US2371207A - Corrosion protection of metals - Google Patents

Description

Patented 13, 1945 CORROSION PROTECTION OF METALS Ernest W. Zulilin, Sausalito, Emmett R. Barnum,

Berkeley, and Ellis R. White, Albany, Calif., assignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing.

The present invention relates to metals or metal-containing articles of manufacture which are normally subject to corrosion and which have been rendered substantially non-corrodible by.

treatment with a dispersion of a certain free dicarboxylic acid in a suitable vehicle.

Metallic surfaces, particularly those containing iron, require protection against the hazard of corrosion in the presence of water. To illustrate: Moisture readily attacks finished or semifinished metal objects unless the metal surface is covered during storage or shipment by a protective coating such as a, slushing oil; water in Diesel engine fuels often corrodes closely fitted parts such as are found in Diesel engine unit type injectors; water in turbines corrodes turbine Application February 8, 1943', Serial No. 475,204

17 Claims.

although lower or higher temperatures may be employed. The lower temperature limit is usually determined by the solidification temperature of the liquid, and temperatures should'be below the boiling temperature of the vehicle and below the decomposition temperatures of both the vehicle and the dicarboxylic acid.

Metals capable of being thus protected are in particular the ferrous metals, e. g., soft iron, various steels, cast iron, and to a lesser extent copper, brass, bronze, zinc, aluminum, magnesium alloys, various bearing metals as copperlubricant circulatory systems, particularly the governor mechanismsoi steam turbines; and-water in hydrocarbon oils, such as gasoline, rusts steel storage tanks and drums; water in antifreeze compositions causes corrosion in automobile radiators, etc. Corrosion not only has a deleterious effect upon the metal surfaces, but also frequently loosens finely divided metal oxides which may act as oxidation catalysts increasing the rate of deterioration of various organic compounds with which they come in contact or may enter between movingparts of machinery where they act as abrasives.

It is a purpose of this invention to treat metals or articles of manufacture containing metals in a way so that they become resistant to their normal corrosion. It is a specific purpose to treat in a simple manner accurately machined metal parts so that they may be handled without developing corrosion, particularly in places where fingerprints have been left, Another purpose is to protect iron or "steel equipment exposed to the atmosphere so that its rusting is prevented or at least retarded. Still another purpose is to protect mechanical equipment from rusting,

' which equipment stands idle and/or is shi ped over long distances. We have discovered that structural metals which are used in the construction of various articles of manufacture and are subject. to a normal corrosion can be protected simply and eifectively by treating them with a line dispersion.qf a dicarboxylic acid having at least 16 carbon atoms and a. linkage comprising one or ous to recite.

lead, cadmium-nickel, silver-nickel, etc.

Articles containing these metals are too numer- However, it may be mentioned that the problem of rust prevention is critical, for example, where accurately machined parts are involved, such as piston rings, engine cylin ders, bearing shafts, plungers of pumps, etc. In

other instances, rust prevention may perhaps not be critical, but of vast economic importance as, for example, in the mass production of steel castings which are piled up and often set inthe open for months before being finished.

Corrosion may be due not only to atmospheric exposure, but may be caused or accelerated by contact with acidic materials, for example, by touching with the fingers. It also may occur in closed systems, as-in internal combustion-engines, steam turbines, pipe lines, etc., due to the corrosive influence of various impurities as water, oxygen, CO2, salts, inorganic or organic acids, etc. The treatment, according to this invention, for

" the prevention of corrosion may consist of a single contact of the metal to be protected with the dispersion containing the dicarboxylic acid, or may comprise repeated contacts effected at intervals, or may consist of a continuous treatment lasting as long as the use of the particular dispersion or piece of equipment or both. The choice of any particular type of these treatments is usually dictated by circumstances. For example, if newly machined and finished .machine parts are to be rust-prooied, they may be dipped or sprayed with a suitable dispersion, and then stored away. On the other hand, if rust prevention in a steam turbine is desired, it is preferable that the circulating lubricating oil contain the active rust-preventive compound and more elements selected from the group consisting of sulfur, selenium and tellurium.

The dispersion may be a true or colloidal solution in a suitable vehicle which is capable of flowing under the conditions of the treatment, i. e., is liquid or plastic at the temperature of The treatment.

atmospheric if the vehicle is normally liquid,

contact is made as long as this oil is used. Should, after a while, this oil be discarded and be replaced by another one not containing a rust-preventive, then corrosion protection usually lasts for a long time thereafter, due to the protective film left-behind. In cases where this film is mechanically destroyed, as in bearings or gears, etc., running under extreme loads, the protective film must be renewed continuously; otherwise rust protection fails.

The general formula. of the corrosion-preventive acids of this invention is: ci o on eke-o 0 0 H wherein X, is sulfur,'selenium or tellurium, and

u, v and w are integers, preferably 1 or 2, although 11. and u may be from 1 to about 10. The unoccupied valences are tied to the same or different hydrogen or hydrocarbon radicals, the latter of which may be aliphatic, cycloaliphatio, aromatic or mixed and may-contain substitution radicals which are not too strongly polar, such as halogen, etc., but should preferably be free from strong polar radicals, sucha's"0H, =CO,

H NH2, SH, etc.

The above formula may take the following form:

o wn'o awooon As indicated before, the acid should have a total number of carbon atoms not less than 16, and preferably between about 20 and 60 for good anti-corrosive properties. Both true solutions and colloidal dispersions in various vehicles are effective in the matter of corrosion protection. However, true solutions are preferred for two reasons: first, colloidal solutions may under some circumstances coagulate, in which case at least a portion of the active protective agent is eliminated; and second, colloids tend to cause emul-. sification of oily vehicles with water, which in many instances, such as in the lubrication of steam turbines, is undesirable.

It is, of course, desirable that the acids be relatively resistant to oxidation, and therefore they should not contain more than one aliphatic double bond per hydrocarbon radical and preferably none.

Generally, in the presence of copp r, acids containing a link of a. single X atom (X being S, Se

or Te) seem to impart to oils longer induction periods than acids having XX linkage, while the latter impart lower rates of oxygen absorption after the induction period. Thus disulfide, diselenide or ditelluride acids may be preferred for some oils, while acids with mono linkages may be better for other oils. Polysulflde linkages of more than two sulfur atoms may also be 'used. They are, however, believed to contain only two sulfur atoms in the normal chain between the carboxyl radicals, the remaining sulfur being attached in the form of a branch, such as s s i i etc. If-desired, the carboxyl radicals may be linked through a sulfur radical s o o I The closeness of the sulfur, selenium or tellurium to the carboxyl radical has some bearing on the corrosion-protective properties of the acids. In general, the closer they are, the more potent the compound is, other things being equal. Thus,

from this angle, acids in which the sulfur, selenium or tellurium atoms are in alpha or beta position to at least one, and preferably both carboxyl radicals are the best anti-corrosives.

Accordingly, among the groups of acids are several which are particularly useful. For example, di-fatty acid alpha sulfides, selenides and tellurides having the formula m-on-coon m-tn-coon wherein o is 1 or 2, and R1 and Rs are alkyl radicals whose total number of carbon atoms is not less than 16 (one of them may be hydrogen). If desired, R1 and R2 may comprise alicyclic rings, in which case one or both of the car-boxylic acids are naphthenic acids; or else R1 and R2 may con-.

@mn-wn-ooou (BOOK OOH 00H wherein Rl-R3 are hydrogen or hydrocarbon radicals, the latter preferably being aliphatic although they may comprise cycloaliphatic or aromatic groups. The unoccupied'valences are tied to hydrogen or hydrocarbon radicals, which radicals may be the same or different in different groups. X again is sulfur, selenium or tellurium;

- n is an integer of 1 up to about 8, and preferably 1 or 2; .and o is 1 or preferably 2. The total number of carbon atoms is preferably 20 or more.

The dicarboxylic acids of this invention may be produced in several ways. One convenient method comprises reacting a chlorinated fatty acid or other suitable monocarboxylic. acid with an a.lkali metal sulfide or polysulfide. Commer-v cially available alkali metal sulfides are usually mixtures containing mono-, diand sometimes higher polysulfides. Therefore this reaction may be utilized to produce mixtures of different sulfide dicarboxylic acids. Such mixtures are very excellent for the purpose of this invention, sincev they are usually more soluble in various vehicles and as-oxidation stable as the best of the pure individual compounds.

Disulfides maybe produced by first preparing a hydrosulfide derivative of a fatty acid or other suitable carboxylic acid by reaction of a chlorinated carboxylic acid with NaHS, KHS, etc., then oxidizing the hydrosulflde to the .disulfide.

Higher 'polysulfldes may be obtained by oxidiz-. ing with sulfur in the presence of lead oxide.

Asymmetric dicarboxylic acids may be produced, for example, by reacting a suitable chlorinated monocarboxylic acid with an alkali meta1 salt of thioglycolic acid or of a fatty or other suitable monocarboxylic acid hydrosulfide.

Suitable monocarboxylic acids for the production of our dicarboxylic acids include fatty acids,

such as acetic acid, propionic, butyric, isobutyric valeric, caproic, caprylic, decylic, undecylic, lauric, myristic, palmitic, stearic, arachic, behenic, oleic, phenyl acetic, phenyl propionic, phenyl stearic, tolyl stearic, naphthyl acetic, naphthol stearic, acids, etc. Naphthenic acids, such as are obtained by caustic alkali extraction of relatively high-boiling straight-run petroleum oils, such as kerosene, gas oil, lubricating oils, etc., may be used; or synthetic naphthenic acids, such as cyclohexyl acetic, cyclohexyl propionic, cyclohexyl stearic acids, corresponding alkyl cyclohexyl, tetrallyl, dicyclohexyl fatty acids, or acids derived from naphthenes obtained by hydrogenation of isophorone, diisophorone and homologues, etc. In choosing a monocarboxylic acid from the list for use in a certainreaction, sight must not be lost of the fact that the dicarboxylic acid must have a minimum of 16 carbon atoms.

The vehicles to which dicarboxylic acids of this invention may be added for the purpose of producing corrosion-protective compositions may be divided into several groups. 'In the first place, they may be liquids or plastics, the only requirements as to their physical state being '(in addition to their being able to act as carrier for the acids under normal atmospheric conditions) that they be spreadable over metal surfaces. Spreading may be accomplished by immersing, flooding, spraying, brushing, trowelling, etc.

After being applied, all or part of the vehicle butyl ethers; neutral esters of carboxylic and other acids as ethyl, propyl, butyl, amyl, phenyl, cresyl and higher acetates, propionates, butyrates, lactates, laurates, myristates, palmitates, stearates, oleates, ricinoleates, pthalates, phosphates, phosphites, thiophosphates, carbonates;

natural waxes as carnauba wax, candelilla wax,

distillates, kerosene, gas oil, lubricating oils may be evaporated, or it may bemore or less permanent. In other words, both volatile cariers may be used, or substances which do not materially volatilize under normal atmospheric conditions. As to chemical requirements, the vehicle must be stable under ordinary conditions of storage and use and be inert to the active inhibitors.

Thus the vehicle should preferably be substantially neutral, although it may be weakly acidic or basic, preferably having dissociation constants not above about 10 In vehicles of low dielec-. tric constant, as hydrocarbon oils, which are not conducive to ionization of dissolved electrolytes, relatively small amounts, i. e., about .1% to 5% of various carboxylic acids, such as fatty or naphthenic acids, may be present, and in many instances this may even be beneficial.

Both polar and non-polar vehicles may be employed. Among the former are water, alcohols,

such as methyl, ethyl, propyl, isopropyl, butyl,

amyl, hexyl, cyclohexyl, heptyl, methyl cyclohexyl, octyl, decyl, lauryl, myristyl, cetyl, stearyl, benzyl, etc., alcohols; polyhydric alcohols as ethylene glycol, propylene glycol, butylene glycol, glycerol, methyl glycerol, etc.; phenol and various alkyl phenols; ketones as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl, methyl butyl, dipropyl ketones, cyclohexanone and higher ketones; keto alcohols as benzoin, ethers as diethyl ether, diisopropyl ether, diethylene dioxide, beta-beta dichlor diethyl ether, diphenyl oxide, chlorinated diphenyl oxide, diethylene glycol, triethylene glycol, ethylene glycol m'onomethyl ether, corresponding ethyl, propyl,

(which may be soap-thickened to form greases), petrolatum, parafiin wax, albino asphalt, carbon tetrachloride, ethylene dichloride, propyl chloride, butyl chloride, chlor benzol, chlorinated kerosene, chlorinated paraffin wax, etc.

The amounts of the dicarboxylic acids which must be incorporated in the above vehicles to produce .corrosion-protective compositions vary considerably with the type of vehicle used. As a general rule, the presence of resinous materials, particularly those of a colloidal nature, calls for relatively larger amountsof inhibitors. Resinous materials which interfere with the activity of the inhibitors comprise asphaltenespetroleum resins, various other natural resins, as rosin, resins formed by polymerization of drying fatty oils, phenol-formaldhyde resins, glyptal type resins formed by esterification of polyhydric alcohols with polycarboxylic acids, etc.

In the absence of such resinous materials, amounts required of the dicarboxylic acids vary from about .00l% up to about .l%, although larger amounts may be used. However, where the acids are in colloidal dispersion, rather than in true solution, a concentration in excess ofabout .l% may result in relatively quick loss of part of the inhibitor by precipitation and settling.

In. the presence of resins and other colloid amounts in excess f l. and up to 5% may be required. Inasmuch as resins may act as protective colloids, compositions containing these large amounts of colloidally dispersed inhibitors, together with resin, may be quite resistant to precipitation and settling.

Since resinous and gummy substances in the vehicles do call for greater amounts of inhibitors, it is usually desirable to refine normally liquid vehicles thoroughly and free them from gummy substances, thereby imparting to them maximum inhibitor susceptibility. This is of particular importance, for example, in lubricating oils, specifically steam turbine oils, which are advantage ously highly refined before the inhibitor is introduced. Suitable refining treatments include, for example, extraction with selective solvent for aromatic hydrocarbons as liquid S02, phenol, furfural, nitrobenzene, aniline, beta-beta-dichlorine diethyl ether, antimony trichloride, etc.; treatment with AlCla', sulfuric acid, clay, etc.

If the treatment produces a sludge, special care must be taken to remove it very thoroughly and completely.

Example The effectiveness of several dicarboxylic acids of this invention in suppressing corrosion was Additive Water Time Corrosion Hours 2% NaCl 48 None-perfect pro .0192, alpha alpha di- 7 tection. lauric acid sulfide. Synthetic sea 48 Do.

water.

s thetic sea is Do v atcr. l% alpha alpha di- Synthetic sea 48 Do.

gglmitic acid sulwater. e. .0l% alpha alpha di- 2% N 9.01 48 Do.

stearic acid sulfide.

Do Sea water..." 44 Slight corrosion,

- less than Do Synthetic sea 48 None-perfect prowater. tection. .005% alpha alpha dido a. 25 Slight corrosion,

stearic acid sulfide. less than 10%. .0195 alpha-lauric 8.1- do 48 None-periect pro gga-stearic acid sulction.

e. .0i% alpha alpha di- 2% NaCl 48 Perfect.

stearic acid disul- Synthetic sea 24 Very slight corrofide. water. sion. .0l% alpha hexadecyl 2% NaCl 24 Do.

thioglycolic acid.

We claim as our invention:

1. A structure normally corrodible metal coated with a corrosion-preventive film of a free dicarboxylic acid having atleast 16 carbon atoms, the two acid radicals in said 'acid being linked through an element selected from the group consisting of S, Se and Te. v v

2. The coated metal of claim 1, the film of which contains an acid having between 20 and 60 carbon atoms.

' 3. A structural normally corrodible metal coated with a corrosion-preventive film of a free dicarboxylic acid having at least 16 carbon atoms, and having the formula wherein X is an element selected from the group consisting of S, Se and Te, u and v are integers ranging from 1 up to about 10, and u is l or 2.

4. A structural normally corrodible metal coated with a corrosion-preventive film of a free dicarboxylic acid having at least 16 carbon atoms and the formula wherein R1 and R2 are hydrogen or hydrocarbon radicals, X is an element selected from the group consisting of S, Se, and Te, and o is 1 or 2.

5. A structural normally corrodible metal coated with a corrosion-preventive film of a di(hydrocarbon carboxylic acid) alpha alpha sulfide having at least 20 carbon atoms.

6. A structural normally corrodible metal coated with a corrosion-preventive film of a free difatty acid sulfide having at least 20 carbon atoms.

7. A structural normally corrodible metal coated with a corrosion-preventive film of a di-fatty acid monosulfide having at least 20 carbon atoms.

' 8. A structural normally corrodible metal coated with a corrosion-preventive film of a di-fatty' acid disulfide containing at least 20 carbon atoms.

9. A structural normally corrodible metal coated with a corrosion-preventive film of a di-fatty acid alpha-alpha sulfide having at least20 carbon atoms.

10. A structural normally corrodible metal coated with a corrosion-preventive film of alphaalpha' distearic acid sulfide.

11. A structural normally corrodible metal hicleof a dicarboxylic acid having at least 16- carbon atoms, the carboxyl radicals of said acid being linked through an element selected from the group consisting. of S, Se and Te.

15. Method of protecting a normally corrodible structural metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of a dicarboxylic acid having at least 16 carbon atoms to deposit on said metala protective coating of said free acid, the carboxyl radicals in said acid being linked. through an element selected from the group consisting of S, Se and Te.

16. The method of protecting a normally corrodible structural metal from corrosion comprising spreading over its surface a fine dispersion in a substantially neutral vehicle of a dicarboxylic acid havingat least 16 carbon atoms and having the formula c .-cooir (Iii)- yak-Coon wherein X is an element selected from the group consisting of S, Se and'Te, u and v are integers ranging from 1 up to about 10, audio is l or 2. 17. The method of protecting a normally corrodible structural metal from corrosion comprism-cn-coon wherein R1 and R2 are hydrogen or hydrocarbon radicals, X is an element selected from-the group consisting of S, Se and Te, and o is l or 2.

' ERNEST w. ZUBQLIN.

EMME'II' R. BARNUM. arms R. wnrra.