Materials Literature
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SUMMARY In the preceding paper the effect of the primary beam scattering on contrast in high‐pressure SEM techniques such as moist‐environment ambient‐temperature SEM and environmental SEM was examined. Here, the effect of the scattering of the emissive components on the image formation and contrast in high‐pressure S…
The degradation of the pulsed surface flashover performance of 99.9% pure polycrystalline alumina in an insulator-bridged vacuum gap, due to the mechanical grinding and finishing of the insulator is reported. The flashover characteristics of three different surface finishes—as-fired (0.8 μm), a ground surface (0.25 μm…
We observe bond-selective fragmentation of the nitrous oxide molecule upon site-specific 1 s excitation at either the terminal or the central nitrogen atom. Our results can be interpreted as a chemical "memory effect" where the fragmentation process memorizes the inital site of energy deposition. We empty a new "Zero…
Abstract Ultrasonic emission was found to accompany spherulitic crystallization of polymers from the melt. The source of acoustic waves was identified as an abrupt negative pressure release in regions of melt occluded by spherulites (weak spots) in the course of crystallization. The buildup of a negative pressure in o…
Numerous synthetic biomaterials have been developed as vascular substitutes. In vitro, ex vivo and in vivo studies have demonstrated that in animals, selected materials, i.e., Dacron and ePTFE (expanded polytetrafluoroethylene) grafts, are successfully incorporated in both the large and the small caliber host arteries…
Ceria‐ and yttria‐doped tetragonal polycrystalline zirconia ceramics were ground at temperatures as high as 1100°C. X‐ray diffraction revealed that the intensity ratio I (002) / I (200) increased (to as high as ∼4.5) compared with that from the as‐sintered surfaces (∼0.55). The enhancement in I (002) / I (200) at temp…
To clarify the foreign object damage (FOD) resistance of ceramics, chipping fracture mode and flexural fracture mode were investigated using several types of Si 3 N 4 and Sic. The critical velocity which is the threshold impact velocity of the projectile for chipping fracture and flexural fracture was determined. The…
Abstract Single crystals of optical quality of L‐arginine HCl · H 2 O and L‐arginine HBr · H 2 O with dimensions up to 80 × 60 × 30 mm have been grown from aqueous solutions by controlled evaporation at about 310 K. The isotypic crystals exhibit a quite similar behaviour with respect to morphological, pyroelectric, di…
We present new evidence that two electron traps observed in polycrystalline zinc oxide can be associated with complex intrinsic defects. One deep level, E1, can be assigned to an oxygen vacancy. The second deep level, E2, could consist of a cluster-type defect associated with oxygen vacancies. The two traps were chara…
Abstract Dissolution kinetics of sepiolite from Eskisehir (Turkey) have been investigated at various temperatures and particle sizes using dilute hydrochloric and nitric acids. Dissolution reaction rate constants were calculated and apparent activation energies were dependent on acid concentration. For both acids, app…
Abstract Mass sorption/desorption and volume dilation/consolidation measurements are reported for tetramethyl and hexafluoro polycarbonate samples in the presence of carbon dioxide pressures up to 900 psia at 35°C. These results are combined with previous results for bisphenol‐A‐polycarbonate. The combined sorption an…
Alumina was joined to Ti‐6AI‐4V alloy by active brazing. High reactivity between the Cu‐40Ag‐5Ti braze alloy and these materials led to the formation of interfacial reaction products. These products were characterized by transmission electron microscopy and electron microprobe analysis. A continuous layer, identified…
Abstract Thermotropic liquid-crystalline polyethylenimines with an ammonium halide moiety and those low-mass model compounds exhibited enantiotropically smectic phases. They were homeotropically aligned with the formation of an ammonium bilayer. The homeotropic structure of the liquid-crystalline polyethylenimine rema…
Photocatalytic activity of TiO2 in the oxidation by oxygen of formic acid is considerably enhanced by the presence of dissolved copper ions. The role of oxygen transfer between the gas phase and the slurry is examined. The kinetic results obtained in the absence of mass transfer limitations lead to a mechanism based u…
SUMMARY The mechanisms of electron beam scattering are examined to evaluate its effect on contrast and resolution in high‐pressure scanning electron microscopy (SEM) techniques reported in the literature, such as moist‐environment ambient‐temperature SEM (MEATSEM) or environmental SEM (ESEM). The elastic and inelastic…
Diluted magnetic semiconductors (DMSs), i.e. semiconducting crystals whose lattice is made up in part of substitutional magnetic ions (e.g. Cd/sub 1-x/Mn/sub x/Te, Hg/sub 1-x/Fe/sub x/Se, Zn/sub 1-x/Co/sub x/S), are reviewed. The focus is on materials of the type A/sub 1-x//sup II/ Mn/sub x/B/sup VI/, which are the mo…
Abstract The quantum yields of the photochromic reaction between (E)- and (Z)-2-[1-(2,5-dimethyl-3-furyl)ethylidene]-3-isopropylidenesuccinic anhydride and the cyclized valence isomer were determined in various solvents and polymers. In both media the ring-opening quantum yield (ΦCE) depended on the dielectric constan…
A laser-driven picosecond time-resolved electron diffraction system operating in ultrahigh vacuum is described. A picosecond laser pulse is split into two beams. The first interacts with the sample under study. The second activates the cathode of an electron gun creating a collimated and focused electron pulse that is…
The crystallization of polyamide 6.12 was investigated by X-ray diffraction and infrared spectroscopy. Similar to polyamide 6.6, there exist a pseudohexagonal γ modification and a triclinic α modification. The characteristic IR absorption bands of each modification were identified and assigned. In the amorphous state,…
We present sample numerical solutions of the equation of motion that governs the dynamics of molecular orientation in ferroelectric liquid crystal cells with chevron layer structure. We show that the chevron structure significantly influences the director field, the chevron interface providing surface stabilization on…