Sung-Ki Lim

Influence of stabilizers on Na-β-Al2O3 phase formation in Li2O(MgO)-Na2O-Al2O3 ternary systems

The influences of stabilizers on β- and β′′-Al2O3 phase formations in Li2O(MgO)-Na2O-Al2O3 systems were investigated. When stabilized with 4MgCO3ċMg(OH)2ċ5H2O, most of the β′′-Al2O3 phase formed below 1200°C and further β- to β′′-Al2O3 transformation with an increase of temperature was not observed. On the other hand, when stabilized with Li2CO3,β′′-Al2O3 formation occurred by two steps. First, β′′-Al2O3 was partly formed below 1200°C, and, second, noticeable transformation from β-Al2O3 to β′′-Al2O3 occurred at higher temperature ranges. It was shown that transient eutectic liquid in the Li2O-Na2O-Al2O3 system promoted the β- to β′′-Al2O3 transformation at higher temperatures. Uniform distribution of both Mg2+ and Li+ stabilizing ions enhanced β′′-Al2O3 formation at low temperatures. In the Li-stabilized systems, however, homogeneous distribution of Li+ ions hindered both the formation of transient eutectic liquid and the second β- to β′′-Al2O3 phase transformation at high temperatures.

Fabrication of β- and β′′-Al2O3 tubes by pressureless powder packing forming and salt infiltration

A new forming method, pressureless powder packing (PLPP), was studied to fabricate the β- and β′′-Al2O3 tubes. Alkali sources were infiltrated into the pores of α-Al2O3 tube preforms that had been prepared by the PLPP forming method. The composition for the synthesis of β′′-Al2O3 phase was Na2O · 0. 138Li2 · 4.4Al2O3. The β′′-Al2O3 fraction of calcined and sintered bodies was increased with the increase of calcination temperature, and phase formation was largely affected by the type of starting α-Al2O3. Large particle size and narrow size distribution of fused α-Al2O3 resulted in uniform green microstructure that enhanced the homogeneity of alkali salts after infiltration, which was very important for the β′-Al2O3 formation. Sintered microstructure was uniform in all specimens but further development was required for density improvement.

Effects of calcium impurity on phase relationship, ionic conductivity and microstructure of Na+- β / β″-alumina solid electrolyte

Ca-doped Na+- β/β′′-alumina was synthesized using a solid-state reaction. The changes in the properties of Na+- β/β′′-alumina resulting from the presence of Ca impurity were studied. Ca (0–5 wt%) was added to the respective samples, which were then sintered. The specimens were characterized using X-ray diffraction, scanning electron microscopy, densimetry and impedance analysis. In the sintered specimens, the β′′-alumina phase fraction decreased as Ca content increased, whereas the relative sintered density increased. The surface morphology of Ca-doped Na+- β/β′′-alumina specimens showed a Ca-rich layer, which was the main cause of increase in the specific resistance.

High-intensity focused ultrasound treatment for skin: ex vivo evaluation.

High‐intensity focused ultrasound (HIFU) has been used for skin tightening. However, there is a rising concern of irreversible adverse effects. Our aim was to evaluate the depth of thermal injury zone after HIFU energy passes through different condition.