SELECTING METALS Corrosion Clydebank High （选择金属腐蚀Clydebank高）.pdfVIP

SELECTING METALS Corrosion There are two classes of metals: When choosing metals, resistance to corrosion Ferrous - metals that contain iron and are may be an important factor. affected by magnetism (apart from stainless Corrosion is caused by oxygen in the air steel). combining with the atoms of metal, at the surface of the metal, to create a new chemical Non-ferrous - metals that do not contain iron called an oxide, e.g. iron oxide is called rust. and are not affected by magnetism. In steel the rust layer is loose and can fall away; Metals can also be grouped into: this exposes new atoms that will combine with Pure metals - metals made up from only one oxygen to form new rust. chemical element e.g. copper or aluminium. In non-ferrous metals the oxide layer is dense Alloys - metals made up from a mixture of and does not fall away; this creates a barrier to elements, e.g. copper + zinc (brass) or lead + tin the oxygen in the air and new corrosion occurs (solder) very slowly. The layer is called tarnish. Alloying Properties Metals are alloyed to improve the qualities of Both physical and mechanical properties vary the individual pure metals e.g. both copper and greatly between different metals and alloys and tin as pure metals are both soft metals that ar