Melting point - each has its own
As is known, any substance can be ingaseous, solid and liquid state, and can pass from one state to another. Suffice it to recall the water. Usually, at positive temperatures this is a liquid, while for negative temperatures it is a solid, and at high temperatures it turns into vapor, i.e. into a gaseous state. The transformation of a substance from a solid to a liquid state is called melting, and the temperature at which this process occurs is a melting point.
How does the melting process occur? If we look at the metal, we see that its structure is a crystal lattice, whose atoms are arranged in a certain order relative to one another, making small oscillations. When external energy arrives or the body is heated, the energy of the atoms increases, and they begin to oscillate with a larger amplitude. When the body temperature and the melting point of the substance equalize, the process of metal structure destruction, that is, the melting process, 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 the same, for alloys consisting of several metals - another. For example, the melting point of cast iron is 1100-1130 ° C. Such a spread of the values is determined by the fact that the content of impurities in this metal varies, besides, when heated, refractory oxides are formed. They have a melting point higher than that of cast iron.
For copper, this temperature is 1084 ° C, forzinc - 419 ° C. The melting point of brass, which is an alloy of copper and zinc, is approximately 1000 ° C. This approximate temperature is determined by the fact that it depends on the percentage content of the components. If there is more copper in the composition of the alloy, this will lead to the fact that the melting point of the alloy will be higher if the zinc is more low.
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 drop in pressure decreases.
As already noted, melting is necessaryconstant supply of heat. In practice, it looks like 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 used up, a further increase in temperature will begin, but already of a liquid substance.
There is one more feature in meltingmetals. If the supply of heat is terminated, the melting process stops and the reverse process begins - the liquid metal becomes solid. This process is called crystallization. On cooling the liquid metal and making it a solid is released the same amount of heat which is consumed during its melting.
The role of melting in nature, science and technologyit is difficult to overestimate. Thanks to this process, we can obtain metals or alloys with the properties we need. Practically the whole human civilization is based on metal and its alloys, and therefore on such physical constants as the melting point. After all, there is virtually no industry that does not consume metal.
Thus, we considered what the melting point is, determined what it depends on, and described the melting process itself. The article also defines the crystallization of metals.
