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

Using natural gas as an environmentally sustainable power source with solid oxide fuel cells

Policies, research and pilot projects to commercialize carbon capture in the power sector have focused on coal plants. However, the expected world-wide consumption of natural gas in the power sector is not consistent with a sustainable environmental future without also employing carbon capture technologies to natural gas plants. One reason carbon capture from natural gas has not received much attention is, as will be discussed below, the very high cost of carbon capture from natural gas plants compared to the already considerable cost of carbon capture from coal plants. Capture of carbon with conventional natural gas turbines is not economically practical. Consequently, a different technology is needed to generate electricity from natural gas in the power sector. This technology should be competitive with natural gas turbines (disregarding its ability to employ carbon capture). This technology should permit the capture of carbon at low cost. Ideally, the cost should be significantly lower than the cost of carbon capture from coal plants (as measured by the cost per ton of captured CO2). Solid oxide fuel cells (SOFCs) are the leading technology to meet these requirements. Their emissions of CO2 without carbon capture are relatively low due to their high efficiency. Significantly, in the SOFC exhaust, CO2 is only comingled with water and unreacted CH4. This enables low-cost separation of CO2. In addition, the efficiency losses from the application of carbon capture are minimal compared to the significant efficiency losses when carbon capture is applied to coal power plants or natural gas turbines. The primary barrier to the uptake of SOFCs is the development of a grid-scale SOFC with a comparable cost and reliability compared to the natural gas turbine. With a cost-competitive grid scale SOFC technology, the additional cost of carbon capture would be minimal compared to the cost-prohibitive carbon capture technologies that are available for coal power plants and natural gas turbines. Consequently, commercialization of carbon capture in the power sector could be achieved with policies that impose a much lower burden on the economy and a much lower increase of the cost of electricity than is now the case. While the current research to achieve cost-competitive and reliable SOFCs for grid-scale application is encouraging, these efforts should be significantly increased in order to achieve more rapid technology development and the opportunity to achieve grid-scale commercial application, a necessary step that enables further cost reduction (technology learning, or, learning by doing)

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

Synthesis of LaSrXMg-Oxide with X=Ga, Fe, or Cr

Strontium and magnesium doped lanthanum gallate (LSGM) is a promising electrolyte material for intermediate temperature range (650-800°C) solid oxide fuel cell (SOFC) applications. Formation of unwanted phases and Ga loss at high temperatures (1100-1500°C) during synthesis and under low oxygen partial pressures during operation are major hurdles that stand in LSGM’s way of full utilization. Using a polymeric precursor synthesis method, the feasibility of producing SOFC electrolyte material LSGM is investigated. The method involves complexing each constituent metal ion by the carboxyl and/or hydroxyl group of the citric acid and/or polyvinyl alcohol (PVA) in aqueous solution. The facility of this method compared with the traditional solid state reaction method was shown by synthesis of single phase and pure LSXM (X= Fe, Cr) oxides at reasonable temperatures (800°C). The X-ray diffraction patterns of LSFM and LSCM are also reported here for the first time

Catalytic synthesis of boron nitride nanotubes at low temperatures

KFeO2 is demonstrated to be an efficient catalyst for the formation of boron nitride nanotubes (BNNT) by thermal chemical vapor deposition (TCVD). This alkali-based catalyst enables the formation of crystalline, multi-walled BNNTs with high aspect ratio at temperatures as low as 750 degrees C, significantly lower than those typically required for the product formation by TCVD

Characterization of 1-3 piezocomposites from PNN-PZT piezoceramics

Piezocomposite materials combine best properties of components while minimizing their disadvantages to provide desired properties. This study reports on piezocomposites with 1–3 connectivity prepared from 0.5Pb(Ni1/3Nb2/3)O3-0.5Pb(Zr0.3Ti0.7)O3 (0.5PNN-0.5PZT) fibers and polyurethane matrix. The PNN-PZT powder was synthesized by solid-state reaction method. PNN-PZT green fibers were drawn using the alginate gelation method. Dense sintered fibers with 500–800 µm diameter were embedded in an ordered arrangement in a polyurethane passive matrix. Structural, electrical and electroacoustic properties of PNN-PZT piezocomposite and bulk ceramic were both reported. Bulk PNN-PZT ceramics were found to have properties that are superior than the commercial soft PZT counterparts. The maximum TVR value was measured as 142.5 dB at 444 kHz for the piezocomposite, corresponding to the thickness mode resonance. The FFVS response with 3 dB variation had an average FFVS value of − 210 dB between 250 and 450 kHz band for the piezocomposite