Nanoscale studies of the atmospheric corrosion of copper protected by ultrathin organic films
Time: Fri 2021-10-29 10.00
Subject area: Chemistry
Doctoral student: Weijie Zhao , Yt- och korrosionsvetenskap
Opponent: Professor Guido Grundmeier, Paderborn University
Supervisor: Universitetslektor C. Magnus Johnson, Yt- och korrosionsvetenskap; Professor Christopher Leygraf, Materialvetenskap, Materialvetenskap, Kemi, Yt- och korrosionsvetenskap
Copper (Cu) has been utilised by humans for millenniums and has become an indispensable metal in modern industry and in our infrastructure. However, corrosion, as a natural process for metallic materials, takes place on copper surfaces in most environments. Thus, understanding corrosion and corrosion protection of copper is of utmost importance to maintain its performance and prolong the lifetime of the applications. Corrosion has been revealed to start from local weak areas of the copper surface. However, the corrosion initiation and propagation mechanism on copper on a molecular level are far from clear.
In this thesis, the corrosion initiation of copper under a simulated indoor atmosphere where formic acid and humidity are present was studied. The corrosion process was monitored in-situ, and the formed corrosion products were characterised on the macro-, micro-, and nanoscale by various analytical techniques from both horizontal and vertical directions of the corroded surfaces. The localised dissolution and formation of the Cu2O layer on narrowly separated areas on the nanoscale were observed both microscopically and spectroscopically. A novel technique, nano infrared spectroscopy (nano-FTIR), was used to probe the formed corrosion products on the nanoscale. Due to the novelty of nano-FTIR, only a few studies in corrosion science using this technique were reported. Thus, this thesis also shows the capability of employing nano-FTIR in corrosion studies.
The ability of ultrathin organic films to protect copper under indoor atmospheres was also studied in this thesis. The main focus was on octadecylphosphonic acid (ODPA), for which the self-assembly process was examined in detail. A multilayer formation of ODPA on copper was observed under the self-assembly deposition, and the thickness of ODPA films increased with the deposition time. The reason for forming multilayers was attributed to the Cu+ ion release during the deposition, resulting in the formation of a Cu+-ODPA complex. The protective ability of these self-assembled ODPA films as well as Langmuir-Blodgett (LB)-deposited films on non-oxidised and pre-oxidised copper was examined under the same exposure conditions as for the unprotected copper. A remarkable ability to protect the surface was observed for the self-assembled and LB-deposited ODPA films on pre-oxidised copper.