Materials Literature
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Abstract Graphite as deposited by cracking hydrocarbons around 2000 °C shows marked preferred orientation with consequent anisotropy, but still contains numerous structural defects. Procedures have been investigated for removing these by recrystallization around 3000 °C under a shearing stress, resulting from applying…
Abstract Transition metal complexes with configurations d4, d5, d6 and d7 are of two types—high-spin and low-spin— depending on the strength of the ligand field. Ligand field theory predicts that truly octahedral complexes ML6 could exist in which both types are in thermal equilibrium at ordinary temperatures, but no…
A complete ab initio approximate Hartree-Fock calculation has been carried out on the ${\mathrm{Mn}}_{2}$ molecule at three internuclear distances, $R=4.5, 5.0, \mathrm{and} 5.5 {a}_{0}$. The theory of the Heisenberg exchange interaction, applied in an earlier paper to the nitrogen molecule at large $R$, is used to id…
Monte Carlo calculations are applied to the problem of "hot" electron motion in metals, and measured values of attenuation length, $L$, are related to values of the mean free paths for electron-electron scattering ${l}_{e}$, and electron-phonon scattering ${l}_{p}$. Calculations are done for both specular and diffuse…
The study presented here includes experimental data obtained from three $n$-type and two $p$-type single-crystalline samples of PbTe. Measurements of the Hall coefficient, thermoelectric power, and electrical conductivity have been made between 77 and 300\ifmmode^\circ\else\textdegree\fi{}K, and infrared reflectivity…
The infrared reflection and transmission spectra of CaTi${\mathrm{O}}_{3}$, SrTi${\mathrm{O}}_{3}$, and PbTi${\mathrm{O}}_{3}$ have been measured from 4000 to 30 ${\mathrm{cm}}^{\ensuremath{-}1}$ at room temperature. The reflection data have been analyzed by means of a Kramers-Kronig method, from which the frequencies…
The variations with temperature of the elastic moduli in single crystals of hcp Ti, Zr, and Hf have been experimentally determined from 4\ifmmode^\circ\else\textdegree\fi{}K up to 1155\ifmmode^\circ\else\textdegree\fi{}K, using an ultrasonic wave interference technique. The ${c}_{11}$, ${c}_{33}$, and ${c}_{44}$ diffe…
The approximation is made that the dividing surface between a liquid and its vapor phase is a monomolecular layer, in which a molecule has a free volume larger than for an interior molecule and a potential energy less than for the latter. By introducing the approximation into the significant structure theory of liquid…
The effect of configuration interaction on the validity of the usual method of expanding the crystal field potential in terms of spherical harmonics is examined using second-order perturbation theory. It is found that for a configuration of equivalent electrons lN most mechanisms of configuration interaction lead to a…
The release of hydrogen atoms by a platinum surface in contact with molecular hydrogen occurs if there is oxygen in the system. In particular, it is sufficient that the oxygen be adsorbed at the surface of the metal.
The shell of the freeswimming veliger larval stage of the common North American oyster Crassostrea virginica (Gmelin, 1791) is composed of aragonite. This composition contrasts with that of the adult shell, which is composed mainly of calcite, the rhombohedral allomorph of calcium carbonate, and minor amounts of arago…
Abstract Several features of the pyrolysis of acetylene in the temperature range 500 to 1000 °C suggest that the underlying mechanism is the same as that in operation at both lower and higher temperatures. Thus the rate of consumption of acetylene obeys a second-order kinetic law and is little affected by additions of…
The Overhauser shift of the electron spin resonance due to the natural nuclear polarization at liquidhelium temperatures has been used to measure the conduction-electron density at the nuclei in $n$-type InSb. The results are: ${|\ensuremath{\psi}({R}_{\mathrm{In}})|}^{2}=(9.35\ifmmode\pm\else\textpm\fi{}1)\ifmmode\ti…
The salient feature of the splittings of the crystalline levels of a rare-earth ion in the iron garnets is the difference of their anisotropy from that of the $g$ tensor for the Zeeman effect. This additional anisotropy arises from the dependence of the rare-earth-iron (RE-Fe) exchange interaction on the orbital state…
The anisotropy of the magnetic hyperfine interaction in ferromagnetic Zr${\mathrm{Fe}}_{2}$ has been demonstrated with the M\"ossbauer effect. It is suggested that such anisotropy is responsible for the failure to observe domain-wall enhanced NMR in similar materials. It may also account for the failure to detect the…
The rates of hydrogen penetration through single iron crystals in contact with an H2S-CO2-H2O environment were related to the specific crystallographic orientation of the crystals using a novel, highly reliable penetration cell. The rate of hydrogen penetration was shown to be a function of the lattice packing density…
In estimating the nucleation field of an infinite rectangular bar, Aharoni used a variational method to calculate a lower bound to the magnetostatic energy. He constrained the variable potential to a specified form inside an ellipse circumscribed about the rectangle. In the present article, the method is improved by i…
Polymorphic transitions in CasSiO 6 have been investigated by precise high‐temperature X‐ray diffractometer measurements and by differential thermal analyses. In addition to change caused by normal thermal expansion, three principal crystallographic transformations take place: α‐triclinic–β–triclinic (sluggish) in the…
Abstract The memory of irradiated polyethylene has been studied with emphasis on the magnitude of the restoration force exerted by the deformed polymer during the process of restoration to the nonstressed state and on the degree of completeness with which restoration occurs. The particular form of the memory effect st…
Abstract Measurement of butadiene absorption at constant volume, and of polymer formation, indicated that the rate of polymerization was first order in monomer concentration, up to 1.5 mole/l., and also in initial total catalyst concentration, for given molar ratio of alkyl to titanium ester. The overall activation en…