A free dendritic growth model accommodating curved phase boundaries and high peclet number conditions

A steady-state free dendrite growth model accommodating nonlocal equilibrium tip conditions and curved liquidus and solidus has been developed. The developed model assumes a dendrite tip of a paraboloid of revolution and is applicable to dendrite growth in dilute binary alloys for all values of P _c , and reduces to the BCT model for linear liquidus and solidus. The marginal stability criterion of Trivedi and Kurz is shown to apply even in the presence of kinetic undercooling and curved phase boundaries when used with an appropriate concentration-dependent liquidus slope. The model is applied to Sn-Pb alloys to predict the tip velocity, tip radius, solute trapping, and four components of undercooling in the quasi-solutal, solutal-to-thermal transition and quasi-thermal regions.     

Novel UV absorbers prepared from 2,4-dihydroxybenzophenone and hexachlorocyclotriphosphazene

The UV-stabilizing ability and thermal loss from the polystyrene film of novel UV absorbers, 2-[(3-hydroxy-4-benzoyl) phenoxy] pentachlorocyclotriphosphazene (HBPC) and hexakis[ (2-hydroxy-4-benzoyl) phenoxy] cyclotriphosphazene (HBPP), were investigated. The UV-stabilizing ability of HBPC estimated by the formation of carbonyl groups in polystyrene was comparable to that of 2,4-dihydroxybenzophenone (DHB), suggesting that the phosphazene moiety does not affect the efficiency of the stabilizing ability of DHB units. No significant difference of efficiency per stabilizing units between HBPC and HBPP was observed. HBPC and HBPP are noteworthy for their low thermal losses from the polystyrene film, i.e., the thermal loss of HBPP was completely suppressed and the diffusion coefficient of HBPC at 160°C was two orders of magnitude smaller than that of DHB. The thermogravimetric analysis and differential scanning calorimetry measurement showed that HBPC and HBPP are nonvolatile and stable up to 230 and 300°C, respectively. © 1993 John Wiley & Sons, Inc.     

Morphology and preferred orientation of Y2O3 film prepared by high-speed laser CVD

Yttria (Y₂O₃) films were prepared at high deposition rates of up to 83 nm/s (300 μm/h) by laser chemical vapor deposition (LCVD) using an Y(dpm)₃ precursor. The effects of deposition conditions, mainly total gas pressure and laser power, on morphology, deposition rate and preferred orientation were studied. Plasma was produced around the substrate over a critical laser power resulting in significant increases in deposition temperature and deposition rate. The high deposition rate (300 μm/h) by LCVD was about 100 to 1000 times as high as those by conventional CVD. The morphology of Y₂O₃ films changed from faceted and columnar structures with high (400) orientation to a columnar structure with high (440) orientation, and finally to a cone-like structure with moderate (440) orientation with increasing total gas pressure (P_tot).     

Optical Properties of Dysprosium-Doped Low-Phonon-Energy Glasses for a Potential 1.3 μm Optical Amplifier

Dysprosium-doped glasses were prepared in the system of gallium-based sulfide, tellurite, zirconium-baed and indium-based fluorides and their optical properties were studied. From the absorption cross sections of five f-f bands, three Judd-Ofelt parameters, ω _t ( t = 2, 4, 6), of Dy³⁺ ion were determined. The compositional variaton of the ω₂value showed the order sulfide > tellurite > fluorozirconate > fluoroindate, whereas the ω₆ value showed the opposite tendency. Compositional variaton of the fluorescence intensity ratio of the (⁴F_9/2⁶H_13/2)/(⁴F_9/2)→⁶H_15/2) is explained by the ratio of ω₂/ω₆ of doped Dy³⁺. The emission probabilities A and the branching ratio β from ⁶H_9/2 and ⁶F_11/2 levels, which are the doublet initial level of the 1.3 μm luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of ω₂ against the glass composition. In the sulfide glass, A was 2.6 × 10³S^-1 and β was 93%, both the highest in all of the glasses investigated. By 1.06 μm pumping of a Nd: YAG laser, the sulfide glass showed strong 1.3 μm emission and the lifetime was 25 μs, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr³⁺:¹G₄ level in ZBLAN glass with β= 60%.     

Mechanism of superconductivity in the polyhedral-network compound Ba8Si46

The silicon clathrates--materials composed of metal-doped Si(20) dodecahedra--were identified as the first superconductors based on pure silicon networks. The mechanism of superconductivity in these materials can be obtained by studying their phonon modes, as modified by isotope substitution, and specific-heat measurements. Here, we present experimental studies that provide strong evidence that superconductivity in Ba(8)Si(46) is explained in the framework of phonon-mediated Bardeen-Cooper-Schriefer theory. Analyses using the McMillan approximation of the Eliashberg equation indicate that the superconducting mechanism is in the medium coupling regime, but at the high-end limit. The large density of states at the Fermi level, which arises from hybridization of the Si(20) cluster and Ba orbitals, is responsible for the unexpectedly high superconducting temperature. The temperature evolution of the specific heat unambiguously shows that this is an s-wave symmetry superconductor.     

Novel fabrication of nano-pattern with optical function by selective doping of dye vapor into novolac resin

We report selective doping of vapor of yellow dye, ferrocenedimethanol into exposed (UV-irradiated) areas of novolac resin films. When vapor of the dye was contacted with micro-patterned resin films containing both exposed and unexposed areas, the dye was doped only into the exposed areas, resulting in fabrication of micro-pattern containing the dye. On the contrary, ferrocene and other ferrocene derivatives were doped both exposed and unexposed areas of the resin. A contact angle measurement of aqueous drops on each dye indicated that the chemical affinity between hydroxyl groups of ferrocenedimethanol and exposed areas of the novolac resin will enhance selective doping of the dye into the exposed areas.     

Manufacturing process and properties of nuclear RPV shell ring forged from hollow ingot

A shell ring for an RPV of a 1300 MWe type PWR was forged from a 200-ton hollow ingot, and its very high quality regarding the internal qualities, tensile properties, fracture toughness, fatigue properties and underclad cracking properties were confirmed. The steel was refined by a basic oxygen furnace and degassed by a vacuum treatment furnace.The manufacturing process of a large hollow ingot has been established by an improved core structure which enabled segregation of chemical components to be decreased and a clean inner surface to be obtained.     

Application and development of synthetic polymer membranes. VI. Pervaporation of aqueous ethanol solution through quaternized poly[3-(N′,N′-dimethyl) aminopropylacrylamide-co-acrylonitrile] membranes

Membranes obtained from polymers, quaternized poly[3-(N′,N′-dimethyl) aminopropylacrylamide-co-acrylonitrile]s, showed selective separation of water from aqueous ethanol solution by pervaporation. The separation factor toward water reached over 15,000. Membrane performance showed a good correlation to membrane polarity. Differential scanning calorimetric melting endotherms of the water-swollen membranes were studied to clarify the state of water in the membranes. The results suggested that there are two states of water in the membrane: bound and free. The higher the fraction of bound water in the membrane, clearly, the more preferentially was water permeated.