Influence of the Deposition Parameters on the Properties of Bis-Triethoxysilylpropyl] Tetrasulphide (BTESPT) Layers on AA2024-T3 – An Ellipsometric Study

Abstract

A bis-sulphur silane (BTESPT) was used to produce thin protective layers on AA2024- T3, a structural aluminium alloy widely used in the aeronautic industry, being the coatings analysed ex-situ by ellipsometry. Despite a slight degree of film anisotropy evidenced by measurements at different angles of incidence, an optical model of a single homogeneous phase could be employed to describe the silane based layer. The information obtained allowed to characterize the influence of the operational deposition parameters on the film thickness and structural organization of the silane phase (evaluated by its optical absorption). It is shown that the silane concentration of the solution and immersion time determine the final thickness of the formed layer while the curing time does not affect significantly this parameter. On the other hand, it was observed a marked decrease of the optical absorption of the coatings submitted to curing temperatures of at least 100°C, which should be ascribed to a structural reorganization phenomena induced by the removal of water molecules from the film. The data gathered by ellipsometry were successfully corroborated by independent surface profilometry analysis of the films.