Synthesis of Al2O3-Nb composite by reactive milling

Synthesis of compounds or composites can be achieved by reactive milling, a process in which a powder mixture reacts due to mechanical activation given by high-energy ball milling. Different types of reaction can occur in reactive milling. Reactions of oxide reduction or displacement by a metal as reducing agent are often of the self-sustaining type. In the present work, we report on the microstructural and phase evolution during reactive milling synthesis of Nb+Al2O3 composite from the powder mixtures of Nb2O5 and Al. High-energy ball milling was performed in a SPEX 8000 shaker/mill apparatus with a ball/material mass ratio of 4:1. The reaction was monitored by a thermocouple fixed in the external surface of the vial allowing the detection of the temperature peak associated with the sudden reaction. For the studied reaction, the ignition occurs after 68 min of milling. Samples of powder mixtures were prepared by different milling time, to allow its characterisation at different conditions just before, during and after the reaction. The powder transformations during milling, the microstructural evolution and the completeness of the reaction were determined by X-ray diffraction, specific surface area measurements, scanning electron microscopy and differential scanning calorimetry.