Second‐harmonic generation technique for in situ study of passive film formation on carbon steel surfaces in aqueous solutions

Abstract

The aim of this work was to revisit second-harmonic generation (SHG) as a technique for the in situ analysis of oxide film formation on steel samples immersed in aqueous solutions and during electrochemical experiments. The measurements were compared to active reflectance spectroscopy (ARS), which is a more established in situ spectroscopy technique. Carbon steel electrodes were subjected to polarization in pH neutral and mild-alkaline electrolytes to provoke the formation of passive films. In situ SHG measurements allowed monitoring of compositional changes in the formed film, as the SHG intensity increased in the domain of stability of Fe 3 O 4 and decreased in the domain of stability of Fe 2 O 3 during potentiodynamic polarization. ARS, on the other hand, is suitable to monitor film thickness. ARS absorption increased along with film growth when moving in the anodic direction during potentiodynamic polarization. During 30 min cathodic polarization at −0.9 V Ag/AgCl sat. KCl in initially pH neutral the combination of SHG and ARS revealed the presence of an oxide film that was primarily composed of Fe 3 O 4 and with a thickness up to 0.7 nm.

Tafel slopes and exchange current densities of oxygen reduction and hydrogen evolution on steel

“…Reflectance spectroscopy has been proven to be an useful technique for the in situ monitoring of the oxide film growth, for iron and carbon steel. 48–50…”

“…The recorded reflection spectra were converted to absorption spectra, A , using the following approximation: 48 where λ is the wavelength, I the reflected light intensity, and I0 the light intensity of the initial (oxide-free) steel surface. Using the Beer-Lambert equation, considering the geometry of the current setup, the film thickness, d.1emfilm, can be computed: 50 where α is the reflection angle and Afalse(λfalse) and Kfalse(λfalse) the absorption and the coefficient of absorption for a certain wavelength. Karlsson et al 51 studied the optical properties of metal oxides on stainless steel, including Fe 3 O 4 and Cr 2 O 3 , which are most likely the dominant oxides of an oxide film on a X5CrNi18-10 stainless steel.…”

“…Reflectance spectroscopy has been proven to be an useful technique for the in situ monitoring of the oxide film growth, for iron and carbon steel. [48][49][50] In the current setup, the stainless steel was fixed in a three-dimensional (3D) printed ASA (Acrylic Styrene Acrylonitrile) sample holder, pressed against an O-ring, and placed in the electrochemical cell, orientating the steel surface parallel to the glass, which has a wavelength transparency between 220 and 2600 nm. Optical fibres, connected to a deuterium lamp (30 W) light source and the spectrometer (Thorlabs CCS200) were positioned 1 cm in front of the steel surface, with a reflection angle of 30 degrees.…”