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.

Keywords:

• nanospinel
• nano B2 phase
• decagonal quasicrystal
• Al–Ni–Fe alloy
• mechanical milling

Acknowledgements

We would like to thank Profs. S. Ranganathan, P. Ramachadra Rao, K. Chatapadhyay, G.V.S. Sastry, R.K. Mandal and Dr. M.A. Shaz for many stimulating discussions. We also would like to thankfully acknowledge the critical comments/suggestions of the anonymous referees for improving the quality of the manuscript. The financial support from the Ministry of New-Renewable Energy (MNRE), UNANST (DST) and Project of DST (SR/S3/ME/051/2005-SERC-Engg.), New Delhi, India, is gratefully acknowledged.