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Activation energy of tribochemical and heterogeneous catalytic reactions

100%

Kajdan C. K. , Kulczycki A. , Kurzydłowski K. J. , Molina G. J.

Materials Science Poland

2010

tom Vol. 28, No. 2

523--533

The relationship between the activation energy and enthalpy, either in the presence or absence of a catalyst, is of particular importance. If a catalyst is present, the energy required for a given chemical reaction to go into transition state decreases, thereby decreasing the energy required to initiate the reaction. The dynamics of heterogeneous catalysis is still under discussion. The same applies to tribochemistry and/or tribocatalysis. It has been assumed that heterogeneous solid catalysts decrease the activation energy, reflected as apparent activation energy. The model presented elsewhere has been theoretically evidenced for the first time by reviewing the existing literature data concerning anisotropy features of the angular distribution of exoelectrons emitted from perturbed surfaces. Metal-insulator-metal thin film sandwich structures are of particular interest in this paper. Other evidence supporting the model is also discussed such as the anisotropic desorption emission from a surface during catalytic processes. The conclusions of this work have been applied in practice to design specific measurement techniques and devices for estimating the angular distribution of electrons triboemitted from solid catalyst materials under sliding contact in a high-vacuum tribometer.

Importance of low-energy triboelectrons for the initiation of tribochemical reactions

100%

Molina G. J. , Kajdas C. , Furey M. J. , Ritter A. L.

Tribologia

2003

tom nr 1

103-121

Mechanical energy associated with the boundary lubrication process releases a large number of physical phenomena. Energy outputs from rubbing can be the cause of tribochemical reactions between the friction components and lubricant molecules. In this, different charged-particles, e.g., electrons and positive ions, may be emitted from solids during rubbing. This paper discusses the role of triboemitted charged-particles on the initiation of tribochemical reactions. The hypotheses and mechanisms regarding the possible action of charged-particles, in particular lowenergy electrons, on tribochemical processes are reviewed. Connections are made between relevant tribochemical reactions, tribopolymerization among them, the Negative-Ion Radical Action Mechanism (NIRAM) and recent experimental results in the fields of triboemission and tribochemistry. A new instrument for the measurement of charge intensity and energy spectrum of triboemitted particles is briefly described. The authors' experimental findings, that mostly low-energy electrons (0-5eV) are triboemitted from alumina and sapphire sliding-contacts, are discussed with a focus on the mechanism of vinyl-type tribopolymerization. Finally, future plans are presented to use this instrument for further investigating the role of triboemission on tribochemistry.

Energia mechaniczna związana z procesem smarowania granicznego wywołuje szereg zjawisk fizycznych, które inicjują reakcje tribochemiczne. W artykule omówiono rolę triboelektronów w inicjowaniu procesu tribopolimeryzacji winylowej, zgodnie z koncepcją NIRAM. Opisano nowe urządzenie do badania procesu triboemisji. Najważniejszym osiągnięciem zrealizowanych badań na nowym urządzeniu jest stwierdzenie, że energia głównej części triboelektronów emitowanych z korundu i szafiru w styku ślizgowym jest zawarta w przedziale od O do 5 eV. Przedstawiono plan wykorzystania zbudowanego urządzenia do dalszych badań wpływu procesu triboemisji na proces inicjowania i przebiegu reakcji tribochemicznych.