EXAFS studies of metamict materials

Conference · Sun Jan 01 04:00:00 EST 1984

OSTI ID:5453637

Greegor, R B; Lytle, F W; Ewing, R C; Haaker, R F

An important approach in the evaluation of crystalline wasteforms for nuclear waste storage is to study the long term stabilities of closely related radioactive mineral species which have become metamict (radiation damaged) and have been exposed to weathering processes for geologic periods of time. The metamictization and alteration effects can then be used for comparison with the results of short term laboratory leaching and irradiation experiments which have been designed to simulate long term effects. Phosphates, the Ti-Nb-Ta complex oxide minerals and various selected silicates are natural analogues for phases in proposed radioactive wasteforms. Because of the geochemical similarities with wasteforms, a study of the metamict state and annealing in complex mineral phosphates, silicates and oxides will yield data that is important in evaluating the long term stability of radioactive wasteforms. The investigation reported here is an application of EXAFS and XANES spectroscopy to the study of the structure of the metamict state. The nearest neighbor environment of Ti and Ca in metamict AB/sub 2/O/sub 6/-type complex oxides has been examined using SSRL Beam Line VII-3 in order to evaluate the effect of alpha-recoil damage on these structures. Comparison of the EXAFS/XANES data for metamict samples with data for annealed and crystalline samples suggests minor changes in the first coordination sphere, Ca-O or Ti-O, (a slight decrease in coordination number and bond lengths, and increased distortion of the coordination polyhedron), but major disruption of the second coordination sphere, for the material in the metamict state. These data suggest a mechanism for the transition from the crystalline to the metamict state in which tilting of cation coordiantion polyhedra is a possible effect of damage caused by alpha-recoil events.

• Research Organization: Boeing Co., Seattle, WA (USA); New Mexico Univ., Albuquerque (USA). Dept. of Geology
• DOE Contract Number: FG06-84ER45121
• OSTI ID: 5453637
• Report Number(s): CONF-840764-7; ON: DE85014041
• Country of Publication: United States
• Language: English

Related Subjects

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36 MATERIALS SCIENCE
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ACTINIDE COMPOUNDS
AESCHYNITE
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
ANNEALING
CALCIUM
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CRYSTAL STRUCTURE
DATA
ELEMENTS
EUXENITE
EXPERIMENTAL DATA
FOURIER TRANSFORMATION
HEAT TREATMENTS
INFORMATION
INTEGRAL TRANSFORMATIONS
IRON COMPOUNDS
IRON OXIDES
KINETICS
MANAGEMENT
MATERIALS
METALS
METAMICT STATE
MINERALS
NIOBIUM COMPOUNDS
NIOBIUM OXIDES
NUMERICAL DATA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL RADIATION EFFECTS
RADIATION EFFECTS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RADIOACTIVE WASTE DISPOSAL
RARE EARTH COMPOUNDS
REACTION KINETICS
REFRACTORY METAL COMPOUNDS
THORIUM COMPOUNDS
THORIUM MINERALS
THORIUM OXIDES
TITANIUM
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSFORMATIONS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
URANIUM MINERALS
WASTE DISPOSAL
WASTE FORMS
WASTE MANAGEMENT
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES
ZIRCONOLITE