Showing papers on "Atmospheric temperature range published in 2013"

Tensile lattice strain accelerates oxygen surface exchange and diffusion in La1-xSrxCoO3-δ thin films.

Abstract: The influence of lattice strain on the oxygen exchange kinetics and diffusion in oxides was investigated on (100) epitaxial La1–xSrxCoO3−δ (LSC) thin films grown by pulsed laser deposition. Planar tensile and compressively strained LSC films were obtained on single-crystalline SrTiO3 and LaAlO3. 18O isotope exchange depth profiling with ToF-SIMS was employed to simultaneously measure the tracer surface exchange coefficient k* and the tracer diffusion coefficient D* in the temperature range 280–475 °C. In accordance with recent theoretical findings, much faster surface exchange (∼4 times) and diffusion (∼10 times) were observed for the tensile strained films compared to the compressively strained films in the entire temperature range. The same strain effect—tensile strain leading to higher k* and D*—was found for different LSC compositions (x = 0.2 and x = 0.4) and for surface-etched films. The temperature dependence of k* and D* is discussed with respect to the contributions of strain states, formation en...

Synthesis and Thermophysical Properties of Biocompatible Cholinium-Based Amino Acid Ionic Liquids

Abstract: Nowadays the knowledge of thermodynamic properties for amino acid ionic liquids (AAILs) has been paramount for the design of many chemical processes. In this present work, a series of cholinium-based AAILs ([Ch][AA]) were synthesized by neutralization of choline hydroxide solution with five amino acids and then were characterized by 1H NMR, Fourier transform infrared (FT-IR), elemental analysis, thermogravimetry, and differential scanning calorimetry (DSC) analysis. Physico-chemical properties such as density, viscosity, refractive index, and conductivity were measured and correlated with the empirical equations in a wide temperature range. The thermal expansion coefficient values were also calculated from the acquired experimental density values. From the experimental data, it was found that the density, viscosity, and refractive index decreased while conductivity increased with the increase of temperature. The correlation results were proposed to be in good agreement with the experimental data, and opti...

WGS Catalysis and In Situ Studies of CoO1–x, PtCon/Co3O4, and PtmCom′/CoO1–x Nanorod Catalysts

Abstract: Water-gas shift (WGS) reactions on Co3O4 nanorods and Co3O4 nanorods anchoring singly dispersed Pt atoms were explored through building correlation of catalytic performance to surface chemistry of catalysts during catalysis using X-ray absorption spectroscopy, ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and environmental TEM. The active phase of pure Co3O4 during WGS is nonstoichiometric cobalt monoxide with about 20% oxygen vacancies, CoO0.80. The apparent activation energy (Ea) in the temperature range of 180-240 °C is 91.0 ± 10.5 kJ mol(-1). Co3O4 nanorods anchoring Pt atoms (Pt/Co3O4) are active for WGS with a low Ea of 50.1 ± 5.0 kJ mol(-1) in the temperature range of 150-200 °C. The active surface of this catalyst is singly dispersed Pt1Co(n) nanoclusters anchored on Co3O4 (Pt1/Co3O4), evidenced by in situ studies of extended X-ray absorption fine structure spectroscopy. In the temperature range of 200-300 °C, catalytic in situ studies suggested the formation of Pt(m)Co(m') nanoclusters along with the reduction of Co3O4 substrate to CoO(1-x). The new catalyst, Pt(m)Co(m')/CoO(1-x) is active for WGS with a very low Ea of 24.8 ± 3.1 kJ mol(-1) in the temperature range of 300-350 °C. The high activity could result from a synergy of Pt(m)Co(m') nanoclusters and surface oxygen vacancies of CoO(1-x).

A high temperature and atmospheric pressure experimental and detailed chemical kinetic modelling study of 2-methyl furan oxidation.

Abstract: An experimental ignition delay time study for the promising biofuel 2-methyl furan (2MF) was performed at equivalence ratios of 0.5, 1.0 and 2.0 for mixtures of 1% fuel in argon in the temperature range 1200-1800 K at atmospheric pressure. Laminar burning velocities were determined using the heat-flux method for mixtures of 2MF in air at equivalence ratios of 0.55-1.65, initial temperatures of 298-398 K and atmospheric pressure. A detailed chemical kinetic mechanism consisting of 2059 reactions and 391 species has been constructed to describe the oxidation of 2MF and is used to simulate experiment. Accurate reproduction of the experimental data has been obtained over all conditions with the developed mechanism. Rate of production and sensitivity analyses have been carried out to identify important consumption pathways of the fuel and key kinetic parameters under these conditions. The reactions of hydrogen atom with the fuel are highlighted as important under all experimental conditions studied, with abstraction by the hydrogen atom promoting reactivity and hydrogen atom addition to the furan ring inhibiting reactivity. This work, to the authors knowledge, is the first to combine theoretical and experimental work to describe the oxidation of any of the alkylated furans. The mechanism developed herein to describe 2MF combustion should also function as a sub-mechanism to describe the oxidation of 2,5-dimethyl furan whilst also providing key insights into the oxidation of this similar biofuel candidate.

Magnetic behavior and dielectric properties of aluminum substituted M-type barium hexaferrite

Abstract: Various parameters in the structural features of the aluminum substituted barium hexagonal ferrite particles BaAlxFe12−xO19 with 0≤x≤3.5 which were prepared by the solid state reaction method have been studied. The infrared transmission spectrum was measured in the wave number region 5000–200 cm−1 at room temperature. The results were interpreted in terms of the vibrations of the isolated molecular units in such a way to preserve the tetrahedral and octahedral clusters of metal oxides in the barium aluminum hexagonal ferrites. The infrared features are assigned to Fe–O and Ba–O bonds in M-type hexagonal ferrite (BaFe12O19) molecules. Also, the results explain the structural model, based on the effect of aluminum substitution “Al–O bond”. On the other hand, the magnetic behavior of the samples was studied using the vibrating sample magnetometer technique. The saturation magnetization (Ms) and magneton number (nB) decrease with increasing Al3+ substitution from 61.2 to 28.9 emu/g and from 12.2 to 5.3 µB respectively. Also, all samples were characterized using X-ray diffraction and the values of grain size, microstrain and dislocation density of all samples were calculated. The dielectric parameters and ac conductivity measurements were performed within a temperature range 293–493 K. The ac conductivity showed a linear relation with the frequency power law with an exponent s≈0.69–0.14 for BaFe12O19. It decreases with increasing temperature, indicating that the heterogeneous structures increase. While the dielectric constant (e′) and the dielectric loss (e″) decrease with increasing Al substitution.

Chemical stability of cubic Li7La3Zr2O12 with molten lithium at elevated temperature

Abstract: Cubic garnet of nominal composition Li7La3Zr2O12 (LLZO) is of interest as a possible electrolyte in a Li–metal halide battery composed of molten Li and an insoluble metal halide as electrodes operating in the temperature range of ~300–350 °C. As a consequence, the chemical stability of LLZO with molten Li in this temperature range was investigated. After heating in molten Li, the LLZO surface had undergone chemical coloration. X-diffraction, X-ray photoemission spectroscopy, electron paramagnetic resonance, and heat-treatment experiments suggest that chemical coloration is a result of the formation of color centers, composed of an electron trapped at an oxygen vacancy. It was also observed that after immersion in molten Li that LLZO exhibited intergranular cracking. It is believed that cracking results from stresses generated from an increased Li+ content, gained during immersion.

Optical temperature sensing of NaYbF4: Tm3+@SiO2 core-shell micro-particles induced by infrared excitation.

Abstract: NaYbF(4):Tm3+@SiO(2) core-shell micro-particles were synthesized by a hydrothermal method and subsequent ultrasonic coating process. Optical temperature sensing has been observed in NaYbF4: Tm(3+)@SiO(2)core-shell micro-particles with a 980 nm infrared laser as excitation source.The fluorescence intensity ratios, optical temperature sensitivity, and temperature dependent population re-distribution ability from the thermally coupled (1)D(2)/(1)G(4) and (3)F(2) /(3)H(4) levels of the Tm(3+) ion have been analyzed as a function of temperature in the range of 100~700 K in order to check its availability as a optical temperature sensor. A better behavior as a lowtemperature sensor has been obtained with a minimum sensitivity of 5.4 × 10(-4) K(-1) at 430 K. It exhibits temperature induced population re-distribution from (1)D(2) /(1)G(4) thermally coupled levels at higher temperature range.

Enhanced thermoelectric performance of Ca-doped BiCuSeO in a wide temperature range

Abstract: The effect of Ca substitution on microstructure and thermoelectric transport properties of BiCuSeO oxyselenide has been studied. The substitution of Ca2+ for Bi3+ reduces both electrical resistivity and Seebeck coefficient due to an increased carrier concentration. However, the enhanced electrical conductivity compensates for the decrease of Seebeck coefficient, and consequently the power factor is greatly improved in the whole temperature range from 300 to 773 K, exceeding 600 μW m−1 K−2 in the Bi1−xCaxCuSeO samples with 0.075 ≤ x ≤ 0.125. Additionally, the lattice thermal conductivity is significantly reduced due to the refined grains and the introduced point defects that limit the phonon mean free path, resulting in a total thermal conductivity lower than 1.0 W m−1 K−1 in all the doped samples. Benefiting from the enhanced electrical conductivity and the reduced thermal conductivity, high ZT values, both at low and medium temperatures, 0.3 at 300 K and 0.8 at 773 K, are achieved for the Bi0.925Ca0.075CuSeO composition.

Optical characterization of Er3+-doped zinc fluorophosphate glasses for optical temperature sensors

Abstract: Trivalent erbium doped zinc fluorophosphate glasses have been synthesized and their luminescence properties in the green visible range have been investigated as a function of temperature. The Judd–Ofelt theory has been used to predict the transition probabilities, branching ratios and lifetimes for the various excited states of Er3+ ions in 0.5 mol% of Er2O3-doped glass. The effect of Er3+ concentration on temperature dependent luminescence has been studied for the wide temperature range from room temperature up to 773 K. The fluorescence intensity ratio of the green emissions associated to the two transitions from the thermally coupled 2H11/2 and 4S3/2 levels to the 4I15/2 level of Er3+ ion has been studied as a function of temperature, and in turn used to determine the thermal sensitivity and relative thermal sensitivity of the glasses. In the present study, the maximum value for the thermal sensitivity of 79 × 10−4 K−1 at 630 K has been obtained for the lowest (0.01 mol%) concentration of Er2O3-doped glass, one of the highest sensitivity found in the literature and quite close to the theoretical sensitivity calculated from the Judd–Ofelt theory. The results reveal that the zinc fluorophosphate glass having relatively low concentration of Er3+ ions can be useful as an optical temperature sensor due to their high sensitivity and the absence of radiative energy transfer processes.

Cationic Poly(ionic liquid) with Tunable Lower Critical Solution Temperature-Type Phase Transition

Abstract: A cationic polyelectrolyte based on the styrenic ionic liquid tributyl-4-vinylbenzylphosphonium pentanesulfonate was found to undergo a lower critical solution temperature (LCST)-type phase transition in aqueous solutions. This phase transition occurs in a wide temperature range in terms of polymer concentration as well as type and concentration of externally added salts. Anion exchange and salting out effects are responsible for the flexible phase transition temperature.

Li-cycling properties of molten salt method prepared nano/submicrometer and micrometer-sized CuO for lithium batteries.

Abstract: We report the synthesis of CuO material by molten salt method at a temperature range, 280 to 950 °C for 3 h in air. This report includes studies on the effect of morphology, crystal structure and electrochemical properties of CuO prepared at different temperatures. Obtained CuO was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area methods. Samples prepared at ≥410 °C showed a single-phase material with a lattice parameter value of a = 4.69 A, b = 3.43 A, c = 5.13 A and surface area values are in the range 1.0–17.0 m2 g–1. Electrochemical properties were evaluated via cyclic voltammetry (CV) and galvanostatic cycling studies. CV studies showed a minor difference in the peak potentials depending on preparation temperature and all compounds exhibit a main anodic peak at ∼2.45 V and cathodic peaks at ∼0.85 V and ∼1.25 V vs Li. CuO prepared at 750 °C showed high and stable capacity of ∼620 mA h g–1 at the end of 40th cycle.

Effective bulk and surface temperatures of the catalyst bed of FT-IR cells used for in situ and operando studies

Abstract: The temperature prevailing in the catalyst bed of three different IR spectroscopic reaction cells was assessed by means of thermocouples, an optical pyrometer and reaction rate measurements. One of the cells was a custom-made transmission FT-IR cell for use with thin wafers and the two others were commercial Harrick and Spectra-Tech diffuse reflectance FT-IR (DRIFTS) cells used for the analysis of powdered samples. The rate of CO methanation measured over a 16 wt% Ni/alumina catalyst was used as a means to derive the effective temperature prevailing in the IR cells from that existing in a traditional (non-spectroscopic) reactor having a well-controlled temperature. The sample bed of these three IR cells exhibited a significantly lower temperature than that of the corresponding measure thermocouple, which was yet located in or close to the sample bed. The comparison of Arrhenius plots enabled us to determine a temperature correction valid over a large temperature range. The use of an optical pyrometer was assessed with a view to determining the temperature of the surface of the powdered beds and that at the centre of the wafer. The optical pyrometer proved useful in the case of the catalyst powder, which behaved as a black non-reflecting body. In contrast, the temperature reading was inaccurate in the case of the pressed wafer, probably due to the shiny surface and minute thickness of the wafer, which led to a significant portion of the IR radiation of the surroundings being reflected by and transmitted through the wafer. The optical pyrometer data showed that the temperature of the surface of the powdered beds was significantly lower than that of the bulk of the bed, and that the total flow rate and composition did not affect this value. This work emphasises that the effective bed temperature in spectroscopic cells can be significantly different from that given by measure thermocouples, even when located in the vicinity of the sample, but that the calibration curves derived from rate measurements can be used to overcome this problem.

BaNb0.05Fe0.95O3−δ as a new oxygen reduction electrocatalyst for intermediate temperature solid oxide fuel cells

Abstract: Cobalt-free perovskite BaNb0.05Fe0.95O3−δ (BNF) is synthesized and characterized towards application as a cathode material for intermediate temperature solid oxide fuel cells. In situ X-ray diffraction and transmission electron microscopy are applied to study the crystal structure and thermally induced phase transformation. BNF exists as a multiphase structure composed of a monoclinic phase and a cubic phase at room temperature, and then undergoes a phase transformation to a cubic structure starting at ∼400 °C, which is maintained at temperatures up to 900 °C during a thermal cycle between room temperature and 900 °C; while it retains the cubic perovskite lattice structure on cooling from 900 °C to room temperature. Oxygen temperature-programmed desorption, combined thermal expansion and thermo-gravimetric analysis are used to clarify the thermal reducibility of BNF. A relatively good stability of BNF is demonstrated by electrical conductivity and electrochemical impedance spectroscopy measurements. The activity of BNF for oxygen reduction reaction is probed by symmetrical cell and single fuel cell tests. Favorable electrochemical activities at intermediate temperature, e.g. very low interfacial resistance of only ∼0.016 Ω cm2 and maximum power density of 1162 mW cm−2 at 750 °C, are demonstrated, which could be attributed to the cubic lattice structure of BNF within the temperature range of cell operation.