US2278851A - Lubricating oil composition - Google Patents

Description

Patented A r; 7, 1942 UNITED "STATES PATENT FFICE.

- 2,278,851 LUBRICATVING I COMPOSITION Eric S. Hillman, Oakland, Calif., assignor to Shell Development Company, San Francisco, Calif.,

a corporation of Delaware No Drawing- Application September 9,

Serial No. 294,207 I 5 Claims.

. extreme pressure properties, rate of wear of bearing metals, etc. Considerable confusion has been createdby excessive claims of the beneficial effects of many of the addition compounds and by a lack of a proper understanding of the underlying phenomena which make some of the additive compounds effective'in one way or another It is the purpose of this invention to improve the utility of certain types of compounds used in lubricating oils as anti-wear agents. It is another I purpose to explain in pa'rtthe mechanism of wear prevention attributed vto certain types of lubricating dopes so that the conditions for use and the anti-Wear agent maybe readily selected;

It is a further purposeto effect economies in preparing anti-wear lubricants through a proper understanding of the problems involved. a I

- I have made certain discoveries which have led me to develop a theory regarding success or failure of certain types of the so-callocl anti-wear dopes for lubricating Oils. My theory has been tested and proven in a very large number of experiments, some of which will be disclosed later.

.It has been found that the effectiveness of certain anti-wear agents is due to its polishing effect in smoothing out submicroscopic roughnesses which may exist in the new bearing metals or may have been produced in the course ofthe lubrication.

The types of anti-wear agents to which my discovery relatesand to which the term antiwear agent as used herein will refer, are those oil-soluble compounds of semi-metallic elements capable of forming with the bearing metals, alloys having" substantially lower melting points than the metal components of the later. Under the conditions existing on the metal surfaces during lubrication, they convert high spots of the metal surfaces to the lower melting alloy, possibly the eutectic, the alloy'melting away from the high spot and-filling in the neighboring hollows. To be suitable these anti-wear compounds must, in addition to forming alloys, respond to the usual requirements of. stability and must be substantially non-corrosive.

Compounds potentially capable of forming such alloys are those containing at least one of the semi-metallic elements P, As, Sb, Si, Ti, Ge, Zr,

and B.- In Table I below are given some temperature differentials in C. between a number of metals and their eutectics with the above semi-- metallic elements as taken from the literature.

' T Table I Semi-metal Metal Sb Ge While all oil-soluble ncn-corrosiveanti-wear compounds containing at least one of the above elements have moreor less a polishing effect by way of causing high spots on the metal surfaces to melt off and fill in adjacent crevices, some compounds will do this more readily than others. Alloy formation is predicated on the liberation of the free, semi-metallic-element onthe metal surfaces, and, obviously,.the elements are liberated more easily from some of their compounds than from others. Moreover, some of the elements are more easily liberated than others, and, furthermore, ,the compounds yielding the elements must not drop out of their solution in the oil at any time. before the liberation of the semimetallic element.

Depending upon the 'type. of compound, the liberation of the semi-metallicelement is caused by difierent mechanisms. If the compound is one of an oxidation state lower than the free element such as phosphine,-. arsine, stibine, etc., liberation of the semi-metal may take place by simple decomposition. On the other hand, if the compound is one in which the element is in an chemical polishing and active anti-wear agentsthan' the arsine oxides or sulfides. arsenites. or arsenates. Likewise, the'phosphines are more effective than the 'phosphine oxides-or sulfides,

phosphites or phosphates, provided, however, there are no disturbing influences.

Among the disturbing influences which may completely reverse the order of superiority and cause semi-metallic compounds of a high oxidation stage to be better than those of the lowest, is oxidation itself. Oxidation of the anti-wear agent, while it is in solution in the lubricating oil, may result in the formation of compounds which are oil-soluble or are very difficult to reduce. Oxidation may take place in the body of the oil or on the surface of the bearing metal or both. It may be caused by dissolved air or some addition compounds, or compounds introduced during use of the oil in internal combustion engines through leakage from the combustion chamber.

That oxidation is a definite factor to be considered is proven by the fact that phosphines, arsines, etc., are. easily oxidized to the corresponding oxides by merely exposing an oily solution of these Compounds to air; that. moreover, the oxides of many of the, phosphines, arsines, etc., are substantially insoluble in hydrocarbon oils, particularly those which are relatively easily obtainable, sucha-s the triphenyl phosphine, triphenyl arsine, dipropyl phenyl arsine, etc.; that furthermore, for equal'amounts of dissolved semimetallic element, the phosphine and corresponding compounds of other semi-metals are under normal lubricating conditions far better antiwear polishing agents than their oxides.

I have found that the anti-wear effect of compounds of the nature of those described in the foregoing, is greatly enhanced by the presence of a suitable oil-soluble reducing agent. This effect is in' accordance with my observation and theory because the semi-metallic element being reduced to its lowest oxidation state will more readily form an alloy with the bearing metal. Reducing agents are useful as well in combination with reduced anti-wear agents, because they prevent oxidation of the anti-wear agents to their oxidized forms which are less effective.

Oil-soluble reducing agents to be suitable for use with anti-wear agents should have a stronger reducing power at the temperatures of lubrication than the oil in which the anti-wear compound is dissolved. Some reducing agents may be in effective at one temperature but very effective at another depending upon the relative effect of temperature changes on the reducing powers of the agents and the lubricating oil, In addition, suitable reducing agents should preferably be nonsludging when used in effective quantities, should be relatively non-corrosive to the bearing metals,

under some conditions or other are, for example, many nitrogen derivatives, among which are certain acid amides, e. g. benzanilide, naphthanilide, acyl substituted amino phenols, succinimide, phthalamide, etc.; carbonides, e. g. diphenyl guanidine oleate, urea, etc.; thio carbonides, e. g. thio urea, thio carbanilide, etc.; amines, particularly cyclic amines, e. g. aldol alpha-naphthylamine, para alkyl aniline, alkyl, aryl or dialkyl amino phenols, condensation products of naphthylamine and cresols, diphenylamine,. dicyclohexylamine, dibutyl amine salt of alpha naphthol, reaction products of carboxylic acids such as fatty acids or rosin acids with alkylamines, etc.; nitroso compounds, e. g. nitroso alphanaphthol, etc.; azo compounds, e. g. phenyl azocatechol, azobenzene, etc.; alkaloids, e. g. nicotine, etc.; phenols, e. g. cresylic acids, isoeugenol, vanillin, etc.; hydroxy phenols, e. g. hydroquinone, resorcinol, catechol; aromatic aldehydes, e. g. benzaldehyde; aromatic and unsaturated aliphatic ketones, e. g. benzophenone, benzoin, etc.; esters of polyhydroxy substituted aromatic acids; e, g. alkylesters of gallic acid, etc.;' terpene, e. g. camphor, camphoric acid, etc.; alkali metal alcoholates, e. g; sodium butylate, etc.; metal amides; mixtures of the above.

' Of the above reducing agents those are preferred which in the course of their reducing action, are oxidized to form oil-soluble products. In general, reducing agents of aromatic character have the additional advantage of frequently yieldin products which actas anti-oxidants for the lubricating oil.

The amounts of reducing agent and anti-wear agent employed in a lubricating oil may vary from about .1 to 10% each by weight of the lubricating oil for best results.

In the following are presented data illustrating my invention. While out of the mass of available data only those are presented which'demonstrate most clearly the essentialpoints, it is to be understood that this invention is not so restricted.

The lubricating oils were tested in a four-ball apparatus such as described in Engineering, Vol. 136, (1933), page'46; this apparatus is capable of measuring metal wear. The difierent oils were run for two hours each in the four-ball machine with 7kg. loads and at a rotative speed of 700 R. P. M. The scare areas were then measured for each lubricant tested and the scar pressures tabulated below were calculated from the formula:

Scar pressure=load in kg. per cm. scare area Obviously, the higher the scar pressure at th end of the tests, the less the wear.

Lubricating oil Anti-wear compound Scar pressures at tem' i peratures indicated Reducing agent Western solvent extracted None 1, 000 1, 000 1 lubricating oil SAE 20.

Do 1% tncresyl phosphate... 3, 200 5, 500 ..do 9,000 5 (00 1, one 1, 500 do 3.000 2.300

1% benzaldehyde 5, 500 1% benzom. 5,000 3,300 1% azobenzene. 4. non i. 5011 1% hydroquinone. 4; 000 '5, m0 1% petroleum nlkyl phc- 3, 200 3, 200

and be thermally stable, e. g. should not crack under the conditions of lubrication.

As will be noted from the above data, at relatively low temperatures the added reducing agent Examples of compounds that may be suitable 75 has often insufiicient reducing power to show its effect against the background of the strongly reducing lubricating oils; however, at higher temperatures, the reducing power usually excels that of the lubricating oil and the scar'pressures at the end of the tests are materially increased due to the action of the reducing agent. Of especial significance are the experiments at 180 C. because it is at such temperatures and higher that cylinders of internal combustion engines must be lubricated.

It will further be noted that the effect of the added reducing agent is far greater in combination with diamylnaphthalene than in combination with the western lubricating oil. The former oil is far more oxidation stable than the latter and hence is a weaker reducing agent. Since the tendency inthe manufacture of lubricating oil is decidedly towards oils of improved oxidation stabilities, the importance of adding bination with the anti-wear agents. Examples of such combination reducing and wedging compounds are long chain unsaturated aliphatic ketones, for example, the C24 unsaturated ketone. This C24 ketone was prepared as follows: Mesityl oxide obtained by condensing acetone was mixed with a concentrated sodium hydroxide solution prepared by dissolving 300 grams of sodium hydroxide in 254 grams of water, and refluxed in an iron stiil for more than one hour, while the Water and acetone formed were continuously removed. The resulting oil layer was withdrawn, water washed to remove caustic and fractionall'y distilled, to recover the C24 unsaturated ketone having but a single carbonyl radical as a product distilling between 170 C. and 230 C. at 2 mm. pressure. ,Its effect on the wear is shown by the data below which were obtained in the four-ball apparatus; mentioned earlier:

Anti-wear compound Scar pressures at temperatures indicated, Reducing agent Western solvent extracted None None 1,000 1,000 1,000

lubricatlng oil SAE 20.

Do I.do 1% Cnunsaturated ketone. 1, 000 1, 500 1, 500

Do +l% tricresylphosphate do 9,000 4,000 6,000

reducing agents in combination with anti-wear agents will become more important as time goes on. For example, the blending of certain high boiling aromatic hydrocarbons, such as highly purified extracts from lubricating oils with highly refined lubricating oil rafiinates or synthetic oils, produces lubricating oils of great oxidation stabilities as is disclosed in Buckley, U. S. Patent No. 2,117,602 and in the copending Van Peski application, Serial No. 128,495, filed March 1, 1937. Oils of this type are the ones which are very much benefited by the combination of the addition compounds of this invention.

The reducing agents of this invention are not only valuable in combination with the anti-wear agents alone, but frequently are of even greater value when combined with the anti-wear agents and the wedging compounds disclosed in the pending application Serial No; 274,842, filed May 20, 1939, by Givens-Beeck. Wedging compounds have been defined as high-molecular weight organic compounds soluble in mineral oils possessing a high dipolar moment by virtue of a strongly polar radical which is attached to a long hydrocarbon chain of not less than carbon atoms. These compounds to be effective should preferably be substantially non-corrosive under the conditions of lubrication. The wedg ing and reducing properties may be combined in a single compound, if desired, and such compounds are often of particular usefulness in com- I claim as my invention:

1. An anti-Wear lubricant comprising a mineral lubricating oil containing dissolved small amounts of a free aliphatic unsaturated ketone having at least 10 carbon atoms and an antiwear compound which is substantially non-corrosive under lubricating conditions, and contains as its active ingredient a semi-metallic element capable of forming with bearing metals alloys having melting points substantially lower than said metals. v

2. The lubricant of claim 1 in which the amounts of anti-wear and ketone are from 1% to 10% each.

3. The lubricant of claim 1 in which the mineral lubricating oil is a blendof a lubricating oil of low oxidation stability and high boiling aromatics.

4. The lubricant of claim 1 in which the mineral lubricating oil comprises high boiling aro- 5. An anti-wear lubricant comprising a mineral lubricating oil containing dissolved small amounts of a free aliphatic unsaturated C24 ketone and an anti-wear compound which is substantially non-corrosive under. lubricating conditions, and contains as its active ingredient a semi-metallic element capable of forming with bearing metals alloys having melting points sub stantially lower than said metals.-

ERIC S. HIILMAN.