5. Translate the passage of the text beginning with «When Ghritopher Columbus...» to «... Particularly silver» in writing.

Unit 4

Metals and alloys

Of the 106 elements in the periodic table about 90 are classified as metals. Some elements such as oxygen, chlorine, hydrogen and the inert gases are considered to be non-metallic. There is, however, a gToup of elements including carbon, sulphur, silicon and phosphorus, which is intermediate between metals and non-metals. They are called metalloids. Metals are the most important structural materials of our days. There are chemical elements possessing lustre hardness, malleability, electrical and heat conductivity.

The most widely used metallic elements are iron, copper, lead, zinc, aluminium, tin, nickel and magnesium. Some of them are used extensively in the pure state but by far the largest amount is consumed in the form of alloys.

Metals applied for industrial purposes are called «engineering metals». The commercial importance with one another to produce sub­stances having a wide range of properties which may not be attained

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with pure metals alone. The engineer must know such properties of a metal as strength, hardness and elasticity. These depend on the chemi­cal composition and the physical structure of the material. Such char­acteristics as specific heat, thermal conductivity, coefficient of expan­sion, colour, strength and hardness are known to be the physical prop­erties of a material. The physical properties describing the behavior of materials under mechanical usage such as strength, hardness, ma-chinability and ductility are called the mechanical properties.

Metals are usually divided into two groups, that of ferrous or iron-bearing metals including copper, lead, zinc, aluminium, tin, nickel, etc. Ferrous metals consist of iron combined with carbon, sili­con, phosphorus and other elements. Carbon is the most important of all elements present in ferrous alloys. Ferrous metals are used in indus­try in two general forms: steel and cast iron which differ in the quantity of carbon content. Non-ferrous metals are generally more expensive per pound than ferrous metals. Their characteristics are high electrical and heat conductivity, high corrosion resistance, non-magnetic quali­ties light weight and ease of fabrication. Sometimes non-ferrous metals are applied in the pure state, for example, lead is used for lining pipes and coating electrical cables; copper is utilized as wires, aluminium is used for making different light weight objects.

Pure metals are comparatively seldom used in industry. In most cases some alloying element is added to metals, and thus alloys are formed. An alloy is a combination of elements exhibiting the proper­ties of a metal. It can also be defined as a substance formed by the so­lidification of a metallic solution. Alloys consist of two or more metals or metals and metalloids. Each constituent of an alloy is called a com­ponent. Alloys may be binary (two component), ternary (three compo­nent), etc. The ability of various metals to form alloys differs greatly. If metals do not dissolve in each other when they are molten they will not form an alloy when solid. An alloy looks like a homogeneous mix­ture of metals but under the microscope it is seen as an aggregation of crystals, these crystals being sometimes different from one another in chemical composition as well as in size, hardness and other properties. Some metals do not dissolve in each other when liquid, for example, molten lead and aluminium separate into two liquid layers, each con­taining only a trace of the other metal.

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Aluminium when molten is insoluble in many other metals, such as sodium, potassium, cadmium. Bismuth and iron are insoluble in each other when liquid. Molten lead will dissolve only a small amount of molten zinc, molten copper will dissolve only a little of molten iron and molten iron will dissolve only a little copper. If it were not for this fact, it might be possible to form some very valuable alloys of iron and copper, these two metals being useful and common.

In the liquid state alloys are entirely homogeneous but when an alloy is transformed from the liquid to the solid state non- homogeneity may appear, i.e. several solid phases are formed

The change from the liquid to the solid state is very important in determining the properties of an alloy.

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ability

substance

a wide range of

to attain

which may not be attained with

pure metals alone

strength

elasticity

specific heat

coefficient of expansion

such characteristics as...are

known to be...

behaviour

macbinability

ductility

ferrous metals

a ferrous alloy

manganese

cast iron

quantity

differ in the quantity of...

per pound

corrosion resistance

quality

ease of fabrication

lining pipes

coating electrical cables

alloying element

to define

solidification

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constituent the ability of various metals to form alloys differs greatly to dissolve when solid (liquid, molten) homogeneous an alloy looks like a homogene­ous mixture aggregation these crystals being sometimes different from one another in chemical composition as well as in size liquid trace each containng only a trace of the other metal insoluble sodium potassium will dissolve if it were not for this fact these two metals being useful and common homogeneity to determine

составная часть, составляющая способность различных метал­лов образовывать сплавы значи­тельно различается растворять(ся) в твердом состоянии (в жидком, расплавленном состоянии) однородный сплав похож на однородную смесь скопление, масса причем эти кристаллы иногда отличаются друг от друга по своему химическому составу, а также по размеру жидкость; жидкий след, незначительное количество и каждый содержит остаток дру­гого металла нерастворимый натрий калий обычно растворяет если бы это было не так причём эти два металла являют­ся полезными и обычными однородность определять, устанавливать

Exercises

1. Find international words in the text.

2. Find English equivalents for the following

в Периодической таблице существует, однако, группа элементов при определенных условиях обладающие блеском, твердостью, ковкостью в их способности соединяться друг с другом

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большое разнообразие свойств

такие свойства, как прочность, твердость, эластичность

они зависят от...

описывающие поведение материалов

механические свойства

черные металлы

углерод - наиболее важный из всех элементов

обычно более дорогие

применяются в чистом состоянии

чистые металлы сравнительно редко используются в про­мышленности

соединение элементов

если металлы не растворяются друг в друге

алюминий в расплавленном виде не растворим во многих других металлах

если бы это не объяснялось этим фактом

в жидком состоянии сплавы полностью однородные