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

Abstract

In this paper the feasibility of NbAl₃/Al₂O₃ nanocomposite formation through mechanochemical reaction between Al and Nb₂O₅ 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 Nb₂O₅ by Al takes place in an explosive mode and after 450 min of mechanical alloying leading to the formation a microstructure consisting of NbAl₃ matrix and nanocrystalline Al₂O₃ particles. The results also showed that heating the as-blended powder mixture of Nb₂O₅ and Al, leads to the formation of NbAl₃/Al₂O₃ composite through two exothermic reaction; A thermite reaction at 880 °C followed by the synthesis of NbAl₃ intermetallic at 944 °C. The mechanical activation of Nb₂O₅ and Al powder for 5h decreased the formation temperature of NbAl₃/Al₂O₃ from 944 °C to 625 °C. Five isoconversional methods, of Kissinger-Akahira-Sunose, Tang, Flynn-Wall-Ozawa, Starink and Friedman were used to determine the activation energy, <em>E_α</em>, for NbAl₃/Al₂O₃ formation reaction and its variation with conversion degree <em>α</em>. The results showed that these methods lead to similar or comparable values of <em>E_α</em>.