C. Tuijn

Interstitial impurity diffusion in metals; the apparent size effect

It is demonstrated that the abnormally fast impurity diffusion in Pb and α-Ti, which is interstitial-dominated, mainly depends on the solubility. With decreasing solubility, the fraction of interstitially dissolved impurities increases. This leads to a drastic increase of the diffusivity. In the case of small solubilities, the solubility depends on the atomic radius of the solute. This effect erroneously suggests a direct correlation between diffusivity and atomic size (size effect).

On the impurity diffusion in β-Ti

Abstract The impurity-diffusion data in β-Ti are reanalysed on the basis of the assumption that the vacancy-migration enthalpy H 1v M as well as the vacancy-formation enthalpy H 1v F depend on temperature. A simple linear temperature dependence in the form of H(T)=H(T 0 )+αk(T−T 0 ) is used. The results of the analysis show that the impurity-diffusion energy Q 2 increases linearly with α 2 , i.e. Q 2 (T m )≈Q 0 (T m )+8(α 2 −α 0 ) with Q in kJ/mol. Q 0 and α 0 describe the self-diffusion.

Application of the modified electrostatic model to the impurity diffusion in cobalt

The modified electrostatic model (Neumann and Tolle 1995) is applied to the impurity diffusion in nickel.Z0 = 0.4 is used for the effective charge of the nickel ion.

A modified thermodynamic model for the impurity diffusion via nearest- and next-nearest neighbour jumps in body-centred cubic metals of the groups V and VI

Abstract A modified thermodynamic model ( T m -model) for the impurity diffusion in group V and VI metals is developed, which takes into account nearest-(NN) and next-nearest (NNN) neighbour monovacancy jumps. The correlation factor f is separately calculated with the aid of Monte-Carlo simulation. The calculation of f is based on a nineteen-frequency model for mixed NN and NNN jumps. The comparison of calculated and experimental diffusion coefficients reveals good agreement for several systems. On the other hand, it becomes obvious that the T m -model is not applicable to the diffusion of group VIII metals in metals of the groups V and VI.

The correlation factor of impurity diffusion in body-centred cubic metals for mixed nearest- and next-nearest-neighbour monovacancy jumps

The correlation factor f2 of impurity diffusion in body-centred cubic metals is calculated assuming the competition of nearest- and next-nearest-neighbour monovacancy jumps. A four-frequency model in which only the impurity jump frequencies differ from those of the host atoms is considered. f2 is calculated as a function of temperature for different impurity migration energies and impurity masses. A comparison of f2 with experimental data shows qualitative agreement with the temperature function of the isotope effect for chromium diffusion in tungsten, thus supporting the hypothesis of high-temperature contributions of next-nearest-neighbour vacancy jumps in group V and VI metals.

On the diffusion of scandium and hafnium in tungsten

The modified thermodynamic model of impurity diffusion in BCC metals, which is based on the assumption that monovacancy jumps to nearest and next-nearest neighbour positions are responsible for the transport, is applied to the diffusion of Sc and Hf in tungsten. The agreement with experimental data reveals that the applicability of the model is not restricted to impurities of the groups V to VII of the periodic system.

Self-Diffusion and Impurity Diffusion in Group V Metals

Publisher Summary The chapter discusses the self-diffusion and impurity diffusion in group V metals—namely, vanadium (V), niobium (Nb), tantalum (Ta), and antimony (Sb). In a study described in the chapter, oxygen impurities enhance the diffusivity at lower temperatures in vanadium. This effect is not observed in niobium. Legoux and Merini have studied the diffusion of actinides in tantalum. The α -emitting actinides are generated by ion bombardment of heavy elements and implanted into a Ta foil. Diffusion of the almost insoluble alkaline metals is studied in single as well as polycrystals of vanadium (Cs), niobium (Na, K, Cs) and tantalum (Cs) at temperatures lower than 0.7 T m . In bismuth (Bi) only self-diffusion of 210 Bi in single crystals is studied. Anomalous penetration plots, however, do not permit the determination of credible diffusion coefficients. The chapter presents several tables and diagrams, one among them is a table on lattice structure, lattice constant, and melting temperature of the mentioned group V metals.

Application of the thermodynamic model to the diffusion of substitutionally dissolved impurities in lead

Abstract The thermodynamic model ( T m -model) is applied to substitutionally dissolved impurities in lead. For Tl, Sn, Na, Cs and with some restrictions also for Hg, good agreement is found between calculated and experimental diffusion coefficients. Although Hg and Cd exclusively diffuse via vacancies, the diffusion behaviour of Cd cannot be explained in terms of the T m -model.