Densities of Pt–X (X: Fe, Co, Ni and Cu) binary melts and thermodynamic correlations

The densities of liquid binary Pt–X (X: Fe, Co, Ni and Cu) alloys were measured over a wide temperature range including the supercooled liquid region, using electromagnetic levitation under a static magnetic field. The static magnetic field effectively suppressed translational motion and surface oscillation of the levitated Pt–X sample droplets, enabling high-accuracy density measurement in a non-contact manner. The excess molar volumes (V^E) of the liquid alloys were evaluated from the density measurements, and we demonstrated that the liquid Pt–X systems have positive V^E with negative excess molar Gibbs energy (G^E). The Pt–X systems have the common feature that order–disorder transitions are present in their phase diagrams. It should be also noted that V^E decreases and G^E increases with increasing number of electrons in the 3d orbital of X. This unique feature in the liquid Pt–X systems was discussed with possible rearrangement of electronic structure caused by alloying Pt with X.