LITMIR.BIZ

      IV. Translate at sight

      A valuable contribution to the advancement of the science of materials has been made by Russian scientists. P.P. Anosov (1799-1851) was the first to establish definite correlations between the structure and properties of steels. D.K. Chernov (1839-1921) discovered polimorphic transformations in steels and has been recognized worldwide as the founder of scientific physical metallurgy. The work of N.S. Kurnakov (1860-1941) and his disciples was of large importance for the development of physico-chemical methods of analysis and for the classification of complex phases in metal alloys. The development of the theory and technology of heat treatment of steels is associted with the names of S.S. Steinberg (1872-1940) and N.A. Minkevich (1883-1942).

      A.M. Butlerov (1828-1886), one of the outstanding Russian chemists, worked out the theory of chemical structure of organic substances, the scientific basis for the manufacture of polymer materials. The research work of S.V. Lebedev opened the possibility of industrial production of synthetic rubber. The advancement of polymer technology owes much to the structural studies carried out by V.A. Kargin and his disciples.

      V. Give definitions for the following bonds between the atoms of substances: ionic, atomic, metallic, molecular bonds.

      VI. Retell the text

      Conducting materials

      The most important solid conducting materials used in electrical engineering are metals and their alloys.

      Among metal conductors, one can distingush high-conductivity metals, whose resistivity at normal temperature is not over 0.1 Mflm, and high-resistivity alloys with a resistivity at normal temperature being no less than 0.3 Mfim. The first type is used for wires, cable conductors, coils of electrical machines and transformers, and the second for resistors, electric heaters, etc.

      Of special interest are superconductors and cryoconductors (hyperconductor), which show extremely low resistivity at room temperatures close to absolute zero.

      Liquid conductors are molten metals and various electrolytes. The melting points of most metals are high; only mercury and some special alloys can be used as liquid conductors at normal temperature.

      As has been mentioned above, metals both in the liquid and solid state have a rather large amount of free electrons, which act as carriers of charge when voltage is applied to a metal conductor. Thus, the mechanism of current flow through liquid or solid metals involves the drift of free electrons under the action of an electric field produced in a metal on applying an external voltage to it. Therefore, metals are called conductors of electronic or metallic conduction, or conductors of the first kind.

      Electrolytic conductors or conductors of the second kind are solutions and melts of salt, acids, and alkalis and other substances of ionic structure. The flow of current through electrolytes is associated with the electrolysis phenomenon. In the process of electrolysis, charge-carrying ions migrate in an electrolytic medium, the electrolysis products settle out on the electrodes in accordance with Faraday’s laws, and the electrolyte composition gradually changes as the current passes through it. This is not the case with metals where the current flow does not affect their mass or chemical composition.

      In an electric field of rather low strength, all gases and vapors, metal vapors included, display the properties of dielectrics with very high resistivity. But as soon as the field strength exceeds a certain critical value that makes for the onset of ionization, a gas become a conductor featuring electronic and ionic conduction. A strongly ionized gas, in which the number of electrons equals the number of positive ions in a unit volume, makes a specific current-carrying medium known by the name plasma.

      Exercises:

      I. Memorize the following words and word combinations:

      II. Find the Kazakh (Russian) equivalents to the following word combinations:

      А) High-conductivity metals; high-resistivity alloys; cable conductors; coils of electrical machines; products settle out on the electrodes; exceeds a critical value.

      В) токопроводящий кабель; металлы высокой проводимости; превышать критическое значение; обмоток электрических ма-шин; продукты электролиза выделяются на электродах; сплавы высокого сопротивления.

      С) тоқөткізгіш шоғырсым; жоғары өткізгішті металлдар; кри-тикалық мәннен асу; электрлік машиналардың орамы; электро-лиз өнімдері электродтарда ерекшеленеді; жоғапры кедергілі құймалар.

      III. Translate into English using the active vocabulary of the lesson:

      IV. Translate at sight

      Three States of Matter

      All material is made from tiny particles. These particles are constantly moving. The kinetic theory uses this idea of tiny moving particles to explain the different forms that material can take. “Kinetic” means “to do with movement”. The three states of mattes are solid, liquid and gas.

      Solid. In this state matter tends to keep its shape. If it is squashed or stretched enough, it will change shape slightly. Usually, any change in volume is too small to be noticed. The particles are not moving around, although they are vibrating very slightly. Normally they vibrate about fixed positions. If solid is heated the particles start to vibrate more. The particles in a solid are fixed in position. The forces between particles are strong.

      Liquid. In this state matter will flow. It will take up the shape of any container it is put in. The liquid normally a fills a container from the bottom up. It has a hardly changes at all. The particles, like those in a solid, are vibrating. However, in a liquid the particles are free to move around each other. If a liquid is heated, the particles move faster. In liquids particles can move past each other. They are joined together in small groups. They are not as close as in solids.

      Gas. In this state matter will take up the shape of a container and fill it. The volume of the gas depends on the size of its container. If the gas is squashed it will change both volume and shape. The particles are free to move around, and do not often meet each other. The particles whiz(z) around very quickly. If heated they move even faster. In gases there are hardly any forces between particles. They are a long way apart.

      V. Retell the text.

      Various metals

      Aluminium

      Aluminium

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