TY - JOUR

T1 - Formation of uranium-, vanadium- and chromium-bearing reduction spheroids in karst bauxite of the Unterlaussa mining district (Austria)

AU - Hampl, Ferdinand

AU - Dunkl, István

AU - Schmidt, Burkhard C.

AU - Bertrandsson Erlandsson, Viktor

AU - Melcher, Frank

PY - 2025/2/10

Y1 - 2025/2/10

N2 - Hydrogen embrittlement can cause a sudden failure in metallic materials, especially in industrially relevant alloys like steels. Understanding hydrogen's interactions with microstructural features is key to preventing hydrogen-induced damage and supporting a hydrogen-based economy. We use Kelvin probe-based potentiometric hydrogen electrode methods and thermal desorption spectroscopy to provide quantitative results on how controlled chromium contents, dislocation densities, and grain sizes affect hydrogen diffusion and uptake in FeCr alloys. The effective hydrogen diffusion coefficient for Fe–16Cr is ∼39 % higher than that of Fe–21Cr. While the hydrogen diffusion coefficient decreases with increasing Cr content, the hydrogen uptake increases with higher Cr content. For Fe–21Cr having 0.58 ± 0.01 wt.ppm hydrogen is measured, compared to 0.44 ± 0.02 wt.ppm for Fe–16Cr and 0.43 ± 0.01 wt.ppm for Fe–9Cr. In Fe–21Cr, a two-order of magnitude increase in dislocation density raises the hydrogen absorption from 0.58 ± 0.01 wt.ppm to 1.53 ± 0.05 wt.ppm and reduces the apparent hydrogen diffusion coefficient from (2.86 ± 0.03) × 10−6 cm2/s to (1.29 ± 0.01) × 10−7 cm2/s. Reducing the grain size from 1049 ± 51 μm to 0.3 ± 0.1 μm in the Fe–21Cr alloy lowers the apparent hydrogen diffusion coefficient from (2.86 ± 0.03) × 10−6 cm2/s to (1.92 ± 0.12) × 10−8 cm2/s, while increasing absorbed hydrogen from 0.58 ± 0.01 wt.ppm to 11.08 ± 0.12 wt.ppm. Finally, our newly developed nanohardness-based method is validated to determine the hydrogen diffusion coefficient using in situ nanoindentation testing. This approach allows simultaneous measurement of the dynamic mechanical response and hydrogen diffusivity in FeCr alloys during continuous hydrogen supply, as the hydrogen flow is unidirectional.

AB - Hydrogen embrittlement can cause a sudden failure in metallic materials, especially in industrially relevant alloys like steels. Understanding hydrogen's interactions with microstructural features is key to preventing hydrogen-induced damage and supporting a hydrogen-based economy. We use Kelvin probe-based potentiometric hydrogen electrode methods and thermal desorption spectroscopy to provide quantitative results on how controlled chromium contents, dislocation densities, and grain sizes affect hydrogen diffusion and uptake in FeCr alloys. The effective hydrogen diffusion coefficient for Fe–16Cr is ∼39 % higher than that of Fe–21Cr. While the hydrogen diffusion coefficient decreases with increasing Cr content, the hydrogen uptake increases with higher Cr content. For Fe–21Cr having 0.58 ± 0.01 wt.ppm hydrogen is measured, compared to 0.44 ± 0.02 wt.ppm for Fe–16Cr and 0.43 ± 0.01 wt.ppm for Fe–9Cr. In Fe–21Cr, a two-order of magnitude increase in dislocation density raises the hydrogen absorption from 0.58 ± 0.01 wt.ppm to 1.53 ± 0.05 wt.ppm and reduces the apparent hydrogen diffusion coefficient from (2.86 ± 0.03) × 10−6 cm2/s to (1.29 ± 0.01) × 10−7 cm2/s. Reducing the grain size from 1049 ± 51 μm to 0.3 ± 0.1 μm in the Fe–21Cr alloy lowers the apparent hydrogen diffusion coefficient from (2.86 ± 0.03) × 10−6 cm2/s to (1.92 ± 0.12) × 10−8 cm2/s, while increasing absorbed hydrogen from 0.58 ± 0.01 wt.ppm to 11.08 ± 0.12 wt.ppm. Finally, our newly developed nanohardness-based method is validated to determine the hydrogen diffusion coefficient using in situ nanoindentation testing. This approach allows simultaneous measurement of the dynamic mechanical response and hydrogen diffusivity in FeCr alloys during continuous hydrogen supply, as the hydrogen flow is unidirectional.

KW - reduction spheroids

KW - Karst bauxite

KW - Uranium mineralization

KW - secondary chromium mineralization

KW - Unterlaussa

KW - Gosau

U2 - 10.1016/j.gexplo.2025.107709

DO - 10.1016/j.gexplo.2025.107709

M3 - Article

VL - 272.2025

JO - Journal of geochemical exploration

JF - Journal of geochemical exploration

SN - 0375-6742

IS - May

M1 - 107709

ER -