Date of Award
Doctor of Philosophy
The formation mechanism of boundary film obtained with the overbased calcium sulfonates was investigated.;Firstly a physico-chemical analysis of the overbased calcium sulfonates was achieved. The structure, the size and the polydispersity of the micelles formed by the additive in oil, and the nature of the interactions existing between them were studied using Small Angle X-Ray Scattering (SAXS). Different parameters which can influence the micellar structure such as pressure, temperature and water, were also studied.;Secondly, the formation of the boundary film was studied using an alternating tribometer. The Infrared Reflexion Absorption Spectroscopy by Polarization Modulation (PM IRRAS), the Scanning Electron Microscopy (SEM) and the Atomic Force Microscopy (AFM) were used to investigate the boundary film.;The overbased calcium sulfonates form in oil micelles consisting of a calcium carbonate core of 2.0 nm surrounded by a calcium sulfonate layer of between 0.9 and 2.2 nm in thickness depending on the concentration. In concentrated solutions, the micelles are subjected to steric repulsions caused by the cluttering of the sulfonate chains. In diluted solutions, an attractive energy of the order of 1 kT exists between the micelles leading to their aggregation. When water is added, this attractive energy is increased by a factor of 10. When the additive is submitted to friction constraints, its micellar structure is modified. The film formation is related to the adsorption of the calcium carbonate on the surface and to the expulsion of the sulfonate chains surrounding the micelle cores.;The film formation is achieved during the first seconds of friction and it grows by agglomeration and crystallization of calcium carbonate cores bared of their calcium sulfonate layer. The boundary film partially recovers the friction surface and its thickness increases during the first hour of friction. The maximum local film thickness may reach 1 micron. The crystallization phenomenon carries out principally on the prominent parts of the film and leads to the formation of calcite particles with very polydispersed sizes, of between few ten and few hundred nanometers. In presence of water, the film formation kinetics is slower and the calcium carbonate partially crystallizes.
Giasson, Suzanne, "Mecanisme D'action Des Sulfonates De Calcium Hyperbasiques En Regime De Lubrification Limite" (1992). Digitized Theses. 2233.