Partial atomic volume and partial molar enthalpy of formation of the 3d metals in the palladium-based solid solutions
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I.
INTRODUCTION
THE experimentally obtained thermodynamic data for the binary palladium-based alloys with the 3d transition metals are available in the literature only for the systems Pd-Ti, Pd-Fe, and Pd-Ni.[1,2,3] An investigation of the partial atomic volume for solutes in solid solutions based on the fcc,[4–7] hcp,[8] and bcc structure[9,10] yields alternatively an advantageous information about the bond energy in alloys. Palladium is the only one transition element with the (formal) completely filled d shell (4d10) and shows an exceptional strong metallic bonding with the light B13 metals (aluminum and gallium).[4] No systematical data are available for the bond energy between palladium and the 3d transition metals. The aim of this study is to investigate the partial atomic volume of all 3d metals in the fcc palladium-based solid solutions. These ter– minal phases (cF4, Fm3m, Cu type) show the highest packing density (of 74 pct), the coordination number 12 (and, in contrast to the hcp solid solutions, no change in axial ratio). Differently effective in these phases are (1) the 3d electron contribution of transition metals (Sc . . . Ni) and (2) the 4s or 4p valence electron contribution of B metals (Cu . . . Ga). II.
EXPERIMENT
Metals of the following purity were used for alloy preparation: palladium (99.99 wt pct, supplied by Heraeus, Hanau) vanadium (99.99 wt pct, supplied by Johnson Matthey), chromium (99.999 wt pct, supplied by Koch-Light), manganese (99.99 pct, supplied by HEK), iron (99.99 wt pct, supplied by Johnson Matthey), cobalt (99.9 wt pct, supplied by Johnson Matthey), and nickel (99.98 wt pct, supplied by Goodfellow). Metals (approximately 2 g) were melted under
argon (Messer Griesheim (Krefeld), 5.0, 40 kPa) in an arc furnace. The weight of the samples was measured before and after alloying; no significant differences were observed. Bulk alloys were enclosed for the homogenization heat treatment followed by water quenching. The macroscopic density of alloys was measured by means of a gas pycnometer ACCUPYC 1330 (Micromeritics Instruments Corporation Mönchengladbach) using helium (5.0, Messer Griesheim) as the gas medium, to check the number of atoms in the solidsolution unit cell. For the powder diffraction investigation, the bulk alloys were filed and sieved (mesh size 50 mn). Before X-ray diffraction analysis was performed, the filings were annealed in evacuated small silica tubes to remove residual strain. The homogeneity of the powdered and then heattreated alloys was checked by means of Guinier patterns (Enraf-Nonius Delft camera FR 552) using Cu Ka1 radiation. For the unit-cell parameter measurement, the Guinier patterns with Mo Ka1 radiation and a single-coated CEA REFLEX (Muhlheim/Ruhr, Deutschland) 15 film were used. Silicon powder 640c NIST* was applied as an internal cal*NIST is a trademark of National Institute of Standards and Technology, Gaithersburg, MD.
ibration standard for the powder diffraction experiments at 293 K. The position and the integrated intensities of the diffr
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