Fig. 12 Visualization of the program of interaction of Ni alloys with oxide ceramics


Interakce roztavených slitin s oxidickými keramickými materiály Interaction of molten alloys with oxide ceramic materials Chemické složení taveniny Prvek


Hmotnostní % Rovnice reakce Teplota Tlak


Počítej Závislost logaritmu aktivity kyslíku na teplotě


Chemical melt composition Element Weight %


Equation of reaction Temperature Pressure Count


Dependence of logarithm of oxygen activity on temperature


will ensure zero reduction of oxide ceramics. Both of these solution approaches have been applied in the developed thermodynamic program (Fig. 1). It is clear from the figure that it is possible to choose chemical composition of the nickel alloy, temperature (ranging from 1580°C to 1620°C) and gas pressure above the melt. When pressing the "Count" key, the limit activities for the relevant elements and Gibbs energy values for individual assumed reactions are determined. If the given reaction is thermodynamically improbable, then ΔG is shown in a green box. In the opposite case, when the reaction is thermodynamically highly probable, the ΔG value is displayed in the red field. If the value is negative but at the same time greater than -30,000 J/mol, this value is displayed in the orange box. We are speaking about the cases when the


®


course of the given reaction is thermodynamically possible, but under the real conditions the interaction does not need to occur. The value of 30,000 J/mol is in the thermodynamic practice usually considered an error of thermodynamic data. If the given R element has the activity limit higher than 50 wt. %, in such case reaction cannot be avoided anyhow by modifying chemical composition of the melt. The program on the right shows calculation of the equilibrium activity of oxygen, and/or its logarithm as a function of temperature for activities of the considered elements determined from their concentrations. From the graph, it is thus possible to determine the element or elements having the highest affinity to oxygen under the given condition.


Continued on pg 42 August 2023 ❘ 41


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