PNNL

Abstract

Aluminum hydroxide (gibbsite, ?Al(OH)?_3) powders and their thermally dehydrated forms were rehydrated and irradiated with gamma rays to examine their overall radiation stability, product formation, and the role of adsorbed water. Thermal gravimetric analysis (TGA) measurements of gibbsite dehydration established the temperatures of phase transitions from gibbsite to alumina. Changes to the surface and structure of gibbsite and its transition phases following irradiation were analyzed using nitrogen adsorption, powder X-ray diffraction (pXRD), Raman spectroscopy, electron paramagnetic resonance (EPR), and scanning electron microscopy (SEM). pXRD and Raman spectra showed amorphorization at about 300°C, coupled to a substantial increase in specific surface area due to increasing porosity. The amount of hydrogen gas, H2, production from irradiated gibbsite and it transition phases with adsorbed water increased substantially with increasing temperature for dehydration of the samples, up to a point. The production of H2 for samples without water was considerably lower than the hydrated samples. EPR spectroscopy showed that the major radiolytic products are trapped electrons and related O- centers.