EP0797691B1 - Verfahren zur erhöhung der korrosionsbeständigkeit von metalleund legierung durch behandelnmit seltenen erde-elementen - Google Patents

Verfahren zur erhöhung der korrosionsbeständigkeit von metalleund legierung durch behandelnmit seltenen erde-elementen Download PDF

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EP0797691B1
EP0797691B1 EP95933276A EP95933276A EP0797691B1 EP 0797691 B1 EP0797691 B1 EP 0797691B1 EP 95933276 A EP95933276 A EP 95933276A EP 95933276 A EP95933276 A EP 95933276A EP 0797691 B1 EP0797691 B1 EP 0797691B1
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alloy
rare earth
cerium
treatment
alloys
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EP0797691A1 (de
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Yucheng Lu
Michael Brian Ives
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McMaster University
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    • 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
    • C23F11/04—Inhibiting corrosion of metallic material by applying inhibitors to the surface in danger of corrosion or adding them to the corrosive agent in markedly acid liquids
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/50—Treatment of iron or alloys based thereon
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/52—Treatment of copper or alloys based thereon
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/56—Treatment of aluminium or alloys based thereon
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/68—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous solutions with pH between 6 and 8
    • 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
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/78—Pretreatment of the material to be coated

Definitions

  • the present invention relates to a process of increasing corrosion resistance of metals and alloys by surface treatment with one or more elements from the rare earth group of elements. More particularly, the present invention provides a method of increasing corrosion resistance of metals such as stainless steels, nickel based alloys, aluminum alloys and copper alloys in aqueous solutions by treatment in a solution of rare earth salts.
  • crevice corrosion remains a problem in these alloys. For example, it can be manifest as under-deposit corrosion, as has been found in recent ocean tests even in steels with high molybdenum and chromium contents, see M.B. Ives, in Proceedings “Applications of Stainless Steels '92", Jernechret , Sweden, 436 (1992).
  • crevice corrosion in aerated solutions involves an oxygen concentration cell.
  • cathodic reduction of the depolarizers on the large areas surrounding the attacked site is necessary to support the high rate of anodic dissolution. It has been disclosed by Y.C. Lu, J.L. Luo and M.B. Ives, ISIJ International, Vol. 31, 210 (1991), that the enhanced cathodic reduction of oxidant adjacent to a localized attack site produces an increase of localized corrosion.
  • a powerful means of preventing crevice corrosion would be to constrain or significantly inhibit the cathodic reactions such as oxygen reduction, hydrogen evolution and the like.
  • cerium ion implantation improves the crevice corrosion resistance of UNS S31603 stainless steel as determined by both anodic polarization in aerated 0.1 M Na 2 SO 4 + 0.6 M NaCI solution and by the ASTM G48 B crevice test in 10% ferric chloride hexahydrate solution.
  • ion-implantation is not readily amenable to economically treating large surface areas materials. Further, ion-implantation may induce radiation damage at the surface of the metal or alloy which may have detrimental structural effects so that ion-implantation has practical limitations.
  • Aluminum alloys are of commercial and industrial significance comparable or greater than that of stainless steels. Corrosion and corrosion induced failure is a major problem associated with aluminum alloys. Aluminum alloys are widely used in very corrosive environments, for example in automotive applications such as brazed aluminum heat exchangers, coolers, evaporators, radiators and the like. Known methods of corrosion protection of aluminum and aluminum alloys involve the use of chromate ions to form conversion coatings on the alloys. Environmental concerns associated with chromate ions are a drawback to widespread use of this technique. Other strategies for increasing corrosion resistance of aluminum based alloys based on physical deposition methods such as sputtering are inherently limited since the area being coated is by line-of-sight from the source.
  • Cerium containing solution treatment has been effective in improving the localized corrosion resistance of aluminum alloys.
  • chemical passivation of aluminum alloys immersed in cerium chloride solutions for 7 days or longer produces a conversion coating on the aluminum alloy exhibiting increased corrosion resistance, see F. Mansfield, S.Lin, S. Kim and H. Shih, J. Electrochem. Soc., Vol. 137, 78 (1990).
  • the aluminum alloys have dipped into hot cerium salt solutions followed by direct current (DC) anodic polarization in a molybdate solution to produce an anodized passive layer containing Ce and Mo as disclosed in F. Mansfield, V. Wang and H. Shih, J. Electrochem.
  • Alternating current (AC) passivation of aluminum alloys in the same types of cerium salt solutions has also been used to form conversion coatings exhibiting corrosion resistance as disclosed in H. Shih, V. Wang and F. Mansfield, Corrosion 91, Paper # 136, NACE, Houston (1991).
  • the use of rare earth metal chlorides as inhibitors for aluminum alloys in NaCI has been disclosed in D.R. Arnott, B.R.W. Hinton and N.E. Ryan, Corrosion, Vol. 45, 12 (1989).
  • United States Patent No. 5,194,138 issued to Mansfeld is directed to a multi-step process for forming a corrosion resistant aluminum surface coating by exposure first to a cerium non-halide solution followed by exposure to an aqueous cerium halide (chloride) solution.
  • the purpose of the coating is to provide a uniform coating to protect the Al surface against anodic attack causing pitting corrosion.
  • This patent also teaches exposing the aluminum based surface to molybdenum solutions and electrochemically positively charging the surfaces into the passive region.
  • United States Patent No. 5,221,371 issued to Miller discloses nontoxic corrosion resistance conversion coatings for aluminum and Al alloys. The process is a multi step process using acidic solutions comprising cerium chloride and potassium permanganate alone or in combination with strontium chloride. United States Patent No. 5,356,492 issued to Miller is very similar to '371 but substitutes hydrogen peroxide for potassium permanganate.
  • Patent publication WO-A-95/08008 is directed to a cleaning solution for used in a multi-step method for chemically cleaning surfaces of aluminum and' its alloys.
  • the method provides a means of pre-treating Al alloy surfaces prior to application of other coatings such as paint layers, platings or conversion coatings to improve the coating.
  • the method involves forming a cerium conversion coating to cover the aluminum surface.
  • United States Patent No. 5,362,335 issued to Rungta discloses a four step process directed to forming a corrosion resistant surface on aluminum alloys only using cerous chlorides solutions. A bohmite film is first formed on the aluminum alloy surface after which the bohmite coated sample is then subjected to a drying step at about 200°F.
  • the present invention provides a method for increasing the corrosion resistance of metals and alloys by exposing the surface of the metals to a solution.
  • the methods may be used to treat chromium, molybdenum, nickel, copper, a range of austenitic and ferritic stainless steels, nickel based alloys, aluminum and aluminum alloys, copper and copper alloys, chromium, molybdenum, nickel and the like to improve the localized corrosion resistance of the alloys.
  • the corrosion behaviour of treated and untreated samples has been compared using a combination of electrochemical measurement techniques in an aerated 0.6M NaCl + 0.1M Na 2 SO 4 solution, corrosion tests and field tests in natural seawater.
  • the present invention provides a method of treating a surface of a metal or alloy such as stainless steels, copper and its alloys, nickel based alloys, and aluminium and alloys thereof to increase corrosion resistance by modification of the surface to inhibit cathodic processes.
  • the method consists essentially of exposing a metal or alloy surface to a substantially halide-free aqueous solution comprising a salt of at least one rare earth element selected from yttrium, gadolinium, cerium, europium, terbium, samarium, neodymium, praseodymium, lanthanum, holmium, ytterbium, dysprosium, erbium, and combinations thereof, and a pH-modifying agent present in an amount effective to adjust the pH to from about 0.5 to about 6.5.
  • rare earth element refers to the lanthanide series of elements in the periodic table with proton numbers ranging from cerium (58) to lutetium (71) inclusive.
  • rare earths specifically refers to the oxides of the rare earth elements, it is used more generally to refer to this particular group of elements both in chemical practise and hereinafter.
  • the data indicates that for the untreated UNS N08904 disc the cathodic current is rotation-speed dependent.
  • the cathodic reaction rates, i.e. cathodic currents on the cerium-treated electrodes are shifted to more negative potentials and are greatly restrained.
  • the current for oxygen reduction does not apparently depend on rotation speed.
  • Figure 2 shows the disc current, measured from UNS N08904 discs at -950mV, as a function of the square root of disc angular velocity.
  • the straight line fit of the data indicates the reduction of oxygen on the untreated stainless steel is mass transport limited.
  • the current measured on the cerium-treated UNS N08904 steel was greatly reduced and did not depend significantly on rotation speed.
  • the data show clearly that the cathodic electrode reaction is inhibited by the cerium nitrate treatment.
  • the electrode process is controlled predominantly by charge transfer processes at the electrode surface.
  • the cerium pretreatment was also found to influence the anodic characteristics of these stainless steels.
  • Figure 3 the anodic polarization of untreated and treated UNS S31603 steel are compared.
  • the passive range was extended greatly by cerium treatment.
  • the breakdown potential has been raised about 800 mV.
  • the passive current density was also reduced significantly. This result indicates that the cerium treatment also stabilizes passivity and inhibits breakdown.
  • X-ray photoelectron spectroscopy has previously been used to help identify the chemical state of the cerium present on treated surfaces.
  • the position of the 3d 5/2 peak was determined to be ⁇ 888 eV, which compares with values for a Ce(NO 3 ) 3 standard of ⁇ 889 eV, and a CeO 2 standard of ⁇ 882 eV (data not shown).
  • Clearly the cerium was present in a trivalent form.
  • a very small amount of nitrogen was also detected by XPS analysis on cerium treated steel, and its peak position ( ⁇ 401 eV) may suggest the presence of NO - rather than nitrate (408 eV) or nitride (397 eV).
  • the oxygen spectrum showed both O -2 and OH - signals of about equal intensity.
  • cerium may form Ce 3+ complexes or oxy-hydroxide in the surface of the treated steels.
  • Cerium treatment of iron did not result in an observable improvement in corrosion resistance of the iron, based upon comparison of galvanostatic and potentiodynamic scans on treated and untreated samples (data not shown).
  • the role of the cerium treatment with metals or alloys with chromium present appears to be to produce a surface region enriched with chromium with the cerium oxide/oxyhydroxide either blocking the active sites for cathodic reduction or inhibiting electron transfer through the film.
  • the E Final for samples treated in 0.1 M gadolinium nitrate, neodymium nitrate and praseodymium nitrate are each about -1000 mV(SCE).
  • samples treated in solutions containing cerium, europium, samarium, terbium and ytterbium nitrates exhibited E Final values of about -600 mV (SCE).
  • Samples treated in solutions containing erbium, yttrium, lanthanum, dysprosium and holmium nitrates exhibited values for F Final of about-550 mV(SEC), see Figure 8.
  • the remaining rare earth elements including scandium, lutetium, thulium and promethium were not tested but the inventors contemplate that treatment with their corresponding nitrates would also provide similar results in view of the fact that inhibition was unexpectedly obtained with all the rare earths tested and the chemical behaviour of the lanthanides are very similar.
  • compositions using rare earth chlorides were tested.
  • the chlorides exhibited no efficacy for increasing the corrosion resistance of the steels.
  • the ineffectual nature of the rare earth chlorides may be understood in view of the fact that the presence of chlorides in particular, and halide ions in general, are known to cause the breakdown of passive films formed on most metals including stainless steels.
  • Figure 9 displays four potentiodynamic polarization plots for an untreated UNS S40900 sample, a sample treated in 0.4M gadolinium nitrate, a sample treated in 0.4M cerium nitrate and a sample treated in a composition containing 0.1 M gadolinium nitrate and 0.3M cerium nitrate solution, all treated samples being exposed to the compositions for 20 minutes at 85°C.
  • the formulation containing the combination of gadolinium nitrate and cerium nitrate showed significant improvement in cathodic inhibition of UNS S40900 samples as compared to samples treated in the compositions containing the individual rare earth nitrates.
  • Figure 10 is a flow chart showing the effect of different binary and ternary combinations of lanthanides on weight loss resulting from crevice corrosion tests for UNS S31603 stainless steel samples.
  • UNS S31603 stainless steel samples were treated in solutions containing 0.3M cerium nitrate in combination with 0.1M concentrations of other different lanthanum nitrates.
  • samples treated in 0.4M cerium nitrate and control samples were tested in parallel. The pH of all solutions was adjusted to 1.32 ⁇ 0.01 except for the solution using cerium nitrate alone.
  • the samples were tested by the ASTM G48 B standard method at 22°C for 24 hours. The weight loss was recorded and is presented graphically in Figure 11.
  • Formulation A 130.3 g/l of Ce(NO 3 ) 3 ⁇ 6H 2 O and 45.0 g/l of Gd(NO 3 ) 3 ⁇ 6H 2 O with the pH adjusted to within the range 0.5 - 6.5 depending on the alloys or metals being treated.
  • Formulation B 130.3g/l of Ce(NO 3 ) 3 ⁇ 6H 2 O, 45.0 g/l of Gd(NO 3 ) 3 ⁇ 6H 2 O and 43.5 g/l of La(NO 3 ) 3 ⁇ 6H 2 O with the pH adjusted within the range 0.5 to 6.5 depending on the metal or alloy being treated.
  • the major parameters of the compositions produced in accordance with the present invention are the use of one or more rare earth salt(s), pH range of the composition, temperature of the composition to which the surface of the metal is being exposed, and residence time of the metal therein.
  • the residence time may be limited to from about 15 minutes to about an hour at elevated temperatures (about 60°C to 95°C). Lower temperatures of the compositions necessitate longer exposure times. For example, at ambient temperature, exposure times of the order of several days are required to achieve the corrosion resistance effect obtained for 15 minutes exposure at elevated temperatures.
  • Surface conditioning methods other than by exposure to acid solutions, such as mechanical or other chemical processes may also be variables to consider.
  • the pH value of the aqueous composition should be adjusted in an appropriate range depending on the metal or alloy being treated. Increase in the acidity of the solution to a certain level enhances the surface enrichment of beneficial alloy elements for passivity. However, if the solution pH drop beyond certain values, the effect on cathodic inhibition will be weakened.
  • the galvanostatic polarization plots of Figure 13 illustrates the effect of 30% nitric acid addition can diminish the cathodic inhibition. It also causes attack to the substrate and results in rapid degradation of the treatment solution when treating ferritic stainless steels.
  • the inventors have found that the pH should be adjusted in the range of about 0.5 to about 3.5 for austenitic stainless steels and nickel based alloys and in the range from about 2 to about 4.5 for ferritic stainless steel.
  • the pH of the solution may be adjusted by adding nitric acid to the solution.
  • Formulations A and B given above are nonlimiting examples While treatment in these formulations produce significant corrosion inhibition on stainless steels, it will be appreciated that many other compositions of varying rare earth salt components and concentrations produced in accordance with the present invention will provide improvement in corrosion resistance of alloys.
  • Detergents or surfactants may be added to the compositions for cleaning the metal surfaces.
  • a commercial surfactant such as ARMAK 1997( Akzo Chemicals Inc) may be added to the treatment solution at 0.5-1.0% for samples having surfaces contaminated with for example processing lubricating oils and finger prints which may obstruct effective chemical treatment.
  • the choice of surfactant will be determined in part by the solubility of the surfactant in the composition for the particular pH value.
  • the metal to be cleaned and conditioned may initially be immersed in a preconditioning bath including an acid in addition to a surfactant.
  • compositions disclosed herein for economically treating large quantities of metals or alloys depends on long term stability of the compositions.
  • the present compositions were found to be very stable with no observable precipitation or degradation over a period of three years.
  • compositions for treating large quantities of metal certain materials will accumulate in the treatment bath over time. Ferric ions will build up in solution which changes the acidity of the bath. Addition of sodium hydroxide may be used to control the change in acidity. Therefore, studies were conducted to determine the effect of ferric ion concentration and sodium concentration on the efficacy of the compositions.
  • ferric ions Due to selected dissolution of iron during exposure of iron based alloys to the compositions, ferric ions will accumulate in the solution resulting in a more aggressive solution.
  • the effect of ferric ion on the performance of the compositions was studied by adding Fe(NO 3 ) 3 to formulation A containing 0.3 M cerium nitrate and 0.1M gadolinium nitrate.
  • the addition of 10 ppm and 100 ppm of Fe 3+ into formulation A resulted in a reduction in the pH of the formulations from 2.53 to 2.47 and 2.13 respectively.
  • Sodium nitrate will also accumulate in the treatment compositions as a result of bath maintenance.
  • the effect of sodium content in the treatment formulations was studied by adding sodium nitrate to formulation A at three levels, 0.1M, 0.5M, and 1M. Potentiodynamic polarization plots on UNS S40900 samples in formulation A with the above levels of sodium nitrate showed the presence of sodium had no discernable adverse affects on the corrosion inhibition behaviour (data not shown).
  • Figure 17 is a potentiostatic polarization plot for a brazing aluminum alloy before and after treatment in a solution comprising formulation A diluted by a factor of 7 using water.
  • the alloy was a two-sided clad brazing sheet comprising a core material consistent with AA4045 aluminum alloy and a lower melting Al-Si clad layer on both sides of the core.
  • the composition of the double clad aluminum material was: Element Core Clad Silicon 0.40 max. 9.0-11.0 Iron 0.50 max. 0.50 max. Copper 0.20-.040 0.10 max. Manganese 1.0-1.25 0.10 max. Magnesium 0.35-.55 0.10-0.30 Titanium 0.15 max. ------- Zinc 0.15 max. 0.10 max. Other 0.05 ea. 0.05 ea. Other Tot. 0.15 max. 0.15 max. Aluminum remainer remainder
  • the brazing sheet samples were subjected to a typical brazing cycle (heating to 1100°F for 1-3 minutes in dry nitrogen atmosphere) prior to testing so that the samples were tested in the as brazed condition.
  • the samples were rinsed in acetone and then immersed in diluted formulation A as previously described.
  • the formulation was "aged” by immersing an aluminum sample therein for 8 hours at 85°C after the samples were immersed in the formulation for 1 hour at 85° C.
  • aluminum alloy samples were subjected to a chromate treatment in a 4% by volume chromate solution at 35 to 40°C for 2.7 minutes.
  • the samples were tested for corrosion resistance in a 5% solution of auto coolant, "ZEREX", BASF 340-2 which also contained 150 ppm salts as follows: 0.2077 g/liter NaHCO 3 , 0.2231 g/liter Na 2 SO 4 and 0.2487 g/liter NaCl heated to 75°C stirred with a glass impeller.
  • the corrosion studies comprised free corrosion potential monitoring and cyclic polarization scans. From the cyclic polarization scans the pitting potential and corrosion resistance, R p , were determined as follows: Treatment Control Cr +6 Rare Earth Corr. Rate, R p 3.945 0.207 0.713 Pitting E p , V(SCE) -0.200 0.180 0.130
  • compositions for treating aluminum preferably include aluminum salts in order to reduce the corrosive attack on the alloy by the composition.
  • the salts can be added directly to the compositions, for example aluminum nitrate was added directly and was found to be effective in the range of about 5 to 10 grams of the nitrate per liter of the composition.
  • the salt can be generated in the composition by aging, that is, by placing a piece of aluminum into the freshly prepared composition.
  • Figure 18 is a potentiostatic polarization plot of a C12200 phosphorous deoxidized copper sample before and after treatment in a composition containing 130.3 g/l of cerium nitrate, and 45.0 g/l gadolinium nitrate and 10 g/l Al(NO 3 ) 3 .9H 2 O.
  • the pH was adjusted to 1 with HNO 3 and the solution heated to 350C.
  • the copper samples were first cleaned in 10% H 2 SO 4 and then rinsed in acetone prior to treatment in the rare earth salt solutions.
  • the samples were tested for corrosion resistance in a 5% solution of auto coolant, "ZEREX", BASF 340-2 which also contained 150 ppm salts as follows: 0.2077 g/liter NaHCO 3 , 0.2231 g/liter Na 2 SO 4 and 0.2487 g/liter NaCl heated to 75°C stirred with a glass impeller.
  • the corrosion studies comprised free corrosion potential monitoring and cyclic polarization scans. Several samples were tested in the same composition but for different periods of time with the cyclic potentiodynamic scans for a control sample not exposed to the formulation and samples exposed for 1, 2 and 3 minutes.
  • compositions for treatment of copper and its alloys preferably contains aluminum salts to reduce corrosive attack on the copper. Copper salts may also be used alternative to aluminum salts.
  • the pH of the compositions is preferably adjusted in the range of 1 to 6.5. The data of Figure 18 shows that the method of the present invention may be advantageously used to increase the corrosion resistance of copper and its alloys.
  • the composition used for the treatment of the samples comprised 0.05M cerium nitrate and the samples were treated at 90 to 95°C for 1 hour at a pH between 2.5 to 2.9.
  • Samples for seawater field tests were mounted in treated and untreated pairs for visual comparison.
  • a "TEFLON" crevice washer provided twelve crevice sites on each side of the sample.
  • the sea water tests were performed both in brackish water in a channel and in chlorinated brackish water in an outlet trough of a testing rig. Parallel tests for treated and untreated tubes were also conducted in a simulated heat exchanger rig.
  • Table IV shows that the treatment of UNS S30403, S31603 and N08904 significantly reduced or eliminated crevice corrosion in brackish water chlorinated with 2 ppm free chlorine for 24 days. Most of the untreated control samples of the same material exhibited significant crevice corrosion. Samples of untreated 6 Mo super stainless steels exhibited significant crevice corrosion after immersion in 2ppm chlorinated brackish water for 60 days.
  • Table V below illustrates that cerium treatment resulted in crevice corrosion resistance of stainless steels immersed in chlorinated seawater. Crevice Corrosion Sites Observed On Samples After Field Test In Chlorinated Seawater For 60 Days In 2 ppm Chlorinated Brackish Water Sample Condition VDM 2803Mo UNS 531603 UNS N08367 UNS N08925 Untreated 0 18 1 4 Cerium Treated 0 12 0 0 0
  • Table Vl summarizes the results of steel samples after 100 days of testing in brackish seawater. The effect of the treatment in improving the crevice corrosion resistance in the harsh seawater environment is quite significant. Crevice Corrosion Sites Observed On Samples After Field Test In Brackish Water For 100 Days Sample Condition UNS S304 03 #1 UNS S304 03 # 2 UNS S316 03 UNS N089 04 UNS N0892 50 UNS S31254 AVEST A 6545M O Untreated 20 19 3 2 1 0 0 Cerium Treated 0 4 0 0 0 0 0 0 0 0 0
  • Aqueous compositions using gadolinium nitrate alone give the most improvement in corrosion resistance compared to compositions using the other rare earth nitrates alone. There is a significant synergism among lanthanides in inhibiting the electrode kinetics, especially cathodic kinetics.
  • the pH of the compositions for each the ferritic and austenitic stainless steels is preferably adjusted to assist in the surface enrichment of beneficial alloy elements such as chromium and molybdenum. At pH values too low the metal or alloy will undergo dissolution at rates too high to have a beneficial effect on cathodic inhibition.
  • the surface of the metal or alloy is activated by the pH of the composition.
  • mechanical abrasion may be used as an alternative or in combination with chemical activation. Using mechanical abrasion initially to condition the surface followed by immersion in the composition would facilitate use of higher pH values since a primary effect of the pH is to condition the surface.
  • surface activation may be achieved using mechanical abrasion, sputter etching, particle bombardment and the like.
  • the metal or alloy being treated could be subject to a pretreatment by immersion in an acid bath absent the rare earth salts in order to condition the surface after which the workpiece would be immersed into the particular composition containing the rare earth salt(s).
  • the preferred method disclosed herein of increasing the corrosion resistance of metals comprises exposing the surface of the metal to an aqueous composition containing one or a combination of lanthanides.
  • a liquid solution allows full access to the surface area of any shape of workpiece.
  • other methods of treating the surface of a metal including sputtering, plasma spraying and the like, wherein rare earths are deposited on the alloy surface.
  • Those skilled in the art would be able to determine the operative processing conditions for each deposition procedure.
  • the method disclosed herein is useful for treating products fabricated from commercial alloys which are used in environments prone to aqueous corrosion.
  • the treatment may be carried out after production of the metal or alloy itself or after the product has been produced from the alloy.
  • After a product has been produced from the alloy it can be treated in a composition specifically optimized for the particular material and corrosive environment in which the product will be used.
  • compositions and method of treating metals and alloys for increasing corrosion resistance has been described and illustrated with respect to certain combinations of lanthanides, it will be readily apparent to those skilled in the art that numerous variations of these combinations may be made without departing from the scope of the invention described herein.

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
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  • Preventing Corrosion Or Incrustation Of Metals (AREA)
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Claims (14)

  1. Verfahren zur Behandlung einer Oberfläche eines Metalles oder einer Legierung, wie einem rostfreien Stahl, Kupfer oder einer Legierung hiervon, einer Legierung auf Nickel-Basis oder Aluminium oder einer Legierung hiervon, um den Korrosions-Widerstand durch Modifizierung der Oberfläche zur Inhibierung kathodischer Prozesse zu erhöhen, das im wesentlichen darin besteht, eine Oberfläche eines Metalles oder einer Legierung einer praktisch Halogenidfreien, wäßrigen Lösung zu exponieren, die ein Salz von mindestens einem Element der Seltenen Erden, das ausgewählt ist aus Yttrium, Gadolinium, Cerium, Europium, Terbium, Samarium, Neodymium, Präseodymium, Lanthanum, Holmium, Ytterbium, Dysprosium, Erbium und Kombinationen hiervon sowie ein, den pH-Wert modifizierendes Mittel in einer Menge, die wirksam ist, um den pH-Wert auf etwa 0,5 bis etwa 6,5 einzustellen, enthält.
  2. Verfahren nach Anspruch 1, bei dem das mindestens eine Salz einer Seltenen Erde in einer Menge von etwa 2 Gew.-% bis zur Sättigung vorliegt.
  3. Verfahren nach den Ansprüchen 1 oder 2, bei dem das Metall oder die Legierung ein ferritischer, rostfreier Stahl ist, und bei dem der pH-Wert auf etwa 2 bis etwa 4,5 eingestellt wird und die Temperatur der wäßrigen Lösung bei etwa 60°C bis etwa 95°C liegt.
  4. Verfahren nach den Ansprüchen 1 oder 2, bei dem das Metall oder die Legierung ein austenitischer, rostfreier Stahl ist oder eine Legierung auf Nickel-Basis, und bei dem der pH-Wert eingestellt wird auf etwa 0,5 bis etwa 3,5 und die Temperatur der wäßrigen Lösung bei etwa 60°C bis etwa 95°C liegt.
  5. Verfahren nach den Ansprüchen 1 oder 2, bei dem das Metall oder die Legierung Aluminium oder eine Aluminium-Legierung ist, und bei dem der pH-Wert eingestellt wird auf einen Wert von etwa 4,5 bis etwa 6,5 und bei dem die Temperatur der wäßrigen Lösung bei etwa 60°C bis etwa 95°C liegt.
  6. Verfahren nach den Ansprüchen 1 oder 2, bei dem das Metall oder die Legierung Kupfer oder eine Kupfer-Legierung ist, und bei dem der pH-Wert eingestellt wird auf einen Wert von etwa 0,5 bis etwa 6,5 und bei dem die Temperatur der wäßrigen Lösung bei etwa 60°C bis etwa 95°C liegt.
  7. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5 oder 6, bei dem die mindestens eine Seltene Erde Gadolinium ist.
  8. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5 oder 6, bei dem die mindestens eine Seltene Erde eine Kombination aus Gadolinium und Cerium ist.
  9. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5 oder 6, bei dem die mindestens eine Seltene Erde eine Kombination aus Gadolinium, Neodymium und Präseodymium ist.
  10. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5 oder 6, bei dem die mindestens eine Seltene Erde eine Kombination aus Cerium, Neodymium und Präseodymium ist.
  11. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5, 6, 7, 8, 9 oder 10, bei dem die wäßrige Lösung ein oberflächenaktives Mittel enthält.
  12. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 oder 11, das umfaßt, das Abschleifen der Metall- oder Legierungs-Oberfläche, vor oder während der Exponierung, mit der wäßrigen Zusammensetzung.
  13. Verfahren nach den Ansprüchen 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 oder 12, bei dem die Temperatur bei mindestens etwa 75°C liegt und bei dem die Behandlungs-Dauer etwa eine Stunde nicht übersteigt.
  14. Verfahren nach einem der vorstehenden Ansprüche, bei dem die Legierung auf Nickel-Basis aus Inconel besteht.
EP95933276A 1994-10-07 1995-10-10 Verfahren zur erhöhung der korrosionsbeständigkeit von metalleund legierung durch behandelnmit seltenen erde-elementen Expired - Lifetime EP0797691B1 (de)

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GB9420295 1994-10-07
GB9420295A GB9420295D0 (en) 1994-10-07 1994-10-07 Method of increasing corrosion resistance of steels by treatment with cerium
PCT/CA1995/000565 WO1996011290A1 (en) 1994-10-07 1995-10-10 Method of increasing corrosion resistance of metals and alloys by treatment with rare earth elements

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CZ74996A3 (en) 1993-09-13 1996-12-11 Commw Scient Ind Res Org Process of cleaning and coating metal surfaces and an acid aqueous solution containing rare earth ions for making the same
AUPM621194A0 (en) * 1994-06-10 1994-07-07 Commonwealth Scientific And Industrial Research Organisation Conversion coating and process for its formation
JP3655635B2 (ja) * 1994-11-11 2005-06-02 コモンウェルス・サイエンティフィック・アンド・インダストリアル・リサーチ・オーガナイゼーション 金属表面に化成皮膜を付与する方法およびそのための溶液
GB2328447A (en) * 1997-08-16 1999-02-24 British Aerospace A desmutting solution for use prior to anodising
ES2151405B1 (es) * 1998-07-20 2001-07-01 Univ Sevilla Procedimiento para mejorar el comportamiento refractario de aceros inoxidables.
WO2001029285A2 (en) * 1999-10-19 2001-04-26 Advanced Mechanical Technology, Inc. Corrosion protection of steel in ammonia/water heat pumps
AUPQ633200A0 (en) 2000-03-20 2000-04-15 Commonwealth Scientific And Industrial Research Organisation Process and solution for providing a conversion coating on a metallic surface I
AU774225B2 (en) * 2000-03-20 2004-06-17 Commonwealth Scientific And Industrial Research Organisation Process and solution for providing a conversion coating on metallic surface II
AUPQ633300A0 (en) * 2000-03-20 2000-04-15 Commonwealth Scientific And Industrial Research Organisation Process and solution for providing a conversion coating on a metallic surface ii
AU773837B2 (en) * 2000-03-20 2004-06-10 Commonwealth Scientific And Industrial Research Organisation Process and solution for providing a conversion coating on metallic surface
ES2193846B1 (es) * 2001-07-20 2005-03-01 Consejo Superior Investig. Cientificas. Procedimiento para la obtencion de recubrimientos protectores base cerio sobre hojalata.
US10041176B2 (en) 2005-04-07 2018-08-07 Momentive Performance Materials Inc. No-rinse pretreatment methods and compositions
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CN102586773A (zh) * 2012-03-23 2012-07-18 上海大学 不锈钢稀土转化膜钝化处理方法
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GB9420295D0 (en) 1994-11-23
CA2201619A1 (en) 1996-04-18
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KR970706422A (ko) 1997-11-03
WO1996011290A1 (en) 1996-04-18

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