Tribochemical mechanism

Other theories of initiation, not based on the initial action of a hot spot, have been proposed. One of these, the tribochemical mechanism, postulates the direct breaking of chemical bonds without the conversion of the mechanical energy to heat. Reference 49 discusses this mechanism more thoroughly... 

It is of interest that of the various postulated mechanisms none has passed from the literature direct electronic excitation, frictional processes, and viscous flow mechanisms continue to arouse interest, and even tribochemical mechanisms, discarded by Bowden and Yoffe, have remained alive within the same laboratory in new guise (Chapter 9). 

There are, of course, numerous options of this type, the conventional points of view tending to stress the role of thermal excitations (in basically invariant electronic structures), thermomechanical processes, or tribochemical mechanisms. 

M. Eglin et al./A combinatorial approach to elucidating tribochemical mechanisms... 

M. Eglin, A. Rossi, N.D. Spencer, A combinatorial approach to elucidating tribochemical mechanisms. Tribology Letters 15 (2003) 193-198. 

A Combinatorial Approach to Elucidating Tribochemical Mechanisms Michael Eglin, Antonella Rossi, Nicholas D. Spencer Tribology Letters 2003 15(3) pp 193-198... 

Since the effect of the environment had been eliminated, the overall results demonstrated that tribochemical reactions took place that were selective with respect to the pin-on-flat geometrical configuration, during friction in an UHV environment. A judicious combination of analysis by e.v situ and in situ meth-txls thus allowed the complex tribochemical mechanisms responsible for friction and wear behavior in boundary lubrication to be elucidated. 

Infrared, X-ray diffraction, DTA, TG, electrical conductivity and solubility measurements have been used to investigate the mechanisms of tribochemical reactions between solids [385,386],... 

Carboxylated polymers can be prepared by mechanical treatment of frozen polymer solutions in acrylic acid (Heinicke 1984). The reaction mechanism is based on the initiation of polymerization of the frozen monomer by free macroradicals formed during mechanolysis of the starting polymer. Depending on the type of polymer, mixed, grafted, and block polymers with a linear or spatial structure are obtained. What is important is that the solid-phase reaction runs with a relatively high rate. For instance, in the polyamide reactive system with acrylic acid, the tribochemical reaction leading to the copolymer is completed after a treatment time of 60 s. As a rule, the mechanical activation of polymers is mainly carried out in a dry state, because the structural imperfections appear most likely here. 

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. 

A "Tribochemical Tree" shown in Fig. 1.1 summarizes our knowledge of some of the most important processes occurring in the bulk oil and the effects of those processes on the mechanically activated surfaces under the boundary lubrication conditions (Dowson, 1998 Kajdas, 2001 Martin, 1999 Pawlak, 2001 Sakurai, 1981 Spikes, 2001 Willermet, 1998 . Yinetal., 1997a and 1997b). 

The uncertainty in the mechanism of antiwear tribofilm formation derives in part from observations that exposing metal surfaces to heated ZDDP/oil solution forms films similar to those generated in a tribochemical way. From the utility standpoint, both thermal and tribochemical films seem to provide protection from wear. Thus, the current model involves both a tribochemical and thermooxidative component for the decomposition of ZDDP and tribofilm formation (Aktary et al., 2001 Bancroft et al., 1997 Fuller et al., 1997 and 1998 Martin, 1999 Willermet et al., 1995b Yin et al., 1997a). 

The lubrication system is extremely complex. The mechanism of lubrication is partly dictated by the nature of interactions between the lubricant and the solid surface. Additives blended into lubricating oil formulations either adsorb onto the sliding surfaces, eg., fatty alcohols, fatty amines, amides, phosphoric acid esters (friction modifiers), or react with the surface, eg., ZDDP, MoDTC, MoDDP organic phosphates (extreme pressure). Some interactions affecting the surfaces of metals include adsorption, chemisorption, and tribochemical reactions-these form new compounds on the surface and lubrication by reaction products (Bhushan and Gupta, 1991 Briscoe et al., 1973 Briscoe and Evens, 1982 Heinicke, 1984 Hsu and Klaus, 1978 and 1979 Klaus and Tewksbury, 1987 Lansdown, 1990 Liston, 1993 McFadden et al., 1998 Studt, 1989). 

Nascent surface Explain the difference in the concept of liquid lubrication mechanism in (a) hydrodynamic, (b) elastohydrodynamic and (c) boundary lubrication. Which of the following characterize (a), (b), and (c) lubrication regime continuous fluid film, negligible deformation, complete separation of the surfaces, elastic and plastic deformation, no wear takes place, no contact between the sliding surfaces, involving surface topography, physical and chemical adsorption, catalysis and reaction kinetics, and tribochemical film formation ... 

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. 

Percussion is a repetitive solid body impact, such as experienced by print hammers in high-speed electromechanical applications and high asperities of the surfaces in a gas bearing. Repeated impacts result in progressive loss of solid material. Percussive wear occurs by hybrid wear mechanisms, which combine several of the following mechanisms adhesive, abrasive, surface fatigue, fracture, and tribochemical wear.75... 

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