A multimodal approach to revisiting oxidation defects in Cr2O3

Abstract

The oxidation of chromium in air at 700 °C was investigated with a focus on point defect behavior and transport during oxide layer growth. A comprehensive set of characterization techniques targeted characteristics of chromium oxide microstructure and chemical composition analysis. TEM showed that the oxide was thicker with longer oxidation times and that, for the thicker oxides, voids formed at the metal/oxide interface. PAS revealed that the longer the oxidation time, there was an overall reduction in vacancy-type defects, though chromium monovacancies were not found in either case. EIS found that the longer oxidized material was more electrochemically stable and that, while all oxides displayed p-type character, the thicker oxide had an overall lower charge carrier density. Together, the results suggest anion oxygen interstitials and chromium vacancy cluster complexes drive transport in an oxidizing environment at this temperature, providing invaluable insight into the mechanisms that regulate corrosion.

Electromigrated Gold Nanogap Tunnel Junction Arrays: Fabrication and Electrical Behavior in Liquid and Gaseous Media

“…We hypothesize that this reconfiguration might be related to the electrochemical reduction of chromium oxide in the vicinity of the gold tunnel junction. Chromium in the vicinity of the tunneling gap formed after self-breaking is likely to have oxidized to Cr 2 O 3 during the prolonged immersion in DIW . The abrupt conductance decrease observed at V < −300 mV could then be due to mechanical displacements of the gold junction caused by the electrochemical reduction of Cr 3+ to Cr 2+ (the standard reduction potential is ∼−0.407, indicating that the reduction of chromium is possible at moderately low applied negative bias).…”

“…Chromium in the vicinity of the tunneling gap formed after self-breaking is likely to have oxidized to Cr 2 O 3 during the prolonged immersion in DIW. 62 The abrupt conductance decrease observed at V < −300 mV could then be due to mechanical displacements of the gold junction caused by the electrochemical reduction of Cr 3+ to Cr 2+ (the standard reduction potential is ∼−0.407, 63 indicating that the reduction of chromium is possible at moderately low applied negative bias). If the measured current were dominated by tunneling current across a gold junction and the physical changes due to the reduction of Cr 3+ in the vicinity of the junction caused atomic scale displacements of the cathode with each I – V sweep, it is probable that the tunnel junction would show abrupt changes in conductance above a certain applied negative voltage bias yet remain active afterward, since the gold is still intact albeit displaced.…”

Evolution of micro-pores in Ni–Cr alloys via molten salt dealloying

“…Here we only identified Cr 2 O 3 as the reaction product. The Na 2 CrO 4 formation may be inhibited due to the low amount of O 2 in the environment, which could play a key role in impacting the surface-mediated processes 57 including corrosion as shown in a recent multimodal study 58 but also other functional properties such as catalytic reactivities. The effect of a molten salt environment in contrast to the aqueous corrosion environment should also be discussed further.…”

The effect of different surface treatments of 310S austenitic stainless steel on the corrosion behavior in supercritical water using slow positron methods

“…In this experiment, the defect behaviors and transport processes involved in the growth of near-surface oxide layers are deeply profiled by means of slow positron beam measurements, which are inspired by the limited available publications for the microstructural characterization of the surface oxides and their chemical composition. [33,40,[46][47][48] Slow positron beam techniques, with their unique characteristics of macroscopic probing and microscopic diagnosis, offer novel perspectives and complementary research avenues for future characterization methods in this field.…”