Temperature dependence of Kr ion-induced amorphization of mica minerals

Abstract

Four different mica compositions, i.e., muscovite [KAl 2(AlSi 3O 10)(OH,F) 2], phlogopite [KMg 3(AlSi 3O 10)(OH,F) 2], biotite [K(Mg,Fe) 3(AlSi 3O 10)(OH,F) 2] and lepidolite [K(Li,Al) 3(Al,Si) 4O 10(OH,F) 2], were irradiated with 1.5 MeV Kr + ions in the temperature range between 20 and 1023 K using the HVEM-Tandem Facility at Argonne National Laboratory. The irradiation effects were characterized by in situ and high resolution transmission electron microscopy (TEM). All four micas are susceptible to irradiation-induced amorphization with relatively low critical amorphization doses ( D c) (1–2 × 10 14 ions/cm 2, fractions of a dpa) below or at room temperature. D c increased with irradiation temperature for all phases above 400 K. The predicted critical temperatures ( T c), above which amorphization will not occur, for the four micas are all at or above 1000 K. Lepidolite is the most easily amorphized among the four micas at all irradiated temperatures with a predicted T c of 1300 K. Large gas bubbles (1–2 μm in diameter) were observed in a 800 keV Kr 2+ irradiated biotite after 1 × 10 15 ions/cm 2.