7. Ответьте на вопросы по тексту:

1. When was the first synthetic plastic made?

2. What are polymers composed of?

3. Who introduced a mouldable material made fromcellulose nitrate?

4. Where and when did Parkes exhibit his first successful plastic?

5. Why was large-scale production of plastics possible in 1900?

6. Where are many different plastics used?

7. Why do plastics find applications in replacement surgery?

8. Составьте аннотацию к тексту (2 – 3 предложения).

9. Составьте реферат текста (10 – 15 предложений).

10. Составьте план текста и перескажите текст.

Вариант 17

2. Прочитайте и переведите текст:

Synthesizing Diamond

Laboratories in India have recently reported that they have devel­oped a new technique to make gem quality diamonds. It is said that the diamonds so made are less expensive than those that are mined. This comes at an odd time when the market for diamonds was already de­pressed and is now accentuated by the economic slump in the far East. Gems worth Rs. 48,000 crores are reportedly piled up in vaults all over the world waiting for customers.

Ever since Tennant proved that diamond was another form of car­bon 200 years ago, efforts have been made by scientists to synthesizes diamond. Many experiments claimed that sugar, oil and a host of other carbon containing materials had been subjected to secret processes that turned them into sparkling diamonds. While being very secretive about the details of their work, all of them appear to have used high tempera­tures and high pressures, often with the addition of metal powders and other chemicals in the attempts.

The most stable form of carbon at room temperature and pressure is graphite. It has, however, been known for a long time that the very high temperatures and pressures that existed deep under ground for millions of years arranged the carbon atoms into a cubic lattice arrangement to produce a crystal that was colourless, clear, lustrous and hard. The very hardness and resistance to chemicals gave this carbon crystal its name -adamant or diamant or later, diamond.

The phase diagram, or the graph that depicts how that state of carbon depends on the pressures and temperature, indicates that more than 200,000 atmospheres (kg/sq.cm) and temperatures in excess of 3000 degrees Cclsius must be applied to create diamonds. Early experimenters tried unsuccessfully to produce these conditions by different tricks. Hannay, for ex­ample, sealed oil and lithium metal into iron tubes and heated them; but his claim that he had produced small diamonds proved to be false.

Bridgman was the first scientist to realise that there could be no com­promise with the extremely high pressures and temperatures required to synthesise diamond. In 1910, he designed a screw type press with which he attained a pressure of 400 kilobars. Only tungsten carbide anvils were hard enough to take this pressure and so the 'melt' had to be contained between cylinders of this material. Needless to say, the active volume had to be very small. In his experiments, he could only get a pressure of 35 kilobars at the temperature of 2000 degrees Celsius.

The company General Electric redesigned the press that was capable of reaching 200 kilobars at a temperature of 5000 degrees Celsius for a period of many hours. They were also able to increase the active volume considerably and so were able to produce small, synthetic diamond stones, or grit on a commercial scale. Further improvements in design were made by Hall using a tetrahedral press, where the pressure was applied from four directions. This equipment was successful in making significant quantities of synthetic diamonds in five minutes with a pressure of ten kilobars at 2000 degrees Celsius. Metal powder or boron carbide added as a catalyst increased the production greatly.

In 1970, General Electric improved their technique greatly by intro­ducing seed crystals in the carbon material and could obtain large dia­monds of gem quality. It is reported that it took about one week to grow a five mm size diamond weighing one carat. The addition of metals, however, gave a certain tinge to the stone. It is known, for example, that impurity of 100 parts per million of nitrogen turns the diamond to a pale yellow type Ib crystal.

The General Electric synthetic diamonds varied in shade from F to in the diamond scale of colour and the clarity was sometimes good, up to the VS grade. With the addition of boron carbide in the melt, polycrys-talline diamond, also called carbonado, is grown. This is harder than single crystal diamond but lacks its clarity. It is, however, useful as a diamond cutting tool in scaifes and saws.

The process has been improved very much over the last decade and it is estimated that worldwide, about 40 tonnes of synthetic diamond grit are produced and marketed annually. The manufactures are located in the USA, Russia, South Africa, Ireland, Sweden and Japan. Exotic meth­ods have been used to generate the extremely high pressures and temper­atures that encourage the growth of diamond from carbon. One such method utilises shock wave.

The transient nature of the shock wave permits the use of materials softer that tungsten carbide to contain the carbon melt. Hard-nosed bul­lets or shells were fired into the active volume which was initially heated to a fairly high temperature. The impact of the bullet not only increased the pressure but the compression also heated the sample to the required temperature and beyond. In at least two experiments, the terrific blast wave from underground nuclear explosions was directed on to the car­bonaceous material. The success of these experiments are not generally reported as it is an extremely expensive technique and in any case, nucle­ar explosions are not continued.

Strangely enough, a very simple process can grow diamond crystals. This is by the decomposition of chemical vapour or CVD as it is called. The CVD process starts with a carbon containing gas such as methane which is decomposed by burning, electric discharge or laser heating. A carbonaceous gas, methane or acetylene is mixed with hydrogen and directed towards a hot filament which decomposes the gas and deposits small diamond crystals on a nearby heated surface.

The discharge is often replaced by a laser beam. The cheapest way is to direct an oxyacetylene flame on to surface. If the gas flow and mixture is carefully optimised, diamond crystallites nucleate and grow. The ad­dition of hydrogen seems to passivat e the surface and discourages the growth of graphite. So far only micron size crystals have been grown but efforts are under way to obtain bigger crystals and the recent report from Indian laboratories signifies success in this direction.

The unique properties that make a diamond so rare and expensive are: (a) its high refractive index of 2.42 and dispersion of 0.04 that gives in the lustre, (b) its lack of colour which is due to its purity, (c) its high thermal conductivity, even greater than copper, which makes it cool to touch and gives it the name of "ice", and (d) its being the hardest known material with ten on the Mohs scale of hardness.

There have been many attempts to make a material which is harder than diamond because scaifes can then be used more efficiently than the present method of using diamond to cut diamond. Cubic boron nitride was the first material to be made in the laboratory in the 1960s. Realising that reducing the distance between the atoms in a crystal and finding a crystal arrangement that would make this possible would increase the hard­ness of a material, the Laboratory for Physical Chemistry of Materials in France tried different mixtures of atoms and hit on ruthenium oxide. Crys­talline ruthenium oxide is now the hardest known material but has not been able to displace diamond from its position as the hardness leader.

It will not be very long before scientists discover a synthetic material which has all the properties of diamond such as its hardness, clarity and lustre and thermal conductivity. The demand for this wonder material is potentially so large that the commercial viability of the process to make it will be easily established.

2. Переведите на русский язык следующие английские словосочетания:

1. odd time;

2. economic slump;

3. high tempera­tures;

4. deep under ground;

5. depends on the pressures and temperature;

6. the active volume;

7. commercial scale;

8. extremely high pressures;

9. encourage the growth of diamond;

10. laser heating.

3. Найдите в тексте английские эквиваленты следующих словосочетаний:

1. подземные ядерные взрывы;

2. дорогое оборудование;

3. электрический разряд;

4. алмазные кристаллики;

5. уникальные свойства;

6. твёрдость материала;

7. лаборатория физической химии;

8. высокое давление;

9. синтетический алмаз;

10. самый дешёвый способ.

4. Найдите в тексте слова, имеющие общий корень с данными словами. Определите, к какой части речи они относятся, и переведите их на русский язык:

1. secret;

2. colour;

3. chemicals;

4. to add;

5. success;

6. design;

7. pure;

8. round;

9. hard;

10. to resist.

4. Задайте к выделенному в тексте предложению все типы вопросов (общий, альтернативный, разделительный, специальный: а) к подлежащему; б) к второстепенному члену предложения).

4. Выполните анализ данных предложений, обратив внимание на следующие грамматические явления: времена группы Indefinite ( Present, Past, Future Active& Passive); глаголы to be, to have; конструкция there is, there are; все типы вопросов; степени сравнения прилагательных; модальные глаголы:

1. It is said that the diamonds so made are less expensive than those that are mined.

2. The most stable form of carbon at room temperature and pressure is graphite

3. Bridgman was the first scientist to realise that there could be no com­promise with the extremely high pressures and temperatures required to synthesise diamond. In 1910, he designed a screw type press with which he attained a pressure of 400 kilobars.

4. Further improvements in design were made by Hall using a tetrahedral press, where the pressure was applied from four directions.

5. This is harder than single crystal diamond but lacks its clarity. It is, however, useful as a diamond cutting tool in scaifes and saws.

6. The manufactures are located in the USA, Russia, South Africa, Ireland, Sweden and Japan.

7. Strangely enough, a very simple process can grow diamond crystals.

8. The cheapest way is to direct an oxyacetylene flame on to surface.

9. It will not be very long before scientists discover a synthetic material which has all the properties of diamond such as its hardness, clarity and lustre and thermal conductivity.

7. Ответьте на вопросы по тексту:

1. What is graphite?

2. How did modern chemists manage to synthesize diamonds?

3. What factors could turn graphite into diamond?

4. What kind of equipment was produced for that purpose?

5. Who produced the equipment?

6. What is the hardest known material now?

7. Why can not it displace diamond?

8. Составьте аннотацию к тексту (2 – 3 предложения).

9. Составьте реферат текста (10 – 15 предложений).

10. Составьте план текста и перескажите текст.

Вариант 18