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FRICTION REDUCTION STUDIES ON LUBRICANTS CONTAINING MOLYBDENUM (MOLYVAN 855)

By Thomas J. Karol, Ph.D. and Steven G. Donnelly (Manager of Technical Services)

The synergisms delineated in this disclosure (U.S. Patent and EP 0 874 040 A1 pending) are recommended for lubricating oils and greases. This would include gasoline and diesel motor oil and grease products. This technology is particularly suited for greases used in constant velocity joints (of the fixed type joints or slide type joints) and further discussions will follow in future "Research s" disclosures.

The following series of experiments was conducted to demonstrate the synergistic performance of MOLYVAN® 855 (MV-855) in lubricating compositions. MV-855 is an organomolybdenum complex prepared by reacting about 1 mole fatty oil, about 1.0 to 2.5 moles diethanolamine and a molybdenum source sufficient to yield about 0.1 to 12.0 percent of molybdenum based on the weight of the complex. Since the primary purpose of lubricants is to protect metal surfaces, changes in the surface metallurgy of steel were investigated by using the individual components and the synergistic compositions.

The Base Oil (BO) (UNINAPâ 100SD, commercially available from Diamond Shamrock Corp.) was selected because of its very low sulfur content and good solubility (similar to fully formulated motor oil).


TABLE 1

BASE OIL SPECIFICATIONS

Description: Severely Hydrotreated Naphthenic Oil

Aniline Point, °F	139
Sulfur, wt. %	0.03
% Naphthenic	52.2
% Paraffinic	32.8
% Aromatic	15.0
Viscosity, SUS 100°F	104

The test method and conditions used to evaluate frictional properties of the synergistic compositions, are presented in Tables 2 through 5.


TABLE 2

FALEX NO. 1 FRICTION AND WEAR, TEST SPECIMENS

Test blocks: Low pressure design, 4620 Steel, RC 58 – 63, 6-12rms

Test ring: S-10, 4620 steel, RC 58-63, 6-12 rms.


TABLE 3

4620 STEEL COMPOSITION (G46200 Ni-Mo Alloy Steel), mass percent

C		0.17 - 0.22
Mn		0.45 - 0.65
Mo		0.20 - 0.30
Ni		1.65 - 2.00
P		0.035 Max.
S		0.040 Max.
Si		0.15 - 0.35

Cross Reference Specifications: AISI 4620 AMS 6294 ASTM A29 (4620)


TABLE 4

FALEX NO. 1 FRICTION AND WEAR, TEST CONDITIONS

Test Conditions:

Fluid Volume: 100 mL, Fluid Temperature: 108°C, Rotational Speed: 800 rpm, Bale Load: 2.25 Kg, Actual Load on Specimen: 22.5 Kg, Test Duration: 90 minutes

Low Pressure Block Design creates an area contact with S- 10 Ring.




TABLE 5

FALEX NO. 1 PROCEDURE

1. Clean ring and block with mineral spirits, then acetone and dry.
2. With ring and block in place, add the test fluid.
3. Make sure load has not been engaged and start drive, turn on heater and set automatic shut-off for 90 minutes.
4. When fluid temperature is reached, release the load.
5. When load is engaged, start time and begin chart recording friction force.
6. At end of test, clean in mineral spirits solvent in an ultrasonic cleaner for 20 minutes.

TABLE 6

COEFFICIENT OF FRICTION

	initial	5 min	10 min	20 min	30 min	40 min	50 min	60 min	70 min	80 min	90 min
Base Oil : no additives	>0.20	0.128	0.129	0.121	0.117	0.107	0.099	0.095	0.091	0.089	0.090
BO, ZnDTP1, AFM	>0.20	0.144	0.140	0.130	0.119	0.111	0.106	0.102	0.102	0.099	0.098
BO, ZnDTP, MV-855	0.169	0.121	0.096	0.071	0.059	0.054	0.046	0.040	0.036	0.033	0.031

BO: base oil, ZnDTP¹: zinc dialkyldithiophosphate (0.92%mass LZ-1395 from LUBRIZOL CORP.)., AFM: ashless friction modifier which is the non molybdenum analog of the molybdate, MV-855 : molybdenum complex (0.5 mass % , 400 ppm Mo)

The data in Table 6 show the friction reduction properties of the base oil versus the base oil treated with ZnDTP and ashless friction modifier (MV-855 precursor), and also the base oil treated with ZnDTP and MV-855. This demonstrates little frictional benefit from the ashless friction modifier in combination with ZnDTP versus the base oil. Therefore, the incorporation of molybdenum in combination with ZnDTP results in a substantial reduction in friction.


TABLE 7

COEFFICIENT OF FRICTION

	initial	5 min	10 min	20 min	30 min	40 min	50 min	60 min	70 min	80 min	90 min
Base oil with ZnDTP2	0.200	0.102	0.096	0.088	0.084	0.081	0.079	0.078	0.077	0.076	0.076
Base oil with MV-855	0.118	0.128	0.122	0.096	0.080	0.070	0.060	0.052	0.048	0.046	0.044
BO, ZnDTP, MV-855	0.170	0.050	0.048	0.046	0.043	0.041	0.039	0.038	0.037	0.036	0.035
BO, ZnDTP, MV-855	0.164	0.044	0.040	0.036	0.032	0.028	0.027	0.024	0.023	0.023	0.023

BO: base oil, ZnDTP² :zinc dithiophosphate (1.31% mass OLOA 269R from CHEVRON CHEMICAL CORP.), MV-855: molybdenum complex (0.5 mass % , 400 ppm Mo)

The data in Table 7 show that the MV-855 combination with ZnDTP has a dramatically reduced coefficient of friction (consistent with unexpected synergism) versus the molybdate or ZnDTP performance alone in the base oil. Note in Table 7 that the wear film of ZnDTP does not significantly increase or decrease friction due to the physical difference in the surface coating (iron phosphate) versus the friction resulting from boundary/hydrodynamic lubrication. The molybdate additive-ZnDTP combination demonstrates a dramatic improvement in wear and frictional properties.


TABLE 8

COEFFICIENT OF FRICTION

	initial	5 min	10 min	20 min	30 min	40 min	50 min	60 min	70 min	80 min	90 min
BO, VL-871, MV-855	0.132	0.132	0.073	0.042	0.037	0.032	0.027	0.025	0.023	0.022	0.022
Base Oil, no additives	0.094	0.097	0.094	0.092	0.090	0.088	0.084	0.081	0.079	0.076	0.074
BO, ZnDTP1, MV-855	>0.20	0.068	0.060	0.052	0.048	0.044	0.039	0.037	0.036	0.035	0.034

BO: Base Oil, ZnDTP¹: zinc dithiophosphate (0.92 % mass LZ-1395 from LUBRIZOL CORP.), VANLUBE® 871 (VL-871): 0.94% mass of substituted 1,3,4-thiadiazole described in Appendix 1, MV-855: molybdenum complex (0.5 mass % , 400 ppm Mo).

The data in Table 8 show the synergistic performance of the molybdate complex with substituted 1,3,4-thiadiazole antiwear additive. VL-871 has superior performance versus the ZnDTP. Unlike many other sulfur additives, oxidatively stressed oil containing this additive demonstrates retention of the chemically intact additive (by Liquid Chromatography). Therefore, VL-871 does not function as a "sulfur donor" due to the stability of the compound.

To investigate the interaction of the substituted 1,3,4-thiadiazole (VL-871) in combination with the molybdate (MV-855) on the metal surface, the following tests were conducted. The same base oil and Falex No. 1 test equipment was utilized, but the test procedure has been modified as delineated below.


TABLE 9

COEFFICIENT OF FRICTION - TEST SPECIMENS RUN DRY -

Evaluations:

(1) Conditioning of metal test specimens with molybdate additive (MV-855):

1. 90 minutes with MV-855 in Base Oil (described in Table 1)
2. Ultrasonic cleaning.
3. 90 minutes with Base Oil only.
4. Ultrasonic cleaning.
5. Metal specimen is run with no lubricant to evaluate metal surface for frictional properties.

(2) Conditioning of the metal test specimen with the additives of the investigation :

1. 90 minutes with MV-855 and VL-871 additive in Base Oil.
2. Ultrasonic cleaning.
3. 90 minutes with VL-871 additive in Base Oil.
4. Ultrasonic cleaning.
5. Metal specimen is run with no lubricant to evaluate metal surface for frictional properties.

Results:


TABLE 10

COEFFICIENT OF FRICTION

SECONDS >	1	2	3	4	5	10	15	20	40
#1 (table 9)	.06	.19	.33	.34	.37	.40	.42	.45	-
#2 (table 9)	.05	.11	.13	.145	.15	.15	.15	.16	.16
Reference*	.23	.35	.39	.39	.41	.39	.38	.35	--

*new block and ring without base oil additive formulation conditioning

Results indicate that the surface metallurgy has changed to provide significantly lower frictional properties of the metallurgy when the combination of thiadiazole derivative and molybdate are used. The reference coefficient of friction for the untreated metallurgy is consistent with the literature. Literature reference for coefficient of friction of hard steel on hard steel (dry) is 0.42, [Mechanical Engineers Handbook, Lionel S. Marks, page 218 (5th ed. 1952)].

The following data were obtained via the aforementioned procedure. Two 90 minute (2X 90 min.) lubricated conditioning runs were conducted on each metal specimen prior to the non-lubricant run (except for the reference new block and ring metal specimens).


TABLE 11

COEFFICIENT OF FRICTION METAL SPECIMENS RUN WITH NO LUBRICANT (AFTER CONDITIONING WITH LUBRICANT AND ULTRASONIC CLEANING)

1st conditioning || 2nd conditioning	1 s	2 s	3 s	4 s	5 s	10 s	15 s
BO, ZnDTP, MV-855 || BO, ZnDTP	0.060	0.150	0.165	0.175	0.185	0.290	0.360
Repeat of above	0.045	0.100	0.150	0.160	0.170	0.350	0.390
BO, ZnDTP,VL-896 || BO,ZnDTP	0.060	0.130	0.215	0.235	0.245	0.360	0.395
Repeat of above	0.065	0.120	0.265	0.280	0.300	0.415	0.460
BO || BO	0.100	0.200	0.430	0.460	0.450	0.460	0.460
block and ring metal specimens	0.165	0.310	0.440	0.430	0.400	0.401	0.401

The data in Table 11 (derived from Graph 4 which is a real time plot of the friction data) indicate that the surface metallurgy has changed to provide significantly lower frictional properties of the metallurgy when the combination of ZnDTP and MV-855 are used. To further demonstrate that the metallurgy had significantly changed and that the molybdenum is not forming molybdenum disulfide related to sulfur donor theory, U.S. patent 4,164,473, metal analysis was conducted of the top surface of the test block for elemental composition. Data is expressed as atomic percent and is based on the emission spectra of the XPS method. Metal samples are irradiated by a soft x-ray source causing direct ejection of core level electrons from surface atoms. These electrons are energy analyzed in a high resolution analyzer, producing an emission spectrum of peaks on a sloping background. Every element has its own unique XPS spectrum. XPS peak positions are not fixed, but will shift depending on the valence/oxidation state of the atom and its chemical environment.

X-RAY PHOTOELECTRON SPECTROSCOPY (XPS) ON TEST BLOCK

FROM FALEX NO. 1 FRICTION TEST

Surface analysis on test block was conducted after first 90-minute test run followed by thorough cleaning of the metal specimens to remove lubricant residues. The frictional data of the conditioning with the lubricant are compiled in Table 12. The XPS analysis was accomplished on these metal specimens after ultrasonic cleaning and the data are compiled in Table 13.


TABLE 12

	initial	5 min	10 min	20 min	30 min	40 min	50 min	60 min	70 min	80 min	90 min
BO, ZnDTP2, MV-855	>0.200	0.053	0.047	0.040	0.037	0.036	0.034	0.033	0.032	0.032	0.031

BO: base oil, ZnDTP² :zinc dithiophosphate (1.31% mass OLOA 269R from
CHEVRON CHEMICAL CORP.), MV-855: molybdate additive (400ppm Mo).


TABLE 13

XPS DEPTH PROFILE

Sample:

conditioned block with BO containing molybdate friction modifier
(MV-855) /ZnDTP².

Angstrom Depth	Carbon	Oxygen	Silicon	Sulfur	Phosphorus	Iron	Nickel	Zinc	Molybdenum
0	62.8	29.5	1.7	DL		4.6	DL	0.44	0.99
12	47.3	21.4	0.52	DL		29.8	0.49	DL	0.47
25	49.2	6.7				42.9	0.63	DL	0.33
37	50.0	4.1				44.9	0.57	DL	0.40
50	51.3	3.0				44.5	0.61	DL	0.35
62	49.9	2.4				46.8	0.73	DL	0.24

DL: detection limit (signal is not above background noise); no evidence of element.

The XPS data in atomic percent here demonstrate that molybdenum doping is found down to 60 angstroms supporting the assumption that metallurgical changes have occurred. This is clear when comparing a similar lubricant conditioned block with an ashless friction modifier (the molybdate precursor –but no molybdenum) in the XPS profile in Table 14.


TABLE 14

XPS DEPTH PROFILE

Sample: conditioned block with BO containing ashless friction modifier (molybdate precursor –but no molybdenum)/ZnDTP²; after ultrasonic cleaning of the metal specimens, the XPS analysis was conducted.

Depth	Carbon	Oxygen	Silicon	Sulfur	Phosphorous	Iron	Nickel	Zinc	Molybdenum
0	56.0	32.8	1.7	4.0	0.59	1.8		3.1
12	42.7	16.3	1.3	3.5	DL	33.5	0.30	2.5
25	42.0	16.2	DL	2.1	DL	37.8	0.36	1.6
37	44.2	7.0	DL	1.7	DL	45.1	0.58	1.3	DL
50	42.2	5.8	DL	1.2		49.3	0.60	0.92	DL
62	39.8	5.8		0.89		51.5	0.77	0.91	DL

The XPS data in atomic percent, show that this test metal has no molybdenum at the detection limit of the method.

The following data demonstrate the frictional data which is interrelated to wear of the claimed synergism of the invention. This data further support the unexpected interaction since the above experimental data show that the components perform dramatically differently than would be expected from the individual components.


TABLE 15

Falex No. 1 Friction Test Results - Low Pressure

Base Oil-Uninap 100SD

Friction Force,lb (Coefficient of Friction)

Concentration in Base Oil		At Start		End of 15 minutes
1. MV-855	1.5%	9.10 (0.182)		5.60 (0.112)
2. MV-855	0.5%	9.40 (0.190)		4.05 (0.081)
ZnDTP1	1.0%
3. MV-855	0.5%	8.60 (0.172)		2.80 (0.056)
VL-871	1.0%
4. ZnDTP1	1.5%	9.55 (0.191)		6.85 (0.137)
5. VL-871	1.5%	8.95 (0.179)		2.95 (0.059)
6. VL-SB	1.5%	5.35 (0.107)		2.50(0.050)
7. MV-855	0.5%	5.2 (0.104)		3.35(0.067)
VL-SB	1.0%

VL : VANLUBEâ manufactured by R.T. Vanderbilt Company, Inc. , VL-SB: polysulfurized isobutylene, VL-871: substituted 1,3,4-thiadiazole.

Other than supporting the unexpected performance of the additive combination, the above data also show that all sulfur compounds do not afford this performance. This is clearly the case of the polysulfurized isobutylene additive, which is used for comparison and does not demonstrate synergism with MV-855.

It is clear from metallurgical science that molybdenum iron/steel is harder and thus improves the wear performance of the metal. The data presented within demonstrate that molybdenum is incorporated into the metallurgy and that the specific synergistic combinations of the technology facilitate this metallurgical change. The frictional property changes have been presented. The following data are additional experiments to demonstrate the unexpected wear performance induced by the invention as a direct result of the metallurgical changes demonstrated.


TABLE 16

FALEX PIN AND VEE BLOCK TESTING

Weight Loss, mg

WEAR	LOW WEAR "PASS"		18.7 mg	39.9 mg	39.4 mg	9.4 mg
	HIGH WEAR "FAIL"	543+ mg					****	544+ mg
CONC. IN BASE OIL	MV-855	1.5%	1.25%	1.0%	0.75%	0.5%	0.25%	0%
	OLOA 269	0%	0.25%	0.5%	0.75%	1.0%	1.25%	1.5%

**** Test could not maintain load due to excessive wear on test specimen. This required early termination of test with a "fail" designation (wear would be in excess of 500mg).

The above embodiments have shown various aspects of the MV 855 synergism. Other variations will be evident to those skilled in the art and such modifications are intended to be within the scope of this disclosure.


APPENDIX 1

VANLUBE® 871 is an organic sulfur compound selected from the group consisting of

(i) 1,3,4-thiadiazole compounds of the formula:

				N	-	N
				||		||
R	-	S	-	C		C	-	S	-	R¹	(I)
				\		/
					S

wherein R and R¹ are independently selected from C_1-22-alkyl groups, terpene residue and

maleic acid residue of the formula

		O
		||
H2C	-	C	-	O	-	R
|
HC	-	C	-	O	-	R3
		||
		O

and R² and R³ represent C_1-22-alkyl and C_5-7-cycloalkyl groups, either R² or R³ may be hydrogen and either R or R¹ may be hydrogen when R² or R³ are C_9-22-alkyl groups.

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