CN101760737B - Method for preparing enhanced heat-transfer and scale prevention coating of micron/nanometer titanium dioxide on stainless steel substrate - Google Patents

Abstract

The invention discloses a method for preparing micronano titanium dioxide enhanced heat transfer and anti-scaling coating on a stainless steel substrate, which comprises the following steps: (a) pretreating the stainless steel substrate; (b) preparing ammonium fluorotitanate and boric acid respectively into Uniform solution, and mix the two solutions evenly; (c) put the prepared mixed solution in a water bath to control its temperature at 20-80 °C, after the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution to start deposition Prepare the substrate coated with _TiO2 thin film; (d) after the deposition is completed, take out the substrate and rinse the surface with distilled water; ₂ surface coating. The appearance of the coating prepared by the method is dense and uniform, and the Ra value of the surface coating after sintering is basically the same as that after polishing. The coating is resistant to high temperatures and is more firmly bonded to the substrate.

Description

Preparation method of micronano titanium dioxide enhanced heat transfer and antifouling coating on stainless steel substrate

technical field

The invention relates to a method for preparing micro-nano _TiO2 coatings on stainless steel substrates by liquid phase deposition, in particular to a method for preparing micro-nano _TiO2 coatings on stainless steel substrates such as austenitic 300 series and martensitic 400 series. Liquid-phase deposition preparation method for enhanced heat transfer and antifouling surfaces.

Background technique

At present, more than 90% of heat exchange equipment generally has fouling problems in operation. The formation of dirt on the surface of heat exchange equipment not only affects the utilization of heat energy and the normal and safe operation of production, but also increases production costs. Statistics in 2007 show that the fouling loss of heat exchange equipment in developed countries accounts for about 0.15-0.25% of GNP, while it is higher in developing countries, reaching 0.3%. The prevention and elimination of industrial dirt generally adopts chemical methods such as adding chemical antiscalants and physical methods such as mechanical cleaning and applying external fields. There are common problems such as high cleaning costs and secondary pollution.

The deposition of dirt is related to the adhesion between the dirt and the heat transfer surface, and the size of the adhesion is closely related to the surface energy of the heat transfer surface. The smaller the surface energy, the smaller the adhesion. Therefore, the heat exchange surface can be treated to reduce its surface energy, thereby reducing fouling deposition. At present, a series of relatively effective anti-scaling or enhanced pool boiling or flow boiling heat transfer technologies have been developed at home and abroad, mainly including: magnetron sputtering, ion implantation, chemical composite plating, thermal spraying, chemical vapor deposition, sol- Gels, molecular self-assembly, etc. However, these preparation methods generally have disadvantages such as expensive preparation costs, complicated equipment, difficult industrialization, uneven coating, large thermal resistance, and weak bonding with the substrate.

The liquid phase deposition method is a relatively suitable method for preparing thin film surfaces in large areas. The law was first reported in 1988. The film-forming method has the advantages of convenient operation, simple equipment, mild film-forming conditions, and the ability to form films on complex-shaped substrates. It has been widely used in the preparation of functional thin films, especially in the microelectronics industry for VLSI, It has been applied in the process of forming oxide films in metal-oxide semiconductors and liquid crystal display devices.

The patents related to the liquid phase deposition method include: Chinese patent 200710168732.1 Method for preparing titanium dioxide coated capillary column by liquid phase deposition method, which is characterized by using ammonium fluorotitanate as raw material and depositing a titanium dioxide film layer on the inner wall of the quartz capillary by liquid phase deposition method , there is a low sintering temperature of 300 ° C, and there is no detailed characterization of the properties of the film. Chinese patent 200710060653.9 is a method for preparing a nanometer-thick film surface on the surface of copper, which is characterized in that a liquid-phase deposition method is used to prepare nanometer-thick _TiO2 and other films on the copper substrate, and is used to enhance boiling heat transfer in pools, anti-scaling and anti-corrosion. This method has the problems of easy oxidation of the substrate during sintering in an air atmosphere, low sintering temperature, high temperature resistance, low strength and the like.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for preparing micronano titanium dioxide enhanced heat transfer and antifouling coatings on stainless steel substrates. The coatings prepared by this method are dense and uniform, have low surface energy and are resistant High temperature and high strength.

The method for preparing micronano titanium dioxide enhanced heat transfer and antifouling coating on a stainless steel substrate comprises the following steps:

(a) Pretreating the stainless steel substrate to make the surface roughness Ra＜50nm;

(b) Chemically pure ammonium fluorotitanate and analytically pure boric acid are formulated into uniform solutions respectively, and impurities are filtered to obtain a clear solution, and the two solutions are mixed uniformly, and the obtained mixed solution contains ammonium fluorotitanate and boric acid Concentrations are 0.05-0.5mol/L and 0.07-0.6mol/L respectively;

(c) Put the prepared mixed solution in a water bath to control its temperature at 20-80°C. After the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution and start deposition for 2-50 hours to prepare a _TiO2 film substrate;

(d) After the deposition is complete, the substrate coated with the _TiO2 film is taken out, and the surface is rinsed with distilled water to remove surface residues;

(e) Dry the substrate naturally, then put it into an N2 _- protected resistance furnace for heating, the heating rate is 2-8°C/min, when the temperature rises to 450-800°C, keep the constant temperature for 30-150 minutes, Close the resistance furnace, naturally cool to room temperature to obtain a micro-nano _TiO2 surface coating; the thickness of the surface coating is between 32.6-180.5nm, and the surface coating is anatase and rutile crystal forms;

The pretreatment step in the step (a) includes a grinding step and an ultrasonic cleaning step in turn; wherein the surface roughness Ra of the stainless steel substrate polished by the grinding step is less than 50nm, and the ultrasonic cleaning step includes: Soak and clean the metal sample in a NaOH solution with a mass percentage of 3-10% and a temperature of 30-60°C for 5-10 minutes to remove stubborn grease; Ultrasonic immersion cleaning in hydrochloric acid at ℃ for 5-10 minutes to remove the oxide layer on the surface of the sample; finally rinse with distilled water, air dry and store in an airtight container.

The beneficial effect of the present invention is that: the liquid phase deposition preparation method of the present invention can obtain coatings of different colors during actual operation, and each coating has a dense and uniform appearance. The measured coating thickness is between 32.6-180.5nm, the surface distilled water contact angle is between 81.6-94.4°, and the surface energy is low, with a value between 29.8-47.5mJ/m ² (the standard liquid is water and diiodomethane, the following Same), lower than the surface energy of polished stainless steel (88mJ/m ² ). Detected by X-ray diffractometer (XRD), the crystal forms of the coating can be amorphous, anatase and rutile. According to roughness meter measurement and atomic force microscope (AFM) detection, the Ra value of the surface coating after sintering is basically the same as that after polishing. Compared with the 200710060653.9 patent, the coating thickness, contact angle and surface energy are close, but the market price of the substrate used is cheaper, the roughness of the substrate after polishing is smaller, the coating is resistant to high temperature, and the bond with the substrate is stronger, up to 800 °C The coating still does not fall off, which is more conducive to anti-fouling on the surface.

Description of drawings

Fig. 1 is the schematic flow sheet of preparing micronano titanium dioxide enhanced heat transfer and antifouling coating method on stainless steel substrate of the present invention;

Fig. 2a-Fig. 2b are respectively the electron micrograph and the energy spectrum diagram of 2000 times of the micronano titanium dioxide coating prepared by the method of embodiment 1 of the present invention;

Fig. 3 is the X-ray diffraction figure of the micronano titanium dioxide coating that adopts the embodiment of the present invention 1 method to make;

Fig. 4a-Fig. 4b are respectively the electron micrograph and the energy spectrum diagram of 2000 times of micro-nano titanium dioxide coating prepared by the method of embodiment 2 of the present invention;

Fig. 5 is the X-ray diffraction figure of the micronano titanium dioxide coating that adopts the method for embodiment 2 of the present invention to make;

Fig. 6a-Fig. 6b are respectively the electron micrograph and the energy spectrum diagram of 2000 times of micro-nano titanium dioxide coating prepared by the method of embodiment 3 of the present invention;

Fig. 7 is the X-ray diffraction diagram of the micronano titanium dioxide coating that adopts the method for embodiment 3 of the present invention to make;

Fig. 8a-Fig. 8b are respectively the electron micrograph and the energy spectrum diagram of 2000 times of micro-nano titanium dioxide coating prepared by the method of embodiment 4 of the present invention;

Fig. 9 is the X-ray diffraction diagram of the micronano titanium dioxide coating that adopts the method for embodiment 4 of the present invention to make;

Fig. 10a-Fig. 10b are 2000-fold electron microscope images and energy spectrum images of the micronano titanium dioxide coating prepared by the method of Example 5 of the present invention;

Fig. 11 is an X-ray diffraction diagram of the micronano titanium dioxide coating prepared by the method of Example 5 of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

The operating device of the present invention includes: a set of constant temperature water bath, a hanger for deposition and the like. Reagents required: chemically pure ammonium fluotitanate for coating deposition, analytically pure boric acid, absolute ethanol and analytically pure acetone for substrate cleaning, etc.

The chemical principle of preparing the film: the ions of the metal fluoride are hydrolyzed in water to form a metal hydroxide, and the fluoride ion consuming agent boric acid is added to the solution to maintain the reaction. The reaction equation is

Then [Ti _6-n (OH) _n ] ^2- dehydration reaction forms a titanium dioxide coating with an ordered metal-oxygen network structure.

The present invention is an improvement on the basis of Chinese patent 200710060653.9.

The method of the present invention comprises the following steps: (a) pretreating the stainless steel substrate so that the surface roughness Ra<50nm; the stainless steel substrate can be austenite 300 series, martensite 400 series, etc.; (b) Chemically pure ammonium fluorotitanate and analytically pure boric acid were formulated into homogeneous solutions respectively, and impurities were filtered to obtain a clear solution. The two solutions were mixed evenly, and the concentrations of ammonium fluorotitanate and boric acid in the obtained mixed solution were respectively 0.05-0.5mol/L and 0.07-0.6mol/L; lower than this concentration range, no coating can be deposited, and higher than this concentration range, a large number of white particles will be produced in the deposition solution, which will make the solution turbid and consume the raw material solution. (c) Put the prepared mixed solution in a water bath to control its temperature at 20-80°C. After the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution and start deposition for 2-50 hours to prepare a _TiO2 film substrate; (d) after the deposition, the substrate coated with TiO ₂ film was taken out, and the surface was rinsed with distilled water several times to remove surface residues; (e) the substrate was naturally dried, and then placed in N ₂ Heating in a protected resistance furnace with a heating rate of 2-8°C/min. When the temperature rises to 300-800°C, keep the constant temperature for 30-150 minutes, turn off the heating device, and cool naturally to room temperature to obtain micro-nano TiO ₂ surface coating. layer; in this step, the resistance furnace protected by _N2 can prevent the oxidation of the substrate. In this step, the sintering temperature is 300-800°C. When the temperature is lower than 300°C, because the atomic thermal diffusion effect between the coating and the substrate interface is small, The coating is not firmly combined with the substrate. When the sintering temperature is higher than 800°C, the coating is easy to fall off from the substrate during sintering. When the temperature in step (e) is increased to 450-800° C., coatings of anatase and rutile crystal forms can be obtained.

The pretreatment step in the step (a) includes a grinding step and an ultrasonic cleaning step in turn; wherein the surface roughness Ra of the stainless steel substrate polished by the grinding step is less than 50nm, and the ultrasonic cleaning step includes: Soak and clean the metal sample in a NaOH solution with a mass percentage of 3-10% and a temperature of 30-60°C for 5-10 minutes to remove stubborn grease; Ultrasonic immersion cleaning in hydrochloric acid at ℃ for 5-10 minutes to remove the oxide layer on the surface of the sample; finally rinse with distilled water, air dry and store in an airtight container.

The grinding step may successively include rough grinding, fine grinding, polishing and ultrasonic cleaning steps; wherein,

Coarse grinding steps: First, use 300#-400# sandpaper to grind along the same direction to remove surface dirt and the initial groove of the base until the base surface is completely covered with 300#-400# sandpaper texture; -400# sandpaper texture is polished at an angle of 90° until the substrate surface is covered with 500#-900# sandpaper texture; then use 1000#-1800# sandpaper to polish along the direction of 90° angle with the 500#-900# sandpaper texture until The base surface is covered with 1000#-1800# sandpaper texture;

Fine grinding step: use 2000# or 3000# sandpaper to remove the stripes;

Polishing step: coat commercially available green polishing soap with a wool polishing wheel of a metal polishing machine, and polish the surface of the stainless steel base, and the surface roughness after polishing Ra＜50nm; the metal polishing machine can be selected from the metal polishing machine ( model number C121).

Adopt the comparison result of the inventive method and comparative method (Chinese patent 200710060653.9) to see the table below:

It can be seen from the above table that the crystal forms of the coating prepared by the method of the present invention can be amorphous, anatase and rutile. The comparison method (200710060653.9) is amorphous. Compared with amorphous, anatase and rutile have higher thermal stability, while rutile crystal network structure is tighter, and due to higher sintering temperature, The thermal diffusion and penetration of atoms at the interface between the coating and the substrate is better, and the bonding strength with the substrate is higher. Therefore, the coating prepared by the method of the invention is more resistant to high temperature and has higher strength. At the same time, the surface roughness of the coating prepared by the method is smaller, the coating is smooth and dense, and the appearance color is richer.

Example 1

(a) Coarse grinding: use 300# sandpaper to remove surface dirt and the initial groove of the base until the surface of the base is completely covered with 300# sandpaper texture; use 500# sandpaper to polish until the base surface is covered with 500# sandpaper texture; then use 1000# Sand paper until the substrate surface is covered with 1000# sandpaper texture. Fine Grinding: Grinding with 2000# sandpaper to remove streaks, the base texture is very fine and bright at this time. Polishing: Coat commercially available green polishing soap with the wool polishing wheel of C121 type metal polishing machine, polish the stainless steel substrate surface for 5 minutes, the surface roughness after polishing Ra=23.0nm; Ultrasonic immersion cleaning in NaOH solution with a mass percentage of 3% and a temperature of 40°C for 5 minutes to remove stubborn grease; then immerse the sample in hydrochloric acid with a mass percentage of 3% and a temperature of 30°C for 10 minutes to remove the sample Surface oxide layer; finally rinse with distilled water, air dry and store in an airtight container. (b) Chemically pure ammonium fluorotitanate and analytically pure boric acid are prepared into uniform solutions respectively, and impurities are filtered to obtain a clear solution. The concentrations of ammonium fluorotitanate and boric acid in the mixed solution obtained by mixing are respectively 0.05 mol/L and 0.15mol/L; (c) heat the prepared mixed solution in a water bath to 55°C, and after the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution for deposition for 33 hours; (d) the deposition is completed Finally, the substrate was taken out, and the surface was rinsed with distilled water several times to remove surface residues; (e) the substrate was dried naturally, and then heated in a heating device with a heating rate of 8°C/min, protected by _N2 , When the temperature rises to 300°C, keep the constant temperature for 120 minutes, turn off the heating device, and obtain a bright light blue micro-nano _TiO2 surface coating after natural cooling. The coating is amorphous, the thickness of the coating is 103.2nm, the contact angle of distilled water on the coating surface is 84.2°, and the surface energy is 35.9mJ/m ² .

In Fig. 2a, the SEM image obtained by XL30ESEM electron microscope (secondary electron high vacuum resolution 3.0nm, low vacuum resolution 3.5nm, accelerating voltage 0.2-30kV, low vacuum degree 20torr). It can be seen from the SEM image that the coating is smooth and dense, without cracks and completely covers the substrate. The darker areas in the picture are the holes left by the substrate grinding and polishing. It can be seen from the energy spectrum chart in Fig. 2b (the elemental analysis is shown in the table below) that the content of titanium element on the surface of the coating is 1.96%, and it can be concluded that the surface of the substrate is covered by the _TiO2 coating.

In Figure 3, the Japan Rigaku RIGAKU D/MAX2500 X-ray diffractometer (Cukα ₁ ray, 18KW high-power rotating target X-ray generator, minimum step 0.0001°, positioning speed 1500°/min, scanning speed 0001-100°/min, 2θ angle measurement range -60-163°) obtained XRD pattern. It can be seen from the XRD pattern that all diffraction peaks are the characteristic peaks of the base stainless steel, and there are no characteristic peaks of TiO ₂ crystals. It can be concluded that the coating obtained by sintering at this temperature is amorphous.

Example 2

(a) Coarse grinding: use 400# sandpaper to grind along the same direction to remove surface dirt and the initial groove of the base until the base surface is completely covered with 400# sandpaper texture; use 700# sandpaper to grind along the 90° direction of the 400# sandpaper texture until The base surface is covered with 700# sandpaper texture; then use 1500# sandpaper to polish along the 90° direction of the 700# sandpaper texture until the base surface is covered with 1500# sandpaper texture. Fine Grinding: Grinding with 2500# sandpaper to remove streaks, the base texture is very fine and bright at this time. Polishing: Coat commercially available green polishing soap with the wool polishing wheel of C121 type metal polishing machine, polish the stainless steel substrate surface for 10 minutes, the surface roughness after polishing Ra=36.2nm; Ultrasonic immersion and cleaning in NaOH solution with a mass percentage of 8% and a temperature of 60°C for 10 minutes to remove stubborn grease; then immerse the sample in 3% by mass hydrochloric acid and a temperature of 50°C for 10 minutes to remove the sample Surface oxide layer; finally rinse with distilled water, air dry and store in an airtight container. (b) Chemically pure ammonium fluorotitanate and analytically pure boric acid are formulated into homogeneous solutions respectively, and impurities are filtered to obtain a clear solution. The concentrations of ammonium fluorotitanate and boric acid in the mixed solution obtained by mixing are respectively 0.1 mol/L and 0.6mol/L; (c) put the prepared mixed solution in a water bath at 20°C, and after the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution for deposition for 22 hours; (d) the deposition is completed Finally, the substrate was taken out, and the surface was rinsed with distilled water several times to remove surface residues; (e) the substrate was dried naturally, and then heated in a heating device with a heating rate of 6°C/min, protected by _N2 , When the temperature rises to 500°C, keep the constant temperature for 120 minutes, turn off the heating device, and obtain a bright sky blue micro-nano _TiO2 surface coating after natural cooling. The crystal form of the coating is anatase, and the coating thickness is 77.3nm. The contact angle of distilled water on the coating surface is 88.7°, and the surface energy is 31.3mJ/m ² .

Figure 4a is the SEM photo of the coating. It can be seen from the SEM image that the coating is relatively smooth without cracks and completely covers the substrate. The darker areas in the picture are the holes left by the substrate grinding and polishing. It can be seen from the energy spectrum chart in Fig. 4b (the elemental analysis is shown in the table below) that the content of titanium element on the surface of the coating is 1.11%, and it can be concluded that the surface of the substrate is covered by the TiO ₂ coating.

)，可得出在此温度下烧结得到的涂层为锐钛矿型。Figure 5 is the XRD pattern of the coating. Analysis of the XRD pattern and comparison with the standard PDF card found that there is the strongest diffraction characteristic peak of anatase at the diffraction angle 2θ=25.229° (2θ=25.281°, lattice spacing

), it can be concluded that the coating obtained by sintering at this temperature is anatase.

Example 3

(a) Coarse grinding: use 300# sandpaper to grind along the same direction to remove surface dirt and the initial groove of the base until the base surface is completely covered with 300# sandpaper texture; use 900# sandpaper to grind along the 90° direction of the 300# sandpaper texture until The base surface is covered with 900# sandpaper texture; then use 1800# sandpaper to polish along the 90° direction of the 900# sandpaper texture until the base surface is covered with 1800# sandpaper texture. Fine Grinding: Grinding with 2000# sandpaper to remove streaks, the base texture is very fine and bright at this time. Polishing: Coat commercially available green polishing soap with the wool polishing wheel of C121 type metal polishing machine, polish the stainless steel substrate surface for 5 minutes, the surface roughness after polishing Ra=45.9nm; Ultrasonic immersion cleaning in NaOH solution with a mass percentage of 3% and a temperature of 40°C for 5 minutes to remove stubborn grease; then immerse the sample in hydrochloric acid with a mass percentage of 3% and a temperature of 50°C for 10 minutes to remove the sample Surface oxide layer; finally rinse with distilled water, air dry and store in an airtight container. (b) Chemically pure ammonium fluorotitanate and analytically pure boric acid are prepared into uniform solutions respectively, and impurities are filtered to obtain a clear solution. The concentrations of ammonium fluorotitanate and boric acid in the mixed solution obtained by mixing are respectively 0.5 mol/L and 0.07mol/L; (c) heat the prepared mixed solution in a water bath to 30°C, and after the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution for deposition for 11 hours; (d) deposit After the completion, the substrate was taken out, and the surface was rinsed with distilled water several times to remove surface residues; (e) the substrate was dried naturally, and then heated in a heating device with a heating rate of 2°C/min, protected by _N2 , when the temperature rises to 700°C, keep the constant temperature for 120 minutes, turn off the heating device, and obtain a bright yellow-green micro-nano TiO ₂ surface coating after natural cooling. The crystal form of the coating is rutile, and the coating thickness is 130.3nm. The contact angle of distilled water on the coating surface is 89.2°, and the surface energy is 30.5mJ/m ² .

Figure 6a is the SEM photo of the coating. It can be seen from the SEM image that the coating is relatively smooth without cracks and completely covers the substrate. The darker areas in the picture are the holes left by the substrate grinding and polishing. It can be seen from the energy spectrum chart in Fig. 6b (the elemental analysis is shown in the table below) that the content of titanium element on the surface of the coating is 2.93%, and it can be concluded that the surface of the substrate is covered by the TiO ₂ coating.

)，可得出在此温度下烧结得到的涂层为金红石型。Figure 7 is the XRD pattern of the coating. Analysis of the XRD pattern and comparison with the standard PDF card found that there is the strongest diffraction characteristic peak of anatase at the diffraction angle 2θ=27.318° (2θ=27.446°, lattice spacing

), it can be concluded that the coating obtained by sintering at this temperature is rutile.

Example 4

(a) Coarse grinding: use 300# sandpaper to grind along the same direction to remove surface dirt and the initial groove of the base until the surface of the base is completely covered with 300# sandpaper texture; use 500# sandpaper to grind along the 90° direction of the 300# sandpaper texture until The base surface is covered with 500# sandpaper texture; then use 1000# sandpaper to polish along the 90° direction of the 500# sandpaper texture until the base surface is covered with 1000# sandpaper texture. Fine Grinding: Grinding with 3000# sandpaper to remove streaks, the base texture is very fine and bright at this time. Polishing: Coating commercially available green polishing soap with the wool polishing wheel of C121 type metal polishing machine, polishing the surface of stainless steel substrate for 10 minutes, the surface roughness after polishing Ra=34.6nm; Ultrasonic immersion cleaning in NaOH solution with a mass percentage of 5% and a temperature of 60°C for 8 minutes to remove stubborn grease; then immerse the sample in hydrochloric acid with a mass percentage of 3% and a temperature of 50°C for 5 minutes to remove the sample Surface oxide layer; finally rinse with distilled water, air dry and store in an airtight container. (b) Chemically pure ammonium fluorotitanate and analytically pure boric acid are formulated into homogeneous solutions respectively, and impurities are filtered to obtain a clear solution. The concentrations of ammonium fluorotitanate and boric acid in the mixed solution obtained by mixing are respectively 0.1 mol/L and 0.15mol/L; (c) heat the prepared mixed solution in a water bath to 80°C, and after the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution for deposition for 2 hours; (d) deposit After the completion, take out the substrate, rinse the surface with distilled water several times to remove surface residues; (e) dry the substrate naturally, and then put it into a heating device to heat, set the heating rate to 3°C/min, _N2 protection , when the temperature rises to 600°C, keep the constant temperature for 30 minutes, turn off the heating device, and get a bright wheat yellow micro-nano TiO ₂ surface coating after natural cooling. The crystal form of the coating is anatase type, and the coating thickness is 32.6nm. The contact angle of distilled water on the coating surface is 81.6°, and the surface energy is 47.5mJ/m ² .

Figure 8a is the SEM photo of the coating. It can be seen from the SEM image that the coating is relatively smooth without cracks and completely covers the substrate. The darker areas in the picture are the holes left by the substrate grinding and polishing. It can be seen from the energy spectrum chart in Fig. 8b (see the table below for elemental analysis) that the content of titanium element on the surface of the coating is 0.81%, and it can be concluded that the surface of the substrate is covered by the TiO ₂ coating.

)，可得出在此温度下烧结得到的涂层为锐钛矿型，衍射峰较弱的原因是涂层沉积时间较短，厚度较薄，表面二氧化钛含量较低。Figure 7 is the XRD pattern of the coating. Analyzing the XRD pattern and comparing it with the standard PDF card, it is found that there is the strongest diffraction characteristic peak of weak anatase at the diffraction angle 2θ=25.081° (2θ=25.281°, lattice spacing

), it can be concluded that the coating obtained by sintering at this temperature is anatase type, and the reason for the weaker diffraction peak is that the deposition time of the coating is shorter, the thickness is thinner, and the content of titanium dioxide on the surface is lower.

Example 5

(a) Coarse grinding: use 300# sandpaper to grind along the same direction to remove surface dirt and the initial groove of the base until the surface of the base is completely covered with 300# sandpaper texture; use 500# sandpaper to grind along the 90° direction of the 300# sandpaper texture until The base surface is covered with 500# sandpaper texture; then use 1000# sandpaper to polish along the 90° direction of the 500# sandpaper texture until the base surface is covered with 1000# sandpaper texture. Fine Grinding: Grinding with 2000# sandpaper to remove streaks, the base texture is very fine and bright at this time. Polishing: Coating commercially available green polishing soap with the wool polishing wheel of C121 type metal polishing machine, polishing the surface of stainless steel substrate for 5 minutes, the surface roughness after polishing Ra=49.7nm; Ultrasonic immersion and cleaning in NaOH solution with a mass percentage of 10% and a temperature of 30°C for 10 minutes to remove stubborn grease; then immerse the sample in 3% by mass hydrochloric acid and a temperature of 60°C for 6 minutes to remove the sample Surface oxide layer; finally rinse with distilled water, air dry and store in an airtight container. (b) Chemically pure ammonium fluorotitanate and analytically pure boric acid are prepared into uniform solutions respectively, and impurities are filtered to obtain a clear solution. The concentrations of ammonium fluorotitanate and boric acid in the mixed solution obtained by mixing are respectively 0.25 mol/L and 0.25mol/L; (c) heat the prepared mixed solution in a water bath to 60°C, and after the temperature of the mixed solution is constant, hang the stainless steel substrate vertically in the mixed solution for deposition for 50 hours; (d) deposit After completion, the substrate was taken out, and the surface was rinsed with distilled water several times to remove surface residues; (e) the substrate was dried naturally, and then heated in a heating device with a heating rate of 2.5°C/min, protected by _N2 , when the temperature rises to 800°C, keep the constant temperature for 150 minutes, turn off the heating device, and obtain a bright cyan micro-nano TiO ₂ surface coating after natural cooling. The crystal form of the coating is rutile, and the coating thickness is 180.5nm. The contact angle of distilled water on the coating surface is 94.4°, and the surface energy is 29.8mJ/m ² .

Figure 10a is the SEM photograph of the coating. It can be seen from the SEM image that the coating is relatively smooth without cracks and completely covers the substrate. The darker areas in the picture are the holes left by the substrate grinding and polishing. It can be seen from the energy spectrum diagram in Figure 10b (see the table below for elemental analysis) that the content of titanium element on the surface of the coating is 4.74%, and it can be concluded that the surface of the substrate is covered by the TiO ₂ coating. Comparing the content of coating elements in Figure 2, Figure 4, Figure 6, Figure 8 and Figure 10 shows that the titanium content increases with the increase of coating thickness.

)，可得出在此温度下烧结得到的涂层为金红石型。Figure 11 is the XRD pattern of the coating. Analysis of the XRD pattern and comparison with the standard PDF card found that there is the strongest diffraction characteristic peak of anatase at the diffraction angle 2θ=27.382° (2θ=27.446°, lattice spacing

), it can be concluded that the coating obtained by sintering at this temperature is rutile.

Claims (2)

1. A method for preparing a micro-nano titanium dioxide enhanced heat transfer and anti-scale coating on a stainless steel substrate is characterized by comprising the following steps:

(a) pretreating a stainless steel substrate to ensure that the roughness Ra of the surface of the stainless steel substrate is less than 50 nm;

(b) preparing chemically pure ammonium fluotitanate and analytically pure boric acid into uniform solutions respectively, filtering impurities to obtain clear solutions, and uniformly mixing the two solutions to obtain mixed solution, wherein the concentrations of the ammonium fluotitanate and the boric acid in the mixed solution are 0.05-0.5mol/L and 0.07-0.6mol/L respectively;

(c) placing the prepared mixed solution in a water bath, controlling the temperature of the mixed solution at 20-80 ℃, vertically suspending a stainless steel substrate in the mixed solution, and starting to deposit for 2-50 hours to obtain the TiO-coated substrate₂A substrate of a thin film;

(d) after deposition, the coating is coated with TiO₂Taking out the substrate of the film, and washing the surface with distilled water to remove surface residues;

(e) naturally drying the substrate, and then putting N₂Heating in a protected resistance furnace at a heating rate of 2-8 ℃/min, keeping the constant temperature for 30-150 minutes when the temperature rises to 450-₂Surface coating; the thickness of the surface coating is between 32.6nm and 180.5nm, and the surface coating is in anatase type and rutile type crystal forms;

the pretreatment step in the step (a) sequentially comprises a grinding step and an ultrasonic cleaning step; wherein the roughness Ra of the surface of the stainless steel substrate polished by the polishing step is less than 50nm, and the ultrasonic cleaning step comprises the following steps: firstly, ultrasonically soaking and cleaning a metal sample in NaOH solution with the mass percent of 3-10% and the temperature of 30-60 ℃ for 5-10min to remove intractable grease; then immersing the sample wafer into hydrochloric acid with the mass percent of 3% and the temperature of 30-60 ℃ for ultrasonic soaking and cleaning for 5-10min, and removing an oxide layer on the surface of the sample wafer; finally, washing the mixture by using distilled water, and placing the mixture in a closed container for storage after air drying.

2. The method for preparing the micro-nano titanium dioxide enhanced heat transfer and anti-scale coating on the stainless steel substrate according to claim 1 is characterized in that: the grinding step sequentially comprises the steps of coarse grinding, fine grinding, polishing and ultrasonic cleaning; wherein,

coarse grinding: firstly, grinding and removing surface dirt and an initial groove of a substrate by using 300# -400# abrasive paper along the same direction until the surface of the substrate is completely covered with the texture of the 300# -400# abrasive paper; grinding with 500# -900# abrasive paper in a direction forming an angle of 90 degrees with the grain of 300# -400# abrasive paper until the surface of the substrate is covered with the grain of 500# -900# abrasive paper; then, grinding the substrate by using 1000# -1800# abrasive paper along a direction forming an angle of 90 degrees with the texture of 500# -900# abrasive paper until the surface of the substrate is covered with the texture of 1000# -1800# abrasive paper;

fine grinding: grinding with 2000# or 3000# abrasive paper to remove stripes;

and (3) polishing: a commercially available green polishing soap was coated on the surface of a stainless steel substrate with a wool polishing wheel of a metal polisher, and the surface roughness Ra after polishing was less than 50 nm.

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