Carbon-supported Pd-based binary alloy electrocatalysts (Pd–Co and Pd–Ni) with different particle sizes for polymer electrolyte fuel cells were prepared by a NaBH4 reduction method and investigated to examine effects of the size and lattice constant of the Pd alloy nanoparticles on the oxygen reduction reaction (ORR) activity. The particle size and lattice constant were controlled in the wide ranges 4.2–12.1 and 0.3802–0.3948 nm, respectively by heating the catalysts in specific atmospheres. The alloy structures were characterized by X-ray diffraction, transmission electron microscopy and X-ray absorption fine structure. The electrochemical tests of the Pd–Co/C and Pd–Ni/C catalysts were performed by cyclic voltammetry and rotating disk electrode in 0.1 M HClO4. Nearly linear relationship between the lattice constant and nanoparticle size was observed with the Pd–Co and Pd–Ni nanoparticles. The nanoparticle sizes and lattice constants of the Pd–Co/C and Pd–Ni/C electrocatalysts, which influence the Pd d-band center, showed positive and inverse relations with the ORR specific activities, respectively. The mass activities of the Pd–Co/C and Pd–Ni/C electrocatalysts showed an increasing trend with the lattice expansion. 相似文献
As a pretreatment for membrane microfiltration (MF), the use of powdered activated carbon (PAC) with a particle size much smaller than that of conventional PAC (super-powdered PAC, or S-PAC) has been proposed to enhance the removal of dissolved substances. In this paper, another advantage of S-PAC as a pretreatment for MF is described: the use of S-PAC attenuates trans-membrane pressure increases during the filtration operation. The floc particles that formed during coagulation preceded by S-PAC pretreatment were larger and more porous than the floc particles formed during coagulation preceded by PAC pretreatment and those formed during coagulation without pretreatment. This result was due to increased particle–particle collision frequency and better removal of natural organic matter, which inhibits coagulation by consuming coagulant, before the coagulation reaction. The caked fouling layer that built up on the membrane surface was thus more permeable with S-PAC than with normal PAC. Both physically reversible and irreversible membrane foulings were reduced, and more stable filtration was accomplished with S-PAC pretreatment. 相似文献
To analyze the interplay between crystallization and liquid–liquid phase separation (LLPS), isothermal crystallization behavior of poly(ethylene glycol) (PEG) in blends with isotactic poly(methyl methacrylate) (i-PMMA) was investigated by differential scanning calorimetry (DSC). The blend system had an upper critical solution temperature (UCST) type phase diagram. When the crystallization occurred simultaneously with LLPS, the overall crystallization rate was enhanced at high crystallization temperatures Tc, relatively compared with that of neat PEG. This behavior was interpreted by the combination of the effects of spinodal quench depth ?Ts and usual supercooling degree ?Tc, according to the theory of Mitra and Muthukumar, namely, the crystallization rate is enhanced by the concentration fluctuation-assisted nucleation at high Tc. In the crystallization after LLPS proceeded, on the other hand, the overall crystallization rate was slow and less dependent on the blend composition. In addition, it was revealed by small-angle X-ray scattering measurements that amorphous i-PMMA was excluded from the interlamellar region of PEG crystals in SQ as well as WQ. 相似文献
The present study evaluated the utility of xenon computed tomography (Xe-CT) as a noninvasive diagnostic procedure for the measurement of hepatic tissue blood flow (TBF) in patients with nonalcoholic fatty liver disease (NAFLD) or chronic hepatitis C (CH-C).
Methods
Xe-CT was performed in 93 patients with NAFLD and in 109 patients with CH-C. Subjects were classified into one of three groups, based on fibrosis stage: group 1, no bridging fibrosis; group 2, bridging fibrosis; and group 3, liver cirrhosis. Correlations between hepatic TBFs in each fibrosis stage were examined.
Results
In group 1, portal venous TBF (PVTBF), hepatic arterial (HATBF), and total hepatic TBF (THTBF) were significantly lower in patients with in nonalcoholic steatohepatitis (NASH) than in those with CH-C (p < 0.001, p < 0.05, p < 0.001, respectively). In group 2, PVTBF and THTBF were significantly lower in patients with in NASH than in those with CH-C (p < 0.001, p < 0.05, respectively). In group 3, hepatic TBFs were not significantly different when comparing patients with NASH and those with CH-C.
Conclusions
PVTBF decreased due to fat infiltration. Therefore, hemodynamic changes occur relatively earlier in NAFLD than in CH-C. Patients with NASH should be monitored carefully for portal hypertensive complications in the early fibrosis stage. 相似文献
A very simple and versatile GC method has been developed that can be utilized for quick analysis, in many samples, of the
FA compositions at the sn-2- and sn-1,3-positions of TAG. By using the lipase-catalyzed, sn-1,3-regioselective esterexchange reaction of TAG with ethyl acetate, followed by direct injection of the crude reaction mixture
into the GC apparatus without any pretreatment, the FA located at the sn-2-position could accurately be analyzed as a TAG derivative in which the sn-1,3-positions were substituted by an acetate residue. Furthermore, the FA located at the sn-1,3-positions could simultaneously be analyzed as the corresponding ethyl ester derivatives using this method. The reliability
of the analytical method was compared with conventional methods by analyzing the TAG consisting of caprylic acid (C) at the
sn-2-position and oleic acid (O) at the sn-1,3-positions, giving comparable analytical results. The present method was applied to the analysis of the structured lipids
CCD and CCE, consisting of TAG as a major component in which C and the highly unsaturated FA, DHA (D) or EPA (E), were specifically
bound at the sn-2- and the sn-1,3-positions, respectively. 相似文献
Mullite–ZrO2 composites have been fabricated by attrition milling a powder mixture of zircon, alumina, and aluminum metal with MgO or TiO2 as sintering additives, heating at 1100°C to oxidize the aluminum metal, and consolidation by spark plasma sintering (SPS). The influence of the SPS temperature on the formation of mullite, and the density and the mechanical properties of the resulting composites have been studied. For the mullite–zirconia composites without sintering additives, the mullite formation was accomplished at 1540°C. In contrast, for the composites having MgO and TiO2, the formation temperature dropped to 1460°C. The composites without sintering additives were almost fully dense (99.9% relative density) and retained a larger amount of tetragonal zirconia. Those materials attained the best mechanical properties ( E =214 GPa and K I C =6 MPa·m1/2). To highlight the advantages of using the SPS technique, the obtained results have been compared with the characteristics of a mullite–zirconia composite prepared by the conventional reaction-sintering process. 相似文献
Many dangling bonds in hydrogenated amorphous carbon (a-C:H) films are usually generated by bombardments of high-energy ion precursors in typical chemical vapor deposition (CVD). To generate low dangling bonds, a-C:H films should be deposited from low-energy radical species. Surface wave plasma (SWP) generates low-energy and high-density radicals. We prepare a-C:H films using SWP and investigate the relationship between the plasma characteristics and structures of a-C:H films. The microwave of the TM01 mode was introduced through the dielectric window and SWP generate under the dielectric window. An Ar and C2H2 plasma mixture mainly consists of neutral radical species, and the electron temperature is as low as 1 eV. Electron density significantly decreases with increasing distance from the dielectric window. The a-C:H films are prepared from these hydrocarbon and carbon low-energy radicals as main precursors. The sp2 bonded network cluster size in a-C:H films increase with electron density in SWP. This structure change is the influence of the termination structure of clusters changing to CH from CH3 and CH2. 相似文献
Summary: The effects of various additives: poly(D ‐lactic acid) (PDLA), talc, fullerene C60, montmorillonite, and various polysaccharides, on the non‐isothermal crystallization behavior of poly(L ‐lactic acid) (PLLA), during both the heating of melt‐quenched films from room temperature, and the cooling of as‐cast films from the melt, was investigated. When the melt‐quenched PLLA films were heated from room temperature, the overall PLLA crystallization was accelerated upon addition of PDLA or the stereocomplex crystallites formed between PDLA and PLLA, the mixtures containing PDLA, and the mixture of talc and montmorillonite. No significant effects on the overall PLLA crystallization were observed for talc, C60, montmorillonite, and the mixtures containing C60. Such rapid completion of the overall PLLA crystallization upon addition of the aforementioned additives can be ascribed to the increased density (number per unit volume or area) of PLLA spherulites. When the as‐cast PLLA films were cooled from the melt, the overall PLLA crystallization completed rapidly, upon addition of PDLA, talc, C60, montmorillonite, and their mixtures. Such rapid overall PLLA crystallization is attributable to the increased density of the PLLA spherulites and the higher nucleation temperature for PLLA crystallization. In contrast, the addition of various polysaccharides has no significant effect, or only a very small effect, on the overall PLLA crystallization during heating from room temperature or during cooling from the melt. This finding means that the polysaccharides can be utilized as low‐cost fillers for PLLA‐based materials, without disturbing the crystallization of the PLLA. The effect of additives in accelerating the overall PLLA crystallization during cooling from the melt, decreased in the following order: PDLA > talc > C60 > montmorillonite > polysaccharides.
Polarization optical photomicrographs of pure PLLA, and the PLLA‐F film, with the fullerene additive, during cooling from the melt (Process IIB). Both of the photomicrographs were taken at 120 °C. 相似文献
Novel fluoroalkyl end‐capped oligomer/hydroxyapatite nanocomposites have been easily prepared by the reaction of disodium hydrogenphosphate and calcium chloride in the presence of self‐assembled molecular aggregates formed by fluoroalkyl end‐capped oligomers in aqueous media. The fluorinated hydroxyapatite nanocomposites thus obtained were found to exhibit a good dispersibility in a variety of media, and were applied to the surface modification of glass.