Gaskell, "Introduction to the Thermodynamics of Materials2. Limitation Research and Development, Steelmaking and Casting Research Group CO-CO2 gas mixture as reducing agent (374) MO2+2CO=M+2CO2 At T>Ts CO-CO2 mixture is reducing w.r.t MO2 at pCO/pCO2=1 At T1) must be increasingAt T=Tu pCO/pCO2 should be increased from 1to 10 to maintain reaction equillibrium Research and Development, Steelmaking and Casting Research Group This essentially means Aluminium can be used as a reducing agent for oxides of all the metals that lie above it in the graph. Consider the following reaction: 2CO (g) + O2 (g) = 2CO2 (g) For this reaction, We see that pO2 is equivalent to a ratio: pco/ pco2 Similarly for the reaction 2H2+O2=2H2O pO2 is equivalent to a ratio: pH2O/ pH2 Thus two nomographic scale may be added to the diagram, with a new origin, C and H respectively for pco/ pco2 and pH2O/ pH2 Research and Development, Steelmaking and Casting Research Group The Ellingham curve on the graph actually lies lower than most of the other metals such as iron. Other gas mixtures The oxygen required to cause oxidation in the gas phase need not to come from oxygen gas. Read the partial pressure of O2 from the right hand axis At any oxygen pressure higher than ~10-8.5, the iron will be oxidised at the temperature of 1600C Research and Development, Steelmaking and Casting Research Group Using this point, and the point O in the top left corner, draw a line across the diagram 3. Identify a point corresponding to a selected temperature on the line for: Fe + O FeO, above M 2. Research and Development, Steelmaking and Casting Research Group Jeffes, "The Thermodynamics of Substances of Interest in Iron and Steel Making from 0C to 2400C: I-Oxides," J. Reading pO2 from Ellingham diagram In to avoid calculating the equilibrium partial pressure for each value of G, Richardson2 added a nomographic scale to the Ellingham diagram For a metal oxidation reaction, 2M (s) + O2 (g) = 2MO (s) The equilibrium constant has the form K=1/pO2 G= RT ln(pO2)2 F.D. Additional scales on Ellingham diagram Y=-mX Research and Development, Steelmaking and Casting Research Group The Ellingham Diagrams Research and Development, Steelmaking and Casting Research Group The Ellingham Diagram Research and Development, Steelmaking and Casting Research Group S Enthalpy term Entropy term H: Measure of the actual energy that is liberated when the reaction occurs S: Measure of the change in the possibilities for disorder in the products compared to the reactantsSpontaneity of the Reaction ( G TE Research and Development, Steelmaking and Casting Research Group Before we start: Thermodynamic terminologies Gibbs Free Energy ( G ): Energy of the system available to do work G= H-T*. Technical presentation The Ellingham Diagram Bapin Kumar Rout Research and Development, Steelmaking and Casting Research Group These diagrams must contain only the same type of substances, such as oxides, sulfides, chlorides, etc. The DG diagrams (Ellingham) show the relative stability of various oxides, sulfates, chlorides etc. Also added the carbon and hydrogen reduction lines referred to in the article body, using positions from. DG (Ellingham diagrams) The basic steps for drawing a diagram for all types is almost the same, except for a small difference with the DG diagrams. Click on a date/time to view the file as it appeared at that time.Ĭolor-coded the separate oxygen (red), hydrogen (gray), and carbon (black) axes.
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