CLASSIFICATION OF METALS

There are some classifications of metals based on their chemical purity, physical and chemical properties and composition, their industrial application (= use), etc.

According to (= in respect to; depending on) the chemical purity we may divide all metals into 2 large groups:

1. Simple metals which are more or less pure chemical elements.

2. Alloys which are materials consisting of a simple metal combined with some other elements.

In modern industry we usually divide metals into 2 main groups according to their chemical composition:

1. Ferrous metals; 2. Non-ferrous metals.

Metals consisting of iron combined with some other elements are known as ferrous metals; all the other metals are called non-ferrous metals. Ferrous metals and alloys include a great variety of (= very many) commercially important products which can be grouped into: a) iron (cast iron), b) саrbоn steels; c) alloy steels; d) stainless steels and other types of steels.

The most important ferrous metal is cast iron which is some form of alloy with carbon (C) and other elements. Cast iron finds greater use than аnу other metal. We may classify all cast irons into 3 groups: grey cast iron, white cast iron and malleable cast iron. In respect to their density metals may be divided into light and heavy ones. Metals having a density less than 4 are called light metals, all other having a density over 4 are known as heavy metals.

Light metals are aluminium, berillium, magnesium, titanium. The alkali metals and the alkali earth metals also belong to light metals. The alkali metals include such metals as lithium, sodium, potassium; the alkali earth metals include such metals as calcium, strontium and radium.

Heavy metals include such metals, for example, as lead, tin, silver, copper, nickel, zinc.

The lightest metal is lithium (D – 0.534) and the heaviest is osmium (D – 22.48).

Non-ferrous metals may in its turn bе subdivided into two groups:

a) the so-called group of rare metals (berillium, gallium, bismuth, germanium, selenium, tungsten, tantalum, molybdenum, cobalt, titanium, uranium, zirconium, etc.);

b) and the so-called group of precious (= noble) metals which include silver, gold, platinum, palladium and indium.

Metals may also be classified according to their melting point. Metals which exhibit (= have) high melting point above 3000°F (1650° C) are often called refractory metals. Refractory metals include such non-ferrous metals as tungsten, titanium, molybdenum, tantalum, and chromium. These metals also exhibit great corrosion and wear resistance and are very difficult to produce. The low melting point metals are rubidium, cesium which melts just above room temperature and mercury which melts at – 38, 8° C.

We may also classify hard and soft metals. For example, potassium is so soft that it can be molded like wax, and chromium is so hard that it can even cut glass.

Many elements are classed аs semimetals (arsenic, antimony and bismuth, for example) because they possess much poorer conductivity than true metals and may be classed with the semiconductors.

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1) Into what groups may we divide metals according to their chemical purity?

2) What are a simple metals?

3) What is an alloy? What does it consist of?

4) Into what groups do we usually divide metals in modern industry?

5) How will you call metals consisting of iron combined with some other elements?

6) Into what groups may we divide ferrous metals?

7) What is the most important ferrous metal?

8) How are cast irons classified (into what groups)?

9) How are metals divided according to their density?

10) What are the densities of light metals (of heavy metals)?

11) What alkali and alkali earth metals do you know?

12) What is the lightest (heaviest) metal?

13) Into what two groups may non-ferrous metals be subdivided?

14) Can metals be classified according to their melting point?

15) What metals and alloys are called refractory? Are they easy to produce?

16) What are the low melting point metals?

17) What can you say about potassium and chromium?

18) What are a semimetals?

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