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Wear behaviour and tribochemical reactions of low molecular alcohols under boundary lubrication of the steel-on-aluminium system.

Kajdas Cz., Obadi M.

Tribologia

1999

nr 3

273-287

Tribochemistry of Alcohols is very complex and important from the practical piont of view. This paper relates to the research aiming at better understanding of the aliphatic alcohol tribochemistry.Using mostly the steel ball-on-alluminium disc friction system experiments were carried out to generate tribochemical reaction s on the aluminium discto analyse the formed deposits FTIR surface analysis was used.New adsorptionbandsmostly in the region of 1530-1550 cm-1 were found They are asssigned to the specific structure of organometallic compounds with -in many cases-include duble bonding in the reion of 1600-1650 cm-1.It was also found that the dissocitation constant (pKa)values of C1-C$alcohols control the steel ball wear for both steel-on-aluminium and steel-on-steelsystems.

W niniejszym artykule przedstawiono wyniki badań, mających na celu zrozumienie tribochemii alkoholi alifatycznych. Eksperymenty, polegające na generowaniu reakcji tribochemicznych na powierzchni dysku aluminiowego, przeprowadzano głównie w układzie tarciowym stal-aluminium. Do analizy odłożonych depozytów zastosowano mikrospektrofotometrię FTIR. Stwierdzono obecność nowych pasm absorpcyjnych zwłaszcza w obszarze 1530-1550 cm-1.Są one przypisywane specyficznej strukturze związków organometalicznych które w wielu przypadkach posiadaja wiązanie podwójne 91600-1650cm-1) Stwierdzono również że wartośc stałej dysocjacji pKa) dla alkoholi C1-C4 wpływa na wielkość zużycia kulki stalowej zarówno w układzie tarciowym stal-aluminium jak również w układzie sta-stal.

Kinetyka rozrywania wiązania w aromatycznych anionorodnikach oraz ich tworzenia

Jaworski J.S.

Wiadomości Chemiczne

1998

[Z] 52, 5-6

367-382

The theoretical model proposed by Savéant [10] for the kinetics of the cleavage of aromatic anion radicals containing potential leaving groups and of their formation from aryl radicals and nucleophiles (essential steps of the SRN1 mechanism, shown in the Scheme 1) is presented. In that model the bond cleavage in anion radicals is viewed as an intramolecular dissociative one electron transfer and the reverse reaction as an associative single-electron transfer. It leads to the quadratic relationship of the activation barrier DG= and the reaction driving force DG0 (eq. (9)), similar to the classic equation of the Marcus theory for the outer-sphere electron transfer. Experimental consequences of the Savéant model are also reviewed. They include the relationship between the cleavage rate constants k4 and the formal potentials of the radical anion formation E0RX?RX for the series of aryl chlorides and bromided in DMF (Fig. 3), solvent effects on the k4 values (Chapter 4) and the effect of substituents (Chapter 5). In particula, it was shown that the solvent effect on the thermodynamic contribution to the activation free-energy causes the increase of the cleavage rate constant for chloroanthracene radical anions with the solvent acceptor number (Fig. 4). However, for the dissociationof the C-Cl bond in radical anions of 4-chlorobenzophenone the solvent effect on the intrinsic activation barrier DG0=, given by eqs (13) and (14), is dominant and the intrinsic rate constant depends (Fig.5) on the solvent Pekar factor (1/eop -1/e0). The use of the Hammett equation to the cleavage rate constants is also discussed; it works in the case when the thermodynamic contribution to the activation barrier (eq. (12)) strongly depends on a substituent (Fig.6). All the reviewed experimental data on the kinetics of the bond cleavage and the formation of radical anions can be rationalized on the basis of the Savéant model.