Superconductors Essay Research Paper What do transportation - Реферат

Superconductors Essay, Research Paper

What do transportation vehicles, MRIs, electric generators, and

construction sites all have in common? All have either been made possible or

more effective through the use and development of superconductors.

Superconductors are elements in which electrons or electricity can flow

freely and without resistance below a certain temperature. They are the

closest things to perpetual motion in nature for, once set into motion,

current will flow continuously in a closed loop of a superconducting

material. Superconductivity has captivated the minds of scientists and

researchers as one of the last great frontiers of scientific discovery.

Although science is constantly changing and new technological

advancements and discoveries are made daily, still much remains uncertain about

these mysterious materials.

Dutch physicist Heike Kamerlingh Onnes of Leiden University was the

first to observe superconductivity in mercury in 1911 when he cooled the

mercury to four degrees Kelvin, the temperature of liquid mercury, and

the resistance suddenly vanished. Onnes then later won the Nobel Peace

Prize in physics for his research in superconductors in 1913. The next

great discovery did not occur till 1933 when Walter Meissner and Rober

Ochsenfield discovered superconducting materials? ability to repel a

magnetic field. Many naturally occurring substances like water, wood,

and paraffin exhibit weak diamagnetism; however, the superconductors are

able to exhibit strong diamagnetism. A superconductor?s diamagnetism

ability is today called the ?Meissner effect?. Following Meissner and

Ochsenfield?s discovery, many superconducting metals, alloys, compounds,

and their properties were beginning to become revealed.

The first widely accepted theory that deals with superconductors is

BCS Theory. It was developed in 1957 by American physicists John

Bardeen, Leon Cooper, and John Schreiffer, and won them a Nobel Peace prize in

1972. The BCS Theory says that as electrons pass through a crystal,

the structure of the crystal deforms inward and generates sound packets

that they named phonons. The theory goes on to state that these phonons

make the area of deformation positive, which facilitates subsequent

electrons to pass through that area. In 1962, Cambridge University

graduate student Brian D Josephson predicted that electric current would flow

between two superconducting materials, even if they were separated by a

non-superconductor or insulator. His theory was later proven correct

and won him the Nobel Prize in Physics in 1973. His ?tunneling?

discovery is today known as the ?Josephson effect? and become the key to many

electronic devices.

The mysteries of the field of superconductivity began to slowly

unravel during the 1980s. Bill Little of Sandford University suggested the

possibility of organic, carbon-based, superconductors in 1962, but it

was not until 1980 when Danish researcher Klaus Bechgaard of the

University of Copenhagen and three French team members were able to synthesize

the first of these theoretical organic superconductors. Scientific

research slowly continued afterwards until Alex M?ller and Georg Bednorz,

researchers at the IBM Research Laboratory in R?schlikon, Switzerland

made a breakthrough discovery by creating a superconductor out of a

brittle ceramic compound in 1986. They were able to create a

superconductor out of materials that are normally insulators and until that point

had been mostly ruled out by scientists as possible superconducting

candidates. Their discovery won them the Nobel Prize the following year in

1987 and triggered a flood of activity in the field of

superconductivity. In 1997, researches made a discovery that was believed impossible;

they found an alloy of gold and indium at very near absolute zero was

both a superconductor and a natural magnet. In 1999, a similar

discovery was made in a compound of ruthenium and copper. These discoveries

open the doors to endless possibilities in technological advancement, and

at the same time, raise endless questions about the longstanding

theories of superconductivity.

Although not much is currently known about superconductors, there are

three main types of superconductors about which the most is known. One

of these types is Type I Superconductors, also known as soft

superconductors. Another is Type II Superconductors, the hard superconductors,

which also contain the ceramic superconductors. The final type of

superconductors is the atypical superconductors; the atypical

superconductors category includes Fullerenes, which is also known as buckyballs.

Type I superconductors, or soft superconductors, are comprised chiefly

of pure metals that demonstrate conductivity at room temperature as

shown in the periodic table. These superconductors are the ones that have

extremely low critical temperatures. The critical temperature of a

superconductor is the temperature at which it reaches the state of being

superconductive. The critical temperatures of Type I superconductors

range from 0.000325 K, which is quite close to absolute zero, to 17 K.

The critical temperature of 17 K, however, is sulfur when it is put

under a pressure of 1.6 million atmospheres. This is an enormous amount of

pressure and is much too high to allow this superconductor to be useful

to industry. In fact, all of the Type I superconductors have critical

temperatures much too low to be commercially useful superconductors.

Type I superconductors work because the excessively low temperatures

slow down the molecular vibrations enough so that the material is able to

have unimpeded electron flow. BCS theory suggests that in

superconductive materials, the electrons that make up the current flow travel in

pairs called Cooper pairs to overcome obstacles in the crystal, so that

they can both travel faster. One major characteristic of Type I

superconductors is that there is a steep transition from its former state to

its superconducting state. Type I also exhibit diamagnetism. This

means that this type of superconductor repels magnetic fields.

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