Alloys of metals are liquid andsolid systems. They are formed by fusing two elements or more. Also connect different metals. Originally, this concept applied only to materials possessing metallic properties. However, in connection with the intensive development of technology and physics, the definition has significantly expanded and spread.
Metals and metal alloys are used universallyin the manufacture of structures of equipment, machines, tools and other things. Despite the fairly high prevalence of artificially created products, products from the above materials often form the basis of the design and, according to forecasts of specialists, will retain their positions in the foreseeable future.
Alkaline earth and alkali metals (K, Na, Ca,Li) in a free state are used in atomic reactors in the form of liquid-metal coolants. Sodium is used as a catalyst in the manufacture of rubber, lithium in the alloying of strong and light aluminum compounds. They are used in aircraft construction.
Metals (basic components of alloys) in natureare found in salts, oxides and ores. As a rule, in the pure state in nature there are elements chemically stable (Au, Pt, Cu, Ag). Among the open elements in the periodic system of Mendeleev, seventy-six refer to metals, Si, Se, Ge, Te, As - to intermediate elements between nonmetals and metals, sometimes called semi-metals.
Metal materials are classified into twolarge groups. The first include iron and its alloys (cast iron, steel), to the second - non-ferrous metals and non-ferrous metal alloys. The latter, in turn, are divided into:
- light (density up to 5 grams / cm3);
- heavy (density more than 10 g / cm3);
- fusible (with a melting point from 232 to 410 degrees);
- refractory (with a melting point higher than that of iron);
- noble (possessing high corrosion resistance).
Metals have various properties.For example, mercury freezes under the influence of temperature minus 38.8 degrees, tungsten is able to withstand the operating temperature to 2000 degrees, sodium, lithium, potassium is lighter than water, and osmium and iridium are heavier than lithium forty-two times. Virtually all metal alloys have characteristics that are determined both by the structure and composition of the compound, depending on the conditions of cooling and crystallization, mechanical and thermal treatment. Cooling or heating contributes to a change in the structure of metal compounds. This, in turn, affects the physical, mechanical and chemical properties, the behavior of the material during processing and operation.
Specialists distinguish the following general properties of metals and alloys:
- High thermal conductivity.
- Increased plasticity.
- High electrical conductivity.
- Positive temperature indexelectrical resistance. This coefficient indicates the growth of resistance with increasing temperature, and at temperatures close to absolute zero-the superconductivity of many metallic materials.
- High reflectivity. Metallic materials are not transparent and have a characteristic metallic luster.
- Thermionic emission - the ability to emit electrons when heated.
- In the solid state, the crystal structure.
To define and verify the properties thathave metal alloys, specialists use various control methods, including destructive methods. Thus, metal materials are tested for ductility, strength, heat resistance, and resistance to corrosion. Along with this, non-destructive control methods are also used. These include measurements of magnetic, optical, electrical properties, determination of the hardness index.
