Experiments on the simultaneous partitioning of divalent metal ions were performed in the systems (1) ZnS (sphalerite)−(Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺, Cd²⁺)Cl₂−H₂O and (2) Mn₃Al₂Si₃O₁₂ (spessartine)−(Ni²⁺, Mg²⁺, Co²⁺, Zn²⁺, Fe²⁺, Ca²⁺)Cl₂−H₂O in the temperature range of 500 to 800°C at 1 kb. In the former system for ion partitioning in the 4-fold coordination, parabola-shaped PC-IR curves with a peak near Zn²⁺ were obtained and no anomaly was observed for Zn²⁺ and Ni²⁺ but Cd²⁺. In the latter system for ion partitioning in the 8-fold coordination, parabola-shaped PC-IR curves with a peak near Mn²⁺ were obtained, but Zn²⁺ deviates from such a trend and tends to concentrate into aqueous chloride solutions. The PC-IR curves for spessartine are gentle compared with those for sphalerite. The PC-IR curves both for spessartine and sphalerite become gentle with increasing temperature.

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Ultraviolet photoelectron spectroscopy (UPS) is a powerful tool to investigate the interfaces where two materials contact. The large excitation probability for valence electrons and the high surface sensitivity of UPS enable us to obtain the information of interaction between two materials at the interface. A UPS study on Al/Sn interface is introduced as an example to get insight to the origin of eutectic system formation. A valence band spectrum with two increased and two decreased regions of photoemission intensity was observed only for a very thin Al film deposited on a Sn substrate. This phenomenon suggested that valence bands of Al and Sn caused the interorbital interaction and formed new bonding and antibonding bands. According to the molecular orbital theory, the formation of such an electronic structure has an energy disadvantage. The Al-Sn system is known to be a eutectic binary system which is separated into two phases under the eutectic temperature. The energy disadvantage of the valence electrons was considered to be the origin of phase separation in metallic eutectic binary systems through positive free energy of mixing.

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