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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.
Zinc materials are of high importance in the field of corrosion protection. For example, almost half of the annual production of zinc is used as anti-corrosive layer for steel components, particularly under atmospheric conditions. The corrosion protection is frequently ascribed to zinc carbonate species with low solubility which form on the metal surface under atmospheric conditions. Due to the technological importance and wide use of zinc materials, its corrosion behavior and the formation of reaction products has been intensively investigated over decades.
Assuming atmospheric corrosion conditions, an initial native passive film of few nanometers thickness forms spontaneously. It consists of zinc oxide and hydroxide, transforming into various species in dependence of the surrounding atmospheric conditions.
This study focusses on the investigation of corrosion product layers on massive titanium-zinc sheets, formed during short- and mid-term exposure experiments by Fourier-transformed infrared spectroscopy. This method enables the investigation of extremely thin native passive films which form during the initial hours of exposure. Furthermore, aged surface layers are analyzed which were formed by transformation of initial passive layers over the time of several weeks. The spectroscopic investigations are complemented by scanning electron microscopy (SEM/EDX) in order to obtain information on the chemical composition and morphology of the corrosion products. The combination of both methods offers a comprehensive view on the processes occurring in the early stages of zinc corrosion.