Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F11/00—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent
  • C23F11/08—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in other liquids

Definitions

• the present invention relates to a method and a composition for reducing corrosion of metal surfaces in contact with aqueous systems.
• Chromates are widely referred to in the literature, and their effectiveness in reducing the rate of corrosion of metallic surfaces exposed to corroding aqueous mediums is well known. However, if used in low concentrations these inhibitors can cause considerable pitting and tuberculation. Indeed, if added in insufficient quantities to stop metal surface attack altogether, corrosion can become so severely localized and the intensity of attack so intense that perforations may occur more extensively than if no inhibitor treatment had been added.
• a chromate-based corrosion inhibitor for metal surfaces exposed to a corroding aqueous medium consists essentially of (i) water-soluble chromate and (ii) a particular type of water-soluble polymer comprised of moieties derived from acrylic acid or derivatives thereof (AA) and hydroxylated lower alkyl acrylate moieties (HAA). It was unexpectedly discovered that when combined with the polymer, very low levels of chromate could successfully be used for corrosion inhibition in aqueous mediums without the use of additional treatment compounds such as zinc and phosphate.
• zinc, a heavy metal, and phosphate a compound which causes eutrophication
• zinc, a heavy metal, and phosphate a compound which causes eutrophication
• methods according to the present invention would comprise the use of zinc-free corrosion inhibitor treatments comprising components (i) and (ii) as defined above.
• methods according to the present invention would comprise the use of zinc-free and phosphate free corrosion inhibitors comprising the noted components (i) and (ii).
• the present invention relates to a corrosion inhibitor treatment comprising water-soluble chromate AA/HAA wherein the chromate is added in an amount of less than 5 parts of active chromate per million parts of aqueous medium.
• the present invention is considered to have applicability to any aqueous system, it is particularly useful in cooling water systems. Accordingly, the present invention will hereinafter be described as it relates to cooling water systems.
• AA acrylic acid compound
• M is a water-soluble cation, e.g., NH 4 , alkali metal (K,
• the polymers are considered, most broadly, to have a mole ratio of AA:HAA of from about 1:4 to 36:1. This mole ratio is preferably about 1:1 to 11:1, and most preferably about 1:1 to 5:1.
• the only criteria that is considered to be of importance with respect to mole ratios is that the copolysier should be water-soluble. As the proportion of hydroxylated alkyl acrylate moieties increases, the solubility of the copolymer decreases. It is noted that, from an efficacy pointof view, the polymers having a mole ratio of AA:HAA of 1:1 to 5:1 are considered the best.
• the polymers preferably have a molecular weight of from about 1,000 to about 50,000 with from about 2,000 to about 6,000 being most preferred.
• the polymers utilized in accordance with the invention can be prepared by vinyl addition polymerization or by treatment of an acrylic acid or salt polymer. More specifically, acrylic acid or derivatives thereof or their water soluble salts, e.g., sodium, potassium, ammonium, etc. can be copolymerized with the hydroxy alkyl acrylate under standard copolymerization conditions utilizing free radical initiators such as benzoyl peroxide, azobisisobutyronitrile or redox initiators such as ferrous sulfate and ammonium persulfate. The molecular weight of the resulting copolymer can be controlled utilizing standard chain control agents such as secondary alcohols (isopropanol), mercaptans, halocarbons, etc. Copolymers falling within the scope of the invention are commercially available from, for example, National Starch Company.
• the hydroxy alkyl acrylate can be prepared by the addition reaction between the acrylic acid or its derivatives or water soluble salts and the oxide of the alkyl derivative desired.
• the preferred monomer of the present invention is the propyl derivative. Accordingly, to obtain the hydroxylated monomer, acrylic acid is reacted with propylene oxide to provide the hydroxypropyl acrylate monomer.
• the polymers of the invention may also be prepared by reacting a polyacrylic acid or derivative thereof with an appropriate amount of an alkylene oxide having from 2 to 6 carbon atoms such as ethylene oxide, propylene oxide and the like. The reaction takes place at the COOH or COM grqup of the moieties to provide the hydroxylated alkyl acrylate moiety.
• the polymer prepared either by copolymerization of AA with hydroxypropyl acrylate (HPA) or reaction of AA with propylene oxide would be composed primarily of units or moieties having the structural formulas: where M is as earlier defined. It is noted that in aqueous solution ) the hydroxypropyl acrylate moiety is in equilibrium with a minor amount of 1-methyl-2-hydroxyethyl acrylate.
• chromate compounds which could be used in practicing methods according to the present invention are described in U.S. 2,900,222 to Kahler et al which patent is incor-25 porated herein by reference. These compounds would include alkali metals or any water-soluble compound that contains hexavalent chromate and provides chromate radical in water solutions.
• Illustrative water-soluble chromate compounds are sodium chromate dihydrate, sodium chromate anhydrous, sodium chromate tetrahydrate, sodium chromate hexahydrate, sodium chromate decahydrate, potassium dichromate, potassium chromate, ammonium dichromate and chromic acid.
• the amount of each constituent added to the cooling water would, of course, be an effective amount for the purpose and would depend on such factors as the nature and severity of the corrosion problem being treated and the temperature and pH of the cooling water.
• active polymer As little as about 0.5 part per million parts of cooling water (ppm) should be effective, while about 2 ppm is the preferred lower limit. Based on economic considerations, the polymer could be fed in amounts as high as about 200 ppm, with about 50 ppm being the preferred upper limit.
• ppm part per million parts of cooling water
• active chromate that is, active hexavalent chromate ion
• active hexavalent chromate ion as little as about 0.5 ppm should be effective.
• the upper limit would depend on such factors as cost and toxicity and could be as high as about 150 ppm.
• the preferred upper limit is about 50 ppm. It is most preferred that the chromate be fed in amounts which are less than 5 ppm.
• chromate and the polymer may however be added to the aqueous system separately or together.
• the treatment is preferably used as an aqueous solution.
• the constitutes are combined by simply adding them to water. Should long-term stability problems be experienced, a two-barrel treatment may be more desirable. Of course, the constituents could be combined in any relative proportions in dry form.
• compositions according to the present invention could vary widely and preferably comprise, on a weight basis:
• the cooling water it is possible for the cooling water to have a pH of about 5.5 to 9.5. More commonly, the pH is about 6.5 to 8.5, with about 6.5 to 7.5 being most common.
• Corrosion rate was determined by weight loss measurement. Prior to immersion, coupons were scrubbed with a mixture of trisodium phosphate-pumice, rinsed with water, rinsed with isopropyl alcohol and then air dried. Weight measurement to the nearest milligram was made. At the end of one day, a weighed coupon was removed and cleaned. Cleaning consisted of immersion into a 50% solution of HC1 for approximately 20 seconds, rinsing with tap water, scrubbing with a mixture of trisodium phosphate-pumice until clean and then rinsing with tap water and isopropyl alcohol. When dry, a second weight measurement to the nearest milligram was made. At the termination of the tests, the remaining coupon was removed, cleaned and weighed.
• the results of these tests are reported below in TABLE 1 in terms of per cent ( p ) corrosion inhibition of various treatments as compared to an untreated control test.
• the polymer tested was an acrylic acid/hydroxypropyl acrylate copolymer (AA/HPA) having a mole ratio of AA to HPA of 3:1 and a nominal molecular weight of 6000.
• the chromate compound used was sodium dichromate dihydrate. The amounts of chromate reported are active chromate dosages in ppm, and the pH of the test water was 8. The corrosion rates are reported in mils per year (mpy).

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Chemical Treatment Of Metals (AREA)

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• 1980
  • 1980-06-24 AU AU59557/80A patent/AU533121B2/en not_active Ceased
  • 1980-06-30 NZ NZ19419180A patent/NZ194191A/xx unknown
  • 1980-10-31 CA CA000363696A patent/CA1147137A/fr not_active Expired
• 1981
  • 1981-03-20 DE DE8181301199T patent/DE3164965D1/de not_active Expired
  • 1981-03-20 EP EP81301199A patent/EP0037221B1/fr not_active Expired

Patent Citations (3)

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