Ag Tube Research Articles

Integrated analysis of a membrane-based process for hydrogen production from ethanol steam reforming

The aim of this work is to investigate the performance and energy efficiency achieved by an integrated system based on two different ethanol fuel processor configurations: a Conventional Reactor (CR) and a Membrane Reactor (MR). The CR-based configuration system consists of an ethanol reformer followed by two water-gas shift reactors operating at high and low temperatures. The final hydrogen purification is carried out by a preferential oxidizer in order to reduce the CO concentration before feeding the polymer electrolyte membrane fuel cell (PEMFC). A multi-tubular MR process using thin Pd–Ag tubes has also been considered, where the water-gas shift reaction and the hydrogen separation take place simultaneously. The analysis showed that the MR process configuration possesses a simpler system design with a minor advantage in terms of energy efficiency (30%) compared with the conventional system (27%). Moreover, a detailed parametric analysis concerning the effects of water-to-ethanol molar ratio, reaction pressure, reformer and MR temperature, sweep-gas molar ratio and MR configuration on the achieved performance (hydrogen yield) and energy efficiency of the system has also been done. The importance of optimizing integrated systems is shown since the optimal operating conditions from a global efficiency analysis point of view are in general distinct when compared with those obtained when focusing on the reformer reactor or individual process units alone.

Pd–Ag membranes for auto‐thermal ethanol reforming

AbstractThe auto‐thermal ethanol reforming was carried out at 200 kPa by a two‐step process consisting of a traditional reformer operating at high temperature (700–740 °C) and a Pd–Ag multitube membrane module where the separation of hydrogen took place at 350–380 °C.The membrane module was a bundle of 11 thin‐wall Pd–Ag tubes of wall thickness 50–60 µm, diameter 10 mm, and length 270 mm: permeation tests were performed at 300–395 °C with lumen pressure of 150–200 kPa, and nitrogen sweep flow rates in the shell side ranged from 10 to 30 l min−1 at atmospheric pressure. A hydrogen permeance Pe = 1.317 × 10−2 exp (−3.622 × 103/T(K)) mol m−2 s−1 Pa−0.5 was measured and complete hydrogen selectivity was verified.A water/ethanol mixture of molar ratio 2.50/1.00 was used as feed stream for carrying out ethanol reforming in the traditional fixed‐bed reactor filled with a Ni on alumina catalyst. As a second step, the water gas shift (WGS) membrane reaction was carried out in the multitube membrane reactor: the Pd–Ag alloy of the membrane tubes worked for both catalyzing the reaction and for separating all the hydrogen produced in the reformer and in the membrane reactor itself. The hydrogen separated through the membrane was collected in the shell side of the membrane module: by operating with a water/ethanol feed flow rate of 200 g h−1, up to 1.2 l min−1 of pure hydrogen was produced. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

QuantiFERON®-CMV for Immune-Monitoring in Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Background: CMV infection represents a major complication of allo-SCT affecting transplant related mortality and morbidity. Anti-viral therapy is toxic and prolonged treatment could affect graft function. Monitoring specific immune response against CMV could optimize the timing for anti-viral therapy administration in order to avoid related toxicity and to reduce CMV related mortality and morbidity. A recent ELISA based test (QuantiFERON®-CMV) could measure specific (anti-HCMV) and aspecific production of IFN-γ in whole blood.Aims: to test the reliability of QuantiFERON®-CMV in a cross sectional study in order to identify patients at risk of CMV disease after alloHSCT.Methods: QuantiFERON®-CMV is an in vitro diagnostic test using a peptide cocktail simulating human cytomegalovirus proteins (CMV) to stimulate cells in heparinised whole blood. Detection of interferon-γ (IFN-γ) by ELISA is used to identify in vitro responses to these peptide antigens that are associated with CMV infection. The IFN-γ response in the CMV Ag tube is considered positive if > 0.2 UI/mL as defined by the manufacturer. The mitogen-stimulated plasma sample was used as an IFN-γ positive control (PC) for each specimen tested. CMV reactivation and disease were defined according EBMT recommendations.Results: Among 92 tests no correlation between pp65 antigenemia and IFN-γ production was proved (p=0,346). However, among the 41 tests showing lower levels of anti-HCMV IFN-γ production (<0.2 IU/mL) 8 tests belonging 4 patients were associated with CMV disease, whereas among the 51 tests showing higher levels of anti-HCMV IFN-γ production (>=0.2 IU/mL) none were associated with CMV disease (p=0.001), RR 2.5 (CI95% 1.951–3.321).Conclusions: QuantiFERON®-CMV doesn't seem to represent a significant reliable test for risk of viremia after alloHSCT, but patients with prolonged lower levels of anti-HCMV IFN-γ production (<0.2 IU/mL) are at risk of CMV disease. Prospective studies are required in order to identify the correlation between viremia and the need for treatment.

Hydrogen production from ethanol steam reforming: energy efficiency analysis of traditional and membrane processes

The ethanol steam reforming reaction has been considered for producing pure hydrogen to be used for feeding a PEM fuel cell of power 4 kW. As an innovative technology, Pd–Ag thin wall membranes are proposed for building membrane reactors: accordingly, the energy efficiency analysis of the processes producing hydrogen from ethanol steam reforming has been carried out and, particularly, the comparison among a traditional process and different membrane processes is reported. The traditional process studied consists of an ethanol reformer followed by two water gas shift reactors operating at high and low temperature, respectively: the final hydrogen purification is carried out by a preferential oxidizer in order to reduce the CO concentration below 10 ppm before feeding the PEM fuel cell. Then two membrane processes using Pd–Ag tubes and operating with a feed H 2O/ethanol have been considered. The first one uses a traditional ethanol reformer and a Pd–Ag membrane reactor where the water gas shift reaction and the hydrogen separation simultaneously take place: the pure hydrogen recovered in the permeate side of the membrane reactor is sent to the PEM anode. In the second membrane process, one Pd–Ag membrane reactor performs the ethanol steam reforming with the hydrogen separation: also in this case, the pure hydrogen recovered in the permeate side of the membrane reactor is directly sent to the PEM anode. The analysis showed that the highest values of the energy efficiency have been attained by the process using one membrane reformer: this process has a net electric efficiency of 9% higher than the traditional one. Finally, an efficiency field-to-wheel analysis has been also carried out: a conventional application of the pure bio-ethanol in a reciprocating engine has been compared to a membrane system processing humid bio-ethanol and fuelling a PEM driven electrical engine. Mainly as a consequence of the direct use of water–ethanol mixtures, the membrane process presents a higher energy efficiency up to 50% and, in fact, in this case the distillation and dehydration of the bio-ethanol are avoided thus increasing the energy efficiency.

AC LOSSES EVALUATION OF SILVER-SHEATHEDBI-2223 TAPES WITH CONVERTING DC MAGNETIC FIELD ANGLE

A number of studies showed that the AC losses for B//c are much larger than that for B//ab due to the effects of Ic(B) behavior at 77K. We present the relation between AC losses and the orientations of DC magnetic field by a sample of Bi -2223 tapes with 37 filaments of a superconducting core, which were prepared by the powder-in-(Ag) tube (PIT). A universal formula on the relation between AC losses and the orientations of the DC magnetic field will be found out according to the ellipse model of the Norris equation. The formula will provide some useful hints for the theoretical analysis of AC losses.

Development of Ag-Sheathed Bi2223 Tapes with Interfilamentary Resistive Barriers for Reducing AC Losses

Ag-sheathed Bi2223 composite tapes with interfilamentary resistive barriers were successfully fabricated by using a powder-in-tube (PIT) method and their AC loss properties at 77 K are evaluated. The mixture of Ca2CuO3 and 30 wt% Bi2212 was used as the barrier material for tape fabrication to make an electromagnetic decoupling between the filaments. The barrier layers formed on all surfaces of hexagonal monocore wires by a dip-coating method, and several pieces of the coated wires were stacked and inserted into an Ag tube. Subsequently, the composites deformed into tape shape and subjected to a standard process consisting of a flat rolling and sintering. Degradations in the Jc values at 77 K and self-field by introducing the barriers were estimated to be at most 15%. The transverse resistivity and AC loss properties under AC external magnetic fields for the barrier tapes were examined and compared with those for the tape without barriers. The results showed that an introduction of Ca2CuO3 barriers was effective to suppress the electromagnetic coupling among the filaments and also to reduce the magnetization losses under parallel transverse field. The fabrication of the barrier tapes on the order of several meters, together with the uniformity of superconducting properties along a length direction has been also presented.

Mechanical design of a PERMCAT reactor module

The PERMCAT is a membrane reactor proposed for processing fusion reactor plasma exhaust gas: tritium removal is obtained by isotopic swamping operating in counter-current mode. In this work, a membrane reactor using a permeator tube of length about 500 mm produced via diffusion welding of Pd–Ag thin foils is described. An appropriate mechanical design of the membrane module has been developed in order to avoid any significant compressive and bending stresses on the very long and thin wall permeator tube: two expanded bellows have been applied to the Pd–Ag tube, so that it has been pre-tensioned before operating. The elongation of the metal permeator under hydrogenation has been theoretically estimated and experimentally verified for properly designing the membrane reactor.

Transport AC losses of Ag-sheathed Bi-2223 tapes with different twist-pitch using electricalmethods

A series of Bi-2223 ([Bi,Pb]:Sr:Ca:Cu:O = 2:2:2:3) tapes with 37 superconducting core filaments was investigated in an attempt tocorrelate critical current and alternating current (AC) losses with twist-pitch.The twist-pitch of these multi-filamentary tapes which were produced by thepowder-in-(Ag)tube (PIT) method varies from 8, 10, 13, 30, 50, 70 mm to mm (non-twist). Critical current(Ic)measurements which were conducted in zero field by a four-probe method under liquid-nitrogen temperatureshowed that Ic is greater in the non-twist filament than that in twisted filaments. Among these tapes,three (twist-pitch of 10, 13, and 70 mm) were selected for AC loss experiments under atime-varying transport current. The results of AC loss measurements in general agree withthat of the AC loss simulation using the ellipse model of the Norris equation. Simulationresults show that the hysteretic AC loss is lowest in the non-twist tape and increases as thetwist-pitch decreases. A much greater loss was found in tapes with small twist-pitch, i.e. 10and 8 mm. Among different possible loss contributions to the total AC losses, the hystereticloss was determined to be the main source. In addition, microstructural damage of tapeswith small twist-pitch appears to contribute to the overall AC losses as well.

Phase Formation and Evolution, Texturing and Current Transport in Ag/Bi2212 PIT Monofilamentary Tapes

Superconducting tapes of ceramic material capable of transporting high current densities at high operation temperatures have been revealed as promising conductors in applied superconductivity. Tapes of Ag/Bi2212 present excellent characteristics and their processing techniques are being improved. This work presents a study on the formation of phases and the texturing behavior of Ag/Bi2212 monofilamentary tapes after several heat treatments with different cooling rates from 890/spl deg/C to 830/spl deg/C and silver doping, allowing an optimization of the heat treatment profiles aiming the obtainment of close to stoichiometric superconducting phases with high texturing. The tapes were fabricated using Bi2212 precursor powder and the powder-in-tube (PIT) method. The powder was pressed inside the Ag tube, and the set was mechanically deformed by swaging and rolling to the final thickness of 150 /spl mu/m. After heat treatment, the samples were characterized by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectrometer (EDS). The results show the effect of each heat treatment profile on the microstructure and superconducting characteristics of the Ag/Bi2212 tapes, as well as they show the ways to obtain the best texturing of the samples aiming high current transport.

ＡｇＣｕ／Ｂｉ‐２２１２超伝導丸線材の臨界電流密度特性

The critical current densities of round AgCu alloy-sheathed Bi-2212 wires have been studied for superconducting magnet use. The wires have been fabricated by the powder-in-tube method, using co-precipitated powders with a nominal composition of 2 : 2 : 0.64 : 1.64 (Bi : Sr : Ca : Cu). In these wires each core has been designed to consist of a twofold tube of the oxide layer to increase the interfacial area of the Ag-sheath and the oxide core. The critical current densities per overall cross-sectional area of the wires (Jc) have been increased by increasing the number of cores to 37. Sheathing Ag/Bi-2212 wires with the AgCu-alloy tube as the outermost sheath has enhanced both the mechanical strength and Jc values compared with Ag/Ag/Bi-2212 wires where the sheath is made of pure Ag tubes only. Jc values exceeding 2.6×108 A/m2 at 4.2 K and 10 T have been obtained for AgCu/Ag/Bi-2212 wires heat-treated in air. Heat treatments under oxygen gas flow have caused deleterious effects on Jc values. The micro-structural analyses of the smoothness of the Ag-sheath/oxide-core interface and the packing density of the oxide core have indicated that there is much room for improving weak links within the wires.

Study of Ag and Cu/MgB2 powder-in-tube composite wires fabricated by in situ reaction at low temperatures

Superconducting Ag or Cu sheathed MgB2 wires have been fabricated by conventional powder-in-tube techniques. The in situ reactions of Mg and B powders with atomic proportions of 1:2 and 1.33:2 inside Ag or Cu tubes at low temperatures have been explored. An active alloying of Mg with Ag or Cu sheaths at temperatures below 660 °C has been observed. For Ag sheaths, there is a strong diffusion of Mg, which does not allow the formation of large amounts of MgB2 at the core. For Cu sheaths, the diffusion of Mg is stopped by the formation of a MgCu2 layer around the superconducting core and an appropriate excess of Mg leads to superconducting cores with Tc ≈ 39 K and good Jc values. Thus, the development of Cu/MgB2 composite wires is possible.

Characterization of thin wall Pd–Ag rolled membranes

A thin wall Pd–Ag tube (thickness 50 μm ) obtained by a procedure of cold-rolling and annealing of thin metal foils has been characterized in long-term tests for determining the hydrogen permeability under operating condition of a temperature range from 300°C to 400°C and transmembrane differential pressure from 50 to 100 kPa . During testing, the physical and mechanical stability of the rolled membranes have been observed and high hydrogen fluxes have been measured. The long-term tests have also shown the modification of the surface structure of the membrane due to the hydrogen–metal interaction and the thermal cycling: as a consequence, an increase of the mass transfer properties of the hydrogen through the material (diffusivity and solubility) has been observed and the membrane tube has attained very high performances in about 3 months of operation in terms of hydrogen permeability. Furthermore, the tests have demonstrated that these Pd–Ag membranes have the capability to separate hydrogen from gas mixtures with a complete hydrogen selectivity and can be used to produce ultra-pure hydrogen for applications in energetic fields in membrane reactors by molecular reforming in membrane reactors (i.e. isotopic hydrogen separation, fuel cell, etc.).

A study of spatially coupled bipolar electrochemistry on the sub-micrometer scale: colloidal particles on surfaces and cylinders in nuclear-track etched membranes

In the present study we explore the feasibility of applying spatially coupled bipolar electrochemistry to the sub-micrometer regime. This is a technique where electrically isolated objects can be interconnected by the application of electric fields and has previously been demonstrated on the millimeter and micrometer scales. Three experimental designs were explored: annealed Au and Ag films on glass, annealed Ag films on silicon nitride membranes and Ag tubes immobilized within polycarbonate nuclear-track etched membranes. In the evaporated and annealed film part of this study, particles on the order of 20–50 nm were exposed to electric fields up to 2 kV cm −1 for periods up to 180 s, in a mixture of toluene and acetonitrile. Plasmon resonance measurements and scanning electron microscopy (SEM) were used to characterize the changes following field application. At all field intensities and times studied, the gold particle sub-monolayers did not appear to be discernibly affected. The plasmon resonance absorption of the silver sub-monolayers displayed significant peak broadening after field application. Further experiments using transmission electron microscopy (TEM) analysis of annealed silver films on silicon nitride membranes demonstrated particle agglomeration without evidence for particle interconnection or morphological change. This result suggests that, under these experimental conditions, physical movement of the Ag particles occurs instead of electrochemical processes. In order to prevent particle movement, polycarbonate membranes were used to anchor silver cylinders with diameters of 1 μm, 400nm and 200 nm. Results from these experiments demonstrated that for Ag in 1:1 toluene–acetonitrile, spatially coupled bipolar electrochemistry (SCBE) reaches a practical limit for structures between 200 and 400 nm since the width of the deposit approaches the size of the metal particles. At 200 nm the result is electrochemical migration of the particles, where a commensurate amount of Ag is deposited on one side and dissolved on the other. This size limitation is specific only to SCBE, where structures are required to electro-dissolve, not to the application of bipolar electrochemistry to structures below 200 nm.

Preparation of polymeric and metallic nanostructures using a template-based deposition method

Arrays of micro- and nanoscopic Ag and Au tubes with different thicknesses were prepared by electroless deposition of the corresponding metal within the pores of polycarbonate particle track-etched membranes.

Large transport critical currents in unsintered MgB2 superconducting tapes

The powder-in-tube process has been employed to fabricate tape-like conductors with a strong metallic sheath and based on the newly discovered MgB2 superconducting phase. Long superconducting tapes have been prepared by packing reacted MgB2 powders inside pure Ag, Cu, and Ni tubes which are then cold worked by drawing and rolling. Such tapes have shown transport properties as good as bulk MgB2 samples sintered in high pressure and high temperature conditions. At 4.2 K, the highest critical current density of 105 A/cm2 has been achieved on nickel-sheathed single-filament conductors. A direct correlation between the sheath tensile strength and the critical current of the unsintered tape has been observed.

BSCCO/Ag tapes made by a tape-in-rectangular tube process

Multi-core tape composites with various filament configurations havebeen made by a tape-in-rectangular tube (TIRT) process. This TIRT process isbased on the deformation of multifilamentary composites assembled from arectangular Ag (Ag-alloy) tube filled by pre-deformed single-core BSCCO/Agtapes. Two-axial rolling induces texture in the filaments in two rolling planes,with the filament planes oriented parallel or perpendicular to the tape width,thus reducing the high Ic anisotropy which can degrade the total current incoils working at high temperatures (77 K). The homogeneity of the filaments wasstudied by a magneto-optical technique. Roll-sintered samples were measured at77 K in an external magnetic field up to 1 T and at constant fields (0.1 T and0.5 T) at various orientations (between parallel and perpendicular) to the tapesurface. The results demonstrate the possibility of using these tapes forselected parts of a coil winding to reduce the apparent effect of the radialfield component on the reduction of the total coil current.

Sr&lt;SUB&gt;6&lt;/SUB&gt;V&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;11&lt;/SUB&gt;バリアをもつAgシースBi2223多芯テープ線材の作製と超伝導特性

Ag-sheathed Bi2223 multifulamentary tapes (7 and 19 filaments) with and without Sr6V2O11(SVO) barriers have been prepared by the powder-in-tube method. The SVO barrier layers are arranged in three different configurations as inside (7 & 19SV10), outside (7 & 19SV01), and inside-outside (7 & 19SV11) of each filament. All of the barrier tapes have much higher critical-current density Jc than the non-barrier tapes (7 & 19SV00). In these cases, the compound SrCO3 contaminated in the process of SVO preparation must be eliminated in the inside-barrier tapes, and a thick-walled Ag tube must be used in the inside-outside barrier tapes with thicker barrier layers. This result will overcome the serious problem of the decrease in Jc in barrier tapes obtained so far. Furthermore, the inside barrier configuration will be possible using only SVO. The increase in Jc will be due to the enhancements of the Bi2223 phase formation and its crystal alignment by the reaction of the inside-coated SVO with a Bi-oxide core for the inside- and inside-outside barrier tapes (SV10 and SV11) and due to the reduction in oxygen partial pressure at the Bi-oxide core site during the heat treatment for the outside-barrier tapes (SV01). Furthermore, for all the barrier tapes, the transport a. c. losses at 77 K in self field are lower than those of the non-barrier-tapes. These results suggest that SVO will be one of the most important candidates for a resistive barrier with the view of a. c. applications. The inside-barrier tapes, especially, will permit the tape to be fabricated with ease and provide good potential for improving the overall Jc.

Preparation and characterization of clean, single-crystalline YHx films (0⩽x⩽2.9) on W(110)

Yttrium can be loaded with hydrogen up to high concentrations causing dramatic structural and electronic changes of the host lattice. We report on the preparation of clean, single-crystalline YHx films (0⩽x⩽2.9). The films have been characterized in situ combining angle-resolved photoelectron spectroscopy (ARPES) and low energy electron diffraction. Direct Y dihydride growth, i.e., Y evaporation under a H2 partial pressures of ≈5×10−6 mbar at 500 K on W(110), is the most convenient starting point for the preparation of clean single-crystalline Y hydride films covering H concentrations from the “clean metal” (x≈0) up to the lower boundary of the pure trihydride phase (x≈2.9). Upon annealing Y dihydride films the desired H concentration can be adjusted within the α-phase or the (α+β) two-phase regime. On the other hand, the extension of our photoelectron spectrometer with an homemade ultrahigh vacuum (UHV) compatible hydrogenation system allows to induce the transition from Y dihydride to Y trihydride within a few minutes. The hydrogenation system combines a high-pressure reaction cell with hydrogen permeation through a Pd–24%Ag tube. The overall design is such that the sample never gets in contact with non-UHV compartments. For direct Y dihydride growth on W(110) two equally populated face-centered- cubic(111) domains rotated by 180° with respect to each other are observed. In the α- and γ-phase the Y atoms form a hexagonal-close-packed(0001) oriented lattice. Furthermore, the previously established model for in situ H concentration estimation in Y [J. Hayoz et al., Phys. Rev. B 58, R4270 (1998)] is extended successfully from the α to β to the β to γ-phase transition. Ultraviolet photoemission spectroscopy data unequivocally reveal the opening of a gap extending as far as 1 eV below EF for normal electron emission upon the phase-transformation from Y dihydride to Y trihydride. It also appears that the H absorption rate strongly depends on the H2 purity. Our experimental results demonstrate the capability of this setup for in situ preparation and investigations on the geometrical and electronic structure of Y hydride films and, more generally, rare-earth hydride films using ARPES.

The formation mechanism and the development of grain texture in the preparation of Ag-sheathed Bi-2223 superconducting tapes

The mechanism and development of cold-working and grain-growth texture of Bi-2212 and the corresponding inheritance of texture by Bi-2223 in Ag-sheathed tapes has been investigated. Precursor powder in the Ag tube was found to flow, rotate and fracture along the crystallites. This together with sliding among crystallites forms the basis of the deformation process in Bi-2212 texturing during the cold-working process. Bi-2212 was formed via a rapid melting process, yielding a strong epitaxial melt-textured microstructure from a subsequent heat treatment. Bi-2223 was found to form on Bi-2212, with the Bi-2223 texture being inherited from the Bi-2212 texture. This is best explained by an intercalation mechanism for Bi-2223 phase formation.

Strain tolerance of Ag-sheathed BSCCO (2223) superconductors with various geometrical configurations

Strain tolerance (retained critical current as a function of applied strain) of Ag-sheathed monofilament and wire-in-tube (WIT) tapes sintered for various time periods was evaluated. Strain tolerance of the WIT tapes sintered for 100 h was significantly lower than that of the monofilament tapes. This is attributed to a sharp increase in volume fraction of the superconducting core in WIT tapes (compared with that in monofilament tapes) subjected to a strain value greater than the fracture strain of BSCCO . This limitation was overcome by fabricating tube-within-tube tapes containing an additional BSCCO layer that runs along the neutral plane. Strain tolerance of these was superior to those of both the monofilament and the WIT configurations. This improvement is related to crack pinning effects induced by the inner Ag tube and by increased volume fraction of undamaged superconducting core. Experimental evidence indicates that the effective strain experienced by the current-carrying regions of the cross-section will determine the strain tolerance of the tape. At strains below 1% where there is a significant decrease in the volume fraction of superconducting core within subcritical strain, only a relatively low decrease in critical current density was observed, indicating possible current shunting in all of the tape configurations investigated.