Enthalpies of mixing of liquid systems for lead free soldering: Al-Cu-Sn system.

The present work refers to high-temperature drop calorimetric measurements on liquid Al-Cu, Al-Sn, and Al-Cu-Sn alloys. The binary systems have been investigated at 973 K, up to 40 at.% Cu in case of Al-Cu, and over the entire concentrational range in case of Al-Sn. Measurements in the ternary Al-Cu-Sn system were performed along the following cross-sections: x(Al)/x(Cu) = 1:1, x(Al)/x(Sn) = 1:1, x(Cu)/x(Sn) = 7:3, x(Cu)/x(Sn) = 1:1, and x(Cu)/x(Sn) = 3:7 at 1273 K. Experimental data were used to find ternary interaction parameters by applying the Redlich-Kister-Muggianu model for substitutional solutions, and a full set of parameters describing the concentration dependence of the enthalpy of mixing was derived. From these, the isoenthalpy curves were constructed for 1273 K. The ternary system shows an exothermic enthalpy minimum of approx. -18,000 J/mol in the Al-Cu binary and a maximum of approx. 4000 J/mol in the Al-Sn binary system. The Al-Cu-Sn system is characterized by considerable repulsive ternary interactions as shown by the positive ternary interaction parameters.

Mass spectrometric and quantum chemical studies of the thermodynamics and bonding of neutral and ionized LnCl, LnCl2, and LnCl3 species (Ln = Ce, Lu).

The mass spectral patterns of CeCl3(g) and LuCl3(g) and appearance energies for the identified ions were measured using a Nier-type mass spectrometer coupled with a Knudsen cell. The molecular ion CeCl3+ was found to be considerably less stable in comparison to LuCl3+. Partial pressures and sublimation enthalpies of LnCl3(s) to monomeric LnCl3(g) and dimeric Ln2Cl6(g) species were obtained in the ranges of 882-1028 (Ln = Ce) and 850-1004 K (Ln = Lu). The contribution of dimeric Ce2Cl6(g) species to equilibrium vapors of CeCl3(s) is considerably smaller than the Lu2Cl6(g) contribution in LuCl3(s) vapors. The measurements were supplemented by quantum chemical ab initio studies of structures, energetics, and vibrational frequencies of neutral and singly ionized LnCl, LnCl2, and LnCl3 species (Ln = Ce, Lu). The theoretical appearance energies of different ions, calculated from the energies of the gaseous species, are in good agreement with experimental data. The fragmentation energies of LnCl, LnCl2, and LnCl3 were also computed and compared with the mass spectral patterns of respective vapor species. The Mulliken and natural bond orbital electron population methods were applied for the systematic analysis of the bonding scheme in molecules and cations.