Bae-Yeon Kim

Influence of alumina particle size on fracture toughness of (Y,Nb)-TZP/Al2O3 composites

Abstract ZrO 2 /Al 2 O 3 composites were prepared by mixing a tetragonal ZrO 2 , stabilized with 5.31 mol% Y 2 O 3 and 4.45 mol% Nb 2 O 5 , and Al 2 O 3 having different particle size (0.2 μm and 2.8 μm) to investigate the influence of the Al 2 O 3 particle size on flaw tolerance of the composites. The composites exhibited rising R-curve behavior and plateau fracture toughness of 7.9 and 8.8 MPa√m for the additions of 20 vol.% of 0.2 and 2.8 μm Al 2 O 3 particles, respectively. The difference in the fracture resistance was attributed mainly to the grain size of tetragonal phase in the composites, which scaled with the Al 2 O 3 particle diameter, and partially to the dispersion toughening.

Influence of TiO2 coating thickness on energy conversion efficiency of dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) were synthesized using a 0.25 cm2 area TiO2 nanoparticle/nanorod layer as an electrode and platinum (Pt) as a counter electrode. The TiO2 nanoparticle/nanorod layer was prepared by spin coating and spray coating on fluorine-doped tin oxide glass, respectively. The Pt counter electrode and the ruthenium dye anchored electrode were then assembled as a function of thickness of the TiO2 nanorod layer in a range of 8 to 30 µm. The best photovoltaic performance was observed in the case of a DSSC consisting of a 600 nm thick TiO2 nanoparticle layer and a 20 µm thick TiO2 nanorod layer: a short circuit current density of 11.54 mA·cm−2, open circuit voltage of 0.72V, fill factor of 61.2%, and energy conversion efficiency of 5.07%. A TiO2 nanorod/nanoparticle electrode layer with good adhesion was successfully fabricated.

Effect of Al Alloy Composition on Physical and Crystallographical Properties of Plasma Electrolytic Oxidized Coatings II. Crystallographic Analysis of PEO Layer

Physical properties of Plasma electrolytic oxidized 8 different kinds of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was Na₂SiO₃ and NaOH and some alkali earthen metal salts system solution. η-alumina, as well as γ-alumina, was main crystal phase, which were ever reported. Also, Al 4.95 Si 1.05 O 9.52 was found only in this research. So we can conclude that the process conditions of PEO apparatus and composition and concentration of its electrolyte affects crystal structure and physical properties of PEO layers much more than the compositions of Al alloy.

Analysis of Oxide Coatings Formed on Al1050 Alloy by Plasma Electrolytic Oxidation

The crystal structure of surface coatings on Al1050 alloy by PEO (Plasma Electrolytic Oxidation), were investigated. The electrolyte for PEO was Na-Si-P system solution. The main crystalline phase were γ-alumina and α-alumina. Crystallinity was increased with applied voltage and applied time. The dominant crystalline phase were affected not only chemical composition of Al alloy substrate and electrolyte, but also the +/? ratio of applied voltage.

Characterization of Vacuum Dried Y, Ba, and Cu Oxalate Precipitates

Y, Ba and Cu nitrates were precipitated by oxalic acid at pH 4. The Y, Ba and Cu oxalate powders were vacuum dried and characterized by XRD, DT/TGA and etc. Yttrium nitrate precipitated as NH₄Y(C₂O₄)₂H₂O and converted to Y₂O₃ above 450℃. Ba precipitated with two phases, Ba(HC₂O₄)₂2H₂O and Ba(C₂O₄). The amount of each precipitates was 4 : 1. Cu precipitated nonhydrated form, Cu(C₂O₄). The vacuum drying was successful to characterize precipitated powder, which had been generally known as amorphous gel.

Effect of Al Alloy Composition on Physical and Crystallographical Properties of Plasma Electrolytic Oxidized Coatings I. Physical Properties of PEO Layer

Physical properties of Plasma electrolytic oxidized 8 different types of Al alloys, A-1100, A-2024, A-5052, A-6061, A-6063, A-7075, ACD-7B and ACD-12 were investigated. The electrolyte for PEO was Na₂SiO₃ solutions with NaOH and some alkali earthen metal salts. Porous layer near the surface of PEO coating was not found, and surface roughness Ra50 was below 2.5 ㎛. Surface roughness was affected by growth rate of plasma electrolytic oxidized layer, not by Si content in Al alloy.

Bond Strength of TiO 2 Coatings onto FTO Glass for a Dye-sensitized Solar Cell

The bond strength of three types of coatings onto fluorine-doped (FTO) glass was investigated with the aid of a tape test according to ASTM D 3359-95. Transmittance was then measured using an UV-vis spectrophotometer in the wavelength range of 300 nm to 800 nm to evaluate the extent of adhesion of nanorods/nanoparticles on FTO glass. A sharp interface between the coating layer and the substrate was observed for single coating ( nanorods/FTO glass), which may be detrimental to the bonding strength. In multicoating sample ( nanorod/ nanoparticle/ nanoparticle/FTO glass), the tape test was not performed due to severe peeling-off prior to the test. On the other hand, the dual coating sample ( nanorod/ nanoparticle/FTO glass) showed minimum variation of transmittance (4%) after the test, suggesting that the topcoat adheres well with the FTO substrate due to the presence of the nanoparticle buffer layer. The use of a nanorod electrode layer with good adhesion may be attributed to the excellent dye sensitized solar cell performance.

Effect of process conditions on crystal structure of Al PEO coating. I. Unipolar pulse and coating time

Crystallographic phases of Plasma electrolytic oxidized Al alloy, A1050, were investigated. The electrolyte of PEO was and KOH. Unipolar pulse, with impulse, were applied for 2 min, 5 min, 15 min, and 30 min. , as well as , was main crystal phase. was appeared in the beginning, then the amount of was increased with time, but the amount of remained constant without any increasing. So, it is concluded that plasma gas produce at the first, and then transform finally. During the transformation, high temperature of micro plasma gives transformation energy.

Photocatalytic activity of TiO 2 nanomaterials for methylene blue dye degradation

TiO2 nanomaterials were prepared by a sol-gel derived electrospinning, calcination from 500°C to 650°C, and subsequent mechanical grinding to investigate the effect of calcination temperature on crystal structure, crystallinity, and photocatalytic activity of methylene blue (MB). XRD results indicated that TiO2 nanorods calcined at 500°C is composed of anatase TiO2 only. However, mixed crystals of anatase and rutile were observed for TiO2 calcined above 550°C. Higher MB degradation was found for the TiO2 nanorods calcined at 550°C probably due to the mixed crystals and larger surface area. However, the improved photocatalytic activity was achieved for TiO2 nanotube due to the synergic combinations of mixed crystals, larger specific surface area, and light trapping effect.

Effect of PEO Process Conditions on Oxidized Surface Properties of Mg alloy, AZ31 and AZ91. II. Electrolyte

MST Technology, Incheon 21129, Korea(Received March 11, 2016; Revised March 15, 2016 ; Accepted March 16, 2016)Abstract: Effect of electrolyte composition and concentration on PEO coating layer were investigated. Mg alloy, Surface of AZ31 and AZ91 were oxidized using PEO with different electrolyte system, Na-P and Na-Si. and applied voltage and concentration. We measured thickness, roughness, X-ray crystallographic analysis and breakdown voltage of the oxidized layer. When increasing concentration of electrolyte, the thickness of oxide layer also increased too. And roughness also increased as concentration of electrolyte increasing. Breakdown voltage of coated layer showed same behavior, the voltage goes high as increasing thickness of coating layer, as increasing concentration of electrolyte, and increasing applied voltage of PEO. Mg