>Exercise 1. Вспомните значения следующих словосочетаний и подберите к ним соответствующий перевод из правого столбца.
1. to reflect light 1. тяжёлые металлы
2. tо withstand forces 2. выдерживать нагрузку, силу
3. light metals 3. сила притяжения
4. conductors of heat 4. низкоуглеродистые стали
5. solid bodies 5. промышленные цели
6. low-carbon steels 6. отражать свет
7. industrial purposes 7. легкие металлы
8. gravity 8. твердые тела
9. heavy metals 9. проводники тепла
Exercise 2. Read and translate the text. (Перевод текста необходимо предоставить для проверки. Можно выполнить на вордовском файле).
PHYSICAL PROPERTIES OF METALS
What is a metal? Technically, it is an element which has the following properties: It is solid at room temperatures (mercury is an exception).
It is opaque (that is, you can’t see through it). It conducts heat and electricity.
It reflects light when polished.
It usually has a crystalline structure.
Some metals – gold, silver, copper and zinc, for example, are often used in almost pure form. However, most metals used for industrial purposes are actually alloys, not pure metals. An alloy is a metal to which another metal (or metals) or a non-metallic element such as carbon or silicon has been added to modify the physical or mechanical properties of the pure metal. Iron, aluminium, titanium and magnesium are used mainly in an alloy form. Pure iron, in fact, is sometimes, of a laboratory curiosity. Steel and cast iron are properly considered alloys of iron. Even though a low-carbon steel may contain more than 99% iron, and not more than 0.3% carbon, that little amount of carbon makes a lot of difference.
The physical properties of a material are properties not related to the ability of the material to withstand external mechanical forces such as pushing, pulling, twisting, bending…
These properties include density, melting point, specific heat, thermal conductivity, thermal expansion, electrical conductivity.
Density and Porosity. The measure of a unit mass; or the weight of a unit volume. Density is expressed as grams per cubic centimetre (g/cm3 ), kilograms per cubic metre (kg/m3), pounds per cubic foot (lb/ft3). Density is often expressed as specific gravity, the ratio of the density of the material to the density of water. The specific gravity of aluminium is 2.70 – in other words, it is nearly three times as heavy as water. The specific gravity of iron is 7.86; for gold, the value is 19.3.
Melting and Boiling Point. Every pure metal has a specific melting point. If you apply heat to a solid specimen, its temperature will rise until it reaches that melting point. It will then start to melt, and it will remain at the melting point temperature, even though the heating is continued, until the specimen is completely melted. Then, and only then, will the temperature of the liquid metal start to rise once move.
Specific Heat. The amount of heat required to raise a unit mass of a solid metal one degree in temperature is termed specific heat. The lighter the metal, the greater the specific heat. In other words, it takes more heat to raise the temperature of one kilogram of aluminium one degree than it takes to raise the temperature of one kilogram of iron one degree.
Thermal Conductivity is measured as the heat-conducting ability of a unit length or thickness of a substance per unit of a cross-sectional area. The relative heat conductivities of some metals and alloys are based on the conductivity of silver as 100%.
Thermal Expansion. The increase in dimensions of a solid body due to an increase in temperature is termed thermal expansion. This property is of much significance in welding operations, since the metal close to the weld zone is heated to a higher temperature and therefore expands more than the metal at a greater distance from the weld zone.
Electrical Conductivity. As stated earlier, a metal must be a conductor of electricity. Some are much better than others; generally, the metals which are the best conductors of heat, such as copper, silver and aluminium are also the best conductors of electricity.
Exercise 3. Match the term with its definition.
1) porosity
2) composition
3) melting point
4) boiling point
5) electrical conductivity
6) density
a) the temperature at which a metal melts
b) the electrical conducting power of a unit of cross sectional area
c) the quality of containing pores is lack of denseness
d) the temperature at which the metal boils under normal atmospheric pressure
e) the manner of arrangement of metal atoms as to geometric form in solid crystals
f) weight per unit of volume
Exercise 4. Ответьте на следующие вопросы.
1. What is a metal?
2. What metals are often used in a pure form?
3. What is an alloy?
4. What properties of materials are called physical properties?
5. Give the definitions of density, melting point, specific heat, thermal conductivity, thermal expansion, electrical conductivity.
Exercise 5. Choose the correct (simple, progressive or perfect) verb form in each of the following sentences.
1 In this process, the mixture is (heated/is heating) to 120°C,
2 Once the salts (are dissolving/have dissolved)the heat is reduced,
3 Several people have (survived/are surviving) the earthquake and are treating/are being treated in hospital at the moment.
4 For security purposes the employees (change/are changing) their passwords regularly.
5 Up until now people in this area (have taken/taken) waste plastic to recycling centers, but at present we (have tried/are trying) a curbside collection system.
Exercise 6. Fill the gaps in the sentences with the verbs in their correct tense (preset perfect or simple past).
1 Materials________(always play) a major role in the development of societies.
2 Civilizations ________ (designate) by the level of their materials development.
3 The earliest humans ________ (have) access to only a very limited number of materials.
4 The microstructure of a metal ________ (be) first revealed in 1864 by the Englishman Henry Sorby who ________(develop) a technique for etching the surface layer of a polished metal.
5 Modern techniques such as x-ray diffraction, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) ________(make) it possible to better understand their characteristics.
6 By now, more than 50,000 materials ________(develop).
7 Materials scientists ________ (long envy) the resilience of certain naturally occurring materials.
8 Past efforts to reproduce the architecture of, e.g. a shell ________((not be successful).
9 Galvanized metals ___________(cover) with a thin sheet of zinc.
или напишите нам прямо сейчас
Прикрепленные файлы: |
|
|---|---|
|
Администрация сайта не рекомендует использовать бесплатные работы для сдачи преподавателю. Эти работы могут не пройти проверку на уникальность. Узнайте стоимость уникальной работы, заполните форму ниже: Узнать стоимость |
|
Скачать файлы: |
|
|
|