Annealing of Alpha-Recoil Damage in Natural Titanite, CaTiSiO5.

Abstract

AbstractIsothermal and isochronal annealing of alpha-recoil damage was performed on the mineral titanite, CaTiSiO5. Crushed-grain samples were heated for 21 hrs, at 100°C intervals from 300°-700°C. HRTEM imaging of alpha-recoil collision cascades (amorphized regions), after each temperature interval, showed that there was no change in the abundance or appearance of the cascades at 300°C, but an apparent decrease in cascade size occurs at 400°C (from 3.8 nm to 2.4 nm diameter). A decrease in the size of collision cascades may indicate repair of interstitial defects at cascade boundaries (where interstitials dominate), while the cascade cores remain amorphous (cores acquire more extensive knock-on damage). At 500°C, the number of collision cascades observed decreases by greater than 90%, indicating major annealing of the amorphous cascade cores, and precipitates appear on titanite grain surfaces. At 600°C, changes do not occur. At 700°C, both the cascades and precipitates are absent; the alpha-recoil damage is fully annealed.