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Nanoscale Characterization of the Oxide Formed on a Neutron-Irradiated Zr-2.5Nb Alloy in High Temperature Water

The interaction of metals and alloys with aqueous environments is ubiquitous, leading to oxide formation (passivity) or corrosion in many cases. Although these phenomena have significant importance across various industries and domains of materials science, the fundamental atomic-scale mechanisms by which corrosion and oxide formation operate are still unclear. Oxide films can have complex chemistry and texture, especially at the metal-oxide interface which acts as the primary barrier from solution interaction. The Zr-H2O system has industrial and academic interest due to its use in nuclear reactors.

Product Number: ED22-18364-SG
Author: S.Adil, M. Topping, K. Daub, S.Y. Persaud, M.R. Daymond
Publication Date: 2022
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In this study, the microstructure near the metal-oxide interface of a Zr-2.5Nb alloy is characterized after 567 days of exposure to high temperature heavy water with neutron irradiation in a test reactor. The oxides formed in-reactor look distinctly different from those formed in a non-irradiated environment. Specifically, reactor oxides have a more complex microstructure with shorter columnar grains and lateral cracks are a common feature. Transmission electron microscopy (TEM) was used to investigate the nanoscale, distribution, and connectivity of porosity through the oxide layer. The observed nano-porosity may provide short-circuit pathways for the transport of hydrogen or ions through the film to the metal/oxide or oxide/solution interfaces. Scanning TEM is used to provide complementary chemical information. Energy-dispersive X-ray spectroscopy analysis revealed differences in Nb segregation in the oxide between irradiated and non-irradiated samples. Multiple linear least squares (MLLS) fitted electron energy loss spectroscopy (EELS) maps showed the existence of a Widmanstätten-type, equiaxed, and thin plate morphology of metastable h-ZrO (15.4 eV).


In this study, the microstructure near the metal-oxide interface of a Zr-2.5Nb alloy is characterized after 567 days of exposure to high temperature heavy water with neutron irradiation in a test reactor. The oxides formed in-reactor look distinctly different from those formed in a non-irradiated environment. Specifically, reactor oxides have a more complex microstructure with shorter columnar grains and lateral cracks are a common feature. Transmission electron microscopy (TEM) was used to investigate the nanoscale, distribution, and connectivity of porosity through the oxide layer. The observed nano-porosity may provide short-circuit pathways for the transport of hydrogen or ions through the film to the metal/oxide or oxide/solution interfaces. Scanning TEM is used to provide complementary chemical information. Energy-dispersive X-ray spectroscopy analysis revealed differences in Nb segregation in the oxide between irradiated and non-irradiated samples. Multiple linear least squares (MLLS) fitted electron energy loss spectroscopy (EELS) maps showed the existence of a Widmanstätten-type, equiaxed, and thin plate morphology of metastable h-ZrO (15.4 eV).