Thermochemistry of Acid-Base Stabilized Transition-Metal Alloys by Carbide and Nitride Equilibria and Knudsen Effusion-Vapor Pressures

摘要

The thermochemistry of several Lewis acid-base stabilized transition metal alloys has been investigated and the results interpreted within the context of the Engel-Brewer theory to further clarify and quantify the factors which determine the extent of this type of interaction. Binary alloys of a platinum group metal (Ru, Os, Ir, Pd, Pt, or Au) with a group IVB-VIB transition element (Ti, Zr, Hf, Nb, Ta, or W) were studied by equilibration of the alloy with the appropriate IVB-VIB carbide or nitride or by measuring the vapor pressure of one of the two components by thermogravimetric or mass spectrometric Knudsen effusion experiments. Twenty-seven binary alloys were studied at temperatures ranging from 1425 K to 2750 K and the activities established ranged from a/sub Zr(ZrPt//sub 3/) = 6 x 10 exp -6 to a/sub Pd(82 at. % Pd-Nb/) approx. = 1, both at 1900 K. Among the implications of the results obtained are that reduced bonding ability due to crystal field effects can severely limit the extent of acid-base interaction and the effect of valence d orbital contraction is relatively minor for the 4d (e.g., Zr) compared with the 5d (e.g., Hf) elements but is significant for the 3d (e.g., Ti) elements. 98 references, 14 figures, 10 tables. (ERA citation 08:049497)