The combination of minimally invasive electrochemical investigations and FTIR-spectroscopy to analyze atmospheric corrosion product layers on zinc

The present work describes the combination of electrochemical investigations by using a gel-type electrolyte with Fourier-transformed infrared spectroscopy to investigate partially extremely thin corrosion product films on titanium-zinc. The gel pad method enables the determination of corrosion relevant parameters such as the potential and the linear polarization resistance without altering the corrosion product layers, which are extremely prone to re-dissolution when freshly formed. Complementary infrared spectroscopy enables the determination of main compounds of even very thin surface layers of few tenth of nanometers with a certain lateral resolution. It was found that zinc forms mostly zinc carboxy-hydroxides such as hydrozincite, under various exposure conditions. The protective properties of these hydrozincite layers depend on the structure of the corrosion product film rather than on its thickness. In mid-term exposure tests, shallow corrosion pits were found even in the absence of corrosive agents such as chloride.