Reactive SPS for Sol–gel Alumina Samples: Structure, Sintering Behavior, and Mechanical Properties

This work presents a fast and direct controlled routine for the fabrication of fully dense alumina based on the reactive spark plasma sintering (reactive-SPS) of boehmite (gamma-AlOOH) nano-powders obtained by the sol-gel technique. The evolution of the transition aluminas during sintering has been studied. Some boehmite powders were seeded with alpha-Al2O3 particles prior to the gelation. Boehmite seeded powders exhibited a direct transition to alpha-Al2O3 at 1070 degrees C, enhancing the transformation kinetics and lowering the required temperature by more than 100 degrees C. For comparison, other samples were prepared by previously annealing the seeded and unseeded boehmite powders. Thus, alpha-Al2O3 powders were obtained and were sintered by standard-SPS. A detailed structural and mechanical characterization is presented, comparing the hardness and indentation fracture resistance for different grain sizes and porosities. Both the reactive-SPSed samples and the standard-SPSed samples showed a high hardness (18-20 GPa), whereas the reactive-SPSed samples exhibited a lower indentation fracture resistance due to a large grain size (similar to 10 mu m). Improvements of this procedure for obtaining smaller grain size are discussed. In summary, the presented technique brings a revolutionary fast method for the fabrication of fully dense alumina, as this process reduces the time and temperature required for alumina densification.