• Journal of Powder Materials
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• v.30 no.5
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• pp.394-401
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• 2023

Li_1.5Al_0.5Ti_1.5(PO₄)₃ (LATP) is considered to be one of the promising solid-state electrolytes owing to its excellent chemical and thermal stability, wide potential range (~5.0 V), and high ionic conductivity (~10^-4 S/cm). LATP powders are typically prepared via the sol-gel method by adding and mixing nitrate or alkoxide precursors with chelating agents. Here, the thermal properties, crystallinity, density, particle size, and distribution of LATP powders based on chelating agents (citric acid, acetylacetone, EDTA) are compared to find the optimal conditions for densely sintered LATP with high purity. In addition, the three types of LATP powders are utilized to prepare sintered solid electrolytes and observe the microstructure changes during the sintering process. The pyrolysis onset temperature and crystallization temperature of the powder samples are in the order AC-LATP > CA-LATP > ED-LATP, and the LATP powder utilizing citric acid exhibits the highest purity, as no secondary phase other than LiTi₂PO₄ phase is observed. LATP with citric acid and acetylacetone has a value close to the theoretical density (2.8 g/cm³) after sintering. In comparison, LATP with EDTA has a low sintered density (2.2 g/cm³) because of the generation of many pores after sintering.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3872-3883
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• 2024

This study investigates the effects of Zinc (Zn), Manganese (Mn), and Iron (Fe) additions on the microstructure, corrosion behaviour, biocompatibility, mechanical, and gamma-ray shielding properties of Magnesium (Mg) alloys prepared in various compositions using powder metallurgy (PM). The microstructure and mechanical properties of these alloys were analyzed using electron microscopes (SEM and FE-SEM) and X-ray diffraction (XRD) methods. The results showed positive changes in the material's structure when the percentage of zinc added to pure magnesium increased. It was observed that the material became ductile, and the ductile fracture increased when the zinc ratio increased. The gamma-ray shielding properties of newly produced Mg-based alloys have also been discussed since they have a high potential for use in space technologies. Radiation shielding measurements have been performed using a 3" × 3" NaI(Tl) scintillation detector NaI (Tl) gamma-ray spectrometer. The gamma-ray shielding parameters such as the linear attenuation coefficients (μ_l), mass attenuation coefficient (μ_m), effective atomic number (Z_eff), half-value layer (HVL), and tenth-value layer (TVL) have been determined experimentally at photon energies of 0.511 MeV (emitted from a²²Na radioactive point source) and 1.173 MeV and 1.332 MeV (emitting from a⁶⁰Co radioactive point source). The obtained parameters have been compared to the theoretical results of the XCOM software, and a satisfactory agreement has been found. It can be said from the results that the Mg30Zn alloy has the best shielding properties among the produced materials.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.5
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• pp.255-261
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• 2024

To study the effects of patenting temperature and isothermal holding time on the phase transformation and mechanical property changes of SAE 1078 steel, the patenting process was performed at 460℃, 560℃, and 660℃ for isothermal times (30 s, 60 s, 90 s, 120 s, and 150 s) after nitrogen cooling under austenitizing conditions (1000℃, 2 min). In this study, a scanning electron microscope was used to measure the microstructure and interlamellar spacing of pearlite according to process variables, and an X-ray diffraction analyzer was used to calculate the phase fraction. Cooling rate is approximately 18.6℃/s from the austenitizing temperature to the patenting temperature and pearlite transformation begins at 597~602℃. As the patenting temperature increases, the rate of carbon diffusion during isothermal step increases, so a relatively coarse pearlite structure is formed, and the hardness tends to decrease overall. As the isothermal holding time increased, the hardness of the treated specimens converged to 420Hv, 376Hv, and 268Hv, respectively, because the phase transformation was sufficiently completed at 460℃, 560℃, and 660℃. On the other hand, as the isothermal holding time became shorter, sufficient phase transformation did not occur after the isothermal process, so retained austenite existed, resulting in a decrease in hardness.

• Archives of Metallurgy and Materials
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• v.66 no.3
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• pp.803-808
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• 2021

The influence of nano dispersion on the thermoelectric properties of Bi₂Te₃ was actively investigating to wide-spread thermoelectric applications. Herein this report, we have systematically controlled the microstructure of Bi_0.5Sb_1.5Te₃ (BST) alloys through the incorporation of carbon nanofiber (CNF), and studied their effect on thermoelectric properties, and mechanical properties. The BST/x-CNF (x-0, 0.05, 0.1, 0.2 wt.%) composites powder was fabricated using high energy ball milling, and subsequently consolidated the powder using spark plasma sintering. The identification of CNF in bulk composites was analyzed in Raman spectroscopy and corresponding CNF peaks were recognized. The BST matrix grain size was greatly reduced with CNF dispersion and consistently decreased along CNF percentage. The electrical conductivity was reduced and Seebeck coefficient varied in small-scale by embedding CNF. The thermal conductivity was progressively diminished, obtained lattice thermal conductivity was lowest compared to bare sample due to induced phonon scattering at interfaces of secondary phases as well as highly dense fine grain boundaries. The peak ZT of 0.95 achieved for 0.1 wt.% dispersed BST/CNF composites. The Vickers hardness value of 101.8 Hv was obtained for the BST/CNF composites.

• Archives of Metallurgy and Materials
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• v.65 no.4
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• pp.1255-1259
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• 2020

This paper aims to investigate the microstructural evolution and mechanical properties of hot-deformed AlMg4 alloys with Mn, Fe, and Si as the main impurities. For this purpose, solidification behavior and microstructural evolution during hot-rolling and heat-treatment processes are investigated by using theoretical calculations and experimental characterization. The crystallization and morphological transformation of intermetallic Al₃Fe, Al₆Mn, and Mg₂Si phases are revealed and discussed in terms of the variation in chemical composition. Following a homogenization heat-treatment, the effect of heat treatment on the intermetallic compounds is also investigated after hot-rolling. It was revealed that the Mg₂Si phase can be broken into small particles and spherodized more easily than the Al₃Fe intermetallic phase during the hot-rolling process. For the Mn containing alloys, both yield and ultimate tensile strength of the hot-rolled alloys increased from 270 to 296 MPa while elongation decreased from 17 to 13%, which can be attributed to Mn-containing intermetallic as well as dispersoid.

• Journal of Korea Foundry Society
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• v.15 no.5
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• pp.469-476
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• 1995

The effects of Cr, Mo or B additions were investigated on $B2{\leftrightarrow}DO_3$ structural transition temperature $(T_C)$ and mechanical properties of Fe-28at.%Al. The raw materials were arc-melted in vacuum and then subjected to the following heat-treatments to maximize the $DO_3$ ordered structure : $1000^{\circ}C/7days$, slowly cooled to $500^{\circ}C$ and then held for 5 days. In the effect on the grain refinment, the addition of alloying element B was the most effective. The addition of Cr or Mo had little effect. When 1at.%Mo was added, $T_c$ increase about $30^{\circ}C$, but Cr had a very little effect on $T_c$. On the contrary, when B was added, $T_c$ was apt to come down minutely. In the additional effect of alloying element on the mechanical properties, Cr was apt to decrease the microvickers hardness and yield strength, Mo and B didn't have much effect. In the case of compressure strength test, the effect of the environment on the yield strength was contrary to the result of the tensile strength test.

• Korean Journal of Materials Research
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• v.1 no.3
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• pp.115-124
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• 1991

In this study, the relationship between mechanical properties and the effects of second phase in tri-phase steel which was composed of ferrite-martensite-bainite was investigated. In order to obtain different microstructure of ferrite+martensite(DP), ferrite+bainite(F+B), and ferrite+martensite+bainite(TP, different heat treatment has been accomplished. The effects of volume fraction and microstructure of each specimen were studied on tensile property, Charpy impact energy and stretch-flangeability. As the bainite content in triphase steels increased, the tensile strength, and yield strength decreased as well as the reduction of area and strength-uniform elongation increased. However, ferrite-bainite steel had high yield ratio and yield point elongation. The Charpy impact energy of TP and F+B steel was higher than that of DP steel. In addition, the characteristics of hole expanding limit($\lambda$) of TP steel and F+B steel were higher than that of DP steel. These mechanical properties of tri-phase steel have been improved, because bainite could be deformed easily within ferrite matrix. The effect of bainite on ductility in tri-phase steel has been found to be favorable. In this experiment, tri-phase steel contained within 27% bainite volume fraction had good nechanical properties and superior stretch-flangeability.

• Journal of Life Science
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• v.18 no.2
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• pp.200-205
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• 2008

The purpose of this study is to investigate the effects of the herbal Chokong pill (hereafter HCKP) on the liver cell and enzyme activities of serum in rat. HCKP were mixed with pickled black soybeans and five different kinds of medicinal herbs (Rhynchosia nulubilis, Glycyrrhiza uralensis, Zizyphus vulgaris, Atractylodes macrocephala K., Astragalus membranaceus and Cornus officinalis). Four groups of male Sprague-Dawley rats were fed by different diets for 9 weeks: normal diet (Nor), high-fat diet (HF), high-fat diet supplemented with 1% (T1) and 5% (T5) HCKP powder, respectively. Depending on the presence of HCKP in high fat diet, the activities of the blood serum GOT and GPT were decreased. GOT and GPT activities of T1 and T5 were decreased 6.1%, 17.8% and 25.4%, 32.4% compared with HF. On microstructure observing through the transmission electron microscope (TEM) of liver cell, in normal group, a normal large and clear nucleus, rough endoplasmic reticulum (RER) and mitochondria possessing well-defined double outer-limiting membranes were found. However, in HF, it was hard to observe the microstructures in cytoplasm, because of too many fat granules. It showed severely damaged cell, pyknotic nucleus, swollen disintegrating RER and mitochontria loosing the cristae. In T1, there were more repaired liver cells and less fat granules than HF. In T5, there were much less numbers and smaller size of the fat granules than T1, and the morphology was similar to normal cell.

• Korean Journal of Materials Research
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• v.11 no.8
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• pp.671-678
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• 2001

All solid-state thin film micro supercapacitor, which consists of $RuO_2$/LiPON/$RuO_2$ multi layer structure, was fabricated on Pt/Ti/Si substrate using a $RuO_2$ electrode. Bottom $RuO_2$ electrode was grown by dc reactive sputtering system with increasing $O_2/[Ar+O_2]$ ratio at room temperature, and a LiPON electrolyte film was subsequently deposited on the bottom $RuO_2$ electrode at pure nitrogen ambient by rf reactive sputtering system. Room temperature charge-discharge measurements based on a symmetric $RuO_2$/LiPON/$RuO_2$ structure clearly demonstrates the cyclibility dependence on the microstructure of the $RuO_2$ electrode. Using both glancing angle x-ray diffraction (GXRD) and transmission electron microscopy (TEM) analysis, it was found that the microstructure of the $RuO_2$ electrode was dependent on the oxygen flow ratio. In addition, x- ray photoelectron spectroscopy(XPS) examination shows that the Ru-O binding energy is affected by increasing oxygen flow ratio. Furthermore, TEM and AES depth profile analysis after cycling demonstrates that the interface layer formed by interfacial reaction between LiPON and $RuO_2$ act as a main factor in the degradation of the cyclibility of the thin film micro-supercapacitor.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.5
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• pp.1939-1946
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• 2012

High performance steel for bridges requires higher performance in tensile and yield strength, toughness, weldability, etc. The purpose of this study is to investigate the weldability of HSB 600 steel. The effects of heat input (1.4~3.2kJ/mm) and postweld heat treatment (PWHT, $600^{\circ}C$, 40hr.) on the TMCP HSB600 steel weldments made by GMAW process were investigated. The tensile strength and hardness of as-welded specimens decreased with increasing heat input. Charpy V-notch impact energy did not show any significant difference by postweld heat treatment. The fine-grained acicular ferrite was mainly formed in the 2.1kJ/mm of heat input while polygonal and side plate ferrites were dominated in the high inputs. Meanwhile, tensile strength and hardness of PWHT weldments decreased due to the coarsening and globularization of ferrite microstructure and reduction of residual stresses with increasing heat inputs. However, there was no significant difference in the impact energy absorption.