Trol Rbulnes

Tribology Online, 6, 1 (2011) 55-63. ISSN 1881-2198

DOI 10.2474/trol.6.55

Article

Mechanochemical Friction of Third-Body as an Exergetic Collision

Rodrigo Bulnes*

Department of Mechanical Engineering, Technical University Federico Santa Maria Avenida Espana 1680, Valparaiso, Chile

*Corresponding author: [email protected]

( Manuscript received 14 September 2009; accepted 27 March 2010; published 31 January 2011 ) ( Presented at the World Tribology Congress 2009, Kyoto, 6-11 September, 2009 )

Approximation of a third body proposes that a tribo-contact is conformed by two first bodies (that is to say; elements of a machine), and by an interface -or third body- of different composition, where velocity between the first two bodies accommodates tribo-chemically. In other words, the third body interface is a mecanochemical concept which has the ability to transmit mechanical power in speed. Correspondingly, thermodynamical activity of this third body friction, is of irreversible non-equilibrium, being more coherent to establish an exergetic analysis in order to conclude to a holistic and more advanced formulation for the so badly named Friction Coefficient. Concepts of Irreversible Non-Equilibrium Thermodynamics allow to establish a new formulation for third-body boundary friction. Microscopic analysis of tribo-fluctuations is applied to a generic contact to clarify the bond between friction and dissipation. The resulting mechanochemical formula for the 3rd-bodys boundary friction, falls in the scope of the Physics of the CHAOS and the phenomena of auto-organization of surfaces. Keywords: mechanochemistry, kinetics, Gibbs Free Energy and fluctuation-dissipation

1. Introduction

To describe the dynamics of rugosities among bodies that graze and slide, it is necessary to involve multiple precision levels phenomena going from the simple elastic deformation of rugosities, to the most complex influence that wear particles trapped in the Abbotts volume would have upon the Load-Carrying Capacity of surfaces. This simple argument suggests that friction among bodies () is a phenomenon directly affected by all kinds of considerations of the Non-Equilibrium Irreversible Thermodynamics1). However, every effect originating from those considerations, should be validated employing time-length escalation.

An example of the previous argument situates in the third-body tribology2) (debris, contaminant particles, absorbed films, interface viscosity, tribomutations, rugosities of the continuous-discrete contact, vacancies movement, dislocations, metallurgical defects, etc...). The third-bodies define a combination of effects that belong to both the scale of the Mechanical Engineer (adhesive- and Hertzians pressure distribution theories), an of the Materials Engineer (metallurgical and superficial composition matter changes. In practice the third-bodies are generated almost instantly, transforming the contact of two bodies in one of

3rd.-body, or of mechanochemical mixed contact). A coherent thermodynamic description friction -at least for the scale of both Engineers-, would require synchronization of the effects that provide generic and permanent non-equilibrium irreversible conditions...

Another example phenomenological underlies in the friction heat, but considering it as heat irreversibly accumulated in the surfaces3). The heat accumulated suggests the entropy flow existence in the immeasurable friction interface, that is to say, that there is always a positive internal tribo-entropy, but to microscopic scale (phenomenon that necessarily is not presented in linear, relaxed, static equilibrium conditions). Thus, the thermodynamic analysis of irreversible non-equilibrium of the friction emerges coherently supported in the generic characteristics of operation of any tribological system, especially in the pseudo-lubricated condition (tribo-damage mechanics and lubrication failures).

In virtue of a consisting expression for the entropy rate of a roughness location, this paper explores the physical implications that provide the thermodynamic fluctuations of generic mechanochemical micro-gradients that inhabit the immeasurable friction interface (tribochemistry activated by mechanical means; roughness dynamics, textures, tribomutations, etc.). A conclusion suggests that the best roughness coefficient

Copyright 2011 Japanese Society of Tribologists 55

Rodrigo Bulnes

endures as a collision of dissipated exergy, that is to say, that possesses physical units. Thus defined, this friction number reaffirms the notion of third-body in tribology, and fits well to the Tribology in-situ program4), and sends to surface auto-organization concepts5), nicely shown in the selective transfer zero-wear phenomenon (STP)6).

2. Theoretical and experimental background

The approximation of third tribological body is a clear mechanical explanation about the chemical and metallurgical aspects of friction, wear and lubrication of materials (this approximation applies to the immeasurable and dynamically unstable friction interface in mixed boundary lubrication or without lubrication). It is proponed that a rubbing contact is formed by two first bodies (elements of the machine), and by an interface -or third body -, of a different composition, where the speed of the first two bodies accommodates. This accommodation is basically made up of chemical reactions and metallurgical flows (movements of vacancies, dislocations, composition changes, etc.) The third-body suggests that the friction coefficient is a key factor for understanding the tribochemical aspects of the contact. That is to say, the third-body leads to a mechanochemical concept for friction, in as much as the attribute accommodates tribo-mechanochemically to transmit mechanical power at speed...

The third-body is translates in stationary rubbing (with determinist or constant friction coefficient), when it is assumed that tribo-interface is a thermodynamically stable system. In this case, it would be enough to apply the First Law of Thermodynamics to conclude that friction is a kind of harm thermodynamically dominated via the heat of stationary friction, as proposed by the Bloks theory7), his derived relaxation8,9), the approximation of the temperature integral10) and others11). However, the Garkunovs STP-phenomenon under dry friction, impels us to reflex about the nature of the stationary rubbing itself... Zero wear phenomenon indicates an especial thermodynamic condition in which existing zero wear (with circulation of matter and energy among non-lubricated surfaces), the friction coefficient remains at a very low value (of hydrodynamic order). This only circulation or selective transference of species among surfaces, clearly defines a characteristic which is proper of dissipative systems, and structures far from equilibrium12), that is to say, the tribo-interfaces STP behaves as a self-organized system5), this does not necessarily means that friction is thermally dominated The friction process leads to genuine dissipative potentials, and it is neither necessary to resort to the notion of force (of rubbing) to clarify this.

It is possible to go further in the dissipative nature of the friction coefficient applying certain conditions of Irreversible Non-Equilibrium Thermodynamics to the

immeasurable tribo-interface. On one hand, on tribo-interface, there are dissipative processes of energetic exchange provided and self-reproduced by the gradient impositions (e.g. micro-fluctuations in temperature, speed, concentration, flow of vacancies, dislocation movements, third-bodys dynamics, etc.). On the other hand, and in virtue of the activation of those micro gradients by friction, the tribo-system remains far from thermodynamic equilibrium, including friction coefficient. The fluctuating nature of is widely known among tribologists, no mind if the tribo-system supports or not a thermodynamic stability in accordance with the First Law.

Using a ball-on-disk apparatus, Santner13) registers great friction fluctuations, even when load, speed, temperature and even relative humidity of the essay are constantly maintained. On the other hand, experimentally at nanometric scale, Gourdon et. al.14) confirm the persistent fluctuation of the friction force, assuring that it modifies its value even when maintaining all those (all external) parameters constant; and also the real contact area constant too, friction oscillates. According to Gourdon et al., the surface shear stress among rugosities presents time-spatial alterations due to the existence of superficial chemical inhomogeneities, that is, at last, friction fluctuations are due to a certain type of fundamental tribo-chemical activity grasped (internal) to the oxide layers and pollutants that is always possible to find settle on the surfaces (the idea of a surface of rubbing composed by thermodynamic micro-states -these micro-states understood as variables that obey to diverse thermodynamic potentials manifested as sliding rubbing-, would be very justified to the light of this type of experimental cross-checks. If it is thought that surfaces are formed by thermodynamic micro-states that activate the moment they interact (rub) with the other thermodynamic micro-states that conform the other surface, then a different perspective opens -different to the purely mechanical-, to refer to this thermodynamic process that will result of the rubbing among these micro-states: the friction coefficient).

In this paper, it is suggested that permanent internal micro-fluctuations of mass and energy, (tribomutations according to Duboka Arseni15)), dissipate a fluctuating friction, and do it by convoluting with the memory effect that provides a delay time anchored in the proper kinetic reaction to which those tribomutations force (certainly, this is a non-equilibrium mechanism...). That is to say, the friction coefficient turns out to be a delayed portion of the exergy internally dissipated by the tribo-interface, being this an aspect proper of absolutely irreversible thermodynamic systems16,17). It is demonstrated here that the observed trajectory for the friction coefficient (), comes from the collision between two movements difficult to be observed... and synchronized: 1. Gibbs Free Energy of reactions, (G0) and 2. fluctuations of its proper kinetics of

Japanese Society of Tribologists (http://www.tribology.jp/) Tribology Online, Vol. 6, No. 1 (2011) / 56


reaction coming from internal tribomutations ( )( tg ).

Most of all, a little variation in that internal dynamic dramatically alters the resulting convolution, that is to say, the collision .

3. Development of the third-body mechanochemical friction

Evident thermodynamic activity provided by tribomutations, well justifies the hypothetic existence of a generic internal rate of an always positive entropy production at the level of the immeasurable tribo-interface (friction is a robust irreversible phenomenon). That is to say, it is very possible that this internal tribo-rate of the interface is sustained on indirect factors, especially third-tribologicals body, and metallurgic flows at the friction sub-surface (the typical direct factors are temperature, pressure and speed of the tribo-system). This internal rate of always positive production of tribo-entropy, clearly puts the friction coefficient farther from its orthodox purely adhesive definition18), thermo-reologic8), and/or as a measure of the rubbing force (Da Vinci, Amontons and Coulomb), among others (the tribo-rate of internal entropy production will, sooner or later, complicate any calculation for the estimated average value of the oscillating coefficient of friction that is a non-deterministic quantity).

In agreement with the previous argument, it is very reasonable to suppose that the irregular behavior of the friction coefficient has its origin in the time/gradient complex mechanism that inhabits in the internal part of the immeasurable tribo-interface, as the central hypothesis of irreversible Non-Equilibrium Thermodynamics suggests when it raises the existence of internal kinetic -coordenates. In this sense, the variables or internal inhabitants , have thermodynamic representation (e.g. the fluctuation g, with g: micro-Gibbs Free Energy), but it is also possible to interpret them metallurgical (fluctuations of tribo-mutations, flow of vacancies, dislocations, changes in composition, etc.), and/or they can be considered as a generic mechanochemical activity coming from the third-body. In any way these internal conditions are interpreted, it is certain that the condition of order of the Thermodynamic state of the tribo-interface, will never be constant; the eventual order will be dynamic, because it must accommodate to the external conditions (relative humidity, contact pressure, speed and others), and internal (metallurgic flows, tribomutations, etc.). In synthesis, the immeasurable tribo-interface is a thermodynamically open system (see Fig. 1), and of feedback control (third-body circulation, mass and energy between the surfaces, etc.). In other words, the material tribo-interface has memory, and consequently, a constitutive relation for the friction coefficient, being unnecessary, as demonstrated here, to resort to the

molecular structure of the material components to refer to the fluctuating behavior of the dissipation process ...

The fundamental equation of the Thermodynamics was applied to a generic friction place, but considering a time differential dt sensitive to the internal fluctuations ; that is to say, and in accordance with the hypothesis of the thermodynamic local equilibrium, a differential dt that allowed to incorporate the possible time/gradient third-body mechanism in the definition of a tribo-entropy rate , with internal rate int) of irreversible entropy production. An expression of the type16,17) A

T

was obtained, where the friction coefficient denotes a dissipated thermodynamic process, is the thermodynamic force of stationary action (macro-temperature), denotes density, T an effective temperature, the average fluctuating and dominant internal kinetic process (the internal variable also denotes the advancement degree of a reaction of physicochemical nature), and A the internal affinity of the tribo-system (for example: concentration of species that however

fluctuate, the reciprocal thermic gradients that fluctuate, dislocations, vacancies, tribomutations, etc.). The expression for suggests that the friction coefficient has physical units (inclusive at stationary temperature ; aspect coherent with the treatment of Exergy that is given to the friction here). The friction coefficient corresponds with the extensive specific calorific power variable divided by the square of the effective

Fig. 1. Schematic representation of the immeasurable tribo-interface as an open thermodynamic system of feedback-control16). An exergetic friction coefficient (with physical units), considers the existence of a complex internal time/gradient mechanism that inhabits in the immeasurable tribo-interface (the coordinates definition of a purely mechanical friction coefficient only considers the existence of directly external influence on the tribo-interface)


Rodrigo Bulnes

temperature [W/kgK2] (lets notice Unit [kg] gives accounts of wear).

The expression for the rate of entropy internal production A

T

int , rises from the

physical-chemistry time/gradient-activity between

and A . As shown below: a linear relation between -fluctuations and the -dissipation, to the -stationary temperature, is made, invoking the Fluctuation-Dissipation Theorem (FDT)1):

).( ,)()()(

)()(])[(

with

and

0

00

AdtRt

dtRt

t

t

(1)

Equations (1) bind to each other (t denotes (macro)

time and denotes (micro) kinetic-time). Tribologically, these equations indicate that the immeasurable tribo-interface -at -stationary temperature-, steadily dissipates -friction via (but from the dynamics

provided by

R

). In other words, is associated to an average rate of tribo-chemical micro- reactions that - at a -stationary temperature-, (quasi) steadily dissipate the -process, after the rates compete thermodinamically and internally in the tribo-interface19). Competence is given between submicroscopic Free Energies, thinking they re create from flows of vacancies, movement of dislocations, internal friction, tribo-mutations, absorbed particles, wear particles, etc. Each of these phenomena provide its own submicroscopic flow of Free Energy, but the most evident are the -fluctuations coming from the competence between rates (that yield the response function R).

It will be demonstrated that a linear solution for

-based on the Gibbs Free Energy-, adapts well to certain observed trajectories for the friction coefficient in isothermal conditions5). This solution considers that at stationary temperature , the tribo-interface internal processes suffer small but persistent physicochemical fluctuations in conditions of quasi-static equilibrium. This is equivalent to suppose that the process fluctuates around its thermostatic quasi-equilibrium, always providing irreversibility or internal entropy (by its own microscopic definition).

The linear approximation APN , where N and P are phenomenological coefficients independent from time, requires that gbA ),( , where denotes external coordenates (e.g. pressure, speed, etc.), b is a new phenomenological coefficient, and g is

micro-Gibbs Free Energy internally generated by the friction system (does not seem this energy is susceptible of direct measurement. However, FDT indicates the power spectrum that would cause the dance of thermodynamical micro-fluctuations to tribo-contact level, must be measured, as it is possible to associate those power spectra to characteristic times t[] of processes () that react more internally... The respective autocorrelation analises could perfectly point out the emergency of the fractal dimensions associated to these times t/t ~][ ). This affinity -g~A indicates the degree of advancement of the direct kinetic reaction.

Finally it goes to an equation of the type1):

)( gP (2) where . From this eq. (2) the phenomenological micro-response (R) of the tribo-interface, at a stationary temperature , is extracted (so we have the terms that vary explicitly with the time, assuming that :

bNP 1

0~~GPgt-e(t)-Pgdt

d~G~

G 00

; that is to say,

-Pgte~P-PgttRd

ddR

)~G)(~(Pe

0 , see eq.

(1)2). It is a hypothesis of this work that Gibbs Free macro-energy G0, already out of the exponential scale, behaves as external variable. Thus, exothermic macro-dissipation of Free Energy (G0), fluctuates internally ( ) to stationary temperature ,

R

PgtPgt ee GtRPtR

1

0])[( (3)

where the phenomenological coefficient P denotes the behavioral conduct change of some local physical property of the tribo-system (e.g. a local vibration, a local physicochemical fluctuation linked to a time of relax (1/), local desorption, endothermic, exothermic, etc.).

Making some replacements (eq. (3) into eq. (1)1), the response of the friction coefficient as a genuinely mechanochemical friction of exergetic-linear order range, can be obtained17).

)1(])[( 100 PgteGt (4)

Here t[] = Pgt is the thermodynamic equivalent of the kinetic time . tgt

)/(



phenomenon is especially exergetic because the

fluctuations of Gibbs micro-Free Energy ( ) could perfectly be non-linear (from this we named them micro-Exergy!). On the other hand, if we notice that

G0 as well as denote different scalings linked to one only amount denominated friction, then the eq. (4) already poses the existence of a collision phenomenon

between scales G0 vs. to describe the attribute (this point will be developed in the next section, when implications of inverse kinetic reaction

tgPgt

tge

tge

g~A are explored).

Analysis follows with a viscoelastic analogy related to stationary macro-temperature . It poses an H-function complimentary to R that in the dominium of

time16)

P

PgttH ])[(])[( , where ])[( t

),...

(t[]), is the Diracs impulse function. In other words, and contradicting Continuum Media Mechanics, also appears animated by an energetic-pulsing phenomenon manifested in terms of an in-situ attribute of the tribo-interface ( (),(),(~ 210 ); that is, the time (t[]) = 0 = 0 can be associated to quick local changes in the way of dissipation of Gibbs Free micro-Exergy. Successive pulses indicate quick, intense and successive unfoldings of Exergy, in exothermic or endothermic conditions (states), depending exclusively on the laws of thermal, chemical and mechanical stability (but not exclusively of the stationary temperature...). This mechanism would force a permanent and spontaneous (exothermic) -or induced (endothermic)- adjustment among: the local temperature, the friction coefficient (now mechanochemically in-situ defined), and Gibbss Free micro-Exergy dissipated by the immeasurable tribo-interface. This is demonstrated by the partial integration of certain equation16,17):

dtttHtH

t

)(])[()0][(0

(5)

The integral expression to the right side of the eq.

(5) would correspond to the fluctuating thermodynamic micro-force -linked to g-, that forces to an irregular behavior of (by itself, eq. (5) demonstrates the mechanochemical nature of , inclusive under conditions of isothermic or stationary friction). At last instance, the third-body would be thermodinamically unstably due to a permanent incompatibility between

the state/process variables . Nevertheless, in the isothermal-relax equilibrium the integral of fluctuations of the eq. (5) disappears, and emerges a generic in-situ instantaneous relation of the type (considers a more consistent aspect of external

macro-fluctuation instead of ):

g

0~ G , where is the average friction coefficient and, as it has been explained, G0 (for t[] > 0) is the Gibbs Free macro-Energy of the tribo-system, but different from Gibbs Free micro-Exergy of microscopic and internal reactions that we have denoted for g and appearing linked to pulsations 0, 1, 2, etc. According to the integral expression of the eq. (5), internal phenomena effectively lead to an exponential scaling of in-situ dissipated energy (for t[] > 0 ).

Clearly the eq. (5) and previous, indicate that under the appearance of a thermically dominated friction, actually exists an exergetic dissipation of Gibbs Free micro-Exergy that appropiates the behaviour observed for the then badly named friction coefficient (there is a delay time () involved with all this description of dissipated potencies by friction). That is to say -and inclusive in the range of thermo-linear description of the rubbing phenomenon-, at stationary temperature exists a double in-situ dissipation of power linked to material rubbing..: one of them is the purely mechanical, classical and orthodox power ( VFP Nmec , where FN: normal load and V: sliding speed), and the other is the purely physicochemical power (G0 and g). However, the imbricated existence of a real dance of fluctuations of Gibbs Free micro-Exergy dissipated by the third-body (0, 1, 2, etc.), separates the factible and simultaneous observation of these two powers, but G0 and g appear as responsible for the wear (they would also be responsible for the tribological failures in general...).

3.1.Mechanochemical friction of third body as a collision phenomenon

A first linear link between the friction coefficient of mechanochemically defined (eq. (4)), and the generic Gibbs Free Energy dissipated by the immeasurable tribo-interface, has been deducted (besides, a non-lineal extension of (t[]) is also possible recurring to kinetics reactions dissipated in the sliding speed20)). In that sense, a remarkable quality of this Mechanochemical Friction Theory is that when it is used to calculate the Load Carrying Capacity of surfaces, they appear natural and spontaneously -in the speed-normal load plan of the transmitted power-, the 05 most enigmatic forms of failure of the Tribology (scuffing, pitting, micro-pitting, tooth-fracture and extreme-wear20-23)).

It will be demonstrated that it is possible to relate this deduction with the self-organization of metal surfaces phenomena5). In all this way of understanding friction, the friction coefficient will arise as a collision between Gibbs Free macro-Energy and the kinetic reaction aroused and incubated by the always positive internal tribo-rate of entropy production. Literally speaking, manifests conforms to a collision between time scales.


Rodrigo Bulnes

The + sign that accompanies the external factor

10 G (eq. (4)), comes from considering the

dominant presence of a kinetic of direct-dissipated exothermic reaction by the internal regime-scale of fluctuations ( Pgte~gA ); that is to say, the previous equation (4) has the following two spontaneous solutions (or the case of perfect equilibrium between adsorption and desorption we have : (t[]) = 0, with G0 = 0):

des.) (endoth. 0 ),1(ads.) (exoth. 0 ,

)1(])[(

00

00

100

GG

Gt

Pgt

Pgt

ee

e Pgt

(6)

For the opposite case, dominant presence of a kinetic

of inverse-dissipated reaction by the internal regime of fluctuations ( Pgte~gA ), appears a sign - that accompanies to the factor . The new internal dominant scale (kinetic), modifies the equation (4), the same as the two external solutions that should be considered as non-spontaneous solutions (especially exothermic desorption of reagents; physical adsorption is always Exothermic, but chemical adsorption may also be endothermic (several authors)):

10 G

Fig. 2. Representation of the curves predicted by the mechanochemical friction for a hypothetical homogenous tribo-interface (compare them with Polyakov5)). The curves come from understanding the friction coefficient as a collision between scales of energies present in the immeasurable tribo-interface. A scale is an issue of Gibbs Free macro-Energy (G0), and the other is dissipation of micro-kinetics of internal fluctuations ( , etc. internal fluctuations may be of first, second, etc., degrees, it is even factible to study intermediate degrees (fractals)). In other words fluctuations of internal reaction kinetics, may clearly become non-linear (absolutely irreversible), being more exact to think in internal pulsations of exergy. Thus, the mechanochemical is s certainly exergy dissipated in virtue of a collision between time scales: the external which is G0 and the internal which are kinetic pulsations. It can properly be said that -mechanochemical is a dissipated exergy which is supported for the collision between both scales. The endothermic non-spontaneous adsorption, can be understood as simple imposed desorption and the non-spontaneous exothermic desorption would turn to maintain a very low friction coefficient, so low that it quickly tends to a negative value...

tge

.)(exoth.des 0 ),1(ads.) (endoth. 0 ,

)1(])[(

00

00

100

GG

Gt

Pgt

Pgt

ee

ePgt

(7)

The following Figure 2, shows the trajectories that

this current third-body mechanochemical friction throws, in conformity with the predictions of the equations (6) and (7). It should be noticed that, eventually, the mechanochemical solution for the endothermic adsorption (see eq. (7)) might be interpreted as a desorption of reagents in products (the spontaneous thing is that there is exothermic adsorption of reagents in products). That is to say, the inverse reaction reagents products being endothermic, might perfectly drops to an externally forced desorption -as it is interpreted in curve 1 of Fig. 2 in Polyakov5)-, faced to a sudden imposition of contact load (that for the effects of the present analysis is an influence or external variable ):

In accordance with the ideas here raised, it is theoretically demonstrated that to establish a mechanochemical it is necessary to consider the effect that provides the collision between the time scales

G0 > = < 0 and or . However, such a tge tge



description of raises an important problem, as Fig. 2 scarcely recreates ideally homogeneous conditions. Nevertheless, the tribocontact is certainly heterogeneous, so that a formulation nearer to this aspect of reality is raised by the following non-linear equation for the mechanochemical (deduction of equations (8) and (9) are fully explained in Bulnes21-23)):

0~)( 2 tg (8) where is a parameter and denotes an operator (it could be estochastic). The previous equation has the form of Logic-Map of the Physics of CHAOS:

)( tg

)1()(1 ttt tg

(9)

where is an external parameter. The following Figure 3 shows the results of iterating the eq. (9) for two hypothetical cases: the operator , linked to exergetic fluctuations (which are internal), influences dramatically the dynamics observed for . This operator is dominant if compared with the effect provided bye border external conditions (0 and ).

))(/( tg

)( tg

Prediction of these results has an evidently qualitative character, but the holistic description that raises this mechanochemical of the third tribologicals body, is generic enough to allow the incorporation of effects coming from the coherent states, catalysis, synergy, structures and dissipative phenomena, etc..., all of them linked to the self-organization of surfaces5,24). In other words, this mechanochemical definition of the friction clearly adapts well to topics like selective transference (zero-wear Garkunovs phenomenon), energy dissipation mechanisms (Exergy), dissipation vs. friction (and wear) correlation, Wear Thermodynamics (predictions), CHAOS and complexity to different scales, thermodynamically external forces (radiation, electrical flow, magnetic flow, load, speed, etc.), lubrication failures, tribological harm, etc.

Theoretically, this mechanochemical friction should be fixed (for physical measure). That is, the purely mechanical aspect is directly measured from the friction force. However, the chemical aspect must be made, composed or structured, based on rates of tribo-chemical reactions, a chapter of Tribology which is closer to the triboscopy in-situ (the paper points out that immediatly arises a delay-time () between the coupling of mechanochemical and tribochemical processes). Thus, phenomenological coefficients N, P and b are variable attributes of the interface, that is, that can be transformed in quantities strongly dependent from the undirectional time provided by int. However, this paper only states the need to consider the

immeasurable tribo-interface as a heterogeneous system that dissipates an essentially unstable -process because of the practical incompatibility (and theoretical) synthesized in the expression

0~ G . The word incompatible as a synonymous of surfaces composed of micro-thermodynamic states in-situ, non-homogeneous among themselves.

Fig. 3. Result obtained from iteration of the equation (9) from t = 0, 1, 2, 3... Hypothetically, from the thermodynamic, metallurgic, physicochemical, etc. point of view, the immeasurable tribo-interface is an heterogeneous system, so much so that the observed friction may acquire a cyclical behavior (less heterogeneous (a), with parameter = 3,5), and even chaotic (more heterogeneous (b), with parameter = 4,0). According to the here raised, the microscopic kinetic-operator , is the subjacent-dominant phenomenon of the observed trajectory for (coherently, a coefficient of initial friction 0 = 0.1 and the parameter = 1.0, behave as external coordinates; behaves as a thermomechanical

)( tg

factor, eventually associated to the thermal resilience of the surfaces19)).


Rodrigo Bulnes

Finally, and for corroborating the nature of the collision of the mechanochemical , the Figures 4 and 5, show the resulting collision () between a unique Gibbs Free macro-Energy of reaction (G0) (Fig. 4), opposite to a light quantitative change between two fluctuation dynamics of Gibbs Free micro-Exergy

internal of kinetic reactions ( ) (Fig. 5, upper). Again, the -observed movement (Fig 5, below) comes, fundamentally, from an internal non-observed

movement ( ):

tg

tg

4. Conclusions

The present holistic description of friction suggests that the friction coefficient arises from the transition among the incubated Free micro-Exergy of the internal reaction kinetics ( ), and the Free macro-Energy of the external reaction (G0). Literally speaking, the -mechanochemical of third-body dissipated behaves as a collision among time scales. One of the scales is manifested to macro-measurement level G0 , whereas the other belongs to the probabilities space-state linked to internal kinetics ( ). These ideas are coherent with the physical checking that it is friction with the environment which eliminates probability waves underlying in the sub-atomic world, etc. That is to say, external dissipation of the process () converts reality -or own values G0 -, the probabilistic states that tribo-entropy internal dissipation linked to acquires. This process of tribo-convertion towards reality, could technically lead to the concept of decoherence25).

)( tg

)( tg

)( tg

Fig. 4. Two Gibbs Free macro-EnergiesG0, slightly varied between them (continuous lines and dotted lines. E: units of energy)

Fig. 5. The consistent variations of Gibbs Free

micro-Exergies of kinetics reactions , are expressed in % (upper). These two dynamic

fluctuations of , have the same average value; one is sinusoidal-stationary, and the other is irregular (dotted line). Clearly non-observed kinetics of these fluctuations, are the ones affecting the observed collision

(below)

)(g

)(g

0 G )1()( 10

tgetg

5. References

[1] Woods, L. C., The Thermodynamics of Fluid

Systems, Clarendon Press, Oxford; Oxford University Press, New York, 1975.

[2] Godet, M., The Third-Body Approach: a Mechanical View of Wear, Wear, 100, 1984, 437-452.

[3] Fronius, S., Maschinenelemente - Antriebselemente, VEB Verlag Technik, Berlin, 1971. (in German)

[4] Spikes, H., In-Situ Methods for Tribology Research, Tribology Letters, 14, 1, 2003, 1.

[5] Polyakov, A., Process of Self-Organization in Metals, A. A. Blagonravov Engineering Institute, Russian Academy of Sciences, Moscow, 29, 2, 1993, 19-27. (Traslated from Fiziko-Khimicheskaya Mekhanika Materialov).




[6] Garkunov, D. Kragelsky, I. and Polyakov, A., Selective Transfer in Friction Components, Transport, Moscow, 1969, 104. (in Russian)

[7] Blok, H., Theoretical Study of Temperature Rise at Surface of Actual Contact Under Oiliness Lubricating Conditions, Proc. of the Gen. Disc. of Lub. Inst., London, 2, 1937, 222-235.

[8] Escobar, E., The Additive EP-Condition and the Critical Scuffing Limit for Rolling-Sliding, Trans. ASME, Journal of Tribology (JOT), 118, 1996, 125-130.

[9] Escobar, E. and Escobar, C., Rheological 3-D Modeling of Scuffing for the EP-Additive Condition, Journal of American Standard Testing Material (ASTM) International (JAI), 2, 2, February, 2005, JAI12828.

[10] Winter, H., Michaelis, K. and Collenberg, H., Kontaktzeit-Methode zur Berechnung der Fre btragfhigkeit von Stirnradgetrieben, antriebstechnik, 31, 2, 1992, 57-65. (in German)

[11] Persson, B., Theory and Simulation of Sliding Friction, Phys. Rev. Let., 71, 8, 23 August, 1993, 1212-1215.

[12] Nicolis, G. and Prigogine, I., Self-Organization in Non-Equilibrium Systems, John Wiley and Sons, New York, USA, 1977.

[13] Santner, E., Reibkraftschwankungen- Quelle, Informationsquelle, Probleme, Tribologie - Fachtagung, Gttingen, Germany, 1999. (in German)

[14] Gourdon, D., Burnham, N., Fritz, M., Hhner, G. and Spencer N., Nanotribology and Macrotribology: the Relative Roles of Mechanics and Chemistry in Energy Dissipation Processes, http://www.snf.ch, 2001.

[15] Duboka, . and Arseni, ., Tribo-Mutations in Tribo-Mechanical Systems, 2nd International Conference on Tribology, Proceedings, Thessaloniki, Greece, Balkantrib, 1996, 703-710.

[16] Bulnes, R., Thermodynamical Facts of the Tribo-Interphase, Linked with the Additive EP-Reaction, Dipl.-Ing. Thesis, University La Serena, Chile, 1996. (in Spanish)

[17] Sariego, P. and Bulnes, R., The Friction Coefficient as a Exergetical Reaction (The Mechanochemical Friction), Latinamerican Review of Physics (RIF), 4, 1, 2008, 35-42. (in Spanish)

[18] Bowden, F. and Tabor, D., The Friction and Lubrication of Solids, Oxford University Press, Oxford, 1950.

[19] Zhang, F. and Lee, J., Friction-Induced Oscillatory Behaviour of One-Dimensional Detonations, Proc. R. Soc. Lond. A, 446, 1994, 87-105.

[20] Bulnes, R., Theoretical Friction and Surface Damage: Scuffing, Pitting, Micro-Pitting and Tooth-Fracture Limits, Session IV-special design considerations, Preliminary Program. American Gear Manufacturers Association (AGMA), 2004a.

[21] Bulnes, R., Theoretical Friction and Surface Damage: Scuffing, Pitting, Micro-Pitting and Tooth Fracture Limits, Binational Congress CONAMET/SAM, La Serena-Chile, 2004b. (in Spanish)

[22] Bulnes, R., The Friction Coefficient as a Thermodynamic Reaction, Journal Remetallica, Nr.11, Engineering Faculty, Metallurgical Department, University of Santiago de Chile (USACH), 2004c, 31-40. (in Spanish)

[23] Bulnes, R., Copyright Nr. 139.301, 2004d. [24] Abdel-Aal, H., Complexity, Synergy and

Emergence in Tribosystems: Toward an Alternative Theory for Damage in Sliding Contacts, Int. J. Materials and Product Technology, 38, 1, 2010.

[25] Zeh, H., The Physical Basis of the Direction of Time, 5th Edn., Springer, Berlin, Heidelberg, 2007.

Mechanochemical Friction of Third-Body as an Exergetic Collision1. Introduction 2. Theoretical and experimental background3. Development of the third-body mechanochemical friction4. Conclusions5. References

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