Solid oxide-molten carbonate nano-composite fuel cells: Particle size effect

Varying the amount of specific interface area in the CeO2-Na2CO3 nanocomposite fuel cell electrolyte helped reveal the role of interfaces in ionic conductivity. We mixed ceria particles with micrometer or nanometer size distributions to obtain a specific surface area (SSA) in the composite from 47 m(2) g(-1) to 203 m(2) g(-1). Microstructural investigations of the nanocomposite showed that the Na2CO3 phase serves as the glue in the microstructure, while thermal analysis revealed a glass transition-like behavior at 350 degrees C. High SSA enhanced the ionic conductivity significantly at temperatures below 400 degrees C. Moreover, the activation energy for the Arrhenius conductivity (sigma T) of the composites was lower than that of the Na2CO3 phase. This difference in the activation energies is consistent with the calculated dissociation energy of the carbonate phase. The strong dependence of conductivity on the SSA, along with differences in the activation energies, suggests that the oxide surface acted as a dissociation agent for the carbonate phase. A model for the solid composite electrolyte is proposed: in the nanocomposite electrolyte, the oxide surface helps Na2CO3 dissociate, so that the "liberated" ions can move easily in the interaction region around the oxide particles, giving rise to high ionic conductivities. (C) 2014 Elsevier B.V. All rights reserved

Crystallization of CaAl4O7 and CaAl12O19 powders

Calcium is always present in alumina systems as an unintentional (or intentional) dopant, and yet the fundamental effect of its incorporation into the aluminas is not well understood, and is further complicated by the presence of Si. The synthesis of powders of two calcium aluminate phases (CaAl4O7, which is also known as CaO 2Al2O3 or CA2, and CaAl12O19, which is also known as CaO 6Al2O3 or CA6) has been investigated using low-temperature chemical-processing techniques. The crystallization of these powders from the amorphous precursor has been examined using various characterization techniques. The precursors for the powders were prepared by mixing stoichiometric proportions of the nitrate salts into a 5 wt% aqueous solution of poly(vinyl alcohol). Conversion of the amorphous precursors to crystalline powders and the subsequent phase transitions were monitored using differential thermal analysis (DTA), thermogravimetric analysis (TGA) and powder X-ray diffractometry (XRD). While powders with CA2 stoichiometry crystallized directly at 883C, amorphous powders with CA6 stoichiometry first crystallized into an intermediate structure without partitioning and then transformed into CA6 at 1175C. Fully and partially crystallized powders were analyzed using transmission electron microscopy and electron energy-loss spectroscopy (EELS). Measured near-edge structures (Al-L2,3, Ca-L2,3 and O-K) are presented for the CA2, -Al2O3 and CA6 phases. The intermediate phase, identified as -Al2O3, was found to accommodate a significant concentration of Ca

Characterizing CA(2) and CA(6) using elnes

Calcium aluminates, compounds in the CaO-Al2O3 phase system, are used in high-temperature cements and refractory oxides and have wide range of potential technological applications due to their interesting optical, electrical, thermal, and mechanical properties. They are used in both crystalline and glassy form; the glass is an isotropic material while the crystalline materials may be highly anisotropic. This paper will consider two particular crystalline materials, CA(2) and CA(6), but the results should be applicable to all calcium aluminates. Although CA(2) and CA(6) crystals contain the same chemical species, Ca, Al, and O, the coordination and local environments of these species are different in the two structures and hence they show very different energy-loss near-edge structures (ELNES) when examined by electron energy-loss spectroscopy (EELS) in the TEM. The data obtained using ELNES can effectively provide a fingerprint for each compound and a map for their electronic structure. Once such fingerprints are obtained, they can be used to identify nano-sized particles/grains or material at interfaces and grain boundaries. In the present study, the local symmetry fingerprints for CA(2) and CA(6) structures are reported combining experimental spectra with electronic-structure calculations that allow the different features in the spectra to be interpreted. Al-L-2,L-3 and O-K edge core-loss spectra from CA(2) and CA(6) were measured experimentally using electron energy-loss spectroscopy in a monochromated scanning transmission electron microscope. The near-edge structures were calculated for the different phases using the orthogonalized linear combination of atomic-orbitals method, and took account of core-hole interactions. It is shown that CA(2) and CA(6) structures exhibit distinctive experimental ELNES fingerprints so that these two phases can be separately identified even when present in small volumes

The value of F-18-fluorodeoxyglucose positron emission tomography/computed tomography in carcinoma of an unknown primary: diagnosis and follow-up

WOS: 000272915000010PubMed ID: 19952921Background The management of the patients with carcinoma of an unknown primary represents a difficult challenge in oncology. F-18-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) has provided new insights in the diagnosis, staging, and follow-up of oncological patients. Aim This study aimed to investigate the value of FDG PET/CT in clarifying the primary site in our patients with histologically proven tumor metastasis (HPM) or with a high clinical suspicion of malignancy, and the clinical impact of this technique on the management of these patients. Methods In total 94 patients from two centers underwent FDG PET/CT imaging; 78 patients with HPIVI and 16 patients with a clinical suspicion of malignancy. The histology and/or follow-up data were used as the gold standard. Hypermetabolic findings at the site of the pathological CT changes or at physiological FDG uptake sites were the criteria for malignancy. PET/CT findings were analyzed for the identification of the primary tumor site, for the relationship with survival, and also for the effect in chemotherapy monitoring. Results Primary malignancy was discovered in 53 of 90 patients (59%) histologically and 37 (41%) patients' primary tumor sites were not found during the study period. Amongst 90 patients, five (6%) were normal on FDG PET/CT. Of 85 patients (94%) with pathological findings on FDG PET/CT, 27 patients (32%) had solitary and 58 (68%) patients had multiple organs affected. Regarding the whole study population, a sensitivity of 74% and a specificity of 78% were calculated for FDG PET/CT imaging. Regarding the patients with HPM, the sensitivity and specificity values were 84 and 81%, respectively. The mean survival time of the patients with disseminated disease was significantly shorter than those of the patients with single or no lesion (13.44 +/- 1.61, 20.98 +/- 2.0 and 26.67 +/- 2.73 months, respectively, P = 0.014). In seven of eight patients, follow-up FDG PET/CT scans effectively monitored the patients' therapies. Conclusion Whole-body FDG PET/CT has to be considered a useful method, especially in an early phase of the diagnostic workup of patients with carcinoma of an unknown primary syndrome, to optimize the management. Nucl Med Commun 31:59-66 (C) 2010 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins

Production of Small, Stable PbS/CdS Quantum Dots via Room Temperature Cation Exchange Followed by a Low Temperature Annealing Processes

Here, we discuss a simple low temperature process for the synthesis of small and stable PbS/CdS QDs with emission below 1100 nm. For this, small PbS QDs with emission below 1100 nm synthesized from PbCl₂ in oleylamine with 1-dodecanethiol, as reported by our group recently, were used. A thin CdS shell was grown on PbS at room temperature (RT) via cation exchange (CE), which is a self-limiting process providing about 100 nm blue shift in the emission maxima, hence is quite practical for reaction control and production of predictable particles. RTCE process provides 6–9 times stronger emission than original PbS with better optical stability. Annealing of the PbS/CdS QDs in solid state at mild temperatures (50–100 °C) improves crystallinity of the particles. Final ligand exchange on the annealed PbS/CdS with 1-dodecanethiol (DT) enhances the long-term stability of particles further. The optimum overall process is determined as RTCE followed by annealing at 50 °C for 1 h and finished with ligand exchange with DT. Influence of these processes on QD structure and optical properties were studied as well as stability in chloroform and petroleum products (diesel and gasoline) for possible optical tagging applications of such liquids. Overall, a simple, controllable, and scalable method is developed to produce highly stable, bright, size-tunable PbS/CdS QDs with emission detectable with low cost semiconductor detectors

Al L2,3- and O K-edge ELNES of Strontium Aluminate

In order to study dopant effects on phosphorescence properties, single phase SrAl4O7 was synthesized using a low temperature, modified Pechini process. The resulting powders were characterized by X-ray diffraction, which indicated that the strontium aluminate powder consisted of a single phase. However, EELS was used to characterize the crystal field of the ions in strontium aluminate, and variations in the ELNES fine structure of the Al-L2,3 and O-K edges revealed the presence of multiple phases and hydroxylation, rendering it impossible to obtain a fingerprint ELNES structure for the single phase compound. By incorporating intermediate re-grinding steps during the synthesis heat treatment, the variation in the ELNES fine structure was eliminated, which indicated unequivocally that single phase SrAl4O7 was produced and maintained upon doping with Eu concentrations of < 1 wt%