Low-temperature synthesis of nanocrystalline spinel by mechanical milling and annealing of Al-Ni-Fe decagonal quasicrystals

Abstract

Attempts were made to synthesize a nanocrystalline spinel phase by mechanical milling and subsequent annealing of Al-Ni-Fe decagonal quasicrystalline alloy. The milling of the decagonal phase was carried out in an attritor ball mill at 400 rpm for 1-40 h with ball to powder ratio of 100 : 1 in hexane medium. Subsequently annealing was performed in vacuum as well as an air ambience for 10, 20, 40 and 80 h. The quasicrystal powders milled for 40 h showed the formation of B2-type nanocrystalline phase (a = 2.91 Å). Annealing of 40 h milled powder in air at 500° C resulted in the formation of spinel structure (a = 8.15 Å). X-ray diffraction and transmission electron microscopy investigations confirmed the formation of spinel phase with an average grain size of ∼60 nm. The formation of nanospinels and the advantages of this synthesis route compared to the existing routes for the formation of spinels are discussed.