A great amount of power is lost when currents pass through a conductor due to resistance. More than 50 per cent of global energy is wasted that way. Hence scientists and researchers have always thought of producing materials of zero resistance or super conductors and this very remarkable phenomenon is known as “Superconductivity”.
In 1911, it was Heike Kimberling Ones. A Dutch physicist, who for the first time discovered superconductivity, while studying the variation of electrical resistance of mercury with temperature, he surprisingly observed that at the temperature within a few degrees of absolute zero, the resistance dropped sharply to an immeasurably small value.
Hence he could able to conclude that temperature acts as an important factor for resistance and conductance. When temperature is dropped to its lowest level i.e. to absolute zero or zero degree Kelvin which is 273° C. there is the state of superconductivity. This state could also be attained only at the low temperature of 4.2°k which is the boiling point of liquid helium.
To maintain the required temperature, superconducting devices were kept in liquid helium in tightly sealed and heavily insulated containers where cost was too high. This high cost maintenance restricted the applications of this technology to few devices i.e., a Japanese prototype of a magnetically levitated super train, a few magnetic resonance imaging (MRI) machines and in nuclear fusion research centers.
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Gradually various superconducting materials searched out with increase in temperature up to 100°K. Liquid helium could now be replaced by liquid nitrogen for economy point of view, which is cheaper. Scientists started working vigorously with a hope of generating devices which could have power efficiency of 100 per cent.
But such hopes were soon shattered by the findings of W. Meissner and R. Ochsenfeld in 1933. They discovered that these materials (lead, tin, mercury etc.) which were originally known to be superconductive at low temperatures, would lose this capability as soon as enough current was flowing through them to generate significant magnetic fields.
In other words, when a superconductor is exposed to a high magnetic field, the electrical resistance returns. That is possible only when a current passes through a conductor which generates a high magnetic field. Hence it was confirmed that super conductors would only carry a limited current in the resistance less condition and super conductors were not only perfect electrical conductors but also develop perfect magnetic field. Some materials such as the ceramics, the alloys of oxides of niobium and titanium which are usually called non-conductors can be able to maintain their superconductivity despite strong magnetic fields.
In 1986, it was Karl Alex Miller of IBM’s International Business management) at Zurich laboratory, who could be able to raise the temperature of superconducting materials beyond 230° K taking metallic oxides known as ceramics as test materials. Since then, more than 100 high temperature superconductivity (HTS) compounds have been developed and the highest critical temperature (Tc, the temperature below which the compound is superconducting) has-now been increased unto 134° K.
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Then it was Paul C.W. Chu of Houston University (USA), who could able to develop a superconducting material of Tc 52° K by increasing the pressure. Earlier he was working with barium. But, he cleverly replaced the barium with strontium and was successful in increasing the transition temperature to two more degrees. Later, Chu again tried lanthanum. Maa-kuen-Wu, a student of Chu replaced lanthanum with another rare earth element i.e., yatrium.
Application of Superconductors:
The first practical application of superconductor materials was in making superconducting wires. Initially Yatrium-Barium Copper Oxide (YBCO) was used. But soon it was found that these materials were unsuitable for wire-making. Hence, later on, Bismuth Strontium-Calcium-Copper-Oxygen (BSCCO) wires could be produced.
From developing miniaturized high speed computing machines using millions of superconductive switches to high speed electromagnet super trains, the fields of superconductivity applications are vast. It helps in cryogenieists to build extremely powerful electromagnets, transformers, generators, super computers and motors which would have 100 per cent efficiency. Researches are going on hoping a day for acquiring reliable superconductivity at room temperature. When that is achieved, a remarkable revolution will be visualized in the field of science and technology.
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Super conductivity research in India:
India’s superconductivity researches began in 1987 when Indian Institute of Science and Tata Institute of Fundamental Research, BARC, Bombay, National Physical Laboratory, New Delhi, Indian Institute of Technology had all announced the successful fabrications of their Y-Ba-Cu-O compounds. The research is also going on at the KGCAR, Kalpakkam. India has the world’s largest rare earths deposits. If higher room temperature superconductors could be developed, it would definitely lead to incredible savings in energy.