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604 Lubricant Additives: Chemistry and Applications
A sulfonate rust inhibitor can enhance the four-ball wear performance of a lithium 12-hydroxy
stearate grease in combination with an EP additive, which by itself does not show reduced wear
at low loads [50] (Table 23.15). A widely used AW additive, zinc dialkyldithiophosphate (ZDDP)
exhibits moderate EP performance and low wear scars in both aluminum and lithium complex
greases compared with the base greases alone (Table 23.16).
A multifunctional additive package speci cally designed for greases provides good EP and AW
performance. In general, this additive package also provides antioxidant and anticorrosion proper-
ties and copper metal deactivation (Table 23.17). EP additives can sometimes be detrimental to the
oxidative stability of the grease. The addition of an amine antioxidant can improve the oxidation
stability of EP-containing organoclay grease, as shown in Table 23.18.
Because gear oils can require good EP and AW properties, they are sometimes used in grease
formulations. A sulfur–phosphorus industrial gear oil additive package exhibited good EP and wear
performance in both aluminum complex and lithium complex greases (Table 23.19).
TABLE 23.15
Effect of a Sulfonate Additive in Lithium 12-OH
Stearate Grease
Additive Wt%
Four-Ball EP Weld
Load (kg)
Four-Ball Wear Scar
Diameter (mm)
Vanlube 73 3.0 250 0.73
Vanlube 73 3.0 250 0.47
Na-Sul ZS-HT 1.0
TABLE 23.16
ZDDP Component in Grease
Additive Wt%
Four-Ball EP
Weld Load (kg)
Four-Ball Wear Scar
Diameter (mm)
Aluminum complex base grease
(900 SUS paraf nic base oil blend)
— 140 0.59
Lithium complex base grease
(600 SUS paraf nic base oil)
— 180 0.61
Lubrizol 1395 in lithium complex 3.0 315 0.47
Lubrizol 1395 in aluminum complex 3.0 250 0.55
TABLE 23.17
S-P-Zn-N Additive Package in Aluminum Complex Grease
Additive Wt%
Four-Ball EP
Weld Load (kg)
Four-Ball Wear Scar
Diameter (mm)
Lubrizol 5235 in aluminum complex
(900 SUS paraf nic base oil blend)
3.0 250 0.57
Lubrizol 5235 in lithium complex
(600 SUS paraf nic base oil)
3.0 315 0.50
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Additives for Grease Applications 605
ACKNOWLEDGMENT
We thank Henry Kruschwitz of FedChem LLC for his help and the use of his laboratory.
REFERENCES
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3. Boner, C.J. Modern Lubricating Greases. New York: Scienti c Publication Ltd., 1976.
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7. ASTM D-217. Standard test methods for cone penetration of lubricating grease. Annual Book of ASTM
Standards, Philadelphia, PA, Sec. 5, Vol. 5.01, 1996.
8. Technology of modern greases. Lubrication 77(1), 1991.
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TABLE 23.18
Oxidation Stability in Organoclay Grease
Additive Wt%
Four-Ball EP Weld
Load (kg)
Four-Ball Wear Scar
Diameter (mm)
Oxidation Stability psi Loss
at 500 h, ASTM D 942
Organoclay base grease
(600 SUS paraf nic base oil)
— 140 0.61 13.0
Molyvan A in organoclay 1.4 200 0.52 17.0
Molyvan A 1.4 200 — 12.0
Vanlube NA in organoclay 0.5
TABLE 23.19
S-P Gear Oil Package in Grease
Additive Wt%
Four-Ball EP Weld
Load (kg)
Four-Ball Wear Scar
Diameter (mm)
Lubrizol 5034A in aluminum
complex (900 SUS paraf nic
base oil blend)
3.0 250 0.45
Lubrizol 5034A in lithium
complex (600 SUS paraf nic
base oil)
3.0 315 0.50
Note: Additional additives such as rust and corrosion inhibitors and antioxidants are usu-
ally added to the aforementioned examples to provide fully formulated grease. The
four-ball EP test has a repeatability and reproducibility of one loading. The four-
ball wear test has a repeatability of 0.2 mm wear scar diameter and a reproducibility
of 0.37 mm.
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606 Lubricant Additives: Chemistry and Applications
14. ASTM D 1403. Standard test methods for cone penetration of lubricating grease using one-quarter and
one-half scale cone equipment. Annual Book of ASTM Standards, Philadelphia, PA, Sec. 5, Vol. 5.01,
1996.
15. ASTM D 2265. Standard test method for dropping point of a lubricating grease over wide temperature
range. Annual Book of ASTM Standards, Philadelphia, PA, Sec. 5, Vol. 5.01, 1996.
16. Grease—The world’s rst lubricant. NLGI Spokesman, 59(5):1–8, insert, August 1995.
17. Polishuk, A.T. Properties and performance characteristics of some modern lubrication greases.
Lubrication Engineering 33(3): 133–138, 1997.
18. Hermansson, M., E. Johansson, M. Jansson. Self-Diffusion of Oil in Lubricating Greases by NMR.
Journal of Synthetic Lubrication 13(3):279–288, 1996.
19. ASTM D 2266. Standard test method for wear preventative characteristics of lubricating grease
(four-ball method). Annual Book of ASTM Standards, Philadelphia, PA, Sec. 5, Vol. 5.01, 1996.
20. ASTM D 2596. Standard test method for measurement of extreme-pressure properties of lubricating
grease (four-ball method). Annual Book of ASTM Standards, Philadelphia, PA, Sec. 5, Vol. 5.01, 1996.
21. NLGI Lubricating Grease Guide, 4th Ed., 1996.
22. Fagan, G. Complex soap greases. NGLI 64th Annual Meeting, Carlsbad, CA, 1997.
23. Frye, R.L. An introduction to lubricating greases. NLGI 64th Annual Meeting, Carlsbad, CA, 1997.
24. Boner, C.J. Manufacture and Application of Lubricating Greases. New York: Reinhold Publishing
Corp, 1954.
25. Hotten, B.W. Advances in Petroleum Chemistry and Re ning, Chapter 3, Vol. 9. New York: Interscience
Publishers, 1964.
26. Wilson, J.W. Three-dimensional structure of grease thickener particles. NLGI Spokesman 3:372–379,
1994.
27. Arbocus, G. When greases don’t perform. Lubricant’s World 3(10):7–8, October 1993.
28. Czarny, R. Effect of changes in grease structure on sliding friction. Industrial Lubrication and
Tribology 47(1):3–7, 1995.
29. Hurley, S., P.M. Cann, H.A. Spikes. Tribology Transactions 43(1):9–14, 2000.
30. Williams, J.A. Engineering Tribology. New York: Oxford University Press, 1994.
31. Booser, E.R. (Ed). CRC Handbook of Lubrication, Vol. 2, Boca Raton, FL: CRC Press, 1984.
32. Pemberton, J., A. Cameron. A mechanism of uid replenishment in elastohydrodynamic contacts. Wear
37:185–190, 1976.
33. Boundary Lubrication (Texaco Inc.) 57(1), 1971.
34. Fuller, D.D. Theory and Practice of Lubrication for Engineers. New York: Wiley, 1984.
35. Lubetext DG-400. Encyclopedia for the User of Petroleum Products. Exxon Corp, 1993, p. 10.
36. Rohr, O. NLGI Spokesman 61(6):10–17, 1997.
37. Rohr. O. Presented at NLGI 63rd Annual Meeting, Scottsdale, AZ, October 27–30, 1996.
38. King, J.P. Presented at NLGI Annual Grease Meeting, Dublin, Ireland, 1998.
39. Ischuk, Y.L. et al. NLGI Spokesman 61(6):24–30, 1997.
40. Ogawa, T. et al. Presented at NLGI 64th Annual Meeting, Carlsbad, CA, October 21–29, 1997.
41. Tocci, L. Transparent grease bears a heavy load. Lubes-n-Greases 3:52–54, April 1997.
42. Ogawa, T., H. Kimura, M. Hayama. NLGI Spokesman 62(6):28–36, 1998.
43. Seki, K., M. Nishimura. Lubrication Characteristics of Oils and Grease applied to Ball Bearings for use
in Volvo. Journal of Synthetic Lubrication 9(1):17–27, 1992.
44. Lewis Sr., R.J. Hawley’s Condensed Chemical Dictionary, 13th Ed. New York: Van Nostrand Rheinhold,
1997, p. 977.
45. Rhee, I.-S. NLGI Spokesman 63(1):8–18, 1999.
46. Lawate, S., K. Lal, C. Huang. Vegetable-Oils-Structure and Performances. In E.R. Booser, ed., Tribology
Data Handbook. Boca Raton, FL: CRC Press, 1977, pp. 103–106.
47. Cof n, P.S. Journal of Synthetic Lubrication (1):34–60, 1984.
48. Bassette, P., R.S. Stone. Synthetic Grease. In L.R. Rudnick, R.L. Shubkin, eds., Synthetic Lubricants
and High- Performance Functional Fluids. New York: Marcel Dekker, 1999, pp. 519–538.
49. Schrama, R.C. Greases. In E.R. Booser, ed. Tribology Data Handbook. Boca Raton, FL: CRC Press,
1977, pp. 138–155.
50. Baker, R.F., R.F. Vaast, Jr. NLGI Spokesman 55(12):23-487–25-489, March 1992.
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Part 7
Trends
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609
24
Long-Term Trends in Industrial
Lubricant Additives
Fay Linn Lee and John W. Harris*
CONTENTS
24.1 Introduction ......................................................................................................................... 610
24.2 Additives for Circulating Oils and Turbine Oils ................................................................. 611
24.2.1 Performance Requirements for Circulating Oils
and Turbine Oils ................................................................................................. 611
24.2.2 Additives ...............................................................................................................611
24.2.2.1 Antioxidants ........................................................................................ 611
24.2.2.2 Rust Inhibitors ..................................................................................... 612
24.2.2.3 Metal Deactivators .............................................................................. 613
24.2.2.4 Foam Inhibitor ..................................................................................... 613
24.2.2.5 Demulsi ers ......................................................................................... 613
24.2.3 Turbine Oil Monitoring ........................................................................................ 613
24.2.4 Base Oil Effects on Additives ............................................................................... 613
24.2.5 Environmental Effects of Turbine Oils ................................................................ 614
24.2.6 Turbine Oil Trends ................................................................................................ 614
24.3 Additives for Hydraulic Oils ............................................................................................... 614
24.3.1 Performance Requirements .................................................................................. 614
24.3.2 Additives ...............................................................................................................615
24.3.2.1 Antioxidants ........................................................................................ 615
24.3.2.2 Rust Inhibitors ..................................................................................... 615
24.3.2.3 Antiwear Additives .............................................................................. 615
24.3.2.4 Metal Deactivators .............................................................................. 617
24.3.2.5 Foam Inhibitor ..................................................................................... 617
24.3.2.6 Viscosity Index Improver .................................................................... 617
24.3.2.7 Pour Point Depressants ........................................................................ 618
24.3.3 Environmental Concerns ...................................................................................... 618
24.3.4 Future Trends ........................................................................................................ 618
24.4 Additives for Gear Oils ...................................................................................................... 618
24.4.1 Performance Requirements for Gear Oils ............................................................ 618
* In memory of John W. Harris, his Shell colleagues—Howard B. Mead (United Kingdom), Cliff Henderson, and Fay Linn
Lee (United States)—have contributed this chapter update on behalf of John. In the technical eld of industrial lubricants
and greases, John was recognized as an international expert by Shell Oil colleagues and by his peers in professional
technical societies including the American Society for Testing and Materials (ASTM), the National Lubricating Grease
Institute (NLGI), the European Lubricating Grease Institute, and the Society of Tribologists and Lubrication Engineers.
He wrote and presented numerous technical papers and patents and contributed to the rst edition of this book. As a
technical advisor in Shell Global Solutions, John was known as Dr. AeroShell Grease for his contributions in developing
and patenting aircraft lubricants. Dr. John W. Harris passed away on November 21, 2005.
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610 Lubricant Additives: Chemistry and Applications
24.4.2 Additives for Gear Oils ......................................................................................... 621
24.4.2.1 Extreme-Pressure Additives ................................................................ 621
24.4.2.2 Friction Modi ers ................................................................................ 625
24.4.2.3 Viscosity Index Improvers ...................................................................625
24.4.2.4 Antimisting Additives .........................................................................625
24.4.3 Additives for Open Gear Lubricants ....................................................................625
24.4.4 Environmental Concerns ...................................................................................... 625
24.4.5 Future Trends ........................................................................................................625
24.5 Additives for Compressor Oils ...........................................................................................626
24.5.1 Performance Requirements for Compressor Oils ................................................ 626
24.5.2 Compressor Oil Formulation ............................................................................... 627
24.5.3 Compressor Oil Trends ........................................................................................ 627
24.6 Additives for Lubricating Greases ...................................................................................... 627
24.6.1 Performance Requirements for Lubricating Greases ..........................................627
24.6.2 Additive ................................................................................................................628
24.6.2.1 Rust and Oxidation Inhibitors ............................................................629
24.6.2.2 Antiwear and Extreme-Pressure Additives ........................................ 629
24.6.2.3 Polymers for Water Resistance ...........................................................632
24.6.2.4 Grease Thickeners as Performance Additives .................................... 632
24.6.3 Environmental Concerns .....................................................................................632
24.6.4 Lubricating Grease Trends ................................................................................... 633
References ......................................................................................................................................634
24.1 INTRODUCTION
The formulation of the various types of lubricating oils used in industry varies signi cantly
depending on their application. The types of industrial oil lubricants considered in this chapter, in
decreasing order of volumes consumed by industry, are as follows:
1. Circulating oils, including turbine oils
2. Hydraulic oils
3. Gear oils
4. Compressor oils
Trends in lubricating grease formulations are also considered.
TABLE 24.1
Performance Requirements for Industrial Oils
Performance Property
Type of Oil
Rust and
Oxidation
Inhibition
Ability to
Resist
Foaming
Ability to
Separate
Water
Antiwear
Properties EP
Circulating and
turbine oils
XXX——
Hydraulic oils X X X X —
Compressor oils X X X X —
Gear oil X X X X X
Lubricating grease X — — X X
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Long-Term Trends in Industrial Lubricant Additives 611
Performance requirements relevant to each type of lubricant are listed in Table 24.1. As may
be expected, the greater the number of performance properties required of a lubricant, the more
complex the formulation.
24.2 ADDITIVES FOR CIRCULATING OILS AND TURBINE OILS
24.2.1 P
ERFORMANCE REQUIREMENTS FOR CIRCULATING OILS AND TURBINE OILS
The following performance requirements are typically required for circulating oils and, in particu-
lar, steam and gas turbine oils:
1. Provide bearing lubrication
2. Remove heat through circulation
3. Serve as hydraulic uid for governor and other control equipment
4. Lubricate reducing gears
5. Protect against corrosion
6. Allow rapid separation of water
7. Resist foaming
8. Resist oxidation and sludge formation
As gas turbine oils typically operate at higher temperatures than steam turbine oils, requirement
8 is even more critical for gas turbine oils.
Various military and civilian agencies and turbine builders issue speci cations for turbine oils
[1,2]. Performance tests that usually appear in these speci cations are listed in Table 24.2.
24.2.2 ADDITIVES
The types of additives commonly used in turbine oils are listed in Table 24.2 with the performance
properties they impart and the related test methods.
24.2.2.1 Antioxidants
Antioxidants are used to inhibit the attack of turbine oil by oxygen and to reduce the formation of
adverse oxidation products such as corrosive organic acids and insoluble sludge. In turbine oils, this
is often accomplished with synergistic blends of hindered phenols and diaryl amines, which inhibit
oxidation by donating a hydrogen atom to reactive peroxy radical intermediates formed during the
oxidation process, thus terminating a chain reaction that would otherwise propagate the degrada-
tion of more oil molecules [3–7]. Antioxidants that deactivate peroxy radicals are termed primary
antioxidants. Volatile antioxidants are generally avoided because they can be depleted by evapora-
tion during use.
Another type of antioxidant inhibits oil oxidation by decomposing reactive hydroperoxide inter-
mediates to less-reactive chemical species. Otherwise, these hydroperoxides would decompose to
reactive radicals, resulting in the propagation of the oxidation process. Antioxidants that act as
peroxide decomposers are termed secondary antioxidants [5]. Types of additives that fall into this
class include thioethers, zinc dialkyldithiophosphates (ZDDPs), zinc dialkyldithiocarbamates, and
organic phosphites.
Industrial oil formulators exploit synergistic relationship between hindered phenols and diaryl
amines and between primary antioxidants and secondary antioxidants [8]. Manufacturers of anti-
oxidants have also developed additives that contain both the phenol moiety and the thioether moiety
in the same molecule so that one additive can potentially act as both primary antioxidant and sec-
ondary antioxidant [5].
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612 Lubricant Additives: Chemistry and Applications
24.2.2.2 Rust Inhibitors
Turbine oils are formulated to prevent rust in areas in contact with the oil. Typical turbine oil speci -
cations require that the oil pass corrosion tests using both demineralized water and saltwater, ASTM
D 665, procedures A and B, respectively. Anticorrosion additives are generally polar in nature and
preferentially form water-resistant lms on iron or steel surfaces [5]. Such additives should not be
readily leached from the turbine oil by water entrained in the circulating oil and should not adversely
affect other desirable performance properties such as fast water separation and low-foaming tenden-
cies. Types of rust inhibitors that may be used in turbine oils are listed in Table 24.2.
Rust inhibitor–related compatibility problems can occur if certain turbine oils are contami-
nated with industrial oils that contain organometallic performance additives. For example, antiwear
hydraulic oils may contain zinc-based antiwear additives and metal sulfonate rust inhibitors, and
interactions between acidic rust inhibitors in the turbine oil and metal-containing additives in the
antiwear hydraulic oil can result in the formation of insoluble salts, which can plug lters. Similarly,
TABLE 24.2
Additives Used in Turbine Oils
Additive Function Types of Additives Related Performance Tests
Antioxidant Diaryl amines ASTM
a
D 943, Standard test method for oxidation
characteristics of inhibited mineral oils
ASTM D 2272, Standard test method for oxidation
stability of steam turbine oils by rotating pressure
vessel
Hindered phenols
Organic sul des
ASTM D 4310, Standard test method for the
determination of the sludging and corrosion
tendencies of inhibited mineral oils
ASTM D 6186, Standard test method for oxidation
induction time of lubricating oils by pressure
differential scanning calorimetry (PDSC)
Rust inhibitor Alkylsuccinic acid derivatives ASTM D 665, Standard test method for rust-
preventing characteristics of inhibited mineral oil in
the presence of water
Ethoxylated phenols
Imidazoline derivatives
Foam inhibitor Polydimethylsiloxanes
Polyacrylates
ASTMD D 892, Standard test method for foaming
characteristics of lubricating oils
Metal deactivator Triazoles ASTM D 130, Standard test method for detection of
copper corrosion from petroleum products by the
copper strip tarnish test
Benzotraizoles
2-Mercaptobenzothiazoles
Tolutriazole derivatives
Mild antiwear/EP additive Alkylphosphoric acid esters
and salts
ASTM D 4172, Standard test method for wear
preventive characteristics of lubricating uid
(four-ball method)
ASTM D 5182, Standard test method for evaluating
the scuf ng load capacity of oils (FZG visual
method)
Demulsi er Polyalkoxylated phenols ASTM D 1401, Standard test method for water
separability of petroleum oils and synthetic uidsPolyalkoxylated polyols
Polyalkoxylated polyamines
a
American Society for Testing and Materials, Annual Book of ASTM Standards: Petroleum Products, Lubricants and
Fossil Fuels, Volumes 5.01–5.04, issued annually.
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Long-Term Trends in Industrial Lubricant Additives 613
if a new turbine component is installed in a unit and metal sulfonate rust preservatives on the com-
ponent parts have not been completely washed off, a similar lter-plugging situation can occur.
24.2.2.3 Metal Deactivators
Metal deactivators prevent corrosion of copper and copper alloys such as bronze and brass. They
function by preferentially adsorbing onto the surface of copper alloys, forming a protective layer
that inhibits attack by acids formed during oxidation of the bulk lubricant [5,9]. Conversely, the
metal deactivator can act as a copper passivator protect the oil from the catalytic effects of the
copper alloy, which could accelerate bulk oil oxidation. Table 24.2 lists the types of metal deactiva-
tors that may be used in turbine oils.
24.2.2.4 Foam Inhibitor
Antifoam additives of the type listed in Table 24.2 are added to turbine oils to control foaming
tendencies. One method for measuring foaming tendencies is ASTM D 892. Antifoam additives
are not completely soluble in oil and form dispersions of tiny droplets of low surface tension, which
accelerate the coalescence of air bubbles in oil. Typical dose rates for silicone antifoam additives are
in the 10–20 ppm range, whereas typical dose rates for polyacrylates are in the 50–200 ppm range.
Because antifoam additives are only partially soluble in oil, they can eventually separate from the
oil, resulting in decreased foam control.
It is important that the antifoam additives do not adversely affect the air release properties of
the turbine oil, or otherwise, air entrainment in the oil can result in sluggish operation of hydrau-
lic systems and other problems. Air release is measured by the method ASTM D 3427. Typically,
values of less than 5–10 min are desirable. Overdosing with antifoam additive can adversely affect
air release properties.
24.2.2.5 Demulsifi ers
Demulsi ers facilitate water separation from oil. They concentrate at the water–oil interface and
promote coalescence of water droplets, resulting in faster separation of water so that it can settle to
the bottom of the oil reservoir and be drained off. Types of demulsi ers are listed in Table 24.2.
24.2.3 TURBINE OIL MONITORING
Despite the use of performance additives, turbine oil properties may deteriorate in use, and guide-
lines for condemnation values for various physical properties of turbine oils have been developed.
Such guidelines are described in ASTM D 4378. Turbine manufacturers may also have their own set
of monitoring guidelines for turbine oils.
24.2.4 BASE OIL EFFECTS ON ADDITIVES
Modern engine oil requirements have driven changes in the mineral oil base stocks available for
formulating lubricants, including industrial lubricants. Three of the types of base oils de ned by the
American Petroleum Institute (API) are described as follows [10]:
1. Group I base stocks contain less than 90% saturates and greater than 0.03% sulfur and
have a viscosity index (VI) greater than or equal to 80 and less than 120.
2. Group II base stocks contain greater than or equal to 90% saturates and less than or equal
to 0.03% sulfur and have a VI greater than or equal to 80 and less than 120.
3. Group III base stocks contain greater than or equal to 90% saturates and less than or equal
to 0.03% sulfur and have a VI greater than or equal to 120.
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