Pure titanium micro-arc oxidation coating for vacuum cup and preparation method of pure titanium micro-arc oxidation coating

Abstract

The invention relates to the technical field of coating materials, and discloses a pure titanium micro-arc oxidation coating for a vacuum cup and a preparation method thereof.The preparation method comprises the following steps that surface pretreatment is conducted, specifically, a pure titanium vacuum cup inner container workpiece is sequentially subjected to degreasing, acid pickling and ultrasonic cleaning; preparing an electrolyte, namely adding 15-25 parts by weight of a silicon-containing compound, 5-12 parts by weight of metal salt, 3-8 parts by weight of an antibacterial agent and 1-5 parts by weight of a stabilizer into deionized water, and controlling the pH value to be 8.5-10.5; and performing micro-arc oxidation treatment. According to the invention, a silane compound in the micro-arc oxidation electrolyte contains a high-activity silanol group which is subjected to condensation reaction with titanium hydroxyl on the surface of a pure titanium substrate under the action of an electric field to form stable covalent bonding, so that the bonding strength of the coating and the substrate is enhanced; metal ions generated by metal salt electrolysis are co-deposited with titanium ions through plasma discharge, a composite oxide structure is constructed, and micro defects on the surface of a titanium substrate are sealed.

Description

Technical Field

[0001] The present invention relates to the technical field of coating materials, and in particular to a pure titanium micro-arc oxidation coating for a thermos cup and a preparation method thereof. Background Art

[0002] Micro-arc oxidation, also known as micro-plasma oxidation, is a new technology that uses a combination of electrolyte and corresponding electrical parameters to grow a ceramic film layer mainly composed of matrix metal oxide on the surface of aluminum, magnesium, titanium and their alloys by relying on the instantaneous high temperature and high pressure generated by arc discharge. It has attracted widespread attention due to its simple preparation method, high membrane-base bonding, low cost, and the ability to uniformly prepare coatings on complex materials. At the same time, it can introduce trace elements beneficial to biological activity.

[0003] At present, due to the presence of various surface treatment processes in the production process of thermos liner, when preparing micro-arc oxidation coating on pure titanium substrate, the applied electrical parameters cannot adapt to the dynamic changes of coating growth in real time. The power supply output voltage is mismatched with the reaction process, which will cause uneven distribution of micro-arc discharge energy and lead to local defects in the coating microstructure.

[0004] Therefore, a pure titanium micro-arc oxidation coating for a thermos cup and a preparation method thereof are proposed to solve the above problems. Summary of the Invention

[0005] The main purpose of the present invention is to provide a pure titanium micro-arc oxidation coating for a thermos cup and a preparation method thereof, so as to solve the problems raised in the above background.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a pure titanium micro-arc oxidation coating for a thermos cup and a preparation method thereof, comprising the following steps: Step 1: Surface pretreatment: degreasing, pickling and ultrasonic cleaning of the pure titanium thermos cup liner workpiece in sequence; Step 2: Prepare the electrolyte by adding 15-25 parts of silicon-containing compound, 5-12 parts of metal salt, 3-8 parts of antibacterial agent and 1-5 parts of stabilizer into deionized water, and control the pH value to 8.5-10.5; Step 3: Micro-arc oxidation treatment: the pre-treated pure titanium workpiece is immersed in the electrolyte as the anode, and a pulse power supply is used to apply a gradient voltage to form a micro-arc oxidation coating on the pure titanium surface; Step 4: Post-processing: remove the coated workpiece, wash it with water, and dry it to obtain a pure titanium micro-arc oxidation coating with antibacterial and heat-insulating functions; The gradient voltage includes: a first stage of 250-300V for 5-10 minutes, a second stage of 350-400V for 15-25 minutes, and a third stage of 180-220V for 8-15 minutes.

[0007] Preferably, the surface pretreatment comprises three consecutive stages: Degreasing treatment: immerse the workpiece in an ethanol solution containing 0.5-1.5wt% sodium lauryl sulfate, and treat it with 40kHz ultrasonic wave for 10-20min in a constant temperature water bath at 40-50℃, where the ultrasonic power density is controlled at 0.5-1.0W / cm 2 , after treatment, rinse with deionized water until neutral; Pickling activation: Use a mixed acid solution containing 5-10vol% nitric acid and 2-5vol% hydrofluoric acid, soak for 30-90s at room temperature (20±2°C), with the volume ratio of pickling solution to workpiece being 5:1. After pickling, immediately immerse in 5wt% sodium bicarbonate solution for neutralization. Ultrasonic cleaning: Use deionized water at a frequency of 40kHz for 2-3 times, each time for 5-8 minutes, with a water resistivity greater than 18MΩ·cm. During the cleaning process, maintain a turbulent water flow rate of 0.5-1.0m / s, and finally maintain a continuous, intact water film on the workpiece surface without cracks.

[0008] Preferably, the electrolyte composition includes: The silicon-containing compound is selected from at least one of γ-aminopropyltriethoxysilane, vinyltrimethoxysilane or methyltriethoxysilane, preferably γ-aminopropyltriethoxysilane, wherein the amino functional group contained in the molecular structure thereof can form a coordination bond with the metal oxide; The metal salt is at least one of sodium aluminate, ammonium molybdate or sodium tungstate, wherein the Al 3+ ions can co-deposit with titanium ions to form TiAlO4 spinel structure; The antibacterial agent is at least one of zinc oxide particles with a particle size of 100-200 nm, nanosilver colloid or chitosan quaternary ammonium salt, and the zinc oxide particles are preferably surface-modified with a silane coupling agent; The stabilizer is at least one of sodium citrate, disodium EDTA or potassium sodium tartrate, and its addition amount accounts for 0.1-0.5wt% of the total weight of the electrolyte; The preparation method of the electrolyte includes: first heating deionized water to 40°C±2°C, adding a silicon-containing compound and a metal salt in sequence, stirring at 500 r / min for 15 minutes to form a basic solution, adding an antibacterial agent after the temperature drops to 25°C, and dispersing at a high speed of 800 r / min for 30 minutes under nitrogen protection; finally, adding a stabilizer and adjusting the pH to 9.0±0.5.

[0009] Preferably, the formula of the electrolyte is: 18-22 parts of γ-aminopropyltriethoxysilane, 8-10 parts of sodium aluminate, 5-7 parts of zinc oxide particles, 2-3 parts of sodium citrate, and 1000 parts of deionized water; The electrolyte temperature is controlled at 15-25°C, and the conductivity is maintained in the range of 15-25mS / cm; The zinc oxide particles were pre-silane modified by adding zinc oxide to an ethanol solution containing 3 wt% KH550, refluxing at 60° C. for 2 h, and centrifugally drying to obtain hydrophobic zinc oxide with a contact angle greater than 120°.

[0010] Preferably, the pulse power supply parameters are set as follows: Frequency range 500-1500Hz, preferably 800-1200Hz, frequency change rate does not exceed 50Hz / s; The duty cycle is 20%-40%, and the positive and negative pulses are asymmetrical. The positive pulse duty cycle is 25%-35%, and the negative pulse duty cycle is 5%-15%. The current density is maintained at 6-12A / dm 2 During the second stage of treatment, the current density increases to 8-15A / dm 2 ; A circulating cooling system is used to control the electrolyte temperature at 20±2°C. The cooling medium is ethylene glycol aqueous solution with a flow rate of 10-20L / min. The electrode spacing is fixed at 50-100mm. The cathode uses a stainless steel 316L plate, and its area ratio to the anode area is 1.5-2.5:1.

[0011] Preferably, the specific control method of the gradient voltage is: The first stage: the voltage is increased from 0V to 280±10V at a rate of 50V / min and maintained for 8±1min. During this stage, a dense base layer with a thickness of 5-8μm is formed; The second stage: the voltage was raised to 380±10V at a rate of 30V / min and maintained for 20±2min, during which a 100ms high voltage pulse was applied every 5min. During this stage, a porous structure was generated and functional particles were embedded. The third stage: reduce the voltage to 200±10V at a rate of 20V / min and maintain it for 10±2min, while applying ultrasonic oscillation at a frequency of 1kHz to promote pore sealing and surface smoothing; The voltage fluctuation range during the entire process does not exceed ±5% of the set value.

[0012] Preferably, during the micro-arc oxidation process: Continuously introduce argon gas into the electrolyte for protection, with an argon flow rate of 5-10 L / min, bubble particle size controlled at 0.5-1 mm, and gas purity greater than 99.999%; The electrolytic cell is equipped with a mechanical stirring system, with a blade speed of 100-200 rpm, forming a composite flow field of axial flow and radial flow; After each 5-min treatment, pause for 30 seconds and perform reverse pulse cleaning; During the second stage of treatment, an ultrasonic field with a frequency of 40 kHz was applied synchronously to promote nanoparticle dispersion and micropore formation.

[0013] Preferably, its microstructure includes: Dense structure of the inner layer: thickness 8-15μm, porosity less than 5%, mainly containing TiO2 rutile phase and Al2O3α phase, of which TiAlO4 spinel structure accounts for 30-50%, and grain size 0.2-0.5μm; The outer layer has a porous structure with a thickness of 12-20 μm and a gradient pore size distribution, with a surface pore size of 0.5-1 μm, a middle pore size of 1-2 μm, and a pore size of 2-3 μm near the inner layer. The porosity is 35-50%, of which the proportion of through pores is less than 15%. Functional composite layer: zinc oxide particles and silane polymer network are embedded on the surface to form a micro-nano composite structure with a surface roughness of Ra = 1.2-2.5μm.

[0014] Preferably, the coating has the following performance indicators: The surface contact angle is greater than 150° and the rolling angle is less than 5°, achieving super-hydrophobic self-cleaning effect; Antibacterial performance: The 24-hour antibacterial rate against Escherichia coli and Staphylococcus aureus is greater than 99.5%, and the antibacterial rate remains greater than 98% after 100 dishwasher cycles; Thermal performance: thermal conductivity is less than 0.05W / (m·K), which is more than 50% lower than that of traditional stainless steel liner. The temperature drop in 95℃ hot water environment for 24 hours is less than 2.5℃. Corrosion resistance: The corrosion current density after immersion in 3.5wt% NaCl solution for 30 days is less than 1×10 -8 A / cm 2 , the pitting potential is greater than 1.2V.

[0015] Preferably, the following optimization control is also included: In the third stage of the gradient voltage, mechanical vibration with a frequency of 1-5 kHz is applied synchronously, the amplitude is controlled at 5-20 μm, and the vibration direction is parallel to the workpiece surface; The mechanical vibration starts and stops periodically during the voltage maintenance period, and the working cycle is: vibrate for 10-30 seconds and then stop for 5-10 seconds; The vibration energy density distribution matches the workpiece geometry: the amplitude is increased to 15-20 μm for curved areas and maintained at 5-10 μm for flat areas. The vibration source adopts an electromagnetic exciter or a piezoelectric ceramic array, and the vibration parameters are controlled by a closed-loop feedback system so that the fluctuation range of the coating surface roughness Ra is less than ±0.2μm.

[0016] The present invention has the following beneficial effects: 1. In the present invention, the silane compound in the micro-arc oxidation electrolyte contains highly active silanol groups, which undergo a condensation reaction with the titanium hydroxyl groups on the surface of the pure titanium substrate under the action of an electric field to form a stable covalent bond, thereby enhancing the bonding strength between the coating and the substrate; the metal ions generated by the electrolysis of the metal salt are co-deposited with the titanium ions through plasma discharge to construct a composite oxide structure and seal the microscopic defects on the surface of the titanium substrate; at the same time, the nano-antibacterial particles migrate directionally under the drive of the pulsed electric field, embedding themselves into the micropores to form antibacterial functional units, blocking the microbial attachment path, thereby enhancing the long-term antibacterial properties; the gradient voltage strategy uses multi-stage energy regulation to form a porous layer with a special pore distribution on the outer layer, while retaining a continuous dense layer on the inner layer, thereby reducing the heat conduction rate and synergistically improving the thermal insulation performance.

[0017] 2. In the present invention, the composite pickling activation in the pretreatment stage constructs a micron-scale concave-convex structure on the titanium surface, thereby increasing the specific surface area; the active groups of the organosilane chemically bond with the hydroxyl groups on the fresh surface of the titanium matrix, and the hydrophobic segments are oriented outward to construct a super-hydrophobic interface; during the micro-arc oxidation process, the organic network and the inorganic melt are interwoven and symbiotic, forming a hybrid structure on the outer layer of the coating; the air is trapped inside the porous layer with a special pore distribution to form a thermal barrier, which cooperates with the surface convection inhibition effect to achieve dual-effect thermal insulation enhancement.

[0018] 3. In the present invention, the high-energy discharge stage of the gradient voltage causes the nano-antibacterial particles to melt and penetrate into the pore wall under the impact of plasma, forming a composite antibacterial structure on the inner wall of the micropore; the antibacterial ingredients achieve synergistic sterilization through ion release and active free radicals; the gas protection mechanism maintains the integrity of the antibacterial crystal structure and enhances the antibacterial activity; the porous structure prolongs the action time of the antibacterial agent through physical adsorption, maintains excellent antibacterial effect after multiple cleaning cycles, and cooperates with the thermal barrier network to construct a long-lasting protective barrier. DETAILED DESCRIPTION

[0019] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] Implementation 1: A pure titanium micro-arc oxidation coating for a thermos cup and a preparation method thereof, comprising the following steps: Step 1: Surface pretreatment: degreasing, pickling and ultrasonic cleaning of the pure titanium thermos cup liner workpiece in sequence; Step 2: Prepare the electrolyte by adding 15 parts of silicon-containing compound, 5 parts of metal salt, 3 parts of antibacterial agent and 1 part of stabilizer into deionized water, and control the pH value to 8.5; Step three: micro-arc oxidation treatment, the pre-processed pure titanium workpiece is immersed as an anode into an electrolyte, a gradient voltage is applied by using a pulse power supply, and a micro-arc oxidation coating is generated on the surface of the pure titanium; Step four: post-treatment, the coating workpiece is taken out, washed with water and dried to obtain a pure titanium micro-arc oxidation coating with antibacterial and heat preservation functions; The gradient voltage includes: 250V for 5min in the first stage, 350V for 15min in the second stage, and 180V for 8min in the third stage.

[0021] The surface pretreatment includes three continuous stages: Degreasing treatment: the workpiece is immersed into an ethanol solution containing 0.5wt% sodium dodecyl sulfate, treated with 40kHz ultrasonic waves for 10min in a 40℃ constant temperature water bath environment, and the ultrasonic power density is controlled at 0.5W / cm 2 After treatment, the workpiece is rinsed with deionized water to neutral; Pickling activation: the workpiece is immersed into a mixed acid solution containing 5vol% nitric acid and 2vol% hydrofluoric acid at room temperature 20±2℃ for 30s, the volume ratio of the pickling solution to the workpiece is 5:1, and the workpiece is immediately immersed into a 5wt% sodium bicarbonate solution for neutralization treatment after pickling; Ultrasonic cleaning: the workpiece is cleaned with deionized water at a frequency of 40kHz for 2 times, 5min each time, the water resistivity is greater than 18MΩ·cm, and the water flow rate is maintained at 0.5m / s in a turbulent state during the cleaning process, and the final workpiece surface water film is continuous and intact without rupture.

[0022] The electrolyte composition includes: The silicon-containing compound is at least one selected from γ-aminopropyl triethoxysilane, vinyltrimethoxysilane or methyl triethoxysilane, preferably γ-aminopropyl triethoxysilane, which contains an amino functional group in the molecular structure and can form a coordination bond with metal oxides; The metal salt is at least one of sodium meta-aluminate, ammonium molybdate or sodium tungstate, wherein the Al 3 + ions generated by the decomposition of sodium meta-aluminate in the electrolysis process can be co-deposited with titanium ions to form a TiAlO4 spinel structure; The antibacterial agent is at least one of zinc oxide particles with a particle size of 100nm, nano-silver colloid or chitosan quaternary ammonium salt, preferably zinc oxide particles treated by surface modification with a silane coupling agent; The stabilizer is at least one of sodium citrate, disodium EDTA or potassium sodium tartrate, and the addition amount is 0.1wt% of the total weight of the electrolyte; The preparation method of the electrolyte includes: first heating deionized water to 40℃±2℃, adding silicon-containing compounds and metal salts in sequence, stirring at 500r / min for 15 minutes to form a basic solution, adding an antibacterial agent after the temperature drops to 25℃, and dispersing at a high speed of 800r / min for 30 minutes under nitrogen protection; finally, adding a stabilizer and adjusting the pH to 8.5.

[0023] The formula of the electrolyte is: 18 parts of γ-aminopropyltriethoxysilane, 8 parts of sodium metaaluminate, 5 parts of zinc oxide particles, 2 parts of sodium citrate, and 1000 parts of deionized water; The electrolyte temperature is controlled at 15°C and the conductivity is maintained within 15mS / cm; The zinc oxide particles were pre-silane modified: zinc oxide was added to an ethanol solution containing 3 wt% KH550, refluxed at 60°C for 2 hours, and centrifugally dried to obtain hydrophobic zinc oxide with a contact angle greater than 120°.

[0024] The pulse power supply parameters are set as follows: The frequency is preferably 800Hz, and the frequency change rate does not exceed 50Hz / s; The duty cycle is 20%, and the positive and negative pulse asymmetric mode is adopted, in which the positive pulse duty cycle is 25% and the negative pulse duty cycle is 5%; The current density is maintained at 6A / dm 2 During the second stage of treatment, the current density increased to 8A / dm 2 ; A circulating cooling system is used to control the electrolyte temperature at 20±2°C. The cooling medium is ethylene glycol aqueous solution with a flow rate of 10L / min. The electrode spacing is fixed at 50mm, and the cathode is made of stainless steel 316L plate, with an area ratio of 1.5:1 to the anode area.

[0025] The specific control method of the gradient voltage is: The first stage: the voltage was increased from 0V to 270V at a rate of 50V / min and maintained for 7min. During this stage, a dense base layer with a thickness of 5μm was formed; The second stage: the voltage was raised to 370 V at a rate of 30 V / min and maintained for 18 min, during which a 100 ms high voltage pulse was applied every 5 min. During this stage, a porous structure was generated and functional particles were embedded. The third stage: the voltage is reduced to 190V at a rate of 20V / min and maintained for 8 minutes, while ultrasonic oscillation at a frequency of 1kHz is applied to promote pore sealing and surface smoothing; The voltage fluctuation range during the entire process does not exceed ±5% of the set value.

[0026] During the micro-arc oxidation process: Continuously introduce argon gas into the electrolyte for protection, with an argon flow rate of 5 L / min, bubble particle size controlled at 0.5 mm, and gas purity greater than 99.999%; The electrolytic cell is equipped with a mechanical stirring system, with a blade speed of 100 rpm, forming a composite flow field of axial flow and radial flow; After each 5-min treatment, pause for 30 seconds and perform reverse pulse cleaning; During the second stage of treatment, an ultrasonic field with a frequency of 40 kHz was applied synchronously to promote nanoparticle dispersion and micropore formation.

[0027] The coating microstructure includes: Dense structure of the inner layer: 8 μm thick, porosity less than 5%, mainly containing TiO2 rutile phase and Al2O3α phase, of which TiAlO4 spinel structure accounts for 30%, and grain size is 0.2 μm; The outer layer has a porous structure with a thickness of 12 μm and a gradient pore size distribution, with a surface pore size of 0.5 μm, a middle pore size of 1 μm, and a pore size of 2 μm near the inner layer. The porosity is 35%, of which the proportion of through holes is less than 15%. Functional composite layer: zinc oxide particles and silane polymer network are embedded on the surface to form a micro-nano composite structure with a surface roughness of Ra = 1.2μm.

[0028] The coating has the following performance indicators: The surface contact angle is greater than 150° and the rolling angle is less than 5°, achieving super-hydrophobic self-cleaning effect; Antibacterial performance: The 24-hour antibacterial rate against Escherichia coli and Staphylococcus aureus is greater than 99.5%, and the antibacterial rate remains greater than 98% after 100 dishwasher cycles; Thermal performance: thermal conductivity is less than 0.05W / (m·K), which is more than 50% lower than that of traditional stainless steel liner. The temperature drop in 95℃ hot water environment for 24 hours is less than 2.5℃. Corrosion resistance: The corrosion current density after immersion in 3.5wt% NaCl solution for 30 days is less than 1×10 -8 A / cm 2 , the pitting potential is greater than 1.2V.

[0029] Also included are the following optimization controls: In the third stage of the gradient voltage, mechanical vibration with a frequency of 1 kHz is applied synchronously, with the amplitude controlled at 5 μm and the vibration direction parallel to the workpiece surface; The mechanical vibration starts and stops periodically during the voltage maintenance period, and the working cycle is: vibrate for 10 seconds and then stop for 5 seconds; The vibration energy density distribution is matched to the workpiece geometry: the amplitude is increased to 15 μm for curved areas and maintained at 5 μm for flat areas; The vibration source adopts an electromagnetic exciter or a piezoelectric ceramic array, and the vibration parameters are controlled by a closed-loop feedback system so that the fluctuation range of the coating surface roughness Ra is less than ±0.2μm.

[0030] Implementation 2: A pure titanium micro-arc oxidation coating for a thermos cup and a preparation method thereof, comprising the following steps: Step 1: Surface pretreatment: degreasing, pickling and ultrasonic cleaning of the pure titanium thermos cup liner workpiece in sequence; Step 2: Prepare the electrolyte by adding 20 parts of silicon-containing compound, 8 parts of metal salt, 5 parts of antibacterial agent and 3 parts of stabilizer into deionized water, and control the pH value to 9.5; Step 3: Micro-arc oxidation treatment: the pre-treated pure titanium workpiece is immersed in the electrolyte as the anode, and a pulse power supply is used to apply a gradient voltage to form a micro-arc oxidation coating on the pure titanium surface; Step 4: Post-processing: remove the coated workpiece, wash it with water, and dry it to obtain a pure titanium micro-arc oxidation coating with antibacterial and heat-insulating functions; The gradient voltage included: the first stage was 270 V for 8 min, the second stage was 380 V for 20 min, and the third stage was 200 V for 12 min.

[0031] Surface preparation consists of three consecutive stages: Degreasing treatment: The workpiece was immersed in an ethanol solution containing 1.0 wt% sodium lauryl sulfate and treated with 40 kHz ultrasonic waves for 15 min in a constant temperature water bath at 45 °C, with the ultrasonic power density controlled at 0.7 W / cm 2 , after treatment, rinse with deionized water until neutral; Pickling activation: Use a mixed acid solution containing 8 vol% nitric acid and 3 vol% hydrofluoric acid, soak for 60 seconds at room temperature (20±2°C), with the volume ratio of pickling solution to workpiece being 5:1. Immediately after pickling, immerse in a 5 wt% sodium bicarbonate solution for neutralization. Ultrasonic cleaning: Clean with deionized water at a frequency of 40kHz for 3 times, each time for 7 minutes. The water resistivity is greater than 18MΩ·cm. During the cleaning process, the water flow rate is maintained at a turbulent state of 0.8m / s. Finally, the water film on the surface of the workpiece is continuous and intact.

[0032] The electrolyte composition includes: The silicon-containing compound is selected from at least one of γ-aminopropyltriethoxysilane, vinyltrimethoxysilane or methyltriethoxysilane, preferably γ-aminopropyltriethoxysilane, wherein the amino functional group contained in the molecular structure thereof can form a coordination bond with the metal oxide; The metal salt is at least one of sodium aluminate, ammonium molybdate or sodium tungstate, wherein the Al 3+ions can co-deposit with titanium ions to form TiAlO4 spinel structure; The antibacterial agent is at least one of zinc oxide particles with a particle size of 150 nm, nanosilver colloid, or chitosan quaternary ammonium salt, and the zinc oxide particles are preferably surface-modified with a silane coupling agent; The stabilizer is at least one of sodium citrate, disodium EDTA or potassium sodium tartrate, and its addition amount accounts for 0.3wt% of the total weight of the electrolyte; The preparation method of the electrolyte includes: first heating deionized water to 40℃±2℃, adding silicon-containing compounds and metal salts in sequence, stirring at 500r / min for 15 minutes to form a basic solution, adding an antibacterial agent after the temperature drops to 25℃, and dispersing at a high speed of 800r / min for 30 minutes under nitrogen protection; finally, adding a stabilizer and adjusting the pH to 9.0.

[0033] The formula of the electrolyte is: 20 parts of γ-aminopropyltriethoxysilane, 9 parts of sodium aluminate, 6 parts of zinc oxide particles, 3 parts of sodium citrate, and 1000 parts of deionized water; The electrolyte temperature is controlled at 20°C and the conductivity is maintained within 20mS / cm; The zinc oxide particles were pre-silane modified: zinc oxide was added to an ethanol solution containing 3 wt% KH550, refluxed at 60°C for 2 hours, and centrifugally dried to obtain hydrophobic zinc oxide with a contact angle greater than 120°.

[0034] The pulse power supply parameters are set as follows: The frequency is preferably 1000Hz, and the frequency change rate does not exceed 50Hz / s; The duty cycle is 30%, and the positive and negative pulses are asymmetrical, with a positive pulse duty cycle of 20% and a negative pulse duty cycle of 10%. The current density is maintained at 10A / dm 2 During the second stage of treatment, the current density was increased to 12A / dm 2 ; A circulating cooling system is used to control the electrolyte temperature at 20±2°C. The cooling medium is ethylene glycol aqueous solution with a flow rate of 15L / min. The electrode spacing is fixed at 80mm, and the cathode is made of stainless steel 316L plate, with an area ratio of 2.0:1 to the anode area.

[0035] The specific control method of the gradient voltage is: The first stage: the voltage is increased from 0V to 280V at a rate of 50V / min and maintained for 8min. During this stage, a dense base layer with a thickness of 5-8μm is formed; The second stage: the voltage was increased to 380V at a rate of 30V / min and maintained for 20min, during which a 100ms high-voltage pulse was applied every 5min. During this stage, a porous structure was generated and functional particles were embedded. Third stage: decrease to 200 V at a rate of 20 V / min, maintain for 10 min, while applying ultrasonic oscillation at a frequency of 1 kHz to promote pore closure and surface flattening; The voltage fluctuation range throughout the process does not exceed ±5% of the set value.

[0036] During the micro-arc oxidation process: Continuous argon gas protection is supplied to the electrolyte, with a flow rate of 8 L / min, bubble particle size controlled at 0.7 mm, and gas purity greater than 99.999%; The electrolytic cell is equipped with a mechanical stirring system, with paddle speed of 150 rpm, forming a composite flow field of axial and radial flow; Pause for 30 s after every 5 min of treatment for reverse pulse cleaning; During the second stage of treatment, an ultrasonic field at a frequency of 40 kHz is applied simultaneously to promote nanoparticle dispersion and micropore formation.

[0037] The coating microstructure includes: Dense inner layer: thickness of 12 μm, porosity less than 5%, mainly containing TiO2 rutile phase and Al2O3 alpha phase, with TiAlO4 spinel structure accounting for 40%, and grain size of 0.3 μm; Porous outer layer: thickness of 15 μm, with gradient distribution of pore size, surface pore size of 0.7 μm, middle part of 1.5 μm, near inner layer of 2.5 μm, porosity of 40%, with through-hole proportion less than 15%; Functional composite layer: surface embedded with zinc oxide particles and silane polymer network, forming a micro-nano composite structure, with surface roughness Ra = 2.0 μm.

[0038] The coating has the following performance indicators: Surface contact angle greater than 150°, rolling angle less than 5°, achieving super-hydrophobic self-cleaning effect; Antibacterial performance: 24 h antibacterial rate against Escherichia coli and Staphylococcus aureus greater than 99.5%, and antibacterial rate maintained greater than 98% after 100 cycles of dishwasher; Thermal performance: thermal conductivity less than 0.05 W / (m·K), more than 50% lower than traditional stainless steel inner liner, with 24 h temperature drop less than 2.5℃ in 95℃ hot water environment; Corrosion resistance: corrosion current density less than 1×10 -8 A / cm 2 after 30 days of immersion in 3.5 wt% NaCl solution, and pitting potential greater than 1.2 V.

[0039] Also includes the following optimized control: In the third stage of the gradient voltage, mechanical vibration with a frequency of 3 kHz is applied synchronously, the amplitude is controlled at 15 μm, and the vibration direction is parallel to the workpiece surface; The mechanical vibration starts and stops periodically during the voltage maintenance period, and the working cycle is: vibrate for 20 seconds and then stop for 8 seconds; The vibration energy density distribution matches the workpiece geometry: the amplitude is increased to 17 μm for curved areas and maintained at 8 μm for flat areas. The vibration source adopts an electromagnetic exciter or a piezoelectric ceramic array, and the vibration parameters are controlled by a closed-loop feedback system so that the fluctuation range of the coating surface roughness Ra is less than ±0.2μm.

[0040] Comparative Example 1: The difference between this comparative example and the first embodiment is that no mechanical vibration assistance is applied during the third stage of gradient voltage processing.

[0041] Comparative Example 2: This comparative example differs from Example 1 in that no silicon-containing compound is added to the electrolyte preparation in this comparative example.

[0042] Comparative Example 3: This comparative example differs from Example 1 in that argon gas protection is not introduced during the micro-arc oxidation process.

[0043] Comparative Example 4: The difference between this comparative example and implementation 1 is that the gradient voltage strategy is replaced by a constant voltage mode in this comparative example.

[0044] The performance tests of the pure titanium micro-arc oxidation coatings prepared in Examples 1 to 2 and Comparative Examples 1 to 4 were carried out. The test items and test methods are as follows: Coating bond strength test: The scratch method is used to test the coating. A Rockwell hardness indenter is loaded at a rate of 10 N / min while moving horizontally at a speed of 0.5 mm / s. The critical load when the coating peels off is recorded and the bond strength is calculated. Antibacterial performance test: Escherichia coli and Staphylococcus aureus suspensions were added dropwise to the coating surface, covered with a sterile film, and incubated at 37°C for 24 hours. The suspensions were then rinsed and eluted with normal saline. After gradient dilution, the suspensions were plated and counted, and the antibacterial rate was calculated. Thermal insulation performance test: Using a heat flow method thermal conductivity meter, based on the principle of steady-state heat transfer, under a temperature difference of 50°C, the heat flow per unit area through the coating sample is measured and the thermal conductivity coefficient is calculated; Corrosion resistance test: A three-electrode electrochemical workstation system was used to perform potentiodynamic polarization tests in a 3.5 wt % NaCl solution at a scan rate of 0.166 mV / s, and the self-corrosion potential and corrosion current density were recorded.

[0045] The pure titanium micro-arc oxidation coatings prepared in Comparative Examples 1 to 4 and Examples 1 to 2 were tested, and the specific results are shown in the table: By comparing and analyzing the data in the table, it can be seen that the pure titanium micro-arc oxidation coating prepared by the process of Example 1-2 has superior comprehensive performance compared with the coating prepared by the process of Comparative Example 1-4. This shows that the silane compound in the micro-arc oxidation electrolyte contains highly active silanol groups, which react with the titanium hydroxyl groups on the surface of the pure titanium substrate under the action of the electric field to form a stable covalent bond, thereby enhancing the bonding strength between the coating and the substrate; the metal ions generated by the electrolysis of the metal salt are co-deposited with the titanium ions through plasma discharge to construct a composite oxide structure, which seals the microscopic defects on the surface of the titanium substrate; at the same time, the nano-antibacterial particles migrate directionally under the drive of the pulsed electric field, embed themselves into the micropores to form antibacterial functional units, block the attachment path of microorganisms, and thus enhance the long-term antibacterial properties; the gradient voltage strategy uses multi-stage energy regulation to form a porous layer with a special pore distribution in the outer layer, and retain a continuous dense layer in the interior, thereby reducing the heat conduction rate and synergistically improving the thermal insulation performance. The composite pickling activation of the segments constructs a micron-scale concave-convex structure on the titanium surface, increasing the specific surface area; the active groups of the organosilane chemically bond with the hydroxyl groups on the fresh surface of the titanium matrix, and the hydrophobic segments are oriented outward to construct a super-hydrophobic interface; during the micro-arc oxidation process, the organic network and the inorganic melt are intertwined and symbiotic, forming a hybrid structure on the outer layer of the coating; the air trapped inside the porous layer with a special pore distribution forms a thermal barrier, which cooperates with the surface convection inhibition effect to achieve dual-effect thermal insulation enhancement; the high-energy discharge stage of the gradient voltage causes the nano-antibacterial particles to melt and penetrate into the pore wall under the impact of plasma, forming a composite antibacterial structure on the inner wall of the micropore; the antibacterial components achieve synergistic sterilization through ion release and active free radicals; the gas protection mechanism maintains the integrity of the antibacterial crystal structure and enhances the antibacterial activity; the porous structure prolongs the action time of the antibacterial agent through physical adsorption, maintains excellent antibacterial effect after multiple cleaning cycles, and cooperates with the thermal barrier network to construct a long-term protective barrier.

[0046] Comparison of the data in the table shows that the present invention not only has good bonding strength, antibacterial durability, thermal insulation and long-term protection, but also demonstrates that the method for preparing a pure titanium micro-arc oxidation coating for a thermos cup provided by the present invention has a broader market prospect and is more suitable for promotion.

[0047] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a pure titanium micro-arc oxidation coating for a thermos cup, characterized in that: The following steps are involved: Step 1: Surface pretreatment: degreasing, pickling and ultrasonic cleaning of the pure titanium thermos cup liner workpiece in sequence; Step 2: Prepare the electrolyte by adding 15-25 parts of silicon-containing compound, 5-12 parts of metal salt, 3-8 parts of antibacterial agent and 1-5 parts of stabilizer into deionized water, and control the pH value to 8.5-10.5; Step 3: Micro-arc oxidation treatment: the pre-treated pure titanium workpiece is immersed in the electrolyte as the anode, and a gradient voltage is applied using a pulse power supply to form a micro-arc oxidation coating on the pure titanium surface; Step 4: Post-processing: remove the coated workpiece, wash it with water, and dry it to obtain a pure titanium micro-arc oxidation coating with antibacterial and heat-insulating functions; The gradient voltage includes: a first stage of 250-300V for 5-10 minutes, a second stage of 350-400V for 15-25 minutes, and a third stage of 180-220V for 8-15 minutes.

2. The method for preparing a pure titanium micro-arc oxidation coating for a thermos cup according to claim 1, characterized in that: The surface preparation comprises three consecutive stages: Degreasing treatment: Immerse the workpiece in an ethanol solution containing 0.5-1.5wt% sodium lauryl sulfate, and treat it with 40kHz ultrasonic waves for 10-20 minutes in a constant temperature water bath at 40-50℃, with the ultrasonic power density controlled at 0.5-1.0W / cm². After treatment, rinse with deionized water until neutral; Pickling activation: Use a mixed acid solution containing 5-10vol% nitric acid and 2-5vol% hydrofluoric acid, soak for 30-90s at room temperature (20±2℃), with the volume ratio of pickling solution to workpiece being 5:

1. Immediately after pickling, immerse in 5wt% sodium bicarbonate solution for neutralization; Ultrasonic cleaning: Use deionized water at a frequency of 40kHz for 2-3 times, each time for 5-8 minutes. The water resistivity should be greater than 18MΩ·cm. During the cleaning process, maintain a turbulent water flow rate of 0.5-1.0m / s. Finally, the water film on the workpiece surface is continuous and intact.

3. The method for preparing a pure titanium micro-arc oxidation coating for a thermos cup according to claim 1, characterized in that: The electrolyte composition includes: The silicon-containing compound is selected from at least one of γ-aminopropyltriethoxysilane, vinyltrimethoxysilane or methyltriethoxysilane, preferably γ-aminopropyltriethoxysilane, wherein the amino functional group contained in the molecular structure thereof can form a coordination bond with the metal oxide; The metal salt is at least one of sodium aluminate, ammonium molybdate or sodium tungstate, wherein Al³⁺ ions generated by decomposition of sodium aluminate during electrolysis can co-precipitate with titanium ions to form a TiAlO₄ spinel structure; The antibacterial agent is at least one of zinc oxide particles with a particle size of 100-200 nm, nanosilver colloid, or chitosan quaternary ammonium salt, and the zinc oxide particles are preferably surface-modified with a silane coupling agent; The stabilizer is at least one of sodium citrate, disodium EDTA or potassium sodium tartrate, and its addition amount accounts for 0.1-0.5wt% of the total weight of the electrolyte; The preparation method of the electrolyte includes: first heating deionized water to 40°C±2°C, adding a silicon-containing compound and a metal salt in sequence, stirring at 500 r / min for 15 minutes to form a basic solution, adding an antibacterial agent after the temperature drops to 25°C, and dispersing at a high speed of 800 r / min for 30 minutes under nitrogen protection; finally, adding a stabilizer and adjusting the pH to 8.5-9.

5.

4. The method for preparing a pure titanium micro-arc oxidation coating for a vacuum cup according to claim 1, characterized in that: The formula of the electrolyte is: 18-22 parts of γ-aminopropyltriethoxysilane, 8-10 parts of sodium aluminate, 5-7 parts of zinc oxide particles, 2-3 parts of sodium citrate, and 1000 parts of deionized water; The electrolyte temperature is controlled at 15-25°C, and the conductivity is maintained in the range of 15-25mS / cm; The zinc oxide particles were pre-silane modified by adding zinc oxide to an ethanol solution containing 3 wt% KH550, refluxing at 60° C. for 2 h, and centrifugally drying to obtain hydrophobic zinc oxide having a contact angle greater than 120°.

5. The method for preparing a pure titanium micro-arc oxidation coating for a thermos cup according to claim 1, characterized in that: The pulse power supply parameters are set as: Frequency range 500-1500Hz, preferably 800-1200Hz, frequency change rate does not exceed 50Hz / s; The duty cycle is 20%-40%, and the positive and negative pulses are asymmetrical. The positive pulse duty cycle is 25%-35%, and the negative pulse duty cycle is 5%-15%. The current density is maintained at 6-12 A / dm², and during the second stage of treatment the current density is increased to 8-15 A / dm²; A circulating cooling system is used to control the electrolyte temperature at 20±2°C. The cooling medium is ethylene glycol aqueous solution with a flow rate of 10-20L / min. The electrode spacing is fixed at 50-100 mm, and the cathode is made of stainless steel 316L plate, with the area ratio of the cathode to the anode being 1.5-2.5:

1.

6. The method for preparing a pure titanium micro-arc oxidation coating for a thermos cup according to claim 1, characterized in that: The specific control method of the gradient voltage is: The first stage: the voltage is increased from 0V to 270-290V at a rate of 50V / min and maintained for 7-9min. During this stage, a dense base layer with a thickness of 5-8μm is formed; The second stage: the voltage is raised to 370-390 V at a rate of 30 V / min and maintained for 18-22 min, during which a 100 ms high voltage pulse is applied every 5 min. During this stage, a porous structure is generated and functional particles are embedded. The third stage: reduce the voltage to 190-210V at a rate of 20V / min and maintain it for 8-12 minutes, while applying ultrasonic oscillation at a frequency of 1kHz to promote pore sealing and surface smoothing; The voltage fluctuation range during the entire process does not exceed ±5% of the set value.

7. The method for preparing a pure titanium micro-arc oxidation coating for a vacuum cup according to claim 1, characterized in that: During the micro-arc oxidation process: Continuously introduce argon protection into the electrolyte at a flow rate of 5-10 L / min, with bubble size controlled at 0.5-1 mm and gas purity greater than 99.999%; The electrolytic cell is equipped with a mechanical stirring system, with a blade speed of 100-200 rpm, forming a composite flow field of axial flow and radial flow; After each 5-min treatment, pause for 30 seconds and perform reverse pulse cleaning; During the second stage of treatment, an ultrasonic field with a frequency of 40 kHz was applied synchronously to promote nanoparticle dispersion and micropore formation.

8. A pure titanium micro-arc oxidation coating prepared by the method according to any one of claims 1 to 7, characterized in that: The coating microstructure includes: Dense structure of the inner layer: thickness 8-15μm, porosity less than 5%, mainly containing TiO2 rutile phase and Al2O3α phase, of which TiAlO4 spinel structure accounts for 30-50%, and grain size 0.2-0.5μm; The outer layer has a porous structure with a thickness of 12-20 μm and a gradient pore size distribution, with a surface pore size of 0.5-1 μm, a middle pore size of 1-2 μm, and a pore size of 2-3 μm near the inner layer. The porosity is 35-50%, of which the proportion of through holes is less than 15%. Functional composite layer: zinc oxide particles and silane polymer network are embedded on the surface to form a micro-nano composite structure with a surface roughness of Ra = 1.2-2.5μm.

9. The pure titanium micro-arc oxidation coating according to claim 8, characterized in that: The coating has the following performance indicators: The surface contact angle is greater than 150° and the rolling angle is less than 5°, achieving super hydrophobic self-cleaning effect; Antibacterial performance: The 24-hour antibacterial rate against Escherichia coli and Staphylococcus aureus is greater than 99.5%, and the antibacterial rate remains greater than 98% after 100 dishwasher cycles; Thermal performance: thermal conductivity is less than 0.05W / (m·K), which is more than 50% lower than that of traditional stainless steel liner. The temperature drop in 95℃ hot water environment for 24 hours is less than 2.5℃. Corrosion resistance: The corrosion current density after immersion in 3.5wt% NaCl solution for 30 days is less than 1×10⁻ 8 A / cm², pitting potential greater than 1.2V.

10. A method for preparing a pure titanium micro-arc oxidation coating for a thermos cup according to any one of claims 1 to 7, characterized in that: Also included are the following optimization controls: In the third stage of the gradient voltage, mechanical vibration with a frequency of 1-5 kHz is applied synchronously, the amplitude is controlled at 5-20 μm, and the vibration direction is parallel to the workpiece surface; The mechanical vibration starts and stops periodically during the voltage maintenance period, and the working cycle is: vibrate for 10-30 seconds and then stop for 5-10 seconds; The vibration energy density distribution matches the workpiece geometry: the amplitude is increased to 15-20 μm for curved areas and maintained at 5-10 μm for flat areas. The vibration source adopts an electromagnetic exciter or a piezoelectric ceramic array, and the vibration parameters are controlled by a closed-loop feedback system so that the fluctuation range of the coating surface roughness Ra is less than ±0.2μm.

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