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Pumping of fluids is universally performed by using mechanical or thermal compressors. We introduce a new solid-state molecular pumping approach induced by switching the adsorption affinity for a g...

Fe-Si alloys ranging from 3 to 8 wt% Si were rapidly solidified using melt spinning. Wheel speeds of 30 m/s and 40 m/s were employed to vary cooling rates. Mossbauer spectroscopic studies indicated the Si content significantly influenced the number of Fe sites, relative abundance of various Fe species, and internal magnetic fields/structural environments. Wheel speed altered Fe speciation only in the 3 wt% sample. Scanning electron microscopy confirmed that increasing the wheel speed refined both the ribbon thickness and grain size. Electron backscatter diffraction results suggest tailoring melt spinning process parameters and alloy chemistry may offer the ability to manipulate {001} texture development. Electrical resistivity measurements were observed to increase in response to elevated Si content. Increased hardness was correlated to elevated Si content and wheel speed.

This work presents a new technique for evaluating the solid-liquid phase transformations in complex diesel fuel blends and diesel surrogates under high-pressure conditions intended to simulate those occurring in vehicle fuel injectors. A high-pressure apparatus based on a visual identification of freezing and thawing has been designed and built to monitor phase behavior and determine the crystallization temperature of complex fuels to predict wax precipitation. The proposed methodology was validated using pure substances-n-hexadecane (C16H34), cyclohexane (C6H12), and a mixture of 0.5848 mol fraction n-hexadecane in cyclohexane. The crystallization temperatures of these compounds were measured from atmospheric pressure to 400 MPa for temperatures varying from 290 K to 363 K and compared to those reported in the literature. The standard error of the estimated temperatures for the experimental data obtained in this work, based on a given pressure, was compared to data from the literature. This methodology will be extended to investigate the properties of more complex fuel mixtures.

Exposure of (La0.90Sr0.10)0.98MnO3+δ (LSM-10) to repeated oxygen partial pressure cycles (air/10 ppm O2) resulted in enhanced densification rates, similar to behavior shown previously due to thermal cycling. Shrinkage rates in the temperature range 700°–1000°C were orders of magnitude higher than Makipirtti–Meng model estimations based on stepwise isothermal dilatometry results at a high temperature. A maximum in enhanced shrinkage due to oxygen partial pressure cycling occurred at 900°C. Shrinkage was the greatest when LSM-10 bars that were first equilibrated in air were exposed to gas flows of lower oxygen fugacity than in the reverse direction. The former creates transient cation and oxygen vacancies well above the equilibrium concentration, resulting in enhanced mobility. These vacancies annihilate as Schottky equilibria are reestablished, whereas the latter condition does not lead to excess vacancy concentrations.

A Luggin type reference electrode was fabricated for use in solid state electrolytes. The method of construction allows placement of the reference tip within a few tens of microns of the working electrode surface. The reference was constructed by embedding a platinum wire, previously coated with insulating alumina, into the solid electrolyte. The references held stable potentials and the response was characterized by both cyclic voltammetry with and without electrolyte resistance compensation and AC impedance. Both techniques gave identical values for the Faradaic and ohmic contributions to the electrode overpotentials. Reference electrodes placed at different locations across the working electrode surface gave different results indicating the electrode activity was not uniform.

The oxygen reduction reaction was studied on the La 1− x Sr x Al y Fe 1− y O 3 ( x =0.2, y =0.1, 0.2, 0.3, 0.4) system by cyclic voltametry and electronic conductivity. Activation energies for the bulk and film conductivities were determined. Tafel analysis afforded the activation energies “from the temperature dependence of the exchange current densities” as well as the charge transfer coefficient. The electrical conductivity of bulk material was found to decrease with aluminum content. Formation of the materials into thin porous films further decreased the conductivity after correcting for porosity. Aluminum substitution substantially decreased the performance through influence of the pre-exponential factor in the Butler–Volmer formulation. Neither the activation energies nor the charge transfer coefficient for these materials varied significantly. Aluminum does not adversely influence the basic mechanism of oxygen reduction. It may occupy and block electrochemically active sites on the electrode surface, but it does not appear to decrease the intrinsic activity of available surface sites.

The direct conversion of methane to liquid fuels and chemicals is highly sought, especially at low-scale to more effectively utilize remote natural gas resources. Direct conversion has proven to be a very difficult problem, because methane is highly unreactive, though tends to over-oxidize once activated. Methanol is primarily produced today by the steam reformation of methane at high temperatures and pressures to synthesis gas (carbon monoxide plus hydrogen), followed by catalytic conversion at intermediate temperatures and high pressures. Though highly selective, this technology is not well suited for low production wellheads. The direct conversion of methane to methanol and other liquids would be a game changer, potentially leading to much lower production costs. In our presentation we will be reporting the development of the metal oxide-based electrocatalysts, which provide an oxygen activity needed for the partial oxidation of methane to liquid fuels suitable for applications in intermediate temperature fuel cells. The tests were performed at atmospheric pressure at different CH4 flow rates and different temperatures in the 200-700oC range.The product analysis was performed by online quadrupole mass spectrometer as well as by GC-MS. Methanol is the primary product of methane conversion at temperatures below 400oC. At 600-700oC, ethane, ethylene, propane, propene, n-butane, iso-butane, 2-butyne, and benzene formation was observed. In all tests the formation of carbon oxides was observed as well. Separately, the catalysts were evaluated using diffuse reflectance infrared Fourier Transform Infrared Spectroscopy (DRIFTS), TGA and in operando XRD. The kinetics of oxygen gain appeared to be slower that the oxygen loss. Somewhat longer time was needed to re-oxidize the catalyst. Kinetics are faster and conversion of CH4 was greater at higher temperatures. The post-test analysis was done using SEM and XRD. Figure 1. Methane conversion (right y-axis) and the rates of methanol, CO, and CO2 formation (left y-axis) at 300oC. Figure 2. Relative hydrocarbon distribution at 700oC. Figure 1

Sintering shrinkage curves and phase changes were compared for calcium-substituted lanthanum chromates with either slight Asite enrichment or depletion. Of the former type, La[sub 0.7]Ca[sub 0.31],CrO[sub 3] that was synthesized by the glycine-nitrate method sintered to high density in air at 1250C, exhibiting two rapid-shrinkage events. Weight loss measurements corroborated XRD data showing that, prior to densiflcation, over half the Ca resided in non-perovskite phases, including CaCrO[sub 4]. In the La[sub 0.7]Ca[sub 0.31]CrO[sub 3], densification was closely associated with re-dissolution of the Ca into the perovskite.

Anomalous shrinkage behavior of porous Sr-doped lanthanum manganite (La 1 - x Sr x ) 1 - y MnO 3 + δ , or LSM, where x = 0.0 to 0.4) has been studied as a function of thermal cycling, oxygen partial pressure, and Sr dopant concentration. An anomalous shrinkage due to thermal cycling in doped lanthanum manganite perovskite has previously been reported in the temperature range of 600°C to 1000°C. 1 , 2 However, the shrinkage reported here was in a 150°C range. Shrinkage of LSM during PO 2 cycling between air (2x10 5 ppm O 2 ) and N 2 (lOppm), was much less pronounced than that of thermal cycling in the same temperature range. The two cannot be directly compared due to the difference in cycling time. The effect of Sr dopant concentration on the shrinkage due to thermal cycling reached a maximum at a dopant level of 0.1. The postulated mechanism responsible for anomalous shrinkage is the metal ion vacancy gradient produced by the oxygen nonstoichiometry of LSM. Along with this gradient or driving force for metal ion vacancy diffusion; shrinkage also requires vacancy mobility or thermal excitation to advance the anomalous shrinkage.

The structural, thermal and electrical characteristics of calcium- and cobalt-doped yttrium chromites were studied for a potential use as the interconnect material in high temperature solid oxide fuel cells (SOFCs) as well as other high temperature electrochemical and thermoelectric devices. The Y0.8Ca0.2Cr1-xCoxO3±δ (x=0, 0.1, 0.2, 0.3) compositions had single phase orthorhombic perovskite structures in the wide range of oxygen pressures. Sintering behavior was remarkably enhanced upon cobalt doping and densities 95% and 97% of theoretical density were obtained after sintering at 1300oC in air, when x was 0.2 and 0.3, respectively. The electrical conductivity in both oxidizing and reducing atmospheres was significantly improved with cobalt content, and values of 49 and 10 S/cm at 850oC and 55 and 14 S/cm at 950oC in air and forming gas, respectively, were reported for x=0.2. The conductivity increase was attributed to the charge carrier density increase upon cobalt substitution for chromium confirmed with Seebeck measurements. The thermal expansion coefficient (TEC) was increased with cobalt content and closely matched to that of an 8 mol% yttria-stabilized zirconia (YSZ) electrolyte for 0.1 ≤ x ≤ 0.2. The chemical compatibility between Y0.8Ca0.2Cr1-xCoxO3±δ and YSZ was evaluated firing the two at 1400oC and no reaction products weremore » found if x value was kept lower than 0.2.« less

Sr-substituted perovskite LaCo0.4Fe0.6O3 is known to have excellent mixed ionic and electronic conductivity and increased O2 sorption characteristics. These perovskites are usually prepared by lengthy solid-state reactions of the component oxides at temperatures near 1150°C, and often produce inhomogeneous, multi-phase powders. Presently, it has been prepared by the calcination of combustion-derived fine mixed oxides at 850°C in 6 hrs. Combustion reactions are carried out using precursor solutions containing the corresponding metal nitrates (oxidizers) and glycine (fuel) at 250°C. The metal oxides produced by this process and subsequent calcination were characterized by XRD, TEM and BET surface area analysis.

Electrical, thermoelectric, and structural properties were studied in transition metal ion-substituted LaFeO 3 : La(Mn x Fe 1-x )O 3 , La(Ni x Fe 1-x )O 3 , and La(Cu x Fe 1-x )O 3 . Structural analysis showed that a continuous series of solid solutions with no intermediate phases are forming over a wide range (0 < x < 1) with substitutions of Mn and Ni, whereas the maximum Cu content is 30% from this study. The Ni-substituted LaFeO 3 specimens have substantially higher conductivity than those substituted with either Mn or Cu, measured in air from 100 to 1000°C. The Seebeck coefficient of La(Mn x Fe 1-x )O 3 and La(Cu x Fe 1-x )O 3 has a strong temperature dependence, indicating a thermally activated carrier formation. The activation energy for carrier formation in La(Cu x Fe 1-x )O 3 is greater than that in La(Mn x Fe 1-x )O 3 . Thermoelectric and electrical properties evidence conduction through polaron hopping in both Mn- and Cu-substituted LaFeO 3 , whereas the Ni-substituted LaFeO 3 shows metallic conductivity.

The reduction of oxygen on nickel-doped lanthanum strontium ferrite was studied by current interrupt cyclic voltammetry. Nickel doped on the B site of the perovskite ranged from 0 to 40%. Nickel strongly influenced the sintering of the films. The minimum temperature at which a stable adherent robust film could be formed increased with nickel content. The electrochemical performance for reduction of oxygen was compared with nickel content. Undoped lanthanum strontium ferrite consistently showed greater activity than the doped materials. The data were further analyzed to obtain the exchange current density as a function of temperature and then further analyzed to obtain the activation energy and pre-exponential factor. These values did not correlate with nickel composition but did correlate with one another. The variation in performance was tentatively attributed to subtle variations in microstructure.

In mixed ionic electronic conductors (MIECs) the electrochemistry of oxygen reduction and evolution is complicated by the competition between surface adsorption/desorption, interaction of these surface species with bulk vacancies and diffusion of these species to the MIEC/electrolyte interface. Charge transfer may occur by diffusion of oxygen adsorbates to the triple phase boundary or by diffusion of vacancies from the electrolyte with subsequent exchange with oxygen adsorbed on the porous MIEC wall. A model describing the competition between these two charge transfer pathways is developed. Key to the model is treatment of the boundary condition at the MIEC/electrolyte interface. The absolute potential across this interface is used to relate the surface overpotential of each pathway in terms of the other and terms arising from the concentration overpotentials. Results show the conditions under which one process may dominate over the other.