Development of high Tc (greater than 110K) Bi, Tl and Y-based materials as superconducting circuit elements

This report is presented in two parts. Part 1 deals primarily with Bi-based materials and a small amount of work on a Y-based composition while Part 2 covers work on Tl-based materials. In Part 1, a reliable and reproducible process for producing bulk bismuth-based superconductors has been developed. It is noted however, that a percentage of the tapecast material experiences curling and fracturing after a 30 hour sintering period and is thus in need of further examination. The Bi-Sr-Ca-Cu-O (BSCCO) material has been characterized by critical temperature data, X-ray diffraction data, and surface morphology. In the case of T sub c, it is not critical to anneal the material. It appears that the BSCCO material has the possibility of producing a better grounding strap than that of the 123 material. Attempts to reproduce near room temperature superconductors in the Y-Ba-Cu-O system were unsuccessful. In Part 2, several methods of processing the high temperature superconductor Tl2Ba2Ca2Cu3O10 were investigated; i.e., different precursor compositions were sintered at various sintering times and temperatures. The highest superconductig temperature was found to be 117.8K when fired at 900 C for three hours. Higher sintering temperatures produced a melted sample which was nonsuperconducting at liquid nitrogen temperature. Also, a preliminary study found Li2O substitutions for copper appeared to increase the transition temperature and create fluxing action upon sintering. It was suggested that lower sintering temperatures might be obtained with lithium additions to produce reliable Tl2Ba2Ca2Cu3O10 processing methods

Development and evaluation of superconducting circuit elements

An approach to the application of high Tc ceramic superconductors to practical circuit elements was developed and demonstrated. This method, known as the rigid-conductor process (RCP), involves the combination of a pre-formed, sintered, and tested superconductor material with an appropriate, rigid substrate via an epoxy adhesive which also serves to encapsulate the element from the ambient environment. Emphasis was on the practical means to achieve functional, reliable, and reproducible components. Although all of the work described in this report involved a YBa2Cu3Osub(7-x) high Tc superconductor material, the techniques developed and conclusions reached are equally applicable to other high Tc materials

Grain Oriented Crystallization, Piezoelectric, and Pyroelectric Properties of (BaxSr₂ - X)TiSi₂O₈ Glass Ceramics

Polar, nonferroelectric (BaxSr2 - x)TiSi2O8 glass ceramics with highly oriented crystallites were prepared by a gradient temperature heat treatment technique. The crystallization mechanism and microstructures of (BaxSr2 - x)TiSi2O8 glass ceramics were investigated by means of differential thermal analysis, x-ray diffraction and scanning electron microscopy, and the dielectric, piezoelectric and pyroelectric properties were investigated for various compositions. The results show that polar (BaxSr2 - x)TiSi2O8 glass ceramics have a low dielectric constant and a high hydrostatic figure of merit dh × gh = ~ 2500. This high hydrostatic figure of merit, along with other unique characteristics, such as no aging or depoling problems and good stability at high temperatures, high pressure, and in harsh environments, makes (BaxSr2 - x)TiSi2O8 glass ceramics attractive for use as hydrophones and high temperature infrared detectors

Brief Review on Some Major Factors Affecting Visible Light Activity of Titania Photocatalyst

As sunlight is an excellent source of clean energy, research for harnessing the energy via an efficient photocatalyst that is active under visible light is actively underway. Titania is well accepted as a photosemiconductor and photocatalyst under ultraviolet light. Effort to make it visible light active has been growing. This review article presents some factors involving the photocatalytic activity of titania which is active under visible light in terms of crystallography. Based on recent progress, several suggestions are made for a better visible light active titania

Brief Review on Some Major Factors Affecting Visible Light Activity of Titania Photocatalyst

As sunlight is an excellent source of clean energy, research for harnessing the energy via an efficient photocatalyst that is active under visible light is actively underway. Titania is well accepted as a photosemiconductor and photocatalyst under ultraviolet light. Effort to make it visible light active has been growing. This review article presents some factors involving the photocatalytic activity of titania which is active under visible light in terms of crystallography. Based on recent progress, several suggestions are made for a better visible light active titania

HYDROGEN ADSORPTION ON NITROGEN-DOPED CARBON XEROGELS

Nitrogen-doped (1.2-4.5 wt%) carbon xerogels were synthesized from carbonization of resorcinol-formaldehyde polymer in an ammonia atmosphere at various temperatures. The textural properties and the chemical nature of nitrogen in the nitrogen-doped carbon xerogels were analyzed by Ar adsorption/desorption isotherms and X-ray photoelectron spectroscopy, respectively. The maximum hydrogen uptakes were measured to be 3.2 wt% at -196 degrees C and 0.28 wt% at 35 degrees C. Hydrogen adsorption had a stronger correlation with specific surface area than nitrogen content at the low temperature of -196 degrees C. At the higher temperature of 35 degrees C, optimal nitrogen doping enhanced hydrogen adsorption by electronic modification of carbon in agreement with previous theoretical predictions. (C) 2009 Elsevier Ltd. All rights reservedclose49575

Enhanced electrochemical capacitance of nitrogen-doped carbon gels synthesized by microwave-assisted polymerization of resorcinol and formaldehyde

Nitrogen-doped carbon gels were synthesized by ammonia-assisted carbonization of resorcinol-formaldehyde (RF) polymers obtained under microwave irradiation without any basic catalyst. Compared with the RF polymer synthesized by the conventional hydrothermal method, microwave polymerization produced spherical beads with a higher surface area (1710 m(2)/g vs. 1080 m(2)/g), and smaller (similar to 700 nm vs. similar to 5 mu m) but more uniform bead sizes. The majority of their pores were micropores. As a result, the electrochemical capacitance of microwave-assisted nitrogen-doped carbons was significantly higher than that of materials prepared by the conventional hydrothermal method. Thus microwave-assisted polymerization followed by ammonia-assisted carbonization is a useful method to synthesize nitrogen-doped carbon gels for electrochemical double layer capacitors. (C) 2008 Elsevier B.V. All rights reservedclose232

Enhanced hydrogen sorption on carbonaceous sorbents under electric field

The effect of an applied electric field on hydrogen physisorption isotherm on carbonaceous sorbents was studied. Distinctive sorption enhancement was obtained by applying a positive electrical potential of 2000 V to platinum-supported carbon samples. The phenomenon was ascribed to stronger interactions between hydrogen and the sorbent. Theoretical studies suggested that, the interaction between hydrogen and neutral carbon is primarily the electrostatic attraction between the π-bonds of the aromatic rings and the σ-bonds of H2, which is classified as van der Waals interaction and is weak. However, the interaction between electrically charged carbon and hydrogen might involve orbital interactions between hydrogen and carbon, an interaction stronger than van der Waals attraction. Experimental studies indicated that the presence of platinum would induce dissociation of hydrogen molecules in to hydrogen atoms. The easier accessibility of the atomic orbital might favor the electron transfer from the atomic hydrogen to charged carbon. © 2009 Professor T. Nejat Veziroglu

Visible light photocatalytic properties of polymorphici brookite titania

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