US3146202A - Gelation inhibitors for silicone oils - Google Patents

Description

F 3,146,262 1C Patented Aug. 25, 1964 GELATION i i I riITORS FOR SHJCONE OILS Robert M. Silverstein, Menlo Park, and Frank R. Mayo,

Atherton, Calif., assignors to the United States. of

gmerica as represented by the Secretary of the Air orce No Drawing. Filed Feb. 13, 1961, Ser. No. 89,081 1 Claim. (Cl. 25249.6)

This invention relates to silicone oils and more particularly to antioxidant additives for use therewith.

In general, lubricant materials employed heretofore were based on petroleum hydrocarbons. However, such materials suffer inherent defects with respect to flammability, ease of oxidation, instability at elevated temperatures, lack of lubricity at low temperatures, and concurrent viscosity changes with temperature changes. The use of silicone oils is also well known and to some extent such oils exhibit characteristics which tend to eliminate the problems encountered with the use of petroleum lubricants. The silicone oils, briefly, are derivatives of various polymeric organosiloxarles such as the alkyl sili cones, the aryl-alkyl silicones, and the alkyl silicone halides. These oils are characterized by flat viscosity temperature curves and possess oxidative stability up to approximately 200 C. However, the silicone oils oxidize readily at temperatures in excess of 200 C., becoming gel-like and finally carbonizing to form a hard grit-like material completely unsuitable for lubricating purposes.

The recent advent of high speed engines, aircraft and 7 other propulsion devices has created a problem of considerable importance with respect to the lubrication of such devices, especially at the elevated temperatures produced during their operation. The various antioxidant additives relied upon in the past to abrogate the inherent defects of both petroleum oils and the silicone oils have proven to be ineffective at these elevated temperatures. Ineffectiveness of the silicone oils at elevated temperatures is due in most part to the fact that the eflicacy of presently used additives declines rapidly at higher temperatures resulting in gelation of the oil.

In accordance with this invention it has been found that the aforementioned ineffectiveness of silicone oils when employed at elevated temperatures can be alleviated to a great extent by empolying certain aromatic condensed ring compounds as antioxidant additives.

Therefore, it is the primary object of this invention to provide an improved silicone lubricant.

It is a further object of this invention to provide an improved silicone lubricant which is especially suitable for use at elevated temperatures in excess of 200 C.

Still another object of this invention is to provide an improved silicone lubricant which exhibits a high resistance to oxidation, especially at elevated temperatures.

Still a further object of this invention is to provide an improved silicone lubricant which exhibits little or no viscosity change with each change of temperature.

Still another object of this invention is to provide antioxidant additives which are particularly suitable for use with silicone oils.

The above and still further objects and advantages of this invention will become readily apparent upon examination of the following detailed disclosure of specific embodiments thereof.

In a more specific aspect, it has been found that the foregoing objects, can be accomplished by the addition of minor amounts of aromatic condensed ring compounds to silicone oils. As a class, those condensed ring compounds having at least three angularly or linearly fused rings have been found to be effective in preventing oxidative degradation of silicone oils at temperatures in excessof 200 C. These additives are sufficiently solublein silicone fluids at both high and low temperatures to a degree that makes them especially suitable as lubricants at the wide temperature ranges encountered during the operation of high speed aircraft. The condensed aromatic ring compounds of this invention are effective in achieving the desired temperature stability necessary to insure the operational efficiency of the silicone oils.

The specific additives which have been found to be effective in retarding the gelation or oxidative degradation of silicone oils are disclosed in Table II. These additives were tested, as to their effectiveness in retarding oxidative degradation or gelation of silicone fluids, at 518 F. with dry air at 550 F. with a gaseous mixture of 5 percent 0 and 95 percent N These additives were also tested in a similar manner with silane fluid lubricants, naphthenic mineral oils, pentaerythritol tetracaproate fluid lubricants, and parafiinic mineral oils, but were found to be ineffective in retarding oxidation. In older to determine the effectiveness of the antioxidant additives of this invention, air or a gaseous mixture of 95 percent nitrogen and 5 percent oxygen was bubbled through the additive-containing lubricating fluid which in turn was heated to an elevated temperature. Several metal washers were immersed in the fluid in which the antioxidant additive was dissolved. The tabulation set forth in Table I presents the fluids employed and the temperature, duration of test, type of gas, and combination of metal washers for each fluid tested.

Table 1 TEST CONDITIONS FOR FLUIDS Fluid Temper- Time Gas Washers ture F.) (hr.)

1 500 48 Air (loppenttsilver, aluminum, i s ee 1 anium. Vetsflube F 50 511mm l 550 48 95% N 5% 02--" Coppei, aluminum, steel,

' titanium, stainless.

500 48 Air Copper} tsiliger, aluminum, 2 4 stee i an um. silane MLO 57 628 u 550 48 95% N 5% 0 Coppei, aluminum, steel,

ctitaniumqstamleis. 500 48 Air opper si ver a ummum Paratfinic mineral oil, MLO 57 573 24 O Osteel ,timlnufp' t 1,

' 550 48 95 N 5 upper a unzunum s ee Naphthenic mineral oil, MLO 57 573 2 2, a titamhm Stainless,

18 500 48 Air Copper silver aluminum l/ l fi i i tetraceapmate steel, titanium.

1 Actual temperature was 518 F 2 Silane fluid MLO 57-461 was so severely degraded at 500 F. with dry air that testing was discontinued.

Another object of this invention is to provide an improved silicone lubricant which exhibits stability at elevated temperatures. a v

Table 11 sets forth the antioxidant additive compounds contemplated by this invention together with test results indicating their overall effectiveness.

Table [1 AVERAGE PERCENT VISCOSITY INCREASE AT 100 F. (NUMBER OF RUNS AND APPEARANCE) Additive concentration is highest concentration Additive concentration 0.2%

at which it was soluble at 65 F. 7 Additive Additive 518 F. concen- 550 F. 518 F. 550 F.

tration I. 1,2-benzanthraoene 22 (2, clear, 0. 2 115 (2, dark (4, clear, 115 (2, opaque, yellow). brown). yellow dark brown). II. Pyrene 34 (2, clear. dark 0.1 427 (2, dark 44 (2, clear, 113 (2, opaque,

yellow). brown). yellow.) dark brown) III. Acenaphthene 41 (2, opaque, 1.0 98 (2, opaque, 105 (2, clear, light Very vlscous (1,

' brown dark brown). brown dark brown). IV. Phenanthrene 58 (2, clear, 1.0 Gel (2, dark 68 (3, clear, 7 Gel (1, dark yellow). brown) yellow). brown). V. Fluoranthene 97 (2, clear, 0.5 Very viscous (2, 85 (5, clear, Gel (2, dark yellow). dark brown). yellow). brown). VI. 2,5-diphenyloxazole Gel (2, brown) 0. 5 Gel (2, dark 51 (4, clear, Gel (1, dark brown). yellow). brown). VII. 1,1-binaphthyl 56 (1, clear, 0.2 Gel (1, dark 86 (3, clear, Do.

yellow). brown). yellow). VIII. Benzo(a)pyrene 1 18 (2, clear, dark, 0. 2 39 (2, dark 16, (3, clear, 38 (2, opaque,

brown). brown). yellow). dark brown). XI. Dibeuz(a,h)anthracene 0. 01 12 (3, clear, light 123 (2, opaque,

brown). dark brown). X. Dinaphthylenethiophene 0. 01 14 (4, opaque, Gel (2, dark brown). brown). XI. Perylene 0. 01 19 (3, clear, 113 (2, opaque,

brown). dark brown). XII. Ohrysene 103 (2, clear, 0. 03 Gel (2, dark 68 (2, clear, Gel (1, dark yellow brown). yellow). brown XIII. Decacycl n 0. 01 60 (4, opaque, L500 (2, opaque,

brown). dark brown). XIV. 4.4-bis(di1nethylamino)- 0.05 Gel (2, dark 120 (4, clear Gel (1, dark benzophenone. brown). yellow). brown). XV. Indanthrene Navy Blue 0. 01 80 (2, clear, Gel (1, violet).

BRA Powder. viole XVI. N-phenylferrocenecarboxa- 0. 01 47 (3, opaque, Gal (1, black).

mide. brown XVII. 1,3,5-triphenylbenzene 0. 01 720 (2, l ar,

yellow). XVIII. 1,12-benzoperylene 0. 01 2, opaque,

brown);

1 Potent carcinogen in mice. Due caution in handling should be observed.

This fluid is a dirnethylsilicone polymer in which one out v V out of 55 methyl groups were replaced by a 2,3,5,6- tetrachlorophenyl group. End-groups on the silicone polymer chains are trimethylsiloxy groups. The average molecular Weight is 3000, corresponding to an average chain length of about 40 units. The F- silicone fluid has a fairly low oxygen tolerance at elevated temperatures. When dry air is bubbled through 20 ml. of the unprotected fluid at one liter per hour at 518 F.,

it gels in an average time of 10.4 hours. The presence or absence of Washers had no discernible effect'on gel time. At 550 F. with a mixture of 5 percent oxygen and 95 percent nitrogen gel time with washers was 27.8 hours and without washers 23.0 hours. additives were employed at a concentration of 0.2 percent at 518 F. with dry 'air for 48 hours. At the end of the 48 hour period the unprotected fluid was gelled. A number of the additives contemplated by this invention The antioxidant h M were able to prevent gelation for this period. At 550 F. with a mixture of 5 percent oxygen and 95 percent nitrogen the unprotected silicone fluids were gelled at the end of the 48 hour period and the gel was discolored and yellow in appearance. The additives of this invention were still effective at 550 F. though less so than at 518 F. in spite of the fact that gel time of the untreated fluid was longer at the higher temperature.

The criteria used to establish additive perference were effectiveness in retarding viscosity increase, low temperature solubility, appearance of fluid such as darkening or sludging, and toxicity considerations. Gross weight change, acid number, and washer changes did not appear to afford a consistent criteria. None of the effective antioxidants of this invention caused unduly. high acid numbers nor did they cause excessive attack on the washers. Effectiveness in retarding viscosity increase was, as stated heretofore, evaluated by kinematic viscosities at 100 F. and 210 F.

Low temperature solubility was determined as follows: The additives were agitated in the fluid at 302 F. with a stream of nitrogen for two hours. The solution was held at room temperature for three days, thenat minus 65 F. for three days, and again at room temperature for three days. Theadditives were then evaluated as anti oxidants at the highest concentration at which they were soluble at minus 65 F,

The toxicity factor of some concern was carcinogenic activity. Several of the additives which are effective as antioxidants in silicone fluids exhibit carcinogenic activity, at leastin mice, and due care should be exercised in handling such materials.

On the basis of the criteria mentioned above, the additive of choice for silicone fluids is 1,2-benzanthracene. Pyrene is ranked second and acenaphthene third. Fluoranthene, phenanthrene and 2,5-diphenyloxazole are alternate candidates for fourth rank. Acenaphthene was espec'iallyefiective at 550 F. at a 1.0 percent concentration.

The information by which additive preference was determrned is summarized in Table II, which in turn is a summation of material taken from Tables III through VI.

For each of the effective compounds Table II sets forth the average percentage viscosity increase at 100 F., the number of runs on which the average was based and the appearance of the fluid after the test. These data are given at two concentration levels. The highest concentration at which the additive was soluble at minus 65 F.

and the routine testing level of 0.2 percent. In addition, tests were run at 518 F. with dry air and at 550 F 5 6 with a gaseous mixture of 5 percent oxygen and 95 per- ."5'18 F. in Table IV, and at 550 F. in Table V. Tests cent nitrogen. Solubility tests are presented in Table results for additive concentration at the 0.2 percent level III. The evaluation of the antioxidants in F-SO silicone for 48 hours are shown in Table VI at 518 F., and in fluid at their minus 65 F. solubility level is shown at Table VII at 550 F.

Table III SOLUBILITYI OF EFFECTIVE COMPOUNDS IN F-50 SILICONE Additive 1.00% 0.50% 0.20% 0.10% 0.05% 0.03% 0.01%

1,l'-binaphthy1 (AV: r 2 hours at 150 0. (302 F.) S 3 days at room temp I 3 days at -'65 F 3 days at room temp Decacyclene (A):

2 hours at 150 0. (302 F.) 3 days at room temp- 3 days at 65 F- 3 days at room temp 1,2-benxanthracene (A):

2 hours at 150 0. (302 F.) 3 days at room temp. 3 days at 65 F 3 days at room temp Dinaphthylenethiophene (A):

2 hours at 150 C. (302 F.).... 3 days at room temp 8 days at 65 F 3 days at room temp I 4,4-bis(dimethylamino) benzophenone (E K):

2 hours at 150 C. (302 F.). 3 days at room temp 3 days at 65 F 3 days at room temp Chrysene (EK):

2 hours at 150 0. (302 F.) 3daysatroomtemp 3 days at -65 F 3 days at room temp N,N-dl-2-naphthyl-p-phenylene-diamine (EK):

2 hours at 150 0. (302 F. 3 days at room temp 3 days at 65 F 3 days at room temp Indanthrene Navy Blue' RA powder (GD):

2 hours at 150 0. (302 F.) 3 days at room temp 3 days at 65 F 3 days at room temp 2,5-diphenyloxazole (EK):

2 hours at 150 0. (302 F.) S 3 days at room tem 3 days at -65 F I 3 days at room temp I Fluoranthene (BT00):

2 hours at 150 0. (302 F.) S 3 days at room temp S 3 days at 65 F"; I 3 days at room temp I Perylene (A):

2 hours at 150 C. (302 F.) 3 days at room temp 3 days at 65 F 3 days at room temp Benzo(a)pyrene (EX):

2 hours at 150 0. (302 F.) 3 days at room temp 3 days at 65 F 's-n-n-n-i mmmm HHHH mrnmm HHHH HI-(Hm 3 days at room temp. 3 days at -65 F 3 days at room temp Pyrene (CCC):

2 hours at 150 0. (302 F l-H-(r-U-l UJUJUJUJ UJUJCDU) mmmm HHHH (amt/2m t Phenanthrene (CCC): 2 hours at 150 0. (302 F.)

. 3 days at room temp- 3 days at 65 F 3 days at room temp. E Aeenaphthene (EK):

2 hours at 150 0. (302 F.) 3 days at room temp 3 days at 65 F 3 days at room temp N-phenylierrocenec boxamide (WADC):

2 hours at 150 0. (302 F.) 3 days at room temp 3 days at 65 F 3 days at room tem 1 ,3,5-triphenylbenzene EA) 2 hours at 150 0. (302 F.) 3 days at room temp 1,12-benzoperylene (A):

2 hours at 150 C. (302 F.) 3 days at room temp HHHH mmmm mmmm U UJ 1 The additives were agitated in F-50 silicone fluid at 150 0. (302 F.) with a stream of nitrogen for two hours: the solution was held at room temperature for three days, then at 65 F. for three days, and again at room temiperature for three days.

2 =Aldrich Chemical 00.; EK=Eastman Kodak; GD =Genera1 Dyestufi 00.; RTCC =Reil1y Tar and Chemical Corporation; CCC =Carbide and Carbon Chemicals Co.; WADC =Wright Air Development Center.

8 S=soluble. I=ins0luble.

Table IV 7 h K THE'MOST EFFECTIVE COMPOUNDS AT THE HIGHEST CONCENTRATION AT WHICH THEY WERE SOLUBLE AT -95 F IN 1 -50 SILICONE AT 518 F., 1 LITER DRY AIR/HOUR FOR 48 HOUBS r v V Viscosity Change in metals (mgJcmJ) Note- Fluid Additive Concenbook wt; Percent Percent Acid Appearance of tration, page change Cs. at visc. Cs. at vise. N 0. fluid after test Stainpercent (g.) 100 change 210 change Al Cu Steel less Ti Ag 'F. at 100 F. at 210 Steel Phenanthrene 1 3814-33 0 90 50 36 80 2.1 Clear, yell0w 1'88 33 8'3 31 35 Z2 '3 "6" 4- 3' o 27' 1 paque Acenaphthene 1.00 3893-5 -0.4 89 46 29 45 2 o brown. 4,4bis (di-methyl- 0 05 3814-35 0 7 Yellow gel amlDO()EIi%IZOPhB- none 0.03 3814-36 '-0.8 121 101 '38 90 "1.7 Clear, yellow Chrysen" (EK) 0. 03 3893-3 -0 5 123 105 48 140 d0 Fluoranthene 0. 50 3814-37 -0.3 69 '29 45 1.8 Dark yellow (RT 0. 50 3893-6 -0. 3 125 108 34 70 1. 9 Clear, dark V yellow. 0. 50 3814-38 0 4 Dark brown 2,5-diphelnlyl7iloxazole 0 50 3893 2 0 4 Bgel. l

. rown ge 0. 3893-9 0.3' 113 83 37 85 1.0 Clealii, dark 0.02 -0. 32 +0.02 0.00 +0.16 ye 0W D0 0.35 3893-10 -0.3 '487 711 f 177 785 0.9 do 0.02 0. 24 +0.08 0 02 +0 30 4 0. 20 3893-11 0 1 97 64 28 1. 4 Clear, yel1ow 0. 20 3893-11 0 3 119 98 33 65 1.2 do 0.10 3814-4 0;5 73' 21 '28 40 1.6 Clear, light +0.06 0.00 +0.08 +0.08 +0.06 Pyrene (CCC) s brown. 0.10 3893-7 --0.4 88 46 29 1.9 Clealii, dark 0.4 0. 10 +0.16 +0.02; +0.24

ye ow. 1,1-binaphthyl (A) 0.20 3893-8 0; 6 94 56 30 1. 9 Clear, ye1low 1,2-benzanthracene 0.20 3814-42 0.0 70 16 '23 15 2.0 do

' (A). 0. 20 3893-8 -0. 4 77 28 '25 V 25 2. 3 do Benzo (mpyrme 0. 20 3814-43 0. 3 69 15 24 20 2. 2 Cgaggzugark I 0.20 3893-8 -0.1 r 72 v 20 V 24 :20 2.1 do

l Viscosity of F-50 silicone fluid before test was cs. at 100 F. and 20 cs.'at 210 F 1 Acid number was determined by the procedure given in Scott, Standard Methods 01 Chemical Analysis, 1 01. II, page 1844, 5th Ed., 1939, D. Van Nostrand 00., Inc;, N.Y.

CCC=Carbideand Carbon Chemicals 00.; EK=Eastman Kodak; RTCC=Reilly Tar and Chemical Corporation; A=Aldrich Chemical Co. 4 Lower concentrations tested to check ohseryed deleterious efiectat higher concentration.

I I i. .f I." l'TilblV THE MOST EFFECTIVE COMPOUNDS AT THE HIGHEST CONCENTRATION AT WHICH THEY WERE SOLUBLE AT F.)

' V IN F-50 SILICONE AT'550 E, 1 LITER 5% 0 -95% Nil/HOUR FOR 48 HOURS s Viscosity Chengelnmeta-ls (mg/cm?) Concen- Note- Fluid M s Appearance Additive tration book wt. Percent Percent Acid of flu1d (perpage change cs. at Vise. 05. at Vise; N o. after test Stain- 'cent) (g.) 100 F. change 210 '13; change Al Cu Steel less T1 at 100 at 210 steel j 1 5. i i i- 1,1-binaphthy1(A). 0. 20 3733-45 2.6 D251; brown 1,2-benzanthracene '0. 20 3733-43 -0.5 137 118 44' '120 2.6 Dark brown A l 0.20 3751-9 0.7 133 111 *42' 110 4.2 do +0. 10 0.04 +0.10 +0.02 +0.02 Benzo(a)pyrene 0. 20 3751-2 0.5 89 41 "29" "45 4.4 do E I 0.20 3751-14 0.0 86 '36 28" "'"40 4..7 d0 .1 +0.30 0. 30 +0.08 +0.06 +0.04 i m i H 0 05 3893-21 -1. 1 w g9 0.05 3893-29 -2.0 225 bmwn '0.03 3893-21 -1.9' d0 "-"{"0.03' 3893-28 -415- do 2,5-diphenyloxazole 7 go nu-O Fllroranth'ene "0. 50 3893-23 1.1 Viscous brown (RTCC 0.50 3893-29 0.9 500 733 1.6 Cllear, dark W 7. Town 0.10 3893-24 -1.0 201 235 33 65 2.0 Clcar,brown +0.6 0. 52 +0.02 0.00 +0. 02 ----'-{"0.10 3893-30 0.9 431 "'618' 249" 1,145 1.7 Olgar, dark U. rown. Phenanthrene .3593-25 1&6 1 I (COO) 3893-30 '1 "43"1 5 0 grown 0 10 0 0 10 0 08 0 94 Acenaphthenefl 1.00 3893-26 -0.7 124 00 A w 2. 1;, -p.

(EKM .1 0 3 30 9 9 -5 1 Viscosity of the F-50 silicone fluid before test was 60 cs. at F. and 20 cs. at 210 F. 7 2 Acid number was determined by the procedure given in Scott, Standard Methods of Chemical Analys1s, vol. II, page 1844, 5th Ed., 1939, Van Nostrand Co., Inc., N.Y.

3 A==Aldrich Chemical 00.; EK Eastman Kodak; RTCC Reilly Tar and Chemical 00.; CCC=Carb1de and Carbon Chemicals Co.

4 1.3 mg. petroleum ether insolublcs recovered 3893-26.

5 Insutficient sample. 7

the fluid heated in tubes at 518 F. The time required for gelation of the oil under the various conditions tested served as the most apparent indication of the rate and extent of oxidative degradation.

The degree of chemi-' assumption that all the products of methyl cleavage were volatilized and determined. It is seen that the number of methyls removed is only slightly larger (2.83) in the presence of the additive than for unprotected fluid (2.60), although the time was increased sevenfold. Since each cal change in the fluid itself, up to the point of gelation, was not large enough to be detected by comparison of molecule contains an average of 82 methyl groups, about infrared spectra and, for this reason, the data most pertiof the methyl groups was lost: nent to the oxidation'process involved a determination of the by-products formed from the reaction. N During the reactionleading to gelation, oxygen was gfgg g g g consumed and a number of volatile products were evolved and carried out of the sample tubes in the air stream. Mcthyls cleaved/molecule 2m 1 233 1 The volatile products identified and determined quant T t l th l l l V 2 32 2 29 tatively included formaldehyde, formic acid, carbon dioxide, carbon monoxide, Water, cyclic siloxanes and tetrachlorobenzene. In order to collect. the condensible vola- The presence of '0.2 percent fluoranthene in protected tile products, the exit gases from 6 samples of fluid fluid amounted to 1 molecule per 33 molecules of silicone grams each) were lead through a manifold into a trap polymer, or 1 fluoranthene molecule per 2700 methyls. immersed in a Dry-Ice acetone bath and the resultant Of these 2700 methyls about 93 were lost during oxidative products were analyzed quantitatively. 2O gelation. Tetrachlorophenyl cleavage was relatively un- In experiments in which the silicone fluid contained important, about 1 group from 100 silicone molecules. fluoranthene, 9-fluorenone-l-carboxylic acid and recov- Each silicone molecule contained an average of 1.5 tetraered fluoranthene were obtained. The oxygen consumpchlorophenyl groups. tion'was calculated from the overall weight increase and The number of moles of oxygen comsumed per mole this was compared with the amount of oxygen removed of fluid upjto' gel point, as determined by metering the from the air stream. The rate of oxygen taken up and oxygen content of. the. exitgases, can be checked in two of carbon monoxide and carbon dioxide evolved were ways. Although the fluid itself undergoes a weight loss also determined for the entire reaction period. 'The comduring the oxidation due 'to loss of volatile products, parison of all these factors were rnade for unprotected there is an overall Weight increase when all the products fluid and fluid containing 0.2 percentfluoranthene. The are determined. This increase must be due only to the test results obtained on gelation inhibition are set forth oxygene takenupby the fluid, and its magnitude must be in Table VII. equivalent to the. amount of oxygen. Another check can .7 r Table VII cameras or F w SILICONE FLUID AT 518 F. TO our POINT.

' Without additive Containing 0.2% additive Experiment 7 a A B C D Average E F G a H 7 Average Wt. fluid (g.) 120. 5i0.1 12 0.9 122.0 120.4 121.2 121.1105 Fluoranthene added (g.) None 0.240 0.240 0.240 0.240 0.240 Gel time (hrs) 71i1 HGHO (g.) 2. 26=|;0.04 HCOOH (g 0. 48i0.10 HzOfi 2. 09;l;0. 12 0 (a) 0.75

00, (g) 0. 80i0. 24 Tetrachlorobenzene (g).-- 0. 093:1:0. 005 Siloxanes (g.) 3.25:3:0. Fluoranthene recovered: r

Incondensate (g.) a r 0- 059 0.075 0.088 0. 074:1:0. 010

In gel (g.) 0.060 0.026 0 043i0. 017 Total condensable products (g.) 6 475:0.13 8 03 8.93 9.81 8 925:0. Total volatile products (g.) 7 3 i0. 1 9. 755:0. 6 Wt. loss of fluid (g.) 3.55103 3 85 5.28 e 12 5 085C082 Over-all wt. increase (g.) 3.8 4. 6 Metered Oz uptake:

G. 4.80 4.64 4.72i0.0s

Percent of total availab 4.1 4.1 4.1

The test results on gelation inhibition, as set forth in Table VII, give gram quantities of the various products formed and the amounts ofoxygen consumed up to the gel point. The molar ratios of these products to one mole of silicone fluid were calculated from the averages and are compiled as follows:

I siloxane link. The total number of oxygen atoms is M g Mi i then equal to twicethe moles of oxygen consumed The a Volatile productswithout with 0 .2%-

--molar ratios of oxygen consumed by 1 mole of silicone 2"? 944 Qfluid determined by these three methods are compared as follows: 1 1.60 1.86 I

.34 .26 a a. a. h. Oxygen consumed Unprotected Protected .52 fluid fiuid .14 .045 Tctrachlorobcnzene. 0106 0105 Methyl groups cleaved" Metered 0 uptake 2.39 3.68 Calcd. from weight increase 2. 96 3. 61

O atoms in roductS The number of methyl groups cleaved per molecule of d. f 2.83 3.72 silicone fluid was calculated by adding up the molar ratios I of the carbon-containing products from the oxidation of v g 2.73=|=.22 3. 6531.04

This calculation involves the reasonable methyl groups.

13 Averages of the three methods are seen to be 2.73:0.22 moles of oxygen per mole of unprotected fluid and 3.65:0.04 moles of oxygen per mole of fluid containing fluoranthene.

It appears that gelation of a silicone fluid depends on cleavage of methyl groups from the fluid and this apparently leads to crosslinking of silicone molecules. Tetrachlorobenzene is a very minor product of the oxidation process and the loss of tetrachlorophenyl groups (one from 100 silicone molecules) can in no way account for the gelation of the fluid. The action of the additives seems to be only to delay oxygen pickup, methyl cleavage and crosslinking rather than to change the nature of the chemical reactions involved. This delaying action must occur before cleavage of the Si-C bond since oxygen consumption and methyl cleavage are aifected. It is reasonable to assume that the crosslinks formed are merely additional siloxane bonds (SiOSi) between the linear silicone molecules, since no new type of bonds were detected by infrared comparison of unoxidized and gelled fluid.

From an examination of the foregoing, it will be seen that the instant invention provides silicone lubricants which are especially amenable for use in present day high speed propulsion devices. The flat viscosity temperature curves exhibited by these lubricants as well as their oxidation stability at elevated temperatures makes them highly advantageous for use in devices which encounter wide ranges of temperatures during their operation.

The term percent as used in the instant specification and appended claim refers to percent by weight unless otherwise indicated. It is to be further understood that although the compositions described herein illustrate a preferred form of the invention, modifications and alterations can be made by those skilled in the art without departing from the spirit and scope thereof, and that all such modifications as fall within the scope of the appended claim are intended to be included herein.

What is claimed is:

A lubricating fluid composition comprising a silicone oil and, as a gelation inhibitor, from about 0.2 percent to about 2.0 percent by Weight of 2,5-diphenyloxazole.

References Cited in the file of this patent UNITED STATES PATENTS 1,761,810 Bjerregaard June 3, 1930 1,904,433 Fischer et al Apr. 18, 1933 1,918,593 Dow July 18, 1933 2,191,089 Barth Feb. 20, 1940 2,208,105 Rathbun July 16, 1940 2,221,953 Read Nov. 19, 1940 2,427,766 Diamond Sept. 23, 1947 2,491,120 Loane et a1 Dec. 13, 1949 2,561,178 Burkhard July 17, 1951 2,689,859 Burkhard Sept. 21, 1954 3,026,263 Arimoto Mar. 20, 1962 3,047,501 Brook et a1. July 31, 1962 FOREIGN PATENTS 809,360 Great Britain Feb. 25, 1959