Reaction Kinetics and Microstructural Evolution during the Heating of High Energy Ball Milled Al-TiO_2 and Al-V_2O_5 Composite Powders

摘要

Solid state reactions and corresponding microstructural evolution of the powder particles during heating Al/TiO_2 and Al/V_2O_5 composite powders produced by high energy ball milling have been studied. It is demonstrated that establishment and refining of the composite structure of the powder particles through milling strongly enhances the reaction kinetics. The enhancement is likely due to the creation of a large area of Al/oxide interfaces and the reduction of the inter-particle spacing of the oxide particles inside the powder particles. Al_3Ti or Al_3V or other Al rich Al_xV_y phase is the first phase to be formed from the reaction between Al and TiO_2 or V_2O_5 which starts at a temperature close to the melting point of Al. When the Al/V_2O_5 composite structure is very fine, γ-Al_2O_3 may also form from the initial reaction. The powders must be heated to above 900°C in order for α-Al_2O_3 to nucleate. At temperatures above 1000°C, Al_3Ti is transformed into Ti(Al,O) by reacting with TiO_2.