Transmission electron microscopy analysis of corroded metal waste forms.

Technical Report · Fri Apr 15 00:00:00 EDT 2005

DOI:https://doi.org/10.2172/861616· OSTI ID:861616

Dietz, N L

This report documents the results of analyses with transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (ED) of samples of metallic waste form (MWF) materials that had been subjected to various corrosion tests. The objective of the TEM analyses was to characterize the composition and microstructure of surface alteration products which, when combined with other test results, can be used to determine the matrix corrosion mechanism. The examination of test samples generated over several years has resulted in refinements to the TEM sample preparation methods developed to preserve the orientation of surface alteration layers and the underlying base metal. The preservation of microstructural spatial relationships provides valuable insight for determining the matrix corrosion mechanism and for developing models to calculate radionuclide release in repository performance models. The TEM results presented in this report show that oxide layers are formed over the exposed steel and intermetallic phases of the MWF during corrosion in aqueous solutions and humid air at elevated temperatures. An amorphous non-stoichiometric ZrO{sub 2} layer forms at the exposed surfaces of the intermetallic phases, and several nonstoichiometric Fe-O layers form over the steel phases in the MWF. These oxide layers adhere strongly to the underlying metal, and may be overlain by one or more crystalline Fe-O phases that probably precipitated from solution. The layer compositions are consistent with a corrosion mechanism of oxidative dissolution of the steel and intermetallic phases. The layers formed on the steel and intermetallic phases form a continuous layer over the exposed waste form, although vertical splits in the layer and corrosion in pits and crevices were seen in some samples. Additional tests and analyses are needed to verify that these layers passivate the underlying metals and if passivation can break down as the MWF corrodes. The importance of localized corrosion should also be determined.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 861616
• Report Number(s): ANL-05/09; TRN: US0600740
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

36 MATERIALS SCIENCE
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
AQUEOUS SOLUTIONS
CORROSION
DISSOLUTION
ELECTRON DIFFRACTION
MICROSTRUCTURE
ORIENTATION
OXIDES
PASSIVATION
PRESERVATION
RADIOISOTOPES
SAMPLE PREPARATION
STEELS
TRANSMISSION ELECTRON MICROSCOPY
WASTE FORMS
X-RAY SPECTROSCOPY