Nature of Aging in Ferroelectric Ceramics
N THE ferroelectric and piezoelectric applications of BaTiOa I and Pb(Zr,Ti)O,, dependence on time of many of their
Materials Literature
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New Ductile Permanent Magnet of Fe-Cr-Co System
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…
NaLnF[sub 4]:Yb[sup 3+],Er[sup 3+] (Ln:Y,Gd,La): Efficient Green-Emitting Infrared-Excited Phosphors
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…
Structural changes of drawn polyacrylonitrile during annealing
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…
Morphology and Properties of Crystalline Polymers with Fiber Structure
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…
Developments Leading to the Present Understanding of the Mechanism of Pitting Corrosion of Copper
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…
Crystal and molecular structure of tri-iodoheptakis(tri-p-fluorophenylphosphine)undecagold
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(…
Effect of annealing and temperature on the morphological structure of polymers
Abstract
On the Mechanism of Localized Corrosion of Iron and Stainless Steel
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 Generalized Hysteresis Model
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…
Crystal structure of isotactic polypropylene
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…
Role of the catalyst support in the oxidation of methane over palladium
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…
Turning Value Monitoring of Narrow-band All-dielectric Thin-film Optical Filters
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,…
Surface Preparation and Pit Propagation in Stainless Steels
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 –Crystal Distortions in Cu1-xNixCr2O4 and Fe1-xNixCr2O4–
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…
Kinetics of Iron Corrosion in Concentrated Acidic Chloride Solutions
The kinetics of active iron dissolution at 25°C has been studied in deaerated 1 N and 6 N chloride solutions for hydrogen ion concentrations of 0.1–6.0 N . For 1 N chloride solutions with , the dissolution reaction is described by anodic Tafel slope and electrochemical reaction order with respect to hydrogen ion activ…
Etch Channel Formation during Anodic Dissolution of N-Type Silicon in Aqueous Hydrofluoric Acid
Anodic dissolution of n + ‐, n‐, and n − ‐type silicon in 5% aqueous hydrofluoric acid at moderate current densities results in the formation of etch channels which propagate in crystal‐oriented directions in the monocrystal. Density and depth of the channels are a function of the applied voltage, the donor concentrat…
Metal–metal interactions in transition-metal complexes containing infinite chains of metal atoms
T. W. Thomas and A. E. Underhill, Chem. Soc. Rev., 1972, 1, 99 DOI: 10.1039/CS9720100099
On the schlieren texture in nematic and smectic liquid crystals
Observations on schlieren textures of nematic and smectic-C liquid crystals in thin layers are reported. The theory of schlieren textures is discussed and forces between singularities are considered. A singularity can be characterized by a positive or negative number which is proportional to the number of brushes it s…
Luminescence and Structural Properties of Thiogallate Phosphors Ce+3 and Eu+2-Activated Phosphors. Part I
Thiogallate compounds represented by the formula MGa 2 S 4 [ where M = Ca + 2 , Sr + 2 , Ba + 2 , Pb + 2 , Eu + 2 , ( Na + 1 La + 3 ) and ( Na + 1 Ce + 3 ) ] were prepared by solid‐state reaction. Single crystals of the alkaline earth derivatives were also obtained by vapor transport of the corresponding polycrystalli…