As you know, any substance can be ingaseous, solid and liquid state, and can move from one state to another. It is enough to remember the water. Usually at positive temperatures it is liquid, at negative temperatures it is a solid substance, and at high temperatures it turns into vapor, i.e. in gaseous state. The transformation of a substance from a solid into a liquid state is called melting, and the temperature at which this process occurs is the melting point.
How does the process of melting?If we consider a metal, we will see that its structure is a crystal lattice, the atoms of which are arranged in a certain order relative to each other, making small oscillations. When external energy is received or the body is heated, the energy of the atoms increases, and they begin to oscillate with a greater amplitude. When the body temperature and the melting point of the substance become equal, the process of destruction of the metal structure, that is, the process of melting, begins.
However, the fact that the melting process has begun is notmeans that it will continue on its own. To maintain it, it is necessary to constantly supply heat, which is spent on breaking the bonds of the crystal lattice.
Each substance has its own characteristics.And each metal has its own melting point. It is determined by the crystal lattice and the composition of the substance. For pure substances, this temperature is one, for alloys consisting of several metals - the other. For example, the melting point of cast iron is 1100-1130 ° C. Such a scatter of values is determined by the fact that the content of impurities in this metal changes, moreover, when heated, refractory oxides are formed. They have a melting point higher than that of cast iron.
For copper, this temperature is 1084 ° С, forzinc - 419 ° C. The melting point of brass, which is an alloy of copper and zinc - about 1000 ° C. Such an approximate temperature value is determined by the fact that it depends on the percentage of components. If the composition of the alloy will be more copper, this will lead to the fact that the melting point of the alloy will be higher, if more zinc is lower.
It should be noted that the temperature at which a substance melts depends not only on its purity, but also on pressure. With increasing pressure, it increases, with decreasing pressure decreases.
As already noted, for melting is requiredconstant heat supply. In practice, it looks like the substance is constantly heated, but the temperature remains constant. And only after a certain amount of heat, called the heat of fusion, has been consumed, will a further rise in temperature occur, but already a liquid substance.
There is another melting feature.metals. If you stop the heat supply, the melting process stops and the reverse process begins - the liquid metal becomes solid. This process is called crystallization. When cooling a liquid metal and turning it into a solid, the same amount of heat is released, which was spent on its melting.
The role of melting in nature, science and technologydifficult to overestimate. Through this process, we can produce metals or alloys with the properties we need. Virtually the entire human civilization is based on metal and its alloys, and therefore, on such physical constants as the melting point. After all, in fact there is no industry that would not consume metal.
Thus, we examined what the melting point is, determined what it depends on, and described the melting process itself. The article also defines the crystallization of metals.
