Chemical Analysis of Hydrocarbon Grease
from Spin Bearing Tests
Downloaded by [75.149.200.233] at 08:32 25 July 2012
D. J . CARRE, R. BAUER, a n d P. D. FLEISCHAUER (Member, ASLE)
T h e Aerospace Corporation
El Segundo, California 90245
The rotor bearing running torqzie levels of certain spin bearing
z~nilswere found to increase s ~ p z i j i c a n t during
l~
extended life testillg. Sn7np/es of the greases from t/tese tests were analyzed to delelrnilze i f lzLbricalzl degradation was linked
!he increased
torque levels. By means of chromatographic and spectroscopic techttiques, we were able to determine that oxidation of some of the
greases had occurred and that the oxidative degradation was most
easily obserued in the soap-thickener portion of the grease. A correlation betwee?z the disappeamnce of the fatty acid salts and the
appearance of degradation products was obserued. Polymerization
of the greases war observed i n all samples. W e also determined that
the grease degradation was a symptom of adverse mechanical conditiom i n the bearings and not the primary cause of mechanical
problems.
a n attempt to determine whether lubricant failure was the
sole cause of the increased torque levels o r a symptoln of
adverse n1echanic:al conditions in the bearings. During the
course of the analyses, useful techniques for assessing grease
degradation
developedt and
interesting characteristics concerning the chemistry of the degradation were
revealed.
EXPERIMENTAL,PROCEDURES
Lubricant
T h e lubricant employed in the tests was a specially formulated naphthe:nic-oil-based sodium-complex soap-thickened grease. Prclperties of the oil and the analogous commercial grease arc: given in Table 1. No details o n the thickener
composition were available.
INTRODUCTION
T o meet their mission requirements, current a n d future
satellites must operate in orbit for extended periods of time.
T h e satellite subsystems a n d components, therefore, a r e
required to operate trouble-free d u r i n g the mission lifetime. Bearings a n d their associated lubricants a r e ubiquitous
in satellite systems a n d , as components, must meet these
requirements.
A series of accelerated a n d extended life tests of certain
spin bearing units has been conducted at a contractor's facility with the primary purpose of determining variations
in the r u n n i n g torque levels of the units as a function of
time. Different bearing units attained different torque values d u r i n g the tests a n d , when the bearings were disassembled, the grease lubricant appeared to have degraded to
varying degrees. (It was darker brown a n d more viscous
than the unused grease.) Consequently, chemical analysis
of the lubricant, a specially formulated naphthenic oil sodium-complex soap-thickened grease, was undertaken in
I
1
1
1
1
1
Naphthenic Base Oil
Gravity, OAPI
22.2
1
Viscosity, mm' . S - I at 37.S°C
m~n' . S - I at 98.9"C
Viscosity lnclex
43
pour point. 'C
-28.9
Flash Point, OC
207.2
Color, ASTM D 1500
L 2.5
Naphthenic Oil/Soclium-Complex Soap
Penetration, mmIlD, worked at 25OC
205
Dropping Point, OC
260+
11
1
1
1
Bomb Oxidation, 98.goF, Pressure Drop
Lubrication Life, 204 Bearing, 10 000 rptn
121°C
Presented as an Arnerlcan Society of Lubrication Engineers
paper at the ASMEIASLE Lubrication Conference in
Washington, D.C., October 5-7, 1982
148.9"C
475
1800
400
'
4 76
D. J. CAKKE,R. BAUEK,A N D P. D. FLEISCHAUER
Test Condltlons
'rile lubricant
in bearings under two test conclitions: life tests ( r r )a n d accelerated tests (AT). T h e only
test conclitions available were the test environments: L T test
1 0-2 1% pressure and A T test
l o - ' Pa pressure.
-
-
Downloaded by [75.149.200.233] at 08:32 25 July 2012
Separatlon of Samples
.I. grease samples, including a n unused
were
reccivccl from the test contractor, a n d the components were
sel):"-;itecl and analyzecl according to the sample analysis
scheme shown in Fig. 1. T h e quantity of sample received
was less thiui 200 m g per sample. I n the case of saniples 5,
17, i~ncl18. ~ l l i i ~sl ~l l n p l esizes precludecl emission s p a r o gl-allhic :inalysis (see later). T h e oil portion of the grease
was extl-actecl into heptane a n d subsequently analyzed. T h e
solid resiclue, containing the soap thickener, was refluxed
w i ~I1 I-ICI (1 5 percent)/CH30H to convert the soaps to niethyl
esters. l'he esters were extractecl into heptane a n d analyzed.
-.
I he remaining resiclue, primarily particulate material, was
; ~ l s o;rnalyzecI. 'rhe samples a r e identified in Table 2.
Analytical Methods
'1-lie ilnseparrrred grease saniples were analyzed by inwith the use of sodium chloride
frared s~~ectropliotonietry
salt plates to sanclwicli sample smears and by emission spect rogri~pliy.Infrared spectrophotometry was used to analyze
LIIC sel)aratecl grease components. T h e s e spectra were also
obtainecl with tlie sample sandwiched between salt plates.
'I'l~e sepiuated oil ancl soap niethyl ester portions were
:u~i~lyzecl
Ily means of gas chromatography (GC). T h e colilrrln irsecl was a 25-m, 0.2-mni I D niethyl silicone fused
silica capillary column cleactivated with polyethyleneglycol.
'I'he carrier gas was hydrogen at a flow rate of 0.7 m u m i n .
'I'lle cI'Hirent was split 1 :40 with tlie smaller flow sent through
a flame ionization cletector. T h e sample size employed was
0.5 p,L l'he instrument was used in the temperature programmed mode over the temperature range 175 to 250°C.
Retention times (KT) remained constant within 2 percent
I'rom r u n to run.
A gas chromatograph-mass spectrometer (GC-MS) was
used to iclentify components separated o n the gas chrom;rt.ograpli. l'he column was a 30-m, 0.2-mm I D fused silica
capillary with methyl silicone as the liquid phase. T h e carrier
gas Was "ydr0gen at 34.5 kPa "lumn
Pressure. The Capillary
was interfaced with a quadrupole mass 'pettrometer, which scanned 30 to 400 a m u a t 2 ps.amu-l integration time. T h e instrument was controlled by a dedicated
computer a n d data system. T h e same temperature programming was used for the G C and GC-MS analyses. T o
obtain better molecular weight information, the instrument
was also operated in the chemical ionization mode with
methane used as the carrier gas.
T h e particulate material was analyzed using a n x-ray photoelectron
spectrOnleter
The
gives only surface
analysis to a depth of approximately 4 0 A a n d a sensitivity
of approximately 1 percent (1).T h e particles also were examined nlicrOscopically a t l o
loox.
RESULTS
Emission Spectrographic Analysis
T h e results of the emission spectrographic analysis a r e
given in Table 3. T h e data clearly show enhanced levels of
iron a n d chromium f o r samples 4 and 6 (both L T I), indicating that bearing wear o r chemical reaction was more
significant in L T 1 than in the o t h e r tests. Samples 2 , 9 , a n d
11 ( A T 2) exhibited elevated levels o f nickel. T h e only information we have is that the shaft in the A T test was of a
high-nickel-content maraging steel, which could have been
the source of nickel contamination o f the grease.
Infrared Spectral Analysis
T h e infrared spectra of the unused grease and the A T 2
samples a r e qualitatively identical. T h e spectra for the L T
Unused Grease
(Same batch as used in tests)
A T 2-Bearing
L T 4-Bearing
L T 1-Bearing
LT I-Bearing
LT I-Bearing
L T 3-Bearing
L T 3-Bearing
A T 2-Bearing
A T 2-Bearing
A T 2-Bearing
L T 4-Bearing
L T 4-Bearing
L T 6-Bearing
L T 6-Bearing
L T 6-Bearing
LT 6-Bearing
LT 5-Bearing
LT 5-Bearing
CREASE
SAMPLE'
SPECTROMETRY
SPECTROGRAPHY
0 1 1 PORTION
SOAP llhlckenerl PORTION
INFRARED
t
MASS SPECTROMETRY
lidanlilir~tionl
GAS CHROMATOGRAPHY1
MASS SPECTROMETRY
'SAMPLE WEIGHT OBTAINED
Flg. 1-Grease sample analyals
GAS
CHROMATOGRAPHY
Bt
B
A
A
B
A
B
B
B
A
A
A
A
A
B
B
A
B
*Duplicate lubricant sample from same bearing.
tBearings A and B were separate bearings from the same test fixture in each
test.
Chemical Analysis of Hydrocarbon Grease From Spin Bearing Tests
SAMPLE
' IDEN.~IFICAI'ION
1
2
3
4
6
7
8
9
11
12
13
14
unused
AT 2-Bearing
LT 4-Bearing
LT 1-Bearing
LT I-Bearing
LT 3-Bearing
LT 3-Bearing
AT 2-Bearing
AT 2-Bearing
LT 4-Bearing
LT 6-Bearing
LT 6-Bearing
B
B
A
B
A
B
B
A
A
A
Fig. 2-Typical infrared spectra of unused grease components. (A) unseparated grease; (B) oli portion; (C) soap portion.
B
Downloaded by [75.149.200.233] at 08:32 25 July 2012
*Values in weight percent
samples all exhibit absorption bands centered at approximately 3400 cm-' (hydroxyl) and 1700 cm-' (carbonyl),
which indicate oxidation. T h e carbonyl band is present in
both the oil and soap fractions, indicating that ketones, aldehydes, and carboxylic acids are oxidation possibilities. The
hydroxyl absorption is absent from the oil spectrum but is
present in the analysis fraction that contains the soap portion of the grease. 'This absorption band probably results
from both alcohol species and water, since attempts at drying
the esterified soap fractions with anhydrous CaS04 resulted
in only a partial reduction of the 3400 cm-I absorption
band. Representative spectra are shown in Figs. 2 and 3.
Gas Chromatography and Gas
Chromatography-Mass Spectrometry
Typical gas chromatogra~nsof the oil portion and the
esterified fatty acids are shown in Figs. 4 through 6. T h e
GC trace for the oil portion of the unused grease, Fig. 4,
exhibits a sharp peak at RT = 10.3 min and an envelope.
T h e sharp peak corresponds to the antioxidant phenyl-anaphthylaniine (identified using mass spectral data), and
the envelope corresponds to the naphthenic oil. T h e shape
and position of the envelope are essentially the same for
the oil fractions from all the samples. There is a slight decrease in the lower molecular weight portions of the used
oil chromatograms, indicating some evaporative loss during
the tests. No other significant changes in the oil molecular
weight. distribution occurred. T h e A T No. 2 and L T oil GC
traces (not shown) contain solitary peaks preceding the envelope. These peaks occur at longer K T than the antioxidant
peak and, thus, do not correspond to the antioxidant but
rather to some grease tlegraclation products. (The GC-MS
data indicate that the longer KT peaks were probably caused
by fragmentation of aliphalic hyclrocarbons. No parent peak
data were obtained.)
T h e gas chroniatogram for the esterified soap fraction of
the unusecl grease is given in Fig. 5. T h e chromatogram is
characterized by five major peaks, numbered 7, 9, 1 I, 12,
and 13, and several smaller peaks. T h e identities of the
methyl esters that correspond to the numbered peaks are
given
in Table 4. Peaks 7, 9, and 10 were determined to be
methyl palmitate, methyl oleate, and methyl stearate, re-
Fig. 3--Typical infrared spectra of life test grease components. (A) unseparated grease, LT 3; (8) oil portion, LT 3; (C) soap portlon,
LT 4.
4
5
-
I
20
I
I5
10
TIME,
I
25
min
Fig. 4--Gas chromatogram of unused grease-oil portion in heptane solvent. (For clnrity of presentation,the solvent peak has been shifted
off scale.)
TIME, min
Fig. %Gas chromatogram of unused greasesoap portion methyl esters
in heptane solvent.
D. J. CARRE,K. BAUER.AND P. D. FLEISCHAUER
C7H 1sC0zCH3
C8H 15C02CH9
CSHI~CO~CHS
CIOHISCOZCHS
CI IH~ICO'LCHJ
CI'LHZ~COZCHS
C I ~ H ~ I C O ~ Methyl
C H ~ .Palmitate
CISHZ~CO'LCHS
C I ~ H ~ ~ C O Methyl
~ C H ~Oleate
,
C I ~ H ~ ~ C O ~Methyl
C H J , Stearate
CI~H~ICO~CHS
C17HzgCOzCH3
CISHX~CO'LCHS
Downloaded by [75.149.200.233] at 08:32 25 July 2012
-11
-11
*Assignments wcrc ni:rde based on mass spectral fragmentation patterns and parent peaks. Peaks 7. 9, and 10
wcrc verified using ;litthentic samples.
tl'cak 7, methyl palnlit:~te,remains essentially constant ;rnlong samples.
$Fig. 6-s;~mple 4
%Fig.5-sample 1
IJNo itlcntific;~tionpossible with the data available
spcctively, by comparing the R T values to those of authentic
s:lmples, supported by GC-MS results. Peaks 11 a n d 12 were
determined to be C l s fatty acid methyl esters with two a n d
three cloi~blebonds, respectively, using GC-MS. T h e deternlillations were based upon parent peaks and mass fragments ch;u-acteristic of methyl esters a n d unsaturated hyclrocarl)ons. Peak 1 I was shown not to correspond to methyl
lil~oleate,the methyl ester of a common soap constituent,
IILIL mitst Ile a structural isomer based o n the R T of a n
;~uthenticsample of methyl linoleate. Peak 13 was shown to
correspond to a CZ0polyunsaturated ester by means of GCMS. T h e esterifiecl soap chromatograms for samples 2 a n d
9 through 11, all A T 2, were identical to Fig.
- 5.
Figure 6 gives the esterified soap chromatogram for sample 4, L T 1. It contains all the peaks that a r e present in the
chromatogram of the unused grease esterified fatty acids,
Fig. 5, plits a significant number of peaks that were not
present in Fig. 5. T h e g r o u p of peaks, 1 through 6 and 8 ,
was shown to represent a newly formed homologous series
of unsaturated fatty acid methyl esters. Peaks 14 a n d 15
were determined to be methyl esters, but not enough mass
spectr;il information was available to determine empirical
I'orniulas. T h e s e results a r e given in Table 4. No attempt
was mxde to compare the KTs of peaks 1 through 6 a n d 8
to those of known compounds, because the positions of
~tnsntul.ationa n d possible branching were not determined.
T h e esterified fatty acid chromatograms for the other L T
san~ples,i.e., samples 3, 5 through 8, a n d 12 through 18,
were all similar to Fig. 6. T h e differences between chromatograms were in the relative amplitudes of the peaks.
I he relative areas of the peaks in Figs. 5 a n d 6 a r e given
in Table 4. T h e major peaks corresponding to unsaturated
esters that were present in Fig. 5, peaks 9 a n d 11 through
7
I
I
5
10
I
15
TIME. min
I
I
20
25
I
Fig. +Gas chromatogram of LT 1 s o a p portion methyl e s t e r s in heptane
solvent.
13, a r e much smaller in Fig. 6 relative to peaks 7 a n d 10.
T o determine if the appearance of the new peaks was correlated with the decrease in peaks 9 a n d 11 through 13, the
two groups of peaks were compared for all the samples. As
was d o n e in Table 4, the peak areas were normalized to the
area of peak 7 , methyl palmitate. This peak does not a p p e a r
to change significantly between samples. (Peak 7 could not
be quantitated absolutely because of uncertainties in solution concentrations of grease species.) T o represent the peaks
that decrease relative to the peaks in Fig. 5, peaks 9 and 1 1
through 13 a r e employed. T h e areas of these peaks a r e
summed a n d referred to as the "reactive species sum." T o
represent t h e peaks that increase o r a r e new relative to those
in Fig. 5, peaks 2 through 6 a n d 8 a r e used. These a r e
summed a n d referred to as the "low molecular weight product species sum." T h e s e two sums a r e given in Table 5 a n d
Chemical Analysis of Hydrocarbon Grease From Spin Bearing Tests
TABLE
~-REACTI\'ESPECIES
VS LOWMOLECULAR
WEIGHT
PRODUCT
SPECIES
Downloaded by [75.149.200.233] at 08:32 25 July 2012
SUM
SAMPLEKEACI'IVE SPECIES
Low MOLECULARWEIGHT
PRODUCISPECIES
SUM
I
25.52
24.6 1 *
0
0*
2
25.85
0
3
12.37
0.38
4
5.09
2.09
6
35.27
0.49
7
7.70
0.92
8
8.70
1.54
9
19.68
0
11
22.12
29.79*
0
0*
12
11.61
0.64
13
13.3
20.65*
0.18
0.56*
14
14.14
18.53*
0.26
0.34*
16
10.73
1.27
17
1.73
2.89*
2.19
4.50*
18
8.38
1.13*
1.17
1.80*
*Data from GC runs at a later date o n the same samples.
plotted in Fig. 7. A correlation between the two sums is
evident. Although there were numerous peaks in Fig. 6 that
were new relative to Fig. 5, only peaks 2 through 6 and 8
were used for the comparison because: ( 1 ) some of the new
peaks were too small to integrate for several of the LT
samples, (2) accurate areas could not be obtained for the
smaller, long RT peaks because of an underlying envelope
and congestion, and (3) for those samples in which a large
number of peak areas were available, the correlation between the reactive species sum and the sums of all the available new peak areas was the same as that given by the limited
number of peaks used for Table 5 and Fig. 7.
Microscopic and XPS Analyses of Particles
T h e particles that remained following removal of the oil
and soaps were translucent under microscopic analysis. XPS
analysis indicated that there were no elements other than
carbon, oxygen, and sodium on their surfaces. Note that
XPS sensitivity for hydrogen is approximately four orders
of magnitude less than for carbon and oxygen, so although
hydrogen is not detected, it is undoubtedly present in the
particles. T h e evidence is consistent with the particles being
polymeric without significant quantities of wear metals present. T h e possibility that the particles are metal fragments
that are coated with polymeric material can be ruled out
because of the translucent nature of the particles.
LOW M W PRODUCT SPECIES SUM
Fig. 7-Soap
oxldatlve degradatlon: conversion of soaps to products
DISCUSSION
Chemical analysis of these grease samples indicates that
both the accelerated and real-life bearing tests induced nieasurable degradation reactions. T h e experimental evidence
is consistent with the conclusion that the reactions are oxidations, primarily of the soap portion of the grease. 111the
case of the LT samples, direct evidence of oxidation was
obtained from the infrared and GC data. Indirect evidence,
i.e., the absence of the antioxidant additive, indicates that
oxidation was imminent for the A T samples.
T h e disappearance of the antioxidant, phenyl-a-naphthylamine, from either the A T or LT samples could have
been the result of evaporation (caused by low test e n \'Iron'
ment pressures) or consumption (caused by oxidation conditions) during the bearing tests. Evaporation of the additive
is not consistent with the GC data for the oil portion of the
grease, which did not show evaporation of ihe base oil portions having similar boiling point. Under the GC conditions
employed in these analyses, aromatic amines, such as the
antioxidant, were observed to come off the column earlier
than would be predicted on the basis of their boiling points.
Therefore, if the disappearance of the antioxidant was caused
by evaporation during test, a corresponding loss of base oil
constituents at somewhat longer RT shoulcl have been observed. Such a decrease in the GC envelope was not evident.
Lubricant oxidation proceeded well beyond consumption
of the antioxidant for the LT samples to the point where
aldehydes, ketones, and hydroxyl-containing species were
observed in the infrared, and new homologous series of
methyl esters were observed in the GC traces of the esterified soaps. T h e most consistent explanation for the absence
of oxidation products in the A T samples is that the tests
were terminated coincidentally just as the antioxidant was
consumed. No oxidation products had accumulated to levels
large enough to be detected in our GC and infrared analyses.
T h e formatbn of a new homologous series of carboxylic
acid salts (the free acids probably would have evaporated
under the test pressure conditions), together with the correlation of the appearance of these products of degradation
with the disappearance of the primarily unsaturated (olefinic) parent soap molecules (Tables 4 and 5, Fig. 7), is
strong evidence for a free radical mechanism of grease ox-
Downloaded by [75.149.200.233] at 08:32 25 July 2012
480
D. J.
CARRI?,
R. B A U E R , AND P. D. FLEISCHAUER
idation in rvliicl! a hydrogen abstraction reaction is the ratecontrolling step. T h e rates of hydrogen abstraction and concommitant raclical formation a r e dependent upon the structure of the react:uit hydrocarbons (2)-(5). Olefinic cornIJOLIIICIS c:ui form resonance-stabilized radicals and, thus,
react much faster than saturated hydrocarbons in radical
forming reactions. Hence, the unsaturated soaps would oxidize much I'ister than their saturatecl analogs (Z),(5). This
rciictivity difference also explains why sodiuni palmitate a n d
soclium stearate, saturated soaps, d o not appear to change
signilicantly in concentration. T h e product clistribution can
be expl~iineclby considering that, in unsaturated systems,
tlie radical site catn vary over many of tlie carbon atoms in
the molecule because of resonance ancl double bond isomcriz:itions (6). 'fhe lifetime of the free radical, i.e., the
Icttgtli of time the raclical exists before reacting with oxygen
(with subseq~lentcleavage o r rearrangement) o r with another organic radical (polylnerization), will determine whether
the rnclical sites have been clistributed over the possible positions i t 1 the molecules. T h e observed product distribution
iliclic:ltes that radical sites liave been clistributed. This result
is c o ~ ~ s i s t e with
n t other work in which the autoxidation of
~~t~s:uuratecl
fatty acids has been shown to yield a large numI ~ e 01'
r reaction products (7)-(11).
-I lie
elevated iron :und chromium levels in the satnples
with the highest level of oxidation ( L T 1 , sariiples 4 ancl 6)
co~llclI)e the result of wear o r of interaction of the metal
surliices with oxiclizecl lul~ricantspecies, o r both. (The emission s~~ectrograpl~ically
cle~erniinecllevels of iron of 0 . 1 4
;incl 0. I 0 weight percent for samples 4 :itid 6, respectively,
;ll.e 11011:irge enough to be detected by XPS, which requires
;ipp~.oxiniatelyI atom percent of an element for detection.)
Iron is believecl to react with oxidized lubricant a n d , therel i ~ r e ,can I)e incorporated into the material d u r i n g poly~lieriz:ition (12), (13). In addition, metals have been shown
to cat:~lyze oxidation ot' mineral oils, honiogeneously, and
woirlcl be exl)ectecl to be present if soluble in the oil phase
01' the lubricant (14). With o u r data, we cannot distinguish
attiollg the possible pathways.
I Ile data I'rom Fig. 7 , which correlate unsaturated soap
clis:~l~l)c:it';i~~ce
with clegradation product appearance, also
correlate witli information pertaining to the mechanical
properties of the bearings. T h e bearings from L T 1 a n d
1,'l' 5 app:~retntly exhibited raceway cross curvature deviatiot~s(actu;il n u m l ~ e r snot available) that were consiclerably
1;lrger than those for the bearings used in the other tests.
I;l.oni these results, in conjunction with o u r chemical analysis resirlts, we conclude that the lubricant degradation (oxicl;~tiot~)
is :I symptom of adverse mechanical conditions in
tile I~earitlgs~.atlierthan the cause of anonialous bearing
\vc:~r, I~ecauselubricant clegradation was not as severe in
o t l ~ e rtests 1.1111 ullder iclentical conclitions. O u r results inclic;ite t I I ; I ~ the clegr;~clationin the soap portion of that lu111.ic:int C;III act as iin inclicator of aclverse bearing conditions.
7
-
CONCLUSIONS
T h e analyses of the lubricant samples from the spin bearing tests lead to the following conclusions.
1. Oxidation is the primary degradation pathway for the
lubricant samples. This conclusion is based o n the disappearance of the antioxidant and o n the infrared
spectral, G C , a n d GC-MS data.
2. T h e oxidative degradation of the lubricant affected
the unsaturated soap components much more than the
saturated oil a n d soap components.
3. T h e appearance of unsaturated carboxylic acid o r carboxylate degradation products was directly related to
the disappearance of unsaturated soap components.
4. T h e grease satnples all exhibited polymerization.
5. T h e grease samples that were the most degraded a n d
contained the most metal (from either mechanical o r
chemical action) also exhibited the highest torques in
the testing. (Torque values were not available from the
test contractor.)
ACKNOWLEDGMENT
This work was supported u n d e r U.S. Air Force Systems
Command Space Division contract no. F0470 1 - 8 1-C-0082.
REFERENCES
( I ) Bertrand, P. A,, Kalinowski, W. J., Tribble, L. E., and Tolentino, L. U.,
"Fast Optical Position-Sensitive Detector for McPherson ESCA-36." R N .
Sci. Inslmm., submitted for publication.
(2) Frank, C. E., "Hydrocarbon Autoxidation," Chem. Rev., 46, p p 155-169
(1950).
(3) Bolland, J . L., "Kinetics of Olefin Oxidation,'' Quart. Rev., 3, pp 1-21
(1949).
(4) Bateman, L., "Olefin Oxidation," Quarf. Rev., 8, p p 147-167 (1954).
(5) Waters, W. A,, Mechariism of Oxidafion of Organic Compounds, Wiley, New
York (1964) p p 6-28.
(6) Kerschenbauer, H. G., Fak and Oils: An Oulline of Their Chemistry and
fichi~ulog)',Reinhold, New York (1962) p p 34-35.
(7) Hoffman, B. G. and Kepler, J . G., "The Stereo-Configuration of 2,4Decadienals Isolated from Oils Containing Linoleic Acid," ~\'alure, 185,
pp 310-311 (1960).
(8) Tarladgis, B. G. and Watts, B. M. "Malonaldehyde Production During
the Controlled Oxidation of I'ure. Unsaturated Fatty Acids," J. Am. Oil
Chem. Soc., 37, p p 403-406 (1960).
(9) Nowakowska, J., Melvin, E. H., and Wiebe, R., "Separation of the Oxidation Products of Fatty Acids by Means of Gas-Liquid Partition Chromatography," J. Am. Oil Chem. Soc., 34, p p 41 1-414 (1957).
(10) Kinloto, W. 1. and Gaddis, A. M., "Precursors of Alk-2,4-dienals in Au(oxidized Lard," J. Ani. Oil Chem. Soc., 46, pp 403-408 (1969).
(11) Jones, E. 1'. and Davison, V. L., "Quantivadve Determination of Double
Bond Positions in Unsaturated Fatty Acids After Oxidative Cleavage,"
J. Arn. Oil Chem. Soc., 42, pp 121-126 (1965).
(12) Lockwoocl, F. E. and Klaus, E. E., "Ester Oxidation Under Simulated
Boundary Lubrication Conditions," ASLE Traru., 24, pp 276-284 (1981).
(13) Hsu, S. M. and Klaus, E. E., "Some Che~nicalEffects in Boundary Lubrication, I'art I: Base Oil-hleval Interaction," ASLE Tmns., 22, pp 135145 (1979).
(14) Chakravarty, N. K., "The Influence of Lead, Iron, T i n , and Copper
on the Oxidation of Lubricating Oils, Part 11: O n the Metal Caralyzed
Oxidation of Oils," J. Ilut. Pel., 49, p p 353-358 (1963).