Continuous Monitoring of Oxygen Chemical Potential at the Surface of Growing Oxide Scales during High Temperature Oxidation of Metals

Abstract

The continuous monitoring of the oxygen chemical potential at a surface of a growing oxide surface formed in high temperature oxidation of a metal was developed. During the oxidation of nickel and cobalt at 1373 K in Ar-21%O 2 gas, the oxygen chemical potentials at the surface of formed NiO scale and CoO scale were slightly smaller than that in the atmosphere, because the growths of these oxide scales were mainly ratelimited by the diffusion of the constituent ions in the scales. The difference of the oxygen chemical potential between at the surface of CoO scale and in the atmosphere was larger than that between at the surface of NiO scale and in the atmosphere under the same oxidation condition, since the oxygen consumption rate for the oxidation of cobalt was larger than that of nickel. In the case of the oxidation of iron at 1373 K in Ar-CO-CO 2 gas mixture, the oxygen chemical potential at the surface of formed FeO scale decreased largely from that in the atmosphere, since the growth of FeO scale was very fast and mainly rate-limited by the mass transport from gas phase to the scale surface. The oxygen chemical potential at the surface of FeO scale increased with increment of CO 2 concentration in the atmosphere.

Tuning the Activity of Oxygen in LiNi0.8Co0.15Al0.05O2 Battery Electrodes

“…In the case of vacuum, although the thermodynamic driving force for oxygen loss should theoretically remain the same as in the He case, any loss of oxygen from the NCA surface will be quickly evacuated from the surface by the vacuum environment of TEM, and the O-K prepeak fades slightly early at 150 °C. In the reducing H 2 environment, oxygen from the surface is swiftly consumed 35 (presumably to form moisture), prompting drastic reduction of the TM ion to its metallic form (particularly Ni). 36 The rapid increase of the Ni (L 3 /L 2 ) ratio in P H 2 compared to P O 2 (Figure 3g) suggests that the Ni 4+ in the NCA undergoes reduction to Ni 2+ (or even Ni 0 ) rather quickly in the low-temperature regime.…”

Determination of Thermodynamic and Transport Properties of Non-Stoichiometric Oxides

“…Provided the oxygen pressure in the gas phase near the surface is known (as an example using a microsensor described in Section 2.1), the oxygen activity on the surface can be determined (see Section 4.1). Similar designs using calcia-stabilized zirconia cells have been tested for continuous monitoring of oxygen activity on the surface of growing scale during high temperature oxidation of metals [Akida et al, 2008].…”