Evaluation électrochimique de la protection contre la corrosion d'une bicouche organique autoassemblée sur des substrats de laiton

Abstract

Brass is an alloy (Cu/Zn) commonly used in the manufacture. The major problem of brass is, as a lot of other metals and alloys, its corrosion. To further enhance corrosion resistance of brass we shall consider to the chemistry of self-assembly and more precisely the grafting of alkanethiol molecules. Prior to modification, it is of major importance to find an optimal pretreatment. The (3-mercaptopropyl)trimethoxysilane, (MeO)3Si-(CH2)3-SH, is the organothiol molecule which has been chosen. Once this bifunctionnal molecule chemisorbs onto brass by the thiol function forming a self-assembled monolayer, it presents a trimethoxysilane terminal group ('Si(OMe)3) pointing out at the surface. The next challenge is the determination of hydrolysis conditions able to bring those groups trough a siloxane framework containing silanol functions. To further prevent oxidation of the brass modified by the hydrolyzed monolayer, the grafting of a second organic molecule is considered. The (3-heptafluoroisopropoxy)propyltrichlorosilane, SiCl3-(CH2)3-O-CF(CF3)2, has been chosen for that purpose. This molecule reacts by condensation of its terminal -SiCl3 group on silanol functions still present in the network. Techniques used to characterize the bidimensional films formed on brass substrates are X-ray Photoelectron Spectroscopy (XPS) and contact angle measurements. The electrochemical cyclic voltammetry technique has been performed to evaluate the blocking of the substrate and the polarization curves provide essential information on the dissolution rate of the alloy along with the chemical modifications of the substrate.

Date of Award	2003
Original language	French
Supervisor	Zineb Mekhalif (Supervisor) & Joseph DELHALLE (Co-Supervisor)