US3135632A - Method of protecting ferrous metal surfaces from rerusting - Google Patents

Description

United States Patent 3 135 632 METHOD or rno'rlicrilso rnnnons METAL SURFAE FROM RERUSTING William R. Lucas, Huntsville, Ala., and Karl F. Eager,

Clear-field, Pa, assignors to the United States of Amerion as represented by the Secretary of the Army No Drawing. Filed May 24, 1957, Ser. No. 661,548

8 Claims. (Cl. 134-28) (Granted under Title 35, U.. Code (1952), sec. 266) 10 The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalties thereon.

This invention relates to the protection of ferrous metal surfaces against rerusting. In particular, it is directed to a new and improved method for the prevention of the rerusting which normally occurs upon the removal of freshly pickled carbon or low alloy ferrous metals from a pickling bath by the addition of acridine, certain substituted acridines and mixtures thereof to the picking acid bath.

It is well known that after various mill operations and at numerous stages in the fabrication of finished products, for instance, for galvanizing, tinning, electroplating and painting, it is necessary to remove oxides and other scales from various metal surfaces. Commercially for carbon or low alloy ferrous metals, this is done by the process called pickling wherein the ferrous metals being treated are immersed in acid solutions. Various acids are used in commercial pickling, such as sulfuric, hydrochloric and phosphoric acids. Because of its relative commercial availability, sulfuric acid is more widely used than all others.

It is also known that in order to reduce the attack of the pickling acids on the base ferrous metal and thus to prevent the waste both of the acid and the metal, additives termed inhibitors are incorporated into the pickling baths. Many satisfactory commercial inhibitors exist which accomplish this function of protecting the metal surfaces from acid attack while the metal is immersed in the pickling bath.

To the knowledge of the inventors however, none of these inhibitors had the attribute of protecting the highly active, freshly pickled metal surfaces from rerusting upon removal from the bath.

After the metal has been removed from the pickling bath, by known methods, portions of the thin residual film of pickling acid and salts, as well as portions of the inhibitor additive, are then rinsed from the metal. At this stage and in order to protect the metal surfaces while in temporary or semi-permanent storage from the rusting caused by exposure to the elements, i.e., the cf- .fects of atmospheric type oxidation, it is necessary to vide for the protection of the metal surface against rerusting by the use of a substance which is non-oily.

A further obejction to this type of treatment arises as the result of the fact that the oily film must subsequently be removed by any of the well-known methods when further use of the metal is desired. Accordingly, it is an additional object of the present invention to eliminate the operational necessity for removal of a rust protective coating when further use of the ferrous metal is desired.

It can then be seen that the elimination of these repetitive coating and removal operations during the processing of the metal would expedite and simplify overall production-line type fabrication processes. It is a further object of this invention to provide a method to expedite and simplify the overall fabrication process by the elimination of the coating, coating removal and recoating operations.

According to our method, once the pickling bath oporation has been completed the freshly pickled metal may be simply allowed to dry or, alternately, rinsed in water and then allowed to dry. Accordingly, it is a still further object of the present invention to provide a method whereby freshly pickled ferrous metal surfaces are rendered resistant to rerusting. Other objects will in part be apparent and will in part appear hereinafter.

Unexpectedly it was found that the addition to the pickling bath of a small amount of acridine, l-amino acridine, l-bromo-acridine or mixtures thereof, either alone or in combination with other inhibitors, would result in rendering the highly active, freshly pickled metal resistant to rerusting upon exposure to atmospheric or other elemental effects. Acridine is a benzolog of quinoline having a structural formula corresponding to:

Relatively, acridine appears to afford more protection than the substituted acridines mentioned, as will more fully appear from the following examples.

It can be seen that by this new and novel method the coating, coating-removal and recoating operational steps of presently available methods can be entirely eliminated from pickling bath procedures. Furthermore, the use of this new and novel method wherein the more effective inhibitors are also incorporated in the pickling bath will tend to give the optimum for not only the protection from pickling acid action on the ferrous metals, but after-rust protection as well.

It has been our experience that samples of ferrous metals removed from picking baths, if not otherwise treated, will be almost completely covered with rust within 24 hours. Samples of steel surfaces pickled in a solution contaniing acridine, an additional inhibitor and sulfuric acid have been exposed to ambient laboratory temperatures for several months without the slightest evidence of rust.

This peculiar property of acridine, l-amino-acridine, l-bromo acridine and mixtures thereof could not be de duced from either test comparisons with other substituted acridines or from comparisons with other related heterocyclic compounds, for instance, acridone, quinoline, pyridine or B-naphthoquinoline. Although some of these compounds are acid attack inhibitors, as shown in our copending application, Serial No. 668,283, filed January 25, 1957, now US. Patent 2,981,617, they afford, as will be indicated by the test data contained in the examples hereafter set forth, no protection to the metal against rerusting after pickling.

Thus the value of this invention can be appreciated when it is considered that, by the addition of a small amount of acridine, l-amino acridine, l-bromo-acridine, and mixtures thereof to the pickling bath, the necessity for immediate rust prevention treatment of the metal following pickling is eliminated. Furthermore, without any additional treatment, ferrous metals thus protected may be primed and painted at any time up to one year after pickling. V

The following examples are given by way of illustration only and are not intended to limit the scope of this invention in any way:

The hydrogen evolution method was employed to determine the percentage retardation (inhibition) in each of the following examples. This method consists of immersing the metal samples in a gas burette filled with the pickling acid under consideration. Below this specimen, a small orifice leads to the overflow tube so that the system is at atmospheric pressure, and the rate of attack of the acid upon the metal could be followed by reading the volume of hydrogen evolved. An inhibited acid test is always compared with an uninhibited acid test for control purposes, and the percentage retardation is calculated as follows:

Percent retardation volume of H2 uninhibited X The employment of this method makes it possible to obtain data at very frequent intervals which is not feasible when using the weight-loss method. The sample immersions hereinafter described were continued for 24 hours; the specimens were then removed from the bath; rinsed with Water and placed on a rack to dry. Within 24 hours after being placed on the drying rack, the metal samples were examined to determine the extent of the protection against rerusting. This determination was made by measuring the percentage of surface covered by rust. In all cases, the samples of uninhibited metals were found to be almost completely covered by rust within one hour.

EXAMPLE I Table I contains the results of tests which indicate the type of inhibition and after-rust protection afforded by acridine when tested alone. Samples of SAE 1010 steel were cut to give a surface area of 37 cm. and were ground to a smooth surface. After degreasing, therspeci mens were placed in different gas burettes completely filled with l-N sulfuric acid. The resultsof the tests in which acridine alone was added to the acid are shown in Table I:

Table I AFTER RUST OF SAE 1010 STEEL WHEN PICKLED IN SUL- FURIC ACID TO WHICH ACRIDINE WAS ADDED tested for the different concentrations by weight percent of the acridine.

EXAMPLE II Table II involves a comparison of the protective effect afforded by acridine, l-amino acridine and l-bromo acridine as well as a comparison of the effectiveness of acridine, l-bromo acridine and 1-amino acridine with respect to the ineffectiveness of the other substituted acridines tested.

Tests were performed under the same conditions and in the same manner as in Example I except that varying concentrations by weight percent of the acridine and substituted acridines were used. This table illustrates both the retardation effectiveness and the after-rust protection afforded by the various concentrations of acridine, 1- bromo acridine and l-amino acridine.

Table II IIiPlII IBITION AND AFTER RUST PROTECTION FROM THE TACK OF 1-N SULFURIC ACID ON MILD STEEL BY ACRIDINE AND SUBSTITUTED ACRIDINES Ooncen- Retar- After-pick- Samples tration, dation, ling rust weight percent protection,

percent percent Acridinc 0. 1 57 100 D 0. 05 67 100 0. 025 62 100 0. 1 69 90 0. 05 62 90 0. 025 62 90 O. 05 77 100 0. 025 -76 80 0. 1 92 0 0. 05 90 p o 0. 025 0 0. 1 7o 0 O. 05 .74 0 0. 025 71 0 0. l 81 0 O. 05 86 0 0. 025 79 0 EXAMPLE III parison with that of the particular acid solution to which acridine had been added.

Table III AFTER RUST PROTECTION OF ME 1010 STEEL WHEN PICKLgD IN VARIOUS ACIDS TO wrnon ACRIDINE WAS ADDE Concen- Concen- After rust Acid tratlon of tration of protection,

acid noracridine percent mality l-N nil 0 2-N nil O 5-N nil 0 l-N 0.05 100 2-N 0. 05 mo 5-N' 0.05 90 1-N nil 0 l-N 0.1 l-N 0.05 100 I-N 0.025 100 l-N nil 0 l-N 0. i 100 .1-N 0.05 100 l-N 0. 025 100 D EXAMPLE IV Tests were conducted under the same conditions and in the same manner as in Example I. However, other inhibitors were added to the acid solution along with the acridine for the purpose of illustrating that a more effective combined inhibition-after-rust protection could be obtained by the addition of a more effective inhibitor in combination with the acridine. The compounds used were inhibitors of acid attack, but which, of themselves, afforded no protection against rerusting.

Table IV AFTER RUST OF SAE 1010 STEEL WHEN PIOKLED IN IN HIBIIED SULFURIO ACID TO WEICH AGRIDINE WAS EXAMPLE V To illustrate that mixtures of acridine and the specified substituted acridines were as eifective when mixed together as when used alone, tests were conducted under similar conditions and in the same manner as in Example I except that both SAE 1010 and SAE 4130 steels were tested. A mixture of 0.05% acridine and 0.025 l-bromo acridine resulted in a 100% after rust protection for SAE 1010 steel. When tested with different samples of SAE 1010 and SAE 4130 steel, a mixture of 0.05% acridine and 0.025% l-bromo acridine resulted in a 90% after rust protection in each case.

EXAMPLE VI To test the efiectiveness of acridine and l-bromo acridine with low alloy steels, experiments were conducted in the same manner and under similar conditions as those of Example I except that SAE 4130 steel was used and 0.05 acridine added to l-N sulfuric acid. The results indicated an 80% after rust protection. 0.025% l-bromo acridine added to a l-N acid bath which contained a sample of SAE 4130 low alloy steel gave an 80% after rust protection.

EXAMPLE VII Although the tests listed in the previous examples ran 24 hours, much less time is required for the reaction which affords the protection against rerust. Tests were conducted in the same manner and under the same conditions as discussed in Example I except that specimens were removed from the solution after short, graduated periods of time, rinsed and allowed to air-dry. vThe specimens were examined for rust 24 hours after rinsing. The results of these tests are listed in Table V. I

6 Table V AFTER RUST OF SAE 1010 STEEL WHEN PICKLED IN l-N SULFURIO ACID Acrldine, weight percent Length of pickle After rust protection, percent 24 hours bon-ferrous metal surfaces, and low alloy ferrous metal surfaces from rerusting after removal from acid pickling baths, the steps which comprise: adding to the acid pickling bath a small amount of an organic compound selected from the group consisting of acridine, l-amino acridine, l-bromo acridine and mixtures thereof, whereby the metal surfaces are rendered substantially inactive to the normal effect of atmospheric oxidation; removing the inactivated freshly pickled metal from the acid pickling bath; and allowing the metal to dry.

2. The method of claim 1 wherein the organic compound is an amount between .005 and .2% by weight acridine.

3. The method of claim 1 wherein the organic compound is an amount between .025 and .1% by weight 1- amino acridine.

4. The method of claim 1 wherein the organic compound is an amount between .025 and .1% by weight 1- bromo acridine.

5. The method of claim 1 wherein the organic compounnd is a mixture of acridine and l-amino acridine.

6. The method of claim 1 wherein the organic compound is a mixture of acridine and l-bromo acridine.

7. The method of claim 1 wherein the organic compound is a mixture of l-amino acridine and l-bromo acridine.

8. In the method of protecting metal surfaces selected from the group consisting of ferrous metal surface, carhon-ferrous metal surfaces, and low allow ferrous metal surfaces from rerusting after removal from acid pickling baths, the steps which comprise: adding to the acid pickling bath a small amount of an organic compound selected from the group consisting of acridine, l-amino acridine, l-bromo acridine and mixtures thereof, whereby the metal surfaces are rendered substantially inactive to the normal effect of atmospheric oxidation; removing the inactivated freshly pickled metal from the acid pickling bath; rinsing the metal with water; and allowing the metal to dry.

References Cited in the file of this patent UNITED STATES PATENTS 1,503,443 Gravell July 29, 1924 1,678,775 Gravell July 31, 1928 2,037,762 Cole Apr. 21, 1936 2,814,593 Beiswanger Nov. 26, 1957

Claims (1)

1. IN THE METHOD OF PROTECTING METAL SURFACES SELECTED FROM THE GROUP CONSISTING OF FERROUS METAL SURFACES, CARBON-FERROUS METAL SURFACES, AND LOW ALLOY FERROUS METAL SURFACES FROM RERUSTING AFTER REMOVAL FROM ACID PICKING BATHS, THE STEPS WHICH COMPRISE: ADDING TO THE ACID PICKLING BATH A SMALL AAMOUNT OF AN ORGANIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF ARCIDINE,1-AMINO ACRIDINE, 1-BROMO ACRIDINE AND MIXTURES THEREOF, WHEREBY THE METAL SURFACES ARE RENDERED SUBSTANTIALLY INACTIVE TO THE NORMAL EFFECT OF ATMOSPHERIC OXIDATION; REMOVING THE INACTIVATED FRESHLY PICKED METAL FROM THE ACID PICKING BATH; AND ALLOWING THE METAL TO DRY.