Locally Condensed Water as a Solution for In Situ Wet Corrosion Electron Microscopy

Abstract

In microstructural corrosion studies, knowledge on the initiation of corrosion on an nm-scale is lacking. In situ transmission electron microscope (TEM) studies can elucidate where/how the corrosion starts, provided that the proper corrosive conditions are present during the investigation. In wet corrosion studies with liquid cell nanoreactors (NRs), the liquid along the electron beam direction leads to strong scattering and therefore image blurring. Thus, a quick liquid removal or thickness control of the liquid layer is preferred. This can be done by the use of a Peltier element embedded in an NR. As a prelude to such in situ work, we demonstrate the local wetting of a TEM sample, by creating a temperature decrease of 10 ± 2°C on the membrane of an NR with planar Sb/BiSb thermoelectric materials for the Peltier element. TEM samples were prepared and loaded in an NR using a dual-beam focused ion beam scanning electron microscope. A mixture of water vapor and carrier gas was passed through a chamber, which holds the micro-electromechanical system Peltier device and resulted in quick formation of a water layer/droplets on the sample. The TEM analysis after repeated corrosion of the same sample (ex situ studies) shows the onset and progression of O2 and H2S corrosion of the AA2024-T3 alloy and cold-rolled HCT980X steel lamellae.

In-situ Electron Microscopy Observation of Initiation and Propagation of Wet H2S Corrosion on Steel

“…1a-c). A planar Peltier cooler on a thin SiN membrane (with thickness of 400-1µm) is fabricated to dissipate heat from the central part of the membrane to the Si body of the MEMS device, enabling local water condensation by reducing T~10°C only on the sample area [2]. To allow usage of the chip in a corrosive environment the whole chip is covered with a 40 nm Al2O3 layer using atomic layer deposition (ALD).…”

“…Wet H2S corrosion damages in the grain boundaries (GBs) are observed. Initiation and propagation of a corrosion pit in images (2)(3)(4)(5)(6) in the middle of pictures are imaged at each interval. At the beginning, by depletion of Fe ions, the intensity in the pit area drops and later on by forming the corrosion products, slightly greyish contrast appears in (5-6).…”