Melting point of metals
Melting of metal is a definite thermodynamic process in which the crystal lattice of a metal is destroyed and it passes from a solid phase state to a liquid one.
The melting point of metals is the indexthe temperature of the metal being heated, upon which the process of phase transition (melting) begins. The very process of reverse crystallization is inextricably linked with it. In order to melt the metal? it must be heated using an external heat source to the melting point, and then continue to supply heat to overcome the energy of the phase transition. The fact is that the very value of the melting temperature 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, pure metal can exist simultaneously in both the solid and liquid state. To perform 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 push to the process.
The melting point of metals is constant onlyfor 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 that are present in pure materials. Depending on the value of the melting point, the metals are divided into fusible (up to 600 ° C, such as gallium , mercury), medium-melting (600-1600 ° C, copper, aluminum) and refractory (> 1600 ° C, tungsten, molybdenum).
In the modern world, pure metals userarely due to the fact that they have a limited range of physical properties. Industry has long and densely used various combinations of metals - alloys, varieties and characteristics of which are much larger. The melting point of the metals that make up the 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 forming part of the alloy solidify or melt simultaneously, that is, behave like a homogeneous material. Such alloys are called eutectic.
Knowing the melting point is very important whenwork with metal, this value is necessary both in production, for calculating the parameters of alloys, and when operating metal products, when the temperature of the phase transition of the material from which the product is made determines the limitations when using it. 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 depends significantly on pressure, so the tables are relevant for a particular pressure value (usually normal conditions when the pressure is 101.325 kPa). The higher the pressure, the higher the melting point, and vice versa.
