Friction chemical effects

The goal of lubrication is elimination of this wear and minimizing friction otherwise encountered in dry sliding. This is accompHshed ideally with complete separation of the mbbing surfaces with a full film of lubricant. When complete hill-film separation is impossible, surface chemical effects of a lubricating oil and its additives, or solid-film lubricants such as graphite and molybdenum sulfide, can assist. 

Syllabus (1957-1958) pp 137-38 (Frank-Kamenetskii formulation) 151-62 [Session 13, entitled "Hetergeneity of the Initiation Process , includes initiation of solid expls by impact, friction, thermal effect, elastic waves by ultrasonic vibrations, electromagnetic energy and chemical influence. 

There are, in principle, two ways in which solvents can affect the reaction rates of homogeneous chemical reactions through static, or equilibrium, solvent effects and through dynamic, or frictional, solvent effects [463, 465, 466]. 

The implantation of a considerable dose of metals or non-metals in materials led to large changes of the friction coefficient. The effect of Ar" is certainly mainly due to the creation of a new surface topography or to variations of the natural oxide layer of the material. Non-inert ions as Pb, Mo and Se showed some chemical effect dependent on the type of element introduced. The greatest effect came from lead implantation and was interpreted as a change in the plastic properties of the junction events. Eventually, also the formation of PbO at the surface should be considered. 

The similar chemical effects of frictional and voltaic electricity led him to conclude that they were identical, long before such a view became commonplace. Later, after perfecting the process of drawing extremely fine platinum wires, Wollaston constructed his "thimble battery", which was a very small galvanic cell capable of bringing a platinum filament to incandescence upon iimiersion in dilute vitriolic acid. Both demonstrations illustrate Wollaston s talent for eadiibiting natural phenomena by means of inexpensive "shirt-pocket" devices. 

O Geometry and Chemical Effects on Friction and Adhesion under Negligible Loads... 

Motivated by this recent interest in monolayer lubricants, molecular dynamics (MD) simulations have been used to examine monolayers of w-alkanes that are chemically bound or anchored to diamond substrates. A new empirical-potential energy function, which is capable of modeling chemical reactions in hydrocarbons of all phases, has been developed for this work (15). A single-wall, capped armchair nanotube is used to indent these hydrocarbon monolayers and to investigate friction. The effects of tip flexibility and tip speed on indentation and friction are examined. Particular attention will be paid to the formation of defects and bond rupture (and formation) during the course of the simulations. Previous MD simulations have examined the structure (16-18) and compression of -alkanethiols on Au (19,20). The major difference between those studies and the work discussed here is that irreversible chemical changes (or changes in hybridization associated with bond rupture and formation) are possible in these studies. 

One of the possible origins of static friction in macroscopic systems is the presence of third bodies between the solids (67). These typically include wear debris, adsorbed atmospheric molecules, dust, and thin lubricant films. Like the thin films considered here, third bodies have more degrees of freedom than crystalline surfaces. This allows the combined system of bounding surfaces and third bodies to lock into local energy minima, and can produce static friction. Chemical heterogeneity, surface roughness and length scale can also lead to static friction (67), and more work is needed to establish which effects dominate in different limits. 

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