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... Rev, Lett. 58, 1676 (1987). *'F. С Wellstood, MJ Ferrari, Î. Clarke, AM Stacy, A. Zettl, and ML Cohen, Phys. Lett. A Í22, 61 (1987). 5Wei-Jiang Yeh, Lie Chen, Fengzhi Xu, Baokang Bi, and Peiran Yang, Phys. Rev. В 36, 2414... more
... Rev, Lett. 58, 1676 (1987). *'F. С Wellstood, MJ Ferrari, Î. Clarke, AM Stacy, A. Zettl, and ML Cohen, Phys. Lett. A Í22, 61 (1987). 5Wei-Jiang Yeh, Lie Chen, Fengzhi Xu, Baokang Bi, and Peiran Yang, Phys. Rev. В 36, 2414 (1987). 6D. ...
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ABSTRACT The quantitative relationships of calcination temperature (CT), powder specific surface area (SA) and densification parameters (DP) for oxalate-derived YBCO superconductor were determined. Phase development and change of SA were... more
ABSTRACT The quantitative relationships of calcination temperature (CT), powder specific surface area (SA) and densification parameters (DP) for oxalate-derived YBCO superconductor were determined. Phase development and change of SA were measured as a function of the CT in the 300–910 °C range. A strong correlation between powder SA and phase composition in the Y-Ba-Cu-O system was demonstrated. Between 300 and 500 °C only crystalline CuO and BaCO3 were detected by X-ray and SA decreased slightly from 11 to 10 m2 g−1 with increasing temperature. In the 500–700 °C range Y2O3 was also detected and the specific surface area gradually dropped to 6.62 m2 g−1. Sharp reduction of SA from 6.62 to 2.36 m2 g−1 was observed in passing from oxide-carbonate mix to YBCO monophase system. During calcination at 750–910 °C the SA of YBCO powder decreased from 2.36 to 0.46 m2 g−1 and varied logarithmically with inverse temperature with a constant effective activation energy of 26.4 Kcal mol−1. The densification profiles were determined by dilatometry of extruded samples obtained from differently calcined powders. The dependence of densification onset, shrinkage rate and asymptotic density on both CT and SA of YBCO precursors has been shown. In addition, the effect of heating rate on asymptotic density of the materials upon sintering was found. Finally, the possibility of using specific surface area of oxalate-derived YBCO powders as a universal cumulative parameter for predicting suitability was evaluated.
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ABSTRACT Detailed study of the synthesis parameters of silver doped with the organic dye Congo-red (CR@Ag) have led to an understanding of the origins of the superior performance of this novel-type methanol-oxidation catalyst (compared to... more
ABSTRACT Detailed study of the synthesis parameters of silver doped with the organic dye Congo-red (CR@Ag) have led to an understanding of the origins of the superior performance of this novel-type methanol-oxidation catalyst (compared to pure silver) as demonstrated by the significant lowering of the temperature needed to reach maximal conversion by more than 100 °C. The origins of the effect of the organic dopant on the catalytic properties of silver are suggested and discussed in terms of its effects on morphology, on oxygen chemisorption properties, on the surface area, on the thermal behavior and on the sinterability of the silver aggregated crystallites. For instance, the organic dopant affects the surface area dramatically, increasing it from 600–3000 cm2 g−1 for undoped silver to 46000 cm2 g−1 for CR@Ag; and oxygen chemisorption, crucial for this catalytic process, increases from 32 cm2 g−1 for Ag to 893 cm2 g−1 for CR@Ag. Preliminary work with CR@copper provides a positive outlook for the general use of organic dopants to improve catalytic properties of other metals.
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select... more
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
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... thermodynamic, and transport properties of the Bi2Sr3 - CaxCu208+ 8 superconductor GS Grader, EM Gyorgy, PK Gallagher, HM O'Bryan, DW Johnson ... 2R. M. Hazen, CT Prewitt, RJ Angel, NL Ross, LW Finger, CG Hadidiacos, DR... more
... thermodynamic, and transport properties of the Bi2Sr3 - CaxCu208+ 8 superconductor GS Grader, EM Gyorgy, PK Gallagher, HM O'Bryan, DW Johnson ... 2R. M. Hazen, CT Prewitt, RJ Angel, NL Ross, LW Finger, CG Hadidiacos, DR Veblen, PJ Heaney, PH Hor, RL Meng, YY Sum ...
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ABSTRACT Alumina gels were synthesized by catalyzed gelation of aluminum sec-butoxide (ASB) via the Yoldas process. The gels were aged for up to 6 months and then supercritically dried (SCD) with CO2. The molar ratio of acid to ASB was in... more
ABSTRACT Alumina gels were synthesized by catalyzed gelation of aluminum sec-butoxide (ASB) via the Yoldas process. The gels were aged for up to 6 months and then supercritically dried (SCD) with CO2. The molar ratio of acid to ASB was in the range of 0.01–0.6. Viscosity measurements of the gels showed a shear thinning and plastic behavior with no response up to a limiting yield stress. The gel rheology obeys the Casson model. Analysis of the viscosity as a function of the acid to alkoxide molar ratio, showed that the average molecular weight of the gels is inversely proportional to the acid to alkoxide molar ratio.The viscosity of all the gels increased with aging time for a period of about 6 months reaching an asymptotic value after 1–2 weeks. The viscosity is shown to correlate with the microstructure of these nanomaterials during aging. Aging gives rise to a nearly constant surface area of 350 m2/g regardless of acid to alkoxide ratio in an aging period of about 6 months.
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PbZr0.52Ti0.48O3 (PZT) was deposited on three substrates: Pt/Ti/SiO2/Si, PbTiO3/Pt/Ti/SiO2/Si and LaNiO3/SiO2/Si. The final PZT film morphology, orientation, piezoelectric and ferroelectric properties were investigated and related to the... more
PbZr0.52Ti0.48O3 (PZT) was deposited on three substrates: Pt/Ti/SiO2/Si, PbTiO3/Pt/Ti/SiO2/Si and LaNiO3/SiO2/Si. The final PZT film morphology, orientation, piezoelectric and ferroelectric properties were investigated and related to the substrate type.
Nonhydrolitic sol-gel processes of aluminum chloride and aluminum bromide with isopropyl ether and aluminum sec-butoxide were performed at various temperatures. Based on the Arrhenius type variation of the gelation time with temperature,... more
Nonhydrolitic sol-gel processes of aluminum chloride and aluminum bromide with isopropyl ether and aluminum sec-butoxide were performed at various temperatures. Based on the Arrhenius type variation of the gelation time with temperature, activation energies for the gelation were found to be in the range 19–25 Kcal/mol range. The energies were found to be sensitive to the nature of the aluminum ligands and the chemical scheme. Due to the large activation energy, it is possible to stop the reaction at any time before gelation by cooling the sol to room temperature. Small angle X-ray scattering (SAXS) of sols from the AlClAlCl3/Pr <img src="/fulltext-image.asp?format=htmlnonpaginated&src=TR20414223805470_html\10971_2004_Article_136473_TeX2GIFIE1.gif" border="0" alt=" $$_2^i $$ " />O system shows unique development of a fractal like structure with nanometer scale order, demonstrated by discrete peaks in the SAXS data. A fractal dimension D = 1.64 was ...
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ABSTRACT Nanometric particles (10–30 nm) of thermally activated Congo-red (CR) entrapped within silver deposited on TiO2 nanofibers form a new triple hybrid—organic, metallic, and ceramic—catalyst (CR@Ag/TiO2-nf). It is shown that the... more
ABSTRACT Nanometric particles (10–30 nm) of thermally activated Congo-red (CR) entrapped within silver deposited on TiO2 nanofibers form a new triple hybrid—organic, metallic, and ceramic—catalyst (CR@Ag/TiO2-nf). It is shown that the downscaling and the use of nanofibers as supports cause CR@Ag/TiO2-nf to considerably outperform the unsupported powder CR@Ag as well as the supported undoped Ag/TiO2-nf catalysts in all of the studied parameters of the industrially important oxidation of methanol to formaldehyde. These parameters include the weight hourly space velocity (WHSV), the space time yield (STY), the reaction conversion, and the reaction selectivity values. Typically, the WHSV shows a huge jump—approximately 18 times higher—compared to unsupported powder; the STY shows a 10-fold increase out of which 25% is achieved due to the CR doping; and the fully activated catalyst (second run) provided a conversion of 98% and selectivity of 85%. The high efficiency of this novel type of triple hybrid catalyst is explained on the basis of structural–morphological characteristics such as higher porosity, larger surface area, and relatively low sinterability of the separated doped silver particles which are provided by the TiO2 nanofibers support.
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Different values of Tc were found for the 1:2:3 tetragonal superconductors (CaxLa1−x)(La0.25+xBa1.75−x)Cu3Oy (these compounds have previously been denoted as CLBLCO, CLBCO or CaLaBaCuO) prepared under various conditions but having the... more
Different values of Tc were found for the 1:2:3 tetragonal superconductors (CaxLa1−x)(La0.25+xBa1.75−x)Cu3Oy (these compounds have previously been denoted as CLBLCO, CLBCO or CaLaBaCuO) prepared under various conditions but having the same x and y. The x = 0.1 ceramic samples prepared using various grindings differ in Tc by 8 K and the x = 0.4 ones prepared at various temperatures differ in Tc by 4 K. The different ratios between the unit cells and the various cation distributions might be the causes of this phenomenon.
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The oxygen stoichiometry of Y, Gd and Eu containing superconducting perovskites (of the form BaâYCUâOâ) was determined by measuring the oxygen evolution of these materials (in an initially evacuated closed system), as a function of... more
The oxygen stoichiometry of Y, Gd and Eu containing superconducting perovskites (of the form BaâYCUâOâ) was determined by measuring the oxygen evolution of these materials (in an initially evacuated closed system), as a function of temperature. Results show that both Eu and Gd containing superconductors undergo the orthorhombic/tetragonal phase transition at a lower temperature than the Y analog, and that the Gd-sample tetragonal phase exhibits semiconductor behavior.
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A parametric representation of critical temperature (Tc) vs Tl/Cu for the crossection TlxBa2Ca2Cu3Oy shows evidence of all known superconducting compounds and two additional phases as well. Peaks in Tc vs Tl/Cu fit expected Tl/Cu values... more
A parametric representation of critical temperature (Tc) vs Tl/Cu for the crossection TlxBa2Ca2Cu3Oy shows evidence of all known superconducting compounds and two additional phases as well. Peaks in Tc vs Tl/Cu fit expected Tl/Cu values within a few percent using weight analysis.
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ABSTRACT This paper describes the effect of temperature on the formation of nonhydrolytic alumina foams. The foams are generated by heat treatment of crystals of the aluminum chloride isopropyl ether complex [AlCl3(Pri 2O)], with the... more
ABSTRACT This paper describes the effect of temperature on the formation of nonhydrolytic alumina foams. The foams are generated by heat treatment of crystals of the aluminum chloride isopropyl ether complex [AlCl3(Pri 2O)], with the release of isopropyl chloride (PriCl). The chlorine content in the foams was determined by titration, and their weight loss during sintering was measured by thermogravimetric and differential thermal analysis. Based on these measurements, the condensation degree (CD) in the foams was modeled. The foaming time ranged from several minutes at 70 °C to several seconds at 160 °C. It was found that the chlorine-to-aluminum ratio of the foam (Cl/Al) decreased from 1.79 at 70 °C to 1.56 at 160 °C. Thermogravimetric analysis data confirm that the smaller Cl content gives rise to a smaller weight loss during thermal decomposition, consistent with a higher CD in the foams created at higher temperatures. Finally, about 80% of the PriCl produced during complex decomposition and subsequent –Al–O–Al– condensation reactions is lost during foaming.
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ABSTRACT High quality, uniform PbZrxTi1-xO3(PZT) films were prepared on the 4 inch wafers by chemical solution deposition (CSD) of 1,3-propanediol precursors. Film uniformity was studied as a function of deposition conditions including... more
ABSTRACT High quality, uniform PbZrxTi1-xO3(PZT) films were prepared on the 4 inch wafers by chemical solution deposition (CSD) of 1,3-propanediol precursors. Film uniformity was studied as a function of deposition conditions including spinning rates and co-solvents. Measurements of the surface tension and composition evolution during evaporation and spinning stages showed that the surface tension increases significantly when the co-solvent is nearly completely evaporated. The evaporation of the propanol co-solvent and volatile by-products occurs within the first 5 s of spinning giving rise to defects, whereas octanol is slowly evaporated during 60 s producing uniform coatings. Other co-solvents such as hexanol and pentanol produced uniform films as well. Therefore stabilization of the surface tension in the initial spinning stage is a key to prevent the defect formation. These findings facilitate the deposition of uniform PZT films over large substrates by a simple, scalable, and cost-effective process.
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ABSTRACT In this paper we report a novel process for the production of ultralight cellular ceramics. The foams are generated by the heat treatment of crystals of the aluminum chloride isopropyl ether complex [AlCl3(Pri2O)]. The crystals,... more
ABSTRACT In this paper we report a novel process for the production of ultralight cellular ceramics. The foams are generated by the heat treatment of crystals of the aluminum chloride isopropyl ether complex [AlCl3(Pri2O)]. The crystals, which are the only foam precursor, are obtained from concentrated solutions of AlCl3, Pri2O, and CH2Cl2. The foams consist of an arrangement of closed cells, 50–300 μm in diameter, having cell walls approximately 1–2 μm thick. An exceptionally high porosity is obtained ranging from 94 to 99%, and the cellular structure is retained during heating at 1500 °C. The foaming mechanism involves two consecutive nonhydrolytic sol-gel chemical reactions and physical processes including crystal dissociation, solvation, phase separation, and foaming. While other foaming mechanisms cited in the literature utilize one or more of the processes above, no analog mechanism exists in the organic, ceramic, or metal foam production processes. The effectiveness of the process originates from an initial precursor which contains all the necessary foaming components in such a way that the application of mild heating accelerates its transformation to a solid, dry, ultralight foamed material.
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Activated carbons impregnated with a mixture of copper(ii), iron(iii) and chromium(iii) oxide catalysts were prepared in order to facilitate catalytic regeneration of AC saturated with phenols. The temperature ranges of phenol oxidation... more
Activated carbons impregnated with a mixture of copper(ii), iron(iii) and chromium(iii) oxide catalysts were prepared in order to facilitate catalytic regeneration of AC saturated with phenols. The temperature ranges of phenol oxidation (Tp), carbon oxidation (Tc) and carbon burn-off were determined from DTA/TGA investigations in oxidizing and inert atmospheres. The impregnated catalyst facilitated phenol oxidation but also lowered the Tc
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The resistivity of Ba2YCu3O(x) was measured in the 450-850 C range at various oxygen partial pressures. The tetragonal to orthorhombic phase transition is observed as a change in the slope of the resistivity curve. The lack of a... more
The resistivity of Ba2YCu3O(x) was measured in the 450-850 C range at various oxygen partial pressures. The tetragonal to orthorhombic phase transition is observed as a change in the slope of the resistivity curve. The lack of a discontinuity in the curve is consistent with the phase transition being higher than first order. It was found that decreasing the oxygen content x below 6.2 changed the resistivity of the tetragonal phase from metallic character to semiconducting character. In the metallic region of the tetragonal phase the superconducting transition temperature is depressed below 60 K, while in the semiconducting region, no superconducting onset was observed down to 6 K. In the orthorhombic phase, the resistivity of the material is shown to be governed by the number of oxygens per unit cell, suggesting that the resistivity can serve as a quality control parameter in the production of superconducting devices.
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The presence of circulating circumferential currents in toroids of Tl-Ba-Ca-Cu-O superconductors at 77.3 and 90.2 K has been demonstrated. The nominal composition was Tl1.5Ba2Ca2Cu3O(x); however, both the X-ray diffraction pattern and the... more
The presence of circulating circumferential currents in toroids of Tl-Ba-Ca-Cu-O superconductors at 77.3 and 90.2 K has been demonstrated. The nominal composition was Tl1.5Ba2Ca2Cu3O(x); however, both the X-ray diffraction pattern and the Meissner effect indicate the presence of more than one phase. The circulating current was found to decrease by 27 percent in 3800 s. The nature of the above
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A new superconducting phase with an onset of 123 K and zero resistance at 121 K has been detected in the Tl0.5Ba2Ca2Cu3Oy multiphase system. The composition is reproducible and stable.
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An improved press forging technique has yielded ceramic BaâYCuâO/sub x/ with a very high degree of orientation and mechanical integrity. The as-forged samples are dense and tetragonal, and have an oxygen content of approx. =6.3. By a... more
An improved press forging technique has yielded ceramic BaâYCuâO/sub x/ with a very high degree of orientation and mechanical integrity. The as-forged samples are dense and tetragonal, and have an oxygen content of approx. =6.3. By a partial oxidation of the samples, a superconducting skin 20--100 ..mu..m thick is formed on the outer surface. Transport measurements on this skin show a J/sub c/ >3000 Acm² with an improved field dependence as compared with randomly oriented samples. The restriction of oxidation to the thin outer skin has reduced the microcracking which accompanies the oxidation of tetragonal BaâYCuâO/sub x/.