Surface Chemistry of Components on Aqueous Metal Working Fluids
Doctoral thesis, 1996
The aim of the work presented in this thesis is to contribute to an increased knowledge regarding the basic surface chemistry of water based metal working fluids, in particular the relation between aggregational behaviour in solution and the formation of technical important adsorption layers of e.g. boundary lubricants and corrosion inhibitors on metal oxide surfaces.
Adsorption from simple and more complex model fluids onto solid surfaces has been measured by solution depletion analysis and results have been compared with data for the aggregational behaviour of constituent surfactants in solution. Microcalorimetry has been utilised as a tool not only for the study of enthalpies of solution but also, in combination with oxygen partial pressure measurements, as a rapid and sensitive instrument in corrosion research.
Competitive adsorption on .gamma.-alumina of constituents of a multi component model aqueous metal working fluid under varying conditions of pH, component concentrations, substrate surface porosity and temperature displayed i.e. that high concentrations of a cosolvent may decrease the density of adsorption for all other components and that temperature more greatly affects the composition of the adsorbed layer than the total adsorbed amount.
The bolaform surfactant bis(triethanolammonium) 1,10-decanedicarboxylate was found to exhibit two different critical points of aggregation in solution as indicated by results of pH, surface tension, conductivity and heats of dilution measurements at varying concentrations. The aggregational behaviour in solution was found to relate to two plateaus in the adsorption isotherm of the surfactant on magnetite. A three stage adsorption model was evoked as an explanation for the observations. The corrosion inhibitory performance of the component versus cast iron was also shown to be related to the aggregational behaviour in solution and on a solid surface. The compound behaved as a corrosion inhibitor in the presence of air, but promoted cast iron corrosion under oxygen starved conditions.
metal working fluides