Transition-metal compounds containing clusters of metal atoms
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Materials Literature
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Direct measurement of the variation of double-layer repulsion with distance
Soap films can be subjected to compressive stresses exceeding 1 atm while their thickness is measured optically in an apparatus which is described in detail. It permits forming the film within a ring of porous porcelain whose pores communicate to the outside, whereas the film is in an enclosure in which the air pressu…
Cholesteric Structure-1 Optical Properties
In 1889 Reinitzer,1 working with cholesteryl benzoate, discovered a state of matter that was later ter med cholesteric liquid crystals. It is doubtful whether the discovery of liquied crystals would have been made at that time if the optical properties of the cholesteric phase were less pronounced. Like other liquid c…
ESR Linewidths in Solution. II. Analysis of Spin—Rotational Relaxation Data
In Part I of this series the residual linewidths for vanadyl acetylacetonate in toluene were found to be proportional to (T/η), where η is the viscosity, and independent of applied field. Since the solutions are dilute, spin exchange is not important. The residual linewidth is attributed to a spin—rotational relaxatio…
Analysis of the α, β, and γ relaxations in polychlorotrifluoroethylene and polyethylene: Dielectric and mechanical properties
Abstract Theoretical models for the ac and γ e relaxation effects found in chain‐folded polymer crystals (single crystal mats and bulk) are presented and compared with the available dielectric and mechanical loss data for polyethylene and polychlorotrifluoroethylene. Details of morphology and crystal structure that ca…
SECTION 6: THERMAL EXPANSION
Thermal expansion is the change in shape and volume of a system due to a temperature change. For liquids, gases, and isotropic solids, thermal expansion is isotropic, involving only a change in volume and requiring, therefore, the measurement of a single parameter to uniquely specify the expansion. Crystalline solids…
Instabilité électronique et changement de phase cristalline des composés du type V3Si à basse température
Dans V3Si les atomes de vanadium sont disposés suivant des chaînes linéaires denses et on peut appliquer aux électrons d l'approximation des liaisons fortes à une dimension. On constate que l'énergie électronique ainsi calculée s'abaisse par déformation de la maille. Ceci peut constituer une explication, par un effet…
SECTION 5: X-RAY CRYSTALLOGRAPHIC DATA, DENSITIES, AND MOLAR VOLUMES OF MINERALS
X-ray crystallographic data are of particular importance to the mineralogist. Beyond the considerations of structural chemistry, they provide one of the most accurate methods for phase and/or compositional determination and for obtaining the molar volumes and densities of minerals (Table 5-2). Selected data for approx…
The thermal decomposition of sodium nitrate
The kinetics of the thermal decomposition of molten sodium nitrate have been studied as a function of temperature in the range 570–760°. The effect of replacing the air over the reactant by argon has been examined. From these measurements, it is concluded that atmospheric oxygen does not participate in the reaction an…
On the general solution of linear-elastic problems in isotropic and anisotropic Cosserat continua
The existence of couple stresses acting on the surfaces of elastic continua together with the usual force stresses had been object of numerous fundamental papers [ 1 , 7–16 ]. For describing the complete deformation a geometrically independent rotation vector had been introduced besides the displacement vector. In thi…
The thermal conductivity of pyrolytic graphite
The thermal conductivities of three specimens of well-oriented, annealed pyrolytic graphite have been measured over the temperature range 100–900°K. The conductivity parallel to the deposition plane is analysed in terms of mean free paths using the semi-continuum model of Komatsu and Nagamiya. An expression is derived…
The Modifications of Niobium Pentoxide
Abstract Niobium pentoxide crystallizes in numerous modifications. The present paper describes their mode of formation, structures, and thermal properties.
On the Critical Resolved Shear Stress of Solid Solutions Containing Coherent Precipitates
Abstract A quantitative estimate is made of the increase Δτ 0 of the critical resolved shear stress for the case of solid solutions containing spherical and coherent precipitates. The interaction between edge dislocations and the coherency strain fields is believed to be the strengthening mechanism. The calculation is…
Effect of High Pressure on the Lattice Parameters of Diamond, Graphite, and Hexagonal Boron Nitride
The effect of pressure to several hundred kilobars has been measured on the lattice parameters of diamond, graphite, and hexagonal boron nitride. The linear compressibility of diamond is independent of pressure. The a axis of graphite (characteristic distance in the plane) is considerably more compressible than diamon…
Simple theory of stress‐strain properties of filled polymers
Abstract By the use of simple models of filled plastics, approximate equations are derived for the elongation to break in the case of perfect adhesion between the phases and for the tensile strength in the case of no adhesion between the polymer and filler phases. By combining these equations with equations for the mo…
Phenomenological Theory of High Permittivity in Fine‐Grained Barium Titanate
The anomalously high permittivity in fine‐grained ceramic barium titanate is explained by the absence of 90° twinning within the grains, giving rise to internal stresses as the ceramic cools below the Curie temperature. Using the Devonshire phenomenological thermodynamic method and a simplified model, the stresses inv…
Environmental Factors Affecting the Critical Potential for Pitting in 18–8 Stainless Steel
The concept of a critical potential below which pitting of 18–8 and other passive alloys does not occur in aqueous Cl − media is affirmed. Increasing Cl − concentration shifts the critical potential to more active values. The potential is shifted to more noble values by presence of other anions, e.g. , ClO 4 − , SO 4…
Effects of eddy currents in transformer windings
The effects of eddy currents in transformer windings are considered, and a method is derived for calculating the variation of winding resistance and leakage inductance with frequency for transformers with single-layer, multilayer and sectionalised windings. The method consists in dividing the winding into portions, ca…
Mechanical Properties of Solid Polymers
Several aspects of the mechanical properties of polymers are discussed. These include linear and non-linear viscoelastic behaviour, anisotropy, rubber-like elasticity, breaking and cold drawing.
A complex plane analysis of α‐dispersions in some polymer systems
Abstract The α‐dispersion in many polymer systems is the process to be associated with the glass transition temperature where many physical properties undergo drastic changes. We have measured and analyzed the complex dielectric behavior of the α‐dispersions for five polymers [i.e., polycarbonate and polyisophthalate…