Alumina/molybdenum nanocomposites obtained in organic media

Alumina/molybdenum nanocomposites were obtained from a modified alumina powder in a solution of molybdenum(V) chloride in ethanol. The modified alumina powder was calcined at low temperatures to remove organic residue. A reduction step was necessary to obtain 2–10 nm metallic nanoparticles on the surface of the alumina crystals. Theoretically dense composites containing 0.69, 2.66, and 8.91 vol.% Mo were prepared by cold isostatic pressing and sintering in Ar/H2 atmosphere. In all cases a very narrow homogeneous distribution of Mo nanoparticles was obtained. Molybdenum nanoparticles are very homogeneously distributed in the alumina matrix, with an average nanoparticle size smaller than 90 nm. The presence of such molybdenum nanoparticles drastically affects the microstructural evolution during sintering, mainly the final grain size of alumina. An important improvement in mechanical bevavior was also observed. For example, the composite containing 0.69 vol.% Mo showed a flexural strength (four-point method) of 700 MPa and a fracture toughness K1c (SENB) of 6.26 MPa m1/2.