US3425954A - Four component multipurpose corrosion inhibitor - Google Patents

Description

United States Patent ce 3,425,954 FOUR COMPONENT MULTIPURPOSE CORROSION INHIBITOR Peter M. Ruzeviclr and Ronald F. Adams, Chicago,

and Albert H. Reynolds, Glen Ellyn, Ill., assignors to The Cromwell Paper Company, a corporation of Illinois No Drawing. Filed Jan. 24, 1966, Ser. No. 522,392 US. Cl. 252-392 14 Claims Int. Cl. C23f 11/14, 11/12 ABSTRACT OF THE DISCLOSURE A multipurpose corrosion inhibitor comprising as the active ingredients 2. mixture of an alkali metal salt of aromatic carboxylic acids (sodium benzoate), an alkali metal salt of nitrous acid (sodium nitrite), an alkyl ester of benzoic acid (butyl benzoate) and a stable compound having a triazole function (benzotriazole). The composition is incorporated in a carrier vehicle such as propylene glycol and is adapted to inhibit the corrosion of metals in the presence of hydrogen sulfide and carbon dioxide by direct contact or as a vapor phase inhibitor.

This invention relates to multipurpose corrosion inhibitor compositions and the method of their use. More particularly this invention relates to compositions characterized by the ability to mitigate the corrosion of both ferrous and non-ferrous metals under a variety of conditions, including the corrosive action of ambient or urban atmospheres and atmospheres containing corrosive agents, such as hydrogen sulfide and carbon dioxide. The compositions of this invention are effective while in direct contact With the metal surface and under vapor phase conditions. These properties are highly desired in compositions used to combat corrosion during the packaging, storage and shipment of metal parts.

Many types of compounds have been successfully used as corrosion inhibitors. Some corrosion inhibitors are used to mitigate corrosion in the presence of water vapor and air. It is expedient to mix the corrosion inhibitors with inert carriers and apply them as a paste or grease to the metal surface to be protected. The chemical and physical characteristics of both the carrier and the inhibitor dictate the mode of use, the duration of the protection, the ease of application or removal and the over-all effectiveness of the compositions. These prior art compositions have many drawbacks, such as being expensive or being specific to certain environments or metals and thus are not adaptable to multipurpose usage. The compositions of this invention overcome these difficulties by providing an inexpensive corrosion inhibitor which is useful with a variety of metals under diverse conditions and gives multipurpose usage.

To illustrate, sodium benzoate is known to appreciably reduce the corrosion of steel and afford some protection for solder and solder joints. The combination of sodium benzoate and sodium nitrite affords a small degree of protection for aluminum, brass, solder, nickel and zinc under certain conditions, but this combination increases the rate of corrosion of cadmium and magnesium. Esters of fatty acids or aromatic acids are effective for steel but have or develop distinctive odors which limits their usefulness. Benzotriazole works Well with copper and its alloys when exposed to aqueous environments. In some instances the selection of a carrier having the required inertness, solubility for the components, and volatility limits the effectiveness of what would otherwise be a good inhibitor composition. This invention overcomes these and other disadvantages.

3,425,954 Patented Feb. 4, 1969 In accordance with this invention the discovery has been made that although the vehicle or carrier and the individual components, including but not limited to, sodium benzoate, sodium nitrite, butyl benzoate and benzotriazole, when used alone or in certain combinations have adverse effects on several different metals and in some instances actually induce corrosion, there is a particular combination of all of these components which when used in certain proportions, quite unexpectedly protects both ferrous and non-ferrous metals and alloys from corrosion under a diversity of conditions, thus qualifying as a multipurpose corrosion inhibitor. In addition this proportioned combination of inhibitors is effective over extended periods of time under both contact and vapor phase conditions.

The foregoing discovery is based on the finding that during accelerated corrosion tests such metals as zinc, copper, steel and solder are tarnished or not protected by a vehicle material such as Carbowax, propylene glycol or their mixtures, with or without the presence of a single inhibitor material such as sodium benzoate, sodium nitrite, butyl benzoate or benzotriazole, or even in the presence of certain combinations of these inhibitors. However, when the vehicle contains the benzoate salt and ester, the nitrite and the benzotriazole in combination, satisfactory protection is obtained for extended periods of time, even in the presence of an added corrosive agent such as hydrogen sulfide or carbon dioxide.

Accordingly, it becomes a primary object of this invention to provide a multipurpose corrosion inhibitor composition and a novel method of mitigating the corrosion of metals therewith.

Another object of this invention is to provide a multipurpose corrosion inhibitor comprising a major portion of a vehicle and minor portions of a mixture of alkali metal salts of an aromatic carboxylic acid, alkali metal salts of nitrous acid, alkyl esters of an aromatic carboxylic acid and one or more stable compounds having a triazole function.

A further object of this invention is to provide a corrosion inhibiting mixture comprising alkali metal salts of benzoic acid and alkyl-substituted derivatives thereof, alkali metal salts of nitrous acid, alkyl esters of benzoic acid and alkyd-substituted derivatives thereof and a stable compound having at least one triazole function.

Other objects of this invention are to provide a multipurpose corrosion inhibitor comprising about parts of a vehicle, such as a glycol or a polyglycol and/or combinations thereof, and about 10 to 30 parts of a mixture comprising alkali metal salts of benzoic acid, alkali metal salts of nitrous acid, alkyl esters of benzoic acid and stable compounds having the triazole function; to provide a multipurpose corrosion inhibitor composition comprising about 100 parts of a vehicle, such as a glycol, or a polyglycol, and/or combinations thereof, and about 10 to 30 parts of the aforesaid mixture; to provide a corrosion inhibitor composition comprising about 100 parts of a mixture of monoand polyglycols as the vehicle and about 10 to about 30 parts of a mixture of sodium benzoate, sodium nitrite, butyl benzoate and benzotriazole; to provide a multipurpose corrosion inhibiting composition consisting of about 50 parts of Carbowax (2000 to 8000), about 50 parts of propylene glycol, about 6 parts of sodium benzoate, about 1.5 parts of sodium nitrite, about 4 parts of butyl benzoate and about 3 parts of benzotriazole; to provide a corrosion inhibiting composition adapted to be used as a coating or impregnant for packaging material to inhibit atmospheric corrosion of metallic objects enclosed therein; and to provide an improved method of protecting metal surfaces from corrosion in atmospheric and aqueous media.

mens examined for tarnishing and/or corrosion. The results are shown in Table I.

TABLE I.ACCELERATED CONTACT CORROSION TESTS AT 120 F. AND 100% R. H.

Composition N Component:

Kraft paper" Propylene glycol Carbowax 4000.. Sod. Benzoate. Sod. Nitrite. Butyl Benzoate Benzotriazole Metal and Test Results: Aluminum. Zinc... Copper Steel.-- Solder Seam.

X X X X X X X X 100 50 50 50 50 50 50 50 50 50 50 50 6.0 6.0 1.5 1.5 4.0 4.0 4.0 3.0 3.0 3.0 3.0

G G G G G G G G G G G G P P P E F I G G E G E S G P F P G G E F E F E E P P P F E F P F E E G E E P E E F E G E E G E E No'rE.-Key; P=P0or, adverse, corrosive, tarnish etiect; F=Fair, very slight protective efiect; G Good, intermediate protective effect; E=Excellent, significant protection; S=Super1or, complete protection; X= Indicates that Kraft paper was used throughout.

In order to demonstrate this invention a number of acceler-ated corrosion tests were conducted using laboratory apparatus and known test procedures. The tests were carried out to show both the contact eiiect and the vapor effect of the individual ingredients and various combinations thereof on a number of representative metal specimens in a closed environment at 100% relative humidity and at a temperature of about 120 degrees F. The contact tests were conducted as follows.

To confine each test specimen in a controlled atmosphere, one-quart glass bottles, measuring 3" ID. and approximately 6 /2 tall were used. The cardboard gaskets of the Bakelite screw caps for the bottles were removed and replaced with aluminum foil pieces which extended over the tops of the bottles and onto the threads to provide a tight seal. Lucite tables measuring approximately 2 /2" in diameter and 1 /2" in thickness, with three oneinch legs, served to support the test specimens within the bottles. An oven equipped with circulating fans and capable of maintaining a constant temperature of 120 degrees F., plus or minus 2 degrees, was employed to heat the test bottles.

The metal specimens comprised galvanized iron, aluminum, solder seam, and copper, each measuring 2" by 2", and cold roll steel, measuring 1" by 4". The aluminum, copper and steel specimens were polished to .a clean surface on both faces and all edges with 240 aluminum grit. The galvanized iron and solder seam specimens were not polished. Each specimen was cleaned by immersion in 99% methanol, wiped dry and immersed again in the methanol and again wiped dry. To complete the cleaning and to provide final degreasing and protection from rust and tarnish prior to the tests, each specimen was immersed and maintained in petroleum ether, as is customary in conducting corrosion tests. The solder seam specimen was a section of a commercial can and the solder composition was approximately 95% lead and 5% tin.

The bottles, caps, and Lucite tables were thoroughly washed and oven dried. 30 ml. of distilled water was added to each test bottle. The test specimens were removed from the petroleum ether, allowed to air dry and wrapped in 50# kraft paper which had been impregnated with about 2 grams of the ingredients under test, as indicated in the table infra, per square foot of paper. The kraft paper was held to the specimens by staples. A set of the wrapped test specimens was then placed on the Lucite tables, which were inserted in the test bottles. Each bottle was tightly capped and sealed with the aluminum gasket and placed in the pre-set oven. The bottles remained in the oven for 22 hours at 120 degrees F. after which time they were removed, refrigerated at 35 degrees F. to 40 degrees F. for 2 hours, and returned to the oven for 48 hours. After this time the bottles were removed, again refrigerated at 35 degrees to 40 degrees F. for 2 hours. At this time the kraft paper was removed and the speci- The tests shown in Table I are contact corrosion tests wherein the metal specimen undergoing test is in actual contact with the composition which is impregnated in the kraft paper wrapping. Composition No. 1 is a blank run to show the eifect of using untreated kraft paper to protect the specimens. Propylene glycol alone or with Carbowax (tests 2 and 3) are similar control tests. Tests 4, 5, 6 and 7 are on the individual corrosion inhibitors alone, while tests 8, 9, 10 and 11 are on combinations wherein two and three inhibitors are used together. Composition or test No. 12 represents a preferred embodiment of this invention, incorporating the essential ingredients in combination.

In each of the tests reported in Table I, the kraft paper, used to bring intimate contact between the composition and the metal surface, was treated by wetting or saturation with the individual component or combination of components, including components of the vehicle, as indicated. The tests on propylene glycol were conducted at concentration for this component of the vehicle and when both the propylene glycol and Carbowax were tested as the vehicle combination, the ratio was 1:1. All of the ingredients were of the highest commercial purity and from the same samples to give meaning to and allow direct comparison of the results. The other components were added to the vehicle in the same parts ratio as that present in the preferred composition of this invention, that is, 6 parts of sodium benzoate, 1.5 parts of sodium nitrite, 4 parts of butyl benzoate and 3 parts of benzotriazole, whether used singly or in combination. Under these conditions freedom from adverse effects was observed only in the case of solder seam, however, these samples showed only intermediate protection due to slight discolorations on the metal surfaces.

The test results show that adverse effects, either because of complete failure to inhibit corrosion, rust or tarnish, or because of discolorations, were observed on many of the metal specimens when tested with the vehicle alone, the kraft paper alone, or one, two, or three of the inhibitor components present with the vehicle. These results show that only when the combination of the vehicle, sodium benzoate, sodium nitrite, butyl benzoate and benzotriazole is used, substantially complete protection for all of the metals is obtained.

Although the accelerated corrosion tests conducted to obtain the data shown in Table I are severe and the attainment of significant protection or better for all of these metals under such conditions represents an advance in the art, this invention is further characterized by offering protection to these various metals in the presence of an active corrosive agent, such as hydrogen sulfide and carbon dioxide, e.g. under very severe conditions. Using the same types of metal samples, the same procedure and compositions shown in Table I, a second series of tests was run to show the protection obtainable in the presence of hydrogen sulfide (part A) and carbon dioxide (part B), of Table II.

TABLE II.-(A) ACCELERATED CONTACT CORROSION TESTS AT 120 F.

AND 100% R. H. WITH HYDROGEN SULFIDE (B) ACCELERATED CONTACT CARBON DIOXIDE CORROSION TESTS AS ABOVE WITH MetglI and Test Results:

Solder Seam G Key: Same as in Table I.

The results shown in Table II indicate that in every instance compositions 1 to 11 failed to give protection for one or more of the metal samples, but composition No. 12 offered overall protection for all of the specimens.

Tests were conducted to determine the effectiveness of the compositions of this invention in mitigating the corrosion of metal samples under conditions wherein the inhibitor must functon in the vapor phase. Although the eifect of vapor phase corrosion on metal parts is not as severe as contact corrosion, the attainment of adequate protection under both conditions with the same composition is a distinct advantage over the prior art and another unique aspect of this invention. The composition used in this next series of tests was No. 12 of Table I. For each test a polished-metal specimen was formed into a V trough and placed in the inverted position upon a piece of kraft #50 paper impregnated with Composition No. 12. The treated paper and specimen, with its edges only touching the paper, were housed in an enclosure formed of the same treated kraft paper and subjected to heat at 100 F. under 100% relative humidity for 8 days. As a control, tests were conducted under the same conditions with untreated kraft paper. Under the conditions of these tests, aluminum and copper are not appreciably corroded or tarnished. The results for zinc, steel, and solder seam were as shown in Table 111.

TABLE IIL-ACCELE RATED VAPO R CORROSION TESTS AT 100 F. AND 100% RH.

Note-Key; P=Poor, adverse, corrosive, tarnish cfifiect; E-Excellent, signlliicant protection; F Fair, appreciable but not severe corrosion.

The above results are most significant in relation to Zinc, steel and solder seam.

The instant invention may be embodied in other specific forms and the examples used to demonstrate the effectiveness of the combination of ingredients are merely illustrative. Thus the vehicle may be selected from a large class of inert liquid or semi-liquid materials in which the corrosion inhibitors are either soluble or dispersible. The vehicle may be water, water-soluble wax, mineral oil, long chain alcohols, turbine oils, hydraulic oils, a paraffin oil, Ucon fluids, a synthetic ester lubricant, lanolin, 'butyl Cellosolve, petrolatum, parafiin wax, albino asphalt, diphenyl oxide, sperm wax, and the like, to illustrate a few.

A preferred class of vehicles comprise the water-soluble waxes, such as are described in US. Patent 2,837,432 by S. W. Drigot et al., which materials are polyalkylene glycols and the alkyl ethers thereof containing 2 to 7 carbon atoms in each alkylene group and 1 to 30 carbon atoms in each alkyl group. The sub-genus of poly-1,2- alkylene glycols and their alkyl ethers having molecular weights between about 106 and 10,000 constitute a preferred group. Such glycols may be obtained by polymerizing 1,2-alkylene oxides or mixtures thereof in the presence of a catalyst and a suitable initiator for the reaction, such as water, a monohydric alcohol, in the case of the alkyl ethers, or a mercaptan, and the like. The poly-1,2-alkylene glycols derived from ethylene oxide or from 1,2-propylene oxide or mixtures thereof and their alkyl ethers of l to 18 carbon atoms per alkyl group, which have molecular weights of about 200 to about 8000 can be used. Polyalkylene glycols containing from 2 to 7 carbon atoms in each alkylene and as many as 13 such units can be used.

Some of these are illustrated by:

Also included are the polyethylene glycol mixtures having average molecular weights of 200, 400, 1000, 1540, and 2000; and poly-1,2-propylene glycol mixtures having average molecular weights of 425 and 1025. Of particular utility are the materials known under the trade name of Carbowax. These are polyethylene glycol waxes of high molecular weight, such as Carbowax 2000, Carbowax 4000, Carbowax 5000, Carbowax 6000 and Carbowax 8000, up to Carbowax 25,000. Carbowax 4000, which was used to demonstrate this invention, has a density of 1.204, a melting point range of degrees to degrees C., a viscosity of 689 SUS at degrees C. and a flash point of 535 degrees F. Preferably these materials having intermediate molecular weights in the order of 1500 to 8000 are used in this invention.

For convenience in solubilizing the inhibitors and in handling the finished compositions, especially when the more viscous vehicles are used, a diluent may be incorporated along with the vehicle. For this purpose any material which is capable of reducing the viscosity of the vehicle and aiding the solubility without side efiects may be used. The alkylene glycols, including but not limited to ethylene glycol, propylene glycol, butylene glycol and mixtures of these glycols may be used. Glycols of this series having 2 to 6 carbon atoms per molecule and two hydroxyl groups in the chain can be used. These glycols act as softening agents for the high molecular weight waxes. A preferred group of diluents comprises the water soluble ethylene glycol, propylene glycol, polypropylene glycols and mixtures thereof.

The first essential ingredient of the compositions of this invention comprise the alkali metal salts of aromatic carboxylic acids having 6 to 14 cyclic carbon atoms and 1 to 2 carboxylic acid groups attached to the cyclic carbon atoms. Salts of the formula R(COOM),, wherein R is a member of the group consisting of C to C aryl, C to C alkyl-substituted C to C aryl, C to C alkenyl-substituted C to C aryl and C to C cycloalkyl-substituted C to C aryl, M is an alkali metal and n is an integer of l to 2, may be used.

Species thereunder include the alkali metal salts of benzoic acid, the toluic acids, alpha-naphthoic acid, betanaphthoic acid, 1,2,3,4-tetrahydro-2-naphthoic acid, 1- phenanthroic acid, Z-phenanthroic acid, 3-phenanthroic acid, 9-phenanthroic acid, l-anthroic acid, 9-anthroic acid and the like among the mono-carboxylic acids; phthalic acid, isophthalic acid, terephthalic acid, biphenyl-Z, 2' dicarboxylic (diphenic) acid, biphenyl-3-3-dicarboxylic (diphenic) acid and biphenyl-4,4'-dicarboxylic acid and the like among the dicarboxylic acids.

Species include: sodium benzoate; sodium toluate; sodium naphthoate; sodium phthalate; sodium anthroate; potassium benzoate; potassium toluate; potassium naphthoate; cesium benzoate; cesium naphthoate; lithium benzoate; potassium phthalate; lithium anthroate; and cesium naphthoate.

The preferred group of salts comprises the alkali metal benzoates, namley sodium benzoate, sodium toluate, lithium benzoate, potassium benzoate, potassium toluate and cesium benzoate and mixtures thereof. These salts are soluble or dispersible in the vehicles and are used to the extent of about 12 parts per 100 parts of vehicle. As little as 1 part of said salt per 100 parts of vehicle may be used. The aromatic acid nucleus may contain non-interfering groups such as alkyl groups having 1 to carbon atoms e.g. methyl to decyl, the corresponding unsaturated radicals, and cycloalkyl radicals having 3 to 7 carbon atoms. The presence of such side chains often increases the solubility of the salts, especially in mineral oils and like vehicles.

The second essential corrosion inhibiting ingredient of the compositions of this invention comprise the alkali metal salts of nitrous acid (HNO This group of salts includes sodium nitrite, potassium nitrite, lithium nitrite, cesium nitrite and their mixtures. Because of its low cost and particular effectiveness, sodium nitrite is preferred. These salts are used in the vehicle to the extent of about 1 to 2 parts per 100 parts of vehicle.

The third essential corrosion inhibitor used as a constituent herein comprises the alkyl-, alkenyl-, and cycloalkyl esters of aromatic carboxylic acids having 6 to 14 cyclic carbon atoms in the aromatic portion of the molecule and a single carboxyl group attached to a cyclic carbon atom. This component may be defined by the formula:

R C=O )-R* wherein R is the same as R in the formula for the aromatic salts, previously defined, and wherein R is C to C alkyl, C to C alkenyl or C to C7 cycloalkyl and similar non-interfering groups. Non-limiting examples of R are methyl, ethyl, normal propyl, iso-propyl, butyl, isobutyl, t-butyl, amyl, iso-amyl, hexyl, heptyl, octyl, nonyl, decyl, vinyl, cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups. Other non-interfering groups may be present in the molecules of these esters.

In the preferred embodiment of this invention R is ethyl, propyl, iso-propyl, butyl, isobutyl, t-butyl, or amyl, that is, containing 2 to 5 carbon atoms. Species include butyl benzoate, propyl benzoate, isopropyl benzoate, tbutyl benzoate, amyl benzoate, isobutyl benzoate, butyl naphthoate, and isobutyl naphthoate. This third component is used in the vehicle Within the range of about 2 to 12 parts per 100 parts of the vehicle.

The fourth and last essential corrosion inhibiting ingredient of the instant compositions comprises any stable compound having at least one triazole function, that is, contains the group:

and tautomeric forms thereof. The remaining valences of the two carbon atoms in the triazole function may be connected to any other non-interfering group, such as hydrogen, C to C alkyl, or a C alkylene to form benzotriazole and related compounds. These compounds are all stable, do not react with acids or bases, resist oxidation and reduction and act as extremely weak bases. By replacing the hydrogen atom on one of the nitrogen atoms with an alkali metal, stable salts are formed which may also be used in accordance with this invention. The preferred species are benzotriazole, azimino-toluene, 8- methyl-benzotriazole and mixtures thereof. These compounds are soluble or dispersible in the vehicle and are used in amounts ranging from 1 to 10 parts per parts of vehicle. These triazole compounds have the formulae:

Example I Parts Inert carrier 100 Sodium benzoate 5 Sodium nitrite 1 Ethyl benzoate 3 Benzotriazole 2 Example II Parts Inert carrier 100 Lithium benzoate 4 Potassium nitrite 1.5 Butyl benzoate 3 Azimino-toluene 2.5 Example III Parts Polyethylene glycol (6000) 100 Diluent 100 Sodium benzoate 10 Sodium nitrite 2 Amyl benzoate 6 Benzotriazole 4 Example IV Parts Polyethylene glycol (6000) 40 Ethylene glycol 60 Potassium naphthoate 5 Potassium nitrite 1 Sodium nitrite 0.5 Amyl benzoate 4 Azimino-toluene 4 Example V Parts Polyethylene glycol (4000) 6O Propylene glycol 40 Cesium benzoate 6 Sodium nitrite 2 Ethyl benzoate 4 8-methyl-benzotriazole 4 Example VI Parts Carbowax 8000 45 Ethylene glycol 45 Propylene glycol 10 Potassium naphthoate 2 Potassium nitrite 1 Potassium benzoate 1 t-Butyl benzoate 2.5 Benzotriazole 2.5

Example VII Mineral lubricating oil 100 Triton X-100 10 Sodium benzoate 6 Lithium nitrite 2 Ethyl benzoate 4 Amyl naphthoate 1 Benzotriazole 4 Example VIII Parafiin wax i100 Ethylene glycol 40 Sodium dodecyl benzene sulfonate 10 Cesium naphthoate 5 Lithium nitrite 3 Propyl benzoate 2 Amyl benzoate 1.5 Benzotriazole 4 The corrosion inhibitors used to makethe compositions of this invention are readily compounded by adding the same sequentially, or as a mixture, to the vehicle and applying moderate heat, in theorder of up to 170 degrees F. Generally mere agitation is sufficient to effect solution of the inhibitor combinations. Uniform distribution of the inhibitors in the vehicle, such as mineral oil or water soluble wax is attained by dissolving the inhibitors in the glycol and then adding the solution to the balance of the vehicle. When water, oil, or waxes are used as the vehicle it is expendient, though not always necessary, to use about 1 to .15 parts (per 100 parts of vehicle) of a soap, detergent, surfactant or the like, as described below. Since most of the ingredients are either water-soluble or water dispersible, their dissolution in the water-soluble waxes is not difficult.

The compositions of this invention may be used in a number of ways, as contact corrosion inhibitors, as vapor phase inhibitors, or as a combination of these functions. The corrosion of the metal surfaces of an article within an enclosing means, such as wrapping material, paper, cardboard, textiles, plastic films, metal containers etc. can be mitigated by maintaining therein the compositions of this invention, whereby a non-corrosive atmosphere is thereby produced. The invention is particularly applicable to atmosphere containing water and air. The mixture of ingredients and vehicle need only be allowed to diffuse throughout the atmosphere in the enclosure and contact the metal surfaces. The compositions of this invention may be mixed with an inert absorbent such as paper shreds or saw dust and used as a packing material for metal parts, or applied thereto as a grease, or as part of a grease. A preferred method is to treat a wrapping material with the composition of this invention by use of standard coating or impregnating equipment and apply the treated paper, coated side inward, as a package or container for the metal to be protected. Suitable detergents include Triton X-100, a proprietary product comprising the condensate of 9' to 10 ethylene oxide groups with octyl phenol, sodium dodecyl benzene sulfonate, and the like.

Having thus described thus described our invention, we claim:

1. A composition of matter consisting essentially of (a) about 1 to 12 parts of salts of the formula R(COOM) wherein R is a member of the group consisting of C to C aryl, C to C alkyl-substituted C to C aryl, C to C alkenyl-substituted C to C aryl and C to C cycloalkyl-substituted C to C aryl, M is an alkali metal and n is an integer of 1 to 2,

(b) about 1 to 2 parts of salts of the formula M-NO wherein M is an alkali metal,

(c) about 2 to 12 parts of esters of the formula R COOR wherein R is a member of the group consisting of C to C aryl, C to C alkyl-substituted C to C aryl C to C alkenyl-substituted C to C aryl and C to C cycloalkyl-substituted C to C aryl, and R is a member of the group consisting of C to C alkyl, C, to C alkenyl and C to C cyclo-alkylene, and

-(d) about 1 to 10 parts of a stable triazole compound of the formulae:

wherein R and R are independent substituents of the group consisting of hydrogen and C to C alkyl, x has a value of 0 or 1 and the alkali metal salts thereof.

2. The composition defined by claim 1 wherein the mixture comprises about 6 parts of the ingredient (a) about 1.5 parts of ingredient (b), about 4 parts of ingredient (c) and about 3 parts of ingredient (d).

3. A composition of matter as defined by claim 1, including an inert vehicle therefor.

4. A composition of matter as defined by claim 3 wherein ingredient (a) comprises an alkali metal salt of benzoic acid, ingredient (b) comprises an alkali metal salt of nitrous acid, ingredient (c) comprises an alkyl ester of benzoic acid, and ingredient (d) is a member of the group consisting of benzotriazole, aZimino-toluene, 8-methyl-benzotriazole, and mixtures thereof.

5. A composition as defined by claim 3 wherein the inert vehicle is an alkylene glycol having a molecular weight no greater than about 10,000.

6. A composition as defined by claim 4 wherein the inert vehicle is a member of the group consisting of ethylene glycol, propylene glycol, polypropylene glycols having molecular weights of about 200- to 8,000, and mixtures thereof, and the remaining ingredients total about 10 to 3 0 parts to parts of said vehicle.

7. A composition as defined by claim 3 where the inert vehicle is an alkylene glycol having a molecular weight no greater than about 10,000 and the remaining ingredients comprise sodium benzoate, sodium nitrite, butyl benzoate and benzotriazole.

8. A composition as defined by claim 3 wherein the vehicle is a mixture of an alkylene glycol having a molecular weight of up to about 500 and a polyalkylene glycol having a molecular weight between 1500 and 8000.

9. A composition as defined by claim 8 wherein the remaining ingredients are (a) sodium benzoate, (b) sodium nitrite, (c) butyl benzoate, and (d) benzotriazole.

10. A composition of matter in accordance with claim 9 in which about 100 parts of said vehicle, about 6 parts of sodium benzoate, about 1.5 parts of sodium nitrite, about 4 parts of butyl benzoate and about 3 parts of benzotriazole are present.

11. A composition of matter adapted for use as a coating or impregnant for wrapping material to inhibit atmospheric corrosion of metallic objects wrapped therein which consists essentally of a minor amount of a combination corrosion inhibitor including about one to twelve parts of alkali metal salts of benzoic acid, about one to two parts of alkali metal salts of nitrous acid, about two to twelve parts of alkyl esters of benzoic acid and about one to ten parts of a compound having a triazole function of the group consisting of benzotriazole, azimino-toluene, 8- methyl-benzotriazole and mixtures thereof, and an inert vehicle consisting essentially of about 50 parts of a water soluble wax of the group consisting of polyethylene glycols having molecular weights of about 1500 to 8000, and about 50 parts of a water soluble softening agent for said wax of the group consisting of ethylene glycol, propylene glycol, poly-propylene glycol having molecular weights of about 200 to 800 and mixtures thereof.

12. A composition of matter adapted for use as a coating or impregnant for wrapping material to inhibit atmospheric corrosion of metallic objects enclosed therein consisting of the following ingredients:

Parts Polyethylene glycol (mol. wt. about 1500 to 8000) 50 Propylene glycol 50 Sodium benzoate 6 Sodium nitrite 1.5 Butyl benzoate 4 Benzotriazole 3 13. The method of mitigating the corrosion of metals which comprises maintaining in contact therewith a coating of a polyglycol vehicle having a molecular weight no greater than about 10,000 containing as the active ingredients corrosion-inhibiting amounts of alkali metal salts of benzoic acid, alkali metal salts of nitrous acid, alkyl esters of benzoic acid, and a compound having triazole function of the group consisting of benzotriazole, azimino-toluene, S-methyl-benzotriazole and mixtures thereof.

14. The method of mitigating the corrosion of metals in contact with an aqueous medium which comprises maintaining therein as the active ingredients corrosioninhibiting amounts of alkali metal salts of benzoic acid, alkali metal salts of nitrous acid, alkyl esters of benzoic acid, and a compound having a triazole function of the group consisting of benzotriazole, azimino-toluene, 8- methyl-benzotriazole and mixtures thereof.

References Cited UNITED STATES PATENTS OTHER REFERENCES Hackhs Chemical Dictionary, McGraw-Hill, 1944, p. 32.

2O LEON D. ROSDOL, Primary Examiner.

I. GLUCK, Assistant Examiner.

US. Cl. X.R.