Physical properties of metals and alloys

The physical properties of metalsinclude colour, density, melting temperature, thermal conductivity, thermal expansion, heat capacity, electrical conductivity, and magnetism.

Colour. - Most of the metals are silvery white or grey in co­lour. Copper is the only red metal, and gold the only yellow one, although a number of copper-base alloys are also yellow. All solid metals have metallic lustre, although the true colour and lustre of many metals are often obscured by a coating of oxide — which may be white, grey, red, brown, bluish, or black.

Density and Porosity - Porosity, the quality of containing pores is lack of denseness. Density, on the other hand, denotes weight per unit of volume. Some heavy metals, like grey cast iron, are porous enough to leak under heavy hydraulic pressures, whereas some lightweight metals, like aluminum, are dense and compact.

Melting point. - Melting is the conversion of a metal from the solid to the liquid state at a definite melting temperature, or melting point. The melting point of iron, tin, and copper is 1,539, 232, and 1,083° C, respectively. The metals of lower melting points are usually soft metals and those of high melting points are hard metals. The boiling point of a substance depends on the surrounding pressure. The term "boiling point" refers to the temperature at which the metal boils under normal atmospheric pressure.

Thermal conductivity. – Thermal conductivity is the property of a metal to transfer heat. Silver, copper, and aluminum are the best conductors of heat.

Thermal expansion. – Thermal expansion is the property of a metal to expand on heating and contract on cooling.

Heat capacity. – Heat capacity is the ability of a metal to absorb a definite amount of heat during heating.

Electrical conductivity. – Electrical conductivity is the property of a metal to conduct electric current. Copper and aluminum which have a high electric conductivity go into the production of current-carrying wire. The electrical resistance of metals or al­loys is increased by decreasing the size of the crystals and, there­fore, increasing the number of crystal boundaries. In general, all metals increase in resistance with increase in impurities. The re­sistance of metals is also increased in most cases by an increase in temperature. The alloys of a high electrical resistance, such as nichrome, constantan and manganin, are used in electric heating devices and electric furnaces.

Magnetism. - Magnetism is the metal property associated with magnetic interaction. Iron, cobalt and nickel are the only metals possessing considerable magnetism at room temperature, and they become non-magnetic when heated to a certain temperature. Strong per­manent magnets are made chiefly of one of several compo­sitions of steel, but in recent years a number of magnet alloys of much greater magnetism have been developed. Iron, nickel, cobalt, and their alloys, called ferromagnetic alloys, have good magnetic properties and find the widest application for electric motors, generators, transformers and telephone and telegraph networks. Industry also employs nonmagnetic materials which can be produced by changing the composition and internal structure of alloys.

1. Find in the text English equivalents for the following word-combinations:

саме широке застосування, певну кількість тепла, при охолодженні, передавати тепло, справжній колір, внутрішня структура, металевий блиск, у той час як, розмір кристалів, постійний магніт, в більшості випадків, рідкий стан, з іншого боку, блакитний, при нормальному атмосферному тиску, вага на одиницю об'єму.

1. Answer the questions:

1. Are all metals of the same colour?

2. What is porosity?

3. What does density denote?

4. What is melting? How do melting points of metals differ?

5. What is the electrical conductivity of a substance?

6. How can the electrical resistance of a metal be increased?

7. What is the thermal conductivity?

8. Do metals absorb heat during heating?

9. How do metals behave on cooling?

10. What metals have good magnetic properties at room temperature?

1. Agree or disagree with the following statements. Prove your reason. Use the expression: I’m sure that’s right (wrong) because ….

1. Hard metals have low melting point

2. The "boiling point" is the temperature at which the metal boils under normal atmospheric pressure.

3. The electrical resistance of metals decreases when they are heated.

4. If metals have more impurities their electrical resistance will increase.

5. Red is the most common colour of metals.

6. Iron will lose its magnetic properties if it is heated.

7. Silver does not conduct heat.

8. Current-carrying wire must be made of metals with the low electrical conductivity.

9. Porous metals are usually very compact.

10. Most metals expand when they are heated.

1. Translate the following sentences paying attention to the use of the Gerund. Find the examples of the Gerund in the text:

1. Metals usually contract on cooling.

2. Metallurgy includes the processes of working and shaping metals.

3. Copper smelting became common in the Middle East long ago.

4. Bronze was obtained by adding tin into molten copper.

5. Before using a metal you should study its properties.

6. The electrical resistance of metals can be increased by decreasing the size of their crystals.

7. Copper was used for making simple tools.

8. The chemical process of extracting a metal from its ore is called smelting.

9. Copper was produced by using heat to smelt copper from ore.

10. Non-magnetic materials can be produced by changing the composition and internal structure of alloys.

11. By testing a metal under a load we can define what mechanical properties it has.

12. For determining the elasticity of metals a rupture machine may be used.