Методическая разработка по работе со спецтекстами на английском языке для студентов физического факультета



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Advanced experimental methods, such as thin-foil electron microscope or neutron diffraction analysis, made it possible to study elements and defects of crystal structures and the laws of transformations in materials under the influence of external factors (temperature, pressure, etc.). Analysis of the physical (density, electrical and thermal conductivity, magnetic modulus, etc), technological (fluidity, deformability, machinability, etc), and operating properties (corrosion and wear resistance, fatigue strength, heat and cold resistance, etc) are helpful in determining the most rational and efficient applications for various materials.



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 мΩm, and high-resistivity alloys with a resistivity at normal temperature being no less than 0.3 мΩm. 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 (hyper-conductor), 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. Memorise the following words and word combinations:
Alloys – сплавы; dielectric – диэлектрик; mercury – ртуть; еlectrolytic conductors – электролиты; solutions – растворы; melts of salt – расплавы солей; field strength – напряженность поля; acid – кислота; alkali – щёлочь; resistivity – удельное сопротивление; vapors – пары.

II. Find the 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.
Б) токопроводящий кабель; металлы высокой проводимости; превышать критическое значение; обмоток электрических машин; продукты электролиза выделяются на электродах; сплавы высокого сопротивления.

III. Translate into English using the active vocabulary of the lesson:
1) Сплавы высокого сопротивления применяют при изготовлении резисторов, электронагревательных элементов и.т.д.

2) В металлах как в твердом, так и в жидком состояниях, имеется большое количество свободных электронов, которые являются носителями заряда при прохождении через металл электрического тока.

3) Проводниками второго типа, или электролитами, являются растворы и расплавы солей, кислот, щелочей и других веществ с ионным строением молекул.

4) На электродах в соответствии с законом Фарадея выделяются продукты электролиза, а состав электролита при прохождении через него тока изменяется.


IV. Render in English

Проводники

В проводниках содержится большое число подвижных носителей зарядов. Большую часть твердых проводников составляют металлы. Их высокая электропроводимость объясняется особенностями строения их кристаллической решетки.

В металлах всегда имеется много свободных электронов, которые движутся внутри решетки, состоящей из положительно заряженных ионов.

Однако электропроводность определяется не только значением n, но и тем сопротивление, которое встречают подвижные носители зарядов со стороны решетки вещества при их движении внутри него под действием электрического поля, т.е. подвижностью этих носителей в веществе.

Присутствие в проводнике небольшого количества примесей не вызывает заметного изменения концентрации подвижных носителей зарядов, но сильно влияет на их подвижность. Поэтому проводимость чистой меди значительно больше, чем меди, содержащей небольшое количество примесей.



V. Write an annotation on the text.

VI. Retell the text.

Various metals

Aluminium
Aluminium is a major representative of light metals (with densities below 5,000 kg/m3); the density of cast aluminium is around 2,600 kg/m3, and rolled aluminium 2,700 kg/m3. Aluminium is thus about 3.5 times lighter than copper.

The resistivity of aluminium is approximately 1.63 times that of copper, and therefore aluminium cannot always be substituted by copper, especially in radio electronics. However, an aluminium wire of the same length and resistance as a copper wire would be almost half as heavy as the latter, though thicker. That is why in fabricating the wire of one and the same conductance per unit length, it would be more profitable to use aluminium than copper, if the former is no more than two times as high in cost per ton as the latter. Also of importance is the fact that aluminium is more readily available than copper.

A grade A1 aluminium that has no more than 0.5% impurities is used for general electrical purposes. A grade AB00 aluminium that average 99.97% pure goes for aluminium foil, electrodes and castings of electrolytic capacitors. The highest purity aluminium, grade AB000, has 0.004% impurities.

Aluminium is rolled, and annealed in the same manner as copper. It can be rolled into thin foil, down to 6 to 7мm, which is used for plates of paper and film capacitors.

The surface layer of aluminium readily oxidizes to form a thin oxide film of high resistance. This film protects aluminium against further corrosion, but builds up a high contact resistance (where aluminium wire come in contact) and makes ordinary soldering methods unsuitable for aluminium. This difficulty is obviated by employing special brazing pastes or ultrasonic soldering bits.

Exercises:

I. Memorise the following words and word combinations:
rolled – прокатный; copper – медь; profitable – выгодный; impurities – примеси; pure – чистый; aluminum foil – алюминиевая фольга; electrode – электрод; grade – марка; ordinary soldering methods – пайка обычными способами; ultrasonic soldering bits – ультразвуковые паяльники.

II. Find the Russian equivalents to the following word combinations:

А) the density of cast aluminum; casting of electrolytic capacitors; аluminum is annealed; plates of film capacitors; builds up a contact resistance; employing special brazing pastes.

Б) создавать переходное сопротивление; корпус электролитических конденсаторов; плотность литого алюминия; применение специальных паст припои; отжиг алюминия; обкладки пленочных конденсаторов.

III. Translate into English using the active vocabulary of the lesson:
1.Алюминиевый провод хотя и толще медного, но легче его приблизительно в 2 раза.

2. Чистый алюминий применяют для изготовления алюминиевой фольги, электродов и корпусов электролитических конденсаторов.

3. Из алюминия может прокатываться тонкая фольга, применяемая в качестве обкладок в бумажных и пленочных конденсаторах.

4. Для пайки алюминия применяются специальные пасты – припои или используются ультразвуковые паяльники.



VI .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.



Iron
Iron (steel), the cheapest and most common commercial metal of high mechanical strength, is sometimes used as a conducting material. However, even pure iron has a considerably higher resistivity (about 0.1 мΩm) than copper and aluminium; steel, i.e. iron with carbon and other elements chemically dissolved in it, has a still greater resistivity.

Being a ferromagnetic material, steel is liable to a pronounced skin effect in an a.c. field; therefore steel conductors offer a higher opposition to alternating current than to direct current. Besides, the hysteresis loss appears in steel conductors when they carry alternating current.

Ordinary steel is vulnerable to corrosive attack; even at normal temperature, especially at high humidity, it rusts rather rapidly, while at elevated temperature the rate of corrosion is even higher. This calls for the protection of steel conductors with a surface layer of a more corrosion-resistant material. Commonly, steel conductors are zinc-plated.

Since iron has a high temperature coefficient of resistivity, a thin iron wire, if protected against corrosion by placing it, for example, into a vessel filled with hydrogen, can be used in devices, where the wire resistance rises rapidly with increases in current tends to maintain a constant current despite the variations in the line voltage.



Exercises:

I. Find the Russian equivalents to the following words and word combinations
А) Iron; steel; mechanical strength; carbon; alternating current (а. с.); hysteresis loss; skin effect; vulnerable to corrosive attack; humidity; rust; surface layer; placing into a vessel filled with hydrogen; variations in the line voltage.
Б) колебание напряжения; обладает малой коррозионной стойкостью; сталь; механическая прочность; потеря мощности на гистерезис; железо; поверхностный эффект; поверхность; ржаветь; помещение в баллон, заполненный водородом; углерод; переменный ток; влажность.

II. Translate into English using the active vocabulary of the lesson:
1) Сталь наиболее дешевый и доступный металл, обладающий высокой механической прочностью.

2) При переменном токе в стальных проводниках появляются потери мощности на гистерезис.

3) Поверхность стальных проводов должна быть защищена слоем более стойкого материала, например цинка.

4) Прибор сохраняет постоянную силу тока при колебаниях напряжения.



III. Give the main points of the text

Contact materials
Contacts which serve to periodically switch on and off electric circuits operate under very arduous conditions.

The materials of break contacts intended to open high-current, high-voltage circuits must be reliable enough to exclude burning of contacting surfaces or their sticking as the arc appears at the break, and to provide for low contact resistance when the contacts close the circuit.

Break contacts are made from various alloys and powder-metallurgy composition (cermets) apart from pure high-melting metals. Most popular is the Ag-CdO material containing 12 to 20% cadmium oxide by mass. It is obtained by heating a silver-cadmium alloy in the oxidizing atmosphere. The break contacts designed for service in high-powder devices are from Ag-Co, Ni-Cr-W-Mo-Ta, Cu-W-Mo, and Au-W-Mo compositions.

The materials used for sliding contacts must be highly resistant to abrasion. These are cold-drawn (hard) copper, beryllium bronze, and the materials of the Ag-CdO group.



Solders and fluxes
Solders are special alloys used to obtain a mechanically strong (sometimes tight) joint or a permanent electrical contact of low resistance. Prior to soldering, the metal portions to be joined and the solder must be heated. Since the solder has a much lower melting point than the metals to be joined, it melts, while the metals remain hard. At the place where the molten solder comes in contact with the hard metal, complex physicochemical processes take place. The molten solder wets the metal, spreads over it and fills in the gaps between the metal parts. In this process, the solder diffuses into the base metal which dissolves in the solder and thus forms an intermediate layer (seam) that after hardening fastens the parts together into an integral assembly.

Fluxes are auxiliary materials used in soldering: (1) dissolve and remove oxides and contaminants from the surface of metals to be soldered, (2) protect the metal surface and the molten solder from oxidation, (3) reduce the surface tension of the molten solder, and (4) to improve the ability of the solder to spread over and wet the surface to be soldered.



Exercises:
I. Memorise the following words and word combinations:
Solders – припой; powder-metallurgy composition – металлокерамические композиции; break contacts – разрывные контакты; oxidizing atmosphere – окислительная атмосфера; high-power device – установка большой мощности; sliding contacts – скользящие контакты; resistant to abrasion – стойкость к стиранию; surface tension – поверхностное натяжение; intermediate layer – промежуточный слой; fluxes –флюсы.

II. Find the Russian equivalents to the following words and word combinations:
А) switch on electric circuits; switch off electric circuits; exclude burning of contacting surfaces; sticking as the arc appears; fills in the gaps; spreads over the metal; dissolves; fastens the parts; remove contaminants.
Б) удалять загрязнения; заполняет зазоры; приваривание под действием электрической дуги; замыкание электрических цепей; растекается по металлу; соединять детали; не допускать обгорания контактирующих поверхностей; растворяется; размыкание электрических цепей.

III. Translate into English using the active vocabulary of the lesson:
1) Наиболее ответственными контактами, применяемыми в электротехнике, являются контакты, служащие для периодического замыкания и размыкания электрических цепей.

2) В качестве материалов для скользящих контактов, которые должны обладать высокой стойкостью к стиранию, используют твердую медь и берриллевую бронзу.

3) Припои представляют собой специальные сплавы, применяемые при пайке.

4) Так как припой имеет температуру плавления значительно ниже, чем соединяемые металлы, то он плавится, в то время как основные металлы остаются твердыми.

5) Припой диффундирует в основной металл, а основной металл растворяется в припое, в результате чего образуется промежуточная прослойка, которая после застывания соединяет детали в одно целое.

IV. Give the main points of the text

Non-metallic conductors

Electrical carbon elements


Among the solid non-metallic conductors, of primary importance are carbon base materials. Carbon goes into the production of electrical brushes; electrodes for projectors, electric arc furnaces and electrolytic baths; galvanic cell anode; and so on. Carbon powder is used in microphones which depend for their operation on the variation in resistance of carbon powder contacts with sound pressure. Carbon is also used for high-resistance elements, telephone line discharges, and for the production of some parts employed in the electrode-tube industry.

The raw materials used for the fabrication of electrical carbon elements are carbon black graphite, and hard coal (anthracite).

Carbon electrodes intended to operate at high temperatures are baked at about 3,000C. Carbon powders for microphones are prepared from hard coal. The resistivity of powder depends on grain size, the process of powder baking, and compactness of filling.

Carbon-base resistors differ from wire resistors in that the former are smaller in size and have higher upper limits of rated resistance. They find widespread use in automatic, measuring, computing equipment, etc. They must be low-sensitive to voltage variations and highly stable to heat and moisture.

The materials used for this type of linear resistors are natural graphite, carbon black, pyrolitic carbon, borated carbon films, and also high-resistance alloys and other materials.

Exercises:

I. Memorise the following words and word combinations:
electrical brushes –щётки электрических машин; electric arc furnaces – электроды для дуговых электрических печей; electrodes for electrolytic baths – электроды для электролитических ванн; galvanic cell anode – анод гальванического элемента; telephone line discharges – разрядники для телефонных сетей; carbon black – сажа; graphite – графит; hard coal (anthracite) - антрацит; сarbon electrodes – угольные электроды.
II. Find the Russian equivalents to the following words and word combinations:
А) electrode-tube industry; raw material; intended to operate; grain size; process of powder baking; compactness of filling; limit of rated resistance; moisture ; carbon black; pyrolitic carbon; sound pressure; borated carbon films; high-resistance alloys.
Б) бороуглеродистые плёнки; придел номинального сопротивления; электровакуумная индустрия; звуковое давление; высокоомные сплавы металлов; сажа; сырьё; размер зерна; пиролитический углерод; влажность; плотность засыпки; режим обжига; предназначены для работы;


III,Translate into English using the active vocabulary of the lesson:
1.Угольные порошки используют в микрофонах для создания сопротивления, изменяющегося от звукового давления.

2. Угольные электроды, предназначенные для работы при высоких температурах, обжигают при особо высокой температуре.

3. Непроволочные резисторы, отличающиеся от проволочных уменьшенными размерами и высоким верхним пределом номинального сопротивления, находят широкое применение.

4.При высоких температурах обжига углерод переводится в форму графита.



IV. Render in English
Люминесценция вещества
Молекулы вещества могут быть приведены в возбужденное состояние без увеличения их средней кинетической энергии неупорядоченного движения, иначе говоря, без нагрева вещества. Возбужденное состояние молекул может быть достигнуто не только путем повышения температуры, но и механическим, электрическим, радиационным и химическим воздействиями.

Люминесценцией называют собственное свечение вещества в данной области спектра, если оно превосходит лучеиспускание полного излучателя в той же спектральной области и при той же температуре. По С.И. Вавилову высвечивание запасенной веществом энергии и является люминесценцией, или самосвечением вещества.

Люминесцирующее вещество (люминофор) задерживает часть поглощаемой извне энергии в форме энергии возбужденного состояния молекул вещества и, не преобразуя ее в тепло, раньше или позже испускает эту энергию в виде собственного излучения. Спектр люминесценции вещества может быть расположен как в оптической, так и в рентгеновском области спектра электромагнитных излучений (включающего и гамма-излучение атомных ядер).

V. Retell the text

Dielectric materials

Dielectric polarization

I. Look through the text and give the definition of dielectric materials and dielectric polarization.
In describing electric phenomena, polarization includes, which occur in dielectric materials, it is common practice to consider an insulation specimen fitted out with electrodes made from a metal or any other suitable conductor for applying an electric voltage to the dielectric. This can be an electric capacitor, a cable insulation or any piece of dielectric material specifically prepared for measuring its electric parameters under laboratory conditions.

Whether or not any substance has free charge carriers, it always contains bound charges: electrons revolving in atomic orbits atomic nuclei, and ions. An external electric field applied to a dielectric tends to change the equilibrium position of bound charges so that positive charges displace in the direction of the field strength E, and negative charges in the opposite direction. In consequence, every elementary volume of the dielectric material, dV, acquires an induced electric moment dp. The electric dipole moment p owes its presence in the dielectric to the polarization phenomenon. The intensity of polarization P is equivalent to the electric dipole moment per unit volume of the dielectric material (P=dp/dV).


Thermal properties
Thermal endurance. The ability of electrical insulation to stand up to elevated temperatures without detriment to its reliability has a direct bearing on the operating temperature limits of devices.

Extension of the upper temperature limit, which generally depends on the thermal properties of insulating materials employed, enables the design engineer to reduce the overall dimensions, mass, and cost of an electrical machine or apparatus. The problem of mass and size reduction is of special concern for traction and crane motors, and airborne electronic equipment. The allowable working temperature dictates safety measures which must be taken against fire and explosion at oil deposits of electrical substations, and in oil and mining industries.

In electrical furnaces, heating appliances, electric welding apparatus, lighting facilities, and in electronic and ionic devices, high-temperature requirements for insulation arise from the operational conditions under which these installations and devices are called upon to operate.

At elevated temperatures, some materials inadmissibly degrade in mechanical properties and others in dielectric properties

Unwanted changes in the insulation can also appear due to slow-acting chemical processes at continuous operating temperatures, causing what is called thermal ageing.

It is important that insulating materials, particularly brittle ones, such as glasses and ceramics, be stable to sharp temperature changes, called thermal shocks.

Abrupt heating or cooling of a glass product causes thermal stresses to appear in its outer layer due to a nonuniform distribution of heat, which may lead to cracking.

The ability of electrical insulating materials and insulation systems to withstand both continuous and short-time operating temperatures and also sharp temperature changes without failure is known as thermal endurance.


Cold endurance. In most instances, the insulation used, for example, in airborne electronic equipment, communication lines, outdoor substations, and in similar installations must be cold resistant, i.e. capable of ensuring reliable performance of devices at low-temperatures, say, minus 60 °to minus 70 °C, or even at still lower (cryogenic) temperatures. This characteristic is known as cold endurance, or cold resistance. Under such environmental conditions, the electrical properties of insulating materials generally improve, but some materials, being flexible and elastic at normal operating temperatures, become brittle and stiff. This involves certain difficulties in servicing and maintenance of devices. Test on insulating materials and insulation systems for cold endurance are not infrequently performed under vibration.

Exercises:

II. Memorise the following words and word combinations:
Thermal endurance. – нагревостойкость; traction and crane motors – тяговые и крановые электродвигатели; airborne electronic equipment – самолетное электрооборудование; heating appliances –нагревательные приборы; electric welding apparatus – электросварочная аппаратура; lighting facilities – источники света; сold endurance – холодостойкость; flexible – гибкий; elastic – эластичный; stiff – жесткий; thermal stresses – температурные напряжения; cracking – растрескивание; to withstand – выдерживать.


III. Find the Russian equivalents to the following words and word combinations:
А) to stand up to elevated temperatures; without detriment to its reliability; reduce the overall dimensions; allowable working temperature; oil deposits of electrical substations; mining industry; inadmissibly degrade; without failure.
Б) Масленые хозяйства электрических подстанций; без уменьшения эксплуатационной надежности; выдерживать повышенную температуру; допустимая температура; уменьшение габаритных размеров; без ущерба; недопустимо ухудшаются; угольная промышленность.

IV Translate into English using the active vocabulary of the lesson:
1) От допустимой температуры зависят пожарная безопасность и взрывобезопасность.

2) Помимо ухудшения качества электрической изоляции при длительном воздействии повышенной температуры могут наблюдаться изменения за счет медленно протекающих химических процессов – так называемого теплового старения изоляции.

3) Способность электроизоляционных материалов и изделий без ущерба для них выдерживать высокую температуру, а также резкую смену температуры, называют нагревостойкостью.

4) Способность электрической изоляции не снижать эксплуатационной надежности при низких температурах называют холодостойкостью.



Moisture-resistant properties
Many electrical insulating materials are hygroscopic to a greater or lesser degree, i.e. pervious to moisture.

Hygroscopicity. At a certain humidity and temperature of the surrounding medium, an insulation specimen reaches over some length of time an equilibrium state as regards its content of moisture. Thus, if a comparatively dry insulation specimen is exposed to moist air of relative humidity ц, it will gradually absorb moisture from the air. Its humidity Ψ, or the moisture content per unit mass of the material, will grow during some time t, approaching an equilibrium moisture content Ψ eq at a definite air humidity. On the contrary, if a specimen of the same insulation, but with the initial moisture content in excess of Ψ eq, is exposed to the same humid atmosphere, its humidity will decrease to the equilibrium moisture content Ψ eq. In the later case, the specimen is said to be drying At the same air humidity, the equilibrium moisture content of different materials can vary to a large degree.

In a narrow sense, hygroscopicity (or moisture absorbability) is defined in terms of the equilibrium moisture content of a given material at normal temperature of the air whose relative humidity ц is close to 100%.

Insulating materials are sometimes found to be contact not only with moist air, but also with water. An example is the insulation of open installation exposed to atmospheric precipitations, the insulation of electrical machines and apparatus mounted on board ships, pump insulation, etc. These types of insulation are tested for water absorbability.

Hygroscopicity of a material depends on its structure. In this respect, capillary gaps and their size play a significant part. Highly porous fibrous materials are more hygroscopic than dense materials of uniform stricture. The hygroscopicity of materials, as glasses for example, where pores are practically nonexistent, can be of the surface type only: the moisture absorbed on the glass surface in the form of a thin film of water from the moisture-bearing atmosphere cannot penetrate into the glass bulk.



Exercises:

I. Memorise the following words and word combinations:
Hygroscopicity – гигроскопичность; humidity – влажность; porous materials –пористые материалы; fibrous materials - волокнистые материалы; penetrate into – проникать в глубь; water absorbability – водопоглощаемость;

pervious to moisture – способны собирать влагу; surrounding medium – окружающая среда; equilibrium moisture content – равновесная влажность; atmospheric precipitations – атмосферные осадки; capillary gaps – капиллярные поры.



II. Translate into English using the active vocabulary of the lesson:
1) Многие электроизоляционные материалы способны сорбировать влагу из окружающей среды.

2) Под гигроскопичностью или влагопоглощаемостью подразумевают равновесную влажность данного материала при нормальной температуре в воздухе.

3) Сильно пористые материалы, в частности волокнистые, более гигроскопичны, чем материалы плотного, сплошного строения.

4) Для различных материалов значение равновесной влажности при одном и том же значении относительной влажности воздуха могут быть весьма различны.



Physicochemical properties
Solubility. This property enables one to select requisite solvents for varnishes, plasticizers, and like substances and to estimate the resistance of insulating materials to attack by various liquids with which they come in contact either during manufacture (for example, in the process of impregnation with varnishes) or when in service (as the case for the insulation of oil-filled transformers).

The solubility of solid materials can be estimated from the amount of substance that in contact with a solvent. Moreover, it can be determined from the maximum possible quantity of a substance that dissolves in a given solvent, i.e. from the concentration of the saturated solution.

Substances which chemically match solvents, with the molecules comprising similar atomic groups, are as a rule the most soluble; polar substances are easier to dissolve in polar liquids, and neutral in neutral liquids.

Chemical resistance. Insulating materials greatly differ from one another in stability to the corrosive effect of various chemical agents such as gases, water, acids, alkaline and salt solutions. In prolonged test for chemical resistance of materials, specimens are held under simulated operating (or still more rigorous) conditions as regards the choice of chemical activity of the test medium, temperature (the rate corrosion heavily grows with temperature), and other factors. The specimens are then removed for assessment of the changes in appearance, mass, and other parameters.

Radiation stability. The list of materials and electronic products that must meet requirement for radiation resistance continuously extends with each year. This characteristic is defined without impairment of its basic properties in the conditions of intensive radiation or after exposure to radiation. It should be mentioned that radiation can be harnessed to obtain the desired changes in the structure of a material and to improve or impart some other new properties. Crosslinking of polymers and doping of semiconductors under irradiation are some of the examples.

X-rays and gamma rays, high-energy electrons, heavy charged particles (protons and alfa particles), and neutrons penetrate into a substance and induce a variety of defects. These defects and, hence, after-effects grow in number in the course of time. This why radiation stability is determined from the total (integral) dose of radiation absorbed by a substance.



Light Stability. The ability of materials to perform the assigned functions without noticeable signs of ageing under the influence of light is called light stability. Light rays, in particular ultraviolet rays, are capable of affecting dielectrics and semiconductors. They are responsible for photoconduction, chemical changes, and accelerated aging of a number of organic materials such as petroleum oils, rubber, and capron. Light radiation affects the mechanical strength and elasticity of some materials so cracks appear on their surface, vanish coatings come off the backing, and so forth.
I. Find the Russian equivalents to the following words and word combinations:
А) Solubility; solvents for varnishes; plasticier; impregnation; insulation of oil-filled transformers; dissolves; saturated solution; chemical resistance; rigorous conditions; radiation stability; сrosslinking of polymers; doping of semiconductors; induce a variety of defects; vanish coatings come off the backing; light stability.

Б) растворитель лаков; растворимость; радиационная стойкость; химостойкость; изоляция маслонаполненных трансформаторов; пластификатор; пропитывание; растворять; концентрация насыщения; радиационная сшивка полимеров; суровые условия; создавая различного рода радиационные дефекты; легирование полупроводников; светостойкость; лаковые покрытия отстают от подложек.



II. Give definitions for the following properties of dielectric materials:
Thermal endurance; cold endurance; hygroscopicity; solubility; light stability; radiation stability; chemical resistance
III. Render in English

Диэлектрики


У диэлектриков почти совсем нет подвижных носителей зарядов. Все их электроны связаны с определенными атомами, и, чтобы оторвать электрон от атома, надо затратить значительную энергию. Тепловое движение может привести к отрыву некоторых электронов от атомов, но число таких электронов в диэлектрике очень мало.

Электропроводность диэлектриков в основном определяется содержанием в них посторонних атомов, легко отдающих свои электроны, вызывает появление свободных носителей зарядов, .т.е. увеличивает их концентрацию. Таким образом, введение примесей в диэлектрик обычно приводит к значительному увеличению его электропроводности.



IV. Give the main points of the texts

Materials for quantum electronics

Principles of quantum electronics
The operating frequency range of radio devices broadens quite steadily and now reaches the optical region. The expansion of this range into the infrared, and visual bands of the electromagnetic wave spectrum springs from the need for radically new methods aimed to generate, amplify, and transform electrical signals. These methods make use of quantum effects dealt with in a new branch of radio engineering, called quantum electronics.

Quantum electronics calls for new materials which must often suit requirements differing from those for ordinary electrical and radio engineering.

Quantum devices used for generation and amplification of electromagnetic waves, such as masers(acronym of microwave amplification by stimulated emission of radiation) and lasers (acronym of light amplification by stimulated emission of radiation), depend for their operation on stimulated, or induced, emission of photons by atoms or molecules. That a possibility exists for stimulated emission of radiation, along with spontaneous emission, was first predicted by A Einstein in 1917.

Spontaneous emission occurs when an excited atom makes a spontaneous transition from a higher energy level э to a lower energy level 1. The atom thus gives up part of its energy, ΔW=W2-W1, where W2 and W1 are the energy of states 1 and 2, respectively. The energy difference is emitted in the form of a quantum with a frequency f=ΔW/h where h is Planck’s constant.

Since in this case various atoms emit light independent of each other, spontaneous emission is incoherent. This type of radioactive emission is typical for hot bodies and phosphors.

Stimulated emission of radiation by an excited atom in a body occurs under the action of a photon that falls into the atom from the outside, for example, from a neighbor which has spontaneously emitted the photon. This leads to simultaneous emission of two photons. They force excited atoms, if any, to emit other photons so that the total emission of light by the body becomes coherent. Coherence is the basic feature of stimulated emission.

Under conditions of thermal equilibrium, most particles lie on low energy levels, and casually excited atoms release the excess of energy by the way of spontaneous emission. To drive a laser or a maser into operation, it is necessary to achieve an inverse population of energy levels, i.e. an excess population of atoms in the upper excited state. An electromagnetic wave of frequency f=ΔW/h that travels through a medium state, and , as a result, its energy rises at the expense of quanta of stimulated radiation. This is the principle of operation of quantum oscillators and amplifiers.

Exercises:

I. Memorize the following words and word combinations:
operating frequency range – диапазон рабочих частот; quantum electronics – квантовая электроника; spontaneous emission – спонтанное излучение; phosphor – люминофор; stimulated emission – стимулированное излучение; release excess energy – освобождаться от избытка энергии; an inverse population – обратная заселенность.

II. Translate into English using the active vocabulary of the lesson:
1) Диапазон рабочих частот в радиоэлектронике непрерывно расширяется и в настоящее время достиг оптической области.

2) Стимулированное излучение возбужденного атома происходит под воздействием фотона, попавшего извне, например, спонтанно излученного соседним атомом.

3) Для работы лазера или мазера необходимо создать обратную заселенность энергетических уровней, т.е. добиться избыточной заселенности верхнего уровня.

4) Когерентность является основной особенностью индуцированного излучения.


III.Give the main points of the text
IV. Translate at sight
Lasers
Gas lasers

Gaseous active media exhibits the highest optical purity. Gas molecules interact with each other in a far weaker manner than liquids or solid molecules and thus give the thinnest special lines. This is why gas masers and lasers are used for high-precision measurements, for example, in length and time standards. Another feature that makes gas laser advantageous in use is electrical pumping-the current flowing through the gas after its rupture excites molecules to the upper level, which then decay back to the ground level, emitting light quanta. It is also possible to effect optical and chemical pumping.

Low-power laser of high monochromatic radiation use gases of low dielectric strength. The required system of levels is attained by using a gas mixture. Thus, a helium-neon mixture excited by an electric discharge emits red light with a wave-length of 0.63 мm or gives infrared radiation with a wavelength of 1, 153 мm. If we use mixtures of helium with vapors of cadmium, selenium, and others.

High-power infrared lasers rely on vibrational and rotational transitions of gas molecules. Lasers used for industrial purposes (for cutting, welding, and so on) are based on oxygen dioxide CO2, in which the continuous power of radiation at a wavelength of 10.6 мm reaches 1,000W and over with an efficiency of 10 to 30%. Molecules of water, ammonia, and some other gases are also used.

Chemical quantum oscillators (that rely, for example on the reaction H=F HF+hf) transform chemical energy directly into the energy of coherent radiation, using no intermediate electric power supply.

Materials for solid-state lasers

Three-or four-level quantum systems indispensable for operation of a laser are produced by doping certain substances with activators displaying the required pattern of energy levels

The basic material used for a laser must be transparent to both excitation and generation frequencies, optically homogeneous, have high hardness to allow for fine finish, and increase thermal conductivity. The material must be such that cut no less than 5cm thick can be obtained from it.

Solid-state laser employ high-temperature single crystals of oxides of elements that fall into Group II, III, and IV (ZnO, Al2O3, TiO2, SiO2, and so on), tungstates, molybdates, niobates and other oxidates, single crystals of fluorides of elements belonging to Groups II, III, and VII (CaF2, BaF2, LaF3, and MnF2), and also glasses based on oxides and fluorides. The most popular single crystals are ruby, garnet, and fluorite. Glass can be cast into rods one meter or more in length to be used in high-power lasers. Glass features not only the highest optical homogeneity, but also makes the cheapest material for lasers. However, because of the differences in the positions between active ions in the amorphous phase, glass gives a broad radiation spectrum. Nucleated glasses, which are also used as basic materials for lasers, occupy an intermediate place between single crystals and glasses.



Materials for liquid lasers

Laser crystals and glasses produced even by the most advanced high-temperature techniques are not void of “frozen” structural defects which reduce the degree of crystal purity. Liquids are free from such defects. If in solid-state lasers of high power the working crystal tends to split due to scintillation, this is not the case for liquids. And lastly, the cost of solid-state lasers grows with dimensions and powers, let alone the fact that crystal growth techniques set limits on crystal sizes, whereas such limitations are absent in liquids lasers. The above factors determine the merits of liquids for use as active media in low-cost high-power lasers.


V. Render in English
Молекулы вещества могут быть приведены в возбужденное состояние (т.е. в состояние с потенциальной энергией, превышающей равновесную) без увеличения их средней кинетической энергии неупорядоченного движения, иначе говоря, без нагрева вещества. Возбужденное состояние молекул может быть достигнуто не только путем повышения температуры, но и механическим, электрическим, радиационным и химическим воздействиями. Люминесценцией называют собственное свечение вещества в данной области спектра, если оно превосходит лучеиспускание полного излучателя в той же спектральной области и при той же температуре. По С.И. Вавилову высвечивание запасенной веществом энергии и является люминесценцией, или самосвечением вещества.


VI. Explain the differences between gas, liquid and solid state lasers and what factors determine the advantages and disadvantages of these lasers for use as active media.

Magnetic materials

Basic types of magnetic state of a substance
All substances found in nature possess magnetic properties and interact with an external magnetic field. Magnetic properties of a substance depend on the magnetic properties of individual elementary particles, the structure of atoms and molecules and their groupings.

Studies on the magnetic properties of microparticles reveals that the magnetic behaviour of atoms largely depends on that of electrons. Magnetism of other particles is insignificant. Thus, the magnetic moment of the nucleus is approximately one-thousands that of the electronic shell of the atom. The magnetic moment of an electron arises due to its orbital revolution (orbital moment) and twirling motion (spin moment).

In conformity with modern concepts of magnetism, one recognizes the following basic types of the magnetic state of matter: dismagnetism, paramagnetism, ferromagnetism, antiferromagnetism, and ferrimagnetism (noncompensated antiferromagnetism). Substances where these phenomena take place are respectively called digmagnets, paramagnets, ferromagnets, antiferromagnets and ferrimagnets.

Phenomenologically, these classes are differentiated by the magnitude (and sign) of magnetic susceptibility km=M/H (where M is the intensity of magnetization and H is the magnetic field strength) and also by the response of magnetic susceptibility to temperature and external magnetic field strength.

Diamagnets have a negative susceptibility of about 10-5 which is nearly always independent of temperature and field strength. Diamagnets are commonly forced out of a nonuniform magnetic field.

Paramagnets have positive km of about 10-2 to 10–5 at room temperature. For most paramagnets, km strongly depends on temperature and obeys the Curie law or the Curie-Weiss law, though this is not the case for alkali metals, where km is temperature independent, and also for some other substances where this relation takes an anomalous form. At normal temperatures the susceptibility is weakly dependent on field strength, but at temperatures close to zero K paramagnets can be brought to magnetic saturation. Paramagnets are generally drawn into a nonuniform magnetic field.

Ferromagnets have a high positive susceptibility km, which runs into the hundreds of thousands and millions, and show a complex nonlinear dependence of km on temperature and external field, i.e. they are capable of magnetization even at normal temperature in weak fields. The second feature of these materials is that above the Curie temperature Tc they change into paramagnets.

Antiferromagnets have km of about 10-3 to 10-5, which displays a specific temperature dependence. As the temperature grows from zero K, km rises, traverses its maximum at a certain temperature, called the Neel point Tn, and begins to decline, following the Curie-Weiss law.

Ferrimagnets have in the main the same properties as ferromagnets, though differ from the latter in a number of features.

Dia-, para-, and antiferromagnets can be placed into a group of slightly magnetized materials, and ferromagnets and ferrimagnets into a group of strongly magnetized materials. Of most significance from the viewpoint of industrial application are strongly magnetized materials, and therefore we will consider the nature of these substances only.



I. Find the Russian equivalents to the following words and word combinations:
А) Orbital revolution; in conformity; magnetic susceptibility; magnetic field strength; obeys the law; magnetic saturation.

Б) подчиняется закону; магнитное насыщение; движение по орбите; магнитная восприимчивость; в соответствии; напряженность магнитного поля.



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



  1. Все вещества в природе являются магнетиками, т.е. они обладают определенными магнитными свойствами и определенным образом взаимодействуют с внешним магнитным полем.

  2. Магнитный момент атомного ядра приблизительно в тысячу раз меньше магнитного момента электронной оболочки атома.

  3. Внешне диамагнетики отличаются тем, что они выталкиваются из неоднородного магнитного поля.

  4. Диа-пара- и антиферромагнетики можно объединять в группы слабомагнитных веществ, а ферро- и ферримагнетики в –группу сильномагнитных.

  5. Особенность ферромагнетиков состоит в том, что выше определенной температуры, называемой точкой Кюри Тк, ферромагнитное состояние переходит в парамагнитное.



III.Give the main points of the text


IV. Render in English

Все технические материалы, за исключением ферромагнетиков, которые обладают свойством самопроизвольной намагниченности, принадлежат к диа- или парамагнетикам, т.е. имеют магнитную проницаемость, близкую к единице.

Характерным и необходимым признаком парамагнитного состояния вещества является наличие у атомов магнитных моментов при отсутствии внешнего магнитного поля. Однако эти моменты недостаточны для самопроизвольной упорядоченной ориентации в условиях беспорядочного температурного движения молекул.

Электронным спиновым парамагнетизмом обладают атомы и молекулы, имеющие нечетное число электронов, поскольку в этом случае спин всей системы не может быть равен нулю (например Na, NO, органические свободные радикалы).



IV. Explain the differences between paramagnetism, ferromagnetism, antiferromagnetism, and ferrimagnetism.

Appendix

Supplementary Reading

Noble metals


Gold. A yellow metal of very high plasticity, with a tensile strength of 150 MPa and elongation at rupture of 40%. Its uses in electrical engineering include corrosion-resistant contact coats, photocell electrodes, vacuum-deposited thin-film microcircuits, etc.

Silver. A white, lustrous metal, resistant to oxidation at normal temperature. Of all the metals, silver has the lowest resistivity at normal temperature. The tensile strength of silver wire is about 200MPa, and elongation approximately 50%. This wire is used for contacts intended to operate at low currents.

Silver is also employed for direct deposition of coats by fusion or vacuum evaporation on dielectrics, which serves as silver plates in ceramic and mica capacitors.

The metal presents a drawback in that migrates from the surface of a dielectric into its body at high humidity and also at elevated temperatures of the surrounding medium. Silver is inferior to other noble metals in chemical resistance.

Platinum. A metal that does not react with oxygen and shows rather high resistance to chemical agents. It displays superb ductility and malleability, and readily draws into very thin wire and foil. The tensile strength of annealed platinum is about 150 MPa, with elongation of 30 to 35%. Platinum is used for thermocouples designed to measure temperature up to 1,600C, for the production of pastes intended for fusion of electrodes on to the body of ceramic capacitors, etc.

Platinum filaments drawn to about 1 мm across are used for suspension of movable systems in elecrometers and other sensitive devices. They are obtained through multiple drawing of the composite platinum-silver wire with the subsequent dissolution of the silver coat in nitric acid (platinum is resistant to this acid).

Platinum is too soft for use alone as a contact material, and is generally alloyed with harder metals. Platinum-iridium alloys are wear- and corrosion-resistant, hard and tough, allow for a high repetition rate of switching, but are costly, and so their uses are limited to critical applications.

Palladium. It stands close to platinum in many of its properties, and often serves as a substitute for the latter. It is valued in the electron-tube industry for hydrogen absorption. Palladium and its alloys with silver and copper go into the production of contacts. Palladium paste, like platinum paste, is used for the deposition of electrodes on to ceramic capacitors.

Annealed palladium has a tensile strength of 200MPa with an elongation at rupture up to 40%.


Nickel
Nickel. A silver-white metal widely used in the electron-tube industry. It can readily be isolated to 99.99% purity. Nickel is sometimes alloyed with silicon, manganese, and other metals.

The by-product obtained from the ores is submitted to electrolytic refining. A very pure powderlike nickel can be produced by thermal dissociation of the nickel pentacarbonyl Ni(CO)5 at about 220C.Nickel is marketed in various purity grades and shapes; in sheet, plate, band, tubing, rod, and wire. It retains sufficiently high mechanical strength after annealing.Nickel is cold worked by forging, pressing, rolling, stamping, drawing, etc., and allows for the precision making of parts complex in shape and varying in size.

Nickel is used in electron devices, for production of various magnetic and conducting alloys, protective and decorative coats on iron parts, etc.

Ferromagnets and ferrimagnets
The principal ferromagnetic materials are iron, nickel, cobalt, and some rare-earth metals (REM) such as gadolinium, terbium, dysprosium, holmium, erbium, and thulium, though they (excluding gadolonium) exhibits antiferromagnetism within a certain temperature region. Some alloys and compositions of manganese, silver, and aluminum are ferromagnetic too.

Ferromagnets belong to transition elements where, as is known, the electron structure of an atoms has a disturbed order in which electrons fill the shells, so that some inner electronic shells remain unfilled (incomplete). In elements of the iron group, the 3d orbital is incomplete; in REM this is a 4f orbital. The atoms whose electron configuration features incomplete shells have a noncompensated magnetic moment (where an atom has shells completely filled with electrons, the net magnetic moment is zero). In ferromagnets of the iron group and REM, the orbital moments differ from spin moments in relative value.

In ferromagnets of the iron group, the orbital moment is largely cancelled by the crystal lattice’s electric field: here the magnetic spin moment plays the leading role in the formation of the magnetic moment of an atom. The magnetic spin moment, which will be called the spin for brevity in further discussion, is equal to 1 Bohr magneton мb=9.27x10-24 Am2. In a first approximation, the magneton moment of an atom in elements of the iron group is determined as an algebraic sum of electron spins in the incomplete shell. Thus, of the six electrons in the incomplete 3d shell of an iron atom, 5 have spins directed parallel to each other and 1 antiparallel. The resultant magnetic moment of the iron atom is equal to 4 мb for ferromagnets of the REM group, the role of the orbital moment in creating the net magnetic moment of an atom cannot be disregarded. Therefore, the above reasoning based on the spin concept does not apply here. Consider the nature of ferromagnets of the iron group. Prior to discussing their properties, let us describe in brief the essential of the theory of magnetism.

For ferromagnets, even in the absence of an field, it proves favorable from the energy standpoint that the spin of neighboring atoms are arranged in parallel. Such a state is called atomic ferromagnetic ordering. Hence, even when a ferromagnet is not exposed to an external field, it retains spontaneous magnetization, which is equivalent to saturation magnetization Ms. This magnetization is temperature dependent; it grows with decreasing temperature and reaches true magnetization Mo at zero K. At T>Tc, the atomic ferromagnetic ordering of a substance collapses and, as has been noted earlier, the substance become a paramagnet.

In order that atomic magnetic ordering could emerge, the ordering energy must counteract the thermal disordering energy. Weiss believed that the ordering energy had a magnetic origin. But Ya. G. Dorfman has shown in his calculations and experiments that the magnetic energy which aids in setting up spontaneous magnetization account for only 0.1% of the required energy. Reasoning from the concepts of quantum physics. Ya I. Frenkel and W. Heisenberg have disclosed the nature of this energy independently of each other. Atomic ferromagnetic ordering sets in due to the presence of an electrostatic energy of interaction between microparticles, which has no analog in classical physics.

Other materials for permanent magnets
Martensite Steel. The steel derives its name from the martensite microstructure obtained after hardening. The formation of martensite entails substantial changes in volume, and leads to large internal stresses of the lattice and increased coercive forces.

Martensite steels were the first materials used for production of permanent magnets. Nowadays, they find rather limited application due to inferior magnetic properties. Yet these steel are not totally abandoned because they are cheap and amenable to mechanical treatment on metal-working machines.

Plastically Deformable Alloys. These alloys are quite treatable. They readily forge, draw into wire, cut into strips, sheets, plates, and are machinable on all machine tools. Wherever the need arises for the production of small-size magnets of complex configuration, it is useful to resort to ceramic-metallurgy techniques. Industry produces many grades of plastically deformable alloys. The physical process responsible for the high magnetic properties of these alloys are manifold. The most widespread alloys of this group are cunife (Cu-Ni-Fe) and vicalloy (Co-V). Cunife alloys are anisotropic and magnetized in the direction of rolling; they come in small-diameter wires and stampings for use in various applications. Vicalloy goes into the production of minute magnets of complex and delicate configuration and high-strength magnetic tape and wire.

Noble Metal-base Alloys. These are silver-manganese-aluminum alloys (silmanals), 77.8% Pt - 22.2% Fe alloys, and 76,7% Pt - 23.3% Co alloys. The materials in this group are very expensive, especially so are alloys containing platinum, and therefore their uses are restricted to superminiature magnets a few milligrams in mass. Powder-metallurgy techniques are the basic methods for the production of magnets from the alloys of this group.

Elastic Magnets. As mentioned earlier, the main drawback to the basic group of magnetic materials (cast alloys and hard-magnetic ferrites) used for permanent magnets is increased hardness and brittleness. The high cost of plastically deformable alloys, which are free from the above drawback, set limits on their wider application. In the last few years, rubber-based magnetic materials have come into commercial use. They can be shaped to any form attainable with rubber manufacturing methods - to cords, long strips, sheets, and so on. Such a material easily cuts, pressed, bends, and twists. The known uses of ‘magnetic rubber’ are sheets for magnetic computer memory, TV deflection system magnets, correction magnets, etc.

Elastic magnets are produced from a rubber (binder) and fine-powder hard-magnetic materials (filler). Barium ferrite is often used as a filler.



Materials for Magnetic Tapes. Magnetic tapes are magnetic recording media. Most widespread are solid metallic tapes from stainless steel, bimetallic tapes, and plastic-base tapes with a powder like layer deposited on the surface. Solid metallic tapes are largely intended for special purposes and for work in a wide temperature range; plastic-base finds wider applications. Since the tape retains magnetic variations imparted to it during magnetic recording, it produces on the surface of a reproducing head a magnetic field whose strength varies with time (as the tape passes through the head) in the same manner as recorded signal. The head thus converts magnetic variations into electric variations. The properties of tapes coated with magnetic emulsion strongly depend not only on the quality of starting materials. But also on the magnetic powder grain size, volume density of the magnetic material in the working layer, orientation of particles if they show anisotropy of form, etc.

The working layer (or the thickness of metallic tape) must be as thin as possible, and the tape itself smooth and flexible to provide maximum interaction (magnetic contact) with the head. The remnant magnetization of a magnetic material must have the highest possible value.

The requirements imposed on coercive force are conflicting: on the one hand, it should be highest wherever possible (not below 24 kA/m) to avoid self-demagnetization, on the other, it should be low in facilitate erasure. The requirements for high remnant magnetization and the least sensitivity to self-demagnetization are best satisfied if the hysteresis loop has a rectangular shape of the demagnetized portion, i.e. if the fullness factor for this portion is at a maximum. Variation in the magnetic properties of tape material or temperature and other influences must be kept to a minimum.

Properties of some hard-magnetic materials at cryogent temperatures. Research into the properties of various materials at very low (cryogenic) temperatures has both scientific and practical significance. For example, it is important to harness the phenomenon cryoconductivity (superconductivity) for production of super-power magnetic fields and for solution of a number problems. The magnetic properties of materials cooled to cryogenic temperatures do not change instantaneously, but vary in a complex and ambiguous fashion.


Phosphors
Luminescence is incoherent electromagnetic emission of light by a body in excess of its thermal emission. The wavelength of this type of light emission by far exceeds the oscillation period. Luminescence arises from the excitation of atoms by an external source, whose subsequent transition to a stable state are accompanied by emission of light quanta. Depending on the source of excitation, luminescence can be classed into photoluminescence (excitation by light), radioluminescence (by radiant energy), cathodoluminescence (by an electron beam), elctroluminescence (by an electric field), chemiluminescence (by chemical reactions), and others.

The luminescence phenomenon (phosphorence of rotting wood, glow of fireflies, and nothern lights) was known from ancient times and was harnessed for practical use. In ancient Pompeu, for example, luminescence minerals were embedded in the middle of cobble-stone roads to make the way visible at night. Nowadays, luminescence is used in oscilloscope cathode-ray tubes, television picture tubes, daylight lamps, luminous paints, electroluminescent panels, display devices and so on. Light-emitting diodes also being to luminescent device

Luminescence substances are called luminophors, or phosphors. By the type luminescence , they are divided into photophosphors, cathodophosphors, lectrophosphors, etc.


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