Preparation method of doped metastable phase iron oxide anti-corrosion coating

Abstract

The present invention relates to the field of coatings, and specifically, to a method for preparing a doped metastable phase iron oxide anti-corrosion coating. The present invention synthesizes a doped metastable phase iron oxide layer by a spray pyrolysis method, wherein the metastable phase iron oxide is cubic iron oxide, and the doping element is tin, titanium or zirconium. The prepared doped cubic iron oxide coating of the present invention has high chemical stability, can maintain a stable structure in a high-salt and high-alkali environment, has strong resistance to chloride ions in seawater, is non-toxic and pollution-free itself, and has a simple preparation method, which is convenient for large-scale spraying.

Description

Technical Field

[0001] The present invention relates to the field of coatings, and specifically, to a method for preparing a doped metastable phase iron oxide anti-corrosion coating. Background Art

[0002] Seawater is a natural electrolyte with extremely strong corrosiveness, and various marine transportation tools, drilling and oil production platforms, coastal equipment, etc. will face serious corrosion problems. The high conductivity of seawater will cause serious electrochemical corrosion of metals. For most metals, the anode has a small blocking effect on chloride ions with a small radius in seawater, and chloride ions can penetrate through the oxide, thus destroying the passivation film of the metal.

[0003] On the other hand, there are also serious problems of biological corrosion in seawater. Aiming at the problem that a large number of marine organisms adhere to the hull, marine platform pillars and other positions for a long time and are difficult to clean, resulting in corrosion, heavy metals, toxic substances, etc. are often added to the hull coating to inhibit the growth of microorganisms. This strategy often causes serious environmental pollution problems, and many poisons, heavy metal compounds, and organic solvents in coatings also pose a serious threat to the life, health and safety of people.

[0004] Iron oxide is a non-toxic, harmless, material with rich raw material reserves and low cost. It has advantages such as resistance to saline-alkali corrosion, good chemical stability, and high temperature resistance. At the same time, it is also a semiconductor photocatalytic material, which can generate energetic photogenerated electrons and holes under light illumination, and its redox ability can play an antibacterial and bactericidal role. At the same time, its semiconductor band gap of 1.9 - 2.1 eV can absorb a part of the ultraviolet spectrum and a part of the visible spectrum in sunlight, and can play a role in protecting the inner layer material. Based on the above advantages, the research on iron oxide in the fields of protective coatings and solar spectrum selective absorption layers has been developed, but its research as an anti-corrosion coating for resisting seawater corrosion is still in its infancy. In the current related technologies, the obtained iron oxides are all stable-phase hexagonal iron oxide (Zhang Zhiping, Research on the preparation of iron oxide thin films by spray pyrolysis and their photoelectrochemical properties, China University of Petroleum, 2018), and the research on metastable-phase cubic iron oxide is still blank. In addition, as the method for preparing a ferrite coating by flame spraying adopted by Zhu Zhixiang et al. in the patent CN103981477A, its coating composition and structure are limited by the sprayed powder material of the ferrite, and it is more difficult to regulate the coating composition. The coatings obtained by powder sintering usually have disadvantages such as weak adhesion, loose structure, large porosity, and being easily penetrated and corroded.

[0005] In addition, the thickness of the currently applied iron oxide anti-corrosion coating is usually in the micron level. Therefore, there is an urgent need to develop a method that can control the thickness of the iron oxide coating at the nanometer level and obtain an iron oxide coating with high density and excellent mechanical properties. Summary of the Invention

[0006] The present invention aims to provide a method for preparing a doped metastable-phase iron oxide anti-corrosion coating to obtain a metastable-phase cubic iron oxide coating. This anti-corrosion coating is non-toxic, harmless, and low-cost, and has excellent anti-corrosion and oxidation antibacterial properties.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a doped metastable-phase iron oxide anti-corrosion coating, wherein the metastable-phase iron oxide anti-corrosion coating adheres to the surface of the workpiece to be sprayed.

[0009] The method for preparing the metastable-phase iron oxide anti-corrosion coating includes the following steps:

[0010] 1) Dissolve the metal oxide precursor powder in a solvent, stir to obtain a uniform solution, add the doping precursor to the above solution, and stir to obtain a spraying solution;

[0011] 2) Ultrasonically atomize the spraying solution, uniformly mix the carrier gas with the atomized spraying solution, and spray it onto the surface of the heated workpiece to be sprayed;

[0012] 3) After spraying, calcine the workpiece sprayed with the doped transition metal iron oxide coating, and then cool it to room temperature.

[0013] Further, the workpiece to be sprayed is specifically metal, quartz glass, conductive glass or silicon.

[0014] Further, the thickness of the metastable-phase iron oxide anti-corrosion coating is 100 - 1000 nm.

[0015] Further, in step 1), the precursor powder is iron acetylacetonate, the solvent is ethanol, the doping agent is one or several of tetrabutyltin, titanium n-butoxide, and zirconium isopropoxide, and the stirring time each time is 12 - 24 h; the dosage ratio of the metal oxide precursor powder, solvent, and doping agent is 70 - 300 mg: 20 - 100 mL: 1 - 10 mg.

[0016] More preferably, in step 1), the metastable-phase iron oxide anti-corrosion coating, in terms of weight fraction, includes: iron 66.6% - 69.6%, oxygen 28.6% - 29.9%, and doping element 0.5% - 4.7%.

[0017] Further, in step 2), the carrier gas is air, the carrier gas flow rate is 4 - 6 L / min, the power of the ultrasonic atomizer is 12 - 100 W, the heating temperature of the workpiece to be sprayed is 400 - 500 °C, and the spraying time is 5 - 60 min.

[0018] Further, in the step 3), the calcination temperature of the workpiece to be coated is 500-700°C, and the calcination time is 1-4 h.

[0019] In the preparation method provided by the present invention, parameters such as the selection of the precursor powder and the solvent, the carrier gas flow rate, the power of the ultrasonic nebulizer, and the heating temperature of the workpiece to be sprayed are closely related to the formation of the metastable cubic phase iron oxide coating. If the selection of the precursor powder and the solvent is changed, or parameters such as the carrier gas flow rate, the power of the ultrasonic nebulizer, and the heating temperature of the workpiece to be sprayed are changed, a dense and strongly adherent coating cannot be formed on the surface of the workpiece to be sprayed, or a metastable cubic phase iron oxide coating cannot be formed. For example, if the carrier gas flow rate and the heating temperature of the workpiece to be sprayed are changed, it is very easy to form the stable hexagonal phase iron oxide.

[0020] Compared with the prior art, the main technical improvement points of the present invention are mainly the following three points:

[0021] (1) A metastable cubic phase iron oxide coating is obtained by using a specific spray pyrolysis method;

[0022] (2) By using the spray pyrolysis method, a metastable iron oxide coating doped with Ti, Sn, Zr and other ions can be obtained by changing the dopant in the precursor solution, thereby changing the relevant properties of the coating. The operation is simple and the cost is low;

[0023] (3) By changing the power of the ultrasonic nebulizer, the size and density of the atomized droplets can be controlled, and the structure morphology and thickness of the coating can be regulated at the nanoscale. Moreover, the obtained coating structure is dense and has good mechanical properties.

[0024] Compared with the prior art, the beneficial effects of the present invention are at least:

[0025] (1) A metastable cubic phase iron oxide coating can be prepared by using this method;

[0026] (2) The coating is non-toxic and harmless, low in cost, simple in preparation method, and has excellent adhesion strength and wear resistance;

[0027] (3) The coating can effectively resist the corrosion of high-salinity and highly corrosive environments represented by seawater and withstand the erosion of high-concentration Cl - ;

[0028] (4) By changing the dopant in the precursor solution, the composition and relevant properties of the iron oxide coating can be regulated, and the operation is simple;

[0029] (5) By changing the power of the ultrasonic nebulizer, the size and density of the atomized droplets are controlled, thereby controlling the structure and thickness of the coating, and the morphology and thickness of the coating can be regulated at the nanoscale;

[0030] (6) The coating will generate photoexcited electrons and holes with redox ability under light illumination, which have the function of antibacterial and sterilizing, and inhibit the growth of microorganisms. Description of the Drawings

[0031] Figure 1 It is a scanning electron microscope photograph of the cross-section of the metastable phase iron oxide anti-corrosion coating in Example 1. It can be seen from Figure 1 that the thickness of the coating is about 400 nm, and there is good adhesion between the coating and the substrate.

[0032] Figure 2 It is an atomic-resolution HADDF-STEM photograph of the doped metastable phase iron oxide anti-corrosion coating material prepared in Example 1. It can be seen from Figure 2 that the coating material is pure-phase cubic iron oxide of the metastable phase, with good crystallinity.

[0033] Figure 3 It is the time-of-flight-secondary ion mass spectrometry signal of the doped metastable phase iron oxide anti-corrosion coating prepared in Example 1 after being immersed in alkaline seawater with a positive potential for 1000 hours for surface Cl - detection. It can be seen from Figure 3 that after a long-term corrosion resistance test, there is only a trace amount of Cl - , and the corrosive Cl - in seawater does not penetrate into the protective layer.

[0034] Figure 4 It is a scanning electron microscope photograph of the surface of the doped metastable phase iron oxide anti-corrosion coating prepared in Example 5. It can be seen from Figure 4 that the surface of the coating is dense and uniform.

[0035] Figure 5 It is the X-ray diffraction pattern of the doped metastable phase iron oxide anti-corrosion coating prepared in Comparative Example 1. It can be seen from Figure 5 that what is prepared under the conditions of Comparative Example 1 is a mixture of stable-phase hexagonal iron oxide and metastable-phase cubic iron oxide. Detailed Embodiments

[0036] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments. The following examples are only used to help those skilled in the relevant art to further understand the present invention, rather than limiting the present invention in any form. Those skilled in the relevant art, on the premise of conforming to the concept of the present invention, make reasonable improvements and adjustments, which all fall within the protection scope of the present invention.

[0037] Ethanol was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Iron(III) acetylacetonate, tetrabutyltin, and titanium(IV) n-butoxide were purchased from Aladdin, and zirconium(IV) isopropoxide was purchased from Merck. All chemicals were used as received without further purification.

[0038] Example 1

[0039] 140 mg of iron(III) acetylacetonate was dissolved in 40 ml of ethanol and stirred for 24 h until completely dissolved. 2.8 mg of tetrabutyltin was added and stirred for 12 h to obtain a precursor solution. Fluorine-doped tin oxide conductive glass was cut into a size of 2 cm * 1.5 cm and placed in a tube furnace, and the temperature was set at 480 °C. The precursor solution was pushed into an ultrasonic nebulizer using an injection pump, and the ultrasonic nebulizer with a power of 36 W was used to disperse it into droplets. Using air as the carrier gas with a flow rate of 5 L / min, the precursor was fed into the tube furnace and sprayed for 16 min. After spraying, the sprayed sample was placed in a muffle furnace and calcined at 600 °C for 2 h at a heating rate of 10 °C / min.

[0040] Under the condition of using the nebulizer with this power, the growth rate of the iron oxide coating thickness was approximately 25 nm / min. The cross-sectional scanning electron microscope results are as Figure 1 shown, and the coating thickness was approximately 400 nm. The HADDF-STEM image under a double spherical aberration corrected electron microscope is as Figure 2 shown. According to the atomic arrangement in the iron oxide crystal, it can be determined that it is a metastable hexagonal phase of iron(III) oxide.

[0041] The conductive glass with the doped metastable phase iron oxide anti-corrosion coating sprayed on the surface was immersed in a strong alkaline salt solution containing 0.5 mol / L of NaCl and 1 mol / L of KOH for one month, and no obvious corrosion occurred on the surface, and the coating structure was intact. Furthermore, the conductive glass with the doped metastable phase iron oxide anti-corrosion coating sprayed on the surface was used as the anode, and a voltage of 1.6 V RHE was applied on the surface and light was introduced. Under conditions such as corrosive electrolyte, anodic oxidation potential, and photocorrosion, no obvious corrosion occurred on the surface after one month. Through the observation of the scanning electron microscope, the thickness of the doped metastable phase iron oxide anti-corrosion coating on the surface did not decrease significantly. Through time-of-flight-secondary ion mass spectrometry analysis as Figure 3 shown, only a small amount of chloride ions existed on the surface part of the coating, and the overall structure was not eroded by chloride ions. This indicates that the doped metastable phase iron oxide anti-corrosion coating has excellent anti-corrosion performance under extreme conditions.

[0042] Example 2

[0043] Dissolve 70 mg of iron acetylacetonate in 20 ml of ethanol and stir for 24 h until completely dissolved. Add 1.4 mg of titanium butoxide and stir for 12 h to obtain a precursor solution. Take a silicon wafer with a size of 1 cm * 1 cm and place it in a tube furnace, setting the temperature to 400 °C. Use a syringe pump to push the precursor solution into an ultrasonic nebulizer, and use a 24 W ultrasonic nebulizer to disperse it into droplets. Using air as the carrier gas with a flow rate of 4 L / min, feed the precursor into the tube furnace and spray for 5 min. After spraying, place the sprayed part in a muffle furnace and calcine it at 500 °C for 4 h at a heating rate of 10 °C / min.

[0044] By increasing the power of the nebulizer, both the diameter and density of the generated droplets increase, the film formation speed increases, the growth rate of the iron oxide coating thickness is about 20 nm / min, and the coating morphology shows a granular accumulation. The coating thickness is observed to be 100 nm by scanning electron microscopy.

[0045] Immerse the silicon wafer with the doped metastable-phase iron oxide anti-corrosion coating sprayed on its surface in a strong alkaline salt solution containing 0.5 mol / L of NaCl and 1 mol / L of KOH for one month. No obvious corrosion occurs on the surface and the coating structure remains intact. While the silicon wafer without surface treatment is corroded more severely. This shows that the silicon wafer with the doped metastable-phase iron oxide anti-corrosion coating attached has excellent anti-corrosion performance.

[0046] Example 3

[0047] Dissolve 100 mg of iron acetylacetonate in 30 ml of ethanol and stir for 24 h until completely dissolved. Add 2 mg of zirconium isopropoxide and stir for 12 h to obtain a precursor solution. Take a titanium sheet with a size of 2 cm * 2 cm and place it in a tube furnace, setting the temperature to 500 °C. Use a syringe pump to push the precursor solution into an ultrasonic nebulizer, and use a 36 W ultrasonic nebulizer to disperse it into droplets. Using air as the carrier gas with a flow rate of 6 L / min, feed the precursor into the tube furnace and spray for 20 min. After spraying, place the sprayed part in a muffle furnace and calcine it at 600 °C for 2 h at a heating rate of 10 °C / min.

[0048] Under the condition of using the nebulizer with this power, the growth rate of the iron oxide coating thickness is about 25 nm / min. The coating thickness is observed to be 500 nm by scanning electron microscopy.

[0049] Immerse the titanium sheet with the doped metastable-phase iron oxide anti-corrosion coating sprayed on its surface in a strong alkaline salt solution containing 0.5 mol / L of NaCl and 1 mol / L of KOH for one month. No obvious corrosion occurs on the surface and the coating structure remains intact. Furthermore, use the conductive glass with the doped metastable-phase iron oxide anti-corrosion coating sprayed on its surface as the anode and apply 1.6 V on the surface RHEVoltage was introduced and light was irradiated. After one month under conditions such as corrosive electrolyte, anodic oxidation potential, and photo-corrosion, no obvious corrosion occurred on the surface. This indicates that the titanium sheet with the anti-corrosion coating of doped metastable-phase iron oxide has excellent anti-corrosion performance under extreme conditions.

[0050] Example 4

[0051] Dissolve 300 mg of iron acetylacetonate in 100 ml of ethanol and stir for 24 h until completely dissolved. Add 1 mg of tetrabutyltin and stir for 12 h to obtain a precursor solution. Take a 304 stainless steel plate with a size of 2 cm * 2 cm and place it in a tubular furnace, setting the temperature at 480 °C. Use an injection pump to push the precursor solution into an ultrasonic nebulizer, and use a 12 W ultrasonic nebulizer to disperse it into droplets. Using air as the carrier gas with a flow rate of 5 L / min, feed the precursor into the tubular furnace and spray for 60 min. After spraying, place the sprayed part in a muffle furnace and calcine it at 700 °C for 1 h with a heating rate of 10 °C / min.

[0052] The droplets generated by using a low-power nebulizer have a small diameter and low density, and the film-forming speed is relatively slow. The growth rate of the thickness of the iron oxide coating is about 10 nm / min. At the same time, the coating structure is dense. The coating thickness is observed to be 600 nm by scanning electron microscopy.

[0053] Immerse the 304 stainless steel plate with the anti-corrosion coating of doped metastable-phase iron oxide sprayed on its surface in seawater for one month. No obvious corrosion occurs on the surface and the coating structure remains intact. This indicates that the stainless steel plate with the anti-corrosion coating of doped metastable-phase iron oxide has excellent anti-corrosion performance.

[0054] Example 5

[0055] Dissolve 300 mg of iron acetylacetonate in 100 ml of ethanol and stir for 24 h until completely dissolved. Add 10 mg of tetrabutyltin and stir for 12 h to obtain a precursor solution. Take an iron sheet with a size of 2 cm * 2 cm and place it in a tubular furnace, setting the temperature at 480 °C. Use an injection pump to push the precursor solution into an ultrasonic nebulizer, and use a 100 W ultrasonic nebulizer to disperse it into droplets. Using air as the carrier gas with a flow rate of 5 L / min, feed the precursor into the tubular furnace and spray for 20 min. After spraying, place the sprayed part in a muffle furnace and calcine it at 500 °C for 1 h with a heating rate of 10 °C / min.

[0056] By further increasing the power of the nebulizer, the generated droplets have a high density and a fast film-forming speed. The growth rate of the thickness of the iron oxide coating is about 50 nm / min. The surface scanning electron microscopy results are as Figure 4 shown, and the coating morphology presents a stacked shape of iron oxide blocks with a dense structure. The coating thickness is observed to be 1000 nm by scanning electron microscopy.

[0057] The iron sheet with the doped metastable phase iron oxide anti-corrosion coating on its surface was immersed in seawater for one month, and no obvious corrosion occurred on the surface, and the coating structure was intact. This shows that the stainless steel plate with the doped metastable phase iron oxide anti-corrosion coating has excellent anti-corrosion performance.

[0058] Comparative Example 1

[0059] 140 mg of iron acetylacetonate was dissolved in 40 ml of ethanol and stirred for 24 h until completely dissolved. 2.8 mg of tetrabutyltin was added and stirred for 12 h to obtain a precursor solution. The fluorine-doped tin oxide conductive glass was cut into a size of 2 cm * 1.5 cm and placed in a tube furnace, and the set temperature was 520 °C. The precursor solution was pushed into an ultrasonic nebulizer using a syringe pump, and a 36 W ultrasonic nebulizer was used to disperse it into droplets. Using air as the carrier gas with a flow rate of 6.5 L / min, the precursor was fed into the tube furnace and sprayed for 16 min. After spraying, the sprayed part was placed in a muffle furnace and calcined at 600 °C for 2 h at a heating rate of 10 °C / min.

[0060] Compared with Example 1, the heating temperature of the part to be sprayed in Comparative Example 1 was higher than 500 °C, and the carrier gas flow rate was higher than 6 L / min. As Figure 5 shown in the X-ray diffraction pattern in, under this condition, the metastable cubic phase iron oxide cannot be completely formed, but a mixture of the stable hexagonal phase iron oxide and the metastable cubic phase iron oxide is formed.

[0061] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent transformations made using the content of the specification of the present invention, directly or indirectly applied in other related technical fields, are similarly included in the patent protection scope of the present invention.

Claims

1. A preparation method of a doped metastable-phase iron oxide anti-corrosion coating, wherein the metastable-phase iron oxide anti-corrosion coating adheres to the surface of a workpiece to be sprayed, and is characterized in that, the preparation method includes the following steps: 1) Dissolve the metal oxide precursor powder in a solvent, stir to obtain a uniform solution, add a dopant to the above solution, and stir to obtain a spraying solution; 2) Ultrasonically atomize the spraying solution, uniformly mix the carrier gas with the atomized spraying solution, and spray it onto the surface of the heated workpiece to be sprayed; 3) After spraying, calcine the workpiece sprayed with the doped transition metal iron oxide coating, and then cool it to room temperature; the workpiece to be sprayed is specifically metal, quartz glass, conductive glass or silicon; the thickness of the metastable-phase iron oxide anti-corrosion coating is 100 - 1000 nm; in the step 1), the precursor powder is iron acetylacetonate, the solvent is ethanol, the dopant is one or several of tetrabutyltin, titanium n-butoxide, zirconium isopropoxide, and the stirring time each time is 12 - 24 h; the dosage ratio of the metal oxide precursor powder, the solvent, and the dopant is 70 - 300 mg: 20 - 100 mL: 1 - 10 mg; in the step 2), the carrier gas is air, the carrier gas flow rate is 4 - 6 L / min, the power of the ultrasonic atomizer is 12 - 100 W, the heating temperature of the workpiece to be sprayed is 400 - 500 °C, and the spraying time is 5 - 60 min; in the step 3), the calcination temperature of the workpiece to be coated is 500 - 700 °C, and the calcination time is 1 - 4 h.

2. The preparation method according to claim 1, characterized in that, The composition of the metastable-phase iron oxide anti-corrosion coating by weight percentage includes: iron 66.6% - 69.6%, oxygen 28.6% - 29.9%, and dopant element 0.5% - 4.7%.

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