Smaller Atomic Radius Research Articles

A simple interpolation formula for the Debye temperatures of disordered alloys

A simple formula is derived which expresses the Debye temperature of a disordered multicomponent alloy with small atomic radius disparity in terms of the Debye temperatures of the pure components, the mole fractions of the components, and a set of undetermined parameters, each of which can be found from the Debye temperature for one composition of each possible binary alloy made from the components. The formula is an improvement on a similar formula for the binary case due to Mitra and Chattopadhyay because the physical significance of the undetermined parameters is more readily apparent. The influence of short-range order in the binary case is considered. Application is made to the Ag-Au-Pd, Cr-Fe, and Cu-Ni systems in order to test the formula.

Kristallstruktur von Pt 3Ga(r) und einigen phasen der mischung PtAl

The structure of Pt 3Ga(r) is a tetragonal variant of the Cu 3Au structure, which has a displacive superstructure stabilized by the small atomic core radius of the minority component. Pt 3Al(r) is isotypic or at least closely related to Pt 3Ga(r). The new phases Pt 2Al(h) (Ni 2Si type) and Pt 2Al(r) (Pt 2Ga(r) type) are reported. Pt 2Al 3 crystallizes in the Ni 2Al 3 type of structure. The results are-interpreted by means of the two-correlations model.

Mo中のFeの不純物拡散

The residual activity technique was employed to determine the impurity diffusion coefficients of Fe59 in Mo in the temperature range of 1000 to 1350°C. The diffusion coefficient at 1350°C was 1.2×10−12 cm2/sec, which was larger than the value for the impurity diffusion coefficient of Co in Mo obtained by Peart et al., but smaller than any value for the impurity diffusion coefficient of Fe in refractory metals as Nb, Ta and W at the corresponding temperature. It was found that the temperature dependence of Fe59 diffusivity in Mo showed the Arrhenius relationship, DFe→Mo=(0.15+0.09−0.06)exp(−82.7±1.9⁄RT) cm2/sec, and no anomaly as in the impurity diffusion of Fe in β-Ti was observed. The activation energy for the diffusion of Fe in Mo was found to be smaller than that for the self-diffusion in Mo by about 10 kcal/mol. This trend holds in case of the impurity diffusion of Fe in the refractory metals such as Nb, Ta and W. The size effect appears to be important for the impurity diffusion of Fe in those metals, and the above trend may be tentatively explained by the small atomic radius of Fe with respect to those of such other elements. Using Swalin’s model, the activation energy for the impurity diffusion of Fe in Mo was calculated to be 84.4 kcal/mol, which was in good agreement with the experimental value. The empirical equation, lnD0=0.12Q−11.6, was obtained by the data on the self-diffusion of Mo, Nb, Ta and W the impurity diffusion of Fe and the other elements in these metals.

The influence of additives on the formation of periodic precipitation (Liesegang bands) in the Ag-Cd system

Extensive regions of Liesegang bands, or periodic precipitation, are observed in composite materials prepared by the internal oxidation of Ag-9 Cd alloys containing small amounts of certain metallic elements: Al, Be, Mg, Sc, and Y. The elements which induce this form of distribution of oxide particles possess the following characteristics: relatively small atomic radius (less than 1.80A), high oxidation potential (higher than 1.66 v), and some solid solubility in silver at 800°C. In this solid-state system the constancy of the spacing coefficient, the ratio of distances from the surface of consecutive bands, is generally satisfied. The spacing coefficient is found to be dependent on a) the specific additive, b) the concentration of the additive, c) the concentration of the oxygen, and in some case d) the crystal orientation.

DISPERSION, MECHANICAL COMPOSITION, AND FRACTIONATION OF WEST INDIAN VOLCANIC YELLOW EARTH SOILS (ANDEPTS)

SummaryMethods of dispersion used in Japan and New Zealand for soils formed on recent volcanic ash (Andepts) which involved adjusting the pH of organic matterfree soil suspensions to 4 or 10·5 were not effective on similar soils in the Caribbean. Partial dispersion was obtained by adjusting the pH to between 2 and 3 but lower (down to pH 1) and higher (up to pH 11·1) pH values were ineffective. Substantial amounts of Al dissolved at pH 1–3 probably as a result of some disintegration of the allophanoid minerals. Zirconium nitrate solutions were very efficient in causing dispersion, a concentration of 12 me Zr being necessary for complete dispersion of 20 g samples of soil. Excess Zr did not adversely affect dispersion but resulted in depression of pH of the suspensions. The high ionic charge, small atomic radius, and low ionization potential of Zr apparently resulted in saturation of the cation exchange capacity and some isomorphous substitution of Al leading to a net positive charge of the clay and an increase in anion exchange capacity. This was considered to be responsible for dispersion.

High density expansion for the Thomas-Fermi-Dirac function

An expansion is derived for the T.F.D. function at high densities (small atomic radii). Corresponding expansions are derived for the pressure and energy. The latter is compared with the somewhat similar Gell-Mann-Brueckner series for the correlation energy of a free electron gas moving in a background of positive charge.

Thermodynamics of interstital solid solutions

On the assumption that within the bounds of one sublattice the interstitial atoms and vacancies are arranged in a disordered manner, while the larger atoms are in complete order, we have compiled an equation for the entropy of formation of an interstitial solid solution with two interstitial sublattices. Equations have been compiled for the free energy of formation and activities of the components and they contain a small number of constants. As a first approximation the activity of a component possessing a large atomic radius is only a function of the crystal structure and composition. The homogeneity of boundaries of isostructural interstitial solid solutions formed with the participation of the same components with a large atomic radius are close to one another, provided the phases in equilibrium with them are also isostructural. A method of using the phase diagram to find the constants in the free energy and activity equations is demonstrated. Briefly considered are the energy and formation entropy of two types of ternary solid solutions (depending on whether two similar components have a large or small atomic radius).

Scattering of Electrons by Carbon Films

Intensity distribution of electrons scattered by carbon films was measured by the photographic method using a sector camera. The absolute intensity was obtained by the use of an intensity scale. The angular range of the measurement was 1.0×10 -2 ∼1.2×10 -1 rad., the thickness of films 350∼4,400A and the accelerating voltage 47 kv. Results of the measurement were in fair agreement with the theory of Lenz (Z. Naturforschg. 9 a (1954), 185). For the detailed agreement, however, we must take a smaller atomic radius than that of Lenz and we must take into account the inter-atomic interference effect.