US2635078A - Grease compositions - Google Patents

Description

Patented Apr. 14, 1953 GREASE COMPOSITIONS Fred H. Stross and Stanley T. Abrams, Berkeley,

Calif., assigncrs to Shell Development Company, Emeryville, Calif., a corporation of Delaware No Drawing. Application November 27, 1950, Serial No. 197,836

7 Claims.

This invention relates to novel lubricant compositions. More particularly, it is concerned with lubricating compositions comprising lubricating proportions of an oleaginous liquid and an added agent possessing a combination of gelling and extreme pressure properties. The compositions are characterized by their ability to withstand high temperatures, excellent resistance to disintegration by water, and antifriction properties at extreme pressures.

There have been disclosed to the art a number of fluid and grease-like compositions containing sulfurized materials especially for use as extreme pressure lubricants. In most in stances, these compositions have contained either sulfurized fatty acids or sulfurized fatty oils. Where greases are desired particularly for use at high temperatures, such sulfurized materials show the shortcomings that the compositions are excessively corrosive and tend to soften or lose their grease-like structures progressively with increasing temperatures.

It has been proposed to add finely divided disulfides to silicone fluids, said disulfides being derived from metalloids such as molybdenum, tungsten and titanium. Such compositions may be useful under certain conditions of operation, but in many instances are unsatisfactory due to the unstable nature of the suspension. This unstable character appears to be due to two principal causes. In the first place, the disulfides previously used for this purpose, although called colloidally fine, are not actually believed to be of such highly dispersed nature as to enable them to exist as a true colloidal gel. This is indicated from the fact that the disulfides are derived from ores which have been finely ground to an average dimension of 1 to 50 microns. Although these ground ores are subsequently subjected to various extraction treatments, it is not believed that this particle size is appreciably altered. On the other hand, true colloidal gel particles are defined as those hav ing dimensions of between 0.001 and 0.1 micron. Secondly, according to the teachings of the art, these disulfides are of a plate-like structure in which it is postulated that three layers exist, namely, a middle metalloid layer having on either side a layer of sulfur atoms. Structures of this character exhibit little attraction between the molecular layers, and, hence, a true gel structure is not formed when the particles are dispersed in a liquid.

It is an object of the present invention to provide lubricating compositions exhibiting improved extreme pressure characteristics. It is another object of the present invention to provide stable grease-like compositions especially efiective as extreme pressure lubricants at elevated temperatures. It is a further object of the invention to provide compositions having the foregoing characteristics and in addition thereto being comparatively stable to the disintegrating infiuences of water. The foregoing and other objects will be understood from the following description of the invention.

Now in accordance with the present invention, it has been found that hydrocarbon lubricating oils are provided with grease-like structures by the dispersal therethrough of colloidal gels of sulfides of metals having a water solubility no greater than 0.0005 g. per 100 cc. H2O at 20 C. Still in accordance with the present invention, it has been found that outstanding members of the present series of greases comprise those gelled with copper sulfides, since copper sulfides exhibit peculiar oleophilic properties common to sulfides of the hydrogen sulfide group metals as compared with other metallic sulfide compounds.

These colloidal particles have sizes varying from 0.01 to 0.3 micron, and usually between 0.01 and 0.1 micron. Electron micrographs indicate that the particles are three dimensional units showing an agglomerating tendency which accounts for their stable gel-forming property. It.

has been found that, dependent in part upon the conditions of preparation, mixtures of the various types of sulfides are sometimes formed having, for example, arbitrary formulae such as Nl'sSz, which is believed to be a mixture of NizS and MS. Other mixtures are known to exist, such as F6384. It is essential that these sulfides be dispersed in the lubricating medium in gel form, the inorganic skeleton of which is substantially the same as that of an aerogel. While the sulfides may be prepared by the previously known aerogel process, it is possible to prepare the present compositions without resorting to the expensive drying operations usually involved in the preparation of an aerogel. However, if the exact steps involved in the preparation of a dry aerogel are to be avoided, they should be such as to permit the formation of a gel skeleton structure similar to that of an aerogel.

The lubricating oils useful as the fluid lubricant in the present compositions comprise hydrocarbon oils of either natural or synthetic origin. Preferably, these oils have a viscosity between about SSU" and about 3,000 SSU at and still more preferably between 300 SSH and 1,000 SSU at 100 F. These lubricating oils should have a medium or high viscosity index, preferably between 25 and 150. While the usual source for such oils is from petroleum crudes, other hydrocarbon oils. may be used as well. These include especially polymerized-olefins. and particularly polymers of normal aliphatic 'olefins having from 6 to 12 carbon atoms and copolymers thereof with olefins having from 2. to 6 carbon atoms. Polymers having high "viscosity indices and low pour points derived from such sources may be prepared by either catalytic or non-catalytic means. They may. for-example, be prepared by heating the olefins at temperatures between 600 and 900 F. in the absence of catalysts or in the presence of-such'catalysts as lead tetraacetate at lower temperatures such-"as 400 F'.-600 F. The clay-type catalysts of either natural or synthetic origin such as silica-alumina catalysts. may .be used as well. The advantages of emp oying lubricants .compri'sing..,polymeric olefins. are principally .jthat..of'.quality control .as ompared with the variable nature of'lubricants obtained from- .naturalscurces. which vary from on oil field to another and even from. one well to another .within a. given field.

The lubricants are, preferably at least moderately refined but, except. when used. as dielectric compositions, need not behighly. refined; however, highly refined lubricating oils. are equally suitable. While the. principal object, of the present invention has been stated'to .be the production. of grease-like lubricants, another type of composition. contemplated is that of thixotropic gels especially useful. as. cuttingfiuids Qr,,.mo.re particularly. for well-drilling operations. Inthe. latter instance especially, lower molecularweighthydrm carbonfiuids areespeciallydesirable and particularly. thoseinthe kerosene stove. oil .orgas, .oiLboiling; ranges. .Compositionspontaining oils ofi-such low boiling .propertijesihave,beenfound to. exhibit desirable. thixotropic properties especially .useiul in the operation of well-.drillingmechanisms.

'I'he sulfides to be used in the present -compositionsare metallicsulfidesha ingawatersoluhility less than.0.0005. gram per IOQcQ-pf water at.20. .0. f particular importanceis. the group. of sulfides. of metals. oi therhydrogensulfide i oupflnamely thosemetals. precipitated .by hydrogen sulfide-as. sulfidesfromtheir solutions.in0..3l\l'acid; Thelat-. ter groupincludes mercury, lead, copper, bismuth, cadmium,..arseni c, antimonyand tin... .In.addi-- tion. to this group, other. suitable ,sulfldesare thoseof. iron, nickeland cobalt.v

The. essential characteristic of'an. aeroselstructurev and of structures suitably similar thereto. is that of maximum expansionsoasto permit ready dispersalina liquidmediumandthe maintenance of apermanent dispersion thereby... An aerogelispreferably formed by replacing, water. in ahydrogel with alow. boiling. water-miscible solventsuch as ethyl alcohol or acetone. heating the resulting organo. gel under pressure tov a temperature above the critical temperature of the solvent, and at this point flashing off the solvent,'leaying a highly expanded. dry el structure usually .known. as an aerogel. This structure is opposed to. thestructuresordinarily employed for catalysts which are termed xerogels. gels are generally heated at extremely .high .temperatures with no effort being taken to maintain an expanded structure; hence, these .products are hard, shrunken structures. ordinarily totally .unsuitable for use. as. grease-forming agents even In the latter instance, the

. transfer conditions by use of suitable surface-am- .4 though they may be comminuted to the smallest size attainable-by mechanical means.

Alternative means of preparing suitable gels for use in the present compositions comprises forming a hydrogel oi the sulfide, displacing water with a water-miscible s.clvent...suchasalcohol or acetone. and then replacing the solvent. with a lubricating oil. Alternatively, the gels may be Originally prepared under anhydrous conditions such as by reaction of an organic acid salt of the desired metal with hydrogen sulfide in a nonaqueous medium, such as ethyl alcohol. The an- I hydrous. gel so formed is then transferred to oil and the surrounding low boiling medium removed.

greases by especially economical methods. It has been discovered that the hydrogels. oicopper S111- fldeffor example) tend to shed water upon ,the

addition, .of oil; hence, a, copper sulfidejhydrogel may be directly transferred to cilandi water re; moved therefrom by simple decantation or distillation underreducedflpressure. The .oil and hydrogelv are preferably milled to produce. .a finely;

dispersed mixture prior to water removal. v, Still another process foruse in'the'prepara'tion of the present compositions comprises the transfer of a hydrogel into oil under so-called direct tive agents? The presence of surface-active. agents such as high molecular weight amines and their derivatives enables the production of. the

present compositions. by simple incorporation of the sulfide hydrogel. in oil followed bymilling'to produce a fine dispersion. of the hydrogelinthe oilandlsubsecuent removal of the. vszater,v preferably by distillation underreducedpressure. Suitable surface-active agents for. usein thislatter process include cationic surface-active materials.

such. as high molecular weightaminesamine salts and quaternary ammonium. compounds. While. the. cationic surface-active. agents. are. especially preferred, non-ionic or anionic. agents .may also.

eused. Typical speciesof these. agents-include heptadccylamine, .heptadecylimidazolina amide.

amines of .dieth-ylenetriamine.andoleic acid,,soaps.

such as .ammomum-12-hydroxystearate orlead oleate, soaps, .01: hydroxy amines. such-as, diethanolamine oleate. and glycerinemonostearate- Thecompositions. of the. presentinventionmay:

vary within widelimits. of one. componenttoranother, dependent upon the specific. use. forwhich the. compositions are to be employed. Preferably, however, the compositions comprise a major amount of the hydrocarbon lubricating .oil,. and a minor amount. of the colloidally dispersedlsuls.

ent, they are ordinarily employed inamountsbe..

tweenabout 2% and 40% by weight of the sulfide or from 1 to 5% based on the total grease.

Other ingredients may bepresentinthese. compositions including other grease-forming. agents. such as other inorganic gelling .agents. .or molecular weight soaps. The former include gels. having structures similar to an. aerogeland also similar (in their gelling action). to the subjectsulfides. These include aerogel-like structures of silica, alumina, magnesia, lime, aluminum silicates, alkaline earth metal oxides and hydroxides and similar inorganic gelling agents of either natural or synthetic origin. The natural materials include the swelling-type clays such as Wyoming bentonite and hectorite, which have been converted to oleophilic gelling agents by ionexchange with oleophilic cationic surface active agents as represented by quaternary ammonium bases such as dimethyldicetylammonium chloride. When these auxiliary gelling agents are present, they may be used in an amount supplementary to the colloidal sulfide and may be included in the maximum ratio of said sulfide of between 5% and 45% by weight of the total composition. A typical grease of this character includes a composition comprising 70% mineral lubricating oil, silica aerogel and 20% copper sulfide aerogel. The term "aerogel is used throughout the specification to denote the type of porous gel structure desired rather than the specific method by which the gel was prepared.

Typical and illustrative but not limitative preparations of the sulfide greases are as follows:

EXAMPLE I Fifty-six parts by weight of ferrous sulfate heptahydrate was dissolved in 100 parts of water made slightly acidic with sulfuric acid to repress hydrolysis. To this solution a solution of 38.7 parts of hydrogen sulfide dissolved in 434 parts of concentrated aqueous ammonia was added slowly with stirring. The temperature was maintained at about 0 C. After addition of the sulfide solution was completed, the reaction mixture was stirred for an additional minutes. The ferrous sulfide gel was then filtered, washed with 750 parts of water saturated with hydrogen sulfide and finally with 1,000 parts of methyl alcohol. The alcogel so prepared was intimately mixed with a refined mineral lubricating oil having a viscosity of 300 SSU at 100 F. The mixture was heated to 74 C. and then at a temperature of 50 C. under vacuum for 14 hours to remove the last traces of alcohol. The resulting mixture was then milled to a grease-like structure and had a concentration of 21% by weight ferrous sulfide based on the total grease.

EXAMPLE I] 408 parts by weight of nickel nitrate hexahydrate was dissolved in 700 parts of water. To this solution a solution of 190 parts of hydrogen sulfide dissolved in 2,140 parts concentrated aqueous ammonia were added slowly with stirring. The resulting gel of nickel sulfide so prepared was dehydrated with methanol and dispersed in lubricating oil as described in Example I. The resulting grease contained 35.7% by weight nickel sulfide.

EXAMPLE III Copper sulfate pentahydrate was dissolved in water to form a concentrated solution. To this was added just enough concentrated aqueous ammonia to produce a copper-ammonia complex. Hydrogen sulfide was then bubbled into the solution. The resulting gelatinous precipitate was thoroughly washed with distilled water. Oil was mixed with the washed precipitate and the mixture was warmed. As heating progressed, it was possible to decant all most of the water. Progressive addition of oil followed by milling and dehydration under vacuum produced a, grease gel containing 23% copper sulfide in oil.

then decanted. The remainder of the alcohol was then removed by heating on a sand bath. The resulting mixture was milled to produce a grease containing 27.3% cupric sulfide.

EXAMPLE V In order to determine the extreme pressure properties of the compositions prepared as described above, each of the greases was diluted with mineral lubricating oil to a gel concentration of 1.5%. These were tested in three-inch spur gears at 3,000 r. p. m. and 45 0., increasing the loading until scoring of the surfaces occurred. The extreme pressure loads of the greases were as follows:

Extreme Composition Pressure Load, Lbs.

Mineral lubricating oil 5 Nickel sulfide grease (Example II) 45 Ferrous sulfide grease (Example I) 45 Copper sulfide grease (Example IV) 30 Best commercial extreme pressure additive l 50 1 Mixture of benzyl disulflde, chlorodibenzyl disuli'lde and chlorinated paraffin wax.

This application is a continuation-in-part of copending application, Serial No. 782,694, filed October 28, 1947, which has matured into U. S. Patent 2,554,222, issued May 22, 1951.

We claim as our invention:

1. A lubricating grease composition comprising a major proportion of a hydrocarbon lubricating oil and as the principal gelling agent therefor a minor amount sufiicient to form a grease structure of a colloidally dispersed copper sulfide, said gel being one which has its normal water content replaced by said oil.

2. A lubricating grease composition comprising a major proportion of a hydrocarbon lubricating oil and as the principal gelling agent therefor a minor amount sufficient to form a grease structure of a colloidally dispersed nickel sulfide, said gel being one which has its normal water content replaced by said oil.

3. A lubricating grease composition comprising a major proportion of a hydrocarbon lubricating oil and as the principal gelling agent therefor a minor amount sufficient to form a grease structure of a colloidally dispersed iron sulfide, said gel being one which has its normal water content replaced by said oil.

4. A lubricating grease composition comprising 55-98% by weight of a mineral lubricating oil and 2-45% by weight of a colloidally dispersed metallic sulfide having a water solubility less than 0.0005 gram per cc. of water at 20 C., said gel being one which has its normal water content replaced by said oil.

5. A lubricating grease composition comprising 65-85% by weight of a mineral lubricating oil and 15-35% by weight of a colloidally dispersed metallic grease-forming sulfide having a water solubility less than 0.0005 gram per 100 cc. of water at 20 C.. said sulfide having a colloidal ,miiiiliii aeeaova 7 gel structure substantiallythesame as that of the gel asoriginally formed.

6. A lubricating grease composition comprising a major proportion of alhydrocarbon' lubricating oil and as a gelling agent therefor'a minor amount sufficient toform agrease structure of a colloidally dispersed metallic. sulfide vhaving a water solubility less than 0i0005gram per 10000. of water Vati20" 'C.,,said'su1fide having a colloidal gel structure substantially the same as that of they gel as. originally'formed.

'7. A lubricating, grease composition comprising a major proportion of a hydrocarbon lubricating oil and as a gelling agent therefor a minor amount sufficient to form a grease structure of a --colloidally dispersed metallic= sulfide-having a water'solubiIity-less than 0.0005 gram per 100 cc.

of water at 20 0., said sulfide having acollo'iclal gel structure wherein thehgelparticles have. dimensions between 0.001 andolmicroneach, the metallic radical of said sulfide being a metal of the group of metals precipitated by hydrogen sulflde as sulfides from their solutions in 0.3N acid, said gel being one which has its normal water content replaced by said oil.

FRED I-I. STROSS.

STANLEY T. ABRAMS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,260,625 Kistler' Oct. 28, 1941 2554;222 Stress May 22', I951 2,573,650 Peterson Oct.30, 195-1 2,584,085 Stross Jan. 29,1952

Claims (1)

1. 4. A LUBRICATING GREASE COMPOSITION COMPRISING 55-98% BY WEIGHT OF A MINERAL LUBRICATING OIL AND 2-4% BY WEIGHT OF A COLLOIDALLY DISPERSED METALLIC SULFIDE HAVING A WATER SOLUBILITY LESS THAN 0.0005 GRAM PER 100CC. OF WATER AT 20*C., SAID GEL BEING ONE WHICH HAS ITS NORMAL WATER CONTENT REPLACED BY SAID OIL.