CORROSION INHIBITOR COMPOSITION FOR MAGNESIUM OR MAGNESIUM ALLOYS

Abstract

The present invention relates to novel corrosion inhibitor compositions for magnesium or magnesium alloys and to a process for inhibiting the corrosion of such metals using such compositions. The corrosion inhibitor composition comprises a compound comprising a carboxyl group preventing the re-deposition of noble impurities which significantly decreases the corrosion rate by complexing said noble impurities, e.g. iron, nickel and copper.

Claims

1. An article made of magnesium or a magnesium alloy coated with a coating composition comprising at least one corrosion inhibiting compound of Formula (1): ##STR00002## wherein R.sup.4 is one or more substituents selected from the group consisting of hydroxy; alkyl, wherein the alkyl group is optionally substituted with one or more substituents selected from hydroxy and carboxy; carboxy; SO.sub.3H and NH.sub.2, and salts thereof; or the coating composition comprises 3,5-dinitro salicylic acid or salts thereof as at least one corrosion inhibiting compound.

2. The article of claim 1, wherein the compound of Formula (1) is selected from the group consisting of 3-methylsalicylic acid, 4-methylsalicylic acid, 5-methylsalicylic acid, 6-methylsalicylic acid, 3-sulfosalicylic acid, 4-sulfosalicylic acid, 5-sulfosalicylic acid, 6-sulfosalicylic acid, 3-aminosalicylic acid, 4-aminosalicylic acid, 5-aminosalicylic acid, 6-aminosalicylic acid, 3,5-dinitro salicylic acid and salts thereof.

3. The article of claim 2, wherein the compound of Formula (1) is selected from the group consisting of 4-aminosalicylic acid, 5-aminosalicylic acid, 5-methylsalicylic acid, 3,5-dinitro salicylic acid and salts thereof

4. The article of claim 1, wherein the salts of compounds of Formula (1) are selected from their alkali metal or earth alkaline metal salts.

5. The article of claim 1, wherein the corrosion inhibiting compound is present in cavities of porous nano- or microparticles distributed within the coating.

6. The article of claim 1, wherein the corrosion inhibiting compound is present in micro- and nano-pores produced on the surface of magnesium or magnesium alloys.

7. The article of claim 6, wherein the corrosion inhibiting compounds are incorporated in nano- and microparticles distributed in micro- and nano-pores produced on the surface of magnesium or magnesium alloys.

8. A method for inhibiting the corrosion of magnesium or magnesium alloys comprising the steps of: a) providing magnesium or a magnesium alloy and b) coating the magnesium or magnesium alloy with a corrosion inhibiting coating comprising at least one corrosion inhibiting compound of Formula (1): ##STR00003## wherein R.sup.4 is one or more substituents selected from the group consisting of hydroxy; alkyl, wherein the alkyl group is optionally substituted with one or more substituents selected from hydroxy and carboxy; carboxy; SO.sub.3H and NH.sub.2, and salts thereof; or the coating composition comprises 3,5-dinitro salicylic acid or salts thereof as at least one corrosion inhibiting compound.

9. The method of claim 8, further comprising a step a1) between steps a) and b), wherein in step a1) the magnesium or magnesium alloy is pretreated with the corrosion inhibiting composition.

Description

[0020] FIG. 1 shows the results (normalized values) of hydrogen evolution measurements during immersion of CP Mg (commercial purity Mg containing Fe220 ppm) in 0.5% NaCl containing 0.05 M of salicylic acid (sodium salt), 5-sulfosalicylic acid (sodium salt), 4-aminosalicylic acid (sodium salt), 5-methylsalicylic acid (sodium salt), 3,5-dinitrosalicylic acid (sodium salt), 3-methylsalicylic acid (sodium salt), 1,2,4-triazole (comparative), benzotriazole (comparative) and NaCl (comparative); pH of resulting solutions of sodium salts (adjusted by NaOH) was 5.6 to 6.9). Concentration of 3,5 dinitrosalicylic acid sodium salt was 0.002M. Concentration of all other inhibitors was 0.05M.

[0021] FIG. 2 shows the inhibiting efficiency (%) calculated from the data of FIG. 1 at 20 hours of immersion. Concentration of 3,5 Dinitrosalicylic acid was 0.002M. Concentration of all other inhibitors was 0.05M.

[0022] FIG. 3 shows the results (normalized values) of hydrogen evolution measurements during immersion of magnesium alloy WE43(Fe38 ppm) in 0.5% NaCl containing 0.05 M of salicylic acid (sodium salt), 4-methylsalicylic acid (sodium salt), 4-aminosalicylic acid (sodium salt), 5-methylsalicylic acid (sodium salt), 3,5-dinitrosalicylic acid (sodium salt), 3-methylsalicylic acid (sodium salt), 5-aminosalicylic acid (sodium salt) 1,2,4-triazole (comparative), benzotriazole (comparative) and NaCl (comparative); pH of resulting solutions of sodium salts (adjusted by NaOH) was 5.6 to 6.9). Concentration of 3,5-dinitrosalicylic acid sodium salt was 0.002M. Concentration of 5-methylsalicylic acid sodium salt was 0.03M. Concentration of all other inhibitors was 0.05M.

[0023] FIG. 4 shows the results (normalized values) of hydrogen evolution measurements during immersion of magnesium alloy AZ91(Fe22 ppm) in 0.5% NaCl containing 0.05 M of salicylic acid (sodium salt), 4-methylsalicylic acid (sodium salt), 4-aminosalicylic acid (sodium salt), 5-methylsalicylic acid (sodium salt), 3,5-dinitrosalicylic acid (sodium salt), 3-methylsalicylic acid (sodium salt), 5-aminosalicylic acid (sodium salt) 1,2,4-triazole (comparative), benzotriazole (comparative) and NaCl (comparative); pH of resulting solutions of sodium salts (adjusted by NaOH) was 5.6 to 6.9). Concentration of 3,5-dinitrosalicylic acid sodium salt was 0.002M. Concentration of all other inhibitors was 0.05M.

[0024] In the examples shown in FIGS. 1 to 4, the corrosion of the magnesium or magnesium alloy in solution was determined by measuring the amount of evolving hydrogen because hydrogen is formed upon oxidation (corrosion) of Mg to Mg.sup.2+ at the surface of the magnesium or magnesium alloy. The more magnesium is oxidized to Mg.sup.2+ during corrosion, the more hydrogen is formed.

[0025] As can be seen in FIGS. 1 to 4, the novel corrosion inhibiting compounds efficiently protect the magnesium and magnesium alloys from corrosion and show significantly improved corrosion inhibiting efficiencies compared to 1,2,4-triazole and benzotriazole as known from U.S. Pat. No. 6,569,264 B1.

[0026] As it is shown in FIG. 2, salicylic acid shows a corrosion inhibiting efficiency of more than 60% better than benzotriazole and about 55% better than 1,2,4-triazole known from the prior art. Further improvements are achieved when 4-aminosalicylic acid, 5-aminosalicylic acid, 5-methylsalicylic acid, 3,5-dinitro salicylic acid and salts thereof are used as corrosion inhibitors. The values of the inhibiting efficiency (IF) were calculated using the following equation:

[00001]$\mathrm{IE}=\frac{{\mathrm{CR}}_0-{\mathrm{CR}}_{\mathrm{inh}}}{{\mathrm{CR}}_0}.Math.100.Math.\%.$

were CR.sub.0 is the corrosion rate in pure 0.5% NaCl and CR.sub.inh is the corrosion rate in the presence of NaCl and inhibitor. The corrosion rate was determined as amount of H.sub.2 (ml) evolved at 20 hours of immersion (one mole of evolved hydrogen is equal to one mole of dissolved magnesium).

[0027] The inhibitors are active in a wide range of concentrations, as demonstrated in FIGS. 3 and 4.

[0028] As it is evident from FIG. 4, the corrosion inhibiting effect of the novel corrosion inhibiting compounds is not restricted to a specific magnesium alloy, but present for a large variety of different magnesium alloys, e.g. HP Mg 51, CP Mg 220, WE43, ZE41, E21, AZ31, AZ91 or AM50. Independently of the magnesium alloy, the novel corrosion inhibiting compounds show a significantly improved corrosion inhibiting effect compared to 1,2,4-triazole.