COATING FOR CORROSION PROTECTION

Abstract

There is provided a coating for corrosion protection of metal objects, said coating comprising at least one cerium oxide and at least one polypeptide, wherein the polypeptide comprises 29 or less amino acid residues wherein at least 15% of the number of amino acid residues are DOPA. Advantages include a fast establishment of the corrosion protective properties in an applied coating.

Claims

1. A coating for corrosion protection of metal objects, said coating comprising at least one cerium oxide and at least one polypeptide, wherein the polypeptide comprises 29 or less amino acid residues wherein at least 15% of the number of amino acid residues are DOPA.

2. The coating according to claim 1, wherein the at least one cerium oxide is CeO.sub.2.

3. The coating according to claim 1, wherein the at least one cerium oxide is in the form of particles with a diameter of less than 250 nm.

4. The coating according to claim 1, wherein at least one of the amino acid residues of the polypeptide is lysine.

5. The coating according to claim 1, wherein the polypeptide comprises at least one lysine located next to a DOPA.

6. The coating according to claim 1, wherein the coating in addition comprises at least one second polypeptide comprising 30 or more amino acid residues.

7. The coating according to claim 1, wherein the coating comprises a phosphate.

8. The coating according to claim 1, wherein the coating comprises at least one layer comprising the at least one polypeptide, and wherein the coating further comprises at least one other layer comprising the at least one cerium oxide.

9. The coating according to claim 1, wherein the coating comprises a layer comprising both the at least one polypeptide and the at least one cerium oxide.

10. The coating according to claim 1, wherein the coating is at least partially applied to a metal object.

11. The coating according to claim 1, wherein the coating is at least partially applied to an object comprising at least one material selected from the group consisting of: carbon steel, a Fe-based alloy, zinc an alloy comprising zinc, a magnesium alloy, and an aluminum alloy.

12. The coating according to claim 1, wherein the coating comprises a molecule comprising at least one DOPA, the ratio between the molecule and the at least one polypeptide is in the range 10:1-1:10, the molecular weight (M.sub.w) of the molecule being less than 2000.

13. A method for corrosion protection of metal objects, said method comprising applying a coating according to claim 1 to a metal object.

14. The method according to claim 13, further comprising the step of heating the coating to at least 60° C. during at least 10 minutes.

15. The method according to claim 13, wherein the metal object is coated by at least one method selected from the group consisting of: immersing, spraying, and roll coating.

16. The method according to claim 13, wherein at least one buffer solution is used and wherein the buffer solution comprises at least one component selected from the group consisting of citric acid, phosphoric acid, citrate ions, phosphate ions, hydrogen phosphate ions, and dihydrogen phosphate ions.

Description

DETAILED DESCRIPTION

[0030] Before the invention is disclosed and described in detail, it is to be understood that this invention is not limited to particular configurations, process steps and materials disclosed herein as such configurations, process steps and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention is limited only by the appended claims and equivalents thereof.

[0031] It must be noted that, as used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural referents unless the context clearly dictates otherwise.

[0032] If nothing else is defined, any terms and scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this invention pertains.

[0033] The term “about” as used in connection with a numerical value throughout the description and the claims denotes an interval of accuracy, familiar and acceptable to a person skilled in the art. Said interval is ±10%.

[0034] As used throughout the claims and the description, the term “metal object” denotes an object comprising at least partially a metal surface. An object made of a metal and a non-metal where a part of the surface is a metal surface is thus encompassed within the term metal object. Further objects at least partially made of different metals as well as metal alloys are encompassed within the term.

[0035] As used throughout the claims and the description, the term “coating” denotes a layer of material that is applied at least partially to the surface of an object.

[0036] As used throughout the claims and the description, the term “polypeptide” denotes polymerized amino acids. A polypeptide can comprise any number of amino acid residues. Proteins are encompassed within the term polypeptide. Polypeptides comprising 50 or more amino acid residues are also denoted proteins. The polypeptide can be extracted from a natural source or it can be synthetically manufactured. Both natural and synthetic polypeptides are thus encompassed by the term.

[0037] As used throughout the claims and the description, the term “DOPA” denotes the chemical compound dihydroxyphenylalanine and may refer to either of D-3,4-dihydroxyphenylalanine L-3,4-dihydroxyphenylalanine. Both D-DOPA and L-DOPA are encompassed by the term DOPA. When a peptide or protein is said to comprise DOPA then it is understood that the DOPA molecule is bound to other amino acid(s). When DOPA is used in the term “a molecule comprising DOPA”, then it is understood that DOPA is reacted with another entity to create such a molecule comprising DOPA. A molecule comprising DOPA is thus the result of a reaction of DOPA with another molecule.

[0038] As used throughout the claims and the description, the term “cerium oxide” denotes a chemical compound or complex comprising the chemical element cerium (Ce) and the chemical element oxygen (O). The term “cerium oxide” includes but is not limited to Ce.sub.2O.sub.3 and CeO.sub.2. The terms ceric oxide, ceria, cerium(III) oxide, cerium(IV) oxide and cerium dioxide are also encompassed by the term cerium oxide.

[0039] In a first aspect there is provided a coating for corrosion protection of metal objects, said coating comprising at least one cerium oxide and at least one polypeptide, wherein the polypeptide comprises 29 or less amino acid residues, wherein at least 15% of the number of amino acid residues are DOPA.

[0040] One advantage of using the polypeptide comprising 29 or less amino acid residues are that the corrosion protection effect is achieved faster. By using short polypeptides, the corrosive protecting properties of the coating are obtained faster and without the necessity to wait for a long time before it becomes efficient. In one embodiment, the polypeptide comprises 28 or less amino acid residues.

[0041] In one embodiment. In one embodiment, the polypeptide comprises 27 or less amino acid residues. In one embodiment, the polypeptide comprises 26 or less amino acid residues. In one embodiment, the polypeptide comprises 25 or less amino acid residues. In one embodiment, the polypeptide comprises 24 or less amino acid residues. In one embodiment, the polypeptide comprises 23 or less amino acid residues. In one embodiment, the polypeptide comprises 20 or less amino acid residues. In one embodiment, the polypeptide comprises 19 or less amino acid residues. In one embodiment, the polypeptide comprises 18 or less amino acid residues. In one embodiment, the polypeptide comprises 17 or less amino acid residues. In one embodiment, the polypeptide comprises 16 or less amino acid residues. In one embodiment, the polypeptide comprises 15 or less amino acid residues. In one embodiment, the polypeptide comprises 14 or less amino acid residues. In one embodiment, the polypeptide comprises 13 or less amino acid residues. In one embodiment, the polypeptide comprises 12 or less amino acid residues. In one embodiment, the polypeptide comprises 11 or less amino acid residues. In one embodiment, the polypeptide comprises 10 or less amino acid residues. In one embodiment, the polypeptide comprises 9 or less amino acid residues. In one embodiment, the polypeptide comprises 8 or less amino acid residues. In one embodiment, the polypeptide comprises 7 or less amino acid residues.

[0042] The net charge of the polypeptide generally varies with the pH and is in one embodiment, positive at the application of the polypeptide. Suitable pH varies with the characteristics of the amino acid residues in the polypeptide.

[0043] In one embodiment, the at least one cerium oxide is CeO.sub.2. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 250 nm. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 200 nm. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 150 nm. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 100 nm. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 50 nm. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 40 nm. In one embodiment, the at least one cerium oxide is in the form of particles with a diameter of less than 20 nm.

[0044] In one embodiment, at least one of the amino acid residues of the at least one polypeptide is lysine. In one embodiment, the at least one polypeptide comprises at least one lysine located next to a DOPA.

[0045] In one embodiment, the coating in addition comprises at least one second polypeptide comprising 30 or more amino acid residues. In one embodiment, the at least one second polypeptide comprises 30-3000 amino acid residues. In one embodiment, the at least one second polypeptide comprises 100-2000 amino acid residues. In one embodiment, the at least one second polypeptide comprises 200-1000 amino acid residues. The mixture of a short and a long polypeptide has the advantage of giving both a quick corrosion protection as well as a good long term corrosion protection. The short peptides in the mixture give a quick corrosion protection already a short time after the application. The longer peptides give an additional long term protection, although the effect from the longer peptides occur after some time. For many applications the combination of a short term quickly arising corrosion protection and a slower occurring long term protection is adequate. The polypeptide comprising 29 or less amino acid residues allows a corrosion resistance to be built up quickly, the longer second polypeptide complements the protection and improves the long term corrosion resistance.

[0046] In one embodiment, the coating comprises a phosphate.

[0047] In one embodiment, the coating comprises alternating layers of polypeptide and cerium oxide. In one embodiment, the coating comprises at least one layer comprising the at least one polypeptide, and the coating further comprises at least one other layer comprising the at least one cerium oxide. In one embodiment, the coating comprises a layer comprising both the at least one polypeptide and the at least one cerium oxide. It is an advantage of the invention that several layers can be made. In this way, it is possible to control the layer thickness. A thicker coating comprising several layers offers a more resistant coating. The multiple layer structure is in one embodiment, made by depositing polypeptide and cerium oxide in an alternating way. In an alternative embodiment the polypeptide and the cerium oxide is mixed before application to the surface whereby no structure with alternating layers is obtained.

[0048] In one embodiment, the coating is at least partially applied to a metal object. In one embodiment, the coating is at least partially applied to an object comprising at least one material selected from the group consisting of carbon steel, Fe-based alloy, zinc, an alloy comprising zinc, a magnesium alloy and an aluminum alloy.

[0049] In one embodiment, the coating comprises a molecule comprising at least one DOPA. Such a molecule comprising at least one DOPA is in addition to the polypeptide where at least 15% of the number of amino acid residues are DOPA. The ratio between the molecule comprising at least one DOPA and the at least one polypeptide is in one embodiment 10:1-1:10. The ratio between the molecule comprising at least one DOPA and the at least one polypeptide is in one embodiment in the range 5:1-1:5. The ratio between the molecule comprising at least one DOPA and the at least one polypeptide is in one embodiment in the range 2:1-1:2. In one embodiment the ratio is 1:1. When the coating comprises a molecule comprising at least one DOPA the pH in the solution comprising the ingredients which are applied to the surface is preferably between 8-10. In one embodiment the pH is at least 8.5. In one embodiment the molecular weight (M.sub.w) of the molecule comprising at least one DOPA is less than 1000. In another embodiment the molecular weight of the molecule comprising at least one DOPA is less than 2000.

[0050] In a second aspect there is provided a method for corrosion protection of metal objects, said method comprising applying a coating as described above.

[0051] In one embodiment an aqueous solution comprising the ingredients is applied onto the surface to be treated.

[0052] In one embodiment, the method further comprises the step of heating the coating to at least 60° C. during at least 10 minutes. The combination between the polymer and small particles comprising cerium oxide gives the excellent corrosion protection in particular after heating.

[0053] In one embodiment, the coating is at least partially applied to a metal object. In one embodiment, the coating is at least partially applied to an object comprising at least one material selected from the group consisting of carbon steel, a Fe-based alloy, a magnesium alloy, and an aluminum alloy.

[0054] In one embodiment, the metal object is coated by at least one method selected from the group consisting of: immersing, spraying, and roll coating. In one embodiment, the metal object is coated by immersing during a period of time ranging from 10 minutes to 2 hours. Also shorter and longer durations for dipping a metal object are possible.

[0055] In one embodiment, at least one buffer solution is used and wherein the buffer solution comprises at least one selected from the group consisting of citric acid, phosphoric acid, citrate ions, and phosphate ions, hydrogen phosphate ions, and dihydrogen phosphate ions.

[0056] In one embodiment, the concentration of the at least one polypeptide is 0.01-10 g/l and the concentration of the at least one cerium oxide is 0.1-10 g/l, calculated for a solution/suspension used for contacting with the metal object.

[0057] In one embodiment, the concentration of phosphate is 1-10 wt % calculated for a solution/suspension used for contacting with the metal object.

[0058] In one embodiment, the method comprises the steps of: a) applying at least one layer comprising the at least one cerium oxide, and b) applying at least one other layer comprising the at least one polypeptide. In one embodiment, a layer comprising the at least one cerium oxide, and a layer comprising the at least one polypeptide are applied sequentially several times. In one embodiment, the method comprises the step of applying a layer, said layer comprising both the at least one cerium oxide and the at least one polypeptide.

[0059] In one embodiment, the metal object is ground prior to contacting the metal object with the coating. This may further enhance the adhesion in particular for smooth surfaces.

EXAMPLES

[0060] Electrochemical impedance spectroscopy (EIS) of polypeptide/ceria nanocomposite film coated on a carbon steel surface exposed to 0.1 M NaCl solution at pH 6.5 was performed. The polypeptides tested were labelled as AT-M5D (SEQ ID No. 3), AT-M5D-4 (SEQ ID No. 2) and AT-M5D-8 (SEQ ID No. 1) and Mefp-1, where AT-M5D has a length of 37 amino acid residues, AT-M5D-4 (19 amino acid residues) is about a fourth of the length of AT-M5D and AT-M5D-8 (10 amino acids) is about an eighth of the length of AT-M5D. AT-M5D, AT-M5D-4 and AT-M5D-8 are synthetic polypeptides. Mefp-1 is about 800-1000 amino acid residues according to the literature. For a closer description of Mefp-1 and its sequence we refer to J. Herbert Waite in The Journal of Biological Chemistry Vol. 258, No. 5, pp 2911-2915, 1983 as well as J. Herbert Waite et al. in Biochemistry Vol. 24, No. 19, pp 5010-5014, 1985. The samples were deposited on a cold-rolled carbon steel surface in combination with ceria nanoparticles through alternative immersion processes. Four layers of AT-M5D/ceria, AT-M5D-4/ceria, AT-M5D-8/ceria or Mefp-1/ceria respectively were deposited on the different steel surfaces by first dipping the steel in the peptide solution for 40 minutes, then dipping in the ceria suspension, and repeating the process three more times.

[0061] 1 h after application, the AT-M5D-8 (l0aa) provides the highest increase in the Rp values, as compared to the control sample, followed by the AT-M5D-4 (19aa), the full length AT-M5D (37aa) and the Mefp-1/ceria, in that order. The Rp value of the AT-M5D-8 (10aa) and AT-M5D-4 (19aa) 1 hour after application is higher than levels reached by the full length AT-M5D (37aa) within 1 hour to 7 days of application (Table 1, 2, 3) and higher than levels reached by the Mefp-1 within 1 hour to 2 days of application (Table 1, 2, 4).

[0062] 1 day or more after application, the AT-M5D (37aa) and Mefp-1 generally provide a higher increase in Rp value, as compared to the control sample, than the AT-M5D-4 (19aa) and AT-M5D-8 (10aa) do at the corresponding times.

[0063] In order to evaluate the EIS data the following simple equivalent circuit was used to describe the steel-solution interface.

##STR00001##

[0064] Rs: solution resistance between the reference electrode and working electrode, Rp: polarization resistance, CPE: constant phase element. The constant phase element (CPE) is used to instead of capacitance to account for the imperfect capacitive response of the interface. The impedance of the CPE is expressed by

Z.sub.CPE=[Y.sub.0(jω).sup.n].sup.−1

where Y.sub.0 is the magnitude of CPE, j is the imaginary unit, and ω is the angular frequency. The exponential factor n is a fit parameter with less clear physical meaning. It is often related to the degree of surface roughness, a smaller deviation from 1, is a more homogeneous surface or surface film.

TABLE-US-00001 TABLE 1 Fitted results of EIS data of AT-M5D (37aa) (SEQ ID No. 3) samples. Rp is a measure of the corrosion resistance. The control samples were bare carbon steel. Rp (AT-M5D Rp (37aa))/ (control)/ Y.sub.0/F cm.sup.−2 n ohm * cm.sup.2 ohm * cm.sup.2 1 h (4.4 ± 1.3) × 10.sup.−4 0.8 (1.6 ± 0.3) × 10.sup.3 (1.3 ± 0.1) × 10.sup.3 1 d (1.2 ± 0.4) × 10.sup.−3 0.7 (2.2 ± 0.2) × 10.sup.3 (1.7 ± 0.6) × 10.sup.3 2 d (1.4 ± 0.4) × 10.sup.−3 0.7 (2.4 ± 0.1) × 10.sup.3 — 3 d (1.4 ± 0.3) × 10.sup.−3 0.7 (1.5 ± 0.1) × 10.sup.3 (1.5 ± 0.4) × 10.sup.3 4 d (1.4 ± 0.4) × 10.sup.−3 0.7 (2.5 ± 0.3) × 10.sup.3 — 5 d (1.4 ± 0.4) × 10.sup.−3 0.7 (2.1 ± 0.1) × 10.sup.3 (1.4 ± 0.3) × 10.sup.3 6 d (1.4 ± 0.4) × 10.sup.−3 0.7 (1.6 ± 0.1) × 10.sup.3 — 7 d (1.4 ± 0.4) × 10.sup.−3 0.7 (2.5 ± 0.6) × 10.sup.3 (1.4 ± 0.2) × 10.sup.3

TABLE-US-00002 TABLE 2 Fitted results of EIS data of AT-M5D-4 (19aa) (SEQ ID No. 2) samples. Rp is a measure of the corrosion resistance. The control samples were bare carbon steel. Rp (AT-M5D-4 Rp (19aa))/ (control)/ Time Y.sub.0/F cm.sup.−2 n ohm*cm.sup.2 ohm * cm.sup.2 1 h (5.4 ± 2.4) × 10.sup.−4 0.8 (2.8 ± 1.6) × 10.sup.3 (1.3 ± 0.1) × 10.sup.3 2 d (1.0 ± 0.2) × 10.sup.−3 0.8 (1.8 ± 0.3) × 10.sup.3 (1.5 ± 0.2) × 10.sup.3 4 d (1.0 ± 0.1) × 10.sup.−3 0.8 (1.6 ± 0.1) × 10.sup.3 (1.5 ± 0.4) × 10.sup.3 6 d (1.1 ± 0.2) × 10.sup.−3 0.8 (1.8 ± 0.4) × 10.sup.3 (1.4 ± 0.3) × 10.sup.3 8 d (1.1 ± 0.3) × 10.sup.−3 0.7 (2.0 ± 0.3) × 10.sup.3 (1.4 ± 0.2) × 10.sup.3

TABLE-US-00003 TABLE 3 Fitted results of EIS data of AT-M5D-8 (lOaa) (SEQ ID No. 1) samples. Rp is a measure of the corrosion resistance. The control samples were bare carbon steel. Rp (AT-M5D-8 Rp (10aa))/ (control)/ Time Y.sub.0/F cm.sup.−2 n ohm * cm.sup.2 ohm* cm.sup.2 1 h (5.4 ± 2.4) × 10.sup.−4 0.7 (3.1 ± 1.0) × 10.sup.3 (1.3 ± 0.1) × 10.sup.3 2 d (1.0 ± 0.2) × 10.sup.−3 0.7 (1.3 ± 0.2) × 10.sup.3 (1.5 ± 0.2) × 10.sup.3 4 d (1.0 ± 0.1) × 10.sup.−3 0.7 (1.3 ± 0.2) × 10.sup.3 (1.5 ± 0.4) × 10.sup.3 6 d (1.1 ± 0.2) × 10.sup.−3 0.7 (1.3 ± 0.3) × 10.sup.3 (1.4 ± 0.3) × 10.sup.3 8 d (1.1 ± 0.3) × 10.sup.−3 0.6 (1.4 ± 0.4) × 10.sup.3 (1.4 ± 0.2) × 10.sup.3

TABLE-US-00004 TABLE 4 Fitted results of EIS data of Mefp-1 samples. Rp is a measure of the corrosion resistance. The control samples were bare carbon steel. Rp (Mefp- 1/ceria)/ Y.sub.0/F cm.sup.−2 n ohm * cm.sup.2 1 h (5.6 ± 1.5) × 10.sup.−4 0.8 (1.0 ± 0.2) × 10.sup.3 1 d (9.3 ± 3.2) × 10.sup.−3 0.8 (2.4 ± 0.2) × 10.sup.3 2 d (1.1 ± 0.3) × 10.sup.−3 0.8 (2.4 ± 0.2) × 10.sup.3 4 d (1.1 ± 0.2) × 10.sup.−3 0.8 (2.9 ± 0.2) × 10.sup.3 Rp (control)/ Y.sub.0/F cm.sup.−2 n ohm * cm.sup.2 1 h (5.5 ± 1.1) × 10.sup.−4 0.8 (1.6 ± 0.3) × 10.sup.3 1 d (8.6 ± 3.0) × 10.sup.−3 0.7 (1.7 ± 0.4) × 10.sup.3 2 d (1.1 ± 0.3) × 10.sup.−3 0.7 (1.6 ± 0.2) × 10.sup.3 4 d (1.2 ± 0.3) × 10.sup.−3 0.6 (1.6 ± 0.1) × 10.sup.3