304 stainless steel was oxidized using an induction coil under the following conditions: atmospheric atmosphere at 900°C, steam atmosphere at 900°C, and steam atmosphere at 1000°C. After the experiment, the oxide film thickness of the specimen oxidized in the atmospheric atmosphere at 900°C was approximately 5 μm, while the oxide film thickness of the specimen oxidized in the steam atmosphere at 900°C was about 20 μm, and the oxide film thickness of the specimen oxidized in the steam atmosphere at 1000°C was 45 μm. To determine the composition of the oxide films, XRD analysis was conducted. In the XRD data for the specimen oxidized in the atmospheric atmosphere at 900°C, Cr₂O₃ was detected at a high level, and an increasing trend in the background was observed. I am curious why only this specimen shows an increasing trend in the background.
In dry air at 900°C and a short holding time, a thin and dense oxide layer of Cr2O3 forms on the surface of AISI 304. If the temperature is increased or the holding time is extended, the oxide layer becomes much thicker, more porous and no longer consists of pure Cr2O3, but of oxides of all three elements (Fe, Ni and Cr), with the amounts of iron and nickel oxides exceeding the amounts of chromium oxide. The same also occurs in moist air with short exposure times at 900°C, because moist air is more aggressive to the steel surface than dry air.
Vadim Verlotski
Thank you for your previous response. What I’m curious about is why the background data in the XRD pattern, excluding the peaks, shows an upward trend for the sample heated at 900°C in air. Do you happen to know the reason for this? For your reference, all samples were heated for 2 hours.
Thin Cr2O3 layers are amorphous and the thicker layers of mixed oxides are crystalline. This explains the background data.
The background of an oxide film oxidized under atmospheric conditions increases mainly due to surface roughness, contamination, and changes in microstructure. These factors lead to increased light scattering and absorption, as well as potential interference effects, which contribute to a higher baseline in analyses.
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