ИСТИНА

Palladium based alloys, containing metals of 11th group and low-melting metals like tin, are of interest for various fields, such as hydrogen purification and dentistry. Data on phase relations in these system are also of value for analysis of interaction of newly developed Pb free solders with substrates [1]. Phase equilibria in the Ag-Pd-Sn ternary are studied for tin content less than 50 at.% at 500°C. Alloys were prepared from high-purity elements and annealed in evacuated silica ampoules during 2640 h. After annealing the samples were examined by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD). A ternary т phase (Pd(1-x)Agx)4Sn having tetragonal structure of In type (or its ordered derivative) is found. Analogous phases were found also in Au-Pd-Sn [2] and Cu-Pd-Sn [3] systems. Silver exhibits significant solubility, about 17 at.%, in the y-Pd2-xSn phase with the Ni2In type structure. Its solubilities in Pd2Sn phase with Co2Si type structure and Pd20Sn13 with GaGe2Ni4 structure does not exceed correspondingly 3 and 5 at.%. The Pd3Sn phase with Cu3Au type structure dissolves about 9 at.% of silver. The homogeneity range of resulting phase is directed approximately to Ag corner of concentration triangle instead of expected 25 at.% Sn isoconcentrate. Analogous abnormal behavior was noted earlier in the Au-Pd-Sn ternary [2]. This may be considered as indication of Ag (Au) entering equally into both Pd and Sn positions of the Cu3Au structure.