Oxidation kinetics of cobalt and cobalt—iron alloys at high temperatures

The oxidation kinetics for cobalt and two cobalt—iron alloys alloys, CoFe and CoFe₃, were determined between 1073 and 1280 K in 1 atm. of oxygen. The oxidation of cobalt and CoFe follows a parabolic law, while the oxidation of CoFe₃ is better described by a direct logarithmic law. The oxidation rates for the cobalt—iron alloys alloys are lower than those expected from combining oxidation kinetics of pure iron and pure cobalt, thus suggesting a significant cobalt enrichment occurs at the oxide surface. This cobalt enrichment is observed using energy dispersive analyses. The logarithmic kinetics of CoFe₃ during oxidation is discussed, and a model is proposed to explain this behavior.     

Anisotropy of the normal state properties of the superconducting Co1−x Ni x Zr2 system

Anisotropic behavior of the normal state thermoelectric power, electrical resistivity, and magnetic susceptibility is reported for the superconducting Co_1–x Ni _x Zr₂ system.This research was supported by the U.S. Department of Energy under Contract Number EY-76-S-03-0034-PA227-3 (ZH, WAF, MBM) and by the National Science Foundation under Grant Number NSF/DMR77-08469 (ZF, DCJ).Deceased.     

Anomalous pressure dependences of the superconducting transition temperature of dilute alloys of LaSn3 containing light rare earth impurities

The initial depressions of the superconducting transition temperature T _c of LaSn₃ by rare earth (RE) impurities are known to be anomalous. In an attempt to clarify this behavior, we have measured the pressure dependence of the T _c of (LaRE)Sn₃ alloys (RE = Y, Ce, Pr, Nd, Sm, Eu, Gd, and Lu) to pressures up to 25 kbar. The magnitude of the pressure dependence of the T _c of (LaRE)Sn₃ alloys containing RE impurities with partially filled 4f electron shells decreases monotonically with increasing RE atomic number. A general discussion of existing zero- and high-pressure data for various physical properties of (LaRE)Sn₃ alloys demonstrates that the association of large pressure dependences of T _c with the occurrence of unstable impurity 4f shells (the Kondo effect) should be made with caution. The experimental high-pressure results are analyzed in terms of appropriate theoretical models for magnetic and nonmagnetic localized impurity states in superconductors.Supported by the US DOE Contract E(04-3)-34PA227.National Science Foundation Postdoctoral Fellow.     

Superconducting and normal state properties of Li1+x Ti2−x O4 spinel compounds. II. Low-temperature heat capacity

Heat capacity data are reported which confirm as a bulk effect the previously reported superconductivity in LiTi ₂ O ₄ . These data also establish LiTi₂O₄ as a weak couplingd-band superconductor with superconducting state properties well described by the Bardeen—Cooper—Schrieffer theory of superconductivity. The properties of LiTi ₂ O ₄ are compared with those of other superconducting spinel compounds, and the composition dependence ofT _c for Li _1+x Ti _2–x O ₄ is discussed. The disappearance of superconductivity forx0.1 was found to be correlated with a rapid decrease in the normal-state linear heat capacity coefficient.Research sponsored by the U.S. Energy Research and Development Administration under Contract No. ERDA E(04-3)-34 PA227.Research sponsored by the Air Force Office of Scientific Research, Air Force Systems Command, USAF, under AFOSR Contract Number AFOSR/F-44620-72-C-0017.