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 ( γ -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 α -Al 2 O 3 particles prior to the gelation. Boehmite seeded powders exhibited a direct transition to α -Al 2 O 3 at 1070 ° C, enhancing the transformation kinetics and lowering the required temperature by more than 100 ° C. For comparison, other samples were prepared by previously annealing the seeded and unseeded boehmite powders. Thus, α -Al 2 O 3 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 ( ∼ 10 μ 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.