Oxygen and carbon dioxide separation membranes based on mixed conductors

Gas separation is one of the key technologies to improve the efficiency of combustion process, and to reduce the emission of global warming gases. By using pure or concentrated oxygen, flame temperature governing the Carnot efficiency and the concentration of CO2 in exhaust gas can be raised. Among a number of oxygen separation techniques such as cryogenic separation, oxygen separation membranes based on mixed oxide-ion and electronic conductors have been attracting much attention because of its high selectivity (100% in principle) and the ease of integration into various combustion systems. Figure 1(a) shows how the oxygen separation membrane works; only oxygen can penetrate as a result of ambipolar diffusion of oxide ions and electrons caused by an oxygen potential gradient. To date, a number of oxygen separation membranes such as perovskite-type oxides and dual-phase-type composites containing transition metals have been developed; however, to use the membranes in the expected applications, oxygen permeation flux governed by surface exchange kinetics and the tolerance of CO2, which is a main constituent of exhaust gas, need to be further improved. Recently, our group has succeeded in improving the oxygen permeation flux of Ba-Sr-Co-Fe-based oxygen separation membranes by surface modification using a porous body [1]. In which, weight relaxation performed at 400 °C revealed the enhancement of the surface exchange reaction. The chemical surface exchange coefficient (kchem) was 3.1 times larger for the sample with the porous body coating. A technique to further increse the oxygen flux will be discussed. In addition, how the CO2 tolerance of Ba-Sr-Co-Fe-based oxides can be managed will be presented. As well as oxygen separation, CO2 separation is of great interest in the context of CO2 capture and storage. As an analogous application using mixed conduction, CO2 separation membranes has been studied [2]. In this case, as shown in Fig. 1(b), the mixed conduction of oxide ions and carbonate ions plays a key role. In this study, a composite material comprising Sm-doped CeO2 and molten carbonates was prepared. The composite was found to permeate CO2 at around 900°C. The CO2 permeation flux was investigated with respect to its microstructure and electrical conductivity

Local structural analysis on hydration behavior in doped AZrO3 (A = Ba, Ca) protonic conductors

Perovskite-type protonic conductors are candidate electrolytes for intermediate temperature solid oxide fuel cells. For practical application, further improvement in proton conductivity is needed. Proton migration in these materials has been reported to be limited by trapping effects of protons by acceptor dopants [1]. In addition, it is suggested that the formation of percolation path with the trapped protons can lower the activation barrier for long-range proton migration and result in enhancement of proton conductivity. The formation of this percolation path is dominated by the location of protons and their concentrations, and higher proton concentration than the percolation limit is necessary for long range transport of protons. To increase or control the proton concentration in the material, understanding of hydration behavior is important because protons are incorporated into the material via hydration reaction of water vapor and oxygen vacancies. Therefore, this study focuses on investigation of hydration behavior from the local structural viewpoint with respect to protons and oxygen vacancies to explore a strategy to improve proton conductivity. For this purpose, solid-state nuclear magnetic resonance combined with density functional theory (DFT) calculations is used to elucidate the local structure of protons and oxygen vacancies since this technique is sensitive to the difference in chemical environment of probing nuclei. In the previous study base on 45Sc NMR analysis, difference in the local structure around oxygen vacancies in Sc-doped AZrO3 (A = Ba, Ca) is suggested to be related to the hydration behavior [2]. To clarify the influence of the local structure around oxygen vacancies to the hydration behavior, the electric-field gradient (EFG) at Sc sites, an indicator of the local structure, in Sc-doped AZrO3 is calculated by DFT calculation and compared with 45Sc NMR results. EFG at Sc sites is derived from the charge of oxide ions surrounding the nucleus. When the symmetry of the surrounding oxide ions is lowered due to the formation of the oxygen vacancy, large gradient in the electric-field at the Sc site is generated. This EFG interacts with the electric quadrupole moment of Sc nucleus, and this interaction can be observed by 45Sc NMR. Please click Additional Files below to see the full abstract

Defect structure and transport properties of ceria-zirconia-based oxides

CeO2-ZrO2 based oxides (CZ) showing excellent oxygen storage capacity (OSC) are widely used in three-way catalysts. To further improve their storage capacity and kinetics at low temperatures, defect structural analysis appears to play an important role. In this study, 89Y NMR spectroscopy is performed to probe the preference sites of oxygen vacancies in CZ under not only oxidizing but also reducing atmospheres. Figure 1 shows the 89Y NMR spectra taken for (Ce1-xZrx)0.8Y0.2O2-d annealed under (a) air and (b) Ar-5%H2 atmospheres. 7- and 8-coordinated environments are clearly observed for both cases. Based on their integrated intensities as a function of Zr content (Fig. 1 (c)), the oxygen vacancies appear to favor Zr rather than Y and Ce; the same trend has been reported for various fluorite-type oxides [1, 2]. This suggests that doping of smaller cations is effective to enhance their OSC. Furthermore, OSC and kinetics of CoFe2O4-added CZ at around 400°C are evaluated. The spinel-type oxides such as CoFe2O4 has been well known to enhance oxygen transport properties of ceria-based oxides [3, 4]. In this study, CoFe2O4-added CZ were prepared by the Pechini and solid-state reaction methods. 5 vol% CoFe2O4-added Ce0.5Zr0.5O2-d shows higher OSC and faster kinetics at 400°C than Ce0.5Zr0.5O2-d itself. The microstructure including the distribution of CoFe2O4 was analyzed by TEM; their morphology was found to strongly depend on the volume fraction of CoFe2O4 and fabrication techniques. Their surface exchange kinetics is also discussed based on pulse isotope exchange results for powder samples. Please click Additional Files below to see the full abstract

Pressure-induced defects in zirconates

Defects, e.g. vacancies and interstitials, play an important role on the physical properties of oxides, especially on their ionic transport. Those defects in oxides are generally controlled and analyzed as functions of dopant concentration, c, temperature, T, and oxygen chemical potential, O2, but not of total pressure, P. This is not surprising given that a molar volume, Vm, of solids is much smaller than that of gas phase by a factor of ≈1/1000. Meanwhile, under high pressure such as several GPa, the effect of total pressure on free energy, i.e. VmP, reaches 20~100 kJ/mol, which is high enough to affect the defect formation and migration in solids. In fact, pressure-induced phenomena are recently of great interest in solid state ionics. In this study, we focus on the pressure effects on the defect formation in some stabilized ZrO2 and acceptor-doped BaZrO3. For Y-stabilized ZrO2, reduction was found to be enhanced under high pressure. Figure 1 shows the lattice constant of 8YSZ electrochemically reduced under high pressure as a function of oxygen deficiency introduced. Under high pressure such as 1 to 6 GPa, 8YSZ was easily reduced even at 3VDC at 500°C. The oxygen deficiency reaches = 0.05. Unlike reduced CeO2 which shows lattice expansion, the reduced 8YSZ shows 0.5% smaller lattice constant. The lattice shrinkage was also confirmed by DFT calculations. This supports that applying high pressure, which in general enhances a reaction with negative volume change, enhances the reducing reaction of cubic ZrO2. Figure 2 shows the temperature dependence of electrical conductivity of reduced 8YSZ. The reduced 8YSZ appears to show mixed ionic and electronic conduction; major carrier is electrons. Acceptor-doped BaZrO3 was also subjected to high pressure on the order of GPa. Their defect equilibrium and proton conductivity will be also discussed. Please click Additional Files below to see the full abstract

Metal-supported SOFC Fabricated by Tape Casting and Its Characterization: A Study of the Co-sintering Process

Metal-supported SOFC consists of metallic and ceramic multilayers. Since the cell has to be flat, interaction between the layers that results in a flat sintered layer needs to be studied. The method used here was changing the starting materials through several experiments. Here, we highlight the effects of pore former in metal slurry on the sintered half-cell multilayer of a 430L metallic support, an NiO-8YSZ anode, and an 8YSZ electrolyte. The results show that by changing the amount of pore former in the 430L metal slurry changed the sinterability of the metal layer. This change of the sinterability of the metal support affected the final warpage state of the cell. This study aid in explaining the sintering phenomena between layers of metal-supported SOFCs

Intra-thyroid blood flow in Plummer\u27s disease.

金沢大学医薬保健研究域医学

Comment on: Nathan DM, Buse JB, Davidson MB et al. (2006) Management of hyperglycaemia in type 2 diabetes: a consensus algorithm for the initiation and adjustment of therapy. A consensus statement from the American Diabetes Association and the European Association for the Study of Diabetes.

金沢大学大学院医学系研究科環境社会医

Erythrocyte sorbitol level as a predictor of the efficacy of epalrestat treatment for diabetic peripheral polyneuropathy

金沢大学医学部附属病院内科The relationship between the effect of aldose reductase inhibitors (ARIs) on the activation of the polyol pathway and on diabetic neuropathy has not been fully established. To address this issue, we investigated the effect of epalrestat (150 mg/day), an ARI, on erythrocyte sorbitol levels as an index of polyol activation and on nerve function test results in 43 patients with diabetic peripheral polyneuropathy. After 6 months of epalrestat administration, erythrocyte sorbitol levels did not decrease in patients as a whole. However, a decrease in erythrocyte sorbitol levels during epalrestat administration was significantly correlated with baseline erythrocyte sorbitol levels (ρ=-.47, P<.01): The higher the level at baseline, the greater the decrease after epalrestat treatment. Moreover, the mean sorbitol level during epalrestat treatment was associated with the beneficial effect of epalrestat on vibration sensitivity as measured with a C-128 tuning fork (ρ=-.66, P<.01) and/or a pallesthesiometer TM-31A (ρ=.53, P<.05). On the other hand, erythrocyte sorbitol levels did not reflect the prognosis of nerve conduction velocity. These findings at least partly suggest a causal relationship between polyol activation and the development of diabetic neuropathy. Aldose reductase inhibitor treatment may be clinically useful in the control of polyol activation, especially in patients with excessive accumulation of sorbitol. © 2006 Elsevier Inc. All rights reserved

Profile of rhythmic gene expression in the livers of obese diabetic KK-Ay mice

金沢大学大学院医学系研究科環境社会医学Although a number of genes expressed in most tissues, including the liver, exhibit circadian regulation, gene expression profiles are usually examined only at one scheduled time each day. In this study, we investigated the effects of obese diabetes on the hepatic mRNA levels of various genes at 6-h intervals over a single 24-h period. Microarray analysis revealed that many genes are expressed rhythmically, not only in control KK mice but also in obese diabetic KK-Ay mice. Real-time quantitative PCR verified that 19 of 23 putative circadianly expressed genes showed significant 24-h rhythmicity in both strains. However, obese diabetes attenuated these expression rhythms in 10 of 19 genes. More importantly, the effects of obese diabetes were observed throughout the day in only two genes. These results suggest that observation time influences the results of gene expression analyses of genes expressed circadianly. © 2006 Elsevier Inc. All rights reserved