For metals are 80 elements of the periodic table. Each metal has its own characteristics. Some metals for a variety of properties similar to each other, and they can be combined into groups. One such group of noble metals: gold, silver, platinum and others. Total between them is that they stand in air, and gloss retention.
Comparing the different metals, we see that along with the general properties and behavior, they also have distinct differences. For example, metals vary greatly in melting temperature. Mercury at ambient temperature and a liquid remains only solidifies at — 38,5 ° C; gallium melt when held in the hand — the melting temperature is 29,5 ° C and to melt tungsten, it must be heated to 3450 ° C.
Metals are good conductors of electricity. Silver conducts electricity six times better than iron, and the electrical conductivity of the last several thousand times larger than the germanium — also metal.
In certain metals, elastic boundaries, changing their shape and size, when removing it disappear. Quantitatively, the elasticity of the metal is characterized by a modulus of elasticity. In this module iron 30 times greater than that of lead, and one hundred times greater than that of cesium.
Most metals are not applied in pure form, as well as alloys. For the preparation of alloys — doping — a metal specifically added one or more other metals or nonmetals. Doping allows you to change the properties of the metal. For example, the relatively soft copper alloyed with tin, is transformed into a much more solid bronze. Iron mainly due to doping of carbon steel is prepared, which is called carbon. Alloy steels contain in addition to carbon and other specially introduced (dopant) elements such as manganese, nickel, chromium and the like. D.
The purpose of the doping lies in the fact that to improve the performance and processing properties of a metallic material. Often, if you do not manage to simultaneously improve all the properties of the material as it would like, it is necessary to seek a compromise solution. For example, copper bronze is stronger and less ductile. Pure aluminum conducts current better than any alloy thereof, but its strength is considerably lower. Therefore, in the manufacture of metallurgical alloys based on the fact what properties in the specific application of the alloy is important and, therefore, should be as far as possible, strengthened, and which properties can be somewhat sacrifice. Knives and ax must be sharp for a long time; the bell should ring loud and clear; casting a molten material should fill the mold well, and therefore must have a high melt flowability, that is. ie low viscosity.; structural steel for the construction of bridges should be strong, viscous and well-welded; metal bearing has to be resistant to wear. In most cases, that would get the desired properties of the metal it has to be doped with several elements and subjected to treatment. In those days, when the scientific basis of doping were unknown, the preparation of alloys seemed mysterious art, magic and accidentally open many laws of this process were the secret of the family or the shop.
When asked steelmakers that such an alloy, they usually provide some general definition of the type: alloy — a metal compound with one or more metals or of metals and nonmetals. Sometimes, before you answer, they are asked to specify what kind of base metal in question, and what metals or nonmetals are used as dopants for the alloy may be present diverse compounds with metals and nonmetals, including the chemical compound type. For example, the steel contains carbon compound of iron — iron carbide, Fe3C, and an alloy of aluminum and copper — compound of these metals Al2Cu. Some metals form alloys selected only mechanical mixture as iron-lead alloy is a mixture of iron and lead crystal, bismuth-cadmium alloy is a mixture of crystals of bismuth and cadmium. In these cases, the heterogeneous crystals at least partially located in a specific, characteristic manner. Finally, two metal may together form a new type crystals; such mixed crystals are called solid solutions.
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