Knudsen effusion mass spectrometric determination of mixing thermodynamic data of liquid Al–Cu–Sn alloy

Abstract

Keywords:Knudsen effusion mass spectrometry Redlich-Kister-Muggianu model Activity Excess Gibbs energy Ternary and binary L-parameter a b s t r a c tThe vaporisation of a liquid Al-Cu-Sn system has been investigated at 1273-1473 K by Knudsen effusion mass spectrometry (KEMS) and the data fitted to a Redlich-Kister-Muggianu (RKM) sub-regular solution model. Thirty-one different compositions (41 samples) have been examined at eight fixed copper mole fractions, X Cu = 0.10, 0.20, 0.30, 0.333, 0.40, 0.50, 0.60 and 0.70. The ternary L-parameters, the thermodynamic activities and the thermodynamic functions of mixing have been evaluated using standard KEMS procedures. In addition, the same quantities were obtained from the measured ion intensity ratios of Al + to Cu + , Al + to Sn + and Cu + to Sn + using a mathematical regression technique. The intermediate data obtained directly are the RKM ternary L-parameters that are, as a function of temperature, as follows:(0) = (14270 ± 1270) + (100.1 ± 7.6)T − (11.77 ± 0.93)T ln(T ); L (1) = (145600 ± 9780) + (101.6 ± 58.7)T − (15.56 ± 7.14)T ln(T ); L (2) = (76730 ± 1240) + (79.2 ± 7.4)T − (15.69 ± 0.91)T ln(T ).From the obtained ternary L-parameters the integral molar excess Gibbs energy, the excess chemical potentials, the activity coefficients and the activities have been evaluated. Using the temperature dependence of the activities, the integral and partial molar excess enthalpies and entropies can be also determined. In addition, for comparison, for some compositions, the Knudsen effusion isothermal evaporation method (IEM) and the Gibbs-Duhem ion intensity ratio method (GD-IIR) were used to determine activities and good agreement was obtained from the RKM model.

Preparation of Al–Cu alloys by aluminothermic reduction of CuO using submerged powder injection assisted with mechanical agitation: thermodynamic approach and kinetic measurements

“…The equilibrium analysis described above is important for stating that the main chemical reaction that must occur is that given by equation (2), no matter that the value of its Gibbs free energy is not as negative as that of the reactions given by equation (7) or (11). In this sense, it can be considered that the main role of magnesium is lowering the surface tension of the molten phase, although some increase in the reactivity of the molten bath can be gained by adding it.…”

“…When stoichiometric amounts of MgO and Al 2 O 3 have formed and equilibrium conditions are obeyed, the reaction given by equation (11) takes place. In this way, the formation of MgO and Al 2 O 3 and the interdiffusion of Al, Mg and Cu occur simultaneously.…”

“…The result is a change in the crystal structure. The processes involved in this phenomenon are governed by the chemical potential values of the partial reactions given by, in this case, reaction (2) or (11). Because MgAl 2 O 4 is the final reaction product, the reaction given by global equation (11) could be accepted since this reaction satisfies the described mechanism.…”

“…11 Therefore, the molten solution can be considered as an ideal one, and then it is reasonable to assume that the activity of copper in the molten solution could be approximated by considering the activity coefficient equal to 1. In this way, the activity can be expressed directly from the molar fraction of copper in the molten solution.…”

Determination of the Mixing Thermodynamic Properties of Liquid Ternary Alloys by Fitting the Knudsen Effusion Mass Spectrometric Data to the Redlich-Kister-Muggianu Sub-Regular Solution Model

“…In contrast to binary alloys, there is a lack of thermodynamic data concerning ternary alloys. Our former KEMS studies on Cu-In-Sn [1], Ag-In-Sn [2], Al-Cu-Sn [3], Cu-Sb-Sn [4] liquid ternary systems in the framework of the EU's COST 531 and MP0602 actions could improve this circumstance, at least to some extent. In 2001 Miki et al, [5] were able to show that by using the Redlich-Kister-Muggianu (RKM) sub-regular solution model for liquid alloys they could obtain the ternary interaction parameters directly from mass spectrometric measurements.…”