KR20210037946A - High corrosion resistance coating material and manufacturing method thereof - Google Patents

Abstract

An object of the present invention is to provide a highly corrosion-resistant coating material, which is environmentally friendly and has excellent corrosion resistance by forming a carbon nanotube and polydopamine complex, and to a manufacturing method thereof.

Description

High corrosion resistance coating material and its manufacturing method {HIGH CORROSION RESISTANCE COATING MATERIAL AND MANUFACTURING METHOD THEREOF}

The present invention relates to a highly corrosion-resistant coating material using polydopamine and carbon nanotubes, and a method of manufacturing the same.

Polydopamine (PDA), an adhesion protein, can be applied to the surface of almost all types of inorganic and organic materials, including conventional adhesion-resistant materials. The excellent adhesion of PDA is because it has highly reactive catechol and amine groups on the PDA surface. Catechol can immobilize the protein-resistant polymer coating to the surface of the inorganic material, and primary amines that do not form a ring can potentially form covalent bonds in the thick polymer barrier layer.

The procedure for applying the polydopamine coating is very simple. Basically, when the substrate is immersed in a diluted weak alkaline dopamine solution, a thin adhesive polymer film is spontaneously deposited. Since dopamine may undergo spontaneous oxidation during immersion, the thickness of the surface coating can be controlled by varying the immersion time. In addition, the coating process is inexpensive and environmentally friendly and does not require high temperatures or additional equipment for deaeration. For this reason, the surface coating using PDA is attracting attention in various research fields. Some studies on how to use PDA coating to mitigate corrosion show that PDA coating imparts excellent corrosion resistance to metal substrates. However, few studies have achieved superior properties by combining PDA coatings with other materials.

Carbon nanotubes (CNTs) are one of the most actively studied one-dimensional materials because mechanical, thermal, electrical, and optical properties can be controlled by length, diameter, atomic distribution and structure. As a coating material, CNT has been studied in several research fields. However, most methods of using CNTs as a coating material such as chemical vapor deposition and physical vapor deposition have disadvantages of high cost and long processing time. In addition, CNTs undergo galvanic corrosion when applied directly to a metal surface due to an electrochemical potential higher than that of the substrate. In order to solve this problem, composite materials of polymers and CNTs are recently attracting attention as advanced materials. According to several studies, composite materials that combine CNT and other materials have excellent properties and stability.

It is an object of the present invention to provide a coating material and a method of manufacturing the same, which is eco-friendly and excellent in corrosion resistance by forming a carbon nanotube and a polydopamine complex.

The highly corrosion-resistant coating material according to the present invention may include carbon nanotubes and dopamine bonded to the surface of the carbon nanotubes.

The carbon nanotubes may include at least one of a carboxyl group (-COOH) and a hydroxy group (-OH) at at least one of the surface and the terminal.

The carbon nanotube and the dopamine may be bonded to form an amide group.

The carbon nanotubes may have a length of 15 nm to 550 nm.

The content of the carbon nanotubes relative to the total weight of the carbon nanotubes modified with dopamine may be 0.1 to 20 wt.%.

In addition, the high corrosion resistance coating material of the present invention comprises the steps of forming at least one of a carboxyl group (-COOH) and a hydroxy group (-OH) on the surface of the carbon nanotubes by acid treatment of the carbon nanotubes, among the carboxyl groups Chlorinating at least a portion to form an acyl chloride functional group (-COCl), and by reacting at least a portion of the acyl chloride with an amine group of dopamine to bond the dopamine to the surface of the carbon nanotubes to form a dopamine-modified carbon nanotube. It can be prepared including steps.

In addition, the manufacturing method may further include cutting the dopamine-modified carbon nanotubes.

The acid treatment may be performed by including at least one of sulfuric acid and nitric acid.

The length cutting of the dopamine-modified carbon nanotubes may be performed by ultrasonic treatment.

A carboxyl group may be formed on at least one of the surface and the end of the dopamine-modified carbon nanotube by the ultrasonic treatment.

The ultrasonic treatment may be performed for 1 to 6 hours.

In addition, the present invention is coated with a high corrosion resistance coating material comprising a substrate formed of carbon steel containing iron, a coating layer formed of a high corrosion resistance coating material that coats the surface of the substrate and includes at least one of the characteristics of the high corrosion resistance coating material. It can be carbon steel.

The highly corrosion-resistant coating material may be coated with a thickness of 40 to 60 nm on the surface of the carbon steel.

The coating material obtained by modifying the carbon nanotubes of the present invention with dopamine and a method of manufacturing the same can produce a coating material having excellent adhesion to a substrate and corrosion resistance.

1 shows the length distribution of DOPA-CNT.
2 is an FT-IR and Raman spectroscopy results for confirming that the carbon nanotubes are modified.
3 is a Raman spectroscopy and SEM image for confirming that the carbon steel is coated with DOPA-CNT.
4 is a result of the adhesion test of DOPA-CNT.
5 is an EIS test result of DOPA-CNT coated carbon steel.
6 is a PD test result for evaluating the corrosion rate of DOPA-CNT coated carbon steel.
7 is a diagram showing a corrosion mitigation mechanism of DOPA-CNT.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present invention, various modifications may be made and various forms may be applied, and specific embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used in the present application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features or steps. It is to be understood that it does not preclude the possibility of addition or presence of, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms used herein including technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in the present application. Does not.

The present invention discloses a high corrosion resistance coating material modified with dopamine and a manufacturing method thereof, and discloses a carbon steel coated with a high corrosion resistance coating material with improved corrosion resistance by coating the carbon nanotubes modified with dopamine on carbon steel I'm doing it.

The highly corrosion-resistant coating material may include carbon nanotubes and dopamine bonded to the surface of the carbon nanotubes.

The carbon nanotube may be a carbon nanotube including at least one of a carboxyl group (-COOH) or a hydroxy group (-OH) on the surface. For the carbon nanotubes, a carbon nanotube having at least one of a carboxyl group (-COOH) and a hydroxy group (-OH) may be purchased, and a carbon nanotube having no functional group is chemically reacted to form a carboxyl group (-COOH) and At least one of the hydroxy groups (-OH) may be formed.

The carboxyl group on the surface of the carbon nanotube reacts with the amino group of dopamine to form an amide group, so that the carbon nanotube and the dopamine may be bonded to each other. The carbon nanotubes bonded to the dopamine may be referred to as dopamine-modified carbon nanotubes.

The dopamine-modified carbon nanotubes may have a length of about 15 nm to 550 nm, and preferably may have a length of about 20 nm to 500 nm.

The content of the carbon nanotubes relative to the total weight of the dopamine-modified carbon nanotubes may be about 0.1 to 20 wt.%, preferably 0.3 wt.%.

In addition, the high corrosion resistance coating material of the present invention comprises the steps of forming at least one of a carboxyl group (-COOH) and a hydroxy group (-OH) on the surface of the carbon nanotube by acid treatment of the carbon nanotube, at least one of the carboxyl groups. Chlorinating a part to form an acyl chloride functional group (-COCl), and forming dopamine-modified carbon nanotubes by bonding the dopamine to the surface of the carbon nanotubes by reacting at least a part of the acyl chloride functional group with the amino group of dopamine It can be prepared, including including.

The acid treatment of the carbon nanotubes may be performed by immersing the carbon nanotubes in an acid. The acid treatment may include at least one of sulfuric acid and nitric acid, and preferably a mixture of sulfuric acid and nitric acid may be used. At least one of a carboxyl group and a hydroxy group may be formed on the surface of the carbon nanotube by the acid treatment.

The manufacturing method may further include cutting the dopamine-modified carbon nanotubes. The length cutting of the dopamine-modified carbon nanotubes may be performed by ultrasonic treatment. The ultrasonic treatment may be performed for about 1 to 6 hours while giving a pulse. The longer the sonication time, the shorter the length of the cut carbon nanotubes modified with the dopamine. When the ultrasonic treatment is performed for about 6 hours, it may have a length of about 15 to 25 nm, and preferably, may have a length of about 20 nm. The sonicated dopamine-modified carbon nanotube may have a carboxyl group formed on at least one of its surface and end.

In addition, the present invention is coated with a high corrosion resistance coating material comprising a substrate formed of carbon steel containing iron, a coating layer formed of a high corrosion resistance coating material that coats the surface of the substrate and includes at least one of the characteristics of the high corrosion resistance coating material. It can be carbon steel.

The high corrosion resistance coating material may be coated to a thickness of about 40 to 60 nm on the surface of the carbon steel, and preferably may be coated to a thickness of about 50 nm.

The highly corrosion-resistant coating material according to the present invention was prepared by the manufacturing method according to the following examples and coated on carbon steel, and then properties were evaluated.

Example

In an embodiment of the present invention, carbon steel was coated with carbon nanotubes (DOPA-CNT) modified with dopamine.

1. Preparation of CNT modified with dopamine

Single-walled CNTs without functional groups were used to prepare PDA/CNTs. CNT 20 mg in a 20 ml container, 2 ml of sulfuric acid/nitric acid mixture (3:1 by volume) was magnetically stirred (100 rpm) at room temperature for 24 hours, and then washed with DI water to give CNT a carboxylic acid functional group (CNT-COOH). Formed. CNT-COOH was obtained by vacuum filtration on a PTFE filter paper, dried in vacuum at 60° C. overnight, and chlorinated with thionyl chloride (SOCl ₂ ) at 70° C. for 24 hours.

Thereafter, unreacted SOCl ₂ was evaporated at 100° C., and the chlorinated CNT was modified with 50 mg of dopamine in dichloromethane. CNT modified with dopamine (DOPA-CNT) was obtained by vacuum filtration with a PTFE filter (2000 nm), and dopamine that did not react was washed with 100 ml of DI water. DOPA-CNT was dispersed in DI water for 1 hour with a bath sonicator. The DOPA-CNT dispersion was probe-sonicated at 110W for 6 hours with 3 s pulse on and 1 s pulse off. Filtered DOPA-CNT was referred to as “long DOPA-CNT”, and “short DOPA-CNT” was prepared by adjusting the length of long DOPA-CNT by ultrasonic assist cutting for 6 hours.

2. DOPA-CNT coating on carbon steel

Carbon steel was used as a coated substrate, and a substrate containing a maximum of 0.25 wt% of carbon (C), a maximum of 0.04 wt% of phosphorus (P), and a maximum of 0.004 wt% of sulfur (S), and the remaining iron (Fe) was used. The surface of the specimen was polished for coating, rinsed with ethanol, and dried with nitrogen gas. Carbon steel specimens were added to a solution in which 2 mg/mL of a coating agent (PDA, long DOPA-CNT, short DOPA-CNT) was added to a 0.1 mM Tris buffer solution of pH 8.5, and the carbon steel was added with a rotating shaker (100 rpm) while supplying sufficient oxygen. Stirred. After immersion for 24 hours, the coated carbon steel was separated from the charged dopamine buffer, washed with DI water, and dried in a gentle stream of nitrogen gas to obtain a DOPA-CNT coated carbon steel.

Characteristic tests were performed in various fields with the carbon steel coated with DOPA-CNT and DOPA-CNT prepared above.

Figure 1 shows the manufacturing process of DOPA-CNT (Figure 1-A) and the length distribution of the long DOPA-CNT and the short DOPA-CNT. The length of the short DOPA-CNT becomes shorter as the sonication time increases, and it can be seen that the long DOPA-CNT, which was about 500 nm, shortens to about 20 nm when the ultrasonic treatment is performed for 6 hours (FIG. 1-B). Figure 1-C shows the distribution of the long DOPA-CNT, D shows the distribution of the short DOPA-CNT, it can be seen that the size of the particles decreased after the ultrasonic treatment. In the photographs of the DOPA-CNT suspension inserted in the graphs of Figs. 1-C and D, it can be seen that the shorter DOPA-CNT than the long DOPA-CNT has no precipitate and is well dispersed, which means that the short DOPA-CNT is stabilized by the functional group. Because it became.

Figure 2 is a result of FT-IR and Raman spectroscopy for confirming that CNT is modified with dopamine. Figure 2-A is FT-IR data, ^{dopamine is treated with an acid at 3000 ~ 3600cm -1} to react with the carboxyl group of CNTs having a carboxyl group (-COOH) to form more OH bonds, and by the NH bond of dopamine It can be seen that the peaks are combined and a wider peak appears than the unmodified CNT. Even at 1600~1750cm ^-1 , a stronger peak appeared as a result of the reaction between the aromatic amino group of dopamine and CNT. ^{In addition, a peak of 1000~1500cm -1} appears in the absence of the unmodified CNT, and it can be confirmed that dopamine is bound to the CNT, which is due to the dopamine aromatic ring. Fig. 2-B is a result of the Raman spectrum, and it can be seen that the graphite structure of CNTs was preserved by the ^{G-band peak (1590cm -1} ) and the D-band peak (1310cm ^{-1) and modified with dopamine.} In addition, the ID/IG intensity ratio was changed from 1.03 to 1.27, indicating that some defects occurred on the surface of CNTs during the modification with dopamine.

3 is a SEM image of Raman analysis and coated topography to confirm that carbon steel is coated with DOPA-CNT. In FIG. 3-A, it can be seen that in carbon steel coated with PDA or DOPA-CNT, wide peaks appear in the D-band and G-band, unlike uncoated carbon steel, which is due to dopamine and CNT, which is well coated in carbon steel. You can see what happened. In addition, the increase in peak intensity when DOPA-CNT is coated than when only dopamine is coated is due to the G-band and D-band of CNT, and it can be confirmed that the coating layer is formed in the form of DOPA-CNT. 3B to E are SEM images of uncoated carbon steel, PDA-coated carbon steel, carbon steel coated with short DOPA-CNT, and carbon steel coated with long DOPA-CNT in that order. The round part of the coated surface is a form that generally appears when coated with PDA. It can be seen that coating occurs with a thickness of about 50 nm in the coated cross-sectional images of FIGS. 3-C to E.

Figure 4 is a test according to ASTM D3359 (class 5B according to the standard) to determine whether the adhesion of dopamine is well maintained even after binding to CNT. Figures 4-A to F are respectively PDA coating (A), short DOPA-CNT coating (B), long DOPA-CNT coating (C), PDA coating test (D), short DOPA-CNT coating test ( E) shows the test (F) for the long DOPA-CNT coating. It can be seen that the adhesion to all coated specimens is excellent as it does not appear to be peeling off of the coating material other than the scratch line.

5 is an electrochemical impedance spectroscopy (EIS) test result of DOPA-CNT coated carbon steel. Impedance spectra were obtained in the form of a Nyquist plot of data from a three-electrode system (Fig. 5-A). Table 1 shows EIS data calculated using an equivalent circuit. Where R _s is the solution resistance, CPE2 is the capacitance generated by the metal dissolution and the electric double layer at the electrolyte/substrate interface, R _ct is the resistance caused by the metal dissolution, R _coating is the PDA-based coating resistance, and CPE1 is the film. It is the dielectric strength of and water absorbed by the coating. The optimal resistance parameter was determined by fitting the EIS data using the ZSimpWin program of the defined equivalent circuit. Specimens were tested in 0.1M NaCl solution. In order to compare the effect of the coating, the equivalent electric circuit of uncoated carbon steel (FIG. 5-B) and the electric circuit of PDA coated carbon steel (FIG. 5-C) are schematically shown. According to the test results of FIGS. 5-D and E, all coated specimens had better corrosion resistance than uncoated carbon steel. In particular, it can be seen that the DOPA-CNT coating has a very high charge transfer resistance compared to the PDA-coated or uncoated sample, and the short DOPA-CNT has a higher resistance than the long DOPA-CNT. This indicates the excellent corrosion protection properties of DOPA-CNT, and indicates that when the length of the CNT is short, there is a better corrosion protection effect.

Coating material applied to carbon steel R _s
(Ω-cm ² ) CPE1
(C _coating )
(F/cm ² ) n ₁ R _coating
(Ω-cm ² ) CPE2
(C _dl )
(F/cm ² ) n ₂ R _ct
(Ω-cm ² ) Uncoated carbon steel 58.9 - - - 6.1x10 ^-6 0.8 795.5 PDA 68.1 6.1x10 ^-6 0.59 18.9 6.1x10 ^-6 0.6 2227.0 Short DOPA-CNT 79.6 3.3x10 ^-4 0.64 900.4 6.1x10 ^-6 One 6851.0 Long DOPA-CNT 116.2 3.1x10 ^-4 0.66 751.8 6.1x10 ^-6 0.6 6369.0

6 is a Potentiodynamic Polarization (PD) test result for evaluating the effect of the coating on the corrosion rate. The test was carried out in 0.1M NaCl solution. When the corrosion current density was determined, the corrosion rate was calculated using the following equation (1). Table 2 summarizes the test data.

[Equation 1]

Coating material applied to carbon steel E _corr
(mVsce) I _corr
(mA/cm ² ) β _a
(mVsce) β _c
(mVsce) Corrosion rate
(mm/year) Uncoated carbon steel -582.2 2.7x10 ^-2 484.3 107.5 19.3 PDA -555.0 7.8x10 ^-3 284.5 136.2 5.6 Short DOPA-CNT -597.0 8.4x10 ^-4 210.0 86.4 0.6 Long DOPA-CNT -534.8 2.8x10 ^-3 257.5 139.2 2.0

In Equation 1, I _corr is the corrosion current density (mA/cm ² ), n is the number of equivalents exchange, D is the density (g/cm ³ ), and a is the atomic weight. When comparing the carbon steel coated with PDA or DOPA-CNT, the test results _{showed no significant difference in the corrosion potential (E corr} ) in all specimens (Fig. 6-A), but there was a large difference in the corrosion current density and the corrosion rate (Fig. 6- B) Compared with uncoated carbon steel, the corrosion rate of PDA-coated carbon steel was about 3 times lower, the long DOPA-CNT coated carbon steel was about 10 times lower, and the short DOPA-CNT coated carbon steel was about 32 times lower. It can be seen that DOPA-CNT according to the present invention is an excellent anti-corrosion material, and it can be seen that the shorter the length of CNT, the more excellent properties are exhibited, and when the corrosion rate is tested by varying the weight ratio of CNT Compared with the uncoated carbon steel, CNTs of 0.1 wt.% to 20 wt.% showed excellent anti-corrosion effects, and 0.2 wt.% of CNTs showed the best corrosion protection effect (Table 3).

Coating material applied to carbon steel E _corr (mV) I _corr (mA/cm ² ) Corrosion rate (mm/year) Uncoated carbon steel -582.2 2.68x10 ^-2 19.3 PDA -555.0 7.81x10 ^-3 5.6 PDA+0.1wt.% CNT -597.0 8.44x10 ^-4 0.6 PDA+0.2wt.% CNT -508.6 5.11x10 ^-4 0.3 PDA+0.5wt.% CNT -540.1 10.43x10 ^-4 0.7 PDA+1wt.% CNT -552.4 8.38x10 ^-4 0.6 PDA+2wt.% CNT -378.2 9.42x10 ^-4 0.8 PDA+10wt.% CNT -425.2 3.59x10 ^-3 3.2 PDA+15wt.% CNT -398.7 5.13x10 ^-3 4.1 PDA+20wt.% CNT -345.2 6.24x10 ^-3 4.6

7 shows the corrosion mitigation mechanism of DOPA-CNT, and the following reaction equation is a reaction mechanism at the anode and the cathode when corrosion occurs.

[Equation 2]

Anodes: 2Fe → 2Fe ²⁺ + 4e ^-

_{Cathode: O 2 + 2H 2 O +} 4e - → 4OH -

In Fig. 7-A, it can be seen that the CNT oxidized by the peak in the D-band has a defect (-COOH). The defects may be generated while acid-treating CNTs in the DOPA-CNT synthesis step, and may also be generated in the process of cutting long DOPA-CNTs into short DOPA-CNTs by sonication. The defects adsorb oxygen to inhibit the progress of the cathodic reaction of Equation 2 and consequently reduce the corrosion rate. The defects can be generated not only on the surface of the CNT, but also on the edges. 7-B is a C1s X-ray photoelectron spectroscopy (XPS) profile to confirm the suppression of such cathodic reaction, and measures the oxidation of carbon atoms in an aqueous environment. Before the corrosion test, the peak of the C1s core level appeared predominantly at the binding energy 283.6eV, which is the peak for C=C of the CNT surface and the aromatic ring of dopamine, but after the corrosion test, the C1s profile was changed. The change in the profile is due to the attachment of oxygen atoms to the carbon atoms, resulting in the transition of the carbon atoms' binding energy to higher levels. The transfer of the binding energy of the carbon atom is converted to an oxidation state corresponding to the high binding energy at a site having a high electron density such as a CNT end or a defect site, which reduces penetration of oxygen atoms into the carbon steel surface to prevent corrosion. This is consistent with the experimental results showing that the shorter DOPA-CNT has a better anti-corrosion effect among the DOPA-CNTs in the EIS and PD tests.

Although the above has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the present invention described in the following claims. You will understand that you can.

Claims (13)

Carbon nanotubes; And
Containing dopamine bonded to the surface of the carbon nanotubes,
High corrosion resistance coating material. The method of claim 1,
The carbon nanotube is characterized in that it contains at least one of a carboxyl group (-COOH) and a hydroxy group (-OH) at at least one of the surface and the terminal,
High corrosion resistance coating material. The method of claim 2,
Characterized in that the dopamine and the carbon nanotube are bonded to form an amide,
High corrosion resistance coating material. The method of claim 3,
The carbon nanotubes are characterized in that having a length of 15nm to 550nm,
High corrosion resistance coating material. The method of claim 4,
The content of the carbon nanotubes relative to the total weight of the carbon nanotubes modified with dopamine is characterized in that 0.1 to 20wt.%,
High corrosion resistance coating material. Acid-treating the carbon nanotubes to form at least one of a carboxyl group (-COOH) and a hydroxy group (-OH) on the surface of the carbon nanotubes;
Chlorinating at least some of the carboxyl groups to form an acyl chloride functional group (-COCl); And
Forming a dopamine-modified carbon nanotube by bonding the dopamine to the surface of the carbon nanotube by reaction of at least a portion of the acyl chloride functional group with the amino group of dopamine; including,
High corrosion resistance coating material manufacturing method. The method of claim 6,
It characterized in that it further comprises the step of cutting the dopamine-modified carbon nanotubes,
High corrosion resistance coating material manufacturing method. The method of claim 7,
The dopamine-modified carbon nanotubes are cut to length by ultrasonic treatment,
High corrosion resistance coating material manufacturing method. The method of claim 8,
Characterized in that a carboxyl group is additionally formed at at least one of the surface and the end of the dopamine-modified carbon nanotube by the ultrasonic treatment,
High corrosion resistance coating material manufacturing method. The method of claim 9,
The ultrasonic treatment is characterized in that performed for 1 to 6 hours,
High corrosion resistance coating material manufacturing method. The method of claim 6,
The acid treatment is characterized in that it is carried out by including at least one sulfuric acid and nitric acid,
High corrosion resistance coating material manufacturing method. A substrate formed of carbon steel containing iron;
Coating the surface of the substrate, comprising a coating layer formed of the high corrosion resistance coating material of any one of claims 1 to 6,
Carbon steel coated with a highly corrosion-resistant coating material. The method of claim 12,
The coating layer is characterized in that it has a thickness of 40 to 60nm,
Carbon steel coated with a highly corrosion-resistant coating material.

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