Cinar Oncel

Carbon Nanotube Synthesis via the Catalytic CVD Method: A Review on the Effect of Reaction Parameters

Abstract 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.

Chemical Synthesis of Mixed Oxide Powders for Solid Oxide Fuel Cell (SOFC) Electrolyte and Electrodes

Synthesis of LSGM (La0.9Sr0.1Ga0.8Mg0.2O3-δ), LSFM (La0.9Sr0.1Fe0.8Mg0.2O3-δ), and LSCM (La0.9Sr0.1Cr0.8Mg0.2O3-δ) powders were achieved via an organic precursor method. Different organic “carrier” molecules were used for powder synthesis. Citric acid (CA), tartaric acid (TA), Pechini precursors, polyvinyl alcohol, and ethylenediaminetetraacetic acid (EDTA) 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. It was determined that amorphous LSGM first crystallizes at 625°C. However, elimination of undesired phases requires higher temperatures. Possible implications of limited MgO solubility on the ionic conductivity are presented. 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. ______ * To whom the correspondence should be addressed. Mehmet Ali Gulgun, Sabanci University, FENS, Tuzla, 34956, Istanbul, Turkey; e-mail: m-gulgun@sabanciuniv.edu

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.

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.