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The exploding wire method or EWM is a way to generate
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
that consists in sending a strong enough pulse of
electric current An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The moving pa ...
through a thin
wire Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample diameter 40 mm A wire is a flexible strand of metal. Wire is c ...
of some
electrically conductive Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
material. The
resistive heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor (material), conductor produces heat. Joule's first law (also just Joule's law), also known in c ...
vaporizes the wire, and an
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma (p ...
through that vapor creates an
explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
shockwave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...
. Exploding wires are used as
detonator A detonator, frequently a blasting cap, is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the last two being the most common. The commercial use of explosives uses electri ...
s for
explosives An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An expl ...
, as momentary high intensity light sources, and in the production of metal
nanoparticle A nanoparticle or ultrafine particle is usually defined as a particle of matter that is between 1 and 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 1 ...
s.


History

One of the first documented cases of using electricity to melt a metal occurred in the late 1700s and is credited to
Martin van Marum Martin(us) van Marum (20 March 1750, Delft – 26 December 1837, Haarlem) was a Dutch physician, inventor, scientist and teacher, who studied medicine and philosophy in Groningen. Van Marum introduced modern chemistry in the Netherlands after ...
who melted 70 feet of metal wire with 64
Leyden Jars A Leyden jar (or Leiden jar, or archaically, sometimes Kleistian jar) is an electrical component that stores a high-voltage electric charge (from an external source) between electrical conductors on the inside and outside of a glass jar. It typi ...
as a capacitor. Van Marum's generator was built in 1784, and is now located in the
Teylers Museum Teylers Museum () is an art, natural history, and science museum in Haarlem, Netherlands. Established in 1778, Teylers Museum was founded as a centre for contemporary art and science. The historic centre of the museum is the neoclassical Oval R ...
in the Netherlands. Years later,
Benjamin Franklin Benjamin Franklin ( April 17, 1790) was an American polymath who was active as a writer, scientist, inventor, statesman, diplomat, printer, publisher, and political philosopher. Encyclopædia Britannica, Wood, 2021 Among the leading inte ...
vaporized thin gold leaf to burn images onto paper. While neither Marum nor Franklin actually incited the exploding wire phenomenon, they were both important steps towards its discovery.
Edward Nairne Edward Nairne (1726 – 1 September 1806) was English optician and scientific instrument maker. Biography Nairne was born in Sandwich, England. He was apprenticed to the optician Matthew Loft in 1741 and established his own business at 20 Cor ...
was the first to note the existence of the exploding wire method in 1774 with silver and copper wire. Subsequently,
Michael Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
used EWM to deposit thin gold films through the solidification of vaporized metal on adjacent surfaces. Then, vapor deposits of metal gas as a result of EWM were studied by
August Toepler August Joseph Ignaz Toepler (7 September 1836 – 6 March 1912) was a German chemist and physicist known for his experiments in electrostatics. Biography August Toepler was born on 7 September 1836. He studied chemistry at the Gewerbe-Insti ...
during the 1800s.
Spectrography Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
investigation of the process, led by J.A. Anderson, became widespread in the 1900s. The spectrography experiments enabled a better understanding and subsequently the first glimpses of practical application. The mid 20th century saw experiments with EWM as a light source and for the production of nanoparticles in aluminum, uranium and plutonium wires. Congruently, Luis Álvarez and Lawrence H. Johnston of the
Manhattan Project The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
found use for EWM in the development of nuclear detonators. Current day research focuses on utilizing EWM to produce nanoparticles as well as better understanding specifics of the mechanism such as the effects of the system environment on the process.


Mechanism

The basic components needed for the exploding wire method are a thin conductive wire and a capacitor. The wire is typically gold, aluminum, iron or platinum, and is usually less than 0.5 mm in diameter. The capacitor has an energy consumption of about 25 kWh/kg and discharges a pulse of
current density In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional ar ...
104 - 106 A/mm2, leading to temperatures up to 100,000  K. The phenomenon occurs over a time period of only 10−8 - 10−5 seconds. The process is as follows: # A rising current, supplied by the capacitor, is carried across the wire. # The current heats up the wire through
ohmic heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law (also just Joule's law), also known in countries of former US ...
until the metal begins to melt. The metal melts to form a broken series of imperfect spheres called
unduloid In geometry, an unduloid, or onduloid, is a surface with constant nonzero mean curvature obtained as a surface of revolution of an elliptic catenary: that is, by rolling an ellipse along a fixed line, tracing the focus, and revolving the resulti ...
s. 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 higher current to flow. # 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 In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a med ...
. #
Electromagnetic radiation In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic field, electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, inf ...
is released in tandem with the shock wave. # The shock wave pushes liquid, gaseous and plasmatic metal outwards, breaking the circuit and ending the process.


Practical Application

EWM research has suggested possible applications in the excitation of optical masers, high intensity light sources for communications,
spacecraft propulsion Spacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. In-space propulsion exclusively deals with propulsion systems used in the vacuum of space and should not be confused with space launch or atmospheric e ...
, 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 nanoparticles.


Detonator

EWM has found its most common use as a detonator, named the
exploding-bridgewire detonator The exploding-bridgewire detonator (EBW, also known as exploding wire detonator) is a type of detonator used to initiate the detonation reaction in explosive materials, similar to a blasting cap because it is fired using an electric current. EB ...
, for nuclear bombs. Bridgewire detonators are advantageous over chemical fuzes as the explosion is consistent and occurs only a few microseconds after the current is applied, with variation of only a few tens of nanoseconds from detonator to detonator.


Light Source

EWM is an effective mechanism by which to get a short duration high intensity light source. The peak intensity for copper wire, for example, is 9.6·108 candle power/cm2. J.A. Anderson wrote in his initial spectrography studies that the light was comparable to a black body at 20,000 K. The advantage of a flash produced in this way is that it is easily reproducible with little variation in intensity. The linear nature of the wire allows for specifically shaped and angled light flashes and different types of wires can be used to produce different colors of light. The light source can be used in
interferometry Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber opt ...
,
flash photolysis Flash photolysis is a pump-probe laboratory technique, in which a sample is first excited by a strong pulse of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a fla ...
, quantitative
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
, and
high-speed photography High-speed photography is the science of taking pictures of very fast phenomena. In 1948, the Society of Motion Picture and Television Engineers (SMPTE) defined high-speed photography as any set of photographs captured by a camera capable of 69 ...
.


Production of Nanoparticles

Nanoparticles are created by EWM when the ambient gas of the system cools the recently produced vaporous metal. EWM can be used to cheaply and efficiently produce nanoparticles at a rate of 50 – 300 grams per hour and at a purity of above 99 %. The process requires a relatively low energy consumption as little energy is lost in an electric to thermal energy conversion. Environmental effects are minimal due to the process taking place in a closed system. The Particles can be as small as 10 nm but are most commonly below 100 nm in diameter. Physical attributes of the nanopowder can be altered depending on the parameters of the explosion. For example, as the voltage of the capacitor is raised, the particle diameter decreases. Also, the pressure of the gas environment can change the dispersiveness of the nanoparticles. Through such manipulations the functionality of the nanopowder may be altered. When EWM is performed in a standard atmosphere containing oxygen, metal oxides are formed. Pure metal nanoparticles can also be produced with EWM in an inert environment, usually argon gas or distilled water. Pure metal nanopowders must be kept in their inert environment because they ignite when exposed to oxygen in air. Often, the metal vapor is contained by operating the mechanism within a steel box or similar container. Nanoparticles are a relatively new material used in medicine, manufacturing, environmental cleanup and circuitry. Metal oxide and pure metal nanoparticles are used in
Catalysis Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, sensors, oxygen antioxident, self repairing metal, ceramics, UV ray protection, odor proofing, improved batteries, printable circuits, optoelectronic materials, and
Environmental remediation Environmental remediation deals with the removal of pollution or contaminants from environmental media such as soil, groundwater, sediment, or surface water. Remedial action is generally subject to an array of regulatory requirements, and may al ...
. The demand for metal nanoparticles, and therefore production methods, has increased as interest in nanotechnology continues to rise. Despite its overwhelming simplicity and efficiency, it is difficult to modify the experimental apparatus to be used on an industrial scale. As such, EWM has not seen widespread utilization in material production industry due to issues in manufacturing quantity.


References

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External links


video of the process
Detonators Nuclear weapon design Nanoparticles