Feature Article
Modelling The Interaction Of Molten Metals With Oxide Refractories
By Antonín Záděra 1) , Boris Láník 2) , Vladimír Krutiš 1) , Petr Boháček2) 1) Brno University of Technology, Faculty of Mechanical Engineering, Institute of Manufacturing Technology, Department of
Foundry Engineering, Technická 2, 616 69, Brno, Czech Republic 2)
s the integral part of the joint R&D of the foundry department, FME, BUT Brno and the company LANIK, a program was developed to resolve interaction between the selected elements contained in molten nickel alloys and oxide refractory ceramic materials. The program was created in the DELPHI programming environment. Recently, the algorithm has been created to calculate interaction of the molten nickel alloys with ceramic refractory materials, and works are now focused on extension by the interaction of oxide ceramics with iron-based alloys. Calculation of interaction between selected elements with
A
a higher affinity to oxygen and oxide ceramics is based on the thermodynamic calculation. For each considered element dissolved in the melt and the given oxide ceramic, it was necessary to perform a separate thermodynamic calculation according to the general equation (1). For all reactions, it was assumed that the element with a higher affinity to oxygen dissolved in the Me melt reacts with the RxOy oxide ceramic. The MemOn oxide arisen from the element with a higher deoxidation capacity is the very product of the reaction. Another product of the reaction, the metal reduced from the R oxide ceramic, is then dissolved into the melt. The assumed reaction is expressed according to the scheme by the relation (1), where the equation (2) is applied to the stoichiometric coefficients.
LANIK s.r.o., Chrudichromská 2376/17, 680 01, Boskovice, Czech Republic
unitary, i.e. that they can be understood pure oxide substances. In order to express influence of the elements dissolved in
the melt (Me) as well as the elements arising from reduction of the oxide ceramics (R), the Henry’s activities relative to 1% solution are considered. Interaction coefficients for the selected elements in nickel alloys have been taken from [1]. An example of interaction of hafnium with the assumed oxide ceramics according to equation (1) is expressed in equations
(3), (4) and (5). For the reactions as above, values of the standard Gibbs
energy of the given reaction and the chosen standard states according to the thermodynamic data given in [1] were determined at first. The solution itself of the thermodynamic calculation deals with two basic questions in the compiled program:
Is the given reaction thermodynamically probable? What is the equilibrium content of R metal in the molten
The oxide ceramics based on SiO2, ZrO2 and Al2O3 are considered in the model as the RxOy ceramic refractory materials. Carbon, chromium, zirconium, hafnium and titanium are considered the elements contained in the melt (Me) that can react with the assumed oxides. The thermodynamic model used in the compiled program is based on the assumption that the Raoult’s activities of the oxide ceramics entering the reaction (RxOy) and the Raoult’s activities of the oxides leaving the reaction (MemOn) are
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alloy (metal from oxide ceramics) at which reduction of oxide ceramics by Me metal will not take place. The first point resolves the question whether or not reaction of the selected element dissolved in the Me melt with oxide ceramics for the given chemical composition of the nickel-based melt and the selected temperature will occur, i.e. value of the Gibbs energy of this reaction is determined. If ΔG<0, then the reaction is thermodynamically probable. In the opposite case, i.e. the Gibbs energy of the reaction is higher than 0 (ΔG>0), the given reaction does not take place. In the second case, the equilibrium reaction of R metal in the melt, in the course of which there will be no reaction of the selected elements dissolved in the melt and the given oxide ceramics, is resolved. In this case, change in Gibbs energy equalling to zero is considered and then the minimum activity is calculated - concentration of R elements, which
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