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 attach 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.
• U.S. Patent 4, 209, 398 discloses a water treatment composition
• a water treatment composition comprising a polymer containing a structural unit that is derived from a monomer having an ethylenically unsaturated bond and one or more carboxyl radicals, at least a portion of which radicals have been modified.
• Compounds such as inorganic phosphates, phosphonic acids, organic phosphoric acid esters and polyvalent metal salts are combined with the polymer for treating the particular system.
• the polymer may be used in combination with conventional corrosion inhibitors for iron, steel, copper, copper alloys or other metals, conventional scale and contamination inhibitors, metal ion sequestering agents and other conventional water treating agents.
• corrosion inhibitors there are can be enumerated chromates, bichromates, tungstate, molybdates, nitrites, borates, silicates, oxycarboxylic acids, amino acids, catechols, aliphatic amino surface active agents, benzotriazole, and mercaptobenzotriazole.
• U.S. Patent 3,658,710 discloses a method of removing tubercles of corrosion from a substrate and inhibiting scale formation using organic polymers and silica and/or chromium compounds.
• a second polymer, such as an organic phosphonate may also be used.
• 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 units derived from acrylic acid or derivatives thereof (AA) and 2-hydroxy-propyl acrylate units (HPA).
• AA acrylic acid or derivatives thereof
• HPA 2-hydroxy-propyl acrylate units
• 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/HPA 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
• the polymers are considered, more broadly, to have a mole ratio of AA:HPA of from about 1:4 to 36:1. This mole ratio is preferably 1:1 to 11:1, and most preferably 1:1 to 5:1.
• the only criteria that is considered to be of importance with respect to mole ratios is that the copolymer 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 point of view, the polymers having a mole ratio of AA:HPA of 1:1 to 5:1 are considered the best.
• the polymers preferably have a molecular weight of from 1,000 to 50,000 with from 2,000 to 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 2-hydroxypropyl acrylate can be prepared by reacting acrylic acid with propylene oxide.
• the polymers of the invention may also be prepared by reacting a polyacrylic acid or derivative thereof with an appropriate amount of propylene oxide. The reaction takes place at the COOH or COM group of the units to provide the hydroxylated propyl acrylate unit.
• 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 having the structural formulas: wherein M is as earlier defined. It is noted that in aqueous solution with hydroxypropyl acrylate unit 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. 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 amount 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 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 is 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 HCI 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 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 (%) 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) and millimetres per year (mmpy).

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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/en not_active Expired
• 1981
  • 1981-03-20 EP EP81301199A patent/EP0037221B1/en not_active Expired
  • 1981-03-20 DE DE8181301199T patent/DE3164965D1/de not_active Expired

Patent Citations (1)

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