Porosity evaluation and positron annihilation study of mesoporous aluminum oxy-hydroxide ceramics

The pore size and type of aluminum oxy-hydroxide (boehmite) obtained using an optimized sol–gel method was investigated as a mesoporous material with the calcination temperature varied from 150 to 550 °C. Structural features were characterized by XRD, SEM, TEM, BET. Molecular interactions were identified by using PALS (positron annihilation lifetime spectroscopy) and CDBS (coincidence Doppler broadening spectroscopy). The XRD pattern showed that the sample synthesized at 250 °C has an orthorhombic phase characterizing the boehmite structure. All the samples prepared from pure aluminum metal were mesoporous according to BET results with a strong relationship between microstructure properties and temperature. The highest values of specific surface area and pore volume assigned to the sample prepared at 250 °C with 268.3 m2·g−1 and 0.313 cm3·g−1, respectively. The results of PAL-spectroscopy show that, the lifetime of positrons annihilating at pores of the boehmite at 350 °C increased as the average pore size growths because the free-volume defects in the samples increased.