Changes in properties of alpha-quartz and feldspars under 3 MeV Si-ion irradiation

Abstract

Radiation-induced volume expansion (RIVE) in silicate minerals is recognized as the primary cause of long-term degradation in concrete structures. Although silicate minerals are the most abundant in rock-forming minerals of concrete aggregates, changes upon irradiation in these minerals are not clearly understood, particularly at high irradiation doses. In this study, tectosilicates, i.e., crystal quartz and two feldspars (albite and microcline), were irradiated with 3 MeV Si2+ to a maximum fluence of 2 × 1016 ions/cm2 (approximately two orders of magnitude higher than amorphization fluence), followed by a step height measurement and nano-indentation to quantify the change in volume and mechanical properties. The results show that the fluence dependence of RIVE is similar in quartz and feldspars, but the mechanism of the expansion differs. In quartz, amorphization is completed at a low fluence, followed by the relaxation of network and cavity formation. In feldspar minerals, amorphization occurs slowly. Subsequently, volume expansion is insignificant after the completion of amorphization. Hardness change appears to be a function of amorphization, whereas the Young's modulus is almost correlated with RIVE. The alkali ions in the silicate minerals can affect both the amorphization kinetics and the final amorphous structure.