Euromet 2006 Influence of impurities on the melting temperature of Aluminum Pr. B. Legendre & Dr S. Fries EA 401
Impurities B, C, Cr, Cu, F, Fe, Mg, Mn, N, Ni, O, Pt S, Sc, Si, Ti, V, Zn. Al – X Optimized Al – Y Non optimized (or bad optimized), but the phase diagram is known Al – F no data
Aim Measurement of the slopes of the liquidus and of the solidus : = (dT/dx) l : for the liquidus s : for the solidus The slope may be expressed in atomic fraction or in weight fraction. Determination of K : K = l / s For Al T fus = °C
Phase diagram For this subject we are interested only by a very small region in temperature and composition of binaries Al-X, but it is absolutely necessary to have a perfect knowledge of the full diagram. And to know the Gibbs function versus of T and x for each phase at a fixed pressure.
Phase diagram : Calphad Method A phase diagram is the graphical expression of phase equilibria, for each phase in a binary system G = f(x i, T, P) The limits of a two phase field are given by the common tangent of the G =f(x i ) PT curves. For a eutectic: The three curves G=f(x i ) p,T, have the same tangent.
The whole process
Calculating phase diagrams
Al - Si
Al - B
Al - Pt
Al - Cr
Al - Ni
Al - Fe
Al - Cu
Al - Sc
No data for the solidus…
Al – O: not a good optimization
Al - O Why it is not possible to have a good optimization of the Al-O binary? The oxygen forms with Al an oxide which is a thin film fixed on the surface of Al and then it is a kind of protection (aluminum pans are used on the gas in a kitchen…) after the fixation of a first layer the oxygen cannot go deeper in Al. There is no homogeneity and no equilibrium.
Al - O L Al + Al 2 O 3 T =~ 660°C Van’t Hoff law dln(a Al )/dT = H/RT 2 a Al ~ X Al H = fus H(Al) = J/mol T = K X Al = dT/dX = 676
Results
Comparison of results
Variation of the liquidus temperature versus of the yield of impurities T l = T fus + i T l = temperature of the liquidus T fus temperature of fusion of pure Al = dT/dx x : weight fraction i : yield of impurities in ppm*10 -6 Example : for Al-Cr i = 9.9*10 -2 ppm = 466 T l = °C
Temperature of liquidus and solidus for a yield of impurity
Conclusions It has been possible to determine the influence of impurities in Al for nearly all the selected elements. For O and S just an estimation has been possible. The most important modifications occurs with O and N It is possible to perform a calculation with two impurities.
Acknowledgement This work has been financially supported by LNE and BNM We are very grateful to these organisms for their contribution.
Al - Pt
Al - Ni
Al - Pt
Applications of Gibbs energies descriptions combined to kinetic Information
Creating Gibbs energies for each phase
Al - Si