US3052575A - Method of inhibiting corrosion - Google Patents

Method of inhibiting corrosion Download PDF

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US3052575A
US3052575A US88649A US8864961A US3052575A US 3052575 A US3052575 A US 3052575A US 88649 A US88649 A US 88649A US 8864961 A US8864961 A US 8864961A US 3052575 A US3052575 A US 3052575A
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solution
treating
corrosion
metal surface
metal
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US88649A
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Wilbur G Crane
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Inland Steel Co
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Inland Steel Co
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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
    • 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
    • C23C22/40—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 containing molybdates, tungstates or vanadates

Definitions

  • the present invention relates generally to a method of protectively coating a metal surface and more particularly, to an improved method of coating a ferrous metal to protect the ferrous metal from corrosion on exposure to moist air and other conditions providing high concentration of moisture.
  • the manufacturers of metal sheets, such as black plate of the type commonly used for making metal containers, and manufacturers of metal containers and other fabricators using black plate have long been seeking improved methods for rapidly treating metal surfaces to reduce or prevent rusting thereof due to atmospheric moisture during shipment and storage. It has been required that the surface of the treated metal should be capable of retaining a lacquer coating and preferably should also provide under-film corrosion resistance.
  • the unexpected and unusual corrosion resistance provided by the present process is obtained only when both the strength of the treating solution and the duration of the treatment with the herein disclosed solution are maintained within the narrow limits above specified.
  • concentration of the said salts in the solution and the duration of treatment exceed the specified limits, or if the combination of the concentration of the salt and the time of treatment is excessive, the appearance of the sheet is impaired by retention on the surface of the treated metal of insoluble iron bearing reaction products.
  • a solution containing a mixture of one percent by weight of each of the said nitrite and molybdate salts is entirely unsatisfactory even for shout-time immersion. It will thus be evident that in the present invention both the strength of the salt solution and the duration of the treatment are critical and must be maintained within specified limits in order ,to obtain acceptable results.
  • the ferrous metal surface be first treated by briefiy immersing or otherwise treating with a dilute mineral acid solution, such as with a dilute sulphuric acid pickle bath, for 1 to 2 seconds, followed by a clear water rinse. There should be no inhibitor in the pickle bath for best results.
  • a dilute mineral acid solution such as with a dilute sulphuric acid pickle bath
  • oxides on the metal surface can be removed by pretreating with reducing gases, such as hydrogen.
  • the process of the present invention is particularly suited for the treatment of elongated strips of fully finished ferrous metals, such as full-finish black plate, which are processed by continuous annealing, followed by continuous skin rolling, and thereafter formed into a coil for shipment.
  • the processing steps required by the present invention can be incorporated into the standard black plate production line without in any way interfering with the conventional steps thereof.
  • the strip can be continuously passed through a brief acid pickle bath in which it remains for a period of 1 to 2 seconds to clean the surface of soil and rust, followed by a clear water rinse, and then is passed continuously through the heated nitrite-molybdate bath containing 0.5% by weight sodium nitrite and 0.5%
  • ammonium molybdate in which the strip remains for a period of 2 to 4 seconds.
  • the treated strip is given a water rinse on emerging from the treating bath and is dried before coiling.
  • the foregoing treatment is carried out without in any way reducing or otherwise interfering with the high speed movement of the metal strip and produces a black plate having high resistance to corrosion.
  • the molybdate salt comprises 0.5% by Weight of the solution.
  • the solution is then heated to about 180 F. and to this heated solution is added suflicient sodium nitrite to provide a concentration of 0.5% by weight of the said nitrite salt. Since the ammonium molybdate salt causes the solution to be slightly acidic, said solution exhibiting a pH of about 4.85, nitrous acid is formed in the solution. The nitrous acid is unstable in the hot solution, however, and gradually decompses to yield free oxygen with the oxygen appearing to film the ferrous metal surface.
  • the protective film produced on the steel or other ferrous metal surface is of a light color and is hardly perceptible to the observer. It will withstand the abrasive action without the film being damaged.
  • Steel sheets which have been cleaned and treated in accordance with the present invention can be liberally sprinkled with water and allowed to stand in the air until dry without causing any rusting of the sheet.
  • the sheets treated in accordance with the present invention can also withstand a standard humidity cabinet treatment (high humidity at 100 F.) for 48 hours with only about 5% of the surface rusting whereas an untreated sheet will have 100% of the surface rusted within three hours or less.
  • Tests of the surface of steel panels treated in accordance with the present invention have shown that substantially perfect adherence of the phenolic-type lacquers is obtained. In the later tests, the panel surfaces were not rinsed following the treatment thereof so as to deliberately leave a residue of the treating bath on the surface to determine if there was any adverse effect of a residue on lacquer adherence.
  • While the preferred embodiment of the present invention uses only sodium nitrite and ammonium molybdate salts in substantially equal amounts so that a slightly acidic solution is produced, it should be understood that other water soluble nitrite salts and other water soluble compounds yielding molybdic acid in a heated aqueous solution can be used without departing from the scope of the present invention.
  • water soluble salts and compounds which can be used in place of sodium nitrite and ammonium molybdate are: potassium nitrite, lithium nitrite, ammonium nitrite, calcium nitrite, barium nitrite and strontium nitrite, and sodium molybdate, potassium molybdate and strontium molybdate, respectively.
  • the solution can also be applied to the metal in various other ways, including brushing, flow-coating, and spraying.
  • a method of continuously treating a strip of black plate to increase the corrosion resistance thereof which comprises, continuously passing black plate through a dilute sulphuric acid pickle bath and allowing the said plate to remain in said bath for a period of about 1 to 2 seconds followed by a clear water rinse to clean the surface of said black plate, continuously passing the clean black plate through an aqueous solution containing 0.5% by weight of sodium nitrite and 0.5% by weight ammonium molybdate and maintaining said black plate in contact with said solution for a period of 2 to 4 seconds while holding the temperature of the said solution between 180 F. and 200 F., rinsing the said black plate with water to remove residual solution therefrom, and thereafter drying the said black plate; whereby the surface of the black plate is provided with a thin light-colored protective film which is highly resistant to corrosion.

Description

ite Sttes ice 3,052,575 METHUD F INHKBITING CORROSIQN Wilhur G. Crane, Calumet City, lll., assignor to Inland Steel Company, hicago, Ill., a. corporation of Dela- Ware No Drawing. Filed Feb. 13, 1961, er. No. 88,649 7 Claims. (Cl. 148-6.14)
The present invention relates generally to a method of protectively coating a metal surface and more particularly, to an improved method of coating a ferrous metal to protect the ferrous metal from corrosion on exposure to moist air and other conditions providing high concentration of moisture.
The manufacturers of metal sheets, such as black plate of the type commonly used for making metal containers, and manufacturers of metal containers and other fabricators using black plate have long been seeking improved methods for rapidly treating metal surfaces to reduce or prevent rusting thereof due to atmospheric moisture during shipment and storage. It has been required that the surface of the treated metal should be capable of retaining a lacquer coating and preferably should also provide under-film corrosion resistance.
The use of chemical bath-s or sprays for providing a coating on metal surfaces to improve corrosion resistance has long been practiced. For this purpose, solutions of phosphates, chromates, nitrates, nitrites, tungstates, molybdates, and many other salts have been proposed. None of the prior art method-s, however, has been entirely satisfactory, particularly where the period of treatment must be extremely brief, as when the treatment is carried out continuously on a high-speed continuous annealing line, or on a continuous electrolyte tin line.
It is, therefore, an object of the present invention to provide an improved method of treating ferrous metal surfaces to produce surfaces which have high resistance to corrosion on exposure to atmospheric moisture.
It is a further object of the invention to provide an inexpensive and rapid method of treating a ferrous metal surface to increase the resistance thereof to corrosion on exposure to atmospheric moisture.
It is still another object of the invention to provide an improved method of treating ferrous metal surfaces to increase the corrosion resistance thereof which will also produce a surface having highly satisfactory lacquering properties and having under-film corrosion-resistance.
It is also an object of the present invention to provide an improved process for treating a surface of black plate to improve corrosion-resistance thereof without materially discoloring the treated metal surface.
It is a still further object of the present invention to provide an improved process of treating black plate continuously and rapidly to increase the resistance thereof to corrosion on exposure to atmospheric moisture.
Other objects of the present invention will be apparent to those skilled in the art, from the detailed description and claims to follow.
It has been discovered that the foregoing and other objects of the present invention are readily achieved by immersing a metal surface for a very short time in a heated aqueous solution having a low concentration of sodium nitrite and ammonium molybdate. An unusually high degree of resistance to corrosion by atmospheric moisture is imparted to a ferrous metal surface by immersing said surface in or otherwise completely wetting the metal surface with an aqueous solution containing about one-half of one percent by weight of sodium nitrite and about the same amount of ammonium molybdate, each of the foregoing salts being present in substantially equal amounts to provide an aqueous solution having a slightly acid pH. The temperature of the aqueous solution at the time of immersion should be from about F. to about 200 F., and the duration of immersion of the metal in the solution, or the period during which the hot solution is maintained in contact with the metal surface should be between about 2 and about 4 seconds.
It is well known, of course, that both sodium nitrite and ammonium molybdate have been used heretofore for treating metal surfaces to impart increased corrosion resistance. However, neither one of these salts by itself is very effective for improving corrosion resistance when the duration of the treatment therewith is extremely short. Thus, when sodium nitrite is used alone, the concentration thereof Which must be used to obtain any appreciable protection must be relatively high and the time of treatment prolonged. In addition, it is necessary to allow considerable nitrite salt to remain on the treated surface in order to obtain good corrosion resistance. When ammonium mo-lybdate is used alone it is only partially effective and has the further great disadvantage of discoloring the steel surface treated therewith.
The unexpected and unusual corrosion resistance provided by the present process is obtained only when both the strength of the treating solution and the duration of the treatment with the herein disclosed solution are maintained within the narrow limits above specified. Thus, for example, if the concentration of the said salts in the solution and the duration of treatment exceed the specified limits, or if the combination of the concentration of the salt and the time of treatment is excessive, the appearance of the sheet is impaired by retention on the surface of the treated metal of insoluble iron bearing reaction products. For example, a solution containing a mixture of one percent by weight of each of the said nitrite and molybdate salts is entirely unsatisfactory even for shout-time immersion. It will thus be evident that in the present invention both the strength of the salt solution and the duration of the treatment are critical and must be maintained within specified limits in order ,to obtain acceptable results.
It is also important in order to achieve the desired optimum improvement in resistance to corrosion by atmospheric moisture that the surface treated be free of oil, grease, and other contamination, and in addition be free of surface oxidation. To insure a satisfactory clean surface, it is preferable that the ferrous metal surface be first treated by briefiy immersing or otherwise treating with a dilute mineral acid solution, such as with a dilute sulphuric acid pickle bath, for 1 to 2 seconds, followed by a clear water rinse. There should be no inhibitor in the pickle bath for best results. Other methods of cleaning the surface of the ferrous metal strip can be used, if desired, such as by means of an alkali, bufling, or the like. Also, oxides on the metal surface can be removed by pretreating with reducing gases, such as hydrogen.
The process of the present invention is particularly suited for the treatment of elongated strips of fully finished ferrous metals, such as full-finish black plate, which are processed by continuous annealing, followed by continuous skin rolling, and thereafter formed into a coil for shipment. The processing steps required by the present invention can be incorporated into the standard black plate production line without in any way interfering with the conventional steps thereof. Thus, as the strip of black plates leaves the skin rolling station and before coiling, the strip can be continuously passed through a brief acid pickle bath in which it remains for a period of 1 to 2 seconds to clean the surface of soil and rust, followed by a clear water rinse, and then is passed continuously through the heated nitrite-molybdate bath containing 0.5% by weight sodium nitrite and 0.5%
by weight ammonium molybdate in which the strip remains for a period of 2 to 4 seconds. The treated strip is given a water rinse on emerging from the treating bath and is dried before coiling. The foregoing treatment is carried out without in any way reducing or otherwise interfering with the high speed movement of the metal strip and produces a black plate having high resistance to corrosion.
In preparing the treating solution of the present invention, it is desirable to first add suflicient ammonium molybdate to the desired volume of water to be used in the treating bath so that the molybdate salt comprises 0.5% by Weight of the solution. The solution is then heated to about 180 F. and to this heated solution is added suflicient sodium nitrite to provide a concentration of 0.5% by weight of the said nitrite salt. Since the ammonium molybdate salt causes the solution to be slightly acidic, said solution exhibiting a pH of about 4.85, nitrous acid is formed in the solution. The nitrous acid is unstable in the hot solution, however, and gradually decompses to yield free oxygen with the oxygen appearing to film the ferrous metal surface. It also appears that certain iron molybdate salts are formed and react with the metal surface. In view of the slow decomposition of the salts it is necessary to replenish the salts from time to time in order to maintain the concentration thereof at the herein specified levels. The solution of the salt as herein prepared, however, can be used several hours before it becomes necessary to replenish the said salts.
While it is not essential to the successful practice of the present invention to rinse the treated surface with water as it leaves the treating bath when the nitritemolybdate solution has been freshly prepared, it does become necessary to rinse the treated metal surface after the treating solution has been used for some time, since loosely adhering brownish particles produced during the treatment tend to adhere to the surface of the treated metal. The use of a rubber squeegee roll, or the like, on the surface of the treated metal as the metal strip leaves the treating bath and before the water rinse also helps to prevent adherence of the reaction products to the surface of the metal strip.
The protective film produced on the steel or other ferrous metal surface is of a light color and is hardly perceptible to the observer. It will withstand the abrasive action without the film being damaged. Steel sheets which have been cleaned and treated in accordance with the present invention can be liberally sprinkled with water and allowed to stand in the air until dry without causing any rusting of the sheet. The sheets treated in accordance with the present invention can also withstand a standard humidity cabinet treatment (high humidity at 100 F.) for 48 hours with only about 5% of the surface rusting whereas an untreated sheet will have 100% of the surface rusted within three hours or less. Tests of the surface of steel panels treated in accordance with the present invention have shown that substantially perfect adherence of the phenolic-type lacquers is obtained. In the later tests, the panel surfaces were not rinsed following the treatment thereof so as to deliberately leave a residue of the treating bath on the surface to determine if there was any adverse effect of a residue on lacquer adherence.
While the preferred embodiment of the present invention uses only sodium nitrite and ammonium molybdate salts in substantially equal amounts so that a slightly acidic solution is produced, it should be understood that other water soluble nitrite salts and other water soluble compounds yielding molybdic acid in a heated aqueous solution can be used without departing from the scope of the present invention. Among the water soluble salts and compounds which can be used in place of sodium nitrite and ammonium molybdate are: potassium nitrite, lithium nitrite, ammonium nitrite, calcium nitrite, barium nitrite and strontium nitrite, and sodium molybdate, potassium molybdate and strontium molybdate, respectively.
It will also be understood that while the description has referred to the ferrous metal being dipped or immersed in the nitrite-molybdate treating solution, the solution can also be applied to the metal in various other ways, including brushing, flow-coating, and spraying.
Others may practice the invention in any of the numerous ways which are suggested to one skilled in the art, by this disclosure, and all such practice of invention are considered to be a part hereof which fall within the scope of the appended claims.
I claim:
1. A method of treating a ferrous metal surface to increase the resistance thereof to corrosion, comprising, contacting a surface of a ferrous metal with an aqueous solution containing about 0.5% by weight of a water soluble nitrite salt and about 0.5% by weight of a water soluble compound yielding molybdic acid in said solution while maintaining the said solution at a temperature between about F. and about 200 F. and maintaining the solution in contact with the metal surface for a period of about 2 to 4 seconds, and thereafter drying the treated metal surface; whereby the metal surface is provided with a thin protective film which is highly resistant to corrosion.
2. A method of treating a ferrous metal surface as in claim 1, wherein the said nitrite salt is sodium nitrite.
3. A method of treating a ferrous metal surface as in claim 1, wherein the said water soluble compound is ammonium molybdate.
4. A method of treating a ferrous metal surface as in claim 1, wherein said aqueous solution has a molybdic acid content sufficient to maintain the pH thereof at about pH 4.85.
5. A method of treating a ferrous metal surface as in claim 1, wherein the said ferrous metal comprises a strip of black plate.
6. An improved corrosion resistant ferrous metal product prepared accordin to the process of claim 1.
7. A method of continuously treating a strip of black plate to increase the corrosion resistance thereof which comprises, continuously passing black plate through a dilute sulphuric acid pickle bath and allowing the said plate to remain in said bath for a period of about 1 to 2 seconds followed by a clear water rinse to clean the surface of said black plate, continuously passing the clean black plate through an aqueous solution containing 0.5% by weight of sodium nitrite and 0.5% by weight ammonium molybdate and maintaining said black plate in contact with said solution for a period of 2 to 4 seconds while holding the temperature of the said solution between 180 F. and 200 F., rinsing the said black plate with water to remove residual solution therefrom, and thereafter drying the said black plate; whereby the surface of the black plate is provided with a thin light-colored protective film which is highly resistant to corrosion.
References Cited in the file of this patent UNITED STATES PATENTS 2,557,509 Miller June 19, 1951 2,839,439 Stapleton June 17, 1958 2,854,370 Kronstein Sept. 30, 1958

Claims (1)

1. A METHOD OF TREATING A FERROUS METAL SURFACE TO INCREASZE THE RESISTANCE THEREOF TO CORROSION, COMPRISING CONTACTING A SURFACE OF A FERROUS METAL WITH AN AQUEOUS SOLUTION CONTAINING ABOUT 0.5% BY WEIGHT OF A WATER SOLUBLE NITRITE SALT AND ABOUT 0.5% BY WEIGHT OF A WATER SOLUBLE COMPOUND YIELDING MOLYBDIC ACID IN SAID SOLUTION WHILE MAINTAINING SAID SOLUTION AT A TEMPERATURE BETWEEN ABOUT 180*F. AND ABOUT 200*F. AND MAINTAINING THE SOLUTION IN CONTACT WITH THE METAL SURFACE FOR A PERIOD OF ABOUT 2 TO 4 SECONDS, AND THEREAFTER DRYING THE TREATED METAL SURFACE; WHEREBY THE METAL SURFACE IS PROVIDED WITH A THIN PROTECTIVE FILM WHICH IS HIGHLY RESISTANT TO CORROSION.
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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3275441A (en) * 1963-03-07 1966-09-27 Technilith Inc Printing plate and method of making same
US3907612A (en) * 1974-02-15 1975-09-23 Pennwalt Corp Preanneal rinse process for inhibiting pin point rust
US3919000A (en) * 1973-06-15 1975-11-11 Pennwalt Corp Preanneal rinse process for inhibiting rust on steel strip
JPS512419B1 (en) * 1966-11-16 1976-01-26
JPS5544504A (en) * 1978-09-21 1980-03-28 Natl Res Inst For Metals Treating method for metal surface
US20040036415A1 (en) * 2002-08-22 2004-02-26 Ushiodenki Kabushiki Kaisha Foil seal lamp

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2557509A (en) * 1949-01-21 1951-06-19 Kelite Products Inc Composition and process for protecting ferrous metals from rusting in moist air
US2839439A (en) * 1955-06-07 1958-06-17 Detrex Chem Ind Method and composition for producing phosphate coatings on metal
US2854370A (en) * 1957-10-04 1958-09-30 Oakite Prod Inc Composition and method for phosphate coating of metal

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2557509A (en) * 1949-01-21 1951-06-19 Kelite Products Inc Composition and process for protecting ferrous metals from rusting in moist air
US2839439A (en) * 1955-06-07 1958-06-17 Detrex Chem Ind Method and composition for producing phosphate coatings on metal
US2854370A (en) * 1957-10-04 1958-09-30 Oakite Prod Inc Composition and method for phosphate coating of metal

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3275441A (en) * 1963-03-07 1966-09-27 Technilith Inc Printing plate and method of making same
JPS512419B1 (en) * 1966-11-16 1976-01-26
US3919000A (en) * 1973-06-15 1975-11-11 Pennwalt Corp Preanneal rinse process for inhibiting rust on steel strip
US3907612A (en) * 1974-02-15 1975-09-23 Pennwalt Corp Preanneal rinse process for inhibiting pin point rust
JPS5544504A (en) * 1978-09-21 1980-03-28 Natl Res Inst For Metals Treating method for metal surface
JPS5736348B2 (en) * 1978-09-21 1982-08-03
US20040036415A1 (en) * 2002-08-22 2004-02-26 Ushiodenki Kabushiki Kaisha Foil seal lamp
US7095175B2 (en) * 2002-08-22 2006-08-22 Ushiodenki Kabushiki Kaisha Foil seal lamp

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