KR102465479B1 - Development of Water-repellent Stainless Steel (SUS 316L) Surface by Stepwise Anodizing Technique - Google Patents

Abstract

The present invention relates to a technology for the development of a surface of functional water-repellent stainless steel (SUS 316L) for improving corrosion prevention (corrosion resistance) efficiency. According to the present invention, the method for forming a hydrophobic and corrosion-resistant oxide film on a surface of stainless steel is able to form a uniform porous oxide film even without the conventional pre-patterning process for forming a uniform porous oxide film, have remarkably excellent hydrophobic property and corrosion resistance, be applicable to medical devices, marine transportation means, land-based transportation means, aviation transportation means, water supply and sewer pipes, water supply and sewer pipes filters, and the like including stainless steel, and be useful for a machine learning database for developing a technology for treating a surface of stainless steel.

Description

Development of Water-repellent Stainless Steel (SUS 316L) Surface by Stepwise Anodizing Technique to improve corrosion prevention efficiency

The present invention relates to a technology for developing a functional water-repellent stainless steel (SUS 316L) surface for improving corrosion prevention (corrosion resistance) efficiency. It can be applied to pipes, water and sewage filters, and furthermore, it can be useful as a machine learning database for the development of stainless steel surface treatment technology.

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 properties such as water-repellency, self-cleaning, oil-repellency, anti-icing, anti-frost, etc. It can be used in various industries such as advanced displays, optical films, semiconductors, and thin film coatings.

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-type film and a pore-type film. The barrier-type 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 structure 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 inventor forms a nanostructured oxide film by optimizing the anodization time and voltage using stainless steel (SUS 316L) as a base material, and then coating it with a hydrophobic SAM (Self-assembled Monolayer) coating agent. Inhibition rate) was confirmed to be significantly improved, and the present invention was completed.

Registered Patent No. 10-1832059

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

Another object of the present invention is to provide a stainless steel having a hydrophobic 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, a marine transportation means, a ground transportation means, an air transportation means, a water and sewage pipe, and a water and sewage filter 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 an applied voltage of 80-100 V for 2.5-3.5 hours (step 2);

pore expansion treatment by immersing the anodized stainless steel of step 2 in a 0.05-1.0 M phosphoric acid solution (step 3);

Plasma treatment to remove organic residues and make the surface of the anodized film hydrophilic (step 4); and

Including; coating with a hydrophobic coating agent capable of self-assembled monolayer (SAM) coating (step 5);

A method for forming a hydrophobic and 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 316 or SUS 316L, and particularly preferably SUS 316L.

In the anodizing treatment of step 2, the electrolyte (Electrolyte) may use ethylene glycol containing 0.05-0.15M of NH ₄ F, 0.05-0.15M of 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 washed stainless steel can be anodized at 80-100 V for 2.5-3.5 hours, preferably at 85-95 V for 2.8-3.2 hours, more preferably at 88-92 V for 2.9- It can be performed for 3.1 hours.

In order to realize a hydrophobicity and corrosion inhibition rate of 90% or more, it is preferable to anodize at 88-92 V for 2.9-3.1 hours, and if this condition is exceeded, there may be a problem in that the hydrophobicity and corrosion inhibition rate decrease.

The pore expansion treatment of step 3 may be performed by immersion in a 0.05-1.0M phosphoric acid solution for 1-60 minutes.

As the hydrophobic coating agent capable of SAM coating in step 5, 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. may 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 with a hydrophobic 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, an air transportation means, a water and sewage pipe, and a water and sewage filter including the stainless steel manufactured by the above method.

The method of forming a hydrophobic and corrosion-resistant oxide film on a stainless steel surface according to the present invention can form a uniform porous oxide film without the conventional pre-patterning process for forming a uniform porous oxide film. It has a remarkably excellent effect in hydrophobicity and corrosion resistance.

1 is an EDS measurement result for a sample obtained after performing only steps 1 to 4 of Example 1-4.
2 is an image observed by FE-SEM of the surface shape of the oxide film formed on the surfaces of four samples obtained after performing only steps 1 to 4 in Example.
3 is a result of measuring the contact angle of the sample (SAM coating not carried out) carried out only to steps 1 to 4 in Examples.
4 is a result of measuring the contact angle of the sample (SAM coating is performed) all performed from steps 1 to 5 in the Example.
5 is a view showing the co-potential polarization curve of the samples performed all the steps 1 to 5 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 1-4> Anodizing of stainless steel (SUS 316L)

Step 1: Preparation of stainless steel (SUS 316L) substrate

A stainless steel (SUS 316L) having a size of 3 cm × 3 cm × 0.05 cm 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 316L are shown below. For reference, there is a significant difference in the optimum anodization treatment conditions for forming a superhydrophilic oxide film depending on the type of metal and the type of alloy. Anodizing treatment conditions were found.

Step 2: Anodizing

For the anodization process, stainless steel for the positive electrode and platinum (2.5 cm × 4 cm × 0.05 cm) for the negative electrode were used, 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), 70V (Example 1-3), and 90V (Example 1-4) for 3 hours, and the specimen after anodization was washed with distilled water and dried.

Step 3: Stomach Expansion Treatment

To expand the pores of the nanostructure manufactured by the anodization treatment of step 2, the pores were expanded by immersion in 0.1 M phosphoric acid (Junsei) for 10 minutes, and the specimen was washed with distilled water and dried.

Step 4: 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 5: Self-assembled Monolayer (SAM) coating

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

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

EDS (model name: X-MAX, manufacturer: OXFORD) measurement on a stainless steel (SUS 316L) sample obtained after carrying out steps 1 to 4 (without SAM coating) in Example 1-4 (anodic oxidation 90V, 3 hours) to evaluate whether an oxide film was formed, and the results are shown in FIG. 1 .

1 is an EDS measurement result of a sample obtained after performing steps 1 to 4 of Example 1-4.

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 316L) performed from steps 1 to 4 (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 four samples obtained after performing steps 1 to 4 in Example.

As shown in FIG. 2, it can be confirmed that, unlike the surfaces of (c) and (d), in (a) and (b), since a barrier type oxide film is formed on the surface, pores are not formed on the surface. However, in the case of (c) and (d), it can be confirmed that a porous structure is formed unlike the previous two specimens. The reason for the formation of the porous structure is that the surface roughness of the oxide film increases due to partial dissolution that occurs on the surface of the film when the acidic solution and the oxide film come into contact, and the concentration of the electric field occurs in the place where the thickness of the film is thin among the roughened oxide film. Concentration of the electric field accelerates the dissolution reaction of the oxide film to form a thinner oxide film, and the continuous behavior of this reaction forms pores due to local oxidation.

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 created on the surface after anodization were measured. One result was shown. The diameter of the pores and the interstitial distance are expressed as average values, and the solid fraction was calculated by the following Equation (1).

[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 68.62±8.07 89.78±8.30 0.4559 90V 89.17±8.25 106.45±7.22 0.3466

As shown in Table 1, no pores were found in the oxide film of the 30 V and 50 V specimens with applied voltages made of barrier films, so D _P, D _{int, and} solid fraction values could not be obtained. In the case of 70 V and 90 V, As the porous pores were created, D _P, D _{int, and} solid fraction values were obtained. D _P, D _{int, and} solid fraction values at 70 V were 68.62±8.07 nm, 89.78±8.30 nm, and 0.4559, respectively, and the values at 90 V were calculated as 89.17±8.25 nm, 106.45±7.22 nm, and 0.3466. It was observed that a porous film having regular pores was formed under voltage conditions of 70V and 90V. The solid fraction means 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 4 only and the samples subjected to all steps 1 to 5, 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 4 in Examples.

4 is a result of measuring the contact angle of the sample (SAM coating is performed) all performed from steps 1 to 5 in the Example.

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

Before SAM coating (°) After SAM coating (°) 30V 21.4±0.91 115.5±2.85 50V 18.5±1.59 123.4±1.63 70V 16.5±0.98 130.3±1.82 90V 8.56±0.68 140.3±1.46

As shown in Table 2, it can be seen that the contact angle increases as the applied voltage increases in the sample after SAM coating. According to the Cassie-Baxter theory, it is judged that the contact angle is high in the specimen coated on the surface forming the porous oxide film because the air becomes a shape that pushes the pores or water droplets on the solid surface due to the coating on the porous oxide film on the surface of the specimen. .

<Experimental Example 4> Corrosion Resistance Evaluation

In Examples, the corrosion resistance of the samples performed from steps 1 to 5 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 5 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 SUS 316L -404 2.36×10 ^-7 0 30V -232 1.67×10 ^-7 29.23 50V -192 2.96×10 ^-8 87.46 70V -144 2.49×10 ^-8 89.44 90V -38 9.02×10 ^-9 96.18

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

Corrosion potential is a number that shows the rate at which corrosion occurs. The lower the value, the greater the oxidation tendency, so corrosion tends to occur faster.

Corrosion current density tends to cause a lot of corrosion because more current flows as the current density value increases.

The corrosion inhibition rate is quantified using the corrosion current density value, i is the current density value of the anodized and coated specimen, and i ₀ is the current density value of the untreated specimen, which was calculated by Equation 2 below.

[Equation 2]

i: Corrosion current density of all samples performed from steps 1 to 5 in the example

i ₀ : Corrosion current density of untreated SUS 316L

IE: Corrosion Inhibition Rate of Example Treated Samples vs. Untreated SUS 316L

As shown in Table 3, it can be seen that the corrosion resistance tends to be excellent as the applied voltage increases, and the corrosion inhibition rate is also 29.23% at 30 V, 87.46% at 50 V, 89.44% at 70 V, and 96.18% at 90 V. It can be seen that there is a tendency to increase as the applied voltage increases. This is related to the change of the interfacial structure of the material in contact with the corrosive material (Cl ⁻ ) and the wettability of the water-repellent treated porous oxide film. In the case of a change in the interfacial structure of a material in contact with a corrosive material, it becomes difficult for water molecules to attach to the surface because the coating material with low surface energy does not have polarity. it gets difficult In addition, according to the shape of Cassie-Baxter during water-repellent treatment of the porous oxide film, even if the structure and the corrosive material come into contact with the structure, it is difficult to penetrate the corrosive material into the pores due to the air filled in the pores. do.

<Experimental Example 5> Evaluation of optimal conditions for anodization (time and voltage) for corrosion resistance

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 90V. Therefore, in this Experimental Example 5, the optimum conditions were investigated based on the anodization treatment conditions of 3 hours and 90V, 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) IE (%) Example 2-1 2.8 90 82.23 Example 2-2 2.9 95.87 Example 2-3
(= Examples 1-4) 3.0 96.18 Example 2-4 3.1 95.48 Example 2-5 3.2 85.47

time (h) Voltage (V) IE (%) Example 3-1 3.0 86 89.99 Example 3-2 88 95.31 Example 3-3
(= Examples 1-4) 90 96.18 Example 3-4 92 95.74 Example 3-5 94 87.49

As shown in Tables 4 and 5, in terms of corrosion resistance, the best results were confirmed at an anodization time of 2.9-3.1 h and an applied voltage of 88-92 V.

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 (15)

cleaning and drying the stainless steel surface (step 1);
anodizing at an applied voltage of 88-92 V for 2.9-3.1 hours to form an anodized film on the stainless steel surface (step 2);
pore expansion treatment by immersing the anodized stainless steel of step 2 in a 0.05-1.0 M phosphoric acid solution (step 3);
Plasma treatment to remove organic residues and make the surface of the anodized film hydrophilic (step 4); and
Including; coating with a hydrophobic coating agent capable of self-assembled monolayer (SAM) coating (step 5);
The stainless steel of step 1 is characterized in that SUS 316 or SUS 316L,
A method of forming a hydrophobic and corrosion-resistant oxide film on a stainless steel surface.
delete According to claim 1,
The anodizing treatment of step 2 is characterized in that using a mixture of NH ₄ F, water and ethylene glycol as an electrolyte.
delete delete 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.
delete 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 hydrophobic anodized film manufactured 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 vehicle comprising stainless steel manufactured by the method of claim 1 .
13. The method of claim 12,
The means of transportation is a means of transportation, characterized in that the sea transportation means, ground transportation means or air transportation means.
A water and sewage pipe comprising stainless steel manufactured by the method of claim 1 .
A water and sewage filter comprising stainless steel manufactured by the method of claim 1 .

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