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Evolution of Nanocrystalline Structures Using High Energy Ball Milling of Quaternary Mg_{1.75}Nb_{0.125}C_{0.125}Ni and Binary Mg_2Ni

100%

Sharbati M., Kashani-Bozorg S.

Acta Physica Polonica A

2012

vol. 121

issue 1

211-213

High energy ball milling of two initial quaternary and binary powder mixtures of Mg_{1.75}Nb_{0.125}C_{0.125}Ni and Mg_2Ni has been carried out in pure argon atmosphere for the synthesis of nanocrystalline powders based on Mg_2Ni intermetallic compound. A planetary ball mill was employed using a ball to powder weight ratio of 20:1 for various milling time of 5, 10, 15, 20, 30 and 60 h. Characterization of the crystal structure of the milled products using X-ray diffractometry exhibited the formation of Mg_2Ni-based nanocrystallites after ≈ 5 h of milling for the both powder mixture. However, its volume fraction was greater in the case of quaternary powder mixture than that of binary one. In addition, an amorphous phase was detected in the milled products; its volume fraction showed increase by increasing milling time. The calculated mean crystallite size of Mg_2Ni structure showed decrease by increasing the milling time following the Williamson-Hall procedure and was found to be ≈ 8 and 10 nm after 20 h of milling for the initial powder mixture of Mg_{1.75}Nb_{0.125}C_{0.125}Ni and Mg_2Ni, respectively.

Gradual and Self-Sustaining Processes in the Sn-Zn-Se System

51%

Takacs L.

vol. 126

issue 4

1032-1039

Ball milling induces self-sustaining reaction in binary Sn-Se and Zn-Se powder mixtures. But if such mixtures are blended, the ignition time increases at either end of the concentration scale and the suppression of ignition can take place in an intermediate concentration interval. This phenomenon was investigated in (1-x)(Sn+Se)+x(Zn+Se) and (1-x)(Sn+2Se)+x(Zn+Se) mixtures, by measuring the ignition time as a function of both composition and milling conditions and investigating activated and reacted mixtures using X-ray diffraction and scanning electron microscopy. At the Sn-rich compositions of the first system, ignition happened as soon as the mill was started, in spite of the rather low adiabatic temperature of the reaction. Simultaneous local melting of Sn and Se is suggested as a possible explanation for immediate ignition. It can also explain the asymmetry of the properties of the binary reactions, namely that Sn+Se is less exothermic but easy to ignite, while Zn-Se is more exothermic but difficult to ignite. Similar asymmetry is considered as the reason for the increase of the ignition time and the loss of ignition in other mixed metal-chalcogen systems.

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2 Acta Physica Polonica A

1 2014

1 2012

1 Kashani-Bozorg S.

1 Sharbati M.

1 Takacs L.

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Evolution of Nanocrystalline Structures Using High Energy Ball Milling of Quaternary Mg_{1.75}Nb_{0.125}C_{0.125}Ni and Binary Mg_2Ni

Gradual and Self-Sustaining Processes in the Sn-Zn-Se System