Liquid state is an intermediate state between solid state and gaseous state. Solid metals are composed of many grains, gaseous metals are composed of single atoms that resemble elastic spheres, and liquid metals are composed of many groups of atoms.
1. Structural characteristics of liquid metals
Liquid state is an intermediate state between solid state and gaseous state. Solid metals are composed of many crystal grains, gaseous metals are composed of single atoms that resemble elastic spheres, and liquid metals are composed of many atomic groups, and their structures have the following characteristics
(1) Each atomic group has about a dozen to hundreds of atoms, which still maintains a strong binding energy in the atomic group and can maintain the arrangement characteristics of the solid. However, the bond between the atomic groups is greatly damaged, and the distance between the atomic groups is relatively large and loose, as if there are holes.
(2) The atomic groups that make up the liquid metal are very unstable, sometimes growing up and sometimes getting smaller. It is also possible to leave atomic groups in groups and join other atomic groups, or to form atomic groups.
(3) The average size and stability of atomic groups are related to temperature. The higher the temperature, the smaller the average size of the atomic groups and the worse the stability.
(4) When there are other elements in the metal, due to the different binding forces between different atoms, the atoms with stronger binding forces tend to gather together and repel other atoms at the same time. Therefore, there is also inhomogeneity of composition between atomic groups, that is, concentration fluctuations, and sometimes even unstable or stable compounds are formed.
2. Melting and Dissolving
During the smelting process of the alloy, there are two simultaneous processes of melting and dissolution. When the alloy is heated to a certain temperature, it begins to melt, and its thermodynamic condition is overheating. Dissolution means that the solid metal is eroded by the metal melt and enters the solution to realize the transformation process of solid to liquid. Dissolution does not require heating, but the higher the temperature, the faster the dissolution rate.
In fact, only when the melting point of the alloying element is higher than the temperature of the copper alloy solution, the process of the alloying element entering the melt is a pure dissolution process. In copper alloys, for example, the constituents iron, nickel, chromium and manganese as well as the non-metallic elements silicon, carbon, etc., are understood to have a dissolution process therein. In fact, both melting and dissolving processes take place simultaneously, with the dissolving process promoting the melting process.
There are many factors that affect the rate of metal dissolution.
First, the higher the temperature, the more favorable the dissolution is.
Secondly, it is related to the surface area of the object being dissolved, the larger the surface area, the faster the dissolution rate.
The dissolution rate of metal is also related to the motion of the melt. When the melt flows, the dissolution rate is greater than that of the metal in the static melt, and the faster the melt flows, the faster the dissolution rate will be.
Dissolution and Alloying
When alloys were first made, it was thought that melting should begin with components that are difficult to melt (and have high melting points). For example, when the copper-nickel alloys of 80% and 20% nickel were first made, the nickel with the melting point of 1451°C was first melted and then copper was added. Some melt copper and heat it to 1500 ℃ before adding nickel for melting. After the theory of alloys was developed, especially the theory of solutions, the above two melting methods were abandoned.
Deposition of non-alloying elements
There are many reasons for the continuous increase and precipitation of non-alloying elements in metals and alloys.
Impurities brought into the metal charge
Even if the process waste produced in the production process of our factory is used repeatedly, the content of the impurity elements in the charge will continue to increase due to various reasons. As for mixing materials or using large quantities of purchased materials with unclear origins, the possible impurities and possible effects are often even more unpredictable.
Improper selection of furnace lining material
Certain elements in the melt may chemically react with them at the melting temperature.
Post time: Feb-18-2022