The nature of the amorphous regions and their recovery processes in two natural metamict zircon samples from Sri Lanka have been studied by high resolution and analytical transmission electron microscopy. Samples untreated and annealed at different temperatures were investigated. Nanoprobe analyses on untreated samples and samples annealed at 1000 °K show that within experimental uncertainties, no chemical segregation occurred. In samples annealed at higher temperatures (>= 1100 K) recovery occurs in a two stage process and leads to different microstructures, which depended on the initial amount of metamictization. In highly amorphized samples, recrystallisation starts at 1200 K. Randomly oriented ZrO2 grains embedded in a silica rich matrix are detected. At higher temperature (16 hours at 1600 K), the assemblage transforms into a polygonal texture of small zircon grains. Some untransformed zirconia grains and pockets of silica-rich glass are still present, however. In partially metamict samples, recovery starts at 1100 K. The small surviving oriented zircon domains grow at the expense of the surrounding amorphous material. At 1200 K, new zirconia grains nucleate with random orientations. After 1 hour annealing at 1400 K, the zircon structure is restored and the microstructure coarse-grained. The proportion of crystalline zirconia and silica-rich glass has dramatically decreased.

Capitani, G., Leroux, H., Doukhan, J., Ros, S., Zhang, M., Salje, E. (2000). A TEM investigation of natural metamict zircons: structure and recovery of amorphous domains. PHYSICS AND CHEMISTRY OF MINERALS, 27(8), 545-556 [10.1007/s002690000100].

A TEM investigation of natural metamict zircons: structure and recovery of amorphous domains

CAPITANI, GIANCARLO;
2000

Abstract

The nature of the amorphous regions and their recovery processes in two natural metamict zircon samples from Sri Lanka have been studied by high resolution and analytical transmission electron microscopy. Samples untreated and annealed at different temperatures were investigated. Nanoprobe analyses on untreated samples and samples annealed at 1000 °K show that within experimental uncertainties, no chemical segregation occurred. In samples annealed at higher temperatures (>= 1100 K) recovery occurs in a two stage process and leads to different microstructures, which depended on the initial amount of metamictization. In highly amorphized samples, recrystallisation starts at 1200 K. Randomly oriented ZrO2 grains embedded in a silica rich matrix are detected. At higher temperature (16 hours at 1600 K), the assemblage transforms into a polygonal texture of small zircon grains. Some untransformed zirconia grains and pockets of silica-rich glass are still present, however. In partially metamict samples, recovery starts at 1100 K. The small surviving oriented zircon domains grow at the expense of the surrounding amorphous material. At 1200 K, new zirconia grains nucleate with random orientations. After 1 hour annealing at 1400 K, the zircon structure is restored and the microstructure coarse-grained. The proportion of crystalline zirconia and silica-rich glass has dramatically decreased.
Articolo in rivista - Articolo scientifico
TEM, zircon, zirconia, radiation damage, recovery
English
2000
27
8
545
556
none
Capitani, G., Leroux, H., Doukhan, J., Ros, S., Zhang, M., Salje, E. (2000). A TEM investigation of natural metamict zircons: structure and recovery of amorphous domains. PHYSICS AND CHEMISTRY OF MINERALS, 27(8), 545-556 [10.1007/s002690000100].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/31401
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