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Reducing Atmosphere (reducing + atmosphere)
Selected AbstractsPreliminary Observations on Phase Relations in the "V2O3,FeO" and V2O3,TiO2 Systems from 1400°C to 1600°C in Reducing AtmospheresJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2000Theresa Coetsee Phase relations within the "V2O3,FeO" and V2O3,TiO2 oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10,10, 2.99 × 10,9, and 2.31 × 10,8 atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M2O3, M3O5, and higher Magneli phases (MnO2n,1, where M = V, Ti) were identified in the V2O3,TiO2 system. In the "V2O3,FeO" system, the solid-solution phases M2O3 and M3O4 (where M = V, Ti), as well as liquid, were identified. [source] Preparation, structure and photoluminescence properties of SiO2,coated ZnS nanowiresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2010Changhyun Jin Abstract It is essential to passivate one-dimensional (1D) nanostructures with insulating materials to avoid crosstalking as well as to protect them from contamination and oxidation. The structure and influence of thermal annealing on the photoluminescence properties of ZnS-core/SiO2 -shell nanowires synthesized by the thermal evaporation of ZnS powders followed by the sputter deposition of SiO2 were investigated. Transmission electron microscopy and X-ray diffraction analyses revealed that the cores and shells of the core-shell nanowires were single crystal zinc blende-type ZnO and amorphous SiO2, respectively. Photoluminescence (PL) measurement showed that the core-shell nanowires had a green emission band centered at around 525 nm with a shoulder at around 385 nm. The PL emission of the core-shell nanowires was enhanced in intensity by annealing in an oxidative atmosphere and further enhanced by subsequently annealing in a reducing atmosphere. Also the origin of the enhancement of the green emission by annealing is discussed based on the energy-dispersive X-ray spectroscopy analysis results. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Reactivity in LaGaO3/Ni and CeO2/Ni SystemsFUEL CELLS, Issue 2 2006N. Solak Abstract The reactivity in CeO2/Ni and LaGaO3/Ni systems, which are constituents of intermediate temperature solid oxide fuel cell (IT-SOFC) anodes, has been investigated both computationally and experimentally. The CALPHAD-method (CALculating of PHAse Diagrams), employing BINGSS and THERMOCALC software, was used to obtain a self-consistent set of Gibbs energy functions describing the systems. Interactions in the LaGaO3/Ni system were predicted using a thermodynamic database developed for the La-Ga-Ni-O system. Similarly, to analyze the CeO2/Ni system, the Ce-Ni-O ternary phase diagram was calculated using known thermodynamic data for binary Ce-O, Ni-O, and Ce-Ni systems. The experimental work was designed based on the calculated phase diagrams. While the La-Ga-Ni-O system experiments were conducted in air, the Ce-Ni-O system was also investigated in a reducing atmosphere. The calculated Ce-Ni-O diagram is in good agreement with the experimental results. It has been found that NiO does not react with CeO2. Extended solid solutions of La(Ga,Ni)O3, La2(Ni,Ga)O4, and La4(Ni,Ga)3O10 were found in the La-Ga-Ni-O system. Additionally, the compound LaNiGa11O19, with magnetoplumbite-type structure, has been found, which has not been reported in the literature so far. It is concluded that La2NiO4 is not chemically compatible, as a cathode material, with the LSGM electrolyte. [source] Synthesis and Optical Properties of Europium-Doped ZnS: Long-Lasting Phosphorescence from Aligned Nanowires,ADVANCED FUNCTIONAL MATERIALS, Issue 11 2005C. Cheng Abstract Quasi-aligned Eu2+ -doped wurtzite ZnS nanowires on Au-coated Si wafers have been successfully synthesized by a vapor deposition method under a weakly reducing atmosphere. Compared with the undoped counterpart, incorporation of the dopant gives a modulated composition and crystal structure, which leads to a preferred growth of the nanowires along the [010] direction and a high density of defects in the nanowire hosts. The ion doping causes intense fluorescence and persistent phosphorescence in ZnS nanowires. The dopant Eu2+ ions form an isoelectronic acceptor level and yield a high density of bound excitons, which contribute to the appearance of the radiative recombination emission of the bound excitons and resonant Raman scattering at higher pumping intensity. Co-dopant Cl, ions can serve not only as donors, producing a donor,acceptor pair transition with the Eu2+ acceptor level, but can also form trap levels together with other defects, capture the photoionization electrons of Eu2+, and yield long-lasting (about 4,min), green phosphorescence. With decreasing synthesis time, the existence of more surface states in the nanowires forms a higher density of trap centers and changes the crystal-field strength around Eu2+. As a result, not only have an enhanced Eu2+ 4f65d1,4f7 intra-ion transition and a prolonged afterglow time been more effectively observed (by decreasing the nanowires' diameters), but also the Eu2+ related emissions are shifted to shorter wavelengths. [source] Lanthanum Chromite-Based Interconnects as Key Materials for SOFC Stack DevelopmentINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2004Natsuko Sakai The historical investigations on the physicochemical and transport properties of lanthanum chromite-based perovskite oxides are reviewed to evaluate the compatibility as interconnects in solid oxide fuel cells. These materials improve sinterability in air. This has led to investigations on other physicochemical properties of these materials, such as thermal expansion, mechanical strength, and chemical stability. Lanthanum and chromium ion can be substituted by alkaline earths or transition metals, and this translates into a large flexibility in physicochemical properties. However, the formation of oxygen vacancies in a reducing atmosphere can result in an undesirable isothermal expansion or oxygen permeation. The chemical stability of these materials is governed by the fast cation diffusion at the grain boundary of the polycrystals. [source] The role of Raman microspectroscopy in the study of black gloss coatings on Roman potteryJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2005Francesca Ospitali Abstract Raman microspectroscopy was adopted for the study of black gloss coatings on Roman pottery, found in Rimini (northern Italy) and in Suasa, near Ancona (central Italy), dated second century B.C. This non-destructive technique allowed a very accurate analysis of the crystalline and amorphous components of thin surface layers. The investigated coating is black, homogeneous and glazed, without any crystals, becoming red on approaching to the ceramic body. Magnetite and carbon are the main phases of the black zones, whereas hercynite, quartz, silicates and haematite are the secondary components. In the red zones, approaching the ceramic body, the amount of haematite increases and the amount of magnetite decreases. The presence of carbon, on the surface only, confirms the hypothesis of a firing cycle in a partial reducing atmosphere. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effect of Oxygen Partial Pressure During Firing on the High AC Field Response of BaTiO3 DielectricsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Ichiro Fujii The effect of oxygen partial pressure during firing on the high field dielectric response of formulated and undoped BaTiO3 ceramics was investigated. For formulated ceramics, the dielectric constant of both oxygen- and air-fired samples increased almost linearly with the amplitude of the ac-driving field. Formulated BaTiO3 samples sintered in a reducing atmosphere produced a sublinear increase in the permittivity with the ac field amplitude. For undoped BaTiO3 ceramics, the dielectric constant increased sublinearly over a wide range of oxygen partial pressures during firing. It is proposed for the formulated ceramics that the dopant-oxygen vacancy defect dipoles in the shell region accounted for the curvature in the field dependence of the permittivity. These defects appear to add a concentration of weak pinning centers to the potential energy profile through which domain walls move. [source] Effect of Oxygen Partial Pressure During Liquid-Phase Sintering on the Dielectric Properties of 0.9MgTiO3,0.1CaTiO3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Hee-Kyun Shin Microstructural evolution and microwave dielectric properties of liquid-phase-sintered 0.9MgTiO3,0.1CaTiO3 dielectric ceramic material have been investigated as a function of oxygen partial pressure () during sintering. Sintering in a weakly reducing atmosphere (=10,14 atm) generally increased the density, permittivity, quality factor (Q×f), and the temperature coefficient of resonance frequency (,f), but further reducing atmosphere down toof 10,14 atm generally decreased Q×f and ,f. When the 5 wt% lithium borosilicate glass-added specimen was sintered at 950°C and=10,14 atm, it demonstrated a permittivity of 18.8, Q×f of 19 000 GHz, and ,f of 10 × 10,6 K,1. [source] Influence of Ba/Ti Ratio on the Positive Temperature Coefficient of Resistivity Characteristics of Ca-Doped Semiconducting BaTiO3 Fired in Reducing Atmosphere and Reoxidized in AirJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2007Hideaki Niimi The positive temperature coefficient of resistivity (PTCR) characteristics of donor-doped BaTiO3 fired in a reducing atmosphere and reoxidized in air are investigated. The result reveals that conventional semiconducting BaTiO3 ceramics fired in a reducing atmosphere and reoxidized at a low temperature of 800°C in air show minimal PTCR characteristics, as reported earlier; however, Ca-doped BaTiO3 with compositions in the range of 1.005,(Ba+Ca+La)/Ti,1.010 exhibit pronounced PTCR characteristics, even when reoxidized at such a low temperature. The semiconducting BaTiO3 ceramics with {(Ba+Ca+La)/Ti}=1.005 and Ca-doped to 20 mol% exhibit remarkable PTCR characteristics with a resistivity jump of two orders of magnitude when they have been reoxidized at 800°C after firing in a reducing atmosphere. [source] Effect of Varying Quartz Particle Size and Firing Atmosphere on Densification of Brazilian Clay-Based StonewareJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006G. P. Souza Body mixes for stoneware containing a Brazilian red clay, nepheline syenite, and quartz with two different median particle sizes (,2 and 18 ,m) were fired under oxidizing and reducing atmospheres. The densification behavior was followed by dilatometry simulating the firing schedule, as well as by water absorption, linear shrinkage, and bulk density measurements on as-fired specimens. It was revealed that finer quartz led to interconnected pore closure at 1125°C when fired under an oxidizing atmosphere. Densification was systematically related to the uniformity of the compacts in the unfired state. Phase and microstructural examination by X-ray diffractometry, scanning electron microscopy/energy-dispersive spectroscopy (EDS), and transmission electron microscopy/EDS showed that mullite developed more extensively in the stonewares fired in an oxidizing atmosphere, along with cristobalite and haematite, whereas metallic iron was found in stonewares fired under a reducing atmosphere. [source] Novel Method for Obtaining Corundum Layers of High Surface Area on Ceramic Supports for High-Temperature CatalysisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2002Alejandro Souto The surface of an aluminosilicate ceramic was transformed to a corundum layer of high specific surface area by heating at 1300°,1450°C in a controlled reducing atmosphere. This procedure selectively reduced and volatilized the silica of the glass and mullite, and the alumina of the mullite formed a layer of corundum crystals with a thickness of ,20 ,m and a specific surface area of ,16 m2/g. Specific surface area remained stable at 10.5 m2/g after prolonged heating at 1300°C in air, and at 8.5 m2/g at 1450°C. These materials are well suited for use as catalyst supports in applications such as catalytic combustion at temperatures in this range. [source] Necessary Conditions for the Formation of {111} Twins in Barium TitanateJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2000Byoung-Ki Lee The experimental conditions for {111} twin formation in BaTiO3 were investigated. When BaTiO3 compacts without excess TiO2 were sintered either in an oxidizing atmosphere (air) or in a reducing atmosphere (95N2,5H2), no {111} twins formed within the BaTiO3 grains and no abnormal grain growth occurred. In contrast, many {111} twins were present within the abnormally grown grains in the excess-TiO2 -containing BaTiO3 samples sintered in air, while no twins were observed in the excess-TiO2 -containing samples sintered in 95N2,5H2. X-ray diffraction analysis showed that excess TiO2 forms a Ba6Ti17O40 phase during sintering with the space group A2/a in air and a Ba6Ti17O40,x phase with the space group C in 95N2,5H2. It appears therefore that excess TiO2 and an oxidizing atmosphere are necessary for {111} twin formation in BaTiO3. These results may also indicate that the interface structure between BaTiO3 and Ba6Ti17O40 influences the twin formation. [source] Improved electrical, optical, and structural properties of undoped ZnO thin films grown by water-mist-assisted spray pyrolysisPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2006L. Martínez Pérez Abstract Undoped ZnO thin films were prepared using the ultrasonic spray pyrolysis deposition technique with zinc acetylacetonate dissolved in N,N-dimethylformamide as the source materials solution. The addition of water mist in a parallel flux to the spray solution stream was also used during deposition of the films. The addition of water mist improved the electrical characteristics of the ZnO films. Fresh ZnO samples were then thermally annealed in a H2 reducing atmosphere. X-ray diffraction patterns show mainly the wurzite crystalline ZnO phase in the films. An electrical resistivity (, ) of around 2.7 × 10,2 , cm was measured at room temperature for the best undoped ZnO film. , is approximately one order of magnitude lower than the resistivities found in undoped ZnO films obtained by means of similar non-vacuum deposition techniques. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Deposition of crystalline copper films from tetranuclear copper (II) complexes without application of reducing atmosphereAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 10 2010Muhammad Shahid Abstract Crystalline copper films were deposited by aerosol-assisted chemical vapor deposition (AACVD) in the absence of hydrogen from two newly synthesized complexes [Cu(deae)(TFA)]4·1.25THF (1) and [Cu4(OAc)6(bdmap)2(H2O)2]·4H2O (2) [deae = N, N -diethylaminoethanolate, TFA = trifloroacetate, OAc = acetate and bdmap = 1,3-bis(dimethylamino)-2-propanolato]. These precursors were prepared in high yield using mixed ligands and crystallized in tetragonal and triclinic crystal systems with space groups 141/a and P , 1. Complexes 1 and 2 thermally decomposed at 290 and 250 °C, respectively, to yield copper films which were characterized by SEM/EDX for their morphology and composition and PXRD for their crystallinity and phase. These films have smooth morphologies with particle sizes within the range of 0.3,0.6 µm and may find applications in fabrication of ultralarge-scale integrated circuits. Copyright © 2010 John Wiley & Sons, Ltd. [source] Effect of Varying Quartz Particle Size and Firing Atmosphere on Densification of Brazilian Clay-Based StonewareJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006G. P. Souza Body mixes for stoneware containing a Brazilian red clay, nepheline syenite, and quartz with two different median particle sizes (,2 and 18 ,m) were fired under oxidizing and reducing atmospheres. The densification behavior was followed by dilatometry simulating the firing schedule, as well as by water absorption, linear shrinkage, and bulk density measurements on as-fired specimens. It was revealed that finer quartz led to interconnected pore closure at 1125°C when fired under an oxidizing atmosphere. Densification was systematically related to the uniformity of the compacts in the unfired state. Phase and microstructural examination by X-ray diffractometry, scanning electron microscopy/energy-dispersive spectroscopy (EDS), and transmission electron microscopy/EDS showed that mullite developed more extensively in the stonewares fired in an oxidizing atmosphere, along with cristobalite and haematite, whereas metallic iron was found in stonewares fired under a reducing atmosphere. [source] | ||||||||||||||||