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Экзамен - Темы - 2008 / solid state TEXT

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If you took a paper clip and bent it, it would stay bent, it wouldn't spring back and it wouldn't break. The metal of which the clip is made is ductile. Some other materials are not ductile at all. If you tried to bend a glass rod (unless you are holding it in a flame), it would simply break. It is brittle. In this respect as in many others, glass behaves quite differently from, a metal., The difference must fie either in 'the' particular atoms of which metals and glass are made up or in the way they are put together, probably both. There are of course many other differences between metals and glass.

Metals, for example, conduct electricity and are therefore-used for electrical transmission lines, glass hardly conducts electricity at all and can serve as an insulator. Glass being transparent, it can be used in windows whereas a sheet of metal even more than a millionth of an- inch thick is quite opaque. It is of course interesting to understand the reasons of these differences in behaviour.

During the past 20 years studies of this kind have been called solid-state physics, or sometimes since the subject includes a great dear of chemistry, Just "solid state". It is a major branch of science that has revealed new and previously unsuspected properties in materials. Solid-state physics has become one of the most important branches of technology. It has given rise to technological progress. Having studied this branch of technology, engineers could understand much better the phenomenon of quantum mechanics as it is applied to solids. Though solids, of course, were the subject of exper­imental investigation long before quantum mechanics was

invented. If we considered the fact known since "the earliest studies of electric currents, we should remember that metals conduct electricity well and most other materials do not.

It is only the discovery of electron that could help the scientists to understand some of these facts well. With the discovery of electron it was assumed that in metals sortie or all of the atoms had lost an electron and that in insulators such as glass they had not. The electrons in a metal proved thus to move freely, whereas the electrons in insulators do not. Why did this happen in metals? This very question had to await the discovery of quantum mechanics. The next question was: "How are" the atoms arranged?

As far as this question is concerned we can say that solids can be divided into two classes: crystalline and amorphous. In the crystalline group, which is the largest and includes the metals and most minerals, the atoms are arranged in a regular way. In some metals (for instance copper and nickel), they are packed together. In other metals (such as iron, for example), they are arranged in the form of a cube. The commonest of the amorphous group of solids appears in glass, its atoms are put together in a more disordered way than those of a metal.

The structure of an amorphous material is much more difficult to discover than that of a crystalline solid and consi­derable effort is being made to learn more about the arrange­ment of atoms in such materials.

Much has been learned about solids but much is still to be learned. There is a number of problems which are to be solved. No wonder that many scientists have been working at this interesting, so-called "solid-state" science.

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