US3505230A - Functional ester base fluids containing corrosion inhibitors - Google Patents

Description

United States Patent 3,505,230 FUNCTIONAL ESTER BASE FLUIDS CONTAINING CORROSION INHIBITORS Quentin E. Thompson, Belleville, Ill., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Mar. 29, 1967, Ser. No. 626,703

Int. Cl. Cm 1/26, 1/32, 1/38 U.S. Cl. 252-57 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to functional fluid compositions which inhibit and control corrosion of metal surfaces and more particularly to functional fluid compositions comprising certain functional fluids and an additive amount of certain position substituted aromatic compounds.

Many different types of materials have been utilized as functional fluids and functional fluids are used in many different types of applications. Such fluids have been used as electronic coolants, atomic reactor coolants, diffusion pump fluids, synthetic lubricants, damping fluids, bases for greases, force transmission fluids (hydraulic fluids), heat transfer fluids, die casting release agents in metal extrusion processes and as filter mediums for air conditioning systems. Because of the wide variety of applications and the varied conditions under which functional fluids are utilized, the properties desired in a good functional fluid necessarily vary with the particular application in which it is to be utilized with each individual application requiring a functional fluid having a specific class of properties.

Of the foregoing the use of functional fluids as lubricants, particularly jet engine lubricants, has posed what is probably the'most diflicult area of application. As the operating temperatures for lubricants have increased, it has become'exceedingly difiicult to find lubricants which properly function at engine temperatures for any satisfactory length of time. Thus, the requirements of a jet engine lubricant are as follows: The fluid should possess high and low temperature stability, foam resistance, good storage stability and be non-corrosive and non-damaging to metal mechanical members which are in contact with the fluid. Such fluids should, in addition, posses adequate temperature-viscosity properties and satisfactory lubricity, that is, the lubricants must not become too thin at the very high temperatures to which they are subjected nor must they become too thick at lower temperatures and must at the same time be able to provide lubricity over such range of temperatures. In addition, such lubricants should not form deposits which interfere with the proper operation of a jet engine.

As the speed and altitude of operation of jet enginecontaining vehicles increase, lubrication problems also increase because of increased operating temperatures and higher bearing pressures resulting from the increased thrust needed to obtain high speeds and altitudes. As the service conditions encountered become increasingly severe the useful life of the functional fluid is shortened,

primarily due to the oxidation of the fluid, corrosivity of the fluid towards metal mechanical members and the formation of deposits above 450 F. In general, as the operating requirements of a jet engine are increased, engine temperatures increase and oil temperatures in the range of 550 F. and higher are encountered.

The useful life of any lubricant can be adjudged on the basis of many criteria such as the extent of viscosity increase, the extent of deposits and the extent of corrosion to metal surfaces in contact with the lubricant. Those skilled in the art have found many ways to improve lubricants and to thus retard or prevent the effects which shorten the useful life of a lubricant. Thus, it is a general practice to add small amounts of other materials, or additives, to lubricants in order to affect one or more of the properties of the base lubricant. It is diflicult, however, especially as operating temperatures are increased, to find base stocks which will perform the function for which they are intended and in addition to find additives which will perform a given function for which they are added and yet not inject other problems such as increasing engine deposits or adversely affecting the oxidation of a given base stock.

As is readily apparent from the aforedescribed uses of a functional fluid, a fluid, depending upon the application, contacts various metals as for example, lead, alu minum, copper, bronze, steel and many alloys, which alloys utilize many types of metals in the alloy composition. Corrosion of mechanical members such as bearing cages having lead flashings adversely affects (1) such mechanical members of a system in contact with the fluid, (2) the functional fluid itself and (3) the lubrication function of the fluid. The main problem resulting from corrosion of mechanical members, especially lead corrosion, is the effect of the corrosion products on the functional fluid and the lubrication function of the fluid. The corrosion products can form deposits on the mechanical members in contact with the fluid as well as being solubilized in the functional fluid. Certain corrosion products in addition to forming deposits can promote oxidation by catalyzing the oxidation of a functional fluid, thereby promoting increased sludge and deposit formation.

Thus, deposits can in general be formed from the oxidation of the base stock as well as deposits formed by the corrosion of mechanical members in contact with the fluid. The corrosion products can be formed, for example, by the corrosion of mechanical members by the oxidized fluid. The formation of deposits contaminates the fluid and requires premature draining of the fluid from the system as well as filter clogging and excessive filter replacement. In addition, deposits can adversely affect the proper lubrication of bearings such as by restricting and in some cases completely restricting the ability of a fluid to reach critical mechanical parts so as to perform its lubrication function. In addition, deposits can act as insulating materials when such deposits and other insoluble materials form on mechanical members. When this insulating effect occurs, the fluid does not accept heat as rapidly from mechanical parts at temperatures higher than the fluid and as a consequence metal fatigue and pitting of mechanical members can occur.

As is seen from the foregoing characteristics of a et engine, a functional fluid composition can attain temperatures of up to 550 F. and higher which can result in 0X1- dative and thermal degradation of a lubricant. Thus, a particular base stock which is utilized to prepare a functional fluid composition must have, to a certain extent, the ability to resist oxidative and thermal degradation. In addition, any additive which is incorporated into a given base stock such as to inhibit corrosion damage should not adversely affect other critical base stock properties. Thus, for example, an additive which is incorporated into a base stock for the inhibition and control of lead corrosion should not adversely affect the oxidative stability of a given base stock. In addition, as is readily apparent from the aforedescribed properties of a given functional fluid, the problem of attaining a functional fluid having given characteristics is extremely complex.

It is, therefore, an object of this invention to provide functional fluid compositions which have improved resistance to corrosion damage by the incorporation of a corrosion inhibitor into said functional fluid.

It has now been found that the corrosion of metal surfaces can be inhibited and controlled and thus the useful life of functional fluids can be greatly extended without adversely affecting critical base stock properties even under the severe conditions encountered in jet engine and other devices by the addition to functional fluids of certain position substituted aromatic compounds selected from the group consisting of:

(1) a compound represented by the structure RiAr-R wherein Ar is an aromatic nucleus selected from the group consisting of benzene and naphthalene; R is selected from the group consisting of hydroxyl and R is selected from the group consisting of hydroxyl and b and c are each whole numbers having a value of to 1, provided that the sum of b+c is from 0 to l; a is a whole number having a value of from 0 to 6; R is selected from the group consisting of a hydrocarbon oxy radical, a member of the group represented by R a member of the group represented by R, and when a has a value greater than 1 any two groups represented by R which are attached to adjacent carbon atoms can together with the carbon atoms to which they are attached form a cyclic ring selected from the group consisting of a non-quinonoid carbocyclic ring and a heterocyclic ring, said cyclic ring having from 3 to 10 atoms optionally interrupted by from 0 to 4 hetero atoms selected from the group consisting of oxygen, nitrogen and sulfur; R and R are each selected from the group consisting of a hydrocarbon radical and a heterocyclic ring having from 3 to 10 atoms optionally interrupted by from 1 to 4 hetero atoms selected from the group consisting of oxygen, nitrogen and sulfur; Y is selected from the group consisting of oxygen, sulfur and R is selected from the group consisting of hydrogen and a member of the group represented by R and R and R together with the nitrogen atom to which they are attached can form a heterocyclic ring having from 3 to atoms optionally interrupted by from 1 to 4 hetero atoms selected from the group consisting of oxygen, nitrogen and sulfur; provided that when Ar is selected from benzene or naphthalene and R and R are attached to the same carbocyclic ring, R is positioned ortho to R when c has a value of 0 and R is positioned ortho or meta to R when R is hydroxyl or c has a value of 1, and further provided that when Ar is naphthalene wherein R and R are attached to different carbocyclic rings R and R occupy positions selected from 1,5- and 1,8- and when R occupies a position ortho to R or when Ar is napthalene and R and R occupy positions l,8-, R and R together with the arcmatic nucleus to which they are attached can form a cyclic carbonate; and

(2) Mixtures thereof;

(l) a compound represented by the structure wherein R and R are each selected from the group consisting of hydrogen and lower alkyl; e is a whole number having a value of from 0 to 4; R is selected from the group consisting of hydroxyl, a hydrocarbon radical, a hydrocarbon oxy radical and a heterocyclic ring having from 3 to 10 atoms optionally interrupted by from 1 to 4 hetero atoms selected from the group consisting of oxygen, nitrogen and sulfur; and when e has a value greater than 1 any two groups represented by R which are attached to adjacent carbon atoms can together with the carbon atoms to which they are attached form a cyclic ring selected from the group consisting of a carbocyclic ring and a heterocyclic ring, said cyclic ring having from 3 to 10 atoms optionally interrupted by from 0 to 4 hetero atoms selected from the group consisting of oxygen, nitrogen and sulfur; and

(2) Mixtures thereof; and

Mixtures of (A) and (B).

The functional fluids to which the compounds represented by (A), (B) and (C) are added to provide compositions of this invention, hereinafter referred to as ester base stocks, include base stocks which contain a pentaerythritol base stock, pentaerythritol base stock herein defined to include pentaerythritol esters, dipentaerythritol esters and mixtures thereof, and ester base stocks containing a major amount of a pentaerythrito base stock, a major amount herein defined to include a concentration of the pentaerythritol base stock which is greater than the individual concentration of any other base stock which comprises the functional fluid composition. Typical examples of other base stocks which can be added to the pentaerythritol base stock are monoester base stocks, diester base stocks, triester base stocks, complex ester base stocks and mixtures thereof.

Whereas the incorporation of any foreign element into an ester base stock can alter properties of a functional fluid, the concentration of the compounds represented by (A), (B) and (C) in the ester base stocks is adjusted in terms of the particular system and the ester base stock which is utilized in this system to provide functional fluid compositions of this invention which contain additive amounts of a compound represented by (A), (B) and (C) sufficient to inhibit and control corrosion damage while not adversely affecting critical properties of the ester base stock. It has generally been found that the preferred additive concentration of a compound represented by (A), (B) and (C) for the ester base stocks is generally from about 0.001 weight percent to about 10 weight percent, preferably from about 0.005 weight percent to about 2.5 weight percent.

Therefore, included within the present invention are compositions comprising an ester base stock and a damage inhibiting amount of a compound represented by (A), (B) and (C), that is, a compound represented by (A), (B) and (C) is added to the compositions at a concentration sufficient to inhibit and control corrosion damage. The functional fluid compositions of this invention can be compounded in any manner known to those skilled in the art, as for example, by adding a compound represented by (A), (B) and (C) to the ester base stock with stirring until a composition is obtained. In addition, the compounds can be prepared in situ, that is, in the ester base stocks as aforedescribed. It is also contemplated within the scope of this invention that additive concentrates can be prepared such as additive compositions containing from about to about 60% of the compounds represented by (A), (B) and (C) and the ester base stocks as aforedescribed.

The various groups represented by a hydrocarbon radical, a hydrocarbon oxy radical, a cyclic ring and a heterocyclic ring are defined broadly to include groups which are unsubstituted as well as substituted. In addition, two or more substituents can together form a cyclic or heterocyclic ring. Thus, for example, when a heterocyclic ring is the representing group, substituents on a heterocyclic ring can together with the heterocyclic ring form a cyclic ring. Thus, two or more substituents can, for example, form an aromatic ring, an example of which would be benzimidazolyl which group would be included in the generic description, heterocyclic ring. In addition, the term heterocyclic ring is herein defined to include a heterocyclic ring which is present in a compound such as a compound represented by (A)(1) wherein R and R together with the nitrogen atom to which they are attached form a heterocyclic ring in which the nitrogen atom to which R; and R are attached is the sole hetero atom.

In place of the hydrocarbon radical there may be a hydrocarbon derivative which contains elements such as oxygen, nitrogen and sulfur in addition to carbon and hydrogen. These derivatives may be further substituted and may be saturated or unsaturated. The elements other than the carbon and hydrogen may be substituted upon a base hydrocarbon radical or may link two or more hydrocarbon radicals. It is also contemplated that the hydrocarbon radical can contain both substitution and linkage by one or more elements.

Thus, substituents can be present such as aryloxy, aryl, alkyl, alkoxy, polyaryloxy, arylmercapto, acyl, aroyl, dialkylamino, monoand polyhydroxy aryl, monoand polyacyl aryl, hydroxyand acyl-substituted aryl, cyano, 0x0 and carboalkoxy.

Where as all of the aforedescribed groups, that is, a hydrocarbon radical, a hydrocarbon oxy radical, a cyclic ring and a heterocyclic ring, are contemplated within the scope of this invention, such groups should be non-interferring with respect to the functioning of the compounds represented by (A), (B) and (C). Thus, a group should be non-interferring to an extent such that it does not completely nullify the corrosion control and inhibition of the compounds represented by (A), (B) and (C) when incorporated into an ester base stock. The aforedescribed groups can be adjusted with respect to the number of carbon atoms present and the number of elements present in a group other than carbon and hydrogen such that a compound represented by (A), (B) and (C) would be soluble in a particular ester base stock to which the subject compound is incorporated. Thus, depending on the particular base stock, a compound represented by (A), (B) and (C) can be modified such as by adjusting the chain length of the group or adjusting the branching present in a group in order that the particular compound will be soluble in a given ester base stock. As is apparent from the description of the aforedescribed ester base stocks, the solubilizing properties of the ester base stocks can vary and thus the solubility characteristics of the compounds represented by (A), (B) and (C) can be adjusted. The various aforedescribed groups, that is, the hydrocarbon radical, the hydrocarbon oxy radical, the cyclic and heterocyclic rings are non-critical features of this invention. Thus, these groups can vary over a wide range with respect to the number of carbon atoms present and the number of elements other than carbon and hydrogen which are attached to the various groups. In general, it is preferred that the various groups contain as an upper limit with respect to the number of carbon atoms present per aromatic nucleus of about 28 carbon atoms per aromatic nucleus and more preferably up to about 10 carbon atoms per aromatic nucleus. In addition, the aforedescribed groups can be defined by the number of elements other than carbon and hydrogen which are present per aromatic nucleus. Thus, for the various groups represented by a hydrocarbon radical, a hydrocarbon oxy radical, a cyclic ring and a heterocyclic ring, the upper limit of the number of elements other than carbon and hydrogen such as oxygen, nitrogen and sulfur which can be present per aromatic nucleus is as a preferred upper limit of about 6 elements per aromatic nucleus and more preferably is an upper limit of about 4 elements per aromatic nucleus.

Typical examples of hydrocarbon radicals and hydrocarbon derivatives are alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, amyl, hexyl, heptyl, octyl, nonyl, octadecyl; alkenyl, such as propenyl, butenyl, heptenyl, dodecenyl and the like; cycloaliphatic, such as cyclopropyl, cyclobutyl, cyclohexyl, monoand polymethyl cyclohexyl, monoand polyisopropyl cyclohexyl, naphthenyl, cyclopentyl, nonylcyclohexenyl and the like; aryl, herein defined to include mono-, di and polynuclear hydrocarbons, such as phenyl, naphthyl and anthryl, typical examples of aryl being phenyl, alkylphenyl, xenyl, tert-amylphenyl, naphthyl, tolyl, cresyl, halogenated phenyl, monoand polyhydroxy phenyl, dialkylamino phenyl, monoand polyacyl aryl, hydroxyand acylsubstituted aryl, cyano phenyl, alkylhydroxyphenyl, alkylchlorophenyl, alkylcyanophenyl, butylcyano naphtyl, cyclohexylphenyl, phenoxyphenyl, tert-butylphenoxyphenyl, dialkylaminophenyl and the like; aralkyl, such as benzyl, methylbenzyl, phenylethyl and the like; oxyand/or oxocontaining aliphatic, cycloaliphatic and aromatic radicals, such as aroyl, typical examples of which are benzoyl, 3-methylbenzoyl, acyl such as acetyl, aryl-substituted acyl, alkoxy-substituted alkyl radical, cycloalkoxy-substituted alkyl radical alkenoxy-substituted alkyl radical, carboalkoxy such as carboethoxy, carboalkoxy-substituted aryl or alkyl radical, aroxy-substituted alkyl radical, alkoxysubstituted cyclohexyl, aroxy-substituted cyclohexyl, carboalkoxy-cycloalkyl radical and the like; and the aforedescribed groups further substituted with a heterocyclic group containing from 4 to 10 atoms optionally interrupted by from 1 to 4 hetero atoms, which can be nitrogen, sulfur or oxygen or combinations thereof, such as substituted and unsubstituted pyridyl and the like.

Typical examples of heterocyclic groups are furyl thienyl, piperidyl, pyrryl, thiazolyl, thiadiazolyl, pyrazinyl, pyridyl, pyrazolyl, imidazolyl, oxazolyl, pyrimidinyl or a benz derivative thereof such as benzisoxazolyl, benzimidazolyl, benzofuranyl, benzothiazolyl, benzotriazolyl, benzoxazolyl, benzothienyl, indazolyl or isoindazolyl.

Typical examples of compounds represented by (A) (l) are catechol, resorcinol, 2-hydroxy-3-naphthoylanilide, o-acetyl phenol, o-n-butyryl phenol, 2,4-diacetyl phenol, resorcinol monoacetate, resorcinol hexanoate, catechol monoacetate, sorcinol monobutyrate, catechol monobutyrate, 3,4-dimethyl catechol monoacetate, 3,4-dimethyl resorcinol monoacetate, 3-methyl-4-acetyl catechol monoacetate, 3- methyl-4-acetyl resorcinol monoacetate, 4-methyl-8-ethyl- 1,3-naphthalene diol, 8-butyryl-1,3-naphthalene diol, 1- hydroxy-S-acetoxy naphthalene, 2-hydroxy 4 acetoxy acetophenone, 2-acetoxy-4-hydroxy acetophenone, 2,2- di-hydroxy-4,4-diacetoxy benzophenone, 2-hydroxy-2,4, 4'-triacetoxy benzophenone, Z-hydroxy-S-acetoxy-p-benzoquinone, Z-hydroxy acetophenone, catechol carbonate, 1,8-naphthalene carbonate, 4-acetoxy catechol carbonate and 3-acetoxy-1,8-naphthalene carbonate.

Typical examples of compounds represented by (B) (1) are 1,3-indane dione, 4-acetoxy-1,3-indane dione, 4-hydroxy-1,3-indane dione, .2-methyl-4-hydroxy-1,3-indane dione, 2,2-dimethyl-4,5-hydroxy-1,3-indane dione, 4-acyl- 5-hydroxy-l,3-indane dione, 4,6-dihydroxy-1,3-inda-ne dione, 4-ethyl-1,3-indane dione, 5-ethyl-1,3-indane dione, 5- butyl-l,3-indane dione and 4-methyl-6-methyl-1,3-indane dione.

catechol monohexanoate, re-

The ester base stocks to which the compounds represented by (A), (B) and (C) are incorporated comprise at least a major amount of a pentaerythritol base stock. The pentaerythritol base stocks have been found to have particularly good high temperature oxidation and thermal resistance. Typical examples of pentaerythritol and dipentaerythritol base stocks are pentaerythrityl tetrabutyrate, pentaerythrityl tetravalerate, pentaerythrityl tetracaproate, pentaerythrityl dibutyrate dicaproate, pentaerythrityl butyrate caproate divalerate, pentaerythrityl butyrate trivalerate, pentaerythrityl butyrate tricaproate, pentaerythrityl tributyrate caproate. Suitable dipentaerythrityl esters include dipentaerythrityl hexavalerate, dipentaerythrityl hexacaproate, dipentaerythrityl hexaheptoate, dipentaerythrityl hexacaprylate, dipentaerythrityl tributyrate tricaproate, dipentaerythrityl trivalerate trinonylate and dipentaerythrityl mixed hexaesters of C fatty acids.

Typical examples of base stocks which can be blended together with peutaerythritol base stocks are the monoester base stocks, diester base stocks, triester base stocks, complex ester base stocks and mixtures of the aforedescribed base stocks. Typical examples of monoand diester base stocks are the monoesters of long-chain monobasic acids such as. pelargonic acid with poly glycols such as polyethylene glycols, bis(2-methylbutyl) sebacate, bis(l-methylcyclohexylmethyl) sebacate, bis (2,2,4-trimethylpentyl) sebacate, dipropylene glycol diperlargonate, the diesters of acids such as sebacic, azelaic and adipic acid with complex C primary branched chain alcohols such as those produced by the x0 process, polyethylene glycol 200 bis(2-ethylhexyl) sebacate, diisoamyl adipate, 1,6-hexamethylene glycol di(2-ethylhexanoate), bis(dimethylamyl) azelate, di(2-ethylhexyl) azelate, di(2-ethylhexyl) sebacate, diisooctyl sebacate, 2-ethylhexyl 3:5:5 trimethylhexyl sebacate, diisooctyl azelate, di(3:5:5 trimethylhexyl)sebacate, di(l-methyl-4- ethyloctyl) sebacate, diisodecyl azelate, diisotridecyl azelate, di(1-methyl-4-ethyloctyl) glutarate, di(2-ethylhexyl) adipate, di(3-methylbutyl) azelate, di(3:5 :5 trimethylhexyl) azelate, di(.2-ethylhexyl) adipate, di(C oxo)adipate, bis(diethylene glycol monobutyl ether) adipate, di(isooctyl/isodecyl) adipate, diisotridecyl adipate, triethylene glycol di(2-ethylhexanoate), hexanediol 1,6-di(2ethylhexanoate) and dipropylene glycol dipelargonate.

Typical examples of triester base stocks are trimethylolpropane tri-n-pelargonate, trimethylolpropane tricaprate, trimethylolpropane tricaprylate and the trimethylolpropane triester of mixed octanoates.

Typical examples of complex esters are obtained by esterifying dicarboxylic acids with a mixture of monohydric alcohol and a glycol to give complex esters. Complex esters which can be employed can be prepared by esterifying a dicarboxylic acid (1 mole) with a glycol (2 moles) and a monocarboxylic acid (2 moles) or with 1 mole each of a glycol, a dicarboxylic acid and a monorhydric alcohol or with 2 moles each of a monohydroxy monocarboxylic acid and a monohydric alcohol. Still other complex esters may be prepared by esterifying a glycol (1 mole) with a monohydroxy monocarboxylic acid (2 moles) and a monocarboxylic acid (2 moles).

Other complex esters which are suitable are prepared by polymerizing a dihydroxy compound with a dicarboxylic acid and reacting the terminal hydroxy and acid radical with a mixture of a monocarboxylic acid and a monohydric alcohol. Specific examples of polymers which may be utilized as additives Within the scope of this invention are polymers prepared by the polymerization of adipic acid and 1,2-propane diol in the presence of minor amounts of short-chain monocarboxylic acids and a monohydric alcohol to give molecular Weights of the polymers thereby produced of from about 700 to about 40,000 or higher.

The mono-, di-, triand polyhydric alcohols, and the monocarboxylic acids employed in the preparation of the above esters can also contain either oxygen linkages.

Specific examples of suitable complex esters which are suitable are esters prepared from methylene glycol (1 mole), adipic acid (2 moles) and Z-ethylhexanol (2 moles); esters prepared from tetraethylene glycol (1 mole), sebacic acid (2 moles), and 2-ethylhexanol (2 moles); esters prepared from 2-ethyl-1:3 hexanediol (1 mole), sebacic acid (2 moles) and Z-ethylhexanol (2 moles); esters prepared from diethylene glycol (1 mole), adipic acid (2 moles) and n-butanol (2 moles); esters prepared from polyglycol 200 (1 mole), sebacic acid (2 moles) and ethylene glycol mon0(2-ethylbutyl) ether (2 moles); esters prepared from sebacic acid (1 mole), tetraethylene glycol (2 moles) and caproic acid (2 moles); esters prepared from triethylene glycol (1 mole) adipic acid (1 mole), n-caproic acid (1 mole) and 2- ethylhexanol (1 mole); esters prepared from sebacic acid (1 mole), lactic acid (2 moles) and n-butanol (2 moles); esters prepared from tetraethylene glycol (1 mole), lactic acid (2 moles) and butyric acid (2 moles); complex esters prepared from neopentyl glycol (2 moles), dicarboxylic acids (1 mole) and monocarboxylic acids (2 moles) and complex esters prepared from neopentyl glycol (1 mole), dicarboxylic acids (2 moles) and mono hydric neoalcohols, e.g., 2,2,4-trimethylpentanol (2 moles).

In order to demonstrate the outstanding properties of the compositions of this invention, various compounds represented by (A) and (B) were blended into an ester base stock and the resulting functional fluid composition evaluated for control an inhibition of lead corrosion. One of the major bench scale methods used for evaluating the lead corrosivity of various lubricant formulations is Federal Test Method Standard No. 791, Method No. 5321.1. In this test method, 500 ml. of the test fluid is placed into a tube containing a lead test panel. The tube is inserted in a bath which is maintained at a temperature of 375. Air is bubbled through the sample liquid at approximately 2 cubic feet per hour. The weight loss or net weight gain of the test sample is measured after a period of 5 hours. Th?l weight loss is measured in milligrams per square inc In Table I, Examples 1 through 12, the base stock that was utilized was a mixture of short-chain pentaerythritol esters and short-chain dipentaerythritol esters having an average chain length of about 6 carbon atoms. In Examples 1 through 9 the ester base stock contained 1% phenyl-a-naphthylamine. In Examples 10 through 12, the ester base stock contained a minor amount of a triaryl phosphate, 2% of a mixture of phenyl-a-naphthylamine and dioctyl diphenylamine and a minor amount of a potassium salt. In Table I percent inhibition of lead corrosion was obtained utilizing the following formula Percent inihibition of lead corrosion= mg. /in. loss without additive-mg./in. loss with additive X 100 mg. /m. loss without additive TABLE I C'oncen- Percent Fqrtration, Inhibition Ex. mula- Weight, of Lead No. .tion Corrosion Inhibitor Compound Percent Corrosion 1. I 2 Catechol 0. 05 99. 8 1,3-indane dione 0. 05 75. 0 0.05 89. 0 0. 05 92. 5 4 0. 0s 9s. 0 2,4d1hydroxy aeetop O. 05 96. 7 2,2',4,4-tetrahydroxy 0. 05 99. 2

benzophenone. 1,5-diacetoxy naphthalene 0. O5 93. 7 2-hydroxy-3naphthoylanilide 0. 10 94. 0 Resoreinol diacetate 0. 05 69 Diacetyl resorcinol 0. 05

In order to demonstrate that the compounds represented by (A) and (B) did not adversely affect critical fluid properties such as oxidative stability, certain fluid compositions were prepared with and without additives and the corresponding oxidation rate determined. One of the major bench scale methods used for evaluating the oxidative stability of a lubricant is the procedure given in Federal Test Method Standard No. 591, Method No. 5308, according to which the lubricant to be tested is heated at a specified temperature in the presence of certain metals and oxygen and the viscosity increase of the lubricant is deter-mined. Various functional fluid compositions containing the additive were tested according to the above procedure and the following conditions were utilized:

125 grams of fluid. Temperature, 450 F. Air rate, liters/hour.

The metal specimens used were as specified in said procedure, steel, copper, silver, titanium, magnesium alloy and aluminum alloy. The viscosity of the fluid before and after testing was determined at 100 F. The fluid that was utilized in Table II was the same formulation as was utilized in Examples 10 through 12 in Table I.

As is demonstrated by Table I, it is clearly evident that the incorporation of compounds (A), and (B) into an ester base stock provides a functional fluid composition which has the ability to inhibit and control lead corrosion and therefore to greatly extend the useful life of a functional fluid composition. In particular, Table I clearly illustrates the inhibition and control of lead corrosion damage by the compounds represented by (A) and (B). Thus, the percent inhibition in most cases was in the order of 90% or better. This is of particular significance since the control of lead corrosion damage extends the useful life of a functional fluid composition. Thus, control of lead corrosion inhibits the formation of deposits, which deposits can adversely affect the lubricating function of a particular fluid. In addition, deposits plug filters as well as critical orifices through which a fluid of necessity has to flow in order to lubricate critical areas in a jet engine.

Table II significantly demonstrates that the additives do not adversely affect critical fluid properties, It was found that the oxidative stability was not materially altered by the incorporation of an additive into an ester base stock. Thus, lead corrosion was inhibited and controlled without adversely alfecting other critical fluid properties. As has been stated previously, an additive must perform an intended function w thout adversely affecting critical fluid properties.

As a result of the excellent stabilization of functional fluids which incorporate the compounds represented by (A), (B) and (C), lubrication of gas turbine engines is obtained over extended periods of time. Thus, this invention relates to a novel method of lubricating gas turbine engines which comprises maintaining on the bearings and other points of wear a lubricating amount of a composition of this invention.

In addition, utilizing the functional fluid compositions within the scope of this invention, improved hydraulic pressure devices can be prepared in accordance with this invention which comprise in combination a fluid chamber and an actuating fluid composition in said chamber, said fluid comprising a mixture of one or more of the base stocks hereinbefore described and a m nor amount, sufficient to inhibit and control corrosion damage, of the additive composition of this invention. In such a system, the parts which are so lubricated include the frictional surfaces of the source of power, namely the pump, valves, operating pistons and cylinders, fluid motors, and in some cases, for machine tools, the ways, tables and slides. The hydraulic system may be of either the constantvolume of the variable-volume type of system.

The pumps may be of various types, including centrifugal pumps, jet pumps, turbine vane, liquid piston gas compressors, piston-type pump, more particularly the variable-stroke piston pump, the variable-discharge or variable displacement piston pump, radial-piston pump, axialpiston pump, in which a pivoted cylinder block is adjusted at various angles with the piston assembly, for example, the Vickers Axial-Piston Pump, or in which the mechanism which drives the pistons is set at an angle adjustable with the cylinder block; gear-type pump, which may be spur, helical or herringbone gears, variations of internal gears, or a screw pump; or vane pumps The valves may be stop valves, reversing valves, pilot valves, throttling valves, sequence valves, relief valves, servo valves, non-return valves, poppet valves or unloading valves. Fluid motors are usually constantor variabledischarge piston pumps caused to rotate by the pressure of the hydraulic fluid of the system with the power supplied by the pump power source. Such a hydraulic motor may be used in connection with a variable-discharge pump to form a variable-speed transmission. It is, therefore, especially important that the frictional parts of the fluid system which are lubricated by the functional fluid be protected from damage. Thus, damage brings about seizure of frictional parts, excessive wear and premature replacement of parts.

In addition, due to the excellent physical properties of the compositions of this invention having incorporated therein a metal compound represented by (A), (B) and (C), heat transfer systems can be developed wherein a liquid heat exchange medium is utilized to exchange heat with another material wherein said material is at a given temperature. Thus, the function of the liquid heat exchange medium can be any one or a combination of the following: transfer heat, accept heat and maintain a material at a given temperature.

The fluid compositions of this invention when utilized as a functional fluid can also contain dyes, pour point depressants, metal deactivator, acid scavengers, antioxidants, defoamers in concentration suflicient to impart antifoam properties, such as from about 10 to about parts per million, viscosity index improvers such as polyalkylacrylates, polyalkylmethacrylates, polycyclic polymers, polyurethanes, polyalkylene oxides, polyalkylene polymers, polyphenylene oxides, polyesters, lubricity agents and the like.

It is also contemplated within the scope of this invention that the base stocks as aforedescribed can be utilized singly or as a fluid composition containing two or more base stocks in varying proportions. The base stocks can also contain other fluids which include, in addition to the functional fluids described above, fluids der ved from coal products and synthetic oils, e.g., alkylene polymers (such as polymers of propylene, butylene, etc., and mixtures thereof), alkylene oxide-type polymers (e.g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing the alkylene oxide in the presence of water or alcohols, e.g., ethyl alcohol, alkylbenzenes, (e.g., monoalkylbenzene such as dodecylbenzene, tetradecylbenzene, etc.), and dialkylbenzenes (e.g., n-nonyl 2-ethylhexylbenzene); polyphenyls (e.g., biphenyls and terphenyls), helogenated benzene, halogenated lower alkylbenzene, halogenated biphenyl, monohalogenated diphenyl ethers, trialkyl, phosphine oxides, diarylalkyl phosphonates, trialkyl phosphonates, aryldialkyl phosphonates, triaryl phosphonates, triaryl phosphates, trialkyl phosphates and mixed aryl-alkyl phosphates.

While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

The embodiments of this invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising (A) a major amount of an ester base stock and (B) a corrosion inhibiting amount of a material having the structure group and hydrocarbon radicals and a is a whole number having a value of from 0 to 6. 2. A composition of claim 1 wherein R and R are methyl groups and Ar is a benzene nucleus.

3. A composition of claim 1 wherein the corrosion inhibiting material is resorcinol diacetate.

' hihiting material is catechol diacetate.

5. A composition of claim 1 wherein the ester base stock is selected from pentaerythritol esters, dipentaerythritol esters, and mixtures thereof.

6. A composition of claim 3 wherein the ester base stock is selected from pentaerythritol esters, dipentaerythritol esters, and mixtures thereof.

7. In a method of lubricating a gas turbine engine the improvement which comprises maintaining on the bearings and other points of wear a lubricating amount of a composition of claim 1.

8. In a method of operating a hydraulic pressure device wherein a displacing force is transmitted to a displaceable member by means of a hydraulic fluid, the improvement which comprises employing as said fluid a composition of claim 1.

References Cited UNITED STATES PATENTS 3,145,177 8/1964 Orloff et a1. 252-52 3,282,840 11/1966 Foster et al 252-56 X 3,309,318 3/1967 Aylesworth et al. 252S6- X 3,383,395 5/1968 Schmulkler 252-52 X 3,385,790 5/1968 Davies et al. 252-52 X DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner US. Cl. X.R.