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Ambient Pressure (ambient + pressure)
Selected AbstractsStable Oxoborate with Edge-Sharing BO4 Tetrahedra Synthesized under Ambient Pressure,ANGEWANDTE CHEMIE, Issue 29 2010Shifeng Jin Druck ist nicht alles: Kantenverknüpfte BO4 -Tetraeder treten nur selten in Boratstrukturen auf, und dann nur, wenn diese unter hohem Druck erzeugt werden. Jetzt wurde dieses Strukturmotiv auch in einem bei Umgebungsdruck erhaltenen Borat entdeckt. Während die Hochdruckphasen nur metastabil sind, ist die Struktur der Titelverbindung bis zu ihrem Schmelzpunkt beständig. Die Verbindung kann außerdem mobile Ionen in ihre Tunnelstruktur aufnehmen. [source] ChemInform Abstract: A Pure Bismuth A Site Polar Perovskite Synthesized at Ambient Pressure.CHEMINFORM, Issue 8 2008Craig A. Bridges Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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. [source] Improvement and validation of a snow saltation model using wind tunnel measurementsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 14 2008Andrew Clifton Abstract A Lagrangian snow saltation model has been extended for application to a wide variety of snow surfaces. Important factors of the saltation process, namely number of entrained particles, ejection angle and speed, have been parameterized from data in the literature. The model can now be run using simple descriptors of weather and snow conditions, such as wind, ambient pressure and temperature, snow particle sizes and surface density. Sensitivity of the total mass flux to the new parameterizations is small. However, the model refinements also allow concentration and mass flux profiles to be calculated, for comparison with measurements. Sensitivity of the profiles to the new parameterizations is considerable. Model results have then been compared with a complete set of drifting snow data from our cold wind tunnel. Simulation mass flux results agree with wind tunnel data to within the bounds of measurement uncertainty. Simulated particle sizes at 50 mm above the surface are generally larger than seen in the tunnel, probably as the model only describes particles in saltation, while additional smaller particles may be present in the wind tunnel at this height because of suspension. However, the smaller particles carry little mass, and so the impact on the mass flux is low. The use of simple input data, and parameterization of the saltation process, allows the model to be used predictively. This could include applications from avalanche warning to glacier mass balance. Copyright © 2008 John Wiley & Sons, Ltd. [source] A silica-based monolithic column in capillary HPLC and CEC coupled with ESI-MS or electrospray-atmospheric-pressure laser ionization-MSELECTROPHORESIS, Issue 21 2005Stefan Droste Abstract We describe the successful coupling of CEC and capillary HPLC with the recently developed atmospheric-pressure laser ionization (APLI) method. APLI is suitable for selectively and sensitively ionizing nonpolar aromatic compounds at ambient pressure for subsequent mass-selective detection. The polycyclic aromatic hydrocarbons used as analytes are first separated either by CEC on a silica-based monolithic column or by capillary HPLC. The eluent, along with a sheath flow, is volatilized by microelectrospray and then selectively ionized by excimer laser (KrF*) radiation via two-photon excitation. A QTOF-MS is used as mass-selective detector. This interface combination makes soft ionization of thermally labile nonpolar aromatic analytes possible. [source] Formation of Metastable Na2CrO4 -Type LiNiPO4 from a Phosphate,Formate PrecursorEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2010Violeta Koleva Abstract High-pressure modification of LiNiPO4 with a Na2CrO4 -type structure was obtained at ambient pressure and low temperature from a mixed LiNi,phosphate,formate precursor, LiNiPO4Hx(HCOO)x·yH2O (where x , 1.2 and y , 2.5). The structural and thermal characterization of the precursor and the LiNiPO4 compositions were carried out by powder XRD analysis, IR spectroscopy, and DSC analysis. Thermal treatment of LiNiPO4Hx(HCOO)x·yH2O precursors between 450 and 650 °C yields a mixture of the two structural modifications of LiNiPO4: the Na2CrO4 type and the olivine type. It was established that the obtained Na2CrO4 -type LiNiPO4 is a metastable phase, which completely transforms at 700 °C into the olivine-type phase. The enthalpy of the phase transition is ,H = ,43.40 kJ,mol,1. The mechanism of formation of the two forms of LiNiPO4 from the LiNi,phosphate,formate precursor is discussed. [source] A Complex-Based Soft Template Route to PbSe NanowiresEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 4 2003Yuanfang Liu Abstract PbSe nanowires with an average size of 8 × 350 nm were synthesized by the reaction of Pb(NO3)2 and Se powder at 60 °C under ambient pressure. A mixture of arachidic acid (AA, n -C19H39COOH) and octadecylamine (ODA), which could form a complex with Pb2+, was employed as a soft template to control the morphology of the resultant PbSe nanowires. The products were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy. The photoluminescence (PL) spectrum of the PbSe nanowires is presented. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Full-length prion protein aggregates to amyloid fibrils and spherical particles by distinct pathwaysFEBS JOURNAL, Issue 9 2008Driss El Moustaine As limited structural information is available on prion protein (PrP) misfolding and aggregation, a causative link between the specific (supra)molecular structure of PrP and transmissible spongiform encephalopathies remains to be elucidated. In this study, high pressure was utilized, as an approach to perturb protein structure, to characterize different morphological and structural PrP aggregates. It was shown that full-length recombinant PrP undergoes ,-sheet aggregation on high-pressure-induced destabilization. By tuning the physicochemical conditions, the assembly process evolves through two distinct pathways leading to the irreversible formation of spherical particles or amyloid fibrils, respectively. When the PrP aggregation propensity is enhanced, high pressure induces the formation of a partially unfolded aggregated protein, AggHP, which relaxes at ambient pressure to form amorphous aggregates. The latter largely retain the native secondary structure. On prolonged incubation at high pressure, followed by depressurization, AggHP transforms to a monodisperse population of spherical particles of about 20 nm in diameter, characterized by an essentially ,-sheet secondary structure. When the PrP aggregation propensity is decreased, an oligomeric reaction intermediate, IHP, is formed under high pressure. After pressure release, IHP relaxes to the original native structure. However, on prolonged incubation at high pressure and subsequent depressurization, it transforms to amyloid fibrils. Structural evaluation, using optical spectroscopic methods, demonstrates that the conformation adopted by the subfibrillar oligomeric intermediate, IHP, constitutes a necessary prerequisite for the formation of amyloids. The use of high-pressure perturbation thus provides an insight into the molecular mechanism of the first stages of PrP misfolding into amyloids. [source] Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature,ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008Michael D. Dickey Abstract This paper describes the rheological behavior of the liquid metal eutectic gallium-indium (EGaIn) as it is injected into microfluidic channels to form stable microstructures of liquid metal. EGaIn is well- ;suited for this application because of its rheological properties at room temperature: it behaves like an elastic material until it experiences a critical surface stress, at which point it yields and flows readily. These properties allow EGaIn to fill microchannels rapidly when sufficient pressure is applied to the inlet of the channels, yet maintain structural stability within the channels once ambient pressure is restored. Experiments conducted in microfluidic channels, and in a parallel-plate rheometer, suggest that EGaIn's behavior is dictated by the properties of its surface (predominantly gallium oxide, as determined by Auger measurement s); these two experiments both yield approximately the same number for the critical surface stress required to induce EGaIn to flow (,0 .5,N/m). This analysis,which shows that the pressure that must be exceeded for EGaIn to flow through a microchannel is inversely proportional to the critical (i.e., smallest) dimension of the channel,is useful to guide future fabrication of microfluidic channels to mold EGaIn into functional microstructures. [source] Transition Metal Borides: Superhard versus Ultra-incompressible,ADVANCED MATERIALS, Issue 19 2008Qinfen Gu Borides of several heavy transition metals have been synthesized by arc melting at ambient pressure. The materials are characterized by either low compressibility or high hardness, some of them showing a good compromise between both properties. The structure,property relationship is revealed based on their crystal structures and a chemical bonding analysis by means of the electron localization function. [source] Towards Protein Field-Effect Transistors: Report and Model of a Prototype,ADVANCED MATERIALS, Issue 7 2005G. Maruccio A protein field-effect transistor (Pro-FET) based on the blue-copper protein azurins (see Figure) and operating at room temperature and ambient pressure is demonstrated. The transfer characteristics of the Pro-FET exhibit a pronounced resonance due to the switch from behaving as a n-metal oxide semiconductor FET (n-MOSFET) to a p-MOSFET. Carrier transport through the device is explained in terms of an equilibrium between the two possible oxidation states of the redox site (Cu1+ and Cu2+). [source] Cover Picture: Bidentate Ligands by Self-Assembly through Hydrogen Bonding: A General Room Temperature/Ambient Pressure Regioselective Hydroformylation of Terminal Alkenes (Adv. Synth.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-13 2005Catal. Abstract The cover picture shows a typical industrial reaction, hydroformylation of terminal alkenes, made possible in a test tube with ambient pressure and room temperature with high regioselectivities. For more details, see the Communication by Wolfgang Seiche, Alexander Schuschkowski, and Bernhard Breit on pages 1488,1494. [source] Visualization of the foaming mechanism of polyethylene blown by chemical blowing agents under ambient pressureADVANCES IN POLYMER TECHNOLOGY, Issue 4 2007Remon Pop-Iliev Abstract Understanding the fundamental mechanisms that govern the foaming process is the most essential universal prerequisite for developing effective processing strategies for fabricating high-quality foamed plastic products using any type of foaming technology. Despite chemically blown foaming of thermoplastics under atmospheric pressure has been successfully implemented in rotational foam molding over the last decade, the related open literature does not provide substantial research addressing the fundamentals of this unique foaming mechanism. The present study focuses on clarifying the fundamental foaming mechanisms that govern the successful manufacture of thermoplastic foams using a chemical blowing agent under low-pressure (atmospheric) conditions. The presented research is mainly based on observing a series of visualization experiments conducted using a custom-made visualization system including an optical microscope and a computerized CCD camera imaging system, which was utilized for investigating the behavior of foamable polyethylene samples prepared by using the compression-molding method. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:213,222, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20102 [source] Pressure-induced high-density amorphous ice in protein crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2008Chae Un Kim Crystal cryocooling has been used in X-ray protein crystallography to mitigate radiation damage during diffraction data collection. However, cryocooling typically increases crystal mosaicity and often requires a time-consuming search for cryoprotectants. A recently developed high-pressure cryocooling method reduces crystal damage relative to traditional cryocooling procedures and eases or eliminates the need to screen for cryoprotectants. It has been proposed that the formation of high-density amorphous (HDA) ice within the protein crystal is responsible for the excellent diffraction quality of the high-pressure cryocooled crystals. This paper reports X-ray data that confirm the presence of HDA ice in the high-pressure cryocooled protein crystallization solution and protein crystals analyzed at ambient pressure. Diffuse scattering with a spacing characteristic of HDA ice is seen at low temperatures. This scattering then becomes characteristic successively to low-density amorphous, cubic and hexagonal ice phases as the temperature is gradually raised from 80 to 230,K, and seems to be highly correlated with the diffraction quality of crystals. [source] High-pressure properties of TiP2O7, ZrP2O7 and ZrV2O7JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2001Stefan Carlson High-pressure synchrotron X-ray powder diffraction studies of TiP2O7, ZrP2O7 and ZrV2O7 have been performed. The ZrV2O7 structure undergoes a reversible transition at 1.38,1.58,GPa from cubic ,- to pseudo-tetragonal ,-ZrV2O7 that displays an orthorhombic 2 × 3 × 3 supercell. At pressures above 4,GPa, ZrV2O7 becomes irreversibly X-ray amorphous. No such transformations are observed for TiP2O7 and ZrP2O7, which compress smoothly up to the highest investigated pressures (40.3 and 20.5,GPa, respectively). These differences in high-pressure properties are discussed in terms of the negative thermal expansion of ZrV2O7. The bulk moduli at ambient pressure (B0) for TiP2O7, ZrP2O7, ,-ZrV2O7 and ,-ZrV2O7 were estimated to be 42,(3), 39,(1), 17.0,(7) and 20.8,(10),GPa, respectively. [source] Fabrication of aragonite rosette superstructure through the weak interaction between nonionic polymers and Ca2+JOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Shuxian Shi Abstract The controlled formation of aragonite by simple method under ambient condition is a big challenge for biomaterial scientists. In this article, we took poly (N -vinyl pyrrolidone) (PVP) as an example to investigate the influence of water-soluble nonionic polymers on the polymorphs of CaCO3 via CO2 diffusion method under ambient pressure and temperature, and found that the existence of PVP molecules favors the formation of aragonite with rosette superstructure. A possible mechanism is proposed that nonionic polymers can be doped into amorphous calcium carbonate (ACC) particles and further participate in the transformation process from ACC to aragonite and then promotes the formation of rosette superstructure through parallel aggregation by crosslinking the aragonite nuclei. The experiments of CaCO3 crystallization in presence of poly(ethylene oxide) (PEO) and poly(vinyl alcohol) (PVA) confirmed the mechanism. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Paxillin modulates squamous cancer cell adhesion and is important in pressure-augmented adhesionJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 6 2006William C. Conway Abstract Paxillin is an adapter protein regulating signaling and focal adhesion assembly that has been linked to malignant potential in many malignancies. Overexpression of paxillin has been noted in aggressive tumors. Integrin-mediated binding through the focal adhesion complex is important in metastatic adhesion and is upregulated by extracellular pressure in malignant colonocytes through FAK and Src activation. Neither head and neck cancers nor paxillin have been studied in this regard. We hypothesized that paxillin would play a role in modulating squamous cancer adhesion both at baseline and under conditions of increased extracellular pressure. Using SCC25 tongue squamous cancer cells stably transfected with either an empty selection vector or paxillin expression and selection vectors, we studied adhesion to collagen, paxillin, FAK, and Src expression and phosphorylation in cells maintained for 30 min under ambient or 15 mmHg increased pressure conditions. Paxillin-overexpressing cells exhibited adhesion 121,±,2.9% of that observed in vector-only cells (n,=,6, P,<,0.001) under ambient pressure. Paxillin-overexpression reduced FAK phosphorylation. Pressure stimulated adhesion to 118,±,2.3% (n,=,6, P,<,0.001) of baseline in vector-only cells, similar to its effect in the parental line, and induced paxillin, FAK, and Src phosphorylation. However, increased pressure did not stimulate adhesion or phosphorylate paxillin, FAK, or Src further in paxillin-overexpressing cells. Metastasizing squamous cancer cell adhesiveness may be increased by paxillin-overexpression or by paxillin activation by extracellular pressure during surgical manipulation or growth within a constraining compartment. Targeting paxillin in patients with malignancy and minimal tumor manipulation during surgical resection may be important therapeutic adjuncts. J. Cell. Biochem. © 2006 Wiley-Liss, Inc. [source] Biodiesel production by direct methanolysis of oleaginous microbial biomassJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2007Bo Liu Abstract Biodiesel is a renewable fuel conventionally prepared by transesterification of pre-extracted vegetable oils and animal fats of all resources with methanol, catalyzed by strong acids or bases. This paper reports on a novel biodiesel production method that features acid-promoted direct methanolysis of cellular biomass of oleaginous yeasts and filamentous fungi. The process was optimized for tuning operation parameters, such as methanol dosage, catalyst concentration, reaction temperature and time. Up to 98% yield was reached with reaction conditions of 70 °C, under ambient pressure for 20 h and a dried biomass to methanol ratio 1:20 (w/v) catalyzed by either 0.2 mol L,1 H2SO4 or 0.4 mol L,1 HCl. Cetane numbers for these products were estimated to range from 56 to 59. This integrated method is thus effective and technically attractive, as dried microbial biomass as feedstocks omits otherwise tedious and time-consuming oil extraction processes. Copyright © 2007 Society of Chemical Industry [source] EFFECT OF HIGH PRESSURE TREATMENT ON CYTOPLASMIC 5,-NUCLEOTIDASE FROM RABBIT SKELETAL MUSCLEJOURNAL OF FOOD BIOCHEMISTRY, Issue 3 2007SUNAO MORI ABSTRACT We investigated the effect of high-pressure treatment on the properties of cytoplasmic 5, -nucleotidase (NT), which converts inosine monophosphate (IMP) into inosine. After pressure treatment at 400 MPa, the activity of purified IMP-NT remained at almost 100%, but the activity of partially purified adenosine monophosphate (AMP)-NT decreased to about 40%. These data suggest that there is a difference in the pressure stability between the enzymes. In situ fluorescence spectroscopy of IMP-NT under pressure showed that its pressure-induced denaturation was reversible. When the pressure was reduced from the highest pressure to ambient pressure, hysteresis was observed. This suggests that high pressure treatment may lead to a partial change in the affinity of the subunits for each other once they have dissociated. The activities of IMP-NT and AMP-NT extracted from pressure-treated muscles decreased remarkably between 250 and 450 MPa, but IMP-NT was more stable than AMP-NT. [source] Design of a two-step pulsed pressure-swing adsorption-based oxygen concentratorAICHE JOURNAL, Issue 2 2010V. Rama Rao Abstract A two-step pulsed pressure-swing adsorption (PPSA) process has been modeled to assess the extent to which an oxygen concentrator might be miniaturized for medical applications. The process consists of a single bed of packed adsorbent particles that is alternately pressurized and depressurized at the feed end. An enriched oxygen product is withdrawn at ambient pressure from the product end when the bed is pressurized at the feed end. The product end remains closed during depressurization. The model development addresses the manner in which axial dispersion enters into the describing equations and the formulation of proper boundary conditions, both of which have not been handled rigorously in some prior modeling studies. The describing equations are solved using COMSOL® Multiphysics software. The effect on the performance of the adsorption time, desorption time, bed length, particle diameter, and imposed pressure drop across the bed have been investigated. An interesting novel result is that for a chosen particle size, bed length, and applied pressure drop, there is an optimum combination of adsorption and desorption times that maximizes the product purity. The results suggest that there are operating windows for both 5A and partially Ag-exchanged Li-substituted 13X zeolite adsorbents wherein the product oxygen purity is greater than 90%. At a given product flow rate within this operating window, the extent of miniaturization is limited by the (maximum) cycling frequency that is practically achievable. Sizing of an oxygen concentrator for personal medical applications is also discussed. A principal conclusion is that a compact oxygen concentrator capable of producing a highly oxygen-enriched product is possible using commercially available adsorbents and implementable operating conditions. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Deep desulfurization of transportation fuels by characteristic reaction resided in adsorbentsAICHE JOURNAL, Issue 7 2009Sheng-Qiang Wang Abstract A method for deep desulfurization of transportation fuels was presented. Reactive conversion of sulfur compounds and the following adsorption occurred inside adsorbents. The condensation reaction with formaldehyde catalyzed by phosphomolybdic acid was shown effective for the removal of thiophenic and benzothiophenic compounds. Thiophene or benzothiophene of model fuels was completely removed. Coupling with an oxidation reaction, the total sulfur content of commercial fuels was dropped to below 15 ppm. Appropriate desulfur condition was at 70,80°C and ambient pressure without consumption of hydrogen. Saturated adsorbent was regenerated with heating in air at 400°C, and the sulfur capacity was almost fully recovered. Fuel quality was not negatively affected by the desulfur operation. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Pressure-induced phase transitions in L-leucine crystalJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2009P. F. Façanha Filho Abstract Raman spectra of a crystal of L -leucine, an essential amino acid, were obtained for pressures between 0 and 6 GPa. The results show anomalies at three pressure values, one between 0 and 0.46 GPa, another between 0.8 and 1.46 GPa, and a third at P , 3.6 GPa. The first two anomalies are characterized by the disappearance of lattice modes (which can indicate occurrence of phase transitions), the appearance of several internal modes, or the splitting of modes of high wavenumbers. The changes of internal modes are related to CH and CH3 unit motions as well as hydrogen bonds, as can be inferred from the behavior of bands associated with CO2, moieties. The third anomaly is a discrete change of the slopes of the wavenumber versus pressure plots for most modes observed. Further, decompression to ambient pressure generates the original Raman spectrum, showing that the pressure-induced anomalies undergone by L -leucine crystals are reversible. Copyright © 2008 John Wiley & Sons, Ltd. [source] In situ Raman scattering studies of high-pressure stability and transformations in the matrix of a nanostructured glass,ceramic compositeJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2005Kristina E. Lipinska-Kalita Abstract High-pressure Raman scattering studies have been performed on a glass-based composite consisting of nanometer-sized gallium oxide aggregates embedded in a potassium-silicate host glass using the diamond anvil cell technique. The Raman spectra of this heterophase nanocomposite showed a range of pressure-induced structural transformations occurring in the glass matrix. Compression from ambient pressure up to 10.8 GPa indicated a progressive reduction in the width of the intertetrahedral SiOSi angle distribution, which was completely reversible on decompression to ambient pressure. At higher pressures, the Raman spectra demonstrated a breakdown of the intermediate-range order in the glass matrix of the nanocomposite. The enhancement of scattering intensity in the region of the D-defect band at 565 cm,1 together with the blue shift of the main SiOSi symmetric stretching wavenumber are evidence of a permanent reduction in SiO4 ring statistics toward smaller-than-six-ring configurations in the three-dimensional glass network. Starting from 13 GPa, the Raman spectra displayed a remarkable decrease in the scattering intensity of the SiOSi symmetric stretching that has been related to a coordination change of the silicon atom. The Raman spectrum of the composite quenched from 23 GPa to ambient conditions illustrated the pressure-driven, permanent reconstructive modification of the glass matrix in the nanocomposite. The pressure-induced evolution of the Raman peaks assigned to the gallium oxide phase indicated a progressive densification of the nanocrystalline phase, reversible on decompression to ambient pressure. Copyright © 2005 John Wiley & Sons, Ltd. [source] Crystal Structure and Compressibility of Pb(Zr1,xTix)O3 Ceramics Under High PressureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Young Ho Ko X-ray diffraction patterns of Pb(Zr0.3Ti0.7)O3 and Pb(Zr0.7Ti0.3) O3 have been measured at pressures up to 36 GPa with good signal-to-noise ratio using synchrotron radiation. In order to refine the crystal structure, Rietveld analysis has been performed. The structure of Pb(Zr0.3Ti0.7)O3 is tetragonal in space group P4mm with lattice parameters a=b=3.9843±0.0003 Å and c= 4.1545±0.0003 Å at ambient pressure. A pressure-induced phase transition was found in the pressure range higher than ,7.4 GPa at room temperature. The high-pressure phase is cubic in space groupwith lattice parameter a=3.9600±0.0003 Å at 7.4 GPa. The Birch,Murnaghan equation of state fit to the experimental data yields B0=83.9±1.7 GPa (B,0=4.0 is fixed) for tetragonal phase and B0=102.5±4.4 GPa (B,0=4.0 is fixed) for cubic phase with V0=65.95±0.01 Å3. The structure of Pb(Zr0.7Ti0.3)O3 is monoclinic in space group Cc with lattice parameters a=10.0627±0.0164 Å, b=5.8511±0.0024 Å, c= 5.7949±0.0020 Å, and ,=125.185±0.119 ° at ambient pressure. No pressure-induced phase transition for Pb(Zr0.7Ti0.3)O3 was observed over the pressure range of this study. The Birch,Murnaghan equation of state fit to the experimental data yields B0=73.6±18.9 GPa (B,0=4.0 is fixed) with V0= 278.81±0.63 Å3. [source] Relaxation and Glass Transition in an Isostatically Compressed Diopside GlassJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2007Lothar Wondraczek Relaxation of isostatically compressed CaMgSi2O6 (diopside) glass is explored by ex situ differential scanning calorimetric (DSC) experiments. A diopside melt was compressed above its glass transition temperature under isostatic conditions at a pressure of 500 MPa. DSC analysis was performed at ambient pressure after slowly cooling the compressed melt under pressure (i.e., after freezing-in the densified state). Compression-induced enhancement of the overshoot in heat capacity was observed in the glass transition region. This indicates that a densified, quenched glass possesses a lower apparent fictive temperature, TfA, than a glass that was cooled under ambient pressure at the same cooling rate. However, a thermodynamic analysis indicates that the fictive temperature produced under pressure, Tf0, is actually much higher than that determined from DSC experiments at ambient pressure (Tf0>TfA). [source] From Chelating Precursor to Perovskite Oxides and Hollow Fiber MembranesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007S. Liu Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-, (BSCF) is a promising mixed-conducting ceramic membrane material in addition to being a good electrode catalyst for solid oxide fuel cells. In this study, BSCF powder was synthesized via a chelated water-soluble complex method at relatively low temperatures. The combined ethylenediaminetetraacetic acid and citric acid was used for the synthesis of a complex-based precursor, followed by thermal decomposition of the precursor at high temperatures. Thermal behavior, crystal phases, and structures of the prepared powders were characterized by thermogravimetric analysis/differential scanning calorimetry, XRD, and scanning electron microscopic (SEM) techniques, respectively. Pure and single-phase perovskite could be obtained after sintering at a temperature higher than 800°C for 5 h. The soft precursor powder synthesized at lower temperatures, i.e., 600°C, is water insoluble and more appropriate for use as a membrane material to prepare gas-tight tubular or hollow fiber ceramic membranes. By contrast, the hollow fibers prepared via the traditional techniques where the perovskite powder is used as the starting membrane materials display gas leakage. The fibers were characterized by SEM, XRD, and tested for air separation at ambient pressure and temperatures between 700° and 950°C. The oxygen flux measured in this work reached 3.90 mL·(min·cm2),1 and compares favorably with any experimental values reported in the open literature. [source] High-Temperature Rheology of Calcium Aluminosilicate (Anorthite) Glass-Ceramics under Uniaxial and Triaxial LoadingJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2001Balakrishnan G. Nair The high-temperature creep behavior of two fine-grained (,3 ,m) anorthite-rich glass-ceramics was characterized at ambient pressure and under a confining pressure of ,300 MPa. Experiments were done at differential stresses of 15,200 MPa and temperatures of 1200°,1320°C. Of the two materials, one had a tabular (lathlike) grain structure with finely dispersed second phase of mullite, mostly in the form of ,3,5 ,m grains comparable to that of the primary anorthite phase, whereas the other had an equiaxed grain morphology with fine (,400 nm) mullite precipitates concentrated at the anorthite grain boundaries. The results of creep experiments at ambient pressure showed that the material with the tabular grain structure had strain rates at least an order of magnitude faster than the equiaxed material. Creep in the tabular-grained material at ambient pressure was accompanied by a significant extent of intergranular cavitation: pore-volume analysis before and after creep in this material suggested that >75% of the bulk strain was due to growth of these voids. The equiaxed material, in contrast, showed a smooth transition from Newtonian (n= 1) creep at low stresses to non-Newtonian behavior at high stresses (n > 2). Under the high confining pressure, the microstructures of both materials underwent significant changes. Grain-boundary mullite precipitates in the undeformed, equiaxed-grain material were replaced by fine (,100 nm), intragranular precipitates of silliminate and corundum because of a pressure-induced chemical reaction. This was accompanied by a significant reduction in grain size in both materials. The substantial microstructural changes at high confining pressure resulted in substantially lower viscosities for both materials. The absence of mullite precipitates at the grain boundaries changed the behavior of the equiaxed material to non-Newtonian (n= 2) at a pressure of ,300 MPa, possibly because of a grain-boundary sliding mechanism; the tabular-grained material showed Newtonian diffusional creep under similar conditions. [source] Transparent Anatase Nanocomposite Films by the Sol,Gel Process at Low TemperaturesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000Atsunori Matsuda We have successfully prepared transparent anatase nanocomposite films on various types of substrates, including organic polymers, using the sol,gel method at temperatures <100°C under ambient pressure. This novel process is based on the findings that (i) anatase nanocrystals are uniquely formed in sol,gel-derived SiO2,TiO2 films that have been subjected to a hot-water treatment, and (ii) the addition of an organic polymer such as poly(ethylene glycol) in the films accelerates the formation of anatase nanocrystals. The film coating on the substrates is a promising candidate for use as a photocatalyst to decompose environmental pollutants and harmful microorganisms. [source] Magnetic properties of NdMn2,xFexGe2 (x = 0.3, 0.4 and 1.0) compoundsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003. Gondek Abstract Magnetic properties of the NdMn2,xFexGe2 (x = 0.3, 0.4 and 1.0) are investigated by AC magnetic measurements and neutron diffraction. In ambient pressure in compound with x = 0.3 below 200 K the noncollinear magnetic structure is observed. Above this temperature the magnetic moments transform to the collinear one. For x = 0.4 at 1.5 K the Nd magnetic moments form collinear ferromagnetic structure, while Mn moments noncollinear. With increase of the temperature at T = 50 K Nd moment disappears while Mn moments form two different magnetic structures antiferro- (AF) and ferromagnetic (F). The change between AF and F phases is connected with the change of the lattice constants. For x = 1.0 the Mn moments form collinear antiferromagnetic structure stable in the temperature range between 1.5 K and TN = 203 K. For x = 0.3 the external pressure up to 1.5 GPa causes the change of the critical temperature only, while for x = 0.4 induces the change of the magnetic properties from ferro- to antiferromagnetic. For x = 1.0 the Néel temperature increases with increasing external pressure. The above results indicate that in the NdMn2,xFexGe2 system, the increase in the iron content is followed by a change in chemical bond that influences the magnetic properties. [source] Phase separation in SiOx films annealed under enhanced hydrostatic pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2008G. Yu. Abstract The effect of enhanced hydrostatic pressure (HP, (10,12) × 108 Pa) on thermally stimulated phase decomposition of silicon suboxide layers processed at 450,1000 °C was investigated by infrared spectroscopy and photoluminescence measurements. HP stimulates decomposition of non-stoichiometric SiOx most efficiently at about 450 °C. In spite of enhanced SiOx decomposition, visible photoluminescence appears in HP-treated samples at higher annealing temperatures in comparison to those annealed under ambient pressure (AP, 105 Pa). Contrary to that, application of HP results in essential enhancement of near-infrared emission at lower annealing temperatures as compared to processing under AP. This can be related to pressure-stimulated crystallization of Si inclusions. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Structural, electronic and optical calculations of Cu(In,Ga)Se2 ternary chalcopyritesPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2004M. Belhadj Abstract In this work, we have investigated the structural, electronic and optical properties of the ternary I,III,VI2 chalcopyrite semiconductors ABX2 (A = Cu, B = In, Ga, X = Se) by means of a first-principles density-functional total-energy calculation with the local-density approximation (LDA), using the all-electron full-potential linear-augmented plane-wave method (FP-LAPW). The equilibrium lattice constants and the bulk moduli (a, c, c/a, u and B0) are compared with other theoretical calculations. The energy gap at ambient pressure is found to be direct and the nature of the gap crucially depends on the manner in which the d electrons of the A atoms are treated. We have also reported the optical properties of two chalcopyrite semiconductors CuInSe2 and CuGaSe2. Results on complex dielectric functions, refractive indices n, extinction coefficients k, and normal-incidence reflectivity R in the two crystals are given and compared with earlier data where available. We analyze in detail the structures of the dielectric function observed in the studied energy region. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||||||||||||||