User:Brayhey/sandbox/Exploding Wire Method
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Exploding Wire Method (also known as EWM) is a process by which a dense rising current is applied to a thin electrically conductive wire. The heat vaporizes the wire, and an electric arc over that vapor creates a shockwave and explosion. Exploding Wire Method is most famously known to be used as a detonator in nuclear munitions, but is also used to create dense plasmas, extremely high temperatures, light sources for high speed photography and metal Nanoparticles.
History
The first documented case of using electricity to melt a metal is credited to Martin van Marum who melted 70 feet of metal wire with Leyden Jars as a capacitor. Benjamin Franklin vaporized thin gold leaf to burn an image onto paper. While neither Marum nor Franklin actually incited the exploding wire phenomenon, they were important steps towards its discovery.
Edward Nairne was the first to note the existence of the exploding wire method in 1774 with silver and copper wire. Faraday used EWM to deposit thin gold films. Vapor deposits of metal gas as a result of EWM were studied by August Toepler, during the 19th century. The 20th century brought the discovery that metal aerosols could be produced with this method. Spectrography investigation of the process became widespread around that same. With a better understanding came the first glimpses of practical application.
Current day research has moved onto utilization of EWM to produce nanoparticles and further understanding of the phenomena.
Mechanism
The basic components needed for the exploding wire method is a thin conductive wire and a capacitor. The wire tends to be made of (___) and is usually (____dimentions____). The capacitor discharges a pulse of charge density 104 - 106 A/mm2. The phenomena occurs over only a portion of a second (____)
The Process is as follows:
- A rising current is supplied by the capacitor and is carried across the wire.
- The current heats up the wire until the metal begins to melt. The metal melts to form Unduloids. The current rises so fast that the liquid metal has no time to move out of the way.
- The unduloids vaporize. The metal vapor creates a lower resistance path, allowing an even faster current increase.
- An electric arc is formed, which turns the vapor into plasma. A bright flash of light is also produced.
- The plasma is allowed to expand freely, creating a shock wave.
- The shockwave pushes liquid, gaseous and plasmatic metal radially out, breaking the circuit and ending the process.
Uses
The EWM has many uses. EWM research has suggested possible applications in the excitation of optical masers, high intensity light sources for communications, spacecraft propulsion, joining difficult materials such as quartz, and generation of high power radio-frequency pulses. The most promising applications of EWM are as a detonator, light source, and for the production of nanomparticles.
Detonator
EWM has found its most use as a detonator, named the Exploding-bridgewire detonator, for munitions from nuclear bombs to amateur plastic rockets.
Light Source
EWM is a great mechanism by which to get a short duration high intensity light source. The light source can be used in interferometry, flash photolysis,quantitative spectroscopy, and high speed photography.
Production of Nanoparticles
EWM can be used to cheaply and efficiently create nanoparticles. Aluminum, nickel, and gold are just some of the metals that can be used in this way. Particles can be as small as .01μm in diameter. In general, as the voltage of the capacitor is raised, the particle diameter decreases.
(______ how are nanoparticles actually formed???_____) (_____ what are some applications of metal nanoparticles__)
When performed in a standard atmosphere containing oxygen metal oxides are formed. Nanoparticles can also be produced with EWM in an inert gas environment, usually argon. The inert gas prevents oxides from forming. Since the powders are not oxides, they burn when oxygen is present and must be contained properly in their working environment.
References
- ^ McGrath, J.R. (May 1966). "Exploding Wire Research 1774 - 1963". NRL Memorandum Report: 17.
{{cite journal}}:|access-date=requires|url=(help) - ^ McGrath, J.R. (May 1966). "Exploding Wire Research 1774 - 1963". NRL Memorandum Report: 17.
{{cite journal}}:|access-date=requires|url=(help) - ^ Hansen, Stephen (2011). Exploding Wires Principles, Apparatus and Experiments (PDF). Bell Jar. Retrieved 24 October 2014.