Estudio de nuevos materiales, superficies e interfases en tribología

Abstract

The present PhD thesis includes the results of the research works on the preparation and characterization of nanofluids, carbon nanophases and epoxy matrix nanocomposites, and their applications in the reduction of friction coefficients, wear rates and surface damage of materials under different sliding conditions. Protic ionic liquid crystals with anions derived from fatty acids and other protic ionic liquids with biocompatible carboxylate citrate and succinate anions have been used in the development of new water-based lubricants, and in new dispersions containing graphene and nanodiamonds. Thin lubricant films generated, before the sliding, on the surfaces after water evaporation under mild conditions have shown excellent tribological performances, similar to those of the neat ionic liquids, but using a minimum amount of them. The combined use of commercial imidazolium ionic liquids and graphene gives rise to new dispersions with unprecedented rheological behaviour, as they present constant or increasing viscosity values under increasing temperature, as a function of graphene concentration. The new graphene dispersions in ionic liquids have been used as additives in an additive-free lubricant basestock and in a fully-formulated commercial motor oil, achieving good results even at high temperatures. New epoxy matrix nanocomposites have been obtained. The porous material obtained by addition of a short-chain protic ionic liquid shows a self-lubricating and self-healing behaviour. Uniform dispersions obtained when long-chain ionic liquids are added to the epoxy matrix, reduce friction coefficient and prevent wear even under very severe sliding or abrasion conditions. The new dispersions of long-chain ionic liquids or ionic liquids and graphene have been deposited on unmodified epoxy resin or carbon steel substrates to improve their tribological performance without modifying their bulk properties. In the first case, new materials with gradient composition are obtained, where the additives are localized only where they are needed, that is at the material surface. The research work described here makes use of many experimental techniques, standard tests and characterization equipments, and has been possible thanks to the cooperation with national and international research groups.