Shiwoo Lee

Oxygen-permeating property of LaSrBFeO3 (B=Co, Ga) perovskite membrane surface-modified by LaSrCoO3

Abstract Oxygen permeation fluxes have been investigated as a function of temperature for a mixed ionic–electronic conducting La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and La0.7Sr0.3Ga0.6Fe0.4O3−δ (LSGF) membranes. Ga-doped composition, which is known for its chemical and structural stability, shows limited oxygen permeation flux as compared with a Co-containing system. However, modification of both surfaces with catalytically surface-reactive La0.6Sr0.4CoO3−δ (LSC) makes Ga-doped perovskite an excellent oxygen-permeable membrane. It has been demonstrated that the effective area of reactive free surface is an important factor in determining the effectiveness of surface modification by La0.6Sr0.4CoO3−δ. On the contrary, the oxygen permeation flux of La0.6Sr0.4Co0.2Fe0.8O3−δ is not affected by surface modification. The rate-determining process is discussed in conjunction with the apparent activation energy for oxygen permeation. As cationic substitution occurs in the vicinity of the interface between the coating layer and substrate membrane at elevated temperatures, the intermediate composition, that is, (La1−xSrx)(Coy′GayʺFe1−y′−yʺ)O3−δ, has been formed in La0.7Sr0.3Ga0.6Fe0.4O3−δ membrane surface-modified by La0.6Sr0.4CoO3−δ.

Enhancement of oxygen permeation by La0.6Sr0.4CoO3−δ coating in La0.7Sr0.3Ga0.6Fe0.4O3−δ membrane

Abstract A La0.7Sr0.3Ga0.6Fe0.4O3−δ membrane with perovskite structure is fabricated by a conventional solid-state reaction. As the oxygen permeation flux of the La0.7Sr0.3Ga0.6Fe0.4O3−δ membrane was lower than commercial gas separation membranes, we coated a La0.6Sr0.4CoO3−δ layer to enhance the oxygen permeation flux. The La0.6Sr0.4CoO3−δ coating was very effective for increasing oxygen flux, as the flux was as much as 2 to 6 times higher than that of an uncoated La0.7Sr0.3Ga0.6Fe0.4O3−δ membrane. Moreover, the oxygen permeation flux was strongly influenced by the porosity of the coating layer. XRD analysis after the oxygen permeation confirmed that Ga-based membranes have a phase stability.

Li₂ZrO₃ 분리막의 제조와 이산화탄소 선택투과 전후의 기계적 특성 평가

In this study, we investigated Li₂ZrO₃ membrane as a candidate material for high-temperature CO₂ separation and evaluated mechanical property. Li₂ZrO₃ powder was synthesized by solid state reaction of Li₂CO₃ and ZrO₂. Then we fabricated Li₂ZrO₃ tape using tape casting method. Dense Li₂ZrO₃ membrane prepared by sintering at 1600℃ for 2 h after pressing Li₂ZrO₃ tape using lamination machine. Mechanical properties before and after CO₂ absorption of fabricated Li₂ZrO₃ membrane such as Hertzian indentation, Vickers hardness and 3-point bending testing were evaluated.

Fabrication and characterization of oxide ion conducting films, Zr1−xMxO2−δ (M = Y, Sc) on porous SOFC anodes, prepared by electron beam physical vapor deposition

A key obstacle in reducing temperature loss is ohmic loss, which could be lowered by the use of thin electrolytes in electrochemical devices and thus various thin film processing methods have attracted much attention for applications in the SOFC market. Doped stabilized zirconia, Zr1−xMxO2−δ (M = Y, Sc), thin films were successfully deposited on a porous Ni-YSZ substrate via a commercial 10 kW EB-PVD system. The highly conductive and dense Zr1−xMxO2−δ (M = Y, Sc) thin films could be obtained by optimizing the distance (20–40 cm) between the substrate and target, angle (cos α, α = 0.19π–0.36π) for deposition area and substrate temperature (600–950 °C). Pseudo-cubic phase zirconia, with a preferential crystalline growth (111) and a unique columnar morphology, was observed with a fairly good value of conductivity; ScSZ and YSZ films had conductivities of 0.23 and 0.11 S cm−1 at 900 °C in air. This was achieved on the films which were prepared with proper geometric factors for physical deposition and with a substrate temperature of 950 °C. Finally, the YSZ and ScSZ electrolytes, prepared by EB-PVD, were applied on a solid oxide fuel cell with a Ni-YSZ anode and LSM cathode, which showed 1 W cm−2 of power density under 0.75 V at 900 °C.

Piston guide and magnet assembly for the KRISS watt balance

The piston guide and magnet assembly for the KRISS watt balance were tested. The velocity of the piston guide was controlled within 4×10-3 at the velocity of 2 mm s-1 using a linear motor and linear encoder feedback. The magnet assembly which consists of two permanent magnet rings and closed yokes was fabricated. B-field at the air gap of 25 mm was measured using a Hall probe. The B-field uniformity was within 5×10-4 over the vertical distance of 24 mm.

Dual Phase 전도성 CO₂ 분리막

Novel conductive CO₂ membranes composed of dual phases, molten carbonates and electronic conducting ceramics, were investigated. As the microstructure control of electronic conducting ceramic supports is extremely important to keep the molten carbonates stable in the membranes by a capillary force applied by the pore structure of the supports, we have scrutinized the microstructure of the electronic conducting supports utilizing microscopic images and gas permeability measurement. From the evaluation of the electrical conductivities of the molten carbonates and the electronic conducting ceramic supports, we found that the ionic conductivity of the molten carbonates could determine CO₂ flux through the dual phase membranes if the surface exchange rate were relatively high enough.

고상반응에 의하여 제조된 Li₂ZrO₃의 이산화탄소 흡수 및 소결 특성

We synthesized lithium zirconate using solid-state reaction and analyzed thermal properties (TG/DTA) of starting materials and the synthesized one. When Li₂ZrO₃ powder was exposed to CO₂ environment at 500℃, 93% of the theoretical absorption weight was gained within 280 min with fairly high sorption rate. Almost all the absorbed CO₂ was generated by heating the sample to 800℃. We also investigated densification behavior of Li₂ZrO₃ under CO₂ environment. By sintering Li₂ZrO₃ at 760℃ using 2-step process, we obtained dense product, composed mainly of Li₂ZrO₃ and ZrO₂, with relative density of 92%.

압출공정에 의해 제조된 Ni-YSZ 원통형 음극 지지체의 특성

The microstructure of Ni-YSZ cermets was controlled with fine and coarse starting powders (NiO and YSZ) to obtain a optimum strong and conductive tubular anode support for SOFCs. Three types of cermets with different microstructures, i.e., coarse Ni-fine YSZ, fine Ni-coarse YSZ, and fine Ni-fine YSZ, were fabricated to investigate their electrical and mechanical properties. The cermets from fine NiO powder showed high electrical conductivity due to the enhanced percolation of Ni particles. The cermet by fine Ni and coarse YSZ showed excellent electrical conductivity (＞1000 S/㎝) despite its high porosity (~40%) but it showed poor mechanical strength due to the lack of percolation by YSZ particles and due to large pores. Thus fine NiO and YSZ powders were used to make strong and conductive Ni-YSZ support tube by extrusion. The microstructure of the anode tube was modified by the amount of polymeric additives and carbon black, a pore former. Ni-YSZ tube (porosity ~34%) with the finer microstructure showed better performance both in electrical conductivity (＞1000 S/㎝) and fracture strength (~140㎫). Either flat or circular NiO-YSZ tubes with the length from 20 to 40㎝ were successfully fabricated with the optimized composition of materials and polymeric additives.

Partial Oxidation of CH 4 Using {0.7}Sr 0.3 Ga 0.6 Fe 0.4 O 3-δ for Soild Oxide Fuel Cell

We fabricated mixed ionic-electronic conducting membranes, , by solid state reaction method for solid oxide fuel cell. The membranes consisted of single perovskite phase and exhibited high relative density,

Mechanical properties and structural stability of perovskite-type, oxygen-permeable, dense membranes

>95\%