Silicone Oils for Lubricating Steel Versus Steel U
GORDON C. GAINER Westinghouse Electric Corp., East Pittsburgh, Pa.
of the various classes of synthetic lubricants which are available currently, the silicones alone possess the important combination of high thermal stability and favorable viscosity-temperature relationship. Present commercial silicones, however, fail to provide an adequate lubricating film between sliding ferrous surfaces under heavy load conditions. The incorporation in the silicone molecule of substituted phenyl groups in which the substituents are halogen atoms or halogen-containing groups increases very considerably their loadbearing ability. Data comparing the lubricating properties of experimental silicone oils of this type with those of commercial silicone oils and other lubricants are given. Preparative procedures and evaluation tests are described, and the results are tabulated.
C
URRENT silicone oils are characterized by a high degree of thermal stability together with a very favorable viscositytemperature relationship. I n addition, they exhibit a desirable combination of such properties as high flash point and low pour and freezing points. They are, however, very poor lubricants for ferrous metal surfaces under boundary lubricating conditions ( I , 2, 10). They have high coefficients of friction, about 0.33 as measured on the modified Kyropoulos ( I d ) pendulum, which compares with values of 0.14 to 0.16 for a good petroleum oil, and they permit excessive wear. Wear rates determined on dimethyland methylphenylsilicone oils in the Falex testing machine, 100 pounds gage, 3 hours (5, 9 , 1 8 ) when used on steel test pieces, have been estimated a t 3600 units per hour in this laboratory. The wear rates of these fluids are, therefore, so high as to be indistinguishable by these methods. Acceptable petroleum lubricants give wear rates of the order of only t n o or three units per hour. These rates are expressed in terms of an arbitrary unit, but they are directly related to the amount of metal removed from the test pieces by wear. Of all silicone fluids, the dimethyl oils are unexcelled in their low change of viscosity with temperature. Unfortunately their load-carrying capacity is very poor. Intensive investigation of these oils (a) revealed that higher loads can often be supported when either or both of the bearing surfaces are nonferrous and that, for some metal combinations, the dimethyl oils give quite satisfactory performance. The introduction of phenyl groups in the oil, in partial replacement of the methyl groups, results in considerably improved lubrication for certain of these bearing pairs (6). But, when both surfaces are steel or iron, the methylphenylsilicone oils show little improvement over the dimethyl fluids. Lubrication is still rated poor, and wear is rapid. I n this work the problem of developing boundary lubricating properties for steel versus steel in the silicone system, where sliding frictional phenomena are involved, was approached through modification of the silicone oil molecule. I t was assumed that the conventional polysiloxane molecule is not adsorbed strongly enough by physical forces on ferrous metal surfaces to form a close-packed, condensed film-type, protecting layer or layers. Thus metal to metal contact is not prevented where impinging steel surfaces are involved, and consequent local welding occurs, resulting in inordinate wear. Thus some alteration of the silicone oil mole~ulep a s required to permit the introduction
November 1954
of groups capable of forcing surface chemical reaction a t the metal oil boundary. Such alteration would result in the formation of an oriented molecular layer or layers-a protective film-in much the same manner as is ascribed to the conventional fatty acids, or sulfur-, chlorine-, or phosphorus-containing extreme pressure addition agents. R3Si-O-
il I. Si-0
-SiR,
R = hydrocarbon, usually either phenyl or methyl Examination of the structure of a linear polysiloxane-silicone oil indicates there are two possible areas of modification. One consists in substituting a bivalent radical or atom for bivalent oxygen in the siloxane chain. The second area of possible modification consists in the introduction of novel lubricating groups in the siloxane molecule by attachment to silicon, in place of part or all of the conventional hydrocarbon R groups. Such groups must be capable of surface chemical reaction, yet they must not react in the bulk fluid. Moreover, in order to preserve the great asset of thermal stability characteristic of the polysiloxanes, the lubricating groups must possess the unique property of outstanding resistance to thermal degradation and oxidation. From the standpoint of preparation in the laboratory for screening purposes, the syntheses of such experimental polysiloxane fluids is further complicated by the requirement that the starting materials, silicone monomers, for any experimental polysiloxane usually must be synthesized through use of the Grignard reagent or other organometallic intermediates. This requirement very definitely limits the number of reactive groups that can be so introduced, since organometallic compounds are capable of reacting with a wide variety of functional organic groups. The fluids described in this work were a type in which various halogen-containing phenyl groups were substituted for varying amounts of the usual hydrocarbon groups found in the silicones of commerce. Incorporation in the silicone oil molecule of substituted phenyl groups in which the substituents are halogen atoms or halogen-containing groups, increases very considerably their load-bearing ability, steel versus steel, under boundary conditions of lubrication
INDUSTRIAL AND ENGINEERING CHEMISTRY
2355
lllt,hough the lubrication studies report,ed in this paper m r e initiated in 1947 and completed by 1950, publication was delayed because of company and military security. I n the meant'ime, independent discovery of the effectiveness of halogen s u b stitution in improving the lubricity of phenyl-containing silicone oils has been reported by other laboratories. Fletcher and Hunter ( 1 1 )describe silicone lubricants containing halogenated phenyl and halogenat,ed xenyl radicals, and present torque, temperature, and xear data from Falex test.s on steel versus steel test pieces. One test is reported for steel versus brass test pieces. Burkhard ( 3 ) reports tests on the Shell Four-Ball wear machine, in cvhich both a p-chlorophenylmethyl oil and a In-chlorophenylmethyl oil gave less wear than a dimethyl oil, st,eel versus steel, and steel versus brass. Viscometric data are not given in either of these works and, t,herefore, the effect, on bulk oil propcrt.ics of introduction of halogen to the silicone oil molecule cannot be assessed. The lubricating characteristics attained in certain of the oils described here are superior to any reported in these references. This paper presents the work that \.;as done and the data obtained in an initial examination of the lubricating ability, steel versus steel, of such modified silicone fluids. The nork that has since been done, in an endeavor to minimize adverse effects on bulk oil properties of introduction of the surface reactive halogenphenyl groups in the polysiloxane structure will be publifihed later. The chemistry and technology of the polysilouanes have been reviewed (4,f 5 - 1 7 ) . For determining the effect of substituted phenyl groups on the lubricating properties of silicone oils, the initial screening experiments were based on symmetrical diphenyltetramethyldisiloxanes. Those substituents which were found to impart lubricating properties t o the disiloxane were then introduced in polysiloxane oils. The disiloxanes have the advantage that, while they contain all the essential groupings found in the methylphenylsilicone oils, they are individual compounds not complirated by such factors as varying chain length, distribution of molecular sizes, and viscosity, and they can be freed from impurities by vacuum distillation. The substituted disiloxanes viere obtained by synthesizing, and then hydrolyzing, the correspondingly substituted dimethylphenylethoxysilanes or corresponding chlorosilanes. The substituted methylphenyldiethoxysilanes or corresponding chlorosilanes were used in preparing the modified silicone oils of this paper. MEASURERIENT O F LUBRICATING PROPERTIES
As criteria of the lubricating ability of the fluids prepared in this work, three general propert,ies were determined, coefficient of friction, Falex wear rate, and viscosity-temperature coefficient. Coefficient of Friction. The modified Kyropoulos four-ball pendulum ( l e ) with a 1-kilogram Tveight was used to determine the coefficient of friction. P e r f e d y clean steel balls, having uniform surface characteristics and hardness, were used. For the particular apparatus employed, the number of sTvings, S , from a fixed starting amplitude of the pendulum to rest, iq related to the coefficient of friction, F , by the formula
F
= 9.5i/S
Falex Wear Rate. TT'ear rates xere determined in the Faleu testing machine (6, 8) by the standard Falev wear procedure ( 9 ) . In this machine the test p eces are a cylindiical metal pin and two metal V-blocks betryeen which the pin is rotated under fixed load, while flocded with the oil under test. The test is continued for 3 hours following a preliminary 15-minute break-in period a t lower load, 50 pounds gage. Wear in the test pieces reduces the applied load, and the machine strain gage take up setting is adjusted every 15 minutes to maintain the load a t its initial value, 100 pounds gage. The wear rate is determined by
2356
the amount of take up nee r y j in these adjustments, and it i; recorded as the average number of rachet teeth advaiiced poi' hour, during the 3-hour test, period. The tests reported w r e 1';1n :it 100-pound gage pressurcl. Th:, load during break-in was 50 pounds gage. The T'-bloclis usccl Tvere SAE 2320 steel having a Roclmell hardness value (225. Number 8 pine, of SAE 3115 a t r d and Rocltrvell hardness Cl, were used. Viscosity-Temperature Coefficient. Viscosity of the val,ioiis oils 15-as determined at, tivo temperatures, 100" F. arid 210' I;., in the Cannon modification of the Ostn-ald viscometer. Thr: viscosity-temperat,ure coefficient8, which is calculated from t h e measurements, is defined
V.T.C.
=
viscosit>- a t 100" F.-visco$ity a t 210" 1.' . ~ _ _ ~ viscositj- a t 101)' F.
_ _ _ _
PREPARATIVE PROCEDURES
I n general, the disiloxanes were formed by hydrolysis of tlro aryldimet8hylet8hoxy-or chlorosilane, with 5% sulfuric avid ( I S , 1 4 ) . The resulting product x i s t8henfurther t,reRtpd \vit>h i s % (by .rr-cight)sulfuric acid. Some of the halophenyldimethylet,hoxysilanes failed to hydrolyze to any great degree when treated ivith 5% sulfuric acid. Treatment with i570 sulfuric acid, hov-ever, in all cases yieldeil the desired disiloxane. The experimental silicone oils were prepared in a similar iiianner. h typical preparat,ion ip offered as an example. There are ot,her methods for preparing silicone fluids (3, 11 ).
A &liter, round-bottomed three-necked flask was equipped with a high speed, hook-type glass stirrer, and a 3-liter dropping funnel. The third neck was stoppered x i t h a glass outlet tuho to prevent splashing loss. T o the flask were added 1085 grams (4.45 moles) of p-chlorophenylmethyldiet~hoxysilaneand 1 lit,cr of 5y0sulfuric acid. The mixture v-as rapidly stirred for several hours. (The period of stirring is not critical beyond 1 hour.) The heterogeneous mixture n-as allowed to separate in a largc separatorv funnel, and t'he oily lox-er laver was drawn from the aqueous laver. To the oily product was added 144 grams (0.895 mole) of hexamethvldisiloxane 10.2.11 enuiralent). The resultine solutioo was placed in the original hydGolysis flask and the contents w r e stirred and cooled to about 15' C. (external ice bath). To the cooled, rapidly stirred solution TTW added 1 liter of 757, sulfuric acid (by weight). The acid was added in a thin st,ream from the dropping funnel, and e s rapidly as possible, care being taken to keep t,he flask contents below 25' C. Aft,er the addition T ~ complete (about 10 minutes with external cooling) the resulting p2sty emulsion was stirred for 1 hour at 20" to 25" C. Chopped ice (about, 1 kg.) was added 8 s rapidly as possible, with coiitinuous st,irring. Approximat,ely 1 liter of ether was then added t,o loosen the thick paste. The contents were poured into 1 liter of water contained in a 5-liter separator). funnel, and the organic layer was separated and washed five times n-ith distilled mater. Addition of a little sodium chloride helps t o break any troublesome emulsion t'hat map form. At t'his point in the preparation, a test for sulfate (barium chloride) was alwa?-s negative. The ether extract was dried over anhydrous calcium (or sodium) sulfat'e. The ethereal solut,ion was then t,ransferred to a Claiscii distillation apparatus, and all of the ether was removed by distilla-. tion. Vacuum was applied (1 to 2 mm.) and t,he pot temperature was raised to approximately 120" C. for several hours, to remove the last traces of volatile product. A t r x e of crystalline product, probably the p-chlorophenylmeth~lc~ tends to sublime into t,he condenser a t this stage. The rcsultiiig end-blocked p-chlorophenylmethylsilicone oil was then treatcd lvith activated charcoal to produce a Xvater-TThitc transparent oil, aft,er filtration. By this means, 850 grams of p-chloropbenylmethyl oil was obtained, having the folloning lubricating char-. acterietics: coefficient of friction, 0.14; Fnlex wear, 100 pounds gage, 4 unit,s/hr.; viscosity a t 100" F., 34 centistoke..; a t 210" F., 8.0 cent,istokes; viecosi t>--t8emperaturecoefficient, 0.85. Theoretically, t,his silicone oil has an average chain I m g t h or seven silicon atoms, and contains five p-chlorop'ncnylmeth~lsiloxane units, with one t,riiiiethylsiIhemioxatie groiip 2,t cnch cnd of t h e molecule.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 11
S
-SiliconesLUBRICATING PROPERTIES A S A FUNCTION OF COMPOSITION
Preliminary Experiments. Table I lists the various disiloxanes, together with a few nonend-blocked polysiloxanes, which m r e prepared and examined in the screening experiments.
TABLE 11. LUBRICATINGPROPERTIES OF SILICOKE OILS Oil No
0.40 0.33 0.26 0 16 0.13 0.066 0.033 0
0.26 0.23 0.14 0.15 0.19 0.24 0.23 0.40
2 5 6 7
0.40 0.33 0.26 0.16 0.13 0.066 0.033
0.13 0.14 0.15 0.19 0.22 0.27 0.30
3 1 4 2 5 6 7
0.40 0.33 0.26 0.16 0.13 0.066 0.033
0.15 0.14
3 1 4 2 7
0.40 0.33 0.26 0.16 0.13 0.066 0.033
0.22 O,l5 0.15 0.17 0.19 0.25 0.28
3 5 3 5
1
4
VARIOUS ORGANOSILOXANES
Sample NO.
1
2 3
4 5
6 7 8 9
10
11 12 13 14
Phenyl Substituent
DiEiioxanes-. Polysiloxanes Coeff. Falex wear, Coeff. Falex wear, friction unitr/hr. friction units/hr.
p-Br p-C1
30. 7.7 54. 7.6 high 5 .,7 solid 6.3 4.5
p-F
m-CFa p-OCnHa m-C1 p-CsHs 3,4-C1z x,x-Clz 3-C1, 4-Br 3-CFa, 4-C1 p-OCHs p-CN none
0.13 0.13 0.17 O,l5
...
...
...
0.23 ,..
...
2.6 rough
... 0.15 ...
...
0.33
...
11. 3. 208. 6.5
... I
,
.
2 5 6 7 S
Viscosity V1scositY,CL Temp. Coeff 100° F. 210’ F
~ B r o m o.~ h e.n y l 6 0.99 1 0.98 39 0.87 48 0.79 31 0.72 29 0.63 144 0.58 >3600 0.57
=
3358, 9174. 1.52. 37.7 21.4
59.1 80.9 18.8 7.8 6.0
8 . 95 7.8
3 . 63 3.4
390.5 95.9 59.4 10.9 11.8 26.7 32.8
21.2 10.R 9.9 3.2 3.8 10.0 13 3
0.77 0.76 0.7‘3 0.66 0.65 0.59 0.57
26.8 17.1 22.7 7.7 10.1 5.9 5.1
6 1 4.2 5 4 2.6 3.5 2.4 2 2
3,4-Diohlorophenyl 3.0 0.97 3.3 0.93 2.0 0.85 6.6 0.74 24.6 0.72 27.3 0.66 96.3 0.58
1412. 200. 145.6 17.9 22.2 9.1 5.4
37.9 14.4 16 8 4.7 6.2 3.4 2.3
0.40 0.13
= 3-Trifluorornethyl-4-Chlorophenyl 0.15 1.G 318.6 0.95 0.18 0.6 0.72 16.3
16,s 4.0
0.40 0.13
0.13 0.16
R = p-Chlorophenyl 3 1 4
2 60 63 48 49 135 241
I . .
R = m-Cfs phenyl
3.6
... , . .
0.33
...
,..
>3600
5.3 4.3 2.6 14.6 60.6 83. High
0.15
0.17 0.20 0.23 0.38
R
In general, presence of halogen attached to the aryl group results in a marked reduction in the coefficient of friction and Falex wear rate a8 compared to the control sample No. 14 (also No. 5 , 7, and 12). Of the halogens, bromine and chlorine are more effective than fluorine. The m-trifluoromethgl group, however, is very effective (No. 4). The position of the halogen does not appear to have any appreciable effect (No. 2 and 6). TWOhalogens appear to be more effective than one in enhancing the lubricating properties (compare No. 2 with No. 8 and 9; note also No. 10 and 11). Simple introduction of a polar group does not appear to be effective (Yo. 13). Properties of Copolymer Oils. For further evidence 011 the relative lubricating effect of the various substituted phenyl groups, when introduced into silicone oils, several series of modified silicone oil copolymers were piepared in which the ratio of the lubricating halophenyl groups, here referred to as R groups, to the nonlubricating methyl groups was varied. This ratio is a measure of the internal dilution of the lubricating group, within the molecule, with nonlubricating methyl groups. COPOLYMERS OF CONSTANT CHAIN LEKGTH. For each of several halophenyl groups, two series of copolymer oils were prepared in which the theoretical average chain length was kept constant a t 8 and 14 silicon atoms, respectively. Within each series, the ratio of lubricating to nonlubricating groups was varied. Table I1 lists various R groups on silicone oils prepared in this manner, together with their measured lubricating properties. They are arranged in the table in order of decreasing ratio of R groups to total organic groups in the molecule. All the oils of Table I1 were made to have the average chain lengths and monomer ratios shown in the following list; the composition of the oil 1s thus identified, in each case, by the sample number. Oil No.
Faler Wear Units/Hr.
R 3
TABLEI. COMPOSITION A N D LUBRICATING PROPERTIES OF
R/Totral Coeff. Groups Friotlon
EXPERIMENTAL
5 0
R
R
=
=
m-Trifluorometlr~,Ibensyl 2.0 0.92 23. 0.70
97.6 15.0
8 0 4 5
3-Trifluoromethyl-4-chlorophenyl appears to be the most eff ective of all, in reducing Falex wear. With regard to viscosity-temperature coefficient, the m-trifluoromethyl oils show much the best viscosity-temperature relationship for any given composition, followed, in general by the chlorophenyl, and then the 3,4-dichlorophenyl oils. With the exception of the broinophenyl compound, most of the compositions approach a certain low limit of coefficient of friction, which appears to be 0.14. Explanation for the rise in coefficient of friction of p-bromophenyl oils 1 and 3 lies in the very high viscosities of these samples, which apparently affected the Kyropoulos pendulum swing count.
Average Chain ArylmethylDimethylHexamethylLength siloxane Units siloxane Units disiloxane 8 0 6 3 14 8 12 3
14 14
8 4
14 14
0
14
2 1
0 4 8 10 11 12
I n a given composition, bromine appears to be slightly more effective than chlorine in reducing Falex wear rates. The m-trifluoromethyl group seems to he more effective than bromine, and in this regard, two chlorine substituents on the phenyl group are more effective than the m-trifluoromethyl group. November 1954
5 R A T I O : A R Y L G R O U P S / TOTAL GROUPSFigure 1.
Lubrication l’roperties of Strhstituted Phen~lmethylsiliconeOils
INDUSTRIAL AND ENGINEERING CHEMISTRY
2357
100
I
4
It will be seen in Table 111,and is st,rikingly apparent in Figure 4, that the 3,4-dichloroghenyl group is much the most effect,ive in reducing wear at low concentrations in the molecule; it can withstand greater inkrnal dilution vcith the nonlubricating methyl groups. The p-chlorophenylmethyl oils are slightly better than t,he dichlorophmylmethyl oils in viscosit!.-t,enipc.~~~t8urecoefficient, Appearance of Falex Test Pieces. The appearance of t'lie test pieces at the end of the Falex test gives convincing evidence of the differences in lubricating ability between oils. A comparison is shown in the photograph, Figure 5 . At the left is shown a set of steel T-blocks and test pin from a Falex wear test, run as described, on a dimet,hylsilicone oil. This corresponcl~ to approximately 3G00 wear units per hour. Gross scarring m d welding has occurred. On the right are shown identical test pieces, run under exa,ctly the same conditions, but lubricntcil viith a p-bromophenylmethyleilicone oil. A s further evidence of the lubricating characterist.ics of t,lie experimental oils, Falex seizure using Falex Antiweld Test, (8) was determined. This test is utilized for evaluating the antiweld propert,ies of hypoid lubricants. In this test, if a total 1o:d of 2500 pound gage is attained without a sudden increase i n torque, the test,is discontinued and noted as satisfactory. When a chlorophenylmethylsilicone oil corresponding in composition to that of N o . 5, Table 111, was tested, neither seizure nor sudden torque rise occurred. I n two runs, the sctual bearing pressures involved when the test was discontinued a t 2500 pound gage, obtained through measurement, of the width of the scar on th(? V-block, were 31,250 pounds per square inch and 33,333 pounds per square inch. Figure 6 shows the test pieces used in the t a o test.i;. Figure 7 illust,rates x-elding that occurred a t vcry low pressures Jyhen a high qualit!., nonadditive petroleum oil was used (heavv, medium, Diesel, turbine, engine oil).
3 OIL NO.
FALEX W E A R UNITS
V §.
80
COMPOSITION
c
t
0
DCF3
d
-A
ClZ
5
60
CF3 O----CFsBz
X.41,
v,
cz
3
a
40
Figure 2. Lubrication Properties of Substituted Phenylnieth\ I4lirone Oils
I
21 I
5c o.3p\ \ i
3
5' 6 OIL NO.
4
I
1
1
,
COEFFICIENT OF FRICTION VS CQMPOSITION ~
\
c) LT
AGING T E S T S A 1 ELEVATED TEMPERATURES
LL.
0.2-
These experiments xere undertaken to ascertain the effects of thermal aging on viscosity, coefficient of friction, and Falea wear, both in the absence of metals and in the presence of copper, aluminum, and steel stripe. For these tests, large quantities of p-chloroplien!lmet~i~loil, both having silicone oil and 3,4-dichloropheny1methylailicone
&
z
w
;0.1
W
00 0
I
I
The data of Table I1 pcrt,aining to coefficient of frict,ion are shown graphically in Figure 1. Here, coefficient of friction is plotted as a function of the composition of the oils. Falex wear is treated similarly in Figure 2. COPOLYMERS OF \'ARIED CHAISLEXGTH. For each O f two halophenyl groups (chlorophenyl and 3,4--dichlor0phenyl)~ a series of copolymer oils, compoaed of halophenylniethyl silosane units end-blocked with trimethylsilheinioxane groups, was prepared, in which the average chain length was varied from 3 silicon atoms to 8. This variation in chain length automatically varies also the ratio of lubricating groups to rionlubricating groups. The composition of these oils is shown in Table I11 where the measured lubricating properties of corresponding samples in the two series are directslycompared. The coefficient of friction values are plotted against composition in Figure 3, and the Falex wear rates in Figure 4. For comparison, data on the m-trifiuoromethylphenyl oils of the previous series, taken from Figures 1 and 2, are included in Figures 3 and 4.
2358
-O0
--
5
RATIO: ARYL GROUPS / TOTAL GROUPS Figure 4. Lubrjcation Properties of Substituted Phenylmethylsilicone Oils
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vo%.46, No. 11
-Siliconesfurther heat aging. The second of the duplicates was used (Varied silicone chain length) exclusively for viscosity and R = p-Chlorophenyl coefficient of friction tests. R' = Dichlorophenyl The results of these tests are Viscosity, Cs. Falex Wear, Viscosity Temp. shown in Table IV. Av. Chain Coeff. 100° F. 210' F. ~~~~~h R G ~ Coeff. ~ Friction ~ ~ Units/Hr. ~ / Oil N o . Si Atom$ Total Groups R R' . R R' R R' R R' R R7The Falex wear rate is un6 8 0.33 0.130.14 4 2.0 0.870.88 71.775.2 9 . 7 8 . 7 affected by heat aging a t any 5 7 0.31 0.140.14 4 4.6 0.850.86 54.049.2 8 . 0 6 . 8 of the three temperatures em4 6 0.28 0.15 0.14 3.6 5.6 0.81 0.81 29.1 32.2 5.6 6.1 3 5 0.25 0.16 0.15 5.6 5.0 0.75 0.78 14.7 19.8 3.7 4.3 p l o y e d . If a n y t h i n g , t h i s 2 4 0.20 0.16 0.16 23. 5.0 0.72 0.78 11.2 13.1 3.1 3.2 property is improved. The I 3 0.13 0.16 0.16 High 10.6 0.71 0.74 9.4 11.58 2.7 3.01 coefficient of friction appears to rise slightly as the oils are aged, undoubtedly due to the great increase in viscosity experienced. This is particularly true the composition of oil S o . 5 of Table 111, were prepared. The of the dichlorophenylmethyl oils a t 225' C. lubricating properties of the two oils, as prepared, are indicated in With regard to viscosity changes in the chlorophenylmethyl Table IV. oil a t 200" and 225" C., copper consistently retards the polymerDuplicate sets of four samples of each oil were aged a t each of ization of the oil. The other metals, aluminum and steel, do three different temperatures, 175", 200°, and 225" C. One show some inhibiting effect, but this effect does not appear to be sample in each set was used as a control. The remaining three consistent. were in contact with copper, aluminum, and SAE 1010 steel The data on the 3,4djchlorophenylmethyl oil indicates that, strips, respectively. The strips or sheets were bent to curl around a t 225" C., all of the metals exert an inhibiting effect on the polythe interior of the sample bottles, and extended far enough out of merization process, the effect being greatest in the case of copper the bottle to support an inverted crystallizing dish. The latter At 200" C. copper is still the most effective inhibitor, but steel prevented dust particles from contaminating the samples. This and aluminum compare favorably a t 175' C. arrangement also permitted adequate circulation of heated air The important conclusion that can be drawn from these tests over the samples. Approximately half the area of the metal was is that none of the metals grossly accelerates the polymerization immersed in the oil, and half was exposed to the vapor and atprocess. Indeed, copper appears more likely to extend the liCe mosphere. of the oil. Moreover, the lubricating properties are not affected One of the duplicates of each set was used exclusively €or Falex a t all by the presence of the metals. testing, since it was felt that Falex testing might possibly affect Steel and aluminum show no apparent attack by these oils a t the future course of the heat aging. The samples which were the temperatures involved. I n the case of steel, only that porremoved for Falex testing were filtered through clay after test tion of the metal exposed to the atmosphere had oxidized (blurd). to remove contaminating debris. They were then returned for
PROPERTIES OF EXPERIMENTAL SILICONEOILS TABLE111. LUBRICATING
~~~~
OF TABLE Iv. EFFECT
Meta
Falex Wear, Units/Hr. Test I Test I1
None cu Ai Fe
4 . 0 (382)6 4,7(387) 3.7(406) 5 , O (430)
2,3(2230) 25.3(2235) 2.6(2278) 3.6 (2283)
None cu A1 Fe
5.0(195) 4.0(214) 3.3 1219) 4.3(238)
3.0 (2086) 3.3(2091) 2.3(2110) 4 . 0 (2115)
None cu A1 Fe
3.3(335) 3,O(320) 4.3 334) 3.0{344)
1.311688) 2.3 (1780) 2,3(1784) 2.0(1803)
Xone
2 . 7 (502) 3.3 507) 3 .O j526) 2 . 7 (531)
1 6 (2350) 2 . 6 (2356) 2.3(2374) 3.0(2379)
!LGING
AT
ELEVATED TEMPERATURE O N LUBRICATING PROPERTIES
Viscosity, Cs. Coeff. Friction 1000 F. 210° F. Test I Test I1 Test I Test I1 Test I Test I1 Chlorophenylmethyl Oil A60-2-1" 175' C. 306 (2377) 14.1(241) 21.6(2405) 153 (241) 0.13(241) 0.13 2377) 15.1(241) 25.0(2405) 126 (241); 391 (2377) 0.14(241) 0.1312377) 189 (2377)C 10.5(241)c 24.8(2377) 88 5(241) 0.13(241) 0.1312377) 10.D (241) C 20.3(2377) 90 (241)C 527 (2377) 0.13(241) 0.13(2377) 2000
cu
AI Fe
c.
298 1193) 0.13(2093) 0.13(2093) 99.6(193); 0.13(2093) 130 (193) 0.13 (2093) 189 (193)o 225' C . 0.14(1808) 460 (442) 0.13(442) 250 (442)C 0.14(442) 0.13 1828) 490 (442) 0.13 442) 0.14j1829) 492 (442) 0.15[442) 0.15 1830) Dichlorophenylmethyl Oil A50-2-2d 175' C. 0.16 (2426) 394 (266) 0.15 (266) 440 266) 0.15(266) 0.15(2425) 299 1206): 0.15(266) 0.15(2425) 312 (266) 0.15(266) 0.15(2425) 0.13(193) 0.14(193) n. 14 (193) 0.13(193)
343 (2093) 268 (2093)C 372 (2093) 517 (2093)
15
(193) ll.5(193)C 13.1(193)C 16.4(193)
23.6(2212)
964 (1446) 467 (1446)C
27.6(442)
1145 1446)
29.11442) 29 l ( 4 4 2 )
43 (1440) 27.811446)C 50.5(1446) 78.5(1446)
2358 t1446)
1 9 . 5 442)C
965 (2425)
678 (2425)C 917 (2425)c 735 (2425) c
20. 2 (266)
21.9(266)
20.2 (2212)c 2 5 , 3 (2093)
30.7(2093)
32 .o (2425) 27.2(2425)
2000 c. 1472 (2233) 2 7 . 2 (215) 39.4(2233) 0.16(2233) 722 ( 2 1 6 ) 1174 (2733)0 19.4(215)C 35.4 2233)C 0.16(2233) 338 (215) 1360 (2233)C 19 3(215)c 43 52358) 0.16(2233) 337 (215) A1 1542 (2233) 21.6(215)C 43.5(2358) 0 17 (2233) 419 (215) C Fe 225' C. 5830 1301) 42.2 467) 84 (1301) 1676 (467) None 3.01363) 2.3(11113) 0.18(467) 0.20(1833) 31 $467) 44.611301); 887 (467)C 2022 $1301)0 2.6(1R36) 0.19 467) 0.17 1833) cu 2 , 7(368) 4560 (1301)C 41.2(467) 73.5(1301) 1562 (467) 0 0.161467) 0 , I9 [1834) 2 . 6 (16.59) AI 3.0(435) 39,6(467)C 84 (1301) 5270 11301)C 1362 ,467) 1.3(1683) 0.17 (467) 0.20 (1835) Fe 2,3(440) a Initial values, before heating, were: Falex wear, -8/3 u n i t d h r . (negative value indicating wear less than thermal expansion of test pieces); coeff.of friction, 0.14; viscosity 47.2OR. a t 100' 3' 7.3 OS. a t 210' F. b Figures in parentheses refer t o hours a t the ternperatnre'hdicated and in,the presence of the metals shown in the first column. c Value less than the control under the saine conditions and shows a n inhibitive effect of the metal on polymerization of the oil. d Initial values, before heating, were: Falex wear, -6/3 u n i t d h r . ; coeff. of friction 0.145;viscosity 195 cs. a t 1005F., 1.44ea. a t 210' F.
None
c11
November 1954
4 . 0 (243)
3.3(262) 3.0(358) 3.3(363)
3.3(2182) 2.0(2186) 3.0(2206) 2.5(2211)
0.15 (215)
0.15(216) 0.15(215) 0.15(215)
INDUSTRIAL AND ENGINEERING CHEMISTRY
2359
Figure 5. Test Pieces at the End of Falex Test ( L e f t ) Specimen showing gross weav w h e n lubricntod with dimethylsilicone oil ( R i g h t ) Specimen showing n o wear w h e n lubricated with p-hromophenglmethylsilicone oil
The immersed surfaces were perEectly clean. Copper was very appreciably oxidized both above and below the surface at all these temperatures. The black coating which formed helouthe surface adhered more tenaciously than did the loose flak!. scales which formed on the atmospheric portion. Probsbly oxidation of the immersed portion occurred by diffusion of oxvgen t,hrough t,he heated oil. OXYGE3 ABSORPTION AMD EFFECT OF IKHIBITORS
Method. The oxygen uptake of certain of the experimental oils a t 175' C., alone and in the presence of copper, and with or wit,lioutmthe addition of inhibitors, ivas measured in a modified Sligh apparatus ( 7 ) . In t.tiis test the oil is heated in an atmos1)her.eof oxygen in a closed system att,achedt,o a mercury manomtiiiospheric pressure at rooni t,empersturc, and the course of t.he reaction is followed by thc In t,he present, tests; 5-ml. samples were used, and t'he tests w r c continued for 15-50 hours a t lis" C. 811 the oils were givrn i i &hour heat shock treat,nient a t 250" C. before being t,epted. Each sample was tested alone and in the presence of a copper ytrip. At the end of the tcst, the viscosity of the oil was rcmeasured, except 17-here t,he amount yecovered was too emall, and
Figure 7 . Teliding That Occurred at \-cry Low Pressures with High Quality, Sonadditire Petroleum Oil
Figure 6. Chloropheny lmethj Isilicoiie-Treated Specimens at the End of Falex Antiw eld Test
2360
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, ND. 11
-Silicones
-
made to have the same monomer rat.io as the halophenyl oils (Samples 3 and 8). It appears to be improved by treatment with trimethylchlorosilane (Sample 2), I" E 300 and copper is seen to accelerate deteriof: ration in these samples. 'w rn 4 In the case of the chloroplienylw methyl oil (Samples 3 to 7 , Table V), $200 treatment with trimethylchlorosilane is 0 beneficial (Sample 4), and copper does !#3 not accelerate deterioration in the treated (r, y0 100 sample. Addit,ion of 0.1% chromium chelate is deleterious (Sample 5 ) , but P copper chelate is quite beneficial (Sample 6). Copper is beneficial in conn junction with chromium chelate (Snm0 200 400 600 800 1000 1200 1400 1600 TIME IN HOURS ple 5), but not with copper chelate (Sample 6). Isopropoxydiphenylamine Figure 8. Oxidation of Silicone Oils from Table V a t 175" C., Copper Present (1%) isonlyslightlyeffective (Sample 7 ) . In the 3,4-dichlorophenylmethylseries 8 to 12) treatment, with tri(Samples 400 met,hylchlorosilane is not beneficial (Sample 9). Chroniium chelate is very deleterious (Sample lo), and copper 0 300. chejate slightly so (Sample 11). The E I viscosity of the samples containing isopropoxpdiphenylamine( Sample 12) could not be determined, as too little oil remained. Copper great'ly reduces the deleterious effect of the chromium chelate. S o n e of the treatments applied improved the stability of the original sample (Sample 8). Gaseous Products. I n the modified Sligh test,. any noncondensable gas formed will lead to erroneous results TIME IN HOURS if the pressure drop is assumed to measure oxygen absorption. For this Figure9. Oxidation of Silicone Oils from Table F' at 175" C., No Copper Present reason the gases in equilibrium with the samples at the end of the test were ezamined in the mass spectrometer. Thv the gas phase was evamined by mass spectrometer for carbon results are shown in Table VI. They are of significance mainly monoxide and carbon dioxide content. as showing that carbon monoxide and carbon dioxide are in fact formed in appreciable amount and that the values obtained for Viscosity Changes. Table T' lists the oils and additives tested total oxygen absorbed are accordingly to be considered low. and shows the initial arld final viscosities Conclusions regarding Pressure-Time Curves. The pressure-time data recorded the relative stability of the various oils toward oxygen a t 175' C. can be qualitatively measured by their final viscosities. during the Sligh oxidation tests are presented in Figures 8 and 9 The laboratory ni~th~dp2ieng.l oil (Sample 1 of Table V ) was 111 these graphs the abscissa gives the time in hours, the d i n a t ?
TABLE 1;.
COMPOSITIOS AND \rISCOSITY O F SILICONE OILS USED IX ~ ~ O D I F I E SLIGH D TEST
viscosities,
CY.
I__-
Sample No.
1 2 3
A51-7-1 A5l-8-3 5841-1
4
A51 -8-1 AS1-12-1 A5l-12-2 A5l-12-3 A5l-3-1
5 6 7 8
Initial
Lab. No.
Oil
U.C. 200
Lab. methylphenyl (control) A5 1-7- l a p-Chlorophenylrnethyl (No. 5 Table 111) 58-51-la 58-61-1b 58-51-1 C 68-51-ld 3,4-Dichloroghenvlrnethyl (No. 6. Table fII) ,451-3-1" A51-3-lb A51-3-1 C ,451-3-1d
B A51-8-2 10 A91-12-4 11 A5 1-1 2-5 12 A51-12-6 ~7 Refluxed 24 hr. with (CHshSiCI b Plus 0.1% chrmrum acetylaoetonatF Plus 0.1% popper ethylbenzoylrrcetate. d Plus I .O% 1sopropoxydip1~enylamlne
November 1954
Final, looo 17. Presence of
___~.
100' F. 40 30 5
200° F.
32.8 G7.0 69 0 67.0 67.0 67 0 199.0 223.0 199.0 199.0 199.0
Absence of
c 11
cu
6 94
99 8 75 5
83 4 113 0
7 42 9.23
153 0
67 8
92.5
9.30 9.23 9.23 9.23 14.75
129.0 290.0 120.0 145.0 364 0
128 0 182.0 136.0
15,s 14.76 14.75 14.75
408 0 1819.0 438 0
404.0 527.0
...
INDUSTRIAL AND ENGINEERING CHEMISTRY
...
...
... ... .
.
I
2361
ACKNOWLEDGMENT
TABLETTI.
RESIDUALGASES FROM hlODIFIED SLIGHTESTS
hALYSES OF
sample xo.v (Table V)
Teste in Absence of Copper _Tests in Presence _ _of_Copper _ % Con, 7c CQ, % con, % 5.G 2.2 8.3 3 6 2.0 1.2 3.6 71 3 6.9 1.3 4.0 34.2 4.6 2.8 ... ... 10.4 15.1 ... ... 15.0 19.2 12.3 64.6 0 0.2 ,.. , . 7.7 2.6 ... 1.5 1.1 9.5 13 8 5.9 1.7 0 0 6 9.3 9.1 5.G 64 8 6.3 3.7 ,5 . 4 21.6 7,s 7.1 ...
co,
the decrease in pressure, in millimeters of mercury, from the maximum obtained a t the start of the experiment when the sample and reaction flask have reached the temperature of the block furnace. This maximum pressure is about 1000 mm. and is noimally attained in 15 to 20 minutes. Runs on the samples with and Tl-ithout copper preeent are plotted on separate figures. I n compaiing these curves For the effect of copper on the behavior of the oil, allowance must bo made for the fact that copper alone will absorb oxygen a t this temperature. Measurements made on a dry copper coil, of the size used with the oils, and on a coil in the presence of water vapor, therefore, are included in Figure 8. [FURTHER INYESTIGATIONS
AB a result of the findings presented in this paper a considerable amount of further investigation has been carried out on this class of lubricating silicone oils. The latter work was done in an endeavor to note the eflect of btructure on lubricating ability, freezing point, and viscometric properties of modified silicone fluids of the type described. To date, several fluids have been developed that appear to be a most encouraging answer to the problem of high temperature stability in a projected lubricant for aviation gas turbine engine application. As a result, teets have been initiated, and are being conducted a t the Westinghouse Aviation Gas Turbine Division on components and engines, under the direction of G. P. Townsend of the Gearing and Lubriration Section. An evaluation of the results of these tests should be available in the near future.
The writer would like to acknowledge the help and advice rendered by R . N. W e n d , manager, fundamental chemistry section of the Westinghouse Research Laboratories, where this work was done. Thanks are also due t o D. W. Leivis for the preparation of many of the negatively substituted disiloxaries reported in Table I and to W.0. Bartlett who ran many of t’ho tests for Falex \year and coefficient of frict’ion. The oxygen absorption tests of Figures 8 and 9 w r e peiforniccl by H. E. Xahncke, manager, physical chemistry section of t,hr Westinghouse Research Laborat,ories. LITERATURE CITED
(1) Brophy, J. E., Larson, J., and llilitz, R.O., T r u m , A m . SOC. M e e h . Engrs., 70, 929 (1948). (2) Brophy, J. E., Milits, R. O., and Zihman, W. A , , Ibid., 68, 355
(1946). Burkhard, C. A., J . Am. Chem. Soc.. 74, 6275 (1952). Burkhard, C. A., Rochow, E. G., Booth, H. S., and I-Iartt, J., Chem. Revs., 41, 97 (1947). (5) Crowley, C. A., and Faville, F. A,, presented before the Society of Automotive Engineers, Chicago, Ill., September 1937. (6) Currie, C. C., and Hommel, >I. C., ISD. ENG.CHFX.,42, 2452 (1950). (7) Davis, L. L.. and associates, Ibid., 33,339 (1941). (8) Faville Le Vally Corp., 105 West Sdams St.,Chicago 3 , Ill.,. Bull. 3, Sheet 1. (9) Ibid.,Bull. 121. (10) Fitzsimmons, V. G., Pickett, D. L., Milit,z, R. O., and Zisman. W. A., Trans. Am. SOC.M e c h . E7~g1.5..68, 361 (1946). (11) Fletcher, H. J., and Hunter, YI. J., U. S. Patent 2,599,984 (June 10, 1952). (12) Kyropoulos, S., and Shobert, E. I., “A Simple Method ]’or Aleamring the Coefficient of Konviscous Friction of Thin Lubricating Layers,” Rev. Sei. Instr., 8, 151 (1937). RIodified as indicated in Westinghouse Research Laboratories Scientific Paper 1599, H. E. Mahncke, M a y 1951. (13) Lewis, D. W., and Gainer, G. C., J . Am. Chem. Soc., 74, 2931 (1952). (14) Lewis, D. W., and Gainer, G. C., unpublished studies, Westinghouse Research Laboratories, East Pittsburgh, Pa. (15) McGregor, R. R., “Silicones and Their Uses,” McGraw-HilI, Kew York, 1954. (16) Post, Howard W., “Silicones and Other Organic Silicon Coinpounds,” Reinhold, New York, 1949. (17) Rochow. E. G., “Introduction to Chemistry of Silicones.” John Wiley, New York, 1946. (18) Ryan, T’. A., Lubrication Eng., 2, 102 (1946). (3) (4)
RECEIVED for review 4 u g u s t 5 , 1954,
-4CCEPTED September
7, 1954.
Reprints of this symposium may be purchased for 7 5 cents each from the Reprint Department, American Chemical Society, 1155 Sixteenth St., S.W.,W-ashington 6. D. C.
2362
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46,No. 11
