The effect of irradiation on metakaolin-based geopolymer using Ti+ ion implantation

Abstract

The need for finding a replacement for concrete in nuclear power plants has increased dramatically due to concrete degradation caused by prolonged exposure to neutron irradiation. In this study, we mimicked the effect of neutron irradiation on metakaolin-based potassium geopolymer by using Ti+ as an implantation ion. Several techniques, including laser profilometry, scanning electron microscopy (SEM), backscattered electron (BSE), and nanoindentation, were employed to evaluate the geopolymer’s morphological, microstructural, and mechanical properties. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy were used to identify chemical composition and molecular structure before and after irradiation. Results revealed the formation of new cracks at the geopolymer surface after irradiation due to exposure to Ti+ and localized heating, accompanied by water loss and microcracking, as shown by laser profilometry. SEM and BSE analyses indicated that unreacted metakaolin disappeared, and the geopolymer microstructure became denser after irradiation. The results from nanoindentation showed a 90% increase in microhardness, a 46% increase in the reduced modulus, and a 23% reduction in the contact depth after irradiation. The FTIR spectra demonstrated a reduction in the intensity of O-H stretching vibration and H-O-H peaks after irradiation. XRD patterns indicated no changes in the geopolymer structure following irradiation. However, Raman spectroscopy revealed a decline in intensity, peak shift, and an increase in full-width half maximum (FWHM) after irradiation, likely attributed to the presence of titanium ions in the target and the thermal shock due to the irradiation. The increase in FWHM suggests increased sample disorder and alterations in bond angles, bond distance, or the local environment. This research is crucial for developing eco-friendly and resilient nuclear reactor shielding materials using geopolymers.