparation process, this binder phase corresponds to the in-situ generated titanium dioxide cementing phase. The tantalum pentoxide component is uniformly dispersed in the coating system, forming a composite structure together with the cementing phase and the nano-titanium dioxide framework. Compared to a pure particle stacked coating, the cohesion and density of this structure are significantly improved. Example 4

[0040] In this embodiment, a composite coating on the surface of a titanium substrate is prepared using a hybrid coating process, with nano-titanium dioxide powder as the skeleton reinforcing phase, and the molar ratio of titanium to tantalum in the coating is 1:3.

[0041] The pretreatment steps for the titanium matrix are the same as in Example 1. Take 20 mL of titanium peroxide complex solution prepared according to the above method, add 1.0 g of anatase nano titanium dioxide powder with a particle size of 20~30 nm, and then add 20 mL of ethanol. Disperse the mixture ultrasonically at 300 W power for 20 minutes to obtain a uniform and stable composite slurry.

[0042] A 0.5 mol / L tantalum chloride n-butanol solution was added to the above composite slurry at a titanium to tantalum molar ratio of 1:3, followed by 8 mL of ethanol as a co-solvent. The mixture was ultrasonically stirred for 20 minutes to ensure homogeneity, resulting in a mixed coating solution. The mixed coating solution was then uniformly brushed onto the pretreated titanium substrate surface using a soft brush and dried in a 100°C oven for 10 minutes. This brushing and drying process was repeated five times to obtain the coating precursor.

[0043] The titanium substrate with the coating precursor is placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in air atmosphere. The temperature is held for 30 minutes to allow the titanium peroxide complex to be converted in situ into the titanium dioxide cemented phase, and the tantalum chloride to be completely pyrolyzed into the tantalum pentoxide sealed phase. After the holding time is completed, the heating is stopped and the substrate is allowed to cool naturally to room temperature with the furnace to obtain the composite coating on the surface of the titanium substrate.

[0044] Figure 5 The surface scanning electron microscope (SEM) image of the coating prepared in this embodiment shows, at a 500 nm observation scale, that the coating body is a large-area, continuous, flat, dense phase, locally exhibiting a dendritic diffuse distribution; there are no penetrating microcracks, and the number and size of pores are further reduced compared to the low tantalum content sample. Combined with the preparation process, it can be seen that this dense composite phase is formed by the full fusion of a titanium dioxide cementing phase, a nano-titanium dioxide framework, and a tantalum pentoxide sealing phase, with a higher tantalum content enhancing the pore-filling effect. The above morphology indicates that the coating in this embodiment has superior overall density and structural integrity, and its corrosion resistance and shielding ability are the best among all sample groups.

[0045] Comparative Example 1 This comparative example only uses titanium peroxide complex and nano-titanium dioxide composite slurry to prepare the coating, without introducing tantalum chloride precursor and tantalum pentoxide sealing phase, and the rest of the preparation process is consistent with Example 1.

[0046] The pretreatment steps for the titanium matrix are the same as in Example 1. Take 20 mL of the titanium peroxide complex solution prepared according to the above method, add 1.0 g of anatase nano-titanium dioxide powder with a particle size of 20~30 nm, then add 20 mL of ethanol, and ultrasonically disperse at 300 W power for 20 minutes to obtain a uniform and stable composite slurry.

[0047] The composite slurry was evenly brushed onto the pretreated titanium substrate surface using a soft brush and dried in a 100°C oven for 10 minutes. The brushing and drying steps were repeated a total of 5 times to obtain the coating precursor.

[0048] A titanium substrate with the coating precursor was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in air atmosphere, and held at that temperature for 30 minutes to allow the titanium peroxide complex to be converted in situ into a titanium dioxide cemented phase. After the holding period, heating was stopped, and the substrate was allowed to cool naturally to room temperature with the furnace to obtain the control coating.

[0049] Figure 6The surface scanning electron microscope (SEM) image of the coating prepared for this comparative example shows, at a 500 nm observation scale, that the coating is composed of stacked agglomerates of nano-titanium dioxide particles. The surface is covered with numerous intersecting microcracks and open pores, resulting in a loose overall structure that fails to form a continuous, dense shielding layer. The pores and cracks are interconnected, forming penetration channels. Based on the preparation process, it is evident that, due to the absence of a tantalum pentoxide sealing phase, the titanium dioxide cementing phase alone is insufficient to fully seal the gaps between the particle packings. Corrosive media can rapidly penetrate into the substrate along these interconnected channels, resulting in a significantly shorter enhanced lifespan compared to the test results of the example sample.

[0050] Comparative Example 2 This comparative example uses a process of alternating coating of nano-titanium dioxide suspension and tantalum chloride solution to prepare the coating, without introducing titanium peroxide complex cementing phase. The molar ratio of titanium to tantalum in the coating is 1:2, and the rest of the preparation process and parameters are the same as in Example 1.

[0051] The pretreatment steps for the titanium matrix are the same as in Example 1. Weigh 1.0 g of anatase-type nano-titanium dioxide powder with a particle size of 20-30 nm, add 20 mL of deionized water and 20 mL of ethanol, and ultrasonically disperse at 300 W for 20 minutes to obtain a nano-titanium dioxide suspension.

[0052] The above suspension was evenly brushed onto the pretreated titanium substrate surface using a soft brush and dried in an oven at 100°C for 10 minutes. After removal, a layer of 0.5 mol / L tantalum chloride n-butanol solution was evenly brushed onto the dried coating surface, and dried again at 100°C for 10 minutes. The above alternating coating and drying steps were repeated 5 times to obtain the coating precursor.

[0053] A titanium substrate with the coating precursor was placed in a muffle furnace and heated to 500°C at a rate of 5°C / min in air atmosphere. The temperature was held for 30 minutes to completely pyrolyze tantalum chloride into tantalum pentoxide. After the holding period, heating was stopped, and the substrate was allowed to cool naturally to room temperature with the furnace to obtain the control coating.

[0054] like Figure 7 As shown, this is a scanning electron microscope (SEM) image of the coating prepared in this comparative example. At a 500 nm observation scale, the nanoparticle aggregates are scattered, lacking continuous bridging structures and exhibiting only physical stacking. Numerous micro-gaps and pores exist at particle boundaries and phase interfaces, making it impossible to construct a continuous and dense shielding layer. Combined with the preparation process, it is evident that due to the absence of a titanium peroxide complex precursor, an in-situ bonded interface cannot be formed between the particles. This leads to structural defects during sintering, making it difficult for the tantalum pentoxide component to effectively fill the gaps between the scattered particles. Ultimately, this results in a coating with inferior corrosion resistance and service life compared to the example sample.

[0055] Combination Figure 8As shown, the sample was placed in an H2SO4 electrolyte with a concentration of 1 mol / L and the electrolyte temperature was controlled at 50℃. The constant current electrolysis method was used to test the coating at a current density of 500 A / dm² (500 ASD). The coating failure endpoint was defined as the increase of 5V in the electrolytic cell voltage from the initial value. The continuous electrolysis time from the start of the test to the arrival of the failure endpoint was recorded, which is the enhanced life of the coating.

[0056] Compared to Comparative Example 1, Example 1 simultaneously introduced a cemented phase transformed from titanium dioxide complex and a tantalum pentoxide sealing phase, increasing the coating life from 72.4 h to 112.3 h. Comparative Example 1 relied solely on titanium dioxide particles and the cemented phase to construct the coating, lacking the high corrosion-resistant sealing phase to fill and seal the pores. This resulted in numerous open pores and microcracks on the coating surface, allowing corrosive media to quickly penetrate to the substrate interface. In contrast, the tantalum pentoxide sealing phase filled the gaps formed by the particle stacking, constructing a continuous corrosion-resistant shielding layer that effectively prevented electrolyte diffusion to the substrate side, making it a key component for improving the coating's corrosion resistance.

[0057] Compared with Comparative Example 2, the enhanced lifespan of Example 1 increased from 95.2h to 112.3h after introducing the in-situ generated titanium dioxide cement phase. Comparative Example 2 used pure nanoparticles and tantalum precursors for alternating coating, and the particles were only physically stacked without chemically bonded bridging structures. During sintering, network microcracks were easily generated, and tantalum pentoxide could not effectively fill the gaps between scattered particles. However, the cement phase formed by the in-situ transformation of titanium peroxide complex through heat treatment can form a coating layer on the surface of nanoparticles and form continuous bridging between particles, strengthening the cohesion of the coating and alleviating cracking caused by sintering stress. At the same time, it works in conjunction with the tantalum pentoxide seal to jointly construct a dense composite structure.

[0058] Comparison of samples from different embodiments shows that the component ratio and preparation process jointly affect the final service performance. Example 2, using titanium dioxide nanotubes as the framework, exhibits a slightly longer service life than Example 1, which uses a nanoparticle system. This is attributed to the superior continuity of the one-dimensional tubular structure, allowing for a more complete load-bearing framework after the cementing phase coats the tube walls. Example 3, employing a mixed coating process, outperforms Example 1 with its alternating coating. This process results in a uniform dispersion of the cementing phase, framework particles, and sealing phase components, eliminating bonding defects caused by layering interfaces and further enhancing the overall density of the coating. Example 4, which increases the tantalum content, further enhances the filling effect of the tantalum pentoxide sealing phase, forming a large, continuous, flat, and dense region on the coating surface. The number of pores and defects is minimized, resulting in a service life of 144.7 hours, the best among all samples.

[0059] In summary, this invention utilizes the in-situ conversion of titanium peroxide complexes through heat treatment to generate a titanium dioxide cemented phase, combined with the synergistic effect of the tantalum pentoxide sealing phase, and employs optimized coating and pyrolysis processes to construct a dense and continuous composite protective coating on the surface of a titanium substrate. This effectively enhances the coating's cohesion and interfacial bonding strength, inhibits the generation of sintering microcracks and interconnected pores, and prevents corrosive media from penetrating into the substrate, significantly improving the corrosion resistance and service life of the composite coating on the titanium substrate surface.

[0060] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0061] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes, characterized in that, Includes the following steps: The titanium substrate is subjected to degreasing, sandblasting and acid etching to obtain a pretreated titanium substrate; The titanium hydroxide precipitate obtained by hydrolysis of tetrabutyl titanate was washed and then complexed with hydrogen peroxide solution to obtain a titanium peroxide complex solution. Nano-sized titanium dioxide particles or titanium dioxide nanotubes are dispersed in the titanium peroxide complex solution to obtain a composite slurry; Tantalum chloride is dissolved in an organic solvent to obtain a tantalum chloride solution; The composite slurry and the tantalum chloride solution are alternately coated or mixed and then coated onto the surface of the pretreated titanium substrate. The coating and drying steps are repeated multiple times to obtain a coating precursor. The coating precursor is heated to 400℃~550℃ in air at a rate of 3~8℃ / min and then kept at that temperature to convert the titanium peroxide complex of the precursor into a titanium dioxide cemented phase in situ, and the tantalum chloride is converted into a tantalum pentoxide sealing phase. The mixture is then naturally cooled to room temperature in the furnace to obtain a composite coating on the titanium substrate surface.

2. The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes according to claim 1, characterized in that, In the step of heating the coating precursor to 400℃~550℃ in air at a rate of 3~8℃ / min and then holding it at that temperature, the holding process causes the titanium dioxide cement phase to coat and connect the nano-titanium dioxide particles or titanium dioxide nanotubes, and the tantalum pentoxide sealing phase fills the pores between the nano-titanium dioxide particles or titanium dioxide nanotubes and the titanium dioxide cement phase.

3. The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes according to claim 1, characterized in that, The step of alternately coating or mixing the composite slurry and the tantalum chloride solution onto the surface of the pretreated titanium substrate, drying, and repeating the coating and drying steps multiple times includes: After each coating, dry the product at 80–120°C. Repeat the coating and drying process 3–10 times. When using a mixed coating method, the molar ratio of titanium in the nano-titanium dioxide to tantalum in tantalum chloride is 1:0.5 to 1:

5.

4. The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes according to claim 1, characterized in that, The step of washing the titanium hydroxide precipitate obtained by hydrolyzing tetrabutyl titanate and then complexing it with hydrogen peroxide solution includes: Tetrabutyl titanate was added dropwise to deionized water at 0~5℃ and stirred to obtain titanium hydroxide precipitate. The titanium hydroxide precipitate was washed and dispersed in a hydrogen peroxide solution with a mass concentration of 7% to 30%, and ethanol was added as a co-solvent. The mixture was stirred at room temperature until the precipitate dissolved to obtain a titanium peroxide complex solution.

5. The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes according to claim 1, characterized in that, The step of dispersing nano-titanium dioxide particles or titanium dioxide nanotubes in the titanium peroxide complex solution to obtain a composite slurry includes: Take 0.1~1.0g of nano-titanium dioxide particles or titanium dioxide nanotubes, add them to 5~20mL of the titanium peroxide complex solution, and then add 0~1 times the volume of the titanium peroxide complex solution of ethanol. Disperse the mixture ultrasonically at 200~500W power for 15~30 minutes to obtain a composite slurry.

6. The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes according to claim 1, characterized in that, The step of dissolving tantalum chloride in an organic solvent to obtain a tantalum chloride solution includes: Tantalum chloride was added to n-butanol under ice-water bath conditions and stirred until completely dissolved to prepare a tantalum chloride n-butanol solution with a tantalum ion concentration of 0.3~0.7 mol / L.

7. The method for preparing a composite coating on a titanium substrate surface based on in-situ transformation of titanium peroxide complexes according to claim 1, characterized in that, The nano-titanium dioxide particles are anatase type with a particle size of 20-30 nm.

8. A composite coating on a titanium substrate surface, characterized in that, include: The composite coating comprises nano-titanium dioxide particles or titanium dioxide nanotubes, a titanium dioxide cement phase formed by in-situ transformation of titanium peroxide complex, and a tantalum pentoxide sealing phase. The titanium dioxide cementing phase coats and connects the nano-titanium dioxide particles or titanium dioxide nanotubes, and the tantalum pentoxide sealing phase fills the pores between the nano-titanium dioxide particles or titanium dioxide nanotubes and the titanium dioxide cementing phase.

9. The composite coating on the titanium substrate surface according to claim 8, characterized in that, include: The composite coating on the titanium substrate surface has a layered structure or a homogeneous composite structure. The stacked structure consists of alternating reinforcing layers and sealing layers. The reinforcing bottom layer is composed of nano-titanium dioxide particles or titanium dioxide nanotubes and a titanium dioxide cement phase, and the sealing surface layer is composed of a tantalum pentoxide sealing phase. In the homogeneous composite structure, nano-titanium dioxide particles or titanium dioxide nanotubes, titanium dioxide cement phase, and tantalum pentoxide sealing phase are uniformly distributed.

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