Chemical synthesis of multi-cation oxide powders for solid oxide fuel cell (SOFC) components

This study involves the synthesis of LSGM (Lao.gSro.iGao.sMgo.aOs-a), LSFM (Lao.9Sr0.iFe0.8Mgo.203-5), and LSCM (Lao.gSro.iCro.sMgtuOs-s) powders via organic precursor method by using different organic carrier materials, investigation on the effects of each organic carrier material on the intended and unwanted phase formations, analyses of formed phases during stages of synthesis, characterization of the synthesized powders, crystallographic studies on the several new crystal phases, the effects of holding time during powder calcination, and further work advices. Citric acid, tartaric acid, Pechini precursors, polyvinyl alcohol, and ethylene diaminetetraacetic acid were used as organic carrier materials. Different organic carrier materials exhibited different behavior on the synthesis of powders. Synthesis of powders without carrier materials was conducted and the effectiveness of organic carrier materials was confirmed. In the LSGM synthesis, the effects of different starting materials (namely lanthanum chloride or gallium sulfate) were also investigated. X-ray powder diffraction measurements showed that unwanted phases formed, especially below 1000°C. In powders heat treated at low temperatures (< 1000°C), maximum LSGM concentration was 88% when citric acid was used as the organic carrier material. Above 1000°C, maximum concentration of LSGM phase in the powders was 95.7% when tartaric acid was utilized as the organic carrier material. For low temperature (below 1000°C) synthesis citric acid, and for above-1000°C synthesis tartaric acid are the best organic carrier in terms of LSGM percentages in the powders. It was shown that increasing dwell time at calcination temperature could increase the concentration of the desired phases in the powder. The powder synthesized with PVA as the organic carrier material was calcined at 1100°C and LSGM phase in the powder was 33.7%. When same powder held 7 hours at the calcination temperature, LSGM phase in the powder increased up to 79.8%. Single-phase LSFM was obtained in the powders calcined as low as at 550 C. In contrast to LSFM, maximum concentration of LSCM phase in the synthesized powders was 96.9%, when polyvinyl alcohol (PVA) was the organic carrier material. The factors affecting the purity of the desired phase were stated as the type of the organic carrier material, its cation chelating and/or complexing ability, and the interaction of the functional groups with the constituent cations. The necessity for further studies the organic carrier - cation interaction highlighted. The structures of La4Ga209 and LSCM were discussed in light of the observed shifts in the peak positions in the x-ray spectra

Chemical synthesis of LSGM powders for solid oxide fuel cell (SOFC) electrolyte

Synthesis of LSGM (La0.9Sr0.1Ga0.8Mg0.2O3-delta), LSFM (La0.9Sr0.1Fe0.8Mg0.2O3-delta), and LSCM (La0.9Sr0.1Cr0.8Mg0.2O3-delta) powders were achieved via organic precursor method. Different organic "carrier" molecules were used for powder synthesis. Citric acid, tartaric acid, Pechini precursors, polyvinyl alcohol, and ethylene diaminetetraacetic acid were selected as organic carriers for their ability to stabilize the metal ions. Each organic carrier material exhibited a different degree of effectiveness in the synthesis of the mixed oxide powders. One of the main factors affecting the phase purity appears to be the interaction of the functional groups with the constituent cations. The effectiveness of the organic carrier with varying number and type of functional groups is evaluated and discussed in terms of the phase distribution in the powders after the calcination step

Carbon nanotube synthesis via the catalytic CVD method: a review on the effect of reaction parameters

This review covers the results obtained in carbon nanotube synthesis by chemical vapor deposition. Parameters such as catalysts, supports, carbon precursors, reaction time, temperature and gas flow rates that are used in the production of carbon nanotubes are discussed throughout the text. Purification of the synthesized carbon nanotubes and methods utilized for cost reduction were also explored

X-ray single phase LSGM at 1350 °C

Synthesis of X-ray-phase-pure (La1−xSrxGa1−yMgyO3−δ, LSGM, where x = 0.1, y = 0.15 and 0.17) powders were achieved at temperatures as low as 1350 °C via organic precursor method using tartaric acid as the carrier material. LSGM materials were characterized for their phase purity, crystallization and electrical properties. Pellets sintered at 1350 °C for 6 h were single phase and dense (>99%). Electron microscopy analysis of X-ray single-phase pellets revealed MgO precipitates with sizes ranging from 50–300 nm. Phase formation and distribution in this complicated multi-cation-oxide system as a function of temperature were reported and discussed. Amorphous LSGM first crystallizes at 625 °C. However, elimination of undesired phases require higher temperatures. Impedance measurements as a function of temperature up to 545 °C revealed that the X-ray phase pure pellets may have extrapolated ionic conductivity values as high as 0.14–0.16 S/cm at 800 °C. Possible implications of limited MgO solubility on the ionic conductivity are presented

Microwave assisted processing of ceramics

Microwave heating can provide cost and time effective processing routes for ceramic systems. Microwave heating assisted drying of green compacts, low temperature sintering of certain oxides, and partial or complete nitridization, carburization or reduction of hemi-oxides have been attempted recently. Using a multi-mode microwave cavity, we were able to reduce MeOx (where Me = Cu and Ag) to their sub-oxides or base metal at close to room temperature within minutes. The product sub-oxides or metals were identified and characterized for their crystallinity and phase purity. The results suggest that the microwave heating can provide an alternative, cost effective route for alloying for certain metals. The criteria for effectiveness of microwave heating and the coupling between the materials and the electromagnetic wave are discussed

Yttrium aluminum garnet as a scavenger for Ca and Si

Doped yttrium aluminum garnet, Y3Al5O12 (YAG), has drawn considerable attention for solid-state industrial, medical and scientific laser applications. The crystal optical activity is closely related to the type and amount of doping element. Studies on highly yttrium doped, creep resistant alumina ceramics with Ca and Si contamination have indicated that YAG precipitates in the ceramic had a propensity to allow simultaneous incorporation of Ca and Si impurities on the order of 1 % in their structure. Co-solubility potential for Ca and Si in YAG crystals was investigated through systematic doping and co-doping YAG polycrystals with Ca2+ and/or Si4+. It was shown via X-ray diffraction and electron probe microanalysis techniques, that the ceramic can accommodate more than order of magnitude larger amounts of Ca2+ and Si4+ when incorporated in equal amounts simultaneously than when the dopants are introduced alone. The co-solubility limit for Ca and Si was determined to be between 3 and 4 % of the cation amount in pure YAG. Enhanced co-solubility was discussed in terms of size and charge compensations in the lattice. Co-doping with a suitable element is introduced as a possible way to increase the solubility of useful cations in this ceramic that is the host material for laser

Body mass index and complications following major gastrointestinal surgery: a prospective, international cohort study and meta-analysis.

AIM: Previous studies reported conflicting evidence on the effects of obesity on outcomes after gastrointestinal surgery. The aims of this study were to explore the relationship of obesity with major postoperative complications in an international cohort and to present a meta-analysis of all available prospective data. METHODS: This prospective, multicentre study included adults undergoing both elective and emergency gastrointestinal resection, reversal of stoma or formation of stoma. The primary end-point was 30-day major complications (Clavien-Dindo Grades III-V). A systematic search was undertaken for studies assessing the relationship between obesity and major complications after gastrointestinal surgery. Individual patient meta-analysis was used to analyse pooled results. RESULTS: This study included 2519 patients across 127 centres, of whom 560 (22.2%) were obese. Unadjusted major complication rates were lower in obese vs normal weight patients (13.0% vs 16.2%, respectively), but this did not reach statistical significance (P = 0.863) on multivariate analysis for patients having surgery for either malignant or benign conditions. Individual patient meta-analysis demonstrated that obese patients undergoing surgery for malignancy were at increased risk of major complications (OR 2.10, 95% CI 1.49-2.96, P < 0.001), whereas obese patients undergoing surgery for benign indications were at decreased risk (OR 0.59, 95% CI 0.46-0.75, P < 0.001) compared to normal weight patients. CONCLUSIONS: In our international data, obesity was not found to be associated with major complications following gastrointestinal surgery. Meta-analysis of available prospective data made a novel finding of obesity being associated with different outcomes depending on whether patients were undergoing surgery for benign or malignant disease

Body mass index and complications following major gastrointestinal surgery: A prospective, international cohort study and meta-analysis

Aim Previous studies reported conflicting evidence on the effects of obesity on outcomes after gastrointestinal surgery. The aims of this study were to explore the relationship of obesity with major postoperative complications in an international cohort and to present a metaanalysis of all available prospective data. Methods This prospective, multicentre study included adults undergoing both elective and emergency gastrointestinal resection, reversal of stoma or formation of stoma. The primary end-point was 30-day major complications (Clavien\u2013Dindo Grades III\u2013V). A systematic search was undertaken for studies assessing the relationship between obesity and major complications after gastrointestinal surgery. Individual patient meta-analysis was used to analyse pooled results. Results This study included 2519 patients across 127 centres, of whom 560 (22.2%) were obese. Unadjusted major complication rates were lower in obese vs normal weight patients (13.0% vs 16.2%, respectively), but this did not reach statistical significance (P = 0.863) on multivariate analysis for patients having surgery for either malignant or benign conditions. Individual patient meta-analysis demonstrated that obese patients undergoing surgery formalignancy were at increased risk of major complications (OR 2.10, 95% CI 1.49\u20132.96, P &lt; 0.001), whereas obese patients undergoing surgery for benign indications were at decreased risk (OR 0.59, 95% CI 0.46\u20130.75, P &lt; 0.001) compared to normal weight patients. Conclusions In our international data, obesity was not found to be associated with major complications following gastrointestinal surgery. Meta-analysis of available prospective data made a novel finding of obesity being associated with different outcomes depending on whether patients were undergoing surgery for benign or malignant disease