As you know, metals are the foundation of our current lifestyles. The discovery of metals helped man’s advances even in the prehistoric period. Metallurgy is the process of extracting metals first from the lithosphere. Thermodynamic concepts are used by chemists to aid in this procedure. Let us take a closer look at the general thermodynamic principles of metallurgy. 

Thermodynamics

Physical Chemistry is the branch of chemistry and physics that integrates two disciplines. This is when the idea of thermodynamics comes to an end. Thermodynamics is a branch of physics that studies the link between thermal energy, such as heat, and other types of energy.

The research of the energy transfer that happens during chemical and physical transformations is known as thermodynamics. It also enables us to forecast or track such shifts.

Metallurgical Thermodynamics

Gibbs Free Energy is the most crucial thermodynamic notion of understanding whenever it relates to metallurgy principles. Gibbs Free Energy determines if a procedure can happen suddenly or not in thermodynamics. The letter G. If the value of G is negative, the reaction would occur independently. To arrive at G, we’ll look at the two equations.

ΔG = ΔH – TΔS

  1. denotes the enthalpy change. An endothermic reaction would be represented by a positive value, whereas a negative value would represent an exothermic reaction. As a result, whenever the reaction is exothermic, G is negative. Entropy, or the unpredictability of molecules, is denoted by the letter S. Whenever the structure of the matter changes, this changes dramatically. A further equation that connects Gibbs Free Energy and the equilibrium constant is

ΔG° = RTlnKeq

The equilibrium constant is Keq. The active mass of the product is divided by the reaction’s active group to arrive at this figure. The universal gas component is R. The equilibrium value should now be kept positive to get a negative value of G (which is desirable).

Ellingham Diagram

An Ellingham diagram depicts the relationship between the temperature and a compound’s durability. It’s a graphical illustration of the Gibbs Energy Flow.

The Ellingham diagram is used in metallurgy to illustrate the reduction process formulas. This aids us in determining the best reducing agent used when reducing oxides to produce pure metals. Let’s take a closer look at a few of the thermodynamic principles of the metallurgy Diagram’s most crucial features.

  • G is shown in proportion to temperature in this graph. The entropy is represented by the slope of the curve, whereas the intercept represents the enthalpy.
  • As you may be aware, the H (enthalpy) is unaffected by temperature.
  • The temperature does not affect S, which is the entropy. Nevertheless, there is indeed a stipulation that no phase shift must occur.
  • The temperature will be plotted on the Y-axis, while the G will be plotted on the X-axis.
  • Metals with curves near the bottom of the diagram are less common than metals located higher up.

The reactivity of metal with air could be summed up as follows:

M (s) + O2 (g) → MO (s)

The H is usually harmful when it lowers metal oxides (exothermic). S is also negative since we are going from either a gaseous to a solid-state in the process (as seen above). As a result, as the temperature goes up, T∆S’s value rises as well, and indeed the reaction slope increases.

Ellingham Diagram Exceptions

In some circumstances, the entropy is not harmful, and also the slope is not upward. Take a look at how many of these occurrences there are.

C(s) + O2 (g) → CO2 (g):

Solids have minimal entropy. As a result, one molecular of gas produces one particle of gas. As a result, there’s virtually little net entropy. As a result, there’ll be no slope, and the surface will indeed be perfectly horizontal.

2C (s)+ O2 (g) → 2CO (g):

One mole of gas generates two moles of gas due to this reaction. As a result, the entropy will be positive in this case. As an outcome, this curve will begin to decline.

Ellingham Diagram Limitations

  • The kinetics of the reactions are not taken into account.
  • It also lacks detailed information on the oxides and their origins. Let’s say there’s the possibility of more than one oxide. This scenario is not represented in the diagram.

Ellingham Diagram Applications

  • Thermic Alumino Process

On the graph, the Ellingham curve is lower than most common metals, including iron. This effectively suggests that almost all metals above it in the graph could be utilized as a reduction agent for their oxides. Because aluminum oxide is much more durable, it is used in the thermite process to remove chromium.

  • Iron is extracted

A blast furnace is used to separate iron from its oxide. In the furnace, the metal is mixed with coke or limestone. The elimination of iron oxides takes place at a range of temperatures. The furnace’s bottom section temperature is considerably higher than that in the top. Thermodynamics was used to explain the reactions, which led to the development of this technique. The following are the reactions:

At temperatures of 500-800 K

3Fe2O3 + CO → 2 Fe3O4 + CO2

Fe3O4 + 4CO → 3Fe + 4 CO2

Fe2O3 + CO → 2FeO + CO2

At temperatures of 900-1500 K

C + CO2 → 2CO

FeO + CO → Fe + CO2

Conclusion

The science and technique of metals are referred to as principles of metallurgy. A mineral is a natural substance produced by mining that includes the metal in its pure form or the form of compounds such as oxides, sulfides, and other compounds. Ores are minerals that contain a high percentage of metal and may be mined efficiently and economically from them. Ellingham diagram is a graphical representation of the change of the standard Gibbs free energy of reactions for creating different metal oxides as a function of temperature. The Ellingham diagram assists in selecting the suitable reducing agent and a reduction temperature range.