Table Of ContentPREFACE
Recognition of tribology as a truly interdisciplinary field is growing and this
book provides a review of the rapidly developing field of tribochemistry. The
interaction of chemistry under boundary lubrication is known as tribochemistry.
Chemical reactions between some additives from lubricants and activated surfaces
produce antiwear tribofilm. Friction and wear expose fresh surfaces which are
active catalysts to the reaction of lubricants, especially for the action of the
phosphorus, sulfur and chlorine, the antiwear additives. The detailed physical and
chemical processes occurring in the contact zone are still not well understood. The
word "Tribochemistry" is defined as lubrication under engine conditions that is a
compromise between numerous limitations forced by the nature of the physical and
chemical properties of the lubricant, the material surfaces, the oil formulation, and
the life required. In boundary lubrication, additives react with surfaces under
tribological conditions, resulting in the formation of tribofilm. These tribofilms
have generally been poorly characterized and thus the mechanism of film growth
and removal (wear) is largely unknown. This is particularly true for synthetic oils
and for oils with metal-free additives, which are increasingly being used as an
environmentally friendlier alternative to the ones containing heavy metals.
Considerable progress has been made in studying tribofilms in the last decade.
A number of important surface and thin film techniques have been developed in
recent years, which are contributing to a better understanding of at least some
tribochemical processes of boundary lubrication. In recent years, X-ray absorption
near edge structure XANES spectroscopy, a powerful technique for tribofilm
characterization, was used to identify a layered structure (surface and bulk) of
tribofilms. The chemistry of tribofilms generated by the combination of zinc
dialkyldithiophosphate (ZDDP) and molybdenum dialkyldithiocarbamate
(MoDTC) has been examined.
"Tribochemistry of Lubricating Oils" provides a broad overview of the many
tribochemical problems which may arise under harsh engine oil conditions. In the
conditions of lubrication, the degradation of engine oil is a function of time as well
as temperature. Tribochemical processes have been observed and utilized
technologically for a long time, and the action of many lubricant additives is based
on tribochemical processes. The conscious recognition of tribochemistry as a
science is recent. The term "tribochemistry" introduced by Thiesen in 1967 has
attracted less attention than the term "tribology" introduced by P. lost in 1966. We
vi Preface
can expect the term "tribochemistry" to have an expotentional effect on the
development of this technologically important field.
This volume is a comprehensive text that attempts to deal with the tribochemical
reactions in hydrocarbon formulations affecting the tribofilm formation on metal
surfaces. The most important factor governing the tribochemical processes under
boundary lubrication is connected with the action of soft-core and hard-core reverse
micelles, RMs. The book covers a very broad spectrum of topics, e.g., additives
interactions, acid-base processes in lubricating formulations and the importance of
solubilization. Emphasis is on chemical interpretations of the phenomena of
tribochemistry of reverse micelles, surface tribochemistry, and current analytical
techniques of metal surfaces.
The book starts off with an introduction to tribochemistry, the science concerned
with chemical reactions affecting the tribofilm formation on activated metal
surfaces. The "Tribochemical Tree" summarizes our knowledge of some of the
most important processes proceeding in the bulk lubricant and on mechanically
activated surfaces.
The next chapter is a review of current practice in lubrication of internal
combustion engines and lubricant design. The role of individual lubricant
components and their use in mineral and synthetic formulations is covered. This
is followed by a discussion of the tribochemical effects of additive interactions.
The heart of the manuscript is chapters, "Tribochemical nature of antiwear film",
"Surface tribochemistry and activated processes", and "Analytical techniques in
lubricating practices". Topics covered include tribofilm formation,
organomolybdenum compounds in surface protection, catalytic activity of rubbing
surfaces, introduction of some techniques for evaluation of tribofilms composition
and analytical techniques for evaluation of lubricant degradation. Examples of the
appHcation of basic concepts are introduced, eg., acidity and basicity in the process
of lubricant deterioration.
The final chapter, "Environmental issues", addresses lubricant performance and
suggests ways to improve fuel efficiency of engines by the use of lower viscosity
grade oils and the use of modifiers to reduce metal-metal friction.
The book can be used by practicing scientists or engineers seeking a review of
the state of knowledge of the tribochemistry field; however, it can also be used in
the education of graduate students' one semester courses in chemical and
mechanical engineering. For tribology courses offered in mechanical engineering
departments, the chemistry concepts and application examples presented add
specific knowledge and greater appreciation of the need to consider all aspects of
tribological processes. Engineers looking for guidance on problems involving acid-
base reactions in oil formulations, role of inverse micelle in lubrication and
concerns with the effect of organomolybdenum compounds in engine surface
protection will find the book very useful. Essentially, the content meets its
objective of helping to make reverse micelles formation and solubilization processes
Preface vii
more understandable to lubricant chemists, and explains the principles of the
chemistry of tribofilm formation. It was a very rewarding experience to write a
book which fills an important gap in the reference material on tribochemistry.
May 2003, Salt Lake City Zenon Pawlak
Acknowledgments
The University of Gdansk, Poland, has played a crucial role in my teaching and
research on the thermodynamics of hydrogen bonding in nonaqueous solvents and
engine oils physicochemistry, where I was Professor of Chemistry until 1990.
Over the last 20 years I have benefitted from the help of many people, and need
to mention a few. Professor Lucjan Sobczyk, University of Wroclaw (Poland),
deserves a special word of thanks because he inspired me in my hydrogen bonding
research and he made it possible for me to start my own research program. During
my sabbatical years, 1972-1975 in Florida University, Gainesville, I worked with
Professor Roger G. Bates ("pH man"), who taught me that in solution chemistry
there are other species besides solvated proton (H'^soiv)' but the proton is the most
important yet still very unknown. Therefore, I began the study of proton transfer
reactions in nonaqueous solvents and we pubhshed ten papers. In 1979 I was a
recipient of a Deutscher Akademischer Austauschdient Fundation. I used this
scholarship to work with Professor George Zundel in the Physical Chemistry
Institute, University of Munich, where we studied proton transfer reactions in
aprotic solvents. During my sabbatical year (1981-82) at Leicester Polytechnic
(Great Britain), I had the pleasure of working with Professor Malcolm F. Fox and
Professor Jim D. Picken. It was a memorable time of the Solidarity movement in
Poland. During that time we studied acid-base interactions and micellar processes
in engine oils when engines were run on bio-gas. The 1982-1983 academic year
was spent at the University of Texas, Austin, with Professor Joseph J. Lagowski's
research group. We studied the dissolution of gold by solvated electrons in liquid
ammonia.
I enjoyed my research in Utah, from 1986 to 1990, at Brigham Young
University, Provo, collaborating with Professor Reed Izatt and Professor Noel L.
Owen, where calorimetric and electrometric studies were applied for used and fresh
engine oils and FTER spectrometric studies of solvated electrons in liquid ammonia
with wood surface and wood components were analyzed.
My home in Utah is a great place to write this book while I have continued to
work in environmental chemistry in Salt Lake City. I have enjoyed skiing many
winters in Utah and this provided me with inspiration to write about tribochemistry.
Preface vii
more understandable to lubricant chemists, and explains the principles of the
chemistry of tribofilm formation. It was a very rewarding experience to write a
book which fills an important gap in the reference material on tribochemistry.
May 2003, Salt Lake City Zenon Pawlak
Acknowledgments
The University of Gdansk, Poland, has played a crucial role in my teaching and
research on the thermodynamics of hydrogen bonding in nonaqueous solvents and
engine oils physicochemistry, where I was Professor of Chemistry until 1990.
Over the last 20 years I have benefitted from the help of many people, and need
to mention a few. Professor Lucjan Sobczyk, University of Wroclaw (Poland),
deserves a special word of thanks because he inspired me in my hydrogen bonding
research and he made it possible for me to start my own research program. During
my sabbatical years, 1972-1975 in Florida University, Gainesville, I worked with
Professor Roger G. Bates ("pH man"), who taught me that in solution chemistry
there are other species besides solvated proton (H'^soiv)' but the proton is the most
important yet still very unknown. Therefore, I began the study of proton transfer
reactions in nonaqueous solvents and we pubhshed ten papers. In 1979 I was a
recipient of a Deutscher Akademischer Austauschdient Fundation. I used this
scholarship to work with Professor George Zundel in the Physical Chemistry
Institute, University of Munich, where we studied proton transfer reactions in
aprotic solvents. During my sabbatical year (1981-82) at Leicester Polytechnic
(Great Britain), I had the pleasure of working with Professor Malcolm F. Fox and
Professor Jim D. Picken. It was a memorable time of the Solidarity movement in
Poland. During that time we studied acid-base interactions and micellar processes
in engine oils when engines were run on bio-gas. The 1982-1983 academic year
was spent at the University of Texas, Austin, with Professor Joseph J. Lagowski's
research group. We studied the dissolution of gold by solvated electrons in liquid
ammonia.
I enjoyed my research in Utah, from 1986 to 1990, at Brigham Young
University, Provo, collaborating with Professor Reed Izatt and Professor Noel L.
Owen, where calorimetric and electrometric studies were applied for used and fresh
engine oils and FTER spectrometric studies of solvated electrons in liquid ammonia
with wood surface and wood components were analyzed.
My home in Utah is a great place to write this book while I have continued to
work in environmental chemistry in Salt Lake City. I have enjoyed skiing many
winters in Utah and this provided me with inspiration to write about tribochemistry.
viii Preface
First of all, I would like to thank Professor Duncan Dowson for his personal
input and support to publish this book and Professor Brian Briscoe for constructive
comments and remarks.
It is my pleasure to express thanks to Professor Bamey E. Klamecki, University
of Minnesota, Peter Cartwright, PE, MinneapoUs; Dr. Pierre A. Willermet, Ford
Motor Co; Professor Lucjan Sobczyk, University of Wroclaw (Poland); Professor
Czeslaw Kajdas, Warsaw University of Technology (Poland), and Professor
Stanislaw Plaza, University of Lodz (Poland) for reviewing part or all chapters of
my book and friendly comments.
A special word of thanks is due to my friend. Professor Ryszard Pifkos, Medical
School in Gdansk (Poland), for his permanent support and valuable suggestions
during the preparation of the book.
A word of thanks is due to my friend, Professor Beniamin Lenarcik, University
of Technology and Agriculture, Bydgoszcz (Poland) for his support, where I am
currently a Professor of Chemistry and the Head of Physicochemistry of Surfaces
Department.
I would like to give many thanks to my family for all their support during
preparation of this manuscript.
I also would like to thank the library staff of Brigham Young University, Provo
and University of Utah, Salt Lake City, Utah for their help in finding many
references and for permission of using technical resources during the preparation
of the manuscript.
I would like to thank all those undergraduate and graduate students from Gdansk
University whose participation in the engine oils physicochemistry research
program over many years has been a permanent inspiration.
The author will accept with gratitude all suggestions aimed at the improvement
of this work.
Finally, I would like to thank the following publishers for granting us permission
to reproduce the figures listed below:
Figure 2.3: Reprinted from Lubrication, Vol. 44, 1958, pp. 173-186, with
permission from Society of Tribologists and Lubrication Engineers.
Figures 2.6 and 2.7: Reprinted from D. Klamann, Lubricants and Related Products.
Synthesis, Properties, Applications, International Standards: Verlag Chemie,
Weinheim. Copyright 1984, with permission from John Wiley and Sons.
Figure 2.8: Reprinted from Tribol. Int., Vol. 24, M.F. Fox, Z. Pawlak and D.J.
Picken, Inverse micelles and solubihzation in hydrocarbon formulations, pp. 341-
349. Copyright 1991, with permission from Elsevier.
Preface ix
Figure 2.12: Reprinted from Petroleum Review, Vol., 47, 1993, pp. 84-87, with
permission from The Institute of Petroleum.
Figure 3.2: Reprinted with permission from Critical Rev. Anal. Chem., Vol. 21,
1990, pp. 257-278. Copyright CRC Press, Boca Raton, Florida.
Figure 3.3: Reprinted from Y. Moroi, Micelles Theoretical and Applied Aspects,
Plenum Press, New York. Copyright 1992, with permission from Plenum Press.
Figure 4.1: Reprinted from the Proceedings of European Academy of Surface
Technology, M. Kasrai, G.M. Bancroft, K.F. Laycock, H.A. Tan, and X.H. Feng,
November 1993, Schwabischgmund, Germany E.G. Leuze, SaulgagAVurtt, 1994,
pp. 79-85, with permission of the authors.
Figure 4.2: Reprinted from Phys. Rev. B, Vol. 51, Z. Yin, M. Kasrai and M.
Bancroft, X-ray-absorption spectroscopic studies of sodium polyphosphate glasses,
pp. 742-750. Copyright 1995, with permission of the authors.
Figure 4.3: Reprinted from Wear, Vol. 202, Z. Yin, M. Kasrai, M. Fuller, G.M.
Bancroft, K. Fyfe and K.H. Tan, Application of soft X-ray absorption spectroscopy
in chemical characterization of antiwear films generated by ZDDP: the effect of
physical parameters, Part I, pp. 172-191. Copyright 1997, with permission from
Elsevier.
Figure 4.4: Reprinted from Tribol. Int., Vol. 31, M.L.S. Fuller, M. Kasrai, G.M.
Bancroft, K. Fyfe and K.H. Tan, Solution decomposition of zinc dialkyl
dithiophosphate and its effect on antiwear and thermal film formation studied by X-
ray absorption spectroscopy, pp. 627-644. Copyright 1998, with permission from
Elsevier.
Figure 4.6: Reprinted from D.C. Koningsberger and R. Prins, Eds., X-ray
Absorption: Principles, Applications, Techniques of EXAFS, SEXAFS, and
XANES, Wiley, New York. Copyright 1988 with permission from John Wiley and
Sons.
Figure 4.7: Reprinted from D. Dowson et al., Eds., Lubricants and Lubrication,
Elsevier Science B.V. M. Kasrai, M. Fuller, M. Scaini, Z. Yin, G.M. Bancroft,
M.E. Fleet, K. Fyfe and K.H. Tan, Study of tribochemical film formation using X-
ray absorption and photoelectron spectroscopies, pp. 659-669. Copyright 1995,
with permission of the authors.
X Preface
Figure 4.8: Reprinted from Spectrochim. Acta , Vol. 49A, N.E. Lindsay, R.O.
Carter, ffl, P.J. Schmitz, L.P. Haack. R.E. Chase, J.E. DeVries and P.A. Willermet,
Characterization of films formed at a lubricated cam/tappet contact, pp. 2057-2070.
Copyright 1993, with permission from Elsevier.
Figure 4.9: Reprinted from Wear, Vol. 66, H.J. Mathieu and D. Landolt, The
application of Auger electron spectroscopy to the study of wear surfaces, pp. 87-
100. Copyright 1981, with permission from Elsevier.
Figure 4.10: Reprinted from Tribol. Int., Vol. 25, P.A. Willermet, R.O. Carter, III
and N.E. Boulos, Lubricant-derived tribochemical films-An infra-red spectroscopic
study, pp. 371-380. Copyright 1992, with permission from Elsevier.
Figure 5.1: Reprinted from Lubrication Engineering, Vol. 51, 1995, pp.182-194,
with permission from Society of Tribologists and Lubrication Engineers.
Figure 5.2: Reprinted from Tribol. Int., Vol. 32, P.D. Fleischauer and J.R. Lince,
A comparison of oxidation and oxygen substitution in M0S2 solid film lubricant, pp.
627-636. Copyright 1999, with permission from Elsevier.
Figures 5.3, 5.4, 5.5, 5.6: Reprinted from Tribology Transactions, Vol. 41, 1998,
pp. 69-77, with permission from Society of Tribologists and Lubrication Engineers.
Figure 5.7: Reprinted from Tribol. Int., Vol. 31, C. Grossiord, J.M. Martin, Th. Le
Mogne, C. Esnouf and K. Inoue, M0S2 single sheet lubrication by molybdenum
dithiocarbamate, pp 737-743. Copyright 1998, with permission from Elsevier.
Figure 6.1: Reprinted from JSAE Review, Vol. 16, M. Tomita, H. Komo, Y.
Nomura, M. Nozawa, S. Yamaguti and Y. Toda, Study on deterioration of engine
oil and its sensing, pp. 283-285. Copyright 1995, with permission from Elsevier.
Figures 6.2 and 6.3: Reprinted from Chemistry and Industry, 20 July, 1987, pp.
470-473, with permission from Society of Chemical Industry,
Figure 6.4: Reprinted from Lubrication Engineering, Vol. 56, 2000, pp. 23-29,
with permission from Society of Tribologists and Lubrication Engineers.
Figure 6.5: Reprinted from Tribol. Int., Vol. 24, M.F. Fox, Z. Pawlak and D.J.
Picken, Acid-basedeterminationof lubricating oils, pp. 335-340. Copyright 1991,
with permission from Elsevier.
Preface xi
Figures 6.8 and 6.9: Reprinted from Tribol. Int., Vol. 23, M.F. Fox, J.D. Picken
and Z. Pawlak, The effect of water on the acid-base properties of new and used IC
engine lubricating oils, pp. 183-187. Copyright 1990, with permission from
Elsevier.
Figure 6.10: Reprinted from Wear, Vol. 139, W.S. Moon and Y. Kimura, Wear-
preventing property of used gasoline oils, pp. 351-365. Copyright 1990, with
permission from Elsevier.
Figure 7.1: Reprinted from Synthetic Lubricants and High Performance Functional
Fluids, L.R. Rudnick and R.L. Shubkin, Eds., 2nd Edition, Marcel Dekker, New
York. Copyright 1999, with permission from Marcel Dekker.
Chapter 1
INTRODUCTION TO THE TRIBOCHEMISTRY CONCEPT
It was known that lubricants could be used to influence bothfi'iction and wear, yet
the physical and chemical processes by which this is achieved have been explored
recently and are still being revealed to us.
Duncan Dow son, 1979
The term "tribochemistry"originated from two words "tribo" (Greek: tribos,
tribein - a rubbing, to rub) and "chemistry" of reactions occuring between the
lubricant and the surfaces. It relates directly to the combinations of all sciences
and technologies associated with the chemical reactions in mineral and synthetic
oil formulations and with tribofilm formation on metal surfaces under boundary
lubrication. Tribochemistry is of practical importance because lubricants are an
essential component of engine and other machine operations. Mechanical energy
is lost at the power train due to changes occurring in lubrication, friction, and
wearing processes. Because of this interplay of friction and chemistry, these
reactions are called tribochemical. Tribochemistry not only exploits the
fundamentals of chemistry and physics, but it also encompasses other sciences,
especially mechanics and material sciences. The experimentally observed
influence of friction on the chemical reaction is the acceleration of tribochemical
reactions. Technological importance of tribochemistry extends from antifriction
action of lubricants to material surface quality (Briscoe et al., 1992; Dowson,
1998; Fischer, 1988a and 1988b; Fuller et al., 1997 and 1998; Grossiord et al.,
1998 and 1999; Heinicke, 1984; Hsu et al., 1988 and 2002a; Kajdas , 2001;
Lindsay et al., 1993; Luisi et al., 1988; Martin, 1999; Martin et al., 1986a, 2000a
and 2001; Muratov et al., 1998; Sakurai, 1981; Spikes, 2001; Stolarski, 1999;
Willermet, 1998; Willermet et al., 1991, 1995a and 1997; Varlot et al., 1999, 2000
and 2001; Yin et al., 1997a and 1997b).
The basic processes of dissolution, acid-base interaction, micellization,
solubilization, oxidation and reduction take place in oil formulation. During
engine operation, additives of the lubricant interact continuously with engine
surfaces and themselves. Thus, there is a progressive change in the surface due
to the lubrication, friction, and wearing processes, tribofilm formation, and
oxidation. All these processes are presented and discussed throughout this book.
Surfactant additives are fundamental to reverse micelles (RMs) formation in oil
2 Chapter 1
formulation. The formation of RMs, due to dipole-dipole interactions between the
polar heads of the surfactant molecules, may play an important role in oil
formulation. The structure of individual surfactant-stabilized reverse micelles,
together with their mutual interactions, have been well characterized over recent
years (Bascom et al., 1959; Das et al., 1992; Gon and Kumar, 1996; Inoue, 1993;
Inoue and Watanabe, 1983; Kertes and Gutman, 1976; Kertes and Markowits,
1968; Kertes et al., 1970; Luisi et al., 1988; Pawlak, 2001; Pileni, 1989a; Reemik,
1965; Singleterry, 1995; Ward and du Reau, 1993; Willermet, 1998).
Due to the continuous input of thermal energy necessary to maintain
mechanical work, tribological systems are in progressive equilibrium. In the
tribosystem, the flow of energy is accompanied by an increase in entropy of the
total system and is reflected by the tribochemical reactions and deterioration of
lubricant quality. Our understanding of tribosystems has been seriously limited
by a lack of kinetic information on critical reactions in hydrocarbon formulation
and critical reactions at interfaces.
/ ^^ \
/ I"
^Z" Low or N on polar
^ sol V ents
^' ^'Ij^^* Intermol E cular <»m...M.%
inte R actions
Ashless di S persant + ZDDP \^
^^f.MM^* Metallic det E rgent + ZDDP *>)\\\n((<»
/ Hard & soft core M icelles formation \
•im..MiMut Antiox I dation (ZDDP) t^.MMum?*
^ Molecular de C omposition
J" Acid-base r E actions
<n iMiiLt Solubi L ization «n •••••"J*
Mechanic L ly
activat E d surfaces \
^ Antiwear tribofilm S urface formation \
BASE OILS
+
SELECTED ADDITIVES
Fig. \A. Tribochemical "TREE"
