Thermodynamic Principles of Metallurgy – I

Thermodynamic Principles of Metallurgy 

In metallurgical operations, thermodynamic concerns are critical. These factors can determine the temperature and the type of reducing agent used in the reduction process. The thermodynamics of reactive systems is the focus of thermodynamic principles of metallurgy, which is used by metallurgical and materials scientists around the world. 

Principles of metallurgy

Metallurgy is the application of a metallurgical process to obtain metals in their purest form. Metals and other materials, such as sand and limestone, combine to form minerals. Commercial metal extraction from minerals necessitates cheap costs and little labour. These minerals are referred to as ores. To remove gangue (detritus), flux is added to the furnace as a fuel additive. In metallurgy, metals are purified, and alloys are formed by these methods.

The principles of metallurgy used in the extraction of metals are as follows:

1. Pulverisation: To begin metallurgy, ores must be ground into an extremely fine powder to begin the process. The term “pulverisation” is used to describe this process.
2. The concentration of ores: A mineral concentration, or ore dressing, refers to the process of eliminating contaminants from ores. The following techniques are used mostly in metallurgy to concentrate ores.
3. Hydrolytic process: Ore is poured over a vibrating corrugated table with grooves in the hydrolytic technique. The surface is permitted to be sprayed with a jet of water. Impurities are washed away by water as the ore settles in the grooves.
4. Magnetic separation: The ore is deposited on a conveyor belt for magnetic separation. Magnetised particles are drawn to and separated from non-magnetic ones by this belt’s rotating two wheels, one of which has a magnetic field.
5. Calcination: Crushed ore is placed in a big tank of oil and water, where it is floated to the top. It is compressed by a stream of air. Froth is formed as the ore is wetted by oil and separated from the impurities. Because ore is lighter than contaminants, it rises to the surface.
6. Roasting: It’s called roasting in metallurgy when an ore is heated in the presence of oxygen and then cooled. Sulphide ores are used as a case study for this method. If the ore contains carbonate or hydrated oxides, melting it requires heating it without air, a process called calcination.

General principles of metallurgy

The general principles of metallurgy are the processes involved in converting ores into useful metals. These processes help in refining the ores into their pure state.

The basic principles of metallurgy are based on the idea that impurities are more easily dissolved in liquid metal than in solid metal, which is why zone refining is so effective. As a result, impure metal rods are used to move mobile induction coil heaters in this technique. An area of molten metal has developed on the heater’s moving rod. Pure metal crystallises and leaves behind as the heater moves forward, while impurities flow forward with the molten zone because they are more soluble in a molten state.

The chromatography technique is also utilised to purify elements when the chemical characteristics of contaminants and metals differ by a very small amount. Because the stationary phase has a varied affinity for different mixture components, the chromatographic method is based on this principle. To separate components, they are spread out between stationary and mobile phases. Weak forces and nonionic forces, such as hydrogen bonds or Van der Waals forces, are the mechanisms by which the stationary phase adsorbs components. Components of the mixture travel at different speeds and separate from one other. Differential partitioning of the mobile and stationary phases is used to achieve the separation. These basic principles of metallurgy are used for refining metals.

Thermodynamics principles in Metallurgy

The efficiency of metallurgical processes can be improved and better understood by using thermodynamic principles of metallurgy. For example, the best results in the reduction of metal oxides should be obtained by using the most suitable reducing agent. Thermodynamics may now be used to determine the optimal reducing agent. Reducing agents for oxides can be selected using the Ellingham diagram.

Ellingham Diagram

The temperature and stability of a compound are shown in an Ellingham diagram. The Gibbs Energy Flow is depicted graphically in this diagram. In chemistry, the Ellingham diagram is one of the most fundamental concepts, and it is necessary for understanding the thermodynamics principles of metallurgy. The greatest amount of reversible work that a thermodynamic system can accomplish at constant temperature and pressure is calculated using the Gibbs free energy, a thermodynamic potential. In this case, it’s G. The joule is the unit of measurement.

The Ellingham diagram is used in metallurgy to represent the reduction process equations in thermodynamic principles of metallurgy. The most effective reducing agent for reducing oxides to pure metals can be found in this way.

Limitations of Ellingham Diagram

It does not consider the kinetics of the reactions. Also, it does not provide complete information about the oxides and their formations. Thus this limits the use of the Ellingham diagram in the thermodynamics of metallurgy.

Uses of Ellingham Diagram

1. Alumino Thermic Process

Compared to other metals, such as iron, the Ellingham curve on the graph has a smaller slope. Essentially, this means that all of the metal oxides above aluminium in the graph can be reduced by using aluminium as a reducing agent. Thermite is used to extract chromium from aluminium oxide because it is more stable.

1. Extraction of Iron

A blast furnace is used to extract iron from iron oxide. A furnace is used to heat the ore mixed with coke and limestone. Different temperatures are required for the iron oxides to be reduced. A higher temperature is maintained in the lowest portion of the furnace. Thermodynamics was used to decipher the reactions and devise this procedure.

Conclusion

This chapter is essential to learn about metallurgy’s various processes. Metallurgy’s thermodynamic concept is critical and necessitates in-depth investigation. It is a branch of science that studies the transfer of energy through chemical and physical transformations. In addition, it allows us to predict and measure the changes.