![]() Transformations and is expressed by the equation: STHG where, H is the enthalpy change and S is the entropy change for the process at temperature T. Thermodynamic principles of Metallurgy: Gibbs energy change, Gįor any process at a specified temperature helps us to understand the theory of metallurgical The construction of an Ellingham diagram is especially useful when studying the stability of compounds in the presence of a reductant.ELLINGHAM DIAGRAM NOTES ON THERMODYNAMIC PRINCIPLES OF METALLURGY: The concept is generally useful for studying the comparative stability of compounds across a range of partial pressures and temperatures. The original paper by Ellingham explicitly to the reduction of both oxygen and sulfur by metallurgical processes, and anticipated the use of such diagrams for other compounds, including chlorides, carbides, and sulfates. The concept of plotting the free energies of reaction of various elements with a given gas-phase reactant may be extended beyond oxidation reactions. In pyrometallurgy, aluminium is used as a reducing agent in the alumino-thermic process or thermite process to extract chromium and manganese by reduction of their oxides.Įxtensions to other gas-phase reactions Since the Gibbs free energy change is negative, aluminium can reduce chromium oxide. So aluminium oxide is more stable than chromium oxide (at least at normal temperatures, and in fact all the way up to the decomposition temperatures of the oxides). The slope of the plots d Δ G / d T = − Δ S For the oxidation of each metal, the dominant contribution to the entropy change (Δ S) is the removal of 1⁄ 2 mol OĢ, so that ΔS is negative and roughly equal for all metals. In the temperature ranges commonly used, the metal and the oxide are in a condensed state (solid or liquid), and oxygen is a gas with a much larger molar entropy. the line for the oxidation of chromium shows Δ G for the reaction 4⁄ 3 Cr(s) + Oģ(s), which is 2⁄ 3 of the molar Gibbs energy of formation Δ G f°( Cr The diagram shown refers to 1 mole OĢ, so that e.g. For comparison of different reactions, all values of Δ G refer to the reaction of the same quantity of oxygen, chosen as one mole O ( 1⁄ 2 mol OĢ by others. The Ellingham diagram plots the Gibbs free energy change (Δ G) for each oxidation reaction as a function of temperature. Thermodynamics Ellingham diagram for several metals giving the free energy of formation of metal oxides and the corresponding oxygen partial pressure at equilibrium.Įllingham diagrams are a particular graphical form of the principle that the thermodynamic feasibility of a reaction depends on the sign of Δ G, the Gibbs free energy change, which is equal to Δ H − TΔ S, where Δ H is the enthalpy change and Δ S is the entropy change. Thus, processes that are predicted to be favourable by the Ellingham diagram can still be slow. The analysis is thermodynamic in nature and ignores reaction kinetics. The diagrams are useful in predicting the conditions under which an ore will be reduced to its metal. In metallurgy, the Ellingham diagram is used to predict the equilibrium temperature between a metal, its oxide, and oxygen - and by extension, reactions of a metal with sulfur, nitrogen, and other non-metals. These diagrams were first constructed by Harold Ellingham in 1944. This analysis is usually used to evaluate the ease of reduction of metal oxides and sulfides. JSTOR ( December 2021) ( Learn how and when to remove this template message)Īn Ellingham diagram is a graph showing the temperature dependence of the stability of compounds.Unsourced material may be challenged and removed.įind sources: "Ellingham diagram" – news Please help improve this article by adding citations to reliable sources. This article needs additional citations for verification.
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