AN EXPLORATORY-STUDY OF VAPOR-PHASE LUBRICATION OF CERAMICS BY MONOMERS

Earlier studies on the use of the concept of tribopolymerization as an anti-wear mechanism for ceramics involved liquid carriers such as pure hydrocarbons (e.g. hexadecane) and mineral oils at temperatures ranging from ambient to 150 degrees C. Recent studies have been carried out to determine the effects of potential tribopolymer-forming compounds on ceramic wear in the vapor phase using an inert gas carrier. Three addition-type monomers selected on the basis of the tribopolymerization concept were studied. The liquid additives were heated, vaporized and delivered to an enclosed alumina-on-alumina ''pin-on-disk'' contact region by a stream of dry nitrogen gas. The results of tests at bulk specimen temperatures up to 145 degrees C showed that indeed significant reductions in ceramic wear were produced by the low vapor concentrations of these compounds in the nitrogen carrier gas. Alumina ball wear reductions of up to 99% were observed, and total wear reductions (ball and disk) of over 70% were also common. Colorful surface films visible to the naked eye were frequently observed. Higher compound delivery temperatures have a significant beneficial effect in reducing wear. Analysis of the worn surfaces using Fourier transform infrared micro-spectroscopy shows clear evidence of chemical reactions with the alumina surface to form soap-like compounds; in addition, evidence of surface polymerization with one of the monomers, diallyl phthalate, was obtained. It is believed that the surface films formed reduce adhesion and therefore decrease both wear and friction. These studies are continuing in an attempt to learn more about the detailed mechanisms involved.