Metal melting is a certain thermodynamic process in which the crystal lattice of a metal is destroyed and it passes from a solid phase to a liquid state.
The melting temperature of metals is an indicator of the temperature of the heated metal, upon reaching which the process of phase transition (melting) begins. The process of reverse crystallization itself and is inextricably linked with it. In order to melt the metal? it must be heated using an external heat source to the melting temperature, and then continue supplying heat to overcome the phase transition energy. The fact is that the very value of the melting point of metals indicates the temperature at which the material will be in phase equilibrium, on the boundary between the liquid and the solid. At this temperature, a pure metal can exist simultaneously both in solid and in liquid state. To carry out the melting process, it is necessary to overheat the metal a little more than the equilibrium temperature in order to provide a positive thermodynamic potential. Give a kind of impetus to the process.
The melting point of metals is constant only for pure substances. The presence of impurities will shift the equilibrium potential in one direction or another. This is because the metal with impurities forms a different crystal lattice, and the forces of interaction of atoms in them will differ from those present in pure materials. Depending on the magnitude of the melting temperature, metals are divided into fusible (up to 600 ° , such as gallium , mercury), medium-melting (600-1600 ° , copper, aluminum) and refractory (> 1600 ° , tungsten, molybdenum).
In the modern world, pure metals are rarely used due to the fact that they have a limited range of physical properties. The industry has long and tightly used various combinations of metals - alloys, varieties and characteristics of which are much larger. The melting point of metals included in various alloys will also differ from the melting point of their alloy. Different concentrations of substances determine the order of their melting or crystallization. But there are equilibrium concentrations at which the metals that make up the alloy solidify or melt at the same time, that is, they behave as a homogeneous material. Such alloys are called eutectic.
It is very important to know the melting temperature when working with metal, this value is necessary both in production, for calculating the parameters of alloys, and in the operation of metal products, when the phase transition temperature of the material from which the product is made determines the limitations in its use. For convenience, these data are summarized in a single table. The melting table of metals is a summary result of physical studies of the characteristics of various metals. There are also similar tables for alloys. The melting point of metals also significantly depends on pressure, so these tables are relevant for a specific pressure value (usually these are normal conditions when the pressure is 101.325 kPa). The higher the pressure, the higher the melting point, and vice versa.