Materials Literature
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Artificial layered structures that produce sharp diffraction of x rays are described. The structures were made by alternately evaporating 140 Pb and Mg layers onto a glass slide (d=27 Å). The diffracting efficiency of the layered structures is compared with other structures used in soft x-ray spectroscopy. The usefuln…
The melting temperature of linear polyethylene has been obtained as a function of the time and temperature of crystallization. Recrystallization was minimized by a special melting procedure. By interpreting the melting points as characteristic of a given lamellar thickness, it was found that the thickness of crystals…
The specular reflectance of aluminum films evaporated in ultra-high vacuum has been measured with precision in the 0.3- to 32-μ wavelength region. The measured reflectance of these films, which is good to ±0.1%, is significantly higher than that of films prepared under the usual high-vacuum conditions. The reflectance…
A study, by high‐temperature diffractometry, of the monoclinic‐tetragonal phase changes in pure ZrO 2 and HfO 2 disclosed that the hysteresis loops associated with the transformations have similar shapes which are typical of many martensitic phase changes, but that the widths of the loops differ greatly for the two ma…
Analytical equations of the types required to define ballistic perforation dynamics are developed. These equations concern both blunt and sharp-nosed fragments, perforating plates normally and at oblique impact angles. Residual velocities are defined in terms of magnitude and direction. Analytical models and confirmin…
The high-temperature thermal conductivity of a disordered semiconductor alloy is derived using the Klemens-Callaway theory. It is assumed that the reciprocal relaxation times depend on frequency $\ensuremath{\omega}$ as ${\ensuremath{\omega}}^{4}$ for strain and mass point defects and as ${\ensuremath{\omega}}^{2}$ fo…
A new method of computing the Coulomb self-energy of uniform axial figures is developed. The energy is expressed as a sum of slice-slice interactions plus the self-energy of each slice. Analytical formulas are derived for these energies and are presented in numerical tables. The method is tested numerically by compari…
The thermoelectric effect in single-crystal cuprous oxide, measured at temperatures of 500° to 1130°C and oxygen pressures P of 160 to 2×10—6 Torr, was found always to be positive, indicating that the material is a p-type semiconductor in these ranges of conditions. Plots of the thermoelectric power Q vs 1/T at differ…
The magnetic structures of tetragonal chromium-modified ${\mathrm{Mn}}_{2}$Sb have been determined by neutron-diffraction studies of single crystals. Compositions of ${\mathrm{Mn}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}\mathrm{Sb}$ for $x$ from 0.023 to 0.10 were examined. Three magnetic structures have been observed, de…
The curves of the thermal conductivity versus temperature of some insulating crystals (alkali halides) which are doped with certain impurity centers exhibit a distinct indentation. This suggests a relaxation time of some resonance nature, which is independent of the temperature for molecular impurity centers (KCl: KN$…
The emission excited in the association of atomic oxygen and nitrogen has been studied in a fast-flow low-pressure system by photoelectric and spectroscopic methods. The absolute rates of excitation of the products of these associative processes have been measured, and the effects of added quenching gases have been in…
The ratio rλ of radiogenic daughter to residual parent (with decay constant λ) was investigated for a continuous diffusion model for a diffusion coefficient that is an arbitrary function of time. A solution for simultaneous diffusion of both parent and daughter is given in closed form. A theory is also developed that…
The Green's-function matrix method first developed by I. M. Lifshitz is applied to the problem of the scattering of phonons by a localized perturbation in the lattice. The scattering can be described by a $t$ matrix that is localized to the same extent as the perturbation and has similar symmetry properties. The $t$ m…
When hydrogen is dissolved in palladium, the α phase forms first; the β phase nucleates and grows in this. Because of the large volume change which accompanies the α-to-β transition, plastic deformation of the α phase occurs as it is stretched beyond its elastic limit. Hence, absorption is accompanied by growth of the…
In the ZrO2–CaO system cubic solid solutions of the fluorite-type structure are formed between 12 and 22 mole % CaO for specimens fired at 2000°C and subsequently quenched from 1400°C. The lattice parameter increased linearly from 5.125 to 5.144 Å with increasing CaO content. Results of x-ray diffraction intensity stu…
Phonon scattering by point defects was studied by measuring the thermal conductivity of KCl containing known amounts of Kl, NaCl, and Ca${\mathrm{Cl}}_{2}$ in solid solution. By also measuring the conductivity in crystals in which the impurities were allowed to coagulate, it was possible to distinguish between the eff…
The spectra of eight crystals containing trivalent chromium have been measured, and the energy levels fitted to a four-parameter crystal-field theory. The values of the parameters derived from the spectra are discussed, and some mechanisms responsible for absorption intensities are evaluated.
Abstract Thermal decomposition of the hydrated oxalates of the above rare earth metals was carried out on a Stanton thermobalance. The oxalates after precipitation were dried at 110° C for six hours and then used for the decomposition studies. No indications of the formation of stable lower hydrates or of intermediate…
In order to understand some x-ray excited emission bands in pure alkali halides, crystals were doped with the corresponding copper halides. It has been found that a band, which is also often present in "pure" or thermally treated alkali halides, is due to a Cu center. The excitation spectrum of the Cu impurity at room…
Corrosion hydrogen weight gains were studied for four zirconium base binary systems: Zr-Fe, Zr-Cr, Zr-V and Zr-Sb. Data on twenty compositions for exposures of up to 3000 hours in water at 360 C and in steam at 400 C and 482 C showed three alloys exhibiting less hydrogen weight gain than by Zircaloy-2. The various int…