Volume Self-diffusion Coefficients Research Articles

A Study of the Behavior of Cobalt in Carbonylation of Copper-Nickel Metallurgical Half-Products at Medium Pressure of the Reaction Gas

Dependences of the cobalt recovery into the carbonyl gas phase on the content of sulfur and carbon in sulfidized copper-nickel metallurgical half-products subjected to carbonylation were studied at a medium pressure of the reaction gas (70 gage atm). The behavior of cobalt was examined by means of metallographic analysis of the residue formed in carbonylation. A mechanism of solid-phase interaction of cobalt with copper sulfide and a method for calculation of the volume self-diffusion coefficient of cobalt in the crystal lattice of metallic copper deformed after removal of nickel were suggested.

Microstructure and Texture Development during Recrystallization of Rolled Molybdenum Sheets

Recrystallization is an important tool to adjust the grain size and texture of polycrystalline materials in order to optimize their properties. In the present work recrystallization and the related changes of texture have been studied on rolled molybdenum sheets as a function of temperature and time. The microstructure was investigated by orientation contrast in a scanning electron microscope. The kinetics of recrystallization displayed in a JMAK plot yields Avrami coefficients decreasing with temperature from 2.5 to 1.1. The activation energy amounts to 5 eV, which agrees well with the volume self-diffusion coefficient. The textures of the sheet surface and central layer were measured by X-ray diffraction. The rolling texture in the centre of the sheets is characterized by a strong a-fibre with the rotated cube component {100}<110> dominating. Besides that, there exists a weak g-fibre. In contrast, the surface layer is characterized by a weak cube component. During recrystallization changes in texture are insignificant. With long annealing times all texture components tend to degrade. Conclusions regarding the deep-drawability are drawn.

Diffusion of Cr and Fe in a High-Purity Fe-50 mass%Cr-8 mass%W Alloy

Volume and grain boundary diffusivities of 51 Cr and 59 Fe in a high purity Fe-50 mass%Cr-8 mass%W (Fe-50Cr-8W) alloy have been determined in the temperature range between 1023 and 1373 K with the sputter-microsectioning technique. The volume diffusion coefficients of Cr and Fe in the Fe-50Cr-8W alloy are smaller than those in a high-purity Fe-50 mass%Cr (Fe-50Cr) alloy. Linear Arrhenius lines for the volume self-diffusion coefficients of both tracers have been observed in the temperature range examined. The activation energies for the volume diffusion of both components in the Fe-50Cr-8W alloy are somewhat smaller than those in the Fe-50Cr alloy. On the other hand, the grain boundary diffusivities of Cr and Fe in the Fe-50Cr-8W alloy at 1123 K are about two orders of magnitude smaller than those in the Fe-50Cr alloy.

Volume and Grain-Boundary Self-Diffusion in a High-Purity Fe-50 mass% Cr Alloy

Volume and grain-boundary self-diffusion coefficients of 51Cr and 59Fe in a high-purity Fe–49.7 mass% Cr alloy containing 13 mass ppm carbon and 6 mass ppm nitrogen have been determined in the temperature range between 923 and 1453 K by use of the sputter-microsectioning technique. Linear Arrhenius lines for volume self-diffusion coefficients of both tracers have been observed across the α–σ phase-transformation temperature 1103 K, which is consistent with the suppression of the formation of the σ-phase by purification. The Arrhenius equations can be expressed by DFe = 1.2 × 10—4 exp(—256 kJ mol—1/RT) m2 s—1 and DCr = 1.3 × 10—4 exp(—259 kJ mol—1/RT) m2 s—1. Downward curved Arrhenius lines for the grain boundary diffusivity aδDgb (s segregation factor, δ width of grain boundary, and Dgb grain boundary diffusion coefficient) of both tracers have been observed. This is attributed to the formation of very thin layer of the (Cr, Fe)23C6 phase at the grain boundary near the surface of the specimens.

Dynamics of water and oil at the solid–liquid interface in macroporous media and reservoir rocks

Nuclear magnetic relaxation dispersion experiments at different temperatures, using the magnetic field-cycling method, are reported. These experiments allow the obtaining of original information about water or oil molecular dynamics at solid–liquid interface in porous media, such as grain packing or reservoir rocks. These results on molecular dynamics at the pore surface are of real interest for oil-recovery. The water surface diffusion coefficients are compared to the volume self-diffusion coefficients of water in pores, measured by PGSE method, the latter values being more than an order of magnitude higher than the surface ones. Nous avons obtenu des informations originales sur la dynamique de l’eau et de l’huile aux interfaces solide–liquide de milieux poreux plus ou moins complexes, comme les empilements granulaires et les roches réservoirs. Ces informations proviennent d’expériences de relaxation magnétique nucléaire du proton en champ magnétique cyclé à différentes températures. Ces résultats sur la dynamique des molécules à la surface des pores présentent un réel intérêt dans le domaine de la récupération du pétrole. Des mesures de diffusion par la méthode des gradients de champ pulsés permettent une comparaison entre les coefficients de diffusion en surface et en volume, ces derniers étant de plus d’un ordre de grandeur supérieurs à ceux en surface.

Surface and Volume Diffusion of Water and Oil in Porous Media by Field Cycling Nuclear Relaxation and Pgse NMR

AbstractThe microdynamics of water and oil in macroporous media with SiO2 or CaCO3 surfaces has been probed at various temperatures by magnetic field-cycling measurements of the spin-lattice relaxation rates. These measurements and an original theory of surface diffusion allowed us to obtain surface dynamical parameters, such as a coefficient of surface affinity of the liquid molecules and the surface diffusion coefficient. The water surface diffusion coefficients are compared to the volume self-diffusion coefficients of water in pores, measured by PGSE method, the latter values being more than an order of magnitude higher than the surface ones. Complementary information on the nature of the solid-liquid interface was given by NMR chemical shift experiments at high magnetic field.

The effect of the chemically inert fission products on the chemistry of irradiated UO 2

It is widely assumed that the fission gases and the volatile fission products play little or no role in influencing the chemical state of irradiated UO 2 + x . We show this to be incorrect when even a small quantity of these fission products is retained within the fuel grains. Prior to intragranular release most of the gases and volatiles occupy neutral trivacancy sites in the host lattice. However, these complexes can bind oxygen to be converted into fission product atoms residing in cation vacancies or (cation + one anion) vacancy complexes, and this results in reduction of the oxide. Here we analyse this behaviour and its effect on the oxygen potential and cation volume self-diffusion coefficient.

Diffusion in FeNiCr alloys with an F.C.C. lattice

The volume self-diffusion coefficients of 51Cr and 59Fe in 16 FeNiCr alloys with an f.c.c. lattice were measured using the modified Gruzin method in the temperature ranges 1298–1548 K for iron and 1286–1536 K for chromium. The self-diffusion coefficients, pre-exponential factors and activation energies for iron and chromium are tabulated. The concentration dependence obtained cannot be expressed by a simple mathematical relation; it is of higher order with a local minimum near the composition Fe-55 wt.%Ni-20 wt.%Cr. A critical analysis of the results obtained as well as previous knowledge made it possible to find the following relation between the self-diffusion coefficients of components which are valid over the whole temperature and concentration ranges examined: D Ni ∗: D Fe ∗: D Cr ∗ = 1:1.2:2 From the thermodynamic activity measurements, values of the thermodynamic diffusion factors in the ternary FeNiCr system and further values of the interdiffusion coefficients in this system were calculated. In this way a complete description of the diffusion processes in the ternary system was obtained. A comparison of the calculated interdiffusion coefficients with the experimental values found by other researchers was made.

A constitutive equation for creep deformation of 1CrMoV ferrritic steel at 823–838 K

The creep behaviour of 1CrMoV steel in the tempered bainitic condition at 823–838 K from three separate studies was examined. It was found that two regions of deformation exist: in that at high stresses ( σ > 230 MPa) the stress exponent n is about 14 and the activation energy for creep is about 397 000 J mol −1; at low stresses ( σ < 230 MPa) the stress exponent n is about 4 and the activation energy is about 210 000 J mol −1. Using the concept of friction stress σ 0 a constitutive equation is derived which is in good agreement with the three sets of experimental data. The constitutive equation for creep deformation in 1CrMoV in the tempered bainitic condition at 823–838 K is given by ϵ ̇ = AD V Gb kT ρ−ρ 0 G 3.5 where D v is the volume self-diffusion coefficient for iron, G the shear modulus, b the Burgers vector, k Boltzman's constant, σ the applied stress, A a constant and ε the minimum creep rate. The application of friction stress to the life assessment of engineering components is discussed. It is concluded that it is a useful parameter in assessing the microstructural damage that takes place during long-term creep. However, before it can be of use in the life assessment of components, new techniques (experimental or theoretical) of determining friction stress at low applied stresses are required.

Sintering of iron wires

The sintering mechanisms of iron were investigated by measuring the growth of necks between wires of 1.5 × 10 −2 cm in diameter wound on a spool of iron and expressing as functions of sintering time and temperature. It was found that the sintering mechanisms of iron up to about 1050 and above 1250°C are different from each other. Below 1050°C the 7th and above 1250°C the 5th power relationships derived by Kuczynski which correspond to surface and volume diffusion mechanisms respectively, fitted the experimental results. The surface self-diffusion coefficients and the activation energies of α and γ irons obtained in this work were in satisfactory agreement with those obtained by the grain boundary groove and scratch methods by Blakely and Mykura. The volume self-diffusion coefficient and the activation energy of γ iron were also in agreement with published data obtained by the radioactive tracer method. These sintering mechanisms were confirmed by examining the scaling law suggested by Herring and comparing morphologically the necks formed by low and high temperature sintering.

Current-induced mass transport in aluminum

The motion of transverse scratches on the surface of 99.999 per cent aluminum specimens carrying current densities of about 10 4 A cm 2 was observed as a function of temperature from 460 to 640°C, for periods of several days. The observed motion of the marks was as large as 50 μ/day and always toward the cathode. The magnitude and direction of the motion is clear evidence for mass transport caused by momentum exchange with the electron current. The motion was proportional to the current density and the self-diffusion coefficient. A value of about 2.7 μΩ/% was indicated for the “specific resistivity” of the diffusing atom, and it appeared that this quantity decreased linearly with increasing temperature. Measurement of lateral changes of the specimens showed that the lateral strain was equal to the longitudinal strain for specimens of small cross-sections. For thicker specimens the lateral strain was less than the longitudinal strain, in agreement with a simplified theory. It is concluded that: I. The mass transport is independent of the shape of the specimens, and depends upon only the temperature and current density. II. The motion of the surface scratches is proportional to the mass transport within the volume of the specimens and hence dependent upon the volume self-diffusion coefficient.