VIBRATIONAL SUM FREQUENCY SPECTROSCOPY FOE IN SITU STUDIES OF INITIAL ATMOSPHERIC CORROSION OF ZINC INDUCED BY FORMIC ACID

摘要

With the access and recent development of interface sensitive analytical techniques, it has become possible to perform molecular in situ analyses of the interfaces involved under ambient atmospheric pressure conditions. The initial indoor atmospheric corrosion of zinc has been Investigated by vibrational sum frequency spectroscopy (VSFS). Vibrational sum frequency spectroscopy is an inherent surface sensitive technique which also gives information on the ordering of the molecules. It is used herein for probing the interface between the metal and the spontaneously formed aqueous adlayer. The zinc was exposed to humidified air to which formic acid (HCOOH) was added as corrosion stimulant. VSFS showed evidence of formate on the surface after exposure to 120 ppb formic acid, and the structure of the surface formates were seen to stabilize within approximately 90 minutes of exposure. This is in contrast with near-surface probing Infra red reflection absorption spectroscopy (IRAS) results which monitors a continuous increase in zinc formates beyond 90 minutes of exposure to formic acid and humid air. These results form evidence that the structure of the surface formates stays the same beyond 90 minutes of exposure, even though there is an ongoing corrosion process, as seen by the growth of the thin film of formates.