Synthesis of Al2O3–NbC by reactive milling and production of nanocomposites

Reactive high-energy milling can lead to self-sustaining reactions in the synthesis of a variety of systems, with the reaction being observed after an induction or ignition time which produces a temperature increase in the reactants. The products of such reactions are usually very strong agglomerates which, would be not very useful for further processing; to obtain fully dense sintered samples, it would be necessary an additional and difficult desagglomeration procedure. Therefore, the knowledge and control of the mechanism during reactive high-energy milling may be important in preventing or reducing this agglomeration and improve the physical properties of the powder reaction products. In the present work, high-energy ball milling of the powder mixture Nb2O5–Al–C was performed in a SPEX 8000 shaker/mill. The reaction was monitored by a thermocouple fixed in the external surface of the vial. With the condition of ball to mass ratio of 4:1 ignition occurs after 190 min milling. Powder mixtures were characterized after different milling times before and after the reaction. Also, alumina powder was added as diluent to the reactant mixture aiming to decrease the reaction temperature. The powders were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The reaction products after 1 h were desagglomerated and mixed with commercial ultra-fine alumina powder, producing alumina matrix nanocomposites with 5 wt.% of NbC.