Materials Literature
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Open-circuit dark surface-potential decay characteristics have been measured in positively corona-charged films of solution-cast low-density polyethylene. For initial fields of about 5×105 V/cm, the surface potential V (t) decays linearly for a period of time, after which it is curvilinear. As a result, the time deriv…
Abstract Pit nucleation and repassivation on iron and nickel has been examined by potentiostatic transient measurements. Very short times for the nucleation of corrosion pits of some ms to some 100 ms for prepassivated specimens have been observed. Addition of picrate to the electrolyte can stop pit nucleation for wel…
A method is discussed for measuring the separate spatial distributions of fixed charge and permanent polarization in a uniform insulator. Changes in the potential difference across the insulator are measured when a known nonuniform time-dependent temperature perturbation is established through the sample thickness. Th…
The application of a magnetic field parallel to a ferromagnetic film deposited on one side of a cantilevered substrate causes a small deflection of the free end. This deflection can be measured and the magnetostriction determined since the magnetostriction is proportional to the deflection. An instrument has been devi…
This article surveys theoretical and experimental work on piezo- and pyroelectricity of polymers in the 1970's with special emphasis on the origins of these properties. The origins are classified into three types: (A) internal strain (§2), (B) strain- and temperature-dependences of spontaneous polarization (§3), and (…
If copolymerizations are carried to high conversions, the determination of copolymerization parameters involves significant computational difficulties because the exact integrated form of the copolymerization equation has to be applied. A simple method has been developed to transform experimental data, even at high co…
A statistical-mechanical theory of the elastic constants of a liquid crystal based on the Onsager expansion is reexamined, with emphasis on the terms linear in the gradients of the director. This gives a microscopic theory of the piezoelectric effect in nematic liquid crystals, and of the spontaneous twisting of a cho…
Computational models of dynamic ductile and brittle fracture are developed for wave propagation in one- and two-dimensional geometries. The model features have been taken mainly from detailed observations of samples partially fractured during impacts, but the functional forms are consistent with theoretical results wh…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBlock Copolymer Theory. 4. Narrow Interphase ApproximationEugene Helfand and Z. R. WassermanCite this: Macromolecules 1976, 9, 6, 879–888Publication Date (Print):November 1, 1976Publication History Published online1 May 2002Published inissue 1 November 1976https://pubs.acs.o…
A new calculation following traditional methods is proposed for deducing optical constants and thickness from the fringe pattern of the transmission spectrum of a thin transparent dielectric film surrounded by non-absorbing media. The particular interest of this method, apart from its easiness, is that it makes a dire…
Raman spectra have been obtained on $2H\ensuremath{-}\mathrm{Ta}{\mathrm{Se}}_{2}$ at room temperature and in the commensurate charge-density-wave, superlattice state. At low temperatures six new low frequency modes are seen having symmetries consistent only with a symmetric, three-charge-density wave. A microscopic m…
The second-order Raman scattering and the temperature dependence of the ferroelectric soft mode in $\mathrm{AB}{\mathrm{O}}_{3}$ perovskites are explained quantitatively in terms of a nonlinear shell model by assuming an anisotropy in the oxygen polarizability. This model yields a new explanation for the origin of fer…
The resistivity and the temperature coefficient of resistivity of cobalt films 280-1600 AA thick were studied at temperatures between 30 and 150 degrees C. It was observed that coherent films were obtained by depositing the cobalt films slowly onto a heated (150 degrees C) substrate. The experimental observations coul…
Properties of the nematic-isotropic phase transition in surface-aligned nematic films are calculated using the Landau-de Gennes theory. It is shown that there is a critical thickness ${D}^{c}$ of the film below which the transition from the nematic phase to the isotropic phase becomes continuous. At the critical thick…
The crystallographic properties of the tetragonal spinel MgMn2O4, subjected to different thermal treatments, is studied by neutron diffraction method. At elevated temperatures there is a significant variation in the degree of inversion owing to the migration of Mg2+ ions from the tetrahedral to the octahedral sites. F…
Details are given of the change of the electrical transport properties as well as of the magnetic and thermodynamic properties at phase transition of monocrystalline V3O5. The phase transition above room temperature is investigated. V3O5 monocrystals are produced by chemical transport with TeCl4. The influences of the…
A method is developed to calculate the parameters of a pair potential function with three adjustable parameters. It uses crystalline state properties at any given temperature. As an example, parameters of the Morse potential are calculated for a number of metals using physical properties at room temperature. Elastic c…
The ratio n of cross-sections for inelastic and elastic scattering of 80 keV electrons is measured for thin solid films of the elements Be, C, Al, As, and Sn. The values obtained are in reasonable agreement with theoretical predictions of Lenz and Burge and Smith. Measurements of n are also made for diphenyl anthracen…
Phase anarysis oj boron in steel has been made to establish a practical method Jor the determination oj the content oj "effective boron", i.e., boron which is effective in improving the hardmability oj steel, yielding the Jollowing results:(1) Electrorytic dissolution and iodine-methanol dissolution are reliable and r…
It was found that sintered alloys having a composition of approximately z=8 in Sm(Co0.85Fe0.05Cu0.10)z exhibit a high coercive force on the order of 10 kOe, for 5–10-μm average grain size. Magnetization and demagnetization curves showed that the coercive force is controlled by a nucleation process. Attempts were made…