Synergistic metal polycarboxylate corrosion inhibitors

Abstract

The invention comprises synergistic compositions of at least two metal carboxylates as corrosion inhibitors based on polycarboxylate anions and a variety of different cations. The inhibitors are designed to be added to film forming or other compositions to reduce the corrosion of the metal substrate on which the synergistic compositions are applied.

Claims

1. The process for treating metal to improve the metal's corrosion-resistance comprising coating the metal with a binder containing an effective amount of a corrosion-resistant inhibitor consisting essentially of a synergistic combination of at least one metal polycarboxylate derived from the stoichiometric reaction of a zinc compound and a diphenic acid to obtain the polycarboxylic metal salt; and at least one metal polycarboxylate derived from the stoichiometric reaction of a magnesium compound and succinic acid to obtain the polycarboxylic metal salt, wherein either the metal or the polycarboxylic acid in at least one of the polycarboxylic metal salts is different from the other carboxylic metal salts.

2. The process for treating metal to improve the metal's corrosion-resistance comprising coating the metal with a binder containing an effective amount of a corrosion-resistant inhibitor consisting essentially of a synergistic combination of at least one metal polycarboxylate derived from the stoichiometric reaction of a calcium compound and a diphenic acid to obtain a polycarboxylic metal salt; and at least one metal polycarboxylate derived from the stoichiometric reaction of a zinc compound and a succinic acid to obtain a polycarboxylic metal salt, wherein either the metal or the polycarboxylic acid in at least one of the polycarboxylic metal salts is different from the other polycarboxylic metal salts.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1: Performance of LP-6 aluminum rich primer by itself and with various zinc dicarboxylate compounds after 29 cycles (days) in GMW 14872 (from left to right in top row: LP6-F control (no inhibitors), LP6-F with zinc oxalate, LP6-F with zinc succinate; bottom row: LP6-F with zinc tartrate and LP6-F with zinc citrate, LP6-F with a blend of zinc oxalate and zinc citrate).

(2) FIG. 2: Performance of LP-6 aluminum rich primer by itself and with various zinc dicarboxylate compounds after 3 weeks in ASTM B117 (from left to right in top row: LP6-F control (no inhibitors), LP6-F with zinc citrate; bottom row: LP6-F with zinc oxalate, LP6-F with blend of zinc oxalate and zinc citrate).

(3) FIG. 3: Performance of LP-6 aluminum-rich primer by itself and with various zinc dicarboxylate compounds after 3 weeks in GMW 14872 (from left to right in top row: LP6-F control (no inhibitors), LP6-F with zinc citrate; bottom row: LP6-F with zinc oxalate, LP6-F with blend of zinc oxalate and zinc citrate).

DETAILED DESCRIPTION OF THE INVENTION

(4) The present invention relates to synergistic metal polycarboxylate combinations and to a method of treating metal to improve the metal's corrosion resistance. The method includes applying, to the surface of a metal, a coating or binder which comprises an effective amount of a synergistic mixture of metal polycarboxylates. More specifically, the subject invention is a synergistic blend of corrosion inhibitors, consisting of at least two different metal carboxylates. Anions, such as polycarboxylics chosen from linear and branched aliphatic molecules like oxalate, tartrate, succinate, and adipate, and aromatic molecules like phthalate, diphenate, mellitate and trimellitate. These are examples of some molecules. There are many other polycarboxylics acids which can be used for preparing the synergistic combination.

(5) The cations, for example include elements chosen from: Group IaLithium, potassium and sodium, Group IIaMagnesium, calcium, strontium, and barium, Group IIIbScandium, yttrium, lanthanum and the other lanthanides like cerium, praseodymium, neodymium, samarium, europium, gadolinium, etc., Group IVbTitanium and zirconium, Group VbVanadium and niobium, Group VIbChromium and molybdenum, Group VIIbManganese, Group VIIIIron, cobalt and nickel, IbCopper, Group IIbZinc, Group IIIaAluminum, and Group VaBismuth.

(6) The choice of cations and anions will influence water and organic solvent solubility which needs to be considered for the application of interest. Table 1 and 2 are examples of water solubility and solubility products for combinations of cations and anions. Inhibitors may be blended using the same metal, for example, zinc citrate and zinc oxalate, or they may be blended with different cations with the same or different anions, for example magnesium oxalate and zinc oxalate.

(7) At least two metal polycarboxylate inhibitors are blended with different molar ratios ranging from 0.1 to 20 parts by weight of each of the two metal carboxylates to obtain the maximum synergistic performance for a particular application. Inhibitors are used at varying concentrations in the particular vehicle or binder for the application. This may range from relatively low concentrations of a few weight percent, e.g., from 0.1 up to very high concentrations of 30 weight percent or parts by weight in the binder.

(8) The synergistic corrosion inhibitors may be combined in bulk after synthesis, or they may be blended during synthesis. For example, additional or different synergistic effects may be garnered by reacting oxalic acid with zinc nitrate and magnesium nitrate to achieve a compound with a mixed complex of zinc and magnesium oxalate. The solubility and corrosion-inhibiting properties of this compound can be different than the combination of separately synthesized zinc oxalate and magnesium oxalate compounds. Various synergistic combinations of polycarboxylate anions and cations, per the above show improved corrosion inhibition.

(9) TABLE-US-00001 TABLE 1 Water solubility of selected compounds Chemical Solubility g/100 mL, @ 20 C. unless noted Cation Anion Zn Mg Ca Mn Sr Ba Ce Pr Y Li Citrate Insol in Sol in water @ 0.08496 0.0406 g @ 0.3 61.2 @ water 298 K @ 18 & 18 & 15 nonahydrate 0.0959 0.0572 g @ 0.0482/ @ 25 25 tetradecahy- drate 0.0446 Oxalate 6.4 10{circumflex over ()}4 0.03 @ 18 6.8 Slightly 0.00461 @ 0.0022 4.1 7.4 0.0001 g @ Sol in @ 18 & 7.15 10{circumflex over ()}4 Sol in 18 10{circumflex over ()}5 @ 10{circumflex over ()}5 @ 25 15 parts 10{circumflex over ()}4 @ 26 water 25 25 water Nitrate 118.3 69.5 129.3 57.33 @ 70.5 9.2 50.9 @ 18 & 25 62.37 @ 25 Succinate 24.35 @ 15 & 1.276 0.270 0.418 66.36 @ 100 Tartrate 0.022 g & 0.0475 0.200 0.0279 0.005 @ 0.079 @ 0.041 @ 85 25 0 Carbonate 0.0206 @ 25 26 w/ CO2 0.0065 0.0065 @ 1.09 0.0022 Almost Insol in 1.33 saturation in 25 10{circumflex over ()}3 @ Insol water water 24 in Water Chloride 432 g/100 g @ 54.5 74.5 73.9 52.9 35.7 3 50.96 @ Sol in 78.5 25 & 614 g/ 13 water. 100 g @ 100 Benzoate 2.49 @ 17 & 6.16 @ 15 & 3.02 @ 5.4 @ 4.3 g @ 40 @ 100 2.41 @ 27.8 19.6 @ 100 26 24.7 15 & 10.1 g @ 100 Malate 0.9214 0.448 0.883 @ 18 & 0.8552 @ 25

(10) TABLE-US-00002 TABLE 2 Solubility products for selected compounds Chemical Solubility K.sub.SP, @ 25 C. unless noted Cation Anion Zn Mg Ca Mn Sr Ba Ca Pr Y Li Citrate Oxalate 1.38 4.83 2.32 1.70 10{circumflex over ()} 9 10{circumflex over ()} 8 10{circumflex over ()} 9 10 7 (dihydrate) (dihydrate) (mono (dihydrate) hydrate) Nitrate Succinate Tartrate Carbonate 1.48 2.38 3.36 2.24 5.60 2.58 1.03 8.15 10{circumflex over ()} 10 10{circumflex over ()} 6 10{circumflex over ()} 9 10{circumflex over ()} 11 10{circumflex over ()} 10 10{circumflex over ()} 9 10{circumflex over ()} 31 10{circumflex over ()} 4 (anhydrous) (trihydrate) (Calcite) 5.42 6.82 10{circumflex over ()} 11 10{circumflex over ()} 6 (mono) Chloride Benzoate
Composition Examples and Performance Data of Synergistic Combinations of Metal Carboxylates

(11) Zinc tartrate, zinc succinate and zinc adipate were synthesized by Materials Engineering Division personnel as follows:

EXAMPLE

(12) For a proof of principle synthesis 0.02 moles of the organic acid was dissolved in 30-100 milliliters of deionized/distilled water. NaOH was added to the mixture in equivalent molar ration to the number of carboxylate groups (0.04 moles for the di-carboxylates). The mixture was brought up to boiling temperature and refluxed for 3-6 hours. An equivalent molar ratio of Zinc Nitrate Hexahydrate was added to the reaction mixture. With 1-2 additional hours at reflux, all mixtures precipitated out a white crystalline product, which was vacuum filtered, dried and removed from filter paper. Infrared Spectroscopy of zinc tartrate confirmed the product against the spectrum published in the literature, and spectra of zinc succinate and adipate confirmed reaction completion by lack of remaining acid.

(13) Successful scale-up reactions up to 10 times (2.0 moles) the initial amount of reactants were performed. Reactions yielded greater than 90% product by mass in most cases.

(14) Drying the salts above 120 degrees Celsius overnight was sufficient to remove most residual water, as confirmed by TGA measurements. No significant mass loss was observed below 250 degrees Celsius.

(15) This simple reaction scheme is expected to produce the metal salt of any polycarboxylic acid provided the following are true: The acid is water soluble, the metal cation exists as a soluble reactant compound (such as zinc nitrate), and the product of the metal cation and carboxylate anion has low enough solubility as to precipitate out a majority of the product in water.

(16) Zinc oxalate, zinc tartrate, zinc succinate, zinc citrate, and a blend of zinc oxalate and zinc citrate were added to a base formulation of aluminum rich primer, LP6-F, which contains a two-component epoxy resin system, an epoxy modifier, solvents and AlZnIn powder. Wet primers were spray applied to zinc phosphate coated 1010 steel and 2024-T3 aluminum coated with MIL-DTL-81706 Type II TCP conversion coating. After curing, test panels were scribed and exposed to either ASTM B117 neutral salt fog or GMW 14872 cyclic corrosion tests.

(17) FIG. 1 shows the performance of the coatings on steel after 29 cycles (days) of the GMW 14872 test. It is clear that each inhibitor by itself improves the corrosion resistance of the LP6-F control, and that each inhibitor has different effectiveness, with the zinc oxalate being the least effective and the zinc citrate the most effective. The combination of zinc oxalate and zinc citrate, however, provides unexpected superior corrosion inhibition that is significantly better than either zinc compound by itself. Ratings shown in Table 3 reflect clearly what is seen in FIG. 1.

(18) TABLE-US-00003 TABLE 3 Standing rating data for images in FIG. 1 1st Digit-Scribe Appearance 2nd Digit-Corrosion (ASTM D1654) 3rd/4th Digit-Rusting (ASTM D610) 0 Bright and clean 0 No lifting of coating 0 >50% G: General 1 Bright with very slight staining 1 Lifting or loss of adhesion up to 1/64 (0.5 mm) 1 >33% S: Spot 2 Lusterous with moderate staining 2 Lifting or loss of adhesion up to 1/32 (1.0 mm) 2 >16% P: Pinpoint 3 Loss of luster, no product build up 3 Lifting or loss of adhesion up to 1/16 (2.0 mm) 3 >10% 4 Heavy staining, minor corrosion no product build up 4 Lifting or loss of adhesion up to 1/8 (3.0 mm) 4 >3% 5 Heavy staining, minor corrosion product build up 5 Lifting or loss of adhesion up to 3/16 (5.0 mm) 5 >1% 6 Moderate corrosion product build up 6 Lifting or toss of adhesion up to 1/4 (7.0 mm) 6 >0.3% 7 Major corrosion product build up 7 Lifting or loss of adhesion up to 3/8 (10.0 mm) 7 >0.1% 8 Severe corrosion product build up 8 Lifting or loss of adhesion up to 1/2 (13.0 mm) 8 >0.03% 9 Complete liting of coating above rust around scribe 9 Lifting or loss of adhesion up to 5/8 (16.0 mm) 9 >0.01% 10 Total consumption of coating around scribe 10 Lifting or loss of adhesion over 5/8 (>16.0 mm) 10 0.00% 1st Digit 2nd Digit 3rd Digit: Rusting, Scribe Corrosion Front Panel Number Appearance Reading Isolated Rating Isolated Notes - Comments 16-19-73 7 4 3-G 16-19-74 3 2 10 Crevice Corrosion Along Top Tape Edge 16-19-75 2 0 10 Slight Crevice Corrosion Along Top Tape Edge, Best of 16-19-76 5 0 5-G 16-19-77 5 1 5-G 16-19-78 5 0 2 5-G 16-19-79 4 0 6-P 16-19-80 5 2 3-G 16-19-81 6 3 10 Corrosion Eruption in Lower Left Corner 16-19-82 6 0 10 16-19-83 6 0 10 16-19-84 6 2 10 1 spot

(19) Similar synergistic performance is seen for the zinc citrate/zinc oxalate blend for the LP6-F primer on aluminum. FIGS. 2 and 3 show comparative images for the control and inhibited versions after 3 weeks exposure in ASTM B117 and GMW 14872, respectively. For the blend in FIG. 2, the synergistic performance can best be seen by looking at the scribed area of the topcoated (white) panels. For the control and zinc citrate, there is significant white corrosion present. For the zinc oxalate, the scribe is grayish. For the blend, the scribe is still shiny, similar to the primer-only (gray) panels. For the blend in FIG. 3, the synergistic performance can best be seen by looking at the shininess of the scribes for all the panels, which perform much better in general than in the ASTM B117 test. For the blend, all panels, primer only and with topcoat, the scribes are bright and shiny, which is superior to the control (all grayish scribes) or individual zinc compounds (all gray for the zinc oxalate set and gray for the zinc citrate top-coated panel).

(20) FIG. 2 shows the performance of LP-6 aluminum rich primer by itself and with various zinc dicarboxylate compounds after 3 weeks in ASTM B117 (from left to right in top row: LP6-F control (no inhibitors), LP6-F with zinc citrate; bottom row: LP6-F with zinc oxalate, LP6-F with blend of zinc oxalate and zinc citrate.

(21) FIG. 3 shows the performance of LP6-F aluminum rich primer by itself and with various zinc dicarboxylate compounds after 3 weeks in GMW 14872 (from left to right in top row: LP6-F control (no inhibitors), LP6-F with zinc citrate; bottom row: LP6-F with zinc oxalate, LP6-F with blend of zinc oxalate and zinc citrate).

(22) As illustrated in FIGS. 1, 2 and 3 and in Tables 1-3 the corrosion-resistant inhibitors consist essentially of synergistic combinations of

(23) (A) at least one metal polycarboxylate derived from a stoichiometric reaction of metal compounds and polycarboxylic acids to obtain polycarboxylic metal salts and

(24) (B) at least one metal polycarboxylate derived from a stoichiometric reaction of metal compounds and polycarboxylic acids to obtain polycarboxylic metal salts, wherein either the metal or the polycarboxylic acid in at least one of the polycarboxylic metal salt combinations is different from the other combination of polycarboxylic metal salts. For example, where the corrosion-resistant synergistic combination consist of from about 0.1 to 20 parts by weight of zinc oxalate and from about 0.1 to 20 parts by weight of zinc citrate, it is essential that either the zinc or the polycarboxylic acid of the polycarboxylic metal salt of either paragraph (A) or (B) be different. It is essential that where the carboxylic metal salts are derived from the stoichiometric reaction of several different metal compounds and several different polycarboxylic acids, it is essential that at least one of the polycarboxylic metal salts has a different anion or cation from any of the other polycarboxylic metal salt.

(25) A variety of metals such as steel, aluminum and metal alloys can be protected by using the synergistic compositions and methods of this invention. The present invention relates to coating the metals with compositions comprising the synergistic metal polycarboxylates. The metals to be protected may be part of a structure made of a number of different parts which include different metals in contact with each other. At the point of contact of the different metals is the point of galvanic corrosion. The use of the synergistic polycarboxylic metal salts of this invention in a binder or coating composition allows the corrosion-inhibiting compositions to be applied on substrates of different metals while improving the corrosion resistance of one metal without increasing the corrosion of a different metal component. The method comprises using a binder or coating on the metal which includes an effective amount of the synergistic polycarboxylic metal salts. The coatings can include organic systems such as a simple binder or an organic coating including paints and various other known metal inorganic or organic coatings.

(26) For example, the binder or coating can range from about 50 to 99% or parts by weight of the total composition and the synergistic polycarboxylic metal salts can range from about 0.1 to 10% or 1.0-3.0% by weight of the coating. The coatings include inorganic, polymeric or organic binders, such as paints, lubricants, oils, greases and the like.

(27) Suitable polyisocyanate polymers or prepolymers, include, for example, aliphatic polyisocyanate prepolymers, such as 1,6-hexamethylene diisocyanate homopolymer (HMDI) trimer, and aromatic polyisocyanate prepolymers, such as 4,4-methylenediphenylisocyanate (MDI) prepolymer and combinations of two or more aliphatic polyisocyanate pre-polymers.

(28) A preferred binder for the synergistic metal carboxylate salts comprise the polyurethanes, and more particularly the aliphatic polyurethanes derived from the reaction of polyols and multifunctional aliphatic isocyanates and the precursors of the urethanes. Preferred polyisocyanates include hexamethylene diiocyanate and methylene-bis-(4-cyclohexyl isocyanate) DESMODUR-N. By selecting the proper polyols and by adjusting the NCO to OH ratio, the physical properties and efficiency of the film such as the strength of film, flexibility and solvent resistance can be controlled.

(29) Other binders include the polymers or epoxy prepolymers, for example, any epoxy resin, including at least one multifunctional epoxy resin. Examples of epoxy resins comprise polyglycidyl ethers of pyrocatechol, resorcinol hydroquinone and 4,4-dihydroxydiphenyl methane. Among the commercially available epoxy resins are polyglycidyl derivatives of phenolic compounds, such as the tradenames EPON 828, EPON 1001 and EPON 1031.

(30) While this invention has been described by a number of specific examples, it is obvious that there are other variations and modifications which can be made without departing from the spirit and scope of the invention as particularly set forth in the appended claims.