Micro- and Nanostructure evolution with Exploding Wires
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Micro- and Nanostructure evolution with Exploding Wires. Vandana and P. Sen School of Physical Sciences, Jawaharlal Nehru University, New Delhi – 110067, India ABSTRACT We present an experimental evidence of concentric ring pattern formation in a metal. They form during a single electro-explosion event in a needle-plate configuration. By measuring the dynamic progression of current during the explosion, we discuss evolution of these ring structures. Atomic force microscopy provides details of nanostructures that constitute these rings. From fluctuations in the plasma current recorded during the process, micro and nanostructure evolution is seen to be a self-organization process. INTRODUCTION Nanostructured materials are generally defined as those materials whose component elements - clusters, crystallites or molecules – have dimensions in the 1 to 100 nm range. Academic and industrial interest in these materials over the years arise from the remarkable variations in fundamental electrical, optical and magnetic properties that occur as one progresses from an “infinite solid” to a particle of material consisting of few atoms. It is realized that the properties of materials can be engineered by controlling the size of these building blocks and their assembly. The highly beneficial properties of nanostructured materials are integral to the development of advanced technological innovations. We employ the electro-explosion technique, i.e., a non-equilibrium process, to get nanostructured materials. Electro-explosion of wires, traditionally employed for generating hot plasmas and high-brilliance photon sources is being increasingly used as an application tool for destruction of redundant objects or for preparation of nanomaterials. Explosion of wires [1] is achieved when a very high current, suddenly applied to a thin conducting wire, causes it to fragment explosively. During the passage of very high currents, strong self-induced magnetic forces are generated which tend to crush the plasma towards the central Z-axis and hence sometimes the name Z-pinch system is given for exploding wires. Various experimental and theoretical investigations of this phenomenon exist [2-11]. A study of the literature shows that wire explosion and fragmentation generally tend to proceed in the following manner: 1) Heating of wire and wire melting; 2) Wire explosion (evaporation) and formation of a high density core surrounded by low density ionized corona; 3) Coronal compression by self-induced magnetic fields, and 4) Fast expansion of explosion products resulting in shock wave generation. In this paper, we present an experimental evidence of concentric ring patterns formation in a metal plate during a single electro-explosion event. For this purpose, we employ a modified
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Z-pinch system in the needle-plate configuration. We establish electro-explosion by monitoring time evolution of the current through the wire. For iron needles exploding on an iron plate we find evidence of pattern formation of clear concentric
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