R.J. Farraro

Temperature dependence of the Young’s modulus and shear modulus of pure nickel, platinum, and molybdenum

A pulse-echo technique utilizing a wave guide operating at high temperatures has been used to measure the variation in the Young’s modulus and shear modulus of pure platinum, nickel, and molybdenum in the temperature range from 25 to 1000°. With the exception of Ni in the temperature range below the Curie point, linear behavior was found for all three metals. The significance of the linear relation between temperature and the elastic constants for Mo to the observed nonlinearity of the Arrhenius plot of the diffusivity of carbon in Mo is discussed.

The diffusivity of Hydrogen in palladium

Abstract The permeability time-lag method has been used to determine the diffusivity of hydrogen in palladium in the temperature range 496–946°C. Previous measurements had indicated a large positive deviation from Arrhenius behavior in the temperature range above 600°C. No such deviation was found in the present measurements, which are in good accord with previous determinations made at lower temperatures. The diffusivity in the temperature range 469–946°C can be represented by the equation D = D 0 exp (− Q RT ) m 2 /s where D0 = (2.83 ± 0.15) × 10−7 m2/s and Q = 21.7 ± 1.3 kJ/mole.

Thermodynamics of the iron-nitrogen system

Abstract The temperature variation of the equilibrium between N2 gas and N-Fe solid solutions has been measured. The results give the following values for the partial molar enthalpy and excess entropy of N-atoms in γ and α iron: γ: R u = −459.8 ± 29.1 kJ/mole , S xs u k = 6.59 ± 0.9 α: R u =−423.7 ± 20.1 kJ/mole. , S xs u k = 6.97 ± 1.1 The data for δ-iron show a marked deviation from Arrhenius behavior with respect to a high temperature extrapolation of the low-temperature b.c.c. data (α-iron). This deviation is discussed in terms of several models.

Elastic properties of dilute palladium-hydrogen solid solutions

Abstract A thin-line pulse-echo technique has been used to measure the variation of the Youngs modulus of super-pure palladium as a function of temperature and hydrogen concentration. The resulting measurements have been analyzed so as to yield approximate information relating to the change to be expected in the partial thermodynamic functions of the system due to the lattice relaxation at constant pressure.

Thermodynamic and kinetic properties of iron-based ternary solutions containing interstitial and substitutional solute atoms

Abstract A first-order statistical mechanical model for Fe-based ternary solutions containing a substitutional and an interstitial solute is discussed. The model is used to calculate the variation of the diffusivity of the interstitial species with the concentration of substitutional solute and the diffusivity of carbon in alloyed austenite is discussed. It has been shown that when there is virtually no misfit energy in the Fe-substitutional solute binary system, the energetics of solution formation are largely determined by electronegativity differences.

Diffusivity of oxygen and nitrogen in niobium

Abstract It has been shown that recent measurements of the diffusivity, D , of oxygen and nitrogen in niobium, using both mass flow and internal friction techniques, indicate that the Arrhenius plots of ln D vs. reciprocal temperature are not linear, and diffusion velocities become accelerated at high temperatures. The origin of this phenomenon is discussed.

The diffusion of heavy interstitial solute atoms in body-centered cubic metals

Abstract This paper discusses recent observations of the diffusivity of nitrogen, carbon and oxygen in a series of body-centered cubic metals in which positive deviations from Arrhenius behavior have been seen in some cases at high temperatures. Several models involving both single-stage and two-stage diffusion mechanisms are presented and discussed in terms of the individual systems and current high temperature measurements of the elastic properties o of the solvent metals.

Thermodynamics of molybdenum-nitrogen solid solutions

Abstract Recent measurements of the temperature and pressure variation of the equilibrium between N 2 -gas and N-Mo solid solutions extending up to 2700 K have been analyzed. It has been shown that the enthalpy of solution varies strongly with temperature above ~2100 K. This phenomenon has been attributed to the simultaneous occupation of both octahedral and tetrahedral sites in the metal lattice by nitrogen atoms. The relevance of this concept to the observation of non-linear Arrhenius plots for the diffusivity of the interstitial species in such systems is discussed.

Thermodynamics of nitrogen-molybdenum solid solutions

Abstract The equilibrium between N 2 gas at atmospheric pressure and molybdenum-nitrogen solid solutions has been measured in the temperature range 1618–1883 K. The solvent metal was in the form of single crystals of MARZ-grade Mo. Deviations in the thermodynamic behavior consistent with a dual site occupancy mechanism, suggested by previous data, were not found. The data have been discussed in terms of the effects of hydrostatic pressure on the metal lattice and the presence of trapping sites in the solvent lattice.

Thermodynamic properties of the ϵ-Cr2N phase

Abstract Experimentally determined pressure-temperature-composition data for the ϵ-Cr 2 N phase have been analyzed to yield the composition variation of the partial enthalpy and entropy of the N-atoms in the subnitride. The partial thermodynamic functions have been shown to be in accord with a simple statistical model based on first order mixing behavior.