Effects of Ionizing Radiation on the Thermodynamic Stability of Boehmite and Gibbsite

Abstract

We examined the effect of γ radiation on the stabilities of aluminum hydroxide (gibbsite) and aluminum oxyhydroxide (boehmite) nanoparticles in relation to their thermal decomposition. X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images revealed no significant differences in mineral components or morphologies before and after radiation. However, thermogravimetric and differential scanning calorimetry (TGA/DSC) analyses showed that both boehmite and gibbsite nanoparticles experienced a decreased mass loss following irradiation. Raman and attenuated total reflection-Fourier transfer infrared (ATR-FTIR) spectra indicated that a fraction of the hydroxyl content in both cases was selectively cleaved by radiation, primarily at the particle surfaces. Quantitative analyses of thermal mass loss behavior demonstrated that irradiated boehmite and gibbsite nanoparticles had higher activation energies than their pristine counterparts, with the extent of the increase being dependent on the total dose. Taken together, these findings suggest that exposure to a sufficient dose of ionizing radiation alters these materials such that they are less prone to decomposition by dehydration. This increased stability may be due to the decreased hydrous nature of the samples after radiation exposure, which was supported by further high-temperature drop calorimetry. Additionally, a radiation-induced amorphous phase on the nanoparticle surfaces appears to have a permanent and positive influence on the thermodynamic stabilities.