Phase and microstructural evolution during heating of mechanically milled Al/V 2 0 5 composite powders

Abstract

The reactions between V₂O₅ and aluminium during heating of high energy ball milled powders have been studied using a combination of thermal analysis and various microstructural characterisation techniques. High energy ball milling results in the formation of Al/V₂O₅ composite powder particles. With a coarse composite structure of the powder particles, the reaction between aluminium and V₂O₅ phases occurs in two steps during heating. The low temperature step starts at ∼540°C and causes the formation of unknown phases, while the high temperature step starts at ∼795°C and causes the formation of Al₃V and α -Al₂O₃. When the composite structure of the powder particles is sufficiently refined, the two step reaction is changed into a one step reaction which starts at 520 ° C. The one step reaction causes the formation of Al₃V, γ-Al₂O₃ and other unknown phases. When the powders are heated to above 1000°C, γ-Al₂O₃ is transformed into α-Al₂O₃, and the unknown phases are converted into Al₃V and α Al₂O₃, leading to the formation of new composite powder particles with a microstructure consisting of fine Al₂O₃ particles embedded in a matrix of Al₃V.