By Robert Hazen, Ph.D., George Mason University
The properties of materials depend on the type of atoms and the way they’re bound together by chemical bonds. A basic material property is electrical conductivity, which is the ability of a material to carry an electric current. One of the most important properties of materials in modern life is their ability to control the flow of electrons, of electricity. Electrical conductors and insulators are both essential parts of this process.
Metals and their Electrical Conductivity
Good electrical conductors include all the materials in which electrical charges flow easily; that’s electrons flowing through the material. The most common of these materials are metals. Metals, by definition, have electrons that are free to move under the slightest voltage.
All known materials have some resistance to this electrical flow at room temperature, and that causes heating of wires and it causes a slight loss of electrical energy. Nevertheless, copper, aluminum can be used as wires, and electricity will flow through these for many, many miles; that’s why most common wires used in everyday use are formed of copper.
There’s another kind of conductor as well. These are called fast-ion conductors; a strange kind of conductor in which, instead of electrons moving, actual atoms, charged atoms, the ions move through the material. Many batteries use these kinds of conductors; for example, lithium is a fast-ion conductor.
Learn more about electricity.
Electrical Insulators
Electrical insulators are essential because they restrict the flow of electricity. It is needed for efficiency and safety. When you plug in a wire, you don’t want to get shocked, so you need a good insulator wrapped around that wire.
The best insulators are made from materials in which electrons don’t move, things like ionically bonded materials. The trouble is, most ionically bonded materials are very brittle; they don’t make very good wires. So scientists compromise and use covalently bonded materials, like plastics, to wrap around the wires.
Typical wire, then, will have a plastic coating around a metal core, and that’s the way most wires are built. They’re amazingly flexible—you can tie wires in knots, and crush them and abuse them in all sorts of ways, and they keep on working and working.
This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.
Superconductors
Superconductors are remarkable materials that conduct electricity without any resistance at all, but all of these materials require extremely cold temperatures to work. New materials are being discovered, however, that keep raising the temperature limit. These new superconductors are finding many new applications.
Superconductivity was discovered by Dutch physicist Heike Kamerlingh-Onnes in 1911 when he measured zero resistivity in a sample of mercury at 4°K, that’s at liquid-helium temperature.
Onnes was one of the world’s great authorities on extreme refrigeration; that’s temperatures near absolute zero. He found that an electrical current would flow for years without stopping once started in his mercury. Such a property suggested many practical applications, from powerful, permanent electromagnets that operated forever to no-loss electrical-power transmission over long distances.
Use of Niobium Metal Alloy as a Superconductor
Most of the subsequent research has focused on finding other superconductors that work at higher and higher temperatures, and most of the research focused on metals in the early years. Eventually, an alloy of the metal niobium was found that worked at about 22°K, and that’s used in many practical applications today.
For example, an MRI, a magnetic resonance imaging scan, uses liquid-helium-cooled niobium superconductors; and there are many other applications as well.
Although the properties of materials are the result of atomic-scale activity, superconductor behavior remains very mysterious. No one is really sure exactly how it works.
Typically, they talk about electrons that pair and surf along, following each other through an electromagnetic wave through the material, traveling forever on that electromagnetic wave. But it’s still rather difficult for any of us to imagine how superconductors work.
Learn more about the ultimate structure of matter.
Paul Chu and Invention of a New Superconductor
In February of 1987, the University of Houston scientist Paul Chu, a physicist who had been spending his life on superconductivity, invented the first superconductor that worked at liquid-nitrogen temperature. Liquid nitrogen is very cheap and can actually be used in everyday applications.
This transformed superconductivity from something that is an esoteric and strange phenomenon to one that could be demonstrated on a tabletop.
In order to understand how a material works, you have to know the atoms it’s made of, and you have to know its crystal structure. Paul Chu worked with others to determine the crystal structure of this new material.
If we pour liquid nitrogen on a disk made of this material, it cools it right down, cools it down to about liquid-nitrogen temperature. As that disk cools, the superconducting begins to work. One of the properties of superconductors is that they repel a magnetic field, they push magnetic fields right out. So a magnet material levitates above the disk.
This wonderful property of superconductors can lead to levitating trains, and other transportation techniques, where we literally lift giant objects off the ground and float them to their destination. This is a property of high-temperature superconductivity, and now we can use cheap liquid nitrogen to achieve this goal.
Common Questions about Electrical Conductors, Insulators, and Superconductors
Some materials, such as metals, have a special property called electrical conductivity. Electrons flow easily in materials that have electrical conductivity. Only a slight voltage is sufficient to make electrons move and transfer electricity.
Copper and aluminum are among the best metals that have electrical conductivity. These metals are used to make different kinds of wires. In order to maintain safety (from not getting shocked), electrical conductors must be wrapped up with plastic.
Electrical insulation is the opposite of electrical conductivity. Materials ionically or covalently bonded together are electrically insulating. Covalently bonded materials are mostly used to wrap around wires.
