Abstract:
Compositions of ammonium carbonate and ammonium bicarbonate that are suitable to apply to ferrous materials to inhibit corrosion by chlorides are disclosed.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to corrosion inhibitors, and, more particularly, to compositions of ammonium carbonate and ammonium bicarbonate that are suitable to inhibit the corrosion of ferrous materials exposed to chlorides. 
     There has been a tremendous demand for a chemical which will inhibit the corrosion of steel by chlorides such as sodium chloride, and much research has been conducted in an attempt to discover such a chemical. 
     Steel is commonly exposed to chloride ions in unavoidable open and enclosed environments. Structures containing steel are exposed to salt water environments in and around oceans or other bodies of salt water and are seriously corroded by chlorides present in the water. In an enclosed environment, calcium chloride is added to concrete to accelerate its rate of setting. These chloride additions have, however, caused the reinforcing steel in the concrete to corrode. 
     Another significant source of chloride corrosion has been deicing compositions applied to the paved surfaces of roads and highways. These compositions have been splashed onto the steel contained in the highway structures as well as onto metal vehicle bodies. The corrosion thus produced has been quite visible in the form of corroded structures and vehicle bodies. Another well-known and highly visible chloride-related damage to highways has been potholes. Potholes form as the corrosion deposits caused by the action of the chlorides on the reinforcing steel expand and create various stresses on the concrete which subsequently causes large pieces of concrete to fracture and separate from the roads and highways. 
     Exemplary illustrations of the tremendous amount of research which has been performed in an effort to learn how to inhibit the corrosion of steel and protect it from the effects of chlorides, are found in the following publications: Mozer, Bianchini and Kesler, &#34;Corrosion of Reinforcing bars In Concrete,&#34; Journal of the American Concrete Institute, August 1965; &#34;Concrete Information&#34; by the Portland Cement Association (1968); John G. Hendrickson, &#34;Corrosion of Steel in Concrete,&#34; Portland Cement Association (1968); and Bailey Tremper, &#34;Corrosion of Reinforcing Steel,&#34; American Concrete Institute. These publications in turn list dozens of additional publications focusing on the same subject. 
     Numerous attempts have been made to identify specific corrosion inhibitors capable of preventing the corrosion of steel. Inhibitors are chemical substances which effectively decrease the corrosion rate in an environment. The corrosion rate may be reduced by such a large extent by inhibitors that the corrosion reaction is effectively stopped in some instances. For example, Gouda and Monfore describe in their publication entitled, &#34;A Rapid Method for Studying Corrosion Inhibition of Steel in Concrete,&#34; the testing of some of the well known corrosion inhibitors, such as sodium nitrite, potassium chromate and sodium benzoate. The authors found that to inhibit the corrosion of a 2% addition of calcium chloride to concrete, additions of 1%-2% of sodium nitrite and 2%-4% of potassium chromate were needed. Because sodium benzoate is precipitated by calcium chloride, the authors tested sodium benzoate against 1.6% of sodium chloride and determined that it requires 4%-6% of sodium benzoate to inhibit corrosion in the presence of this amount of sodium chloride. 
     Because of their undesirable side effects, however, most corrosion inhibitors must be carefully administered. For example, the chromates and other effective chromate salts are highly toxic and will produce ulcers on any skin they contact. As a further example, the publication entitled &#34;Effect of Various Substances on Concrete and Protective Treatments, Where Required&#34;, Portland Cement Association (1968), explains that sodium nitrite causes slow disintegration of concrete. To date, a satisfactory corrosion inhibitor for chlorides has not been found. 
     The above-described inhibitors are anodic inhibitors. According to Gouda and Monfore, the inhibitors can form &#34;sparingly soluble iron salts or gamma Fe 2  O 3  films on the anodic areas, thus preventing ferrous ion from passing through into solution.&#34; These salts form according to the classical understanding that the corrosion of steel is an electrochemical process. At the steel anode, iron goes into solution and forms a ferrous ion and releases two electrons: Fe→Fe ++  +2e - . At the steel cathode, the two electrons produced at the anode react with two hydrogen ions to form a hydrogen film: 2H +  +2e +  →H 2 . In instances when the supply of oxygen is limited and the pH is relatively high, an anodic film forms on the steel and prevents further corrosion. When chloride ions are present, however, the protective anodic films are removed by forming soluble chloride compounds and the steel is exposed to further electrochemical attack by the chlorides. 
     To comprehend the severity of the problem of corrosion, in 1976 the Environmental Protection Agency estimated that using sodium chloride or calcium chloride as deicing compounds costs the U.S. about five billion dollars per year. Probably a significant percentage of this amount can be attributed to the corrosion of steel. Despite the damage salt has produced, it has proven to be a good deicing chemical and has undoubtedly saved thousands of lives and injuries, which would otherwise have resulted from ice-covered roads. 
     Although salt has been successful for the purpose of deicing roads and highways, it has caused the corrosion of many thousands of highway structures. Consequently, a large amount of money will continue to be needed to repair or replace these damaged structures until a suitable corrosion inhibitor is available for large-scale application. 
     Thus, there has been an urgent need for a composition which can be applied directly to steel or to structures containing steel so as to inhibit the corrosion already started by deicing chemicals containing chlorides. Such a composition would have the potential to save billions of dollars which would otherwise be spent to rebuild the presently corroding highway structures. Once this corrosion is arrested, the saved repair money can be used to purchase improved deicers having the desirable deicing qualities of salt but lacking its damaging corrosive side effects. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described inadequacies of the related art and has as an object to provide a composition which is suitable for applying to metals exposed to chloride environments so as to inhibit their corrosion. 
    
    
     Additional objects and advantages of the present invention will become apparent from the detailed description which follows. To achieve the objects of the invention, as embodied and broadly described herein, the composition of the present invention comprises ammonium carbonate or ammonium bicarbonate in an amount effective to inhibit the corrosion of a metal by a corrosive agent. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is directed to compositions that are capable of reducing the need and thus the cost of highway repair by stopping the ongoing corrosion in highway structures which chloride compounds have initiated. The use of such compositions would eliminate the necessity of spending billions of dollars to mechanically remove the corroded steel from these structures and replace it with more expensive epoxy coated type steel. 
     The test work in support of the present invention demonstrates that when corroding steel is exposed to ammonium carbonate or ammonium bicarbonate, continued corrosion is inhibited even in the presence of sodium chloride. 
     Moreover, ammonium carbonate and ammonium bicarbonate are commercially available and relatively small expense will be needed to demonstrate on a large scale how compositions of these chemicals can be used to prevent or stop further corrosion of highway structures. 
     To demonstrate the effectiveness of ammonium carbonate and ammonium bicarbonate with respect to inhibiting the corrosion of metal which chlorides have initiated, two series of tests were conducted, namely the F13 and G6 series. The F13 Series and a portion of the G6 Series were run in duplicate to determine how additions of ammonium carbonate alone or in the presence of various percentages of sodium chloride inhibit the chloride corrosion of mild steel. The remaining portion of the G6 series of tests was conducted to demonstrate how the addition of ammonium bicarbonate alone or in the presence of various percentages of sodium chloride inhibit the corrosion of mild steel. 
     The following working examples are provided to illustrate some of the advantages of the present invention and are not in any manner limitative of its scope. All of the following parts and percentages are by weight. 
     EXAMPLE 1 
     Tests were conducted by preparing one inch square pieces of 16 gage mild steel. The pieces were prepared for testing by removing mill scale deposits with an inhibited muriatic acid solution and rounding their corners and sides with a fine emery wheel. Each test piece was then marked for identification purposes. Both sides of the test piece were then polished with fine emery paper to a bright surface finish. Dust was removed from the test pieces with a paper towel and their surfaces were then washed with a 1--1--1-- trichloroethane solvent. The cleaned test pieces were weighed on a Mettler H10 Balance to the closest 0.1 mg. The test pieces in the two series of tests varied in weight from 6.25 g to 6.99 g. After weighing, each test piece was immersed into 60 g of a 3% solution of sodium chloride in water. The solutions were contained in polystyrene vials which were about 50 mm in diameter, 85 mm in height and having polyethylene caps. The solutions were maintained at about 96° F. for three days in a Labline constant temperature water bath. 
     After this period of time, the condition of each test piece was noted and the test pieces were removed from the salt solution, brushed and washed with water, rinsed with a solvent, dried and weighed. The test pieces of the F13 series lost from 7.7 mg to 9.0 mg of weight due to corrosion, and the test pieces of the G6 series lost from 4.1 mg to 5.1 mg of weight. 
     The test pieces were next placed in a second test solution. These solutions were duplicate, 60 g weights of 3% solutions of salt, ammonium carbonate, and various ratios of salt and ammonium carbonate, in distilled water. 
     It should be explained that when ammonium carbamate (NH 2  COONH 2 ) is combined with water, a portion of the ammonium carbamate slowly hydrates to so-called commercial ammonium carbonate, which is actually a double salt of ammonium carbamate and ammonium bicarbonate, and ammonia is released: 
     
         2NH.sub.2 COONH.sub.2 +H.sub.2 O→NH.sub.4 COONH.sub.2.NH.sub.4 HCO.sub.3 +NH.sub.3 
    
     The ammonium carbonate used in the EXAMPLES was so-called commercial ammonium carbonate. 
     The second solutions were maintained at about 96° F. for three more days. After six days, the presence of any corrosion deposits was noted for each piece. The test pieces were then brushed in a water solution, rinsed with solvent, and weighed. 
     In deciding the appropriate composition of the solutions to be used to determine whether or not ammonium carbonate would inhibit the corrosion process which had already begun, it was decided to add salt to the second solutions so as to approximate the condition in which salt corroded the steel before the ammonium carbonate was added. 
     The following TABLE 1 illustrates the solution compositions and the test results for the F13 series and the ammonium carbonate portion of the G6 series. 
     
                                           TABLE 1__________________________________________________________________________F13 Series and Ammonium Carbonate Portion of the G6 Series         SECOND SOLUTION INTO WEIGHT (g)         WHICH CORRODING TEST LOST (-) % OF SALTWEIGHT (g)    PIECE WAS PLACED     OR       CORROSION LOST IN      % AMMONIUM                       %      GAINED (+)                                       SAVED IN 3% SALT      CARBONATE                       DISTILLED                              IN SECOND                                       SECONDTEST NO. SOLUTION         % SALT              CRYSTALS WATER  SOLUTION SOLUTION                                               REMARKS__________________________________________________________________________F13C1 0.0083  0.0  3.0      97     0.0000   100     NO                                               VISIBLE                                               NEW                                               CORROSIONFI3C2 0.0089  0.0  3.0      97     0.0000   100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C3 0.0084  0.231              2.769    97     0.0000   100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C4 0.0084  0.231              2.769    97     + 0.0001 100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C5 0.0087  0.69 2.31     97     +0.0001  100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C6 0.0089  0.69 2.31     97     0.0000   100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C7 0.0077  0.891              2.109    97     +0.0001  100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C8 0.0088  0.891              2.109    97     +0.0001  100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C9 0.0087  1.149              1.851    97     0.0001   100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C10 0.0079  1.149              1.851    97     0.0000   100     NO                                               VISIBLE                                               NEW                                               CORROSIONF13C11 0.0088  3.0  0.0      97     -0.0060  0.0     YELLOW                                               PRECIPITATE                                               FORMEDF13C12 0.0086  3.0  0.0      97     -0.0080  0       YELLOW                                               PRECIPITATE                                               FORMEDF13C13 0.0090  0.0  0.0      100    -0.0053  0       YELLOW                                               PRECIPITATE                                               FORMEDF13C14 0.0088  0.0  0.0      100    -0.0071  0       YELLOW                                               PRECIPITATE                                               FORMEDG6C7  0.0045  1.5  1.5      97     -0.0016  79      SLIGHT                                               CORROSION                                               AT TEST                                               PIECE EDGEG6C8  0.0045  1.5  1.5      97     -0.0009  88      SLIGHT                                               CORROSION                                               AT TEST                                               PIECE EDGEG6C9  0.0042  1.35 1.65     97     - 0.0003 100     NO VISIBLE                                               NEW                                               CORROSIONG6C10 0.0050  1.35 1.65     97     -0.0002  100     NO VISIBLE                                               NEW                                               CORROSIONG6C10 0.0049  1.8  1.2      97     -0.0077  0       CORROSION                                               AT TEST                                               PIECE EDGEG6C12 0.0046  1.8  1.2      97     -0.0072  0       CORROSION                                               AT TEST                                               PIECE EDGEG6C13 0.0046  3.0  0.0      97     -0.0076  0       YELLOW                                               PRECIPITATE                                               FORMEDG6C14 0.0047  0.0  0.0      100    -0.0081  0       YELLOW                                               PRECIPITATE                                               FORMEDG6C15 0.0047  0.0  0.0      100    -0.0075  0       YELLOW                                               PRECIPITATE                                               FORMED__________________________________________________________________________ 
    
     The following TABLE 2 illustrates the corrosion inhibiting effects of ammonium carbonate on as-corroded steel previously exposed to sodium chloride for a complete range of solid compositions of ammonium carbonate and sodium chloride added to distilled water. 
     
                                           TABLE 2__________________________________________________________________________Corrosion Inhibiting Characteristics of Ammonium Carbonate inCompositions of Ammonium Carbonate and Sodium Chloride Based onPercentages of Solids    COMPOSITION OF    SOLIDS ADDED    TO SECOND SOLUTION     AVERAGE WEIGHT         % AMMONIUM                  % DISTILLED                           OF CORROSIONTEST NOS.    % SALT         CARBONATE                  WATER    (g).sup.1   REMARKS__________________________________________________________________________F13C1, F13C2    0.0  100.0    97       0.0000      NO VISIBLE NEW                                       CORROSIONF13C3, F13C4    7.7  92.3     97       +0.00005    NO VISIBLE NEW                                       CORROSIONF13C5, F13C6    23.0 77.0     97       +0.00005    NO VISIBLE NEW                                       CORROSIONF13C7, F13C8    29.7 70.3     97       +0.0001     NO VISIBLE NEW                                       CORROSIONF13C9, F13C10    38.3 61.7     97       +0.00005    NO VISIBLE NEW                                       CORROSIONF13C11, F13C12    100.00         0.0      97       -0.0070     YELLOW                                       PRECIPITATE                                       PRODUCEDF13C13, F13C14    0.0  0.0      100      -0.0062     YELLOW                                       PRECIPITATE                                       FORMEDG6C7, G6C8    50.0 50.0     97       -0.00125    SLIGHT                                       CORROSION ON                                       EDGE OF TEST                                       PIECESC6C9, G6C10    45.0 55.0     97       -0.00025    NO VISIBLE NEW                                       CORROSIONC6C11, G6C12    60.0 40.0     97       -0.00745    CORROSION ON                                       EDGE OF THE                                       TEST PIECESG6C13    100.0         0.0      97       -0.0076     YELLOW                                       PRECIPITATE                                       FORMEDG6C14, G6C15    0.0  0.0      100      -0.0078     YELLOW                                       PRECIPITATE                                       FORMED__________________________________________________________________________ .sup.1 The limit of accuracy of the weight measurement was about ±0.0004 g. 
    
     The results reported in TABLE 1 for test numbers F13C11, F13C12 and G6C13 indicate that when steel test pieces which are corroding in a 3% salt solution are placed into a fresh 3% salt solution, they continue to corrode at about the same rate as in the original salt solution. The results from test numbers F13C13, F13C14, G6C14 and G6C15 illustrate that the same results occur when corroding test pieces are placed in 100% distilled water. 
     In contrast, when corroding test pieces are placed in 3% solutions containing at least 1.5% of ammonium carbonate, as in test numbers F13C1 through F13C10 and G6C7 through G6C10, at least about 80% of the corrosion deposit that had formed in the original 3% salt solution was saved. 
     Based on the results of test numbers G6C7, G6C8, G6C9 and G6C10, ammonium carbonate apparently reaches its limit of ability to inhibit corrosion of ferrous metals at a composition somewhere about 50%-55% ammonium carbonate and 45%-50% salt. At lesser percentages of ammonium carbonate, as in test numbers G6C11 through G6C15, new corrosion was produced. 
     EXAMPLE 2 
     The tests in EXAMPLE 2 were conducted using the same procedure as used in EXAMPLE 1. The test pieces were first caused to corrode in a 3% salt solution. After corroding for three days, the test pieces were removed from the solution, cleaned and weighed. The test pieces were than placed in duplicate, 60 g distilled water weights of 3% solutions of salt, ammonium bicarbonate, and various combinations of salt and ammonium bicarbonate, in distilled water. 
     The test pieces were maintained for three additional days in the second solutions. The test pieces were then removed and visually inspected, and the presence of any corrosion deposits was noted for each piece. The test pieces were then cleaned, rinsed and weighed. 
     As in EXAMPLE 1, salt was added to the solutions to determine whether ammonium bicarbonate inhibits the corrosion of steel in the presence of salt. With salt present in the solutions, the conditions in which salt corroded the steel before the ammonium bicarbonate was added were again approximated. The following TABLE 3 illustrates the solution compositions and test results for the ammonium bicarbonate portion of the G6 series. 
     
                                           TABLE 3__________________________________________________________________________Ammonium Bicarbonate Portion of the G6C Series        SECOND SOLUTION        WEIGHT (g)        INTO WHICH CORRODING   LOST (-)WEIGHT (g)   TEST PIECE WAS PLACED  OR GAINED LOST IN 3%   % AMMONIUM                       %       (+) IN  PERCENT OF SALT         BICARBONATE                       DISTILLED                               SECOND  CORROSIONTEST NO. SOLUTION        % SALT              CRYSTALS WATER   SOLUTION.sup.2                                       SAVED   REMARKS__________________________________________________________________________G6C1  0.0049 0.27  2.73     97      +0.0001 100     NO VISIBLE                                               NEW CORROSIONG6C2  0.0051 0.27  2.73     97      -0.0001 100     NO VISIBLE                                               NEW CORROSIONG6C3  0.0041 0.0   3.0      97      +0.0001 100     NO VISIBLE                                               NEW CORROSIONG6C4  .0047  0.0   3.0      97      -0.0001 100     NO VISIBLE                                               NEW CORROSIONG6C5  0.0051 0.531 2.469    97      0.0000  100     VERY SLIGHT                                               CORROSIONG6C6  0.0045 0.531 2.469    97      0.0000  100     VERY SLIGHT                                               CORROSIONG6C13 0.0046 3.0   0.0      97      -0.0076  0      YELLOW                                               PRECIPITATE                                               FORMEDG6C14 0.0047 0.0   0.0      100     -0.0081  0      YELLOW                                               PRECIPITATE                                               FORMEDG6C15 0.0047 0.0   0.0      100     -0.0075  0      YELLOW                                               PRECIPITATE                                               FORMED__________________________________________________________________________ .sup.2 The limit of accuracy of the test measurement was about ±0.0004 g. 
    
     The following TABLE 4 illustrates the corrosion inhibiting effects of ammonium bicarbonate with respect to steel previously exposed to sodium chloride for a range of solid compositions of ammonium bicarbonate and sodium chloride added to distilled water. 
     
                                           TABLE 4__________________________________________________________________________Corrosion Inhibiting Characteristics of Ammonium Bicarbonate inCompositions of Ammonium Bicarbonate and Sodium Chloride   COMPOSITION OF   SOLIDS ADDED TO   SECOND SOLUTION        % AMMONIUM                 % DISTILLED                        WEIGHT (g) OFTEST NO.   % SALT        BICARBONATE                 WATER  CORROSION.sup.3                                 REMARKS__________________________________________________________________________G6C1, G6C2   9.0  91.0     97     0.0000   NO VISIBLE                                 NEW CORROSIONG6C3, G6C4   0.0  100.0    97     0.0000   NO VISIBLE                                 NEW CORROSIONG6C5, G6C6   17.7 82.3     97     0.0000   VERY SLIGHT                                 CORROSION                                 ON EDGE OF                                 TEST PIECEG6C13   100.0        0.0      97     -0.0076  YELLOW                                 PRECIPITATE                                 FORMEDG6C14, G6C15   0.0  0.0      100    -0.0078  YELLOW                                 PRECIPITATE                                 FORMED__________________________________________________________________________ .sup.3 The limit of accuracy of the test measurement was about ±0.0004 g. 
    
     The data for test numbers G6C13, G6C14 and G6C15 demonstrate that, as in EXAMPLE 1, 100% distilled water or a 3% salt solution continues to corrode steel test pieces which had previously corroded in a 3% salt solution. The results from test numbers G6C1 through G6C4 indicate that when the 3% solution contains more than about 2.4% ammonium bicarbonate as in test numbers G6C5  and G6C6, most further corrosion by sodium chloride is inhibited. 
     When commercial ammonium carbonate reacts with carbon dioxide and water or carbonic acid, ammonium bicarbonate is produced according to the following equation: 
     
         NH.sub.4 COONH.sub.2.NH.sub.4 HCO.sub.3 +2H.sub.2 O+CO.sub.2 →3NH.sub.4 HCO.sub.3 
    
     Ammonium bicarbonate is less basic than ammonium carbonate and a less effective inhibitor of corrosion produced by sodium chloride. Based on the data reported in TABLE 4, a composition of about 82% ammonium bicarbonate and 18% sodium chloride contains the minimum amount of ammonium bicarbonate which inhibits chloride corrosion. Some new corrosion was observed for test numbers G6C5 and G6C6 having this composition. Test numbers G6C1, G6C2, G6C3 and G6C4 contained higher percentages of ammonium bicarbonate and no new corrosion was observed for these test pieces. 
     In view of the finding that ammonium carbonate and ammonium bicarbamate inhibit the corrosion of the ferrous metal exposed to even a high percentage of sodium chloride, these chemicals have great potential as reagents for applying to steel to inhibit corrosion by chlorides such as sodium chloride. 
     The foregoing description of the preferred embodiment of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.