Effects of ?-Irradiation, Cation Size, and Salt Concentration on the Aggregation of Boehmite Nanoplatelets

Effects of radiation on the aggregation of nanoplatelets of aluminum oxyhydroxide (boehmite) in slurries of M1+ cation nitrates have been observed using tumbler small-and ultra-small-angle neutron scattering. Nitrate solutions of H, Li, Na, K, and Rb at concentrations of 10(-5) , 10(-3) , 10(-1) , 2, and 4 molal were compared to the results for pure H2O. Primary aggregates consisting of small stacks of boehmite platelets that form immediately after the boehmite is placed in water are smaller for irradiated boehmite than the pristine material. The primary aggregates for irradiated boehmite also appear to have a rougher surface than those observed for unirradiated materials. Both results are possibly due to breaking of the surface OH species and neutralization of the surface. At low salt concentrations, the pH of the irradiated boehmite slurries is lower than that of the corresponding pristine material, indicating that irradiated boehmite adsorbs fewer protons or more hydroxide onto its surface than the pristine boehmite. Increasing the salt concentration decreases the pH to near neutral at 7 due to screening of the electric double layer at the solid/liquid interface. Irradiation does not seem to affect the size of secondary aggregates formed from the aggregation of primary aggregates or the overall size of the primary aggregates.