Jae-Kil Han

Microstructures and material properties of fibrous Al 2 O 3 –(m-ZrO 2 )/t-ZrO 2 composites fabricated by a fibrous monolithic process

Al 2 O 3 –(m-ZrO 2 )/t-ZrO 2 composite having fibrous and homogeneous microstructure was successfully fabricated using a fibrous monolithic process. The composites had a homogeneous microstructure as well as good interfaces between the Al 2 O 3 –(m-ZrO 2 ) and t-ZrO 2 phases. The thickness of each phases were reduced to 375, 50, 5 μm, and 0.7 μm as the number of extrusion passes increased up to 5. The material properties of density, hardness, bending strength, and fracture toughness increased as the passes of extrusion were increased up to a fifth pass, and their maximum values were about 98.5%, 1230 Hv, 570 MPa, and 6.5 MPa⋅m 1/2 , respectively. The fracture toughnesses in the direction of longitudinal and transverse direction of the fifth passed sample showed the different values with about 6.5 and 5.4 MPa⋅m 1/2 , respectively.

Determination of the strontium isotope ratio by ICP-MS ginseng as a tracer of regional origin

This study presents the inductively coupled plasma mass spectrometry (ICP-MS) as a method for tracing the regional origin of ginseng. The results of the analysis of 15 Korean ginsengs from three different regions and of 15 Chinese ginsengs from three different regions reveal that the Sr isotope ratios (87)Sr/(86)Sr of the ginsengs differed according to their origin. For pretreatment, the ginseng samples were dried, and were dissolved through microwave digestion, then were each made to amount to 6ml with 11.9M HCl. Rb was then separated from Sr to enable an interference-free measurement through cation exchange chromatography. Six millilitres of the ginseng sample were injected in the column, and 60ml of 11.9M HCl was passed through the column at a 1mlmin(-1) flow rate to separate Rb from Sr. After Rb was eluted completely, 60ml of 5.0M HCl was passed at a 1mlmin(-1) flow rate to collect Sr. In the Sr collection step, the first 10ml portion of 30ml eluate was discarded, and the next 10ml portion was taken and was diluted with de-ionized water at a ratio of 1:3, for analysis purposes. The results of the analysis of 30 ginseng samples revealed that the Chinese ginsengs have an (87)Sr/(86)Sr ratio range of 0.672-0.701, and the Korean ginsengs 0.705-0.714. The Korean ginsengs, therefore, have a higher (87)Sr/(86)Sr ratio range than the Chinese ginsengs. Of the Korean ginsengs, (87)Sr/(86)Sr ratio range of ginsengs from Punggi, Geumsan and Hongcheon are about 0.706-0.709, 0.705-0.706, and 0.710-0.714, respectively.

Microstructure and Mechanical Property of Hot-Pressed Al2O3-Ni-P Composites Using Ni-P-Coated Al2O3 Powders

Al2O3-Ni-P composite powders with Ni-P contents of 10.9, 14.4, and 20.4 wt.% were synthesized via the Ni-P electroless deposition process. The as-received Al2O3-Ni-P composite powders were composed of Ni-P particles and Ni-P coating layer. Some Ni-P particles randomly adhered to the Al2O3 powders, and their particle diameter ranged from 5 nm to 20 nm. The thin Ni-P layer had about 5 nm thick amorphous structure and directly bonded with Al2O3 powders. Using the Ni-P-coated Al2O3 powders, a dense Al2O3-Ni-P composite can be successfully obtained using the hot press process at 1,350°C for 1 hour in an Ar atmosphere under an applied pressure of 30 MPa. The hot-pressed Al2O3-15 wt.% Ni-P composite showed excellent material properties. Its relative density, Vickers hardness, and fracture toughness were comparatively high: about 99.1%, 2,360 Hv, and 6 MPa·m1/2, respectively. The fracture surface of the hot-pressed Al2O3-Ni-P composite showed a semiductile mode due to the mixed intergranular and transgranular fracture mode. In particular, the fracture toughness of the hot-pressed Al2O3-15 wt.% Ni-P composite was strongly enhanced by the combined action of the crack branching and the crack deflection.

Synthesis and Photo Catalytic Activity of 10 wt%, 20 wt%Li-TiO 2 Composite Powders

【10 wt.% and 20 wt.%

Photocatalysis for Oxidation of Phenol and Reduction of Inorganic Pollutants by Nanocrystalline TiO2-ZrO2 Powders

Li-TiO_2

Microstructure and Synthesis of Ag Spot-coated Cu Nanopowders by Hydrothermal-attachment Method using Ag Colloid

composite powders are synthesized by a sol-gel method using titanium isopropoxide and

Synthesis and Photocatalytic Activity of TiO₂-ZrO₂ Nano-Sized Powders by Sol-Gel Process

Li_2CO_3

Microstructures and Mechanical Properties of Pressureless and Spark Plasma Sintered ZrO₂(3 mol%Y₂O₃) Bodies

as precursors. The as-received amorphous 10 wt.%

A Study of Mechanical Properties and Microstructure of ZrO 2 -Ag Depending on the Composite Route

Li-TiO_2

Synthesis of high purity nano-sized hydroxyapatite powder by microwave-hydrothermal method

composite powders crystallize into the anatase-type crystal structure upon calcination at