What If the Protection against Oxidation of Chromia-Forming Alloys Was Not Always Due to the Chromia Layer?
Abstract
Chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts as a barrier between the oxidizing gases and the alloy substrates, forming a diffusion zone that limits the overall reaction rate and leads to parabolic kinetics. But this was not verified in the study devoted to Inconel®625 the oxidation in CO2 that was followed by TGA, with characterizations by XRD, EDS and FIB microscopy. Contrary to what was expected and accepted in similar studies on other chromia-forming alloys, it was shown that the diffusion step that governs the overall reaction rate is not located inside the chromia layer but inside the alloy, precisely inside a zone just beneath the interface alloy/chromia, this zone being depleted in chromium. The chromia layer, therefore, plays no kinetic role and does not directly protect the underlying alloy. This result was demonstrated using a simple test that consisted in removing the chromia layer from the surface of samples partially oxidized and then to continue the thermal treatment: insofar as the kinetics continued without any change in rate, this proved that this surface layer of oxide did not protect the substrate. Based on previous work on many chromia-forming alloys, the possibility of a similar reaction mechanism is discussed. If the chromia layer is not the source of protection for a number of chromia-forming alloys, as is suspected, this might have major consequences in terms of industrial applications.
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BibTeX
@article{contri2026what,
title = {{What If the Protection against Oxidation of Chromia-Forming Alloys Was Not Always Due to the Chromia Layer?}},
author = {Boris Contri and Stéphane Valette and Marina Soustre and Pierre Lefort},
journal = {American Journal of Analytical Chemistry},
year = {2026},
month = oct,
doi = {10.4236/ajac.2024.159019},
url = {https://unilim.hal.science/hal-05801455v1},
note = {CC BY},
}
RIS
TY - JOUR
TI - What If the Protection against Oxidation of Chromia-Forming Alloys Was Not Always Due to the Chromia Layer?
AU - Boris Contri
AU - Stéphane Valette
AU - Marina Soustre
AU - Pierre Lefort
PY - 2026
DA - 2026/10/15
JO - American Journal of Analytical Chemistry
DO - 10.4236/ajac.2024.159019
UR - https://unilim.hal.science/hal-05801455v1
AB - Chromia-forming alloys have good resistance to oxidizing agents such as O2, CO2, … It is accepted that the protection of these alloys is always due to the chromia layer formed at the surface of the alloys, which acts as a barrier between the oxidizing gases and the alloy substrates, forming a diffusion zone that limits the overall reaction rate and leads to parabolic kinetics. But this was not verified in the study devoted to Inconel®625 the oxidation in CO2 that was followed by TGA, with characterizations by XRD, EDS and FIB microscopy. Contrary to what was expected and accepted in similar studies on other chromia-forming alloys, it was shown that the diffusion step that governs the overall reaction rate is not located inside the chromia layer but inside the alloy, precisely inside a zone just beneath the interface alloy/chromia, this zone being depleted in chromium. The chromia layer, therefore, plays no kinetic role and does not directly protect the underlying alloy. This result was demonstrated using a simple test that consisted in removing the chromia layer from the surface of samples partially oxidized and then to continue the thermal treatment: insofar as the kinetics continued without any change in rate, this proved that this surface layer of oxide did not protect the substrate. Based on previous work on many chromia-forming alloys, the possibility of a similar reaction mechanism is discussed. If the chromia layer is not the source of protection for a number of chromia-forming alloys, as is suspected, this might have major consequences in terms of industrial applications.
SN - 2156-8251
SN - 2156-8278
ER -