The effect of mechanical activation on the kinetic and formation mechanism of a niobium aluminide based nanocomposite

In this paper the feasibility of NbAl۳/Al۲O۳ nanocomposite formation through mechanochemical reaction between Al and Nb۲O۵ and the effect of mechanical activation on the kinetic and reaction mechanism were investigated. Structural and phase evolution during mechanical alloying were studied by employing transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential thermal analysis (DTA) techniques. It was found from the results that the reduction of Nb۲O۵ by Al takes place in an explosive mode and after ۴۵۰ min of mechanical alloying leading to the formation a microstructure consisting of NbAl۳ matrix and nanocrystalline Al۲O۳ particles. The results also showed that heating the as-blended powder mixture of Nb۲O۵ and Al, leads to the formation of NbAl۳/Al۲O۳ composite through two exothermic reaction; A thermite reaction at ۸۸۰ °C followed by the synthesis of NbAl۳ intermetallic at ۹۴۴ °C. The mechanical activation of Nb۲O۵ and Al powder for ۵h decreased the formation temperature of NbAl۳/Al۲O۳ from ۹۴۴ °C to ۶۲۵ °C. Five isoconversional methods, of Kissinger-Akahira-Sunose, Tang, Flynn-Wall-Ozawa, Starink and Friedman were used to determine the activation energy, Eα, for NbAl۳/Al۲O۳ formation reaction and its variation with conversion degree α. The results showed that these methods lead to similar or comparable values of Eα.

Keywords:

Nanostructures , Intermetallic compounds , DTA , Kinetic study , Niobium