Mechanical milling assisted by electrical discharge

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Abstract

Mechanical milling is an effective technique for the preparation of fine metallic and ceramic powders and can also be used to drive a wide range of chemical reactions. Milling devices include planetary machines, attritors and vibrational mills; products include amorphous, nanocrystalline and quasicrystalline materials, supersaturated solid solutions, reduced minerals, high-surface-area catalysts and reactive chemicals1,2,3. During milling, solid–solid, solid–liquid and solid–gas reactions are initiated through repeated deformation and fracture of powder particles. A separate materials synthesis and processing technique involves reacting a material in a gas atmosphere under an electrical discharge4,5,6,7. Here we show that the application of low-current, high-voltage electrical impulses during milling can result in both faster reactions and new synthesis and processing routes. We demonstrate the effects of glow (cold) and spark (hot) discharge milling on particle fracture for brittle, low-conductivity materials and ductile metals. Glow discharge milling was found to promote solid–gas reactions whereas spark discharge milling promotes fast fracturing, recrystallization, mineral reduction and solid–solid reactions.

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Figure 1: Schematic illustrations of magneto-ball milling and electric-discharge-assisted mills.
Figure 2: Fracturing resulting from spark discharge milling of low-electrical-conductivity particles and high-electrical-conductivity metal powders.
Figure 3: Mechanical milling of 50 at% Fe with 50 at% B.
Figure 4: Solid–gas reaction paths during discharge-assisted milling of Ti in nitrogen.
Figure 5: Reduction reaction of haematite to magnetite caused by spark discharge milling.

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Acknowledgements

We acknowledge R. deJong, R. Kinnell and S. Selby for their contributions towards construction of the discharge milling devices. We are especially grateful to D. Dunne for his support and leadership. This project was supported by funding from the Australian Research Council.

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Correspondence to A. Calka.

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The authors declare that they have no competing financial interests.

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Calka, A., Wexler, D. Mechanical milling assisted by electrical discharge. Nature 419, 147–151 (2002) doi:10.1038/nature00985

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