Joo-Sin Lee

Preparation and properties of Y2O3-doped ZrO2 thin films by the sol–gel process

Y2O3-doped ZrO2 (YZ) thin films were prepared on alumina substrates by the dip-coating process. The dip-coating solution consisted of a homogeneous sol, and was prepared by using the respective chlorides as raw materials, with ethylene glycol, 2-butanol and distilled water as solvents. The thin films containing 0–20 mol % Y2O3 were successfully produced by thermal treatment above 600 °C. The characterization for the film preparation was performed by means of thermogravimetric–differential thermal analysis for the thermal analysis, and scanning electron microscopy for the morphological analysis and thickness measurements. The properties of the films were characterized in terms of a study of the crystalline phase, the crystallite size, the microstructure and the electrical conductivity by using X-ray diffraction, scanning electron microscopy and the complex impedance techniques. In all YZ thin films, the tetragonal phase was stable at low temperatures as a result of the crystallite size effect. However, at higher temperatures, the tetragonal phase was transformed into either the monoclinic phase or the cubic phase, depending on the doping concentration. The YZ thin film of 8 mol% Y2O3 content was stabilized to almost cubic phase at 1000 °C. Resonable conductivity behaviour at YZ was observed for the YZ thin films. The electrical conductivity of YZ thin films was similar to the values of the sintered body.

Effect of β-Si3N4 seed particles on the property of sintered reaction-bonded silicon nitride

The effect of seeding on the microstructural development and mechanical properties of sintered reaction-bonded silicon nitride was investigated by the use of β-Si3N4 particles. Seeding of an appropriate amount of the β-Si3N4 particles gave rise to the promotion of density and the resulting increase in fracture strength and hardness. The fracture toughness was also increased due to the development of elongated grains. On the other hand, addition of a large amount of seed particles showed lower strength and fracture toughness owing to the coalescence of large elongated grains. By seeding of 2 wt.% β-Si3N4 particles on Si powders of 7 μm, high fracture strength of 1100 MPa and fracture toughness of 7.2 MPa·m1/2 were obtained in sintered reaction-bonded silicon nitride ceramics.

Synthesis and characterization of CaO-stabilized ZrO2 fine powders for oxygen ionic conductors

Abstract13 mol% calcia-stabilized zirconia (CSZ) powders were synthesized by the coprecipitation method. The characterization of powders has been investigated using thermogravimetry and differential thermal analysis for thermal analysis, X-ray diffraction and infrared spectroscopy for crystalline phases identification, Brunauer-Emmett Teller, X-ray diffraction-line broadening and transmission electron microscopy (TEM) for particle size and morphology determination. The characteristics of powders prepared by the coprecipitation method are discussed.

Molten salt synthesis of YAlO3 powders

In this work, the molten salt synthesis technique was applied to the synthesis of YAlO3 powder using LiCl, NaCl or KCl salt as the flux. YAlO3 powder was synthesized by reacting equimolar amounts of Y2O3 and Al2O3 powders in LiCl salt. The synthesis temperature for YAlO3 using LiCl salt was 1300 °C which is by about 500 °C lower than that in the conventional mixed-oxide method. The synthesized powders have been characterized using powder X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FE-SEM). The effect of the salt type on the formation of YAlO3 has also been investigated.

Effects of gallia addition on sintering behavior and electrical conductivity of yttria-doped ceria

The densification behavior and electrical conductivity of Ce0.8Y0.2O1.9 ceramics with gallia concentrations ranging from 0 to 5 mol. % were investigated. The sintered density was found to increase with increasing Ga2O3 content up to 1 mol. % and then to decrease upon further Ga2O3 addition. Dense Ce0.8Y0.2O1.9 ceramics with 94% of the theoretical density could be obtained by sintering the milled mixture with 1 mol. % Ga2O3 addition at 1400°C for 5 h. The conductivity of the 1 mol. % Ga2O3-added specimen showed a maximum value of 1.37 × 10−2 Ω−1· cm−1 at 700°C. Pure Ce0.8Y0.2O1.9 ceramics needed to be sintered at 1550°C in order to obtain an equivalent theoretical density and conductivity. The introduction of Ga2O3 doping had a good effect on the sintering properties and electrical conductivities of Y2O3-doped CeO2.

Co기 초합금 ECY768에서 응고 조직 및 탄화물 형성 거동

【Directional solidification experiments were carried out at 0.5-150

Solid solubility limits of Al2O3 and Ga2O3 in Gd2O3-doped CeO2

\mu\textrm{m}

Effects of alumina additions on sintering behavior of gadolinia-doped ceria

/s in the Co-base superalloy ECY 768. As increasing solidification rate, the dendrite length increased and it reached the maximum at 150

Effects of gallia additions on sintering behavior of gadolinia-doped ceria

\mu\textrm{m}

Effect of raw-Si particle size on the properties of sintered reaction-bonded silicon nitride

/s, where the tip temperature is close to the liquidus. The liquidus and eutectic temperatures could be estimated by comparing the dendrite lengths and the temperature gradients at the solid/liquid interface and those were estimated as