U N I T 2 METALS This Unit is about the most widely used engineering materials. It deals with metals, their general characteristics and classification as ferrous and non-ferrous. It looks at their different properties and various applications. A. METALS: GENERAL CHARACTERISTICS 1 Listen to the recording and complete the text with the words in the box. non-ferrous semi-metals high substances consisting properties defined carry out malleable mixed classified employed ores conductors components Natural elements are usually (a) ......................... into four main groups: metals, non-metals, noble gases and (b) ......................... . Metals and non-metals (plastics, ceramics) are the engineering materials mostly (c) ......................... in the manufacturing of finished products and mechanical engineers are expected to have a complete knowledge of their (d) ......................... and processing methods in order to choose the best solutions for the task they have to (e) ......................... . As regards the metallic elements, they form less than 25% of the Earth s crust: aluminium, iron, calcium, sodium, potassium and magnesium are the most common ones. The majority are extracted from their (f) ......................... and are in combination with other (g) ......................... , such as carbonates, sulphides, oxides, while only a few metals (silver, platinum, gold and copper) can be found free in nature. Iron meteorite 50