Materials Literature
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The preparation of 21,24-dioxacorroles by condensation of dipyrromethane-5,5′-dicarboxylic acids with 5,5′-diformyl-2,2′-bifuryl or bis-(5-formyl-2-furyl) sulphide is described. It is suggested that the latter reaction involves a non-aromatic meso-thia-macrocyclic intermediate which loses sulphur by a disrotatory cycl…
The values of mechanical quality factor Q m are determined for lead zirconate titanate ceramics containing various oxides as impurities in various amounts. Impurities are found to be classified into two groups with respect to the change of Q m values, viz. , (1) Q m decreases in the presence of impurities ( e. g. Nb 2…
The reduction of zinc (II) tetraphenylporphin (ZnTPP) in dimethylformamide (DMF) was investigated. The products of electron transfer and associated chemical reactions were studied by polarography, cyclic voltammetry, thin‐layer controlled potential coulometry and spectroscopy, and epr. Reduction proceeds initially as…
Abstract The surface tension of a polymer liquid is a property of considerable practical importance. Within the past decade the experimental difficulties in accurately measuring the surface tension of viscous polymer melts have been overcome, and a considerable body of data is now available. This review discusses the…
Description The Second Conference on Composite Materials: Testing and Design was held 20-22 April 1971 in Anaheim, Calif. Committee D30 on High Modulus Fibers and Their Composites of the American Society for Testing and Materials sponsored the conference, in conjunction with the American Institute of Mining, Metallurg…
N THE ferroelectric and piezoelectric applications of BaTiOa I and Pb(Zr,Ti)O,, dependence on time of many of their
The magnetic properties during tempering of Fe‐ 30∼50wt% Cr‐ 10 ∼30wt% Co alloys, which consist of bcc high‐temperature phase (α) obtained by quenching from 1300°C, have been measured. Alloys in a certain range of composition showed desirable permanent‐magnetic properties by a step‐tempering following a thermomagnetic…
Hexagonal NaLnF 4 : Yb 3 + , Er 3 + ( Ln : Y , Gd , La ) was found to be an efficient green‐emitting phosphor with infrared excitation. It was prepared by firing a mixture of Na 2 SiF 6 and coprecipitated Ln 1 − y − z Yb y Er z F 3 at 630°C in an argon atmosphere. The optimum firing condition of NaYF 4 : Yb 3 + , Er 3…
Abstract Fibers and solvent‐cast films of polyacrylonitrile have been investigated by x‐ray small‐angle and wide‐angle measurements and dynamic‐mechanical analysis. It has been found that the structure of this polymer is better described by a two‐phase model consisting of more and less ordered regions. By the aid of x…
The morphological properties as derived from wide- and small-angle x-ray scattering, IR dichroism, electron spin resonance, and electron microscopy, and the anisotropy of mechanical properties of the fiber structure can be well explained by the microfibrillar concept developed on the basis of a detailed study of plast…
The evolution of thought during the last 25 years on the mechanism of pitting corrosion of copper in supply waters is traced and the significance of early observations reconsldered m the light of recent knowledge. A simplified approach to the Membrane Cell Theory, the role of surface films in the initiation mechanism…
The crystal and molecular structure and the absolute configuration of the title compound have been determined from three-dimensional X-ray data collected by counter methods, and refined by least squares to R 0·034 for 1959 independent reflections. The crystals are in space-group R3, with unit-cell dimensions a= 15·96(…
Abstract
The initiation and growth of pits on iron and of crevices and pits on stainless steels in numerous electrolyte solutions, both under potentiostatic and under natural corrosion conditions, have been studied by scanning electron microscopy. The pit morphology on iron is controlled primarily by solution composition: in s…
A new mathematical model of hysteresis, based upon the previous work of Chun and Stromsmoe, is introduced. The model not only provides for hysteresis loops at frequencies down to dc but allows for extensive control over higher frequency behavior. Loop widening with increased frequency can be included, as well as loop…
To account for the observed diffraction pattern of a commercial specimen of oriented fibers of isotactic polypropylene in the a modification, the crystal structure is described as belonging to the space group P 21/c but having a certain disorder in the distribution of “up” and “down” chain direction. As a result of th…
The influence of the catalyst support on the oxidation of methane over palladium has been studied using a microcalorimetric bead reactor. The nature of the support had no detectable influence on the catalytic activity during a given experiment, but was found to affect the long-term stability of the catalyst.Investigat…
The effects, on the performance of all-dielectric interference filters, of errors in the turning value method of film-thickness monitoring, are studied theoretically by both an accurate and an approximate method. It is shown that, although the potential accuracy of the method in monitoring a single layer is very poor,…
A scanning reference electrode has been used to measure the number of active pits on 304 stainless steels in ferric chloride solution with time. The probability of a pit deactivating has been discussed in terms of the physical and chemical properties of solid oxide films over the pit which were originally on the steel…
A theory of the cooperative Jahn-Teller effect is developed for the purpose of discussing the spontaneous crystal distortions in mixed chromites, Cu 1- x Ni x Cr 2 O 4 and Fe 1- x Ni x Cr 2 O 4 . The static Jahn-Teller effect only is taken into account. The theory separates the self-energy of each ion having a degener…