In-situ characterisation of organosilane film formation on aluminium alloys by electrochemical quartz crystal microbalance and in-situ ellipsometry

Organosilane pre-treatments have been studied intensively during the last years in order to replace hexavalent chromium conversion treatments. The aim of this study is to follow in-situ the formation of this organosilane layer in solution. Two in-situ techniques, spectroscopic ellipsometry and electrochemical quartz crystal microbalance, were used to investigate the mechanism and the kinetics of this protective film formation. In-situ measurements highlight that the organosilane film observed after the drying process is not formed into the solution, but during the emersion and drying step. Hence, it has been possible to characterise the presence of a very thin organosilane layer in the order of a few monolayers using the in-situ techniques. This layer is responsible for the adhesion and growth of the overall organosilane layer observed ex-situ after drying.