V. P. Bulatov

Influence of C60 Fullerene on the Oxidative Degradation of a Free Radical Poly(Methyl Methacrylate)

The results of studies of thermal and oxidative degradation of a free-radical poly(methyl methacrylate) (PMMA) and the influence of a fullerene C60 on these processes are considered. The best characteristic of the change of the thermal stability is the temperature shift of the entire thermal gravimetric (TG) curve (or the middle part of it), but not the shift of onset or the starting temperature of the mass loss. During oxidative degradation in air of PMMA, three processes occur practically simultaneously: thermal degradation, or scission of chains; oxidation, or insertion of oxygen atoms in the polymer chains and in products of the degradation; and a sublimation of degradation products. The competition between exothermic and endothermic processes results in sharp changes in the balance of heat energy in the system and the sign of the total heat effect. In accord with these changes all of the process of PMMA oxidative degradation can conditionally be divided into three stages. The introducing of small quantities of C60 in a system results in replacement of oxygen by a fullerene or to a partial avoidance of oxidation, as a result of which, at the first stage, a smaller quantity of degradation products is formed and oxidized. There is a “transfer” of degradation products and heat generation from the first, lowest temperature stage, to the third, highest one. Simultaneous application of DSC and TG techniques has shown that during oxidative degradation of PMMA, especially in the presence of a fullerene, there is a latent degradation manifested in exothermal effects on DSC curves without mass losses on the TG curves. The introducing of C60 results in narrowing of the peaks (by ∼1.5 times) on DTG and MTA curves that may be explained by the narrowing of a set of possible degradation reactions. The C60 molecules are divided during oxidative degradation of PMMA into two groups: linked (∼20%) and nonlinked with macroradicals of PMMA. The nonlinked molecules of C60, in turn, are subdivided into oxidized and volatilizing without oxidation and degradation. The inhibiting effect of C60 on the thermal oxidative degradation reduces basically to two processes: to formation of fullerene-containing chains of PMMA and to nonchain inhibition. The matrix of PMMA also has a significant influence on the thermal behavior of C60.

Express investigations of wear processes by means of cylindrical counterbodies. Part I: Calculations and technique

Abstract Linear wear intensity Ih was calculated for a fixed cylindrical body which is initially in contact along a single line with another cylindrical body rotating at a constant velocity. The equation I h = Zhf(L) L f (L) was obtained for Ih, where h is the depth of the wear groove formed along the path L, f(L) and f(L) are the instantaneous and average friction coefficients, respectively, and Z is a constant in which the shape of the counterbodies is taken into account. The validity of the energy wear concept was assumed in the calculation. On the basis of these calculations a rapid technique for studying wear processes was proposed. In this technique the usual preliminary formation of the wear groove is absent. The technique was used for testing different commercial materials (steels, bronze and brass) lubricated with different oils. The tribological characteristics of the materials, determined by proposed method, are in agreement with literature data.

The effect of fullerene C60 on the thermooxidative degradation of a free-radical PMMA studied by thermogravimetry and calorimetry

Thermogravimetric and calorimetric study of the effect of fullerene C60 on the thermooxidative degradation of free-radical poly(methyl methacrylate) revealed three stages in the process.

On the influence of fatigue on machine part wear

Abstract The main aspects of the relationship between fatigue and machine part wear are considered and the relevant problem is formulated. The results of an investigation of the influence of the fatigue process on machine part wear are given for diesel engine piston rings. As the results show, the solution of the problem could open up new prospects in the development of the theory of machine part cyclic wear and the details of the technology of cyclic straining treatments for increasing fatigue wear resistance.