Method for treating metal surface

Abstract

The present invention relates to a method for treating a metal surface, comprising (A) providing an ionic liquid solution and a substrate of a first metal, wherein the ionic liquid solution comprises an ionic liquid and an ion of a second metal; and (B) immersing the substrate of the first metal in the ionic liquid solution to form a coating layer of the second metal on a surface of the substrate of the first metal by reducing the ion of the second metal. The surface of the substrate of the first metal is protected by the coating layer of the second metal, thereby improving the corrosion resistance.

Claims

1. A method for treating a metal surface, comprising: (A) providing an ionic liquid solution and a substrate of a first metal, wherein the ionic liquid solution comprises an ionic liquid and an ion of a second metal; and (B) immersing the substrate of the first metal in the ionic liquid solution to form a coating layer of the second metal on a surface of the substrate of the first metal by reducing the ion of the second metal, and the second metal has a reduction potential higher than the first metal, wherein the coating layer of the second metal is formed on the surface of the substrate of the first metal without energy supply.

2. The method of claim 1, wherein the substrate of the first metal is selected from the group consisting of magnesium, aluminum, zinc, titanium, iron, cobalt, nickel, silver, vanadium, chromium and alloys thereof.

3. The method of claim 1, wherein the ion of the second metal is selected from the group consisting of a copper ion, a nickel ion, a zinc ion, a titanium ion, an aluminum ion, a cobalt ion, a silver ion, a gold ion, a vanadium ion, a chromium ion, a manganese ion, a platinum ion, a palladium ion, and mixtures thereof.

4. The method of claim 1, wherein the ionic liquid comprises at least one cation selected from the group consisting of the cations represented by Formulas (I) to (VIII); ##STR00006## wherein each of R.sub.1, R.sub.2, R.sub.3 and R.sub.4, independently, is a hydrogen or a C.sub.1-10 alkyl group.

5. The method of claim 1, wherein the ionic liquid comprises at least one cation selected from the group consisting of the cations represented by Formulas (I) to (VIII); ##STR00007## wherein, each of R.sub.1, R.sub.2, R.sub.3 and R.sub.4, independently, is a C.sub.1-5 alkyl group.

6. The method of claim 1, wherein the ionic liquid comprises at least one anion selected from the group consisting of the anions represented by Formulas (1) to (5); ##STR00008##

7. The method of claim 1, wherein the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium dicyanamide, N-butyl-N-methylpyrrolidinium dicyanamide, tributylmethyl ammonium dicyanamide, N-ethylpyridinium dicyanamide, and mixtures thereof.

8. The method of claim 1, wherein the metal ion is present at a concentration of 0.05-0.5M in the ionic liquid solution.

9. The method of claim 1, wherein the ionic liquid has a potential window of above 2.0 V.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a SEM image of the surface of the magnesium metal specimen according to Example 1 of the present invention.

(2) FIG. 2 shows a SEM image of the surface of the magnesium metal specimen according to Example 2 of the present invention.

(3) FIG. 3 shows a SEM image of the surface of the magnesium metal specimen according to Example 3 of the present invention.

(4) FIG. 4 shows a SEM image of the surface of the magnesium metal specimen according to Example 4 of the present invention.

(5) FIG. 5 shows a SEM image of the surface of the zinc metal specimen according to Example 5 of the present invention.

(6) FIG. 6 shows a SEM image of the surface of the aluminum metal specimen according to Example 6 of the present invention.

(7) FIG. 7 is a schematic diagram showing the measurement results of the open circuit potential of the magnesium metal specimen during the metal replacement reaction according to Examples 1-4 of the present invention.

(8) FIG. 8 is a schematic diagram showing the analysis results of the real-time X-ray absorption spectroscopy of the magnesium metal specimen during the metal replacement reaction according to Example 1 of the present invention.

(9) FIG. 9 is a schematic diagram showing the analysis results of the real-time X-ray absorption spectroscopy of the magnesium metal specimen during the metal replacement reaction according to Example 2 of the present invention.

(10) FIG. 10 is a schematic diagram of the polarization curve according to Examples 1-4 of the present invention and Comparative Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Example 1

(11) An adequate amount of CuCl was dissolved in an N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA) ionic liquid, to form an ionic liquid solution containing 0.1M of Cu+ ion, wherein, the N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA) ionic liquid is represented by Formula (IX):

(12) ##STR00003##

(13) Then, the magnesium metal specimen was immersed in a metal ionic liquid solution containing Cu+ ions to proceed with a replacement reaction. After 24 hours of reaction, the surface of the magnesium metal specimen was washed with the anhydrous ethanol, and the change of the surface morphology was observed by a scanning electron microscope (SEM). As can be clearly observed from the surface morphology illustrated in FIG. 1, a copper layer was coated on the surface of the magnesium metal specimen.

Example 2

(14) An adequate amount of NiCl.sub.2 was dissolved in an N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA) ionic liquid, to form a NiCl.sub.2 ionic liquid solution containing 0.1M of Ni.sup.2+ ion. Then, the magnesium metal specimen was immersed in a metal ionic liquid solution containing Ni.sup.2+ ions to proceed with a replacement reaction. After 24 hours of reaction, the surface of the magnesium metal specimen was washed with the anhydrous ethanol, and the change of the surface morphology was observed by using a scanning electron microscope (SEM). As can be clearly observed from the surface morphology illustrated in FIG. 2, a nickel layer was coated on the surface of the magnesium metal specimen.

Example 3

(15) An adequate amount of ZnCl.sub.2 was dissolved in an N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA) ionic liquid, to form an NiCl.sub.2 ionic liquid solution containing 0.1M of Zn.sup.2+ ion. Then, the magnesium metal specimen was immersed in a metal ionic liquid solution containing Zn.sup.2| ions to proceed with a replacement reaction. After 24 hours of reaction, the surface of the magnesium metal specimen was washed with the anhydrous ethanol, and the change of the surface morphology was observed by using a scanning electron microscope (SEM). As can be clearly observed from the surface morphology illustrated in FIG. 3, a zinc layer was coated on the surface of the magnesium metal specimen.

Example 4

(16) An adequate amount of TiF.sub.4 was dissolved in an N-butyl-N-methylpyrrolidinium dicyanamide (BMP-DCA) ionic liquid, to form an NiCl.sub.2 ionic liquid solution containing 0.1M of Ti.sup.4+ ion. Then, the magnesium metal specimen was immersed in a metal ionic liquid solution containing Ti.sup.4+ ions to proceed with a replacement reaction. After 24 hours of reaction, the surface of the magnesium metal specimen was washed with the anhydrous ethanol, and the change of the surface morphology was observed by using a scanning electron microscope (SEM). As can be clearly observed from the surface morphology illustrated in FIG. 4, a titanium layer was coated on the surface of the magnesium metal specimen.

Example 5

(17) An adequate amount of CuCl was dissolved in a 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA) ionic liquid, to form an ionic liquid solution containing 0.1M of Cu.sup.+ ion, wherein, the 1-ethyl-3-methylimidazolium dicyanamide (EMI-DCA) ionic liquid is represented by Formula (X):

(18) ##STR00004##

(19) Then, the zinc metal specimen was immersed in a metal ionic liquid solution containing Cu.sup.+ ions to proceed with a replacement reaction. After 24 hours of reaction, the surface of the zinc metal specimen was washed with the anhydrous ethanol, and the change of the surface morphology was observed by using a scanning electron microscope (SEM). As can be clearly observed from the surface morphology illustrated in FIG. 5, a copper layer was coated on the surface of the zinc metal specimen.

Example 6

(20) An adequate amount of CuCl was dissolved in a tributylmethyl ammonium dicyanamide (Bu.sub.3MeN-DCA) ionic liquid, to form an ionic liquid solution containing 0.1M of Cu.sup.| ion, wherein, the Bu.sub.3MeN-DCA ionic liquid is represented by Formula (XI):

(21) ##STR00005##

(22) Then, the aluminum metal specimen was immersed in a metal ionic liquid solution containing Cu+ ions to proceed with a replacement reaction. After 24 hours of reaction, the surface of the aluminum metal specimen was washed with the anhydrous ethanol, and the change of the surface morphology was observed by using a scanning electron microscope (SEM). As can be clearly observed from the surface morphology illustrated in FIG. 5, a copper layer was coated on the surface of the aluminum metal specimen.

Comparative Example 1

(23) The magnesium metal specimen was immersed in a pure BMP-DCA ionic liquid solution. After 24 hours of reaction, the surface of the magnesium metal specimen was washed with the anhydrous ethanol, to serve as a comparative magnesium metal specimen of the present invention.

Test Example 1

(24) In the replacement reactions of Example 1 to Example 4, the magnesium metal specimen was used as a working electrode, platinum was used as an auxiliary electrode, and a platinum wire placed in Ferrocene/Ferrocenium(Fc/Fc.sup.|=50/50 mol %) as the reference electrode. The three electrodes were then connected to Biologic SP-150, to measure the change of the open circuit potential of the magnesium metal specimen during the replacement reactions of Examples 1-4. The measurement results of the open circuit potential was shown in FIG. 7, wherein the magnesium ions contacted with the ionic liquid containing metal to initiate the replacement reaction to reduce the metal ions in solution on the surface of the magnesium metal. Because the reduced metal ions had a higher open circuit potential in the liquid, the open circuit potential was increased soon after the reaction started, and it can be observed for the result of the figure that the open circuit potential was increased rapidly in half an hour, indicating that the replacement reaction was quite fast.

Test Example 2

(25) Real-time analysis of X-ray absorption spectroscopy was conducted on the surface of the magnesium metal specimens of Examples 1-2 when the replacement reaction was taking place.

Test Example 2-1

(26) In Example 1, the magnesium metal specimen was immersed in an ionic liquid solution containing Cu.sup.+ ions, to carry out the replacement reaction. The real-time analysis of X-ray absorption spectroscopy of the magnesium metal surface was conducted after 1, 2, 3, 4, and 5 hours and 1 day after the replacement reaction started, and the X-ray absorption spectroscopy was shown in FIG. 8. In the replacement reaction of Example 1, as the Cu.sup.+ ions in the ionic liquid into were converted into a metallic state (Cu) and adhered onto the surface of the magnesium metal specimen to form a metal coating layer, the absorption peak of X-rays gradually shifted to the lower energy of pure metallic state with the progress of the replacement reaction, and the inflection point was close to the position of pure copper. Therefore, it can be deduced that the metal coating layer formed on the surface of the magnesium metal specimen during the replacement reaction in the ionic liquid was copper metal.

Test Example 2-2

(27) In Example 2, the magnesium metal specimen was immersed in an ionic liquid solution containing Ni.sup.2| ions, to carry out the replacement reaction. The real-time analysis of X-ray absorption spectroscopy of the magnesium metal surface was conducted after 1, 2, 3, 4, and 5 hours and 1 day after the replacement reaction started, and the X-ray absorption spectroscopy was shown in FIG. 9. In the replacement reaction of Example 2, as the Ni.sup.2+ ions in the ionic liquid were converted into a metallic state (Ni) and adhered onto the surface of the magnesium metal specimen to form a metal coating layer, the absorption peak of X-rays gradually shifted to the lower energy of pure metallic state with the progress of the replacement reaction. Therefore, it can be deduced that the metal coating layer formed on the surface of the magnesium metal specimen during the replacement reaction in the ionic liquid was nickel metal.

Test Example 3

(28) The coated magnesium metal specimens prepared in Example 1 to Example 4 and Comparative Example 1 and a pure magnesium metal specimen as the working electrode, a platinum wire as the auxiliary electrode, and Ag/AgCl as the reference electrode, were placed in an etching solution (0.1 M of Na.sub.2SO.sub.4) in an anaerobic environment. The polarization curve was measured at a scanning speed of 5 mV/sec, and the measurement result was shown in FIG. 10. The corrosion potential (E.sub.corr) of the coated magnesium metal specimens prepared in Example 1 to Example 4 and Comparative Example 1 and a pure magnesium metal specimen, and the anodic current density (i.sub.a) under a potential of −1.2 V, shown in FIG. 10 are summarized in Table 1:

(29) TABLE-US-00001 TABLE 1 E.sub.corr i.sub.a (at −1.2 V) (V vs. Ag/AgCl) (A/cm.sup.2) Example 1 −1.34 3.3 × 10.sup.−4 Example 2 −1.24 2.7 × 10.sup.−4 Example 3 −1.38 5.9 × 10.sup.−4 Example 4 −1.40 7.9 × 10.sup.−4 Comparative −1.42 10.1 × 10.sup.−4  Example 1 pure magnesium −1.57 19.0 × 10.sup.−4  metal specimen

(30) It can be can be clearly observed form the test result of this Example, that the corrosion potentials of the magnesium metal specimens provided by Example 1 to Example 4 after the replacement reaction were all higher than the magnesium metal specimen and the pure magnesium metal specimen of Comparative Example 1. Especially, for the pure magnesium metal specimen as the control group, when the potential is higher than its corrosion potential (−1.57 V), the current rises rapidly, showing poor corrosion resistance.

(31) In Example 1, the magnesium metal specimen with surface replacement of copper had a corrosion potential increasing from −1.57 V to −1.34 V (relative to Ag/AgCl). In Example 2, the magnesium metal specimen with surface replacement of nickel had a corrosion potential increasing from −1.57 V to −1.24 V (relative to Ag/AgCl). In Example 3, the magnesium metal specimen with surface replacement of zinc had a corrosion potential increasing from −1.57 V to −1.38 V (relative to Ag/AgCl). In addition, it can be observed from the polarization curves shown in FIG. 10 that in Example 1 and Example 2, when the potential was larger than the corrosion potential, the specimens exhibited a passivation effect, and until the scanning potential was greater than about −1 V, the current density was increased to the limiting current. Accordingly, it can be proved that the magnesium metal specimens having the metal coating (copper and nickel) provided by Examples 1-2 had a significantly improved and quite excellent corrosion resistance.

(32) The magnesium metal specimen having a titanium metal coating provided by Example 4 also had an improved corrosion resistance increasing from −1.57 V to −1.40 V. Although with the rise of the potential, no passivation effect was generated, the increase of the corrosion potential indeed, improved the corrosion resistance of the magnesium metal specimen.

(33) The results of the Test Example indicate that the formation of the copper coating layer on the magnesium metal specimens by the replacement reaction of the present invention may significantly improve the corrosion resistance of the magnesium metal specimens.

(34) Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.