Metal melting is a certain thermodynamic process in which the crystal lattice of the metal is destroyed and it passes from the solid state to the liquid state.
Melting point of metals - an indicator of the temperature of the heated metal, upon reaching which the process of phase transition (melting) begins. The process itself is the reverse of crystallization and is inextricably linked with it. To melt metal? it must be heated using an external heat source to the melting temperature, and then continue to supply heat to overcome the energy of the phase transition. 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, at the boundary between the liquid and the solid. At this temperature, a pure metal can exist simultaneously in both solid and liquid states. To carry out the melting process, it is necessary to overheat the metal slightly above the equilibrium temperature in order to provide a positive thermodynamic potential. Give a kind of boost to the process.
Melting point of metalsis 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 interaction forces of atoms in them will differ from those present in pure materials. Depending on the melting point, metals are divided into fusible (up to 600 ° C, such as gallium, mercury), medium-melting (600-1600°С, copper, aluminum) and refractory (>1600°С, 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 densely used various combinations of metals - alloys, the 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 that make up the alloy solidify or melt simultaneously, that is, they behave like a homogeneous material. Such alloys are called eutectic.
Knowing the melting temperature is very important 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 datasummarized in a single table. The metal melting table 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, therefore, the data in the table 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.
