The industrial and scientific applications of superconductors are limited by the special temperature conditions they require to work their electromagnetic mojo, so it makes sense to classify materials based on their critical temperatures and pressure requirements.
Hundreds of substances, including 27 metallic elements -- such as aluminum, lead, mercury and tin -- become superconductors at low temperatures and pressures. Another 11 chemical elements -- including selenium, silicon and uranium -- transition to a superconductive state at low temperatures and high pressures [source: Encyclopaedia Britannica].
Until 1986, when IBM researchers Karl Alexander Mulller and Johannes Georg Bednorz ushered in the age of high-temperature superconductors with a barium-lanthanum-copper oxide that achieved zero resistance at 35 K (minus 238 C, minus 397 F), the highest critical temperature achieved by a superconductor measured 23 K (minus 250 C, minus 418 F). Such low-temperature superconductors required cooling by liquid helium, which was difficult to produce and tended to break budgets [source: Haldar and Abetti]. High-temperature superconductors bring the temperature range up to around 130 K (minus 143 C, minus 226 F), meaning they can be cooled using liquid nitrogen made cheaply from air [source: Mehta].
Although physicists understand the mechanisms governing low-temperature superconductors, which follow the BCS model, high-temperature superconductors remain enigmatic [source: CERN]. The holy grail would be to achieve a material with zero resistance at room temperature, but thus far that dream remains elusive. Perhaps it cannot be done or, perhaps, like other scientific revolutions, it lies just over the horizon, awaiting the necessary technological or theoretical innovation to make the dream a reality.
In the meantime, the powerful advantages that superconductors offer suggest a wide array of present and future applications in the areas of electric power, transportation, medical imaging and diagnostics, nuclear magnetic resonance (NMR), industrial processing, high energy physics, wireless communications, instrumentation, sensors, radar, high-end computing and even cryogenics [source: CCAS].
In addition to the maglev, MRI and particle accelerator applications we mentioned earlier, superconductors are currently used commercially in NMR spectroscopy, a key tool for biotechnology, genomics, pharmaceutical research and materials science work. Industry also applies them in a magnetic process for separating kaolin clay, a common filler in paper and ceramic products.
As for the future, if researchers and manufacturers can overcome superconductors' limitations of cost, refrigeration, reliability and acceptance, the sky's the limit. Some see green technologies, such as windmills, as the next step in a more widespread acceptance and application of the technology, but larger possibilities loom.
Who knows? Perhaps a future reader will peruse this very article on a computer equipped with near-light-speed processors, hooked to a grid powered by fusion reactors -- all thanks to superconductivity.