As you know, any substance can be in a gaseous, solid and liquid state, and can go from one state to another. Just remember the water. Usually at positive temperatures it is a liquid, at negative temperatures it is a solid, and at high temperatures it passes into steam, i.e. into a gaseous state. The transformation of a substance from solid to liquid is called melting, and the temperature at which this process occurs is called the melting temperature.
How does the melting process take place? If we look at the 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 vibrations. Upon receipt of external energy or heating of the body, the energy of atoms increases, and they begin to oscillate with a larger amplitude. When the body temperature and the melting point of the substance become equal, the process of destruction of the metal structure begins, that is, the melting process.
However, the fact that the melting process has begun does not mean 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, another. For example, the melting point of cast iron is 1100-1130 ° C. Such a spread in values is determined by the fact that the content of impurities in this metal changes, and besides, refractory oxides are formed during heating. Their melting point is higher than that of cast iron.
For copper, this temperature is 1084 ° C, for zinc - 419 ° C. The melting point of brass, which is an alloy of copper and zinc, is approximately 1000 ° C. Such an approximate temperature value is determined by the fact that it depends on the percentage of components. If the alloy contains more copper, this will lead to the melting point of the alloy being higher, if more zinc is lower.
It should be noted that the temperature at which the substance melts depends not only on its purity, but also on pressure. With increasing pressure, it increases, with a decrease in pressure decreases.
As already noted, a constant supply of heat is required for melting. In practice, it looks like there is a constant heating of the substance, but the temperature remains constant. And only after a certain amount of heat, called the heat of fusion, is consumed, will a further increase in temperature, but already of liquid substance , begin .
There is another feature when melting metals. If the heat supply is stopped, the melting process stops and the reverse process begins - the liquid metal goes into a solid state. This process is called crystallization. When cooling a liquid metal and turning it into a solid, the same amount of heat is released that was expended on its melting.
The role of melting in nature, science and technology is difficult to overestimate. Thanks to this process, we can obtain metals or alloys with the properties we need. Almost all of 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 not a single industry that would not consume metal.
Thus, we examined what the melting temperature is, determined what it depends on, and described the melting process itself. The article also defines metal crystallization.