Metals combine with other metals and some non-metallic elements to form a vast number of alloys that enhance the properties of metals in specific applications, e.g., the combination of iron, nickel and chromium provides a series of stainless steel alloys that are in common use. Metals such as nickel, vanadium, molybdenum, cobalt, rare earths and the platinum group metals enable the catalytic reactions for the synthesis of many organic chemicals from petroleum. A wide variety of metal compounds and salts impart beneficial properties to products like plastics in terms of colour, brightness, flame resistance and resistance to degradation. Photography has been made possible by the effect of light on metal salts.
The properties of strength and ductility enable the extensive use of metals in structures and machinery. Metals and alloys exhibit ductility, malleability and the ability to be deformed plastically (that is, without breaking), making them easy to shape into beams (steel beams for construction), extrusions (aluminum frames for doors and windows), coins, metal cans and a variety of fasteners (nails and paper-clips). The strength of metals under pressure (compression), stretching (tensile) and sheer forces makes them ideal for structural purposes in buildings, automobiles, aircraft frames, gas pipelines, bridges, cables, and some sports equipment.
Metals are excellent conductors of both heat and electricity. In general, conductivity increases with decreasing temperature, so that, at absolute zero (-273°C), conductivity is infinite; in other words, metals become superconductors. Thermal conductivity is harnessed in automobile radiators and cooking utensils. Electrical conductivity provides society with the ability to transmit electricity over long distances to provide lights and power in cities remote from electrical generating stations. The circuitry in household appliances, television sets and computers relies on electrical conductivity. Resistance to Wear, Corrosion, Fatigue and Temperature: Metals are hard and durable. They are used in applications sensitive to corrosion such as chemical plants, food preparation, medical applications, plumbing and lead in storage batteries. Wear resistance is critical in bearings for all modes of transportation and in machine tools. Fatigue resistance - the ability to resist breaking after repeated deformation such as bending - enables the use of metals in springs, levers and gears. Temperature resistance makes metals suitable for jet engines and filaments in light-bulbs. Optical Characteristics: Metals are uniformly lustrous and, except for copper and gold, are silvery or greyish. This is because all metals absorb light at all frequencies and immediately radiate it. Metals impart mirrors with their reflective surface. The lustre of metals gives them the attractive appearance that is so important in jewellery and coins. (Interestingly, metals also provide the intangible, distinctive "metallic ring" that is associated with coins.)
Ferromagnetism is exhibited by iron and several other metals. In addition, other metals and alloys can be magnetized in an electrical field to exhibit paramagnetism. Magnetic properties are employed in electric motors, generators, and speaker systems for audio equipment. Emission Properties: Metals emit electrons when exposed to radiation (e.g. light) of a short wavelength or when heated to sufficiently high temperatures. These phenomena are exploited in television screens, using rare earth oxides and in a variety of electronic devices and instruments. Conversely, the ability of metals such as lead to absorb radiation is employed in shielding, for example in the apron provided by dentists during an X-ray examination.