Abstract
The data from the authors’ earlier investigations show that molecules of zinc dithiophosphate (ZDDP) added to a lubricant can absorb energy emitted by a solid surface, which is where triboreactions occur. If the lubricant contains structures able to conduct energy, the ZDDP reactions can occur even at a relatively large distance from the solid surface, which should increase the effectiveness of ZDDP as an antiwear additive. The purpose of this paper was to verify the thesis that the tribocatalytic effect depends on the ability of the solid surface to emit electrons/energy and the ability of ordered molecular structures, such as carbon nanotubes (CNTs), to conduct energy and, most likely, to enhance the energy transfer. The tribological tests were performed using a TRB3 tribotester for 100Cr6 steel balls and uncoated or a-C:H coated HS6-5-2C steel discs. Polyalphaolefin 8 (PAO8) and PAO8 mixed with ZDDP and CNTs were used as lubricants. The results of the tribological tests suggested that: (a) the effect of the interactions between ZDDP and CNTs was clearly visible; (b) the structure and properties of the solid surface layer had a significant influence on the antiwear action of the ZDDP additive.
Highlights
Lubricants containing zinc dithiophosphates (ZDDPs) as antiwear additives have been used for decades
Various mechanisms of lubricating film formation have been developed and described, but most of them assume that molecules of a ZDDP additive undergo adsorption on the solid surface, and the chemical reactions lead to the formation of deposits on the solid surface, as well as the formation of reaction products inside the surface layer
We do not agree with this definition, claiming that, if the lubricant is treated as the environment, the lubricating film does not form in the tribological system; none of the processes occurring inside the thin lubricating film should be taken into account
Summary
Lubricants containing zinc dithiophosphates (ZDDPs) as antiwear additives have been used for decades. All the products of ZDDP reactions are considered to be responsible for lower values of the friction coefficient and better protection of solid elements against wear. Because of this mechanism, ZDDP reactions take place on the surfaces of the solid elements in contact. We do not agree with this definition, claiming that, if the lubricant is treated as the environment, the lubricating film does not form in the tribological system; none of the processes occurring inside the thin lubricating film should be taken into account It is well known, that the physical and chemical properties of the lubricant play a significant role under
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