KR20240057669A - Functional surface treated SUS316L gasket - Google Patents

Abstract

The present invention relates to a method for manufacturing functional stainless steel 316L material for gaskets. It can form a uniform porous oxide film without the conventional pre-patterning process to form a uniform porous oxide film, and has significantly excellent hydrophobicity and corrosion resistance. It works.

Description

Functional surface treated SUS316L gasket {Functional surface treated SUS316L gasket}

The present invention relates to a method of manufacturing functional stainless steel 316L material for gaskets.

Stainless steel is a metal alloy that does not rust due to the addition of chromium and has characteristics such as processability, economic efficiency, and excellent corrosion resistance, so it is used in various industrial fields such as marine, machinery, electronic components, piping, power generation, and nuclear power. However, despite these advantages, stainless steel has the disadvantage of poor corrosion resistance in harsh environments such as gas pipes and marine industries.

To solve these shortcomings, research on anti-corrosion surface treatment technology to improve corrosion resistance is being actively conducted. Recently, research on implementing superhydrophobic surfaces through research using wettability behavior has been attracting attention.

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

Wetability behavior is determined by the surface energy of the material, and by reducing the surface energy, the surface contact angle becomes 150° or more, realizing superhydrophobicity. Such a superhydrophobic surface was developed based on various natural materials such as lotus petals, cicada wings, and rice leaves, and various methods are being studied, such as manufacturing micro- and nano-sized structures to reduce surface energy.

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

Oxide films made by anodizing are divided into barrier-type films and pore-type films. The barrier-type film refers to a film formed densely inside the oxide film without empty spaces such as pores, and the porous film refers to a nano-type film with a regularly arranged pore structure. It is divided into a porous film with a structure and a nanotube-type film with empty spaces between pores.

Here, the anodic oxidation is one of the most widely known metal surface treatment methods. When electricity is passed 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, forming an oxide film. It is a treatment method that improves the physical properties of the base material by forming a .

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, thereby growing a porous oxide film and a hydroxide film near the interface between the base material and the oxide layer. As a result, the physical properties of the base material are further improved.

In increasing the physical properties of the base metal by anodizing, it is most important to appropriately set various functions such as the anodizing voltage, time, and purity of the base metal, which are the most important variables of the anodizing.

There are various types of alloys in stainless steel depending on the ingredient content, and the desired anodizing treatment conditions may vary depending on the ingredient content, so the ingredient content of the base material to be treated is very important.

The present inventor used stainless steel (SUS 316L) as a base material to form a nanostructured oxide film by optimizing the anodizing time and voltage, and then coated it with a hydrophobic SAM (Self-assembled Monolayer) coating to improve hydrophobicity and corrosion resistance (corrosion). The present invention was completed after confirming that the inhibition rate was significantly improved.

Registered Patent No. 10-1832059

The purpose of the present invention is to provide a method of forming a hydrophobic and corrosion resistant oxide film on the surface of stainless steel for gaskets.

Another object of the present invention is to provide stainless steel for gaskets with a hydrophobic anodic oxide film produced by the above method.

In order to achieve the above purpose,

The present invention includes the steps of cleaning and drying the stainless steel surface for the gasket (step 1);

Forming an anodizing film on the stainless steel surface by anodizing for 2.5-3.5 hours at an applied voltage of 80-100 V (step 2);

Processing pore expansion 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

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

A method of forming a hydrophobic and corrosion resistant oxide film on the surface of stainless steel for gaskets is provided.

The stainless steel can be applied to various stainless steels, but is preferably SUS 316 or SUS 316L, and is particularly preferably SUS 316L.

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

Step 2 can anodize the cleaned stainless steel 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 2.9-3.2 hours. It can be carried out for 3.1 hours.

In order to achieve 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. If this condition is exceeded, there may be a problem in that the hydrophobicity and corrosion inhibition rate decreases.

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

As a hydrophobic coating agent capable of SAM coating in step 5, perfluoroalkyl silanes with 1 to 20 fluorocarbon chains with a surface energy of 6 mJ/m ² to 20 mJ/m ² , alkyl silanes with 1 to 20 carbon atoms, etc. can be used. For example, 1 H , 1 H , 2 H , 2 H -perfluorodecyltrichlorosilane (FDTS), trichlorooctylsilane (OTS), octadecyltrichlorosilane (ODTS), etc. can be used.

The gasket includes a ring joint gasket, a corrugated gasket, a serrated gasket, a lens ring gasket, a Bridgeman-type gasket, a delta-type gasket, a double cone-type gasket, and a metal gasket. It may be a hollow O-ring, etc.

In addition, the present invention provides stainless steel for gaskets with a hydrophobic anodic oxide film produced by the above method.

The method of forming a hydrophobic and corrosion-resistant oxide film on the surface of stainless steel for gaskets according to the present invention can form a uniform porous oxide film without the conventional pre-patterning process to form a uniform porous oxide film. This results in significantly superior hydrophobicity and corrosion resistance.

Figure 1 shows the EDS measurement results for samples obtained after performing only steps 1 to 4 of Example 1-4.
Figure 2 is an image of the surface shape of the oxide film formed on the surface of four samples obtained after only steps 1 to 4 in the example were observed using FE-SEM.
Figure 3 shows the results of measuring the contact angle of a sample (without SAM coating) subjected to only steps 1 to 4 in the example.
Figure 4 shows the results of measuring the contact angle of the sample (SAM coating) subjected to all steps 1 to 5 in the example.
Figure 5 is a diagram showing the electropotential polarization curve of the sample subjected to all steps 1 to 5 in the example.

Hereinafter, the present invention will be described in more detail through the following examples. However, the following examples are merely illustrative of the present invention, and the content of the present invention is not limited by the following examples.

<Examples 1-1 to 1-4> Anodizing treatment of stainless steel (SUS 316L)

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

Stainless steel (SUS 316L) measuring 3 cm × 3 cm × 0.05 cm was used. To remove surface impurities and clean the surface, it was immersed in ethanol and acetone and ultrasonic cleaned. It was washed once more with distilled water and dried.

The components of stainless steel such as SUS 316L are shown below. For reference, there are significant differences in the optimal anodizing treatment conditions for forming a superhydrophilic oxide film depending on the type of metal and alloy, and in the present invention, the optimal anodizing treatment conditions for forming a superhydrophilic oxide film are focused on SUS 316L. Anodizing treatment conditions were found.

Step 2: Anodizing

The anodization process used stainless steel for the anode and platinum (2.5 cm × 4 cm × 0.05 cm) for the cathode, and the distance between electrodes was maintained at 5 cm. An electrolyte solution containing 0.1 M NH ₄ F and 0.1 MH ₂ O was added based on an ethylene glycol solution, and the temperature was maintained at 0°C using a double-jacketed beaker and a water-cooled condenser. The applied voltage was set to 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: Pore expansion treatment

To expand the pores of the nanostructure produced by the anodic oxidation treatment in step 2, the sample was dipped in 0.1 M phosphoric acid (Junsei) for 10 minutes to expand the pores, and the specimen was washed with distilled water and dried.

Step 4: Plasma treatment

Using a plasma device, 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. The plasma treatment conditions were 200W, 50KHz, O ₂ 50sccm, and RIE mode for 15 minutes.

Step 5: Self-assembled Monolayer (SAM) coating

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

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

EDS (model name: The formation of an oxide film was evaluated, and the results are shown in Figure 1.

Figure 1 shows the EDS measurement results for samples obtained after performing steps 1 to 4 of Example 1-4.

As shown in Figure 1, after anodization, oxygen and iron appear as the main components, and in addition, chromium, manganese, and nickel are detected, and carbon corresponds to noise due to the influence of the carbon tape for fixing the sample to the stage. These results confirm that an oxide film was formed on the stainless steel surface.

<Experimental Example 2> Surface shape observation using FE-SEM (Field Emission Scanning Electron Microscope)

In the example, the surface shape of the oxide film formed on the surface of stainless steel (SUS 316L) performed from steps 1 to 4 (without SAM coating) was examined using FE-SEM (model name: MIRA 3 LMH In-Beam Detector, manufacturer: TESCAN). Observation was made, and the results are shown in Figure 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 since the structure made by anodization is a non-conductive oxide, platinum coating was performed for 40 seconds and then observed.

Figure 2 is an image of the surface shape of the oxide film formed on the surface of four samples obtained after performing steps 1 to 4 in the example observed by FE-SEM.

As shown in Figure 2, unlike the surfaces of (c) and (d), it can be seen that no pores are formed on the surfaces of (a) and (b) because a barrier-type oxide film is formed on the surfaces. However, in cases (c) and (d), unlike the previous two specimens, it can be seen that a porous structure was formed. The reason for the formation of a 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 oxide film comes into contact with an acidic solution, and the electric field is concentrated in areas where the film thickness is thin among the roughened oxide films. The concentration of the electric field promotes the dissolution reaction of the oxide film, forming a thinner oxide film, and the continuous behavior of this reaction forms pores due to local oxidation.

Using the FE-SEM image in Figure 2 in Table 1, the pore diameter (Pore Diameter, D _p ), the spacing between pores (D _int ), and solid fraction created on the surface after anodization were measured. One result was shown. The pore diameter and pore space distance are expressed as average values, and the solid fraction was calculated using the following equation (1).

[Equation 1]

f _SL : Solid Fraction

a: Distance between pore spaces

r: radius of 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 composed 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 porous pores were created, D _P, D _{int, and} solid fraction values could be obtained. The D _P, D _{int, and} solid fraction values at 70 V were calculated to be 68.62±8.07 nm, 89.78±8.30 nm, and 0.4559, respectively, and the values at 90 V were calculated to be 89.17±8.25 nm, 106.45±7.22 nm, and 0.3466. It was observed that a porous film with regular pores was formed under voltage conditions of 70V and 90V. Solid fraction refers to roughness rate.

<Experimental Example 3> Contact angle evaluation

In the example, the contact angle was measured to determine the surface wettability of the sample performed only from steps 1 to 4 and the sample performed from all steps 1 to 5, and the results are shown in Figures 3, 4, and Table 2.

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

Figure 3 shows the results of measuring the contact angle of a sample (without SAM coating) subjected to only steps 1 to 4 in the example.

Figure 4 shows the results of measuring the contact angle of the sample (SAM coating) subjected to all steps 1 to 5 in the example.

The results of Figures 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, the coating on the porous oxide film on the surface of the specimen creates a shape in which air pushes out water droplets on the pores or solid surface, so it is judged that the contact angle was high in the specimen coated on the surface forming the porous oxide film. .

<Experimental Example 4> Corrosion Resistance Evaluation

In the examples, the corrosion resistance of the samples subjected to all steps 1 to 5 was evaluated, and the results are shown in Figure 5 and Table 3.

Specifically, corrosion resistance was tested in a 3.5 wt% NaCl solution at room temperature using the electrochemical method Potentio-Dynamic Polarization Test (PDP). Before proceeding with the analysis test, the sample was immersed in a 3.5 wt.% NaCl solution at room temperature for 1 hour and then measured. The polarization test was a three-electrode system in which a sample was used as the working electrode, platinum (Pt) was used as the counter electrode, and a silver/silver chloride (Ag/AgCl) electrode was used as the reference electrode. Measurement conditions were -500 mV to +14000 mV (vs. Ag/AgCl), and corrosion resistance was evaluated through electrochemical characterization at a scanning speed of 1 mV/sec.

Figure 5 is a diagram showing the electropotential polarization curve of the sample subjected to all 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 indicating loss of mass

IE: Corrosion inhibition efficiency of the example treated sample compared to untreated SUS 304

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

As the corrosion current density value increases, more current flows, so corrosion tends to occur more often.

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

[Equation 2]

i: Corrosion current density of the sample subjected to all steps 1 to 5 in the example

i ₀ : Corrosion current density of untreated SUS 316L

IE: Corrosion inhibition rate of the example treated sample compared to untreated SUS 316L

As shown in Table 3, it can be seen that the corrosion resistance tends to become superior as the applied voltage increases, and the corrosion inhibition rate is 29.23% at 30 V, 87.46% at 50 V, 89.44% at 70 V, and 96.18% at 90 V. A tendency to increase can be seen as the applied voltage increases. This is related to the change in the interface structure of the material in contact with the corrosive substance (Cl ^- ) and the wettability of the water-repellent treated porous oxide film. In the case of a change in the interface structure of a material in contact with a corrosive material, the coating material with low surface energy is not polar, so it becomes difficult for water molecules to attach to the surface, and as a result, the corrosive ions in the water molecules cause a reaction in the coated metal. It gets difficult. In addition, during the water repellent treatment of the porous oxide film, the corrosion prevention efficiency was determined to have increased by creating a situation in which it is difficult for corrosive substances to penetrate into the pores due to the air filled inside the pores even if the structure and corrosive substances come into contact depending on the shape of Cassie-Baxter. do.

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

Through Experimental Examples 1 to 4, it was confirmed that corrosion resistance was the best when treated under anodizing conditions for 3 hours and 90V. Therefore, in this Experimental Example 5, the optimal conditions were investigated based on anodizing 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 the example, except that the anodizing treatment time and voltage were different.

Time (h) Voltage (V) IE(%) Example 2-1 2.8 90 82.23 Example 2-2 2.9 95.87 Example 2-3
(= Example 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
(= Example 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 obtained at an anodizing treatment time of 2.9-3.1 h and an applied voltage of 88-92 V.

So far, the present invention has been examined focusing on its preferred embodiments. A person skilled in the art to which the present invention pertains will understand that the present invention may be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative rather than a restrictive perspective. The scope of the present invention is indicated in the claims rather than the foregoing description, and all differences within the equivalent scope should be construed as being included in the present invention.

Claims (10)

Cleaning and drying the stainless steel surface for the gasket (step 1);
Forming an anodizing film on the stainless steel surface by anodizing for 2.5-3.5 hours at an applied voltage of 80-100 V (step 2);
Processing pore expansion 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
Comprising: coating with a hydrophobic coating capable of self-assembled monolayer (SAM) coating (step 5);
A method of forming a hydrophobic and corrosion-resistant oxide film on the surface of stainless steel for gaskets.
According to paragraph 1,
A method characterized in that the stainless steel is SUS 316 or SUS 316L.
According to paragraph 1,
The anodizing process in step 2 is characterized in that a mixture of NH ₄ F, water, and ethylene glycol is used as an electrolyte.
According to paragraph 1,
The anodizing process in step 2 is characterized in that the treatment is performed for 2.8-3.2 hours at an applied voltage of 85-95 V.
According to paragraph 4,
The anodizing process in step 2 is characterized in that the treatment is performed for 2.9-3.1 hours at an applied voltage of 88-92 V.
According to paragraph 1,
The hydrophobic coating agent capable of being coated with the SAM is any one of 1 H , 1 H , 2 H , 2 H -perfluorodecyltrichlorosilane (FDTS), trichlorooctylsilane (OTS), and octadecyltrichlorosilane (ODTS). A method characterized by:
According to paragraph 1,
A method characterized in that an anodic oxide film is formed on a stainless steel surface with a contact angle of 160° or more.
According to paragraph 1,
A method characterized by the formation of an anodic oxide film with a corrosion inhibition rate of 90% or more on the surface of stainless steel.
According to paragraph 1,
The gasket includes a ring joint gasket, a corrugated gasket, a serrated gasket, a lens ring gasket, a Bridgeman-type (pressure seal ring) gasket, a delta-type gasket, a double cone-type gasket, and a metal gasket. A method characterized in that it is one of hollow O-rings.
Stainless steel for gaskets with a hydrophobic anodic oxide film produced by the method of claim 1.