The traditional methods for the synthesis of reinforced alumina-based matrix composites with carbon nanotubes (CNTs) have presented serious difficulties for obtaining well dispersed and homogeneously distributed CNTs within the matrix. Besides this, the CNTs are typically found in the grain boundaries of the matrix. These features involve a non-optimal reinforcement role of the CNTs. With the aim of maximizing the efficiency of the reinforcement of the CNT, this work reconsiders a sol-gel based procedure for ceramic composites fabrication with a twofold objective: to achieve a good dispersion of the CNTs and to promote the intragranular location of the CNTs. The mixing of precursors and CNTs has been developed under the presence of high power ultrasounds, followed by a rapid in-situ gelation that "freezed" the nanotubes inside the gel. The chemical and physical relationships between the ceramic matrix and the embedded reinforcing phase has been researched. First results confirm the success of the synthesis procedure for the preparation of alumina-based composite powders starting from a commercial boehmite sol and multiwalled carbon nanotubes. X-ray diffraction and Raman analyses confirmed the formation of the α-Al 2 O 3 and the persistence of the non-damaged nanotube structure. N 2 physisorption and electron microscopy were used to check the evolution of the nanostructure and to confirm the presence of intragranular carbon nanotube within the 2 polycrystalline powder. Therefore, the alumina-based composite powder prepared by this new procedure is a good candidate for the preparation of reinforced ceramic matrix composites.

Highlights • Crack-bridging as toughening phenomena revealed by SEM. • Nanoindentation hardness and elastic modulus shows an increasing behavior with CNTs concentration. • Actual elastic modulus for the calculation of fracture toughness of the composites reveals significant fracture improvement. • Sintering parameters have to be tuned for fully dense composite.

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