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Phase Composition (phase + composition)
Kinds of Phase Composition Selected AbstractsPhase Composition and Vaporization Study of LaGa1,xAlxO3, 0 ,x, 1, and La0.9Sr0.1Ga0.8,xAlxMg0.2O2.85, x= 0.1, 0.2, 0.3JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2003Aleksandra Matraszek The vaporization of the LaGa1,xAlxO3 solid solution, 0 ,x, 1, of the perovskite structure, was investigated using Knudsen effusion mass spectrometry in the temperature range of 1623,1928 K. The partial pressures of the gaseous species O2, Ga, GaO, Ga2O, and LaO were determined for the samples investigated. The equilibrium partial pressures were used for the computation of thermodynamic activities of Ga2O3 and La2O3 at 1800 K. Thermodynamic activities of Al2O3 were obtained using Gibbs,Duhem integration. Gibbs energies of formation of the solid-solution LaGa1,xAlxO3 resulted from the thermodynamic activities of the oxide components. Samples of the chemical composition La0.9Sr0.1Ga0.8,xAlxMg0.2O2.85, x= 0.1, 0.2, 0.3, were of practical importance in solid oxide fuel cell (SOFC) technology and also were investigated. The influence of the aluminum concentration in the perovskite phase on the thermodynamic activity and volatility of Ga2O3 is presented and implications for the potential use of this material in SOFC technology are discussed. [source] Aging Effects on the Phase Composition and Chain Mobility of Isotactic Poly(propylene)MACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2008Cristian Hedesiu Abstract Changes in phase composition and chain mobility in injection-molded isotactic poly(propylene), crystallized from the melt with slow cooling rate and subsequently quenched, associated with aging at temperature well above Tg for 150 and 1 000 h, are studied using time-domain 1H solid-state NMR and XRD. All sample exhibit physical aging when exposed to elevated temperatures, and the physical aging kinetics was observed to depend on the morphology of the homopolymer iPP and aging temperatures. The significant increase in the tensile modulus in time was observed for injection-molded iPP. The observed property changes induced by aging are attributed to microstructural changes within the semi-rigid and amorphous fractions. [source] Fabrication of an Al2O3/YAG/ZrO2 Ternary Eutectic by Combustion Synthesis Melt Casting Under Ultra-High GravityJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2009Rui Liang This work presents a novel method for preparing an Al2O3/YAG/ZrO2 ternary eutectic whereby combustion synthesis melt casting has been combined with the ultra-high gravity (UHG) technique. The fabricated product had a relative density of 99.3% of the theoretical one. Phase composition and microstructure analyses indicated that the application of UHG resulted in a metal-free ceramic microstructure with no porosity or microcracks. The microstructure comprises ZrO2 rods dispersed in Al2O3. The product had 17.82 GPa Vickers hardness and 5.51 MPa·m1/2 fracture toughness. [source] Capillary electrochromatography with monolithic silica column:,I.ELECTROPHORESIS, Issue 3 2003Preparation of silica monoliths having surface-bound octadecyl moieties, applications to the separation of neutral, charged species, their chromatographic characterization Abstract Monolithic silica columns with surface-bound octadecyl (C18) moieties have been prepared by a sol-gel process in 100 ,m ID fused-silica capillaries for reversed-phase capillary electrochromatography of neutral and charged species. The reaction conditions for the preparation of the C18-silica monoliths were optimized for maximum surface coverage with octadecyl moieties in order to maximize retention and selectivity toward neutral and charged solutes with a sufficiently strong electroosmotic flow (>,2 mm/s) to yield rapid analysis time. Furthermore, the effect of the pore-tailoring process on the silica monoliths was performed over a wide range of treatment time with 0.010 M ammonium hydroxide solution in order to determine the optimum time and conditions that yield mesopores of narrow pore size distribution that result in high separation efficiency. Under optimum column fabrication conditions and optimum mobile phase composition and flow velocity, the average separation efficiency reached 160,000 plates/m, a value comparable to that obtained on columns packed with 3 ,m C18-silica particles with the advantages of high permeability and virtually no bubble formation. The optimized monolithic C18-silica columns were evaluated for their retention properties toward neutral and charged analytes over a wide range of mobile phase compositions. A series of dimensionless retention parameters were evaluated and correlated to solute polarity and electromigration property. A dimensionless mobility modulus was introduced to describe charged solute migration and interaction behavior with the monolithic C18-silica in a counterflow regime during capillary electrochromatography (CEC )separations. The mobility moduli correlated well with the solute hydrophobic character and its charge-to-mass ratio. [source] Tartatric Acid and L -Cysteine Synergistic-Assisted Synthesis of Antimony Trisulfide Hierarchical Structures in Aqueous SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 35 2009Jun Pan Abstract Alveolate amorphous Sb2S3 microspheres about 2 ,m in diameter were hydrothermally synthesized in aqueous solution without the use of a surfactant at 180 °C by using SbCl3, L -cysteine, and tartaric acid as starting materials. After annealing at 250 °C for 3 h under a nitrogen atmosphere, polycrystalline Sb2S3 hollow spheres were obtained. The morphology, structure, and phase composition of alveolate Sb2S3 microspheres were characterized by X-ray diffraction, field-emission scanning electron microscopy, energy dispersive X-ray analysis, and X-ray photoelectron spectroscopy. It was demonstrated that tartaric acid and L -cysteine play a key role in the formation of such hierarchical structures. In addition, the possible aggregation mechanism was proposed to illustrate the formation of Sb2S3 microspheres on the basis of the experimental results and analyses.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] The seismic response to overpressure: a modelling study based on laboratory, well and seismic dataGEOPHYSICAL PROSPECTING, Issue 5 2001José M. Carcione We investigate the seismic detectability of an overpressured reservoir in the North Sea by computing synthetic seismograms for different pore-pressure conditions. The modelling procedure requires the construction of a geological model from seismic, well and laboratory data. Seismic inversion and AVO techniques are used to obtain the P-wave velocity with higher reliability than conventional velocity analysis. From laboratory experiments, we obtain the wave velocities of the reservoir units versus confining and pore pressures. Laboratory experiments yield an estimate of the relationship between wave velocities and effective pressure under in situ conditions. These measurements provide the basis for calibrating the pressure model. Overpressures are caused by different mechanisms. We do not consider processes such as gas generation and diagenesis, which imply changes in phase composition, but focus on the effects of pure pore-pressure variations. The results indicate that changes in pore pressure can be detected with seismic methods under circumstances such as those of moderately deep North Sea reservoirs. [source] Gate Dielectric Microstructural Control of Pentacene Film Growth Mode and Field-Effect Transistor Performance,ADVANCED MATERIALS, Issue 18 2007C. Kim Organic semiconductor/dielectric interfacial characteristics play a critical role in influencing organic thin-film transistor (OTFT) performance characteristics (see figure). Clear correlations between pentacene film deposition temperature, estimated polymer dielectric surface microstructural mobility, and the corresponding film growth mode, semiconductor phase composition, and carrier mobilities are established. [source] The influence of the acidic component of the gas-foaming porogen used in preparing an injectable porous calcium phosphate cement on its properties: Acetic acid versus citric acidJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Saeed Hesaraki Abstract In the present study, macroporous calcium phosphate cements (CPCs) were prepared using a porogen; that is, the gas-foaming technique. The objective was to investigate the influence of the acidic component of the porogen (acetic acid versus citric acid) on several properties of a specified CPC. In all of the cements prepared, the basic component of the porogen was the same, namely, NaHCO3, and it was added to the powder phase of the cement, while the acidic component of the porogen was dissolved in the liquid phase of the cement. The cements were characterized in terms of initial setting time, porosity, crystallinity, injectability and compressive strength. Also, XRD, FTIR, and SEM techniques were employed to evaluate the phase composition, the chemical groups and the morphological aspects of the porous cements during setting. It was found that the presence of a porogen in a CPC led to significant decreases in both its initial setting time and compressive strength. A CPC made using acetic acid contained a larger amount of the apatite phase but was significantly less injectable and less porous than when citric acid was used. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] Changes in Apple Liquid Phase Concentration throughout Equilibrium in Osmotic DehydrationJOURNAL OF FOOD SCIENCE, Issue 2 2007J.M. Barat ABSTRACT:, Previous results on apple tissue equilibration during osmotic dehydration showed that, at very long processing times, the solute concentrations of the fruit liquid phase and the osmotic solution were the same. In the present study, changes in apple liquid phase composition throughout equilibrium in osmotic dehydration were analyzed and modeled. Results showed that, by the time osmosed samples reached the maximum weight and volume loss, solute concentration of the fruit liquid phase was higher than that of the osmotic solution. The reported overconcentration could be explained in terms of the apple structure shrinkage that occurred during the osmotic dehydration with highly concentrated osmotic solutions due to the elastic response of the food structure to the loss of water and intake of solutes. The fruit liquid phase overconcentration rate was observed to depend on the concentration of the osmotic solution, the processing temperature, the sample size, and shape of the cellular tissue. [source] A sequence optimization strategy for chromatographic separation in reversed-phase high-performance liquid chromatographyAICHE JOURNAL, Issue 2 2010Xueling Du Abstract A sequence optimization strategy combining an artificial neural network (ANN) and a chromatographic response function (CRF) for chromatographic separation in reversed-phase high-performance liquid chromatography has been proposed. Experiments were appropriately designed to obtain unbiased data concerning the effects of varying the mobile phase composition, flow-rate, and temperature. The ANN was then used to simultaneously predict the resolution and analysis time, which are the two most important features of chromatographic separation. Subsequently, a CRF consisting of resolution and analysis time was used to predict the optimum operating conditions for different specialized purposes. The experimental chromatograms were consistent with those predicted for given conditions, which verified the applicability of the method. Furthermore, the proposed optimization strategy was applied to literature data and very good agreement was obtained. The results show that a strategy of sequential combination of ANN and CRF can provide a more flexible and efficient optimization method for chromatographic separation. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Influence of mobile phase composition on the high-performance liquid chromatographic/electrospray ionization mass spectrometric analysis of 11-nor-9-carboxy-,9 -tetrahydrocannabinol (THC-COOH) and its glucuronide in urineJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2004[source] Microstructural analysis of iron aluminide formed by self-propagating high-temperature synthesis mechanism in aluminium matrix compositeJOURNAL OF MICROSCOPY, Issue 1 2006ANITA OLSZÓWKA-MYALSKA Summary An aluminium matrix composite with iron aluminide formed in situ as a result of self-propagated high-temperature synthesis was examined. The structural characteristics of the reinforcement investigated by scanning electron microscopy and transmission electron microscopy methods are presented. Iron aluminide particles with a very fine grain size and of two shapes, cubic and needle-like, were observed. No differences in their phase composition were found by the selective electron diffraction pattern method. The composite reinforcement formed in the early stage of self-propagating high-temperature synthesis consisted only of the Al3Fe phase. [source] Solvent-mediated solid phase transformations of carbamazepine: Effects of simulated intestinal fluid and fasted state simulated intestinal fluidJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2009Paula Lehto Abstract Solvent-mediated transformations of carbamazepine (CBZ) anhydrate form III were investigated in Simulated Intestinal Fluid, a simple USP buffer medium, and in FaSSIF, which contains sodium taurocholate (STC) and lecithin, important surfactants that solubilize lipophilic drugs and lipids in the gastrointestinal tract. Raman spectroscopy (in situ) was utilized to reveal the connection between the changes in solid phase composition and dissolution rate while simultaneously detecting the solid state and the dissolved amount of CBZ. Initial dissolution rate was clearly higher in FaSSIF, while the solid phase data revealed that the crystallization of CBZ dihydrate was inhibited in both the dissolution media, albeit by different mechanisms. In SIF this inhibition was related to extensive needle growth, which impeded medium contact with the solid surface by forming a sterical barrier leading to retarded crystallization rates. Morphological changes from the needle-like dihydrate crystals to plate-like counterparts in FaSSIF, combined with the information that the transformation process was leveled off, evidenced strong hydrogen bonding behavior between the CBZ and STC molecules. These results underline the importance of biologically representative dissolution media in linking the in vitro dissolution results of solids that are capable of hydrate formation to their in vivo dissolution behavior. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:985,996, 2009 [source] Raman spectroscopy of Bi-Te thin filmsJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2008V. Russo Abstract The deposition of micro- and nanocrystalline bismuth telluride thin films with tailored structure and composition is of interest in view of improving the well-known material thermoelectric properties. Only a few works exist that discuss Raman scattering of Bi2Te3 crystals and films, while a Raman characterization of other phases, i.e. other lesser known compounds of the Bi-Te system, such as tsumoite (BiTe) and pilsenite (Bi4Te3), is still completely lacking. We here present a Raman investigation of Bi-Te polycrystalline thin films with controlled structure (stoichiometry and growth orientation), morphology and phase composition, produced by nanosecond pulsed laser deposition. Interpretation of Raman spectra from Bi-Te films was supported by scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-Ray diffraction measurements, together with the predictions of the group theory. In this way, the first Raman characterization of Bi-rich phases (namely BiTe and Bi4Te3) has been obtained. For Bi-Te compositions characterized by a high Bi or Te content, Raman spectra reveal that segregation of elemental Bi or Te occurs. Copyright © 2008 John Wiley & Sons, Ltd. [source] Methacrylate ester-based monolithic columns for nano-LC separation of tocopherols in vegetable oilsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17-18 2010María Jesús Lerma-García Abstract The separation and determination of tocopherols (Ts) in vegetable oils by nano-LC chromatography with UV,vis detection using lauryl methacrylate ester-based monolithic columns has been developed. The separation of Ts was optimized in terms of mobile phase composition on the basis of the best compromise among efficiency, resolution and analysis time. Using a mobile phase composed of ACN/methanol/water, an excellent resolution between Ts was achieved within 18,min. The LODs were lower than 0.26,,g/mL, being repeatability values of retention time and peak area below 0.15 and 3.1%, respectively. The method was applied to the quantification of Ts and tocotrienols present in several vegetable oils from different botanical origins. [source] Comparison of HPLC enantioseparation of substituted binaphthyls on CD-, polysaccharide- and synthetic polymer-based chiral stationary phasesJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9 2010Lucie Loukotková Abstract Retention and enantioseparation behavior of ten 2,2,-disubstituted or 2,3,2,-trisubstituted 1,1,-binaphthyls and 8,3,-disubstituted 1,2,-binaphthyls, which are used as catalysts in asymmetric synthesis, was investigated on eight chiral stationary phases (CSPs) based on ,-CD, polysaccharides (tris(3,5-dimethylphenylcarbamate) cellulose or amylose CSPs) and new synthetic polymers (trans -1,2-diamino-cyclohexane, trans -1,2-diphenylethylenediamine and trans -9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-11,12-dicarboxylic acid CSPs). Normal-, reversed-phase and polar-organic separation modes were employed. The effect of the mobile phase composition was examined. The enantiomeric separation of binaphthyl derivatives, which possess quite similar structures, was possible in different enantioselective environments. The substituents and their positions on the binaphthyl skeleton affect their properties and, as a consequence, the separation system suitable for their enantioseparation. In general, the presence of ionizable groups on the binaphthyl skeleton, substitution with non-identical groups and a chiral axis in the 1,2, position had the greatest impact on the enantiomeric discrimination. The 8,3,-disubstituted 1,2,-binaphthyl derivatives were the most easily separated compounds in several separation systems. From all the chiral stationary phases tested, cellulose-based columns were shown to be the most convenient for enantioseparation of the studied analytes. However, the polymeric CSPs with their complementary behavior provided good enantioselective environments for some derivatives that could be hardly separated in any other chromatographic system. [source] Determination of pKa values of nonsteroidal antiinflammatory drug-oxicams by RP,HPLC and their analysis in pharmaceutical dosage formsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2009Ebru Cubuk Demiralay Abstract In this study, pKa values were determined by using the dependence of the capacity factor on the pH of the mobile phase for four ionizable substances, namely, tenoxicam, piroxicam, meloxicam, and naproxen (I.S.). The effect of the mobile phase composition on the ionization constant was studied by measuring the pKa at different ACN concentrations, ranging from 30 to 40%. The adequate condition for the chromatographic determination of these compounds in pharmaceutical dosage forms was established based on the different retention behaviors of the species. An octadecylsilica Nucleosil C18 column (150×4.6 mm, 5 ,m) was used for all the determinations. The chromatographic separation of oxicams was carried out using acetonitrile (ACN)/water at 35% v/v, containing 65 mM phosphoric acid and UV detection at a wavelength of 355 nm. The method developed was successfully applied to the simultaneous determination of these drug compounds in laboratory-prepared mixtures and their commercial pharmaceutical dosage forms. Each analysis requires no longer than 12 min. [source] HPLC enantioseparation of ,2 -homoamino acids using crown ether-based chiral stationary phaseJOURNAL OF SEPARATION SCIENCE, JSS, Issue 7 2009Róbert Berkecz Abstract RP high-performance liquid chromatographic methods were developed for the enantioseparation of eleven unusual ,2 -homoamino acids. The underivatized analytes were separated on a chiral stationary phase containing (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as chiral selector. The effects of organic (alcoholic) and acidic modifiers, the mobile phase composition and temperature on the separation were investigated. The structures of the substituents in the ,-position of the analytes substantially influenced the retention and resolution. The elution sequence was determined in some cases: the S enantiomers eluted before the R enantiomers. [source] Pharmaceutical analysis by supercritical fluid chromatography: Optimization of the mobile phase composition on a 2-ethylpyridine columnJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2008Claudio Brunelli Abstract The separation of neutral, acidic, and basic pharmaceuticals with diverse physicochemical properties by packed column supercritical fluid chromatography (pSFC) on a 2-ethylpyridine column (25 cm×4.6 mm id, 3 ,m particles) is presented. The optimization strategy involved separations at 100% methanol (MeOH) and at 50% MeOH/50% ACN while keeping the peak symmetry additives formic acid (FA) and isopropylamine (IPA) at constant levels of 0.25% v/v. By plotting the adjusted retention times as a function of the MeOH/ACN ratio, an optimal modifier ratio composition of 65% MeOH/35% ACN was found. The total set of 26 neutral, acidic, and basic pharmaceuticals was analyzed and the optimal composition experimentally verified. This mobile phase composition is currently used in pharmaceutical method development and open-access generic screening environments. [source] Development and validation of a stereoselective HPLC method for the determination of the in vitro transport of nateglinide enantiomers in rat intestineJOURNAL OF SEPARATION SCIENCE, JSS, Issue 12 2007Srinivas Maddi Abstract A simple stereoselective high performance liquid chromatographic method was developed for the determination of the in vitro transport of the enantiomers of nateglinide (N -(trans -4-isopropylcyclohexyl-carbonyl)-phenylalanine) in the rat intestine using a Chiralcel OJ-RH column (150×4.0 mm, 5 ,m). The effects of the mobile phase composition, pH, the flow rate, and the temperature on the chromatographic separation were investigated. The enantioseparation was achieved at 33°C using a mobile phase containing 100 mM potassium dihydrogen phosphate, pH 2.5, and ACN (32:68 v/v) delivered at a flow rate of 1 mL/min. The analytes were monitored at 210 nm and linearity (r >0.99) was obtained for a concentration range of 0.5,50 ,g/mL. The LOD and LOQ were 0.2 and 0.5 ,g/mL for the R -enantiomer and 0.2 and 0.8 ,g/mL for the S -enantiomer, respectively. Both, the intra- and interday accuracy and precision of the calibration curves were determined. The method was successfully applied to estimate the in vitro passage of the enantiomers and the racemate of nateglinide in duodenum, jejunum, and ileum of rats. Generally, higher concentrations of nateglinide and the S -enantiomer were observed when the racemate was administered compared to administration of the individual enantiomers of nateglinide. [source] High-performance liquid chromatographic resolution of 1-(1,4-benzodioxane-2-formyl)- piperazine enantiomers after chiral derivatizationJOURNAL OF SEPARATION SCIENCE, JSS, Issue 2 2005Zhiqiong Chen Abstract Chiral separation of racemic mixtures is of the greatest importance to the pharmaceutical industry, as the isomers of a given racemate may exhibit substantially different pharmacological effects, not to mention possibly differing toxicity behaviour. A novel chiral separation method is developed for the determination of 1-(1,4-benzodioxane-2-formyl)piperazine (BFP) enantiomers. The indirect resolution is performed by applying precolumn derivatization with the chiral reagent 2,3,4,6-tetra- O -acetyl-,-D-glucopyranosyl isothiocyanate (GITC). The resulting diastereoisomers are separated on a reversed-phase ODS column with methanol-potassium dihydrogen phosphate (0.02mol/L, 50:50) as mobile phase. UV detection is at 250 nm. The effect of mobile phase composition upon resolution and analysis time is investigated. Two diastereoisomers show nearly base-line separation under optimal chromatographic conditions. The presented study provides a simple and accurate method for the enantiomeric quality control and the optical purity assay of BFP. [source] A theoretical explanation for the retention mechanism of ion exclusion chromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 17 2003Bronis, aw K. G Abstract Ion Exclusion Chromatography is classically used for the separation of weak acid anions. Dilute strong acids (e.g. sulphuric or perchloric acid) or just water are used as eluents. To increase the exclusion effect, strong cation exchangers, characterized by high concentration of functional groups, are applied. The inner column volume of commercially available columns is increased by increasing their size in comparison to traditional ones (usually 300×7.8 mm ID). The description of the retention mechanism of this technique implicitly assumes that both mobile and stationary phases are typical aqueous solutions, and their dielectric constants are thus equal. This equality implies the equality of solute dissociation constants in both phases. Another implicit assumption is that the dead- and inner volumes of the column are constant, and independent of the mobile phase composition. The present paper shows that stationary and mobile phases are generally characterized by different physicochemical parameters. Thus, they cannot be considered as regular aqueous solutions. Additionally, we show that weak cation exchanger resins, which are characterized by a relatively small concentration of the functional groups, and weak acid based buffers can also be used in IEC. This would expand the possible applications of this method and enable, for example, the separation of strong acids (anions). The influence of ionic strength on the retention and dead- and inner column volumes is also discussed. Finally we also briefly describe the retention mechanism of Electrostatic Ion Chromatography. [source] Stationary and mobile phases in capillary electrochromatography (CEC)JOURNAL OF SEPARATION SCIENCE, JSS, Issue 15-16 2003Jan Jiskra Abstract This review describes the state of the art of capillary electrochromatography (CEC). Properties of and interactions between stationary and mobile phases applied in CEC are described and discussed; developments in stationary phases, partly also monolithic stationary phases, are reviewed. Special attention is paid to the comparison of the behaviour of stationary and/or mobile phases under CEC versus HPLC conditions with respect to variables such as particle and pore size of the stationary phase, mobile phase composition, and temperature. These issues are discussed throughout the paper. A number of applications in CEC is presented as well. [source] Investigation of factors influencing the performance of open-tubular stationary phases in capillary electrochromatographyJOURNAL OF SEPARATION SCIENCE, JSS, Issue 9-10 2003Ruth Freitag Abstract Silica-based, open-tubular capillary columns bearing C8-moieties were produced by the sol gel approach. The influence of experimental conditions adjusted during the preparation of the stationary phase on the performance of the resulting capillary column were investigated in terms of the plate height, the resolution, and the capacity factors, taking the separation of three non-charged polyaromatic hydrocarbons (naphthalene, phenanthrene, pyrene) as example. Acetone served as EOF marker. The optimal synthesis protocol was then used to prepare columns for an analogous investigation of the chromatographic parameters, namely the mobile phase composition, the applied voltage and temperature, as well as the column length, thickness, and inner diameter on the performance of the capillary columns. [source] Solid-state kinetics from time-resolved in situ XAFS investigations: reduction and oxidation of molybdenum oxidesJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001T. Ressler The reduction of MoO3 with hydrogen was studied by in situ X-ray absorption spectroscopy. The experiments performed focused on elucidating phase composition and evolution with time under isothermal reduction conditions. From temperature programmed experiments short-range structural details about the early stage of the reduction were obtained. [source] Bi2O3,MoO3 Binary System: An Alternative Ultralow Sintering Temperature Microwave DielectricJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Di Zhou Preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver and aluminum electrodes were investigated on a series of single-phase compounds in the Bi2O3,MoO3 binary system. All materials have ultralow sintering temperatures <820°C. Eight different xBi2O3,(1,x)MoO3 compounds between 0.2,x,0.875 were fabricated and the associated microwave dielectric properties were studied. The ,-Bi2Mo2O9 single phase has a positive temperature coefficient of resonant frequency (TCF) about +31 ppm/°C, with a permittivity ,r=38 and Qf=12 500 GHz at 300 K and at a frequency of 6.3 GHz. The ,-Bi2Mo3O12 and ,-Bi2MoO6 compounds both have negative temperature coefficient values of TCF,,215 and ,,114 ppm/°C, with permittivities of ,r=19 and 31, Qf=21 800 and 16 700 GHz at 300 K measured at resonant frequencies of 7.6 and 6.4 GHz, respectively. Through sintering the Bi2O3,2.2MoO3 at 620°C for 2 h, a composite dielectric containing both , and , phase can be obtained with a near-zero temperature coefficient of frequency TCF=,13 ppm/°C and a relative dielectric constant ,r=35, and a large Qf,12 000 GHz is also observed. Owing to the frequent difficulty of thermochemical interactions between low sintering temperature materials and the electrode materials during the cofiring, preliminary investigations are made to determine any major interactions with possible candidate electrode metals, Ag and Al. From the above results, the low sintering temperature, good microwave dielectric properties, chemical compatibility with Al metal electrode, nontoxicity and price advantage of the Bi2O3,MoO3 binary system, all indicate the potential for a new material system with ultralow temperature cofiring for multilayer devices application. [source] Sintering Diamond/Cemented Carbides by the Pulse Plasma Sintering MethodJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2008Andrzej Michalski Under the conditions of thermodynamic instability, we produced dense sintered composites built of diamond particles (30 vol%) and a cemented carbide matrix. The composites were consolidated by high-current electric pulses at a temperature of about 1100°C and load of 75 MPa for 5 min. The diamond particles are strongly bound with the cemented carbide matrix, by a transition layer composed of a solid solution of carbon and tungsten in cobalt. No graphite precipitates were found in the sintered composites, as examined by microstructure observations, examinations of the phase composition, and an analysis of the Raman scattering spectra. The hardness of the diamond/cemented carbide was 23 GPa. [source] Controlling the Size and Morphology of TiO2 Powder by Molten and Solid Salt SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Banasri Roy Nano and submicrometer scale titanium oxide (TiO2) powders were synthesized by solid and molten salt synthesis (SSS and MSS) from amorphous titanium hydroxide precipitate. Sodium chloride (NaCl) and dibasic sodium phosphate (Na2HPO4·2H2O, DSP) separately or as mixture with different weight ratios were used as the salts. At the eutectic salt composition (20% DSP/80% NaCl), the microstructure and phase composition of the TiO2 was changed from equiaxed nanoparticles of anatase with size ,40,50 nm, to mixed microstructure of bundle and acicular particles of rutile with 0.05,0.2 ,m diameter, 6,10 ,m length, and aspect ratio 20,60 depending on treatment time and temperature. At high temperature (825°C) and long time (30 h), microstructural differences were significant for the powders treated with different salts. Particle morphologies ranged from equiaxed, to acicular, to bundles, to nanofibers with very high aspect ratio. At lower treatment temperature (725°C) for shorter time (3 h), the morphology of the products did not change with different salt compositions, but the crystallite sizes changed appreciably. Different starting titanium precursors influenced particle size at lower temperature and time. Titanium hydroxide heat treated without salt resulted in significant grain growth and fused secondary particles, as compared with more finely separated and lightly agglomerated powders resulting from SSS and MSS treatments. [source] Thermophysical Properties of Complex Rare-Earth Zirconate Ceramic for Thermal Barrier CoatingsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2008Liu Ling Two complex rare-earth zirconates (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 and (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 for thermal barrier coatings (TBCs) were synthesized by the coprecipitation method. Their phase composition, microstructure, and thermophysical properties were investigated. X-ray diffractometry results revealed that single-phase (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 and (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 with pyrochlore structure were prepared, and the scanning electron microscopy results showed that the microstructures of the products were dense and no other phases existed among the grains. With the temperature increasing, the thermal expansion coefficient (CTE) of the ceramics increased, while the thermal conductivity decreased. The results indicated that the CTE of (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 was slightly higher than that of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 and the thermal conductivity of (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 was lower than that of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4. These results imply that the thermophysical properties of (Sr0.1La0.3Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.3 are better than that of (La0.4Sm0.5Yb0.1)2(Zr0.7Ce0.4)2O7.4 as the material for the ceramic layer in the TBC system. [source] Neutron Diffraction of Zirconia-Dispersed Alumina with Increasing Stress and TemperatureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2008Geoffrey A. Carter Neutron and X-ray diffraction were used to investigate changes in the phase composition and lattice parameters with temperature and pressure of a 20-wt% zirconia-dispersed alumina composite. Neutron diffraction was used to determine the variation of tetragonal/monoclinic zirconia phase abundance for the bulk with stress. The bulk tetragonal/monoclinic ratio decreased by 40% for a stress of 550 MPa. A difference in the tetragonal/monoclinic ratio between the near-surface and the bulk of the processed samples is believed to contribute to observed variations in nonuniform strain in the matrix, which has the effect of prestressing the sample. Placing a stress on the sample initially releases this prestressing. [source] | ||||||||||||||||||||||