A Kelvin probe force microscopy study of hydrogen insertion and desorption into 2024 aluminum alloy

Abstract

Hydrogen was inserted into 2024 aluminum alloy by cathodic polarization in sulfuric acid at 25 C. Scanning Kelvin Probe Force Microscopy (SKPFM) measurements performed perpendicularly to the charging side revealed a potential gradient and confirmed the insertion of hydrogen over hundreds of microns. A hydrogen diffusion coefficient of 1.7 Â 10 À9 cm 2 s À1 was calculated from SKPFM measurements of H-charged samples for different durations. The evolution of the potential gradient during desorption of hydrogen in air, at room temperature and at 130 C was investigated. Additional experiments performed at a corrosion defect showed that SKPFM could detect both reversibly and irreversibly bounded hydrogen. These results show that SKPFM is a cutting-edge technique for hydrogen detection and localization at a local scale.

Hydrogen mapping in an aluminum alloy using an alternating current scanning electrochemical microscope (AC-SECM)

“…Note that the peaks in | i norm | at x~50 μm before heat treatment and at x~300 μm after heat treatment are associated with the presence of intermetallic compounds. Similar changes in the potential gradient were observed using SKPFM after heat treatment [13,14]. This result confirms that the current gradient observed before the heat treatment is due to the presence of H in the material.…”

“…The potential gradient was observed at a similar distance as for the current gradient, i.e.~400 μm. The potential gradient observed in SKPFM for H-charged AA 2024 samples was confirmed to be due to hydrogen in an independent gas fusion analysis [13], and also in secondary ion mass spectroscopy (SIMS) measurements by Larignon et al [16]. The good agreement between the distances over which the current and potential gradients are observed confirmed that the observed | i ac | increase for small x is due to the presence of hydrogen.…”

“…Full details of the charging procedure can be found elsewhere [13,14]. Briefly, hydrogen was inserted into the AA 2024 by electrochemical charging at 25°C in 10 mM H 2 SO 4 (≥95% Sigma Aldrich).…”

“…A Pt counter electrode and a saturated calomel reference electrode (SCE) were used. A charging potential, E, of − 0.8 V vs SCE was applied for 15 h or 48 h to ensure that a detectable amount of hydrogen was introduced into the material with a homogeneous distribution of H in a plane parallel to the charging side [13,14]. The solution was stirred with a magnetic stirrer during cathodic charging.…”

“…All SKPFM measurements were performed in air at room temperature. More details of the SKPFM measurement procedure are available elsewhere [13,14].…”