MESOPOROUS CARBON BASED NANOCONTAINER COATINGS FOR CORROSION PROTECTION OF METAL STRUCTURES

Abstract

A mesoporous carbon container comprising an embedded organic corrosion inhibitor and having an organic polymeric coating is described. Further described are a coating comprising such a container and a method for producing such a container.

Claims

1. Mesoporous carbon nanocontainer comprising an embedded organic corrosion inhibitor and having an organic polymeric coating.

2. The mesoporous carbon nanocontainer according to claim 1, wherein the corrosion inhibitor is an azole derivative, especially benzotriazole.

3. The mesoporous carbon nanocontainer according to claim 1, wherein the organic polymeric coating is made from a polyelectrolyte, especially from poly (allyl amine) hydrochloride.

4. The mesoporous carbon nanocontainer according to claim 1, wherein the corrosion inhibitor is benzotriazole and wherein the organic polymeric coating is made from poly (allyl amine) hydrochloride.

5. A polymer coating composition comprising a primer and a mesoporous carbon nanocontainer according to claim 1.

6. The polymer coating composition according to claim 5, wherein the primer is selected from vinyl acrylate and polyvinyl butyral, and is especially vinyl acrylate.

7. The polymer coating composition according to claim 5, wherein the coating composition is coated on a steel surface.

8. The polymer coating composition according to claim 5, wherein the polymer coating composition is self-healing, i.e. cracks formed therein disappear over time at least partly.

9. A method for producing a mesoporous carbon nanocontainer comprising an embedded organic corrosion inhibitor and having an organic polymeric coating, the method comprising the following steps in the given order: dispersing the mesoporous carbon in water by sonication to give a mixture of mesoporous carbon and water, degassing mesoporous carbon under vacuum, dissolving the organic corrosion inhibitor in water, adding the dissolved organic corrosion inhibitor to the mixture of mesoporous carbon and water to give a mixture of mesoporous carbon, water and organic corrosion inhibitor, degassing the mixture of mesoporous carbon, water and organic corrosion inhibitor under vacuum, removing excess of corrosion inhibitor by centrifugation and washing with water, drying, adding an organic polymeric coating material in order to form the organic polymeric coating.

10. The method of claim 9, wherein the corrosion inhibitor is benzotriazole and wherein the organic polymeric coating is made from poly (allyl amine) hydrochloride.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention will be described with reference to the accompanying drawings of which:

[0039] FIG. 1 shows characteristics of a release of benzotriazole from meso carbon/(BT)3/PAH (nano)container in different pH solutions.

[0040] FIG. 2 shows the digital image of scratched surface of vinyl acrylate alone coated substrate after 1 day of immersion in 0.35M sodium chloride solution.

[0041] FIG. 3 shows the digital image of scratched surface of vinyl acrylate alone coated substrate after 3 days of immersion in 0.35M sodium chloride solution.

[0042] FIG. 4 shows the optical image of the corroded area of the scratch on vinyl acrylate alone coated substrate marked with circle in FIG. 3.

[0043] FIG. 5 shows the SEM image of corroded area of the scratch on vinyl acrylate alone coated substrate marked with circle in FIG. 3.

[0044] FIG. 6 shows the EDAX of corroded area of the scratch on vinyl acrylate alone coated substrate marked with circle in FIG. 3.

[0045] FIG. 7 shows the digital image of scratched surface of mesoporous carbon/(BT)3/PAH (nano)container coating after 1 day of immersion in 0.35M sodium chloride solution.

[0046] FIG. 8 shows the digital image of scratched surface of mesoporous carbon/(BT)3/PAH (nano)container coating after 3 days of immersion in 0.35M sodium chloride solution.

[0047] FIG. 9 shows the optical image of the corroded area of the scratche on mesoporous carbon/(BT)3/PAH (nano)container coating marked with circle 1 in FIG. 8.

[0048] FIG. 10 shows the optical image of the non-corroded area of the scratche on mesoporous carbon/(BT)3/PAH (nano)container coating marked with circle 2 in FIG. 8.

[0049] FIG. 11 shows the SEM image of the corroded area of the scratch on mesoporous carbon/(BT)3/PAH (nano)container coating marked with circle 1 in FIG. 8.

[0050] FIG. 12 shows the EDAX of the corroded area of the scratch on mesoporous carbon/(BT)3/PAH (nano)container coating marked with circle 1 in FIG. 8.

[0051] FIG. 13 shows the SEM image of the non-corroded area of the scratch on mesoporous carbon/(BT)3/PAH (nano)container coating marked with circle 2 in FIG. 8.

[0052] FIG. 14 shows the EDAX of the non-corroded area of the scratch on mesoporous carbon/(BT)3/PAH (nano)container coating marked with circle 2 in FIG. 8.

[0053] FIG. 15 shows Bode plot of vinyl acrylate coating at different time of immersion in 0.35M sodium chloride solution.

[0054] FIG. 16 shows Bode plot of mesoporous carbon/(BT)3/PAH (nano)container embedded coating at different time of immersion in 0.35M sodium chloride solution.

[0055] FIG. 17 shows OCP plots of mesoporous carbon/(BT)3/PAH (nano)container embedded coatings and vinyl acrylate alone coated substrate at different time of immersion in 0.35M sodium chloride solution.

[0056] FIG. 18 is a schematic representation of mesoporous carbon/(BT)3/PAH (nano)container synthesis and of an application on a carbon steel substrate according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0057] The identified advantages of the self-healing anti-corrosion coating compositions, as per the inventor's provided disclosure are as follows:

[0058] Nanocontainers in the polymer coatings have more freedom of movement than those in the sol-gel coatings where they are tightly bound with the sol-gel.

[0059] Since the cost of the raw materials (metal alkoxides) used the sol-gel coatings are high, this method is economically not feasible. Starting materials used for the nanocontainer-polymer coatings such as vinyl acrylate and polyvinyl butyral (PVB) are most cost effective.

[0060] Curing of nanocontainer-polymer coatings at 30-70 C. is enough to get a uniform thick coating. Sol-gel coatings always require high temperature annealing to achieve a dense microstructure.

[0061] Sintering at high temperatures introduces cracks and/or delamination of sol-gel coatings. Curing of nanocontainer-polymer coatings improve the chemical and physical interaction between the functional groups such as amine, hydroxyl etc. on the outer layer polyelectrolyte shell with the polymeric matrix, which enhances the nanocontainer compatibility and reduces the chances of coating damages.

[0062] Successful commercially available sol-gel coatings are thin films. Thick films of (>1 m) sol-gel coatings always have cracking problems. Uniform coatings with thickness greater than 1 m could easily be obtained from nanocontainer-polymer formulation according to the invention.

[0063] In the present invention so-called nanocontainers are described which are made from mesoporous carbon (Meso C). The use of mesoporous carbon as carrier of corrosion inhibitor is not well reported in the literature. Therefore, the present work has been conducted in the fabrication of corrosion inhibitor encapsulated mesoporous carbon based nanocontainer coatings for the corrosion protection of metal structures. Corrosion inhibitor was added directly into the pores of carbon matrix and then covered by polyelectrolyte layers to prevent the unwanted release. It was applied for coating preparation by mixing with vinyl acrylate primer. The advantage of mesoporous carbon nanocontainer over silica nanocontainer is that the coatings would be more hydrophobic and it can protect the UV radiation as well.

Synthesis of Mesoporous Carbon/(BT)3/PAH Nanocontainer

[0064] Mesoporous carbon (0.5 g) was dispersed in 15 ml of water by sonication. It was then degassed under vacuum to open up the pores. Benzotriazole (BT) (20 mg/ml) dissolved in water was added to this mixture with constant stirring and then again degassed under vacuum. The vacuum was adjusted at the point when the bubbling of air from the pores starts. This degassing process was continued till the bubbles from the mixture is completely disappeared. The excess of benzotriazole was removed by centrifugation and washing with water and then dried at 80 C. for 24 h. These steps were repeated three times to completely fill the pores of mesoporous carbon with benzotriazole. 10 mg/ml of poly (allyl amine) hydrochloride (PAH) was added as the covering layer for the benzotriazole encapsulated mesoporous carbon and a final structure of Meso Carbon/(BT)3/PAH was obtained.

Mesoporous Carbon Nanocontainer Coatings on Carbon Steel

[0065] The final mixtures of Meso Carbon/(BT)3/PAH nanocontainers were dried in oven at 80 C. for overnight. 0.5 g of mesoporous carbon nanocontainer was added slowly to a 30 g of solvent based vinyl acrylate with magnetic stirring and then was coated on the carbon steel substrate by dip coating. After drying at 80 C. for 2 h followed by 60 C. for 12 h all the sides were sealed with quick setting epoxy. A schematic representation of silica nanocontainer synthesis and coating on carbon steel substrate is given in FIG. 12. Corrosion analysis of each coating was conducted by immersion test in 0.35M sodium chloride solution. In order to study the self-healing nature of the coatings a scratch was made before immersing in sodium chloride solution. Corrosion was monitored at periodic intervals using microscopic techniques and measured quantitatively by electrochemical techniques. Release of benzotriazole from the nanocontainers was monitored by UV-Visible-NIR spectrometer at different pH solutions.

Results and Discussion

[0066] FIG. 1 shows the release of benzotriazole from Meso carbon/(BT)3/PAH nanocontainer at different pH solutions measured by UV-Visible-NIR spectrometer. In the UV spectra, nanocontainers at pH 3 and 10 solutions showed a higher absorbance than those in pH 7 solution, indicating the more release of benzotriazole in acidic and alkaline media. It was due to its solubility that benzotriazole dissolves in acidic and alkaline solutions far better than neutral media. Additionally, UV spectra confirmed further the presence of benzotriazole inside the pores of carbon nanocontainer.

[0067] In order to analyze the self-healing nature the scratched coatings of both vinyl acrylate and nanocontainer embedded vinyl acrylate were immersed in 0.35M sodium chloride solution. Sevier corrosion products on the scratches of vinyl acrylate alone coated substrate was clearly visible in FIGS. 2 & 3. Optical and SEM images also showed the corrosion products on the scratches and EDAX results confirmed the formation of iron oxides as well (FIGS. 4, 5 & 6). Corrosion progressed with time and slowly it covered all the scratches.

[0068] Immersion test conducted on the Meso carbon/(BT)3/PAH nanocontainer embedded coatings are given in FIGS. 7 & 8. Compared with vinyl acrylate alone coated substrate nanocontainer coatings showed less corrosion products on the scratches (FIGS. 7 & 8). Optical and SEM images of the corroded area, marked with circle 1 in FIG. 8, was observed to be covered by a precipitate and the EDAX showed the presence of nitrogen in that area (FIGS. 9, 11 & 12). It indicated that benzotriazole released from the nanocontainer diminished the extent of corrosion that was apparent from the less intensity of corrosion products on the scratches of nanocontainer coating compared with vinyl acrylate coating (FIGS. 3 & 8). The optical and SEM images of the non-corroded areas of the scratches given in FIG. 10 and FIG. 13 respectively showed clean surfaces. EDAX of this area also showed the presence of nitrogen and oxygen atoms along with iron (FIG. 14). It indicated that benzotriazole released from the nanocontainer formed resistive layers with iron and oxygen on the metal surface which prevented corrosion. It can be suggested therefore that mesoporous carbon nanocontainers were effective carriers of benzotriazole which got released on demand at required areas of metal structures for corrosion protection.

[0069] Self-healing performance of the nanocontainer embedded coatings were quantified by measuring impedance and open circuit potential (OCP) at different time of immersion in 0.35M sodium chloride solution. Electrochemical impedance (EIS) of vinyl acrylate coating and nanocontainer coating, measured using a three electrode set up, are given in FIGS. 15 & 16 respectively. Low frequency impedance (logZ) of nanocontainer coatings at initial time of immersion was at 5.5 cm.sup.2 which is slightly lower than the vinyl acrylate coating (6.2 cm.sup.2). Low frequency impedance of vinyl acrylate coating decreased continuously and reached 4.6 cm.sup.2 by 4 d whereas for nanocontainer coating low frequency impedance reached a similar value by 13 d. This behavior of nanocontainer coating was due to the corrosion inhibitive nature of benzotriazole released from the Meso carbon/(BT)3/PAH nanocontainer.

[0070] Open circuit potential (OCP) related to the corrosion potential, measured when no current or potential being applied to the cell, showed a decreasing trend to nanocontainer coating during the initial days of exposure and then started to increase after 50 hours (FIG. 17). This type of OCP behavior clearly shows the self-healing nature of the coating. At the same time OCP of vinyl acrylate alone coated substrates didn't increase after the initial decrease and it continued to remain at the lower value during the further immersion in sodium chloride solution. Both immersion test and electrochemical analysis concluded that mesoporous carbon nanocontainers are effective in providing protection by inhibiting corrosion on the metal surface by the release of encapsulated corrosion inhibitor.