KR102465483B1 - Development of functional super water-repellent stainless steel surface technology for improving corrosion resistance - Google Patents

Abstract

The present invention relates to a technology for developing a functional super water-repellent stainless steel surface for improving corrosion resistance, and the method for forming a corrosion resistance oxide film on a stainless steel surface according to the present invention is a conventional method for forming a uniform porous oxide film. It is possible to form a uniform porous oxide film without a pre-patterning process, and also has remarkably excellent effects in superhydrophobicity and corrosion resistance without a pore expansion step after conventional anodization, thereby reducing manufacturing cost.

Description

Development of functional super water-repellent stainless steel surface technology for improving corrosion resistance

The present invention relates to a technology for developing a functional super water-repellent stainless steel surface for improving corrosion resistance.

Stainless steel is a metal alloy that does not rust by adding chromium, and has characteristics such as machinability, economy, and excellent corrosion resistance. However, despite these advantages, stainless steel has a disadvantage in that it has poor corrosion resistance in harsh environments such as gas pipelines and marine industries.

In order to solve these shortcomings, research on anti-corrosion surface treatment technology to improve corrosion resistance is being actively conducted. Recently, research using a wettability behavior to implement a superhydrophobic surface is attracting attention.

The super water-repellent surface can utilize various characteristics such as water repellency, self-cleaning, oil repellency, anti-icing, anti-frost, etc. , optical film, semiconductor, thin film coating, etc. can be used in various industries.

Wettability behavior is determined by the surface energy of the material, and by reducing the surface energy, the surface contact angle becomes more than 150° to realize super water repellency. Such a superhydrophobic surface was developed by looking at various natural materials such as lotus petals, cicada wings, and rice leaves, and various methods are being studied, such as fabricating micro- and nano-sized structures to reduce surface energy.

However, methods for uniformly implementing micro- and nano-sized structures on metal are limited. Among the various surface treatment methods, the anodization method can artificially form a uniform and thick oxide film on the metal.

The oxide film made by the anodization method is divided into a barrier film and a pore film. The barrier film refers to a film in which the inside of the oxide film is densely formed without empty spaces such as pores. It is divided into a porous film having a nanostructure and a nanotubular film in which pores and empty spaces exist between pores.

Here, the anodic oxidation is one of the most widely known treatment methods among the surface treatment methods of metal. When electricity is energized using a metal base material immersed in an electrolyte as an anode, the surface of the base material is oxidized by oxygen generated from the anode to form an oxide film. It is a treatment method to improve the physical properties of the base material by forming

That is, oxygen ions or hydroxide ions in the electrolyte penetrate into the oxide film formed on the surface of the base material and combine with metal ions to form an oxide layer, whereby a porous oxide film and hydroxide film grow near the interface between the base material and the oxide layer. Thus, the physical properties of the base material are further improved.

In increasing the physical properties of the metal base material by anodization, it is most important to properly set various functions such as anodization voltage, time, and purity of the base metal as the most essential parameters of the anodization.

Stainless steel also has various types of alloys depending on the component content, and the desired conditions for anodization may vary depending on the component content, so the component content of the base material to be treated is very important.

The present inventors have found out the conditions for forming an anodized film with improved superhydrophobicity and corrosion inhibition by optimizing the anodization time and voltage using SUS 304 series stainless steel as a base material, and completed the present invention.

Registered Patent No. 10-1832059

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for forming a corrosion-resistant oxide film on a stainless steel surface.

Another object of the present invention is to provide a stainless steel having a superhydrophobic anodized film prepared by the above method.

Another object of the present invention is to provide a stainless steel with a corrosion-resistant anodized film manufactured by the above method.

Another object of the present invention is to provide a medical device, marine transportation means, ground transportation means, and air transportation means including the stainless steel manufactured by the above method.

In order to achieve the above object,

The present invention comprises the steps of washing and drying a stainless steel surface (step 1);

forming an anodization film on the stainless steel surface by anodizing at a voltage of 65-75 V for 2.5-3.5 hours (step 2);

Plasma treatment to remove organic residues and make the surface of the anodized film hydrophilic (step 3); and

Including the; SAM (Self-Assembled Monolayer) coating with a coatingable hydrophobic coating agent (step 4);

A method for forming a corrosion-resistant oxide film on a stainless steel surface is provided.

The stainless steel is applicable to various stainless steels, but may preferably be SUS 304 or SUS 304L.

In the anodization treatment of step 2, the electrolyte may be 0.05-0.15M of NH ₄ F, 0.05-0.15M of ethylene glycol containing water, preferably 0.08-0.12M of NH ₄ F, Ethylene glycol containing water of 0.08-0.12M may be used, and more preferably, ethylene glycol containing water of 0.09-0.11M NH ₄ F and 0.09-0.11M water may be used, and in the present invention, as an example Ethylene glycol containing 0.1M of NH ₄ F and 0.1M of water was used as an electrolyte, but is not limited thereto.

In step 2, the cleaned stainless steel may be anodized at 65-75 V for 2.5-3.5 hours, preferably at 68-72 V for 2.8-3.2 hours, more preferably at 69-71 V for 2.9- It can be performed for 3.1 hours.

In order to realize superhydrophobicity with a contact angle of 160° or more and corrosion inhibition rate of 90% or more, it is desirable to anodize at 69-71 V for 2.9-3.1 hours. This can be.

As the hydrophobic coating agent capable of SAM coating in step 4, perfluoroalkylsilane having 1 to 20 fluorocarbon chains having a surface energy of 6mJ/m ² to 20mJ/m ² , alkylsilane having 1 to 20 carbon atoms, etc. can be used. and, for example, 1 H , 1 H , 2 H , 2 H -Perfluorodecyltrichlorosilane (FDTS), trichlorooctylsilane (OTS), octadecyltrichlorosilane (ODTS), and the like may be used.

In addition, the present invention provides a stainless steel having a superhydrophobic anodized film prepared by the above method.

Furthermore, the present invention provides a stainless steel with a corrosion-resistant anodized film manufactured by the above method.

In addition, the present invention provides a medical device, a marine transportation means, a ground transportation means, and an air transportation means including the stainless steel manufactured by the above method.

The method for forming a corrosion resistance oxide film on a stainless steel surface according to the present invention can form a uniform porous oxide film without a conventional pre-patterning process for forming a uniform porous oxide film, and also Even without a pore expansion step after conventional anodizing treatment, there is an effect of remarkably excellent superhydrophobicity and corrosion resistance, thereby reducing the manufacturing cost.

1 is an EDS measurement result for three samples obtained after performing steps 1 to 3 of the example.
2 is an image observed by FE-SEM of the surface shape of the oxide film formed on the surfaces of three samples obtained after performing steps 1 to 3 in Example.
Figure 3 is a result of measuring the contact angle of the sample (SAM coating not carried out) carried out only to steps 1 to 3 in Examples.
4 is a result of measuring the contact angle of the sample (SAM coating is performed) all performed from steps 1 to 4 in the example.
5 is a view showing the co-potential polarization curve of the samples performed all the steps 1 to 4 in the Example.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples only illustrate the present invention, and the content of the present invention is not limited by the following examples.

<Examples 1-1 to 1-3> Anodizing treatment of stainless steel (SUS 304)

Step 1: Preparation of stainless steel (SUS 304) substrate

A stainless steel (SUS 304) having a size of 20 mm × 30 mm × 0.5 mm was used. Ultrasonic cleaning was performed by immersing in ethanol and acetone to remove foreign substances on the surface and cleaning the surface. After washing again with distilled water, it was dried.

Components of stainless steel such as SUS 304 are shown below. For reference, there is a significant difference in the optimal anodization treatment conditions for forming a superhydrophilic oxide film depending on the type of metal and the type of alloy, and the present invention focuses on SUS 304 to form a superhydrophilic oxide film. Anodizing treatment conditions were found.

Step 2: Anodizing

In the anodization process, stainless steel was used for the anode and platinum was used for the cathode, and the distance between the electrodes was maintained at 5 cm. Based on the ethylene glycol solution, 0.1 M NH ₄ F, 0.1 MH ₂ O was added to the electrolyte solution, which was maintained at a temperature of 0° C. using a double jacket beaker and a water-cooled cooler. The applied voltage was 30V (Example 1-1), 50V (Example 1-2), and 70V (Example 1-3) for 3 hours, and after anodization, the specimen was washed with distilled water and dried.

Step 3: Plasma Treatment

Using a plasma apparatus, organic residues were removed from the surface with oxygen plasma for 15 minutes, made hydrophilic, and then dried in air at 150° C. for 10 minutes using a heating stirrer. Plasma treatment conditions were 200W, 50KHz, O ₂ 50sccm, plasma treatment for 15 minutes in RIE mode.

Step 4: Self-Assembled Monolayer (SAM) Coating

In order to give super water-repellent properties to the plasma-treated anodized sample, the self-assembled monolayer (SAM) coating was coated with FDTS (1H, 1H, 2H, 2H-Perfluorodecyltrichlorosilane) solution, which is a material with low surface energy. was carried out using

<Experimental Example 1> Evaluation of oxide film formation using EDS (Energy dispersive spectroscopy)

EDS (model name: X-MAX, manufacturer: OXFORD) was measured for three stainless steel (SUS 304) samples obtained after performing steps 1 to 3 (SAM coating not performed) in the Example, and the formation of an oxide film was evaluated. , the results are shown in FIG. 1 .

1 is an EDS measurement result for three samples obtained after performing steps 1 to 3 of the example.

As shown in FIG. 1, after anodization, oxygen and iron are shown as main components, and in addition, chromium, manganese, nickel, etc. were detected, and carbon corresponds to noise due to the influence of the carbon tape for fixing the sample to the stage. From this result, it can be confirmed that an oxide film is formed on the surface of the stainless steel.

<Experimental Example 2> Observation of surface shape using FE-SEM (Field Emission Scanning Electron Microscope)

In the example, the surface shape of the oxide film formed on the surface of the stainless steel (SUS 304) performed from steps 1 to 3 (SAM coating not performed) was measured using FE-SEM (model name: MIRA 3 LMH In-Beam Detector, manufacturer: TESCAN). was observed, and the results are shown in FIG. 2 .

Specifically, in order to observe the surface shape of the sample, the sample was cut and fixed to the stage with carbon tape, and the structure made by anodization was a non-conductive oxide, so platinum coating was performed for 40 seconds and then observed.

2 is an image observed by FE-SEM of the surface shape of the oxide film formed on the surfaces of three samples obtained after performing steps 1 to 3 in Example.

As shown in FIG. 2, (a) and (b) are images at applied voltages of 30V and 50V, and in (a) and (b), a barrier-type oxide film was formed and no pores were observed on the surface. However, in (c), it was observed that a porous structure was formed differently from the conditions of (a) and (b).

In Table 1, using the FE-SEM image of FIG. 2, the pore diameter (Pore Diameter, D _p ), the interpore distance (D _int) , and the solid fraction generated on the surface after anodization were measured. One result was shown. The solid fraction was calculated by the following equation (1) for the solid-liquid ratio.

[Equation 1]

f _SL : Solid Fraction

a: distance of air space

r: the radius of the pore

D _p (nm) D _int (nm) solid fraction 30V None None None 50V None None None 70V 115.79±17.46 137.06±15.31 0.355

As shown in Table 1, the pore diameter is 115.59 nm, the pore distance is 137.06 nm, and the solid fraction is 0.355 on the porous surface of the sample (c) under the 70V voltage condition in FIG. 2 . Through this, it was observed that under the voltage conditions of 30V and 50V, a densely formed film was formed without empty spaces such as internal pores in the anodized film, and a porous film with somewhat regular pores was formed under the voltage condition of 70V. The solid fraction refers to the roughness ratio.

<Experimental Example 3> Contact angle evaluation

In Examples, the contact angle was measured to determine the surface wettability of the samples subjected to steps 1 to 3 and the samples subjected to all steps 1 to 4, and the results are shown in FIGS. 3, 4 and Table 2.

Specifically, 3.5 μl of distilled water was used as a reference liquid in the measurement. After dropping the droplet on the surface, the contact angle was measured after 5 seconds, and measurements were made 10 times per specimen.

3 is a result of measuring the contact angle of the sample (SAM coating not carried out) carried out only to steps 1 to 3 in Examples.

4 is a result of measuring the contact angle of the samples (SAM coating is performed) all performed from steps 1 to 4 in the Example.

The results of FIGS. 3 and 4 are summarized in Table 2 below.

Before SAM coating (°) After SAM coating (°) 30V 59.26±4.45 115.02±2.99 50V 44.87±4.46 119.69±1.78 70V 17.04±3.14 161.80±1.00

As shown in Table 2, it was confirmed that, in the case of the sample not coated with SAM, superhydrophilicity was shown at 59.26° at 30 V and 44.87° at 50 V, while 17.04° at 70 V. It shows hydrophilicity due to the anodization film formed as a sample before SAM coating with an FDTS solution with low surface energy. In the case of the sample coated with SAM with FDTS solution with low surface energy, it was confirmed that super water repellency appeared at 115.02° at 30 V and 119.69° at 50 V, whereas at 70 V, it was 161.8°.

On a surface with a porous oxide film, a superhydrophobic surface is formed because the coating can be shaped to hold water droplets between pores or solid surfaces.

<Experimental Example 4> Corrosion resistance evaluation

In Examples, the corrosion resistance of the samples performed from steps 1 to 4 were evaluated, and the results are shown in FIG. 5 and Table 3.

Specifically, corrosion resistance was conducted in a 3.5 wt% NaCl solution at room temperature by an electrochemical method, Potentio-Dynamic Polarization Test (PDP). Measurements were made after immersing the sample in 3.5 wt.% NaCl solution at room temperature for 1 hour before proceeding with the analysis test. The polarization test is a three-electrode system, using a sample as a working electrode, platinum (Pt) as a counter electrode, and a silver/silver chloride (Ag/AgCl) electrode as a reference electrode. The measurement conditions were -500 mV to +14000 mV (vs. Ag/AgCl) range, and corrosion resistance was evaluated through electrochemical characterization at a scanning rate of 1 mV/sec.

5 is a view showing the co-potential polarization curve of the samples performed all the steps 1 to 4 in the Example.

The results of FIG. 5 are summarized and shown in Table 3 below.

E _corr (mV) I _corr (A/cm ² ) IE (%) Untreated SUS304 -37.8 1.12×10 ^-8 0 30V 112 5.04×10 ^-8 77.58 50V 199 9.97×10 ^-8 88.67 70V 254 1.19×10 ^-9 90.50

E _corr : corrosion potential

I _corr : Corrosion current density representing the loss of mass

IE: Inhibition Efficiency of Example Treated Samples vs. Untreated SUS 304

As shown in Table 3, the corrosion potential (E _corr ) was 30V applied voltage (112 mV), 50V applied voltage (199 mV), 70V compared to untreated stainless steel (Bare SUS304, -37.8 mV). It was confirmed that the positive direction was shifted in the structure subjected to surface modification of the applied voltage (254 mV). In addition, the corrosion current density (I _corr ) was compared to untreated stainless steel (1.12Х10 ^-8 A/cm ² ) at 30V applied voltage (5.04Х10 ^-8 A/cm ² ), 50V applied voltage (9.97Х10 ^{- 8} A/cm ² ) and 70V applied voltage (1.19Х10 ^-9 A/cm ² ), it was confirmed that the corrosion current density decreased as the applied voltage increased in the structure with the surface modification. The corrosion current was used to evaluate the corrosion inhibition rate using the I _corr value because the mass loss reaction is directly related to the corrosion. The corrosion inhibition rate calculated using the corrosion current density was calculated by Equation 2 below. The most important index, corrosion inhibition, was 77.58% at 30V, 88.67% at 50V, and 90.50% at 70V. This result indicates that corrosion resistance can be remarkably improved when SAM coating is performed after realizing a surface shape through anodization.

In other words, since the porous oxide film has hydrophilicity, it was coated with FDTS SAM to realize water repellency, and air was trapped in the pores to improve the anti-corrosion efficiency characteristics. It is considered that corrosion resistance can be improved because the porous structure and the oxide film are thick, which can trap a lot of air in the pores.

[Equation 2]

i: Corrosion current density of all samples performed from step 1 to step 4 in the example

i ₀ : Corrosion current density of untreated SUS 304

IE: Corrosion inhibition rate of Example treated samples compared to untreated SUS 304

<Experimental Example 5> Evaluation of optimal conditions for anodization (time and voltage) for realization of super water repellency

Through Experimental Examples 1 to 4, it was confirmed that the corrosion resistance was the best when treated with anodizing conditions for 3 hours and 70V. Therefore, in this Experimental Example 5, the optimum conditions were investigated based on the anodization treatment condition of 3 hours and 70V, and the results are shown in Tables 4 and 5. A sample (SAM coating) was prepared in the same manner as in Example, except that the anodization treatment time and voltage were changed.

time (h) Voltage (V) Contact angle (°) IE (%) Example 2-1 2.8 70 119.28±2.16 72.97 Example 2-2 2.9 161.26±2.14 90.37 Example 2-3
(= Examples 1-3) 3.0 161.80±1.00 90.50 Example 2-4 3.1 160.87±1.58 90.41 Example 2-5 3.2 120.69±0.89 75.81

time (h) Voltage (V) Contact angle (°) IE (%) Example 3-1 3.0 68 120.12±2.47 77.28 Example 3-2 69 160.29±1.25 90.41 Example 3-3
(= Examples 1-3) 70 161.80±1.00 90.50 Example 3-4 71 160.11±1.36 90.48 Example 3-5 72 119.47±1.89 74.29

As shown in Tables 4 and 5, the best results were confirmed at an anodization time of 2.9-3.1 h and an applied voltage of 69-71 V in terms of super water repellency and corrosion resistance.

So far, with respect to the present invention, the preferred embodiments have been looked at. Those of ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments are to be considered in an illustrative rather than a restrictive sense. The scope of the present invention is indicated by the claims rather than the foregoing description, and all differences within the scope of equivalents thereto should be construed as being included in the present invention.

Claims (14)

cleaning and drying the stainless steel surface (step 1);
forming an anodization film on the stainless steel surface by anodizing at a voltage of 65-75 V for 2.5-3.5 hours (step 2);
Plasma treatment to remove organic residues and make the surface of the anodized film hydrophilic (step 3); and
Including; coating with a hydrophobic coating agent capable of self-assembled monolayer (SAM) coating (step 4);
The electrolyte used for the anodizing treatment of step 2 is ethylene glycol containing 0.09-0.11M of NH ₄ F and 0.09-0.11M of water, and the temperature of the electrolyte is -1 to 1°C, characterized in that,
A method of forming a corrosion-resistant oxide film on a stainless steel surface.
According to claim 1,
The method, characterized in that the stainless steel is SUS 304 or SUS 304L.
delete According to claim 1,
The anodizing treatment of step 2 is characterized in that the treatment is performed at a voltage of 68-72 V for 2.8-3.2 hours.
5. The method of claim 4,
The anodizing treatment in step 2 is characterized in that the treatment is performed at a voltage of 69-71 V for 2.9-3.1 hours.
According to claim 1,
The SAM coatable hydrophobic coating agent is any one of 1 H ,1 H ,2 H ,2 H -perfluorodecyltrichlorosilane (FDTS), trichlorooctylsilane (OTS) and octadecyltrichlorosilane (ODTS) A method characterized in that.
According to claim 1,
A method, characterized in that an anodization film is formed on the surface of the stainless steel with a contact angle of 160° or more.
According to claim 1,
A method, characterized in that an anodization film having a corrosion inhibition rate of 90% or more is formed on the surface of the stainless steel.
A stainless steel with a superhydrophobic anodized film produced by the method of claim 1 .
A stainless steel with a corrosion-resistant anodized film manufactured by the method of claim 1 .
A medical device comprising stainless steel manufactured by the method of claim 1 .
A marine vehicle comprising stainless steel manufactured by the method of claim 1 .
A ground vehicle comprising stainless steel manufactured by the method of claim 1 .
An air vehicle comprising stainless steel manufactured by the method of claim 1 .

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