US 2820764 A
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THICKENED LUBRICANTS Everett C. Hughes, Shaker Heights, and Ernest C. Milherger, Maple Heights, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application October 6, 1954 Serial No. 460,759
6 Claims. (Cl. 252-25) This invention relates to an aerogel grease of good high temperature stability and water resistance.
While the Word grease has usually been employed to describe an oil thickened with a soap, it is here used in a broader sense to include any thickened lubricant.
It is generally known that soap-base greases break down at high temperatures, of the order of 300 to 400 F. This breakdown is accompanied by an irreversible change in the grease structure, so that upon cooling the grease is observed to have lost its grease-like characteristics. The aerogel greases usually are far superior to the soap-base greases in stability at high temperatures as the following table shows:
breaks down late a heavy liquid.
However, after heating at high temperatures some aerogel greases tend to lose consistency upon stirring. This is undesirable because there are many field applications where a grease is agitated or worked While subject to a high temperature and it is important that the grease retain its consistency under these conditions and subsequent thereto.
Accordingly, it is the object of the present invention to provide an aerogel grease having improved stability at high temperatures, particularly after working at high temperatures.
In accordance with the invention, these objects are accomplished by incorporating a water-miscible or watersoluble polyhydric alcohol in an aerogel grease composition comprising a lubricating oil thickened with a nonabrasive, inorganic thickening or gelling agent, and particularly finely divided silica, a silica aerogel being illustrative. Thickened lubricants so prepared have excellent temperature susceptibility properties.
The grease is also rendered more or less resistant to deterioration by water by incorporating a hydrophobic cationic surface-active water stabilizer therein in the form of Amine O, 1-fl-hydroxyethyl Z-heptadecenyl imidazoline.
The presence of the polyhydric alcohol in an amount to obtain improved high temperature stability does not markedly affect the consistency of the thickened lubricant, i. e., the amount of the inorganic gelling agent to impart a given consistency to the thickened lubricant is not materially modified. Furthermore, the inclusion of atent Patenteddan. 21, 1958 the polyhydric alcohol will not effect a change in the consistency of the thickened lubricant upon storage. The
polyhydric alcohol likewise does not affect the water-' thickened lubricant has excellent storage stability. This is to be contrasted with the heat susceptibility and deterioration of fatty materials in soap-base greases.
The preparation of the grease is simple and readily adaptable to continuous operation, as contrasted with the involved grease-making techniques which are often considered in the industryas an art.
The oil stock used in making the thickened lubricant may be widely varied, as contrasted with present greasemaking requirements in which the oil in many cases must meet certain critical specifications.
In addition, the avoidance of the use of soap permits the manufacturer to be independent of the fat supply, which is important in periods in which fats and soaps are scarce and, many times, of pronounced non-uniformity.
The inorganic gelling agent to be used in making the thickened lubricant in accordance with this invention may be any inorganic material which forms a gel with a lubrieating oil and which is so finely divided as to be nonabrasive. The preferred materials are the aerogels, which may be formed from any material not, incompatible with oil, such as silica, alumina, and other gel-forming metal oxides.
A series of silica aerogels which can be used as the inorganic gelling agent of the invention are marketed under the trade name Santocel.
Santocel C is prepared from a sodium silicate solution in the following way: The solution is neutralized with sulfuric acid and then allowed to stand until the mixture sets to form a hydrogel. The by-product sodium sulfate is washed out by the repeated washings with water. The continuous water phase in this hydrogel is then replaced by continued washing with alcohol untilan-alcogel is formed. In order to remove the liquid phase without a collapse of the gel structure, the alcogel is placed in an autoclave which is then heated above the critical temperature of the alcohol and the pressure is allowed to increase to a point above the criticalpressure of the alcohol. The vent valve is then opened and the alcohol allowed to escape. Under these conditions, the silica gel structure remains practically undisturbed and the liquid phase of the gel is replaced with air. The material is then reduced in particle size by blowing it through a series of pipes containing sharp bends with jets of compressed air. Santocel C has a secondary agglomerate particle size of about 3 to 5 microns.
Santocel A is prepared as set forth for Santocel C up to the point of removal of the product from the autoclave. This material is run through a continuous heating chamber where it is heated for /2 hour to a temperature of about 1500 F. to eliminate the last traces of volatile material. It is then broken down in a reductionizer or micronizer to a particle size of about hi inch in diameter. The solids content of the original hydrogel used in preparing Santocel C is approximately 25 higher than that of Santocel A.
AR is a modification of A, differing only in that the.
CDv is a C which has been devolatilized as set forth. for A. CDv is reductionized before being devolatilized.
CDvR differs slightlyfr'om CDv in that the CDvR has been devol'a'tilizedjust after heating in the autoclave andthen reductionized. It differs-from CDv in that the latter is reductionized before being devolatilized.
The primary dilierences, between the and the :Qs.
areas follows}. i
Q(.-1) Thev Cs. are prepared .from a sodiunif. silicatejsolution containing 25 more silica, than, the Afs. "There? fore, in general the. As. are lighter and; composed/of smaller particles than theCs.
2) T.h .-Ash ve. undergone adevolatiliiatibn'step'in their preparation. i
The following are the bulkldensities a preferred silica" sm ele l V p Y, Densitngrams perm. AR 7 9.029 RD: 0.05am 0.064 P g 0.082
In general; AR and AR D -show superior-gelling ability and the As in general are better'tha-n'dhee Gs Silica aerogels which have beendevolatilized generally have a higher gelling eificiency than-the undevola-tilizedaerogels.
. Other types of'inorga-nic gelling agents which maybe used'inelude a Fumed Silica; ltzis finely divided and appears very much like an aerogel. It is made by acornbu'stion' or vaporization process, as a-Lsource oh white carbon black for the rubber inclustryz -The particles are several microns in size and porousib nature.
Another material is" Linde Silica Flour! It is-very similar in-physical appearance-to the silica aerogel. Theparticle-size of" the silica is purported-to be-050l 'to-0;05' micron and-to be manufactured byburning silicon tetrachloride and collecting the combustion productoncool platesanalogous totheproductionof carbon-blacl The particles are thought to be aggregates orclusters' of'particles rather than of sponge-hlecharacterr 1 1 Still'another'inorganijc gelling agentknown isi Ludox silica which is known asa silica sol; and silica derivativesthereotz It has a particle size ofthe order of 0:01" to 0.03 micron. e
In preparing thickened lubricantsit'is' necessary to remove the water fromthe sol and: replace it with an oil; Tl'llSlS' possible by formulating the lubricant and removing the water by flash distillationor azeotropic distillation;
No attempt is made to enumerate all of the inorganic gellingagents which will be suitable, norto present'exsamples of all of them since the novel aspects of'the invention reside in imparting highv temperature stability to the lubricant rather. than the use of novel; gelling agents, per se. f
The lubricating oilto be used in the processinay have any'lubricating viscosity. It may be raw'oil, acid-refined, or solvent-refined; as required for the particular lubricating need. i
The nature of the base oil hasjbeen found to make little, difference in the relative consistencies of the thickened' lubricants and conventionally (acid) *refined oils produce slightly thicker lubricants than solvent-refined oils. Excellent working stability is obtained regardless of the type of the base oil. An increase in, theviscosity of the base oil, as might be expected, brings increased viscosity to: the thickened lubricant and minimizes-bleeding. The change is relatively smalrand fairly linear. The viscosity 0f the. oil doesnot aiiect the Working stabilityof the lubricant;
I The relative. proportions ofthe inorganic gelling agent and the oil will vary somewhat dependingupon the desired body in the thickened lubricant, the 'gelli'ngfabiiity oi the inorganic gelling agent and theviscosity of the oil used. It has been noted, for instance, that with the Linde Silica Flour, the lubricants are somewhat harder, i; e.,'
have a lower penetration than lubricants containing the same weight of Santocel'. Lubricants made with low viscosity-oils. require a somewhat larger amount of the inorganic gelling agent to git/ea lubricant of the same penetration. The thickened lubricant may vary in consistency from the consistency of a'slightly thickenedoil to a solid or semi-solid of" grease-like consistency. In generahthe amount of the inorganic gelling agent falls within the range of 5 to 20%, and in most. cases would fall within the range of Ito-12%.
The amount of the inorganic gelling agent, as might be expected, afi'ects the'cons'istency offthe thickened t lubricant in that an increase, in itsconcentration brings a corresponding. increaseeidconsistency. The' ralnge is In general, the. properties of the thickenedlubricants are remarkably independentof the composition variables. and are: not critical. The relative concentration of the gelling agentfefiects the mo-st' significant alteration particularlywith regardito the final consistency of the productf This permits, the rnanufacture of thickened lubri cants hayinga wide variety of consistenciesf i A wide; variety of Water-nus ible or Water-sOIubZepOly-Q hydricfalcoholscan be: employedin accordance with the. invention to; improve the. highqtemperature stability of aerogel-base greases." Alcohols which are Water-immiscible, i. e., are oleaginoustin character, cannot be used, because they are hydrophobic. The alcohol must be hydrophilic, i. e., not oleaginous, for reasons which will be apparent from the theory of the; action of the alcohol, set forthlater...
Provided the polyhydric alcohol is thydrophilic, itmaya have from 2 to 8 carbon atoms andmust contain at. least.
two hydroxyl groups. It may contain as. manyfa'sflfour.
hydroxyl groups, those having two. and, three hydroxyl' groups being most: available and Qt'hereforezbeing preferred: Other polargroups, such as one or more ether or amino' groups, may also bepresent." The twoand three-hydroXyl' polyhydric alcohols are employed-in the examples because of their low cost and availability. The polyhydric alcohol may contain other inert substituents, such as halogen,- which have been found not to reduce the activity of the compounds.
of the invention, are ethylene glycol, diethylene, glycol;
glycerol a-monomethyl ether, glycerol, dulcitol; erythritol; pentaerythritol, mannitol, sorbitol, glycerol: chlorohydrin, l-rnethyl, glycerol; trirnethylene. glycol, butandiol-ZJ;
pinacol, propylene glycol, butantriol, and polymeric dihyt droxy- .(glycol): .polyetherederived; by condensation; of e ethylene oxideorupropyleneoiddm containingifrom twoto.
ten, oxide units;
The polyhydric alcohol need not be oil-soluble,- -but shonldbe .oili-dispersible: f litshonldihave a: minimumboilingpointofiabout :6. since it'sprima'ry'purposeis to stabilize the. grease atahigh temperatures. I a
The 'polyhdric alcohol: ist-incorporated in the aerogel-" 7 base. gnease'imam amount toimpart high; temperature 7 stability. Ordinarily: a=concentrationof polyhydric alco= hol'. ranging-from 0.25 to about 1% byweight ofthe aerogel-base grease givessatisfactory results. There is no reason to employ more polyhydric alc'ohol than' isknecessary; but excessiveamounts do no harm, and amounts" up to 5% or even-higher have beensuccessfullyemployed; The amount "of hydrophobic-- cationic surface-'active agent to impart water-resistance to theaerogel greasejin the form, of l -B7hydroxylethyl2 heptadecenyl iinida z olihe will varyfrom 0:1% to about 5%, depending-upon ;th" water-stabilizing efiect' desired, the amount andfinaturef of" the gelling agent fused,.and the economics involved" In S'OI'IlBil'lSlfillCCS, the compositioncontaining th pol hydric alcohol high temperature stabilizermay not disi-' Exempli-iying compounds within the. scope;-
play a long life when used continuously at high temperatures. A breakdown in high temperature stability at high temperatures if it appears is due to a decomposition,
through oxidation, of the polyhydric alcohol stabilizer of the invention. In such circumstances, it is desirable to include in the composition an antioxidant for the polyhydric alcohol stabilizer. Conventional amine antioxidants which are more readily oxidized than the polyhydric alcohols of the invention can be employed for this purpose. Tetramethyldiamiuodiphenylmethane is a particularly desirable antioxidant for the polyhydric alcohols of the invention. Only small quantities are required, and ordinarily an amount ranging from 0.1 to about 1% by weight of the aerogel base grease is ample. There is no reason to employ more antioxidant than is necessary to produce the desired effect, but excessive amounts do no harm and amounts up to 5% can be used, if desired.
The composition is made simply by mixing the inorganic gelling agent, the oil, a polyhydric alcohol and the cationic water stabilizer in any order or manner.
In one embodiment, the polyhydric alcohol and the cationic water stabilizer, can be incorporated with the inorganic gelling agent either by mixing directly or, if desired, by dissolving them in a solvent, mixing the solution with the gelling agent and evaporating the solvent.
Generally, the polyhydric alcohol and cationic water stabilizer are dispersed in the oil and the inorganic gelling agent added thereto and mixed therewith. Any simple mixing technique can be employed and, if desired, the
mixture can be homogenized in a colloid mill, although this is not necessary.
The composition of the invention is not limited to the oil, gelling agent, cationic water stabilizer, and polyhydn'c alcohol. Any of the materials conventionally added to lubricants and greases may be included. The expression consisting essentially o as used herein is intended to refer to the components which are essential to the composition, namely, the oil, the inorganic gelling agent and the polyhydric alcohol, and the expression does not exclude other components from the composition which do not render it unsuitable for lubrication, such materials being, for instance, the cationic water stabilizer, high polymers to modify viscosity or viscosity index, materials to impart tackiness, lubricating solids such as graphite, antioxidant additives, corrosion inhibitors of various types, sulfur, additives, to render the lubricant suitable for use in gears, for cutting, grinding, etc.
The following examples illustrated preferred embodiments of the invention. In the examples, water-resistant thickened lubricants are prepared to show the absence of an etfect of the polyhydric alcohol on the water resistance of the grease.
Examples 1 to 6 The base grease used in Examples 2 to 6 was a commercial water-resistant aerogel grease of the following formulation Solvent-extracted neutral oil (250 SSU at 210 F.) 85.98
1 (l-B-hydroxyethyl-2-heptadeceny1-imidazpline) An isobutylene polymer sold by the Emmy Company, Inc. and commonly usecl in nomnounding greases.
A FriedeI-Crat'ts reaction product. useful as a pour point depressant and sold by the Enjay Company, Inc. v
This base grease is referred to hereafter as the Aerogel W. R. Base Formula (Example 2). One of the poly- .hydric alcohols listed in the following table, in the amount stated in the table, was incorporated in this g'ia's'e, by blending it with the oil, and then mixing in the other components of the grease (Examples 3 to 6). The resulting grease compositions were tested for high temperature stability by measurement of micropenetrations before and after heating to 400 F. The results obtained were compared with the results for the base grease formulation above, and also with non-water-resistant aerogel grease containing 10% Santocel C and No. 250 solvent-extracted neutral oil which did not contain Amine 0 (Example 1). Thisformula is referred to hereinafter as the Aerogel Base Formula.
The grease is prepared for the determination of high temperature stability by placing approximately cc. of grease in a 150 ml. beaker. The beakers are heated to the test temperature by placing them in an aluminum block furnace. This furnace consisted of a solid block of aluminum heated 'by internal electrical heaters. Six holes, each large enough to accommodate a 150 cc. beaker, were drilled in the top of the block, together with a thermocouple, so that a measure of the temperature of the block could be obtained. In this manner, six beakers could be heated simultaneously. The beakers containing the grease were placed in the aluminum furnace and held there until the equilibrium temperature of the grease was 400 F. The samples were stirred at five-minute intervals during heating. After this the grease was allowed to cool to room temperature overnight and then was stirred vigorously with a spatula.
Kaufman micropenetration measurements were obtained on the grease before and after the testprocedure (Industrial and Engineering Chemistry, Analytical Edition, volume 11, page 108, 1939), and theresults are expressed in the table below as percent increase in penetration.
The following results were obtained on the aerogelbase greases tested, containing the polyhydric alcohols listed in the amounts stated:
TABLE II Added Percent Increase After Original' Block None (Aerogel 243 Base Formula). None (AerogelW.
R. Base Formu- Soup la). Glyccrlne .do
The results show that an aerogel-base grease which does not contain Amine O in order to improve its water stability (Example 1) has a high temperature stability which while superior to soap types leaves much to be desired. When Amine O and other components are added to this base grease (Example 2) the stability at 400 F. is destroyed and the grease liquefies, and remains liquid after cooling. Through addition of glycerine and ethylene glycol in amounts ranging from 0.5 to 1%, the effect of the Amine O is completely overcome and the aerogel grease possesses a better high temperature stability than the original Aerogel Base Formula.
Examples 7 to 12 Aerogel greases were prepared by blending a poly v hydric alcohol into the base oil and subsequently mixing this composition with Santocel and the other-ingredients aerwas geod.
to prepare ilie grease. frheseigreasesfihad the following (l-heptadeceny1-2-B-hrrlroxyethyldmidazoline.) k
' 'An isobutylenc'polymersold by theEnjayCompany, In'c.
"andic'omjm only used ir' compounding greases. v
A Friedel-Crafrs reaction product. usefuLas a pounpoint depressant-and; soldby heEnjay Company, Inc.
' Specifications for Petroleum Products. The cone and grease cup employed in obtaining the "following 'test results'require'd a minimumsample "size of 35 'rn'l.
"TABLE III.-- -MICR O CONE DIMENSIONS -AS'[-M 801110 Cone Cup -Cone Cup Diameter, mm 65 78 43 Height, mm-" 45 17 Depth, mm Surface, sq.'mm.- Volume, cc Cone, diam .lcnp Surfam Cone. height/cup depth wtnot'assembly, gms (ealcd) wt. of assembly/sq. mm. cone 0. 021 0. 021
'The following results were obtained:
" iTABLEl-IV I 801110 Micropenetrations Ex. f3 No. Santocel A'ddit-ivelPercent Used) v 1 Origi-. -'=After Percent E nal Block. Increase 7 AR I 0.5%GlyceroL; 99 122 p 23 124 (87). ('12) 8 AR'P 1.0% Glycerol 9a 112 19. 2 9 "AR" 0;5%Ethylenc Glycol"; '90 125 39 (117) 10.. AR:v LOVE/Ethylene Glycol... 1465 11'.-. ARE.- N0ne I 120 188 -5(i.5 1'2. "'KRD" 1.0% Glycerol 20 It will be noted that the. grease containing glycerol and Santocel ARD (Example 12")Ih'a's :a" better high temperature stability than the corr sponding grease (Example .11) when did nofcontain fglyc'erol. The high ,tenfiperature station 5116f the greases containinga'pblyhydrie alco- 8 Examples 1370-16 'A-n aerogel water-resistant 'grease ofthe 'followinglforfmulawas .made up:
. Percent *SantocelARD Amine 40M Paratac 2 Y 'Paraflow 3 Methane Base Bright Stock (78 SUS at 210 -F.) Polyhydric-alcohol- :p'olyhydricalcohol in accordance with the-invention (and reducing the bright stock'according'ly) in order "toprepare an aerogelgrease which is "not only water-resistant but also stablelat'high temperatures. a
In. preparing these greases;tthe Aminefo and'the poly- :hydric alcohol to be tested were dissolved; in a stock solutionofthe base oilfcontaiuing the other componentsL The Santocel was added to this. solution and'completely wetted by stirring. 'The grease Was'preparedat 95 'FJbymiXing .for the time indicated in the following table, thetime being varied so as to approximate the final penetration: of 'thetaerogel water-resistant base formula. lfthis time is thesame as or longer and/or if the :original penetration is the same as or less ,thanthat of the base formula,l"it is evident that the'polyhydric alcohol-has either no :onfa
The "penetration ofthe grease .wastaken "beforeand :after-heating-inthe block described in Example 1, imac- =cordance with the Shell,-Microcone'Penetration vTest"(-Institute Spokesman (NLGI) volume -VI,=.Number.12, page TABLE V 'High Temperature Stability Mixing Tmmed V No. Additive ime, Shell 7 i 'Shell' Stabil- Minutes Pen. Il'o. Penetration Lity cles "Initial 'Flnal 13"; Ae'rogel'Base 7 40 159 '5 157 Q02- None.
Formula. 14..-. Aerogel W. R. 30 159 4 171 '267 Good.
Base Formula. 15--.- Ethylene 20 159 4 167 201 Do.
Glycol. A 16.." Glycerol 30 5' 168 "205 D0.
Same formula as Example 1.
The results show that incorporating the Amine (Twin .the aerogel base formula appreciably increasesthepenetration and thus reduces the high temperature:stability. This eflcct of the Amine O is, however, overcome .by
the polyhydric alcohols added to the aerogel waterrresistant base formula.
Examples 17' to '26 I "Microcone Penetration lest before and afterheatizrg in Company, Inc. and
9 the aluminum block to 400 F. The following results were obtained:
Same as formula in Example 1.
These data show that increasing the amount of glycerol beyond 2% has no appreciable effect upon the high temperature stability, although it does no harm. in each case the ethylene glycol and glycerol overcome the effect of the Amine O on the high temperature stability of the aerogel grease, and in Examples 21, 22, 23 and 26 the high temperature stability is improved, compared to the original Base Formula (Example 17).
Examples 27 I 37 A large number of aerogel greases were prepared as follows: A fixed quantity of oil (78 SSU at 210 F. solvent-extracted bright stock) was weighed out into a 400 ml. beaker. 0.8% Amine O was added, and 1% of the alcohol additive was incorporated in the base oil. The oil mix, was heated to 130 F. while being mixed with a Lightnin stirrer, and 8% Santocel ARD was mixed in with hand stirring. The resulting grease Was allowed to stand overnight. An original penetration was then obtained using the Shell Microcone Penetration Test and the grease was then subjected to the block test. Grease samples exhibiting some degree of high temperature stability were cycled three or four times. Each sample was tested also for water stability and given a visual rating for consistency while at 400 F.
The alcohol additives tested included monohyclric and polyhydric alcohols. Ethylene glycol and glycerol were included to evaluate the results obtained. Data from these tests are given in the following table:
TABLE VII Block" Test Ex. Shell Penetrations Water No. Additive Stability Orig. 1 2 3 4 Aerogel W. R. Base For- 139 200 226 Good.
Monohydric Alcohols 27--.. 2-Ethylhexanol 128 290 Do. 28---. Lauryl alcohol. 135 Do. 29.-.. 5 Ethylnouanol 156 D0. 30 HeptadecanoL. 128 Do. 31--.. Cetylalcohol 126 298 Do.
- Polyhydric Alcohols 32...- Diethylene glycol 135 178 180 195 130. 33.... Triethylene glycoL. 127 179 186 190 195 Fair. 34.". Ethylene glycol.... 114 139 165 184 184 Good 35 Pentanediol-l,5 146 186 197 Do. 36.... Glycerol... 130 147 l58 168 173 D0. 37.... Trimetliylol propane. 154 I 194 i 194 207 I"... Do.
Without exception, the five monohydric alcohols tested were unsatisfactory under high temperature conditions The initial penetrations for ethylene glycol, diethylene glycol, triethylene glycol and glycerol are lower than that of the control grease, and indicate that these compounds have no deleterious effect on grease yield. All of the polyhydric alcohols tested exert a stabilizing effect at high temperatures.
Examples 38 and 39 Additional greases were prepared from a blend of bright stocks to produce an oil of approximately 2000 SSU at F. High temperature instability of aerogel greases is aggravated when a heavy base oil is used, and thus this provides a severe test of the high temperature stabilizing effect of the additives of the invention.
The test greases were prepared as outlined in the preceding Examples 27 to 37. The results are given in the following table:
It is evident that the polyhydric alcohols are capable of increasing high temperature stability, even when a heavy base oil is employed.
Examples 40 to 44 Percent Percent Santocel O 10.0 10.0 Amine O L 1.0 1.0 Paratac 2. 0 2. O Paraflow 0. 5 0. 5 Methane base 0.5 0.5 Red dye. 0. 02 O. 02 Glycol 0. 5 to 1. 0 Solvent-extracted neutral oil (250 SSU at 100 F.) 85. 98 84. 98 to 85. 98
2 An isubutylene polymer sold by the Enjay Company, Inc. and commonly used in compounding greases.
3 A Frledel-Gral'ts reaction product, useful as a pour point depressant and sold by the Enjay Company, Inc.
The base grease used in Examples 41 to 44 was the commercial water-resistant aerogel grease of Formula A. This base grease is referred to hereafter as the Aerogel W. R. Base Formula (Example 41). To prepare Examples 42 to 44, one of the glycols listed in the following table, in the amount stated in the table, was incorporated in this grease by blending it with the oil, and then mixing in the other components of the grease. The resulting grease compositions were tested for high temperature stability by measurement of micropenetrations before and after heating to 400 F. as in Examples 1 to 6. The results obtained were compared with the results for the W. R. base grease formulation above, and also with non-water-resistant aerogel grease containing 10% Santocel. C and 9.0% No. 250 solvent-extracted neutral oil which did not contain Amine 0 (Example 40). This latter formula is referred to hereinafter as the Aerogel Base Formula. 0
The results show that an aerogel-base grease which does not contain Amine O in order to improve its water stability (Example 40) has a high temperature stability which, while superior to soap types, leaves much to be desired. When Amine O andother components are added to this base grease (Example 41) the stability at 400 F. is destroyedand the grease liquefies, and remains liquid after cooling. Through addition of diethylene glycol in amounts ranging from 0.5 to 1%, the effect of the Amine O is completely overcome and the aerogel grease possesses a better high temperature stability than the original Aerogel BaseFormula. Polyethylene glycol 900 also overcomes the effcct of the vAmine 70 on high temperature .stability.
Example 45 Aerogel water-resistant greases of the following l-fl-hydroxyethyl-Zhcptadecenyl-imidazollne. ZrAn isobutylene polymer sold by the Enjay Company, Inc. and commonly used in compounding greases.
3A Friedel-Cratts reaction product, useful as a pounpoint depressant and sold by the Enjay Company, Inc.
Example 45 is the water-resistant Formula A modified .by addition of .l%. diethyleneglycol-inaccordance-with the invention "(and reducing the bright. stock accordingly) 'inorder to prepare an aerogel greasewhichis not only water-resistant but also-stable at high temperatures.
In preparing these greases, the Amine O and the glycolto be.tested.were dissolved in a stocksolution of thebase. oil containing'the othercomponents. .ThefSantoeel was added to this. solution and completely wettedby stirring. The-grease was ,prepared at9'5 .by' mixing for the time "indicated-in" the followingtable, the time being variedso as to approximate 'the -final penetration of "the aerogel water-resistant base formula. If thistime is'the same as or longer and/or if the: original penetrait is:;evident;that the ether has either no ora Lben'eficial effect on yield. The penetration of the grease wastaken before and after heating in the block described in accordance with the Shell Microcone Penetration Test (Insti i tute Spokesman NLGI), VI, 12, page 1 1943)).
TABLE X High Temperature f Stability Mixing Immed. Time, Shell Min- Pen. utes Water Sta- 'Shell Penetrability.
Ex. N o. Additive tion No. Cycles 7 Initial Final Formula'A Diethylene glycol.
130. Do. i
aws- The results .show that the Amine O in 'Formu1a-A appreciably increases the penetrationand thus reduces the high temperature stability. This efiect of the Amine O is, however, overcome by the glycol'(Ex'ample 45).
Examples 46 to 48 A number of aerogel greases were prepared-.ofthe following formulations:
Santocel ARD Amine 0 Paratac Parafiow, 3 s Methane base (Oalco MB) Bright stock (78 SSU-at210 F.) Glycol 1 1-,3-hydroxyethyl 2-heptadecenylimidazoline.
2 An isobutylene polymer sold by the En ay Company, Inc.;and commonly used in compounding greases.
3 A Friedel-Orafts reaction .prod uct,..useful as-a pour point-depressant and sold by the Enjay Company, Inc. V p v Tetramethyldiaminodiphenylmethane.
Formula A is Example 46 inthetable whichltollows;
Formula B is the water-resistantformula ofFormula. A, :modified by additionof '.1-% glycol .inaccordance with the invention, reducing the bright stock accordingly in order to prepare an aerogel greasewhichis-notsonly water-resistant but also stable at hightemperatures- .In preparing thesegreases, the Amino O 1and-the glycol to be tested-were dissolved in -a stock-solution of the base oil containing the other components. The
Santocel was added to the solution and completely wetted tion is the-same as or less'than that of the base-formula, following results were obtained:
TABLE'XI i k Biock"-test, Shell Pens. Water =Ex. "Additive Per- Pen. Stabil- ENO- cent Cycle Eity 3 IOrig. 1st 2nd 3rd 4th -16-- -Controlwith1inine0 v139 e00, .226 43.5" iC ood. i
DjfethylenesglycoLn u- 1:0 17s use .197 -15 .Do.
Polyethylene glycol 400..-. 1.0 159 I198 "39 Do.
The results show that incorporating the glycol in the control grease (containing Amine but no glycol) appreciably increases high temperature stability, as ev 1- denced by a reduction in penetration increase. TlJlS is best observable in the change in penetration per cycle noted in the above table. Diethylene glycol is most effective, but even the polyethylene glycol 400 gives a significant improvement in high temperature stability.
in the examples, the high temperature stability of the aerogel greases is tested by heating the greases to 400 F. This is an extreme test, inasmuch as the highest temperature to which a grease is subjected under even extraordinary conditions of use is about 300 F., but it was adopted as a suitable test standard by which to measure the high temperature stability of the greases because a grease stable at 400 F. will definitely have the stability necessary to withstand heating to 300 F. It will be understood that for normal purposes an aerogel grease need not be stable at temperatures above about 300 F., and that the greases of the invention at least meet this requirement. Where the term high temperature stability is used, it will be understood to mean that the aerogel grease is stable at at least 300 F.
The following hypothesis is given as a partial explanation of the reason to which is attributed the action of the polyhydric alcohol in improving the high temperature resistance of aerogel grease, but the invention is not to be bound thereby.
Silica aerogels are known to be in the form of an extremely finely divided material and it is thought that it is capable of forming a colloidal structure in the oil vehicle employed in an aerogel grease. Mixing or stirring in formulating the grease serves to disperse the secondary aerogel agglomerates throughout the body of the oil. The aerogel occupies a greater volume than the liquid oil vehicle, and because of this it is probable that the colloidal structure is aided somewhat by a close packing of the solid silica gel particles, perhaps with mechanical interlocking. It is thought that the basis of the structure is a tying together of the various silica aerogel particles by hydrogen bonding between hydroxyl groups which remain attached to individual silicon atoms in the silica gel molecule.
In setting up the colloidal grease structure, it is postulated that the distances between adjacent hydroxyl groups on different particles of silica aerogel may be too great in some circumstances to form a binding, attractive force between particles. In this e ent, Water, which is always present in the aerogel structure, serves to bridge the gap between adjacent particles through hydrogen bonding be tween the compound and the hydroxyl groups on the adjacent silica aerogel particles. Thus the water in effect aids in setting up the colloidal grease structure, and may also link it together, at least in part.
When the grease under static conditions is submitted to temperatures high enough to volatilize the water no apparent effect is noticed at first, for there is no force to disarrange the structure. Consequently, penetration vs. temperature curves indicate that aerogel greases have excellent high temperature performance with a very low in crease in consistency as the temperature is increased. However, when this static state is disturbed by stirring, the structure can and does collapse, due to the absence of the water which has been volatilized and which formerly served as the connecting links between adjoining silica particles. In consequence, the structure passes from a gel state to a colloidal sol state. This explains why the transformation of the heated aerogel grease from a greaselike condition to a soupy condition occurs only after stirring and Why stirring thus brings about an apparently irreversible gel-to-sol transformation. This transformation may be reversed to some extent by adding Water to the soupy grease, tending to substantiate this hypothesis, but it is not possible to return the grease to its original condition.
Thus, on the basis of this hypothesis, incorporation in the grease, in accordance with the invention, of a polyhydric alcohol which is not volatile at the temperatures to which the grease may be subjected leads to a partial or complete displacement of Water in the aerogel by polyhydric alcohol, possibly before and in any event at the time Water is volatilized at an elevated temperature. The low volatility of the polyhydric alcohol prevents its loss during heating and thus prevents destruction of the colloidal grease structure when the aerogel grease is stirred after it has been heated to high temperatures. It is also apparent from this that a hydrophobic polyhydric alcohol which is immiscible with Water could not function in this Way because it could not act as a substitute for Water in the hydrophilic gel structure.
This application is a continuation-in-part of our applications Serial Nos. 119,752, filed October 5, 1949, 253,984, filed October 30, 1951, and 254,633, filed November 2, 1951, all three now abandoned.
1. A water-resistant thickened lubricant of good temperature susceptibility properties, consisting essentially of a mineral lubricating oil of lubricating viscosity, an inorganic gelling agent imparting a grease-like consistency to the oil upon addition thereto, 1-/3-hydroxyethyl-2-heptadecenyl imidazoline imparting stability against deterioration by water, and a water-soluble polyhydric alcohol imparting high temperature stability.
2. A water-resistant thickened lubricant of good temperature susceptibility properties in accordance with claim 1 wherein the polyhydric alcohol is glycerol.
3. A water-resistant thickened lubricant of good temperature susceptibility properties in accordance with claim 1 wherein the polyhydric alcohol is ethylene glycol.
4. A water-resistant thickened lubricant of good temperature susceptibility properties in accordance with claim 1 wherein the polyhydric alcohol is diethylene glycol.
5. A water-resistant thickened lubricant of good temperature susceptibility properties in accordance with claim 1 wherein the polyhydric alcohol is triethylene glycol.
6. A water-resistant thickened lubricant of good temperature susceptibility properties in accordance with claim 1 wherein the polyhydric alcohol is trimethylol propane.
References Cited in the file of this patent UNITED STATES PATENTS 2,531,440 Jordan Nov. 28, 1950 2,554,222 Stross May 22, 1951 2,563,606 Kimberlin et a1 Aug. 7, 1951 2,573,650 Peterson Oct. 30, 1951 2,662,056 McCarthy Dec. 28, 1953 2,676,148 Iler Apr. 20, 1954 2,711,393 Hughes et a1 June 21, 1955