• Transactions of Materials Processing
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• v.32 no.5
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• pp.239-246
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• 2023

To reduce the forming load due to the temperature drop, during the hot forging process, a reheating hot forging process design is required that to repeat heating and forging. However, if the critical strain required for recrystallization is not induced during forging and grain growth becomes dominant due to the reduction in dislocation density due to repeated heating, the mechanical properties may deteriorate. Therefore, in this study, Inconel 706 alloy was applied, and the grain refinement behavior was comparatively analyzed according to the number of reheating times and effective strain during reheating hot forging process. Reheating was carried out with a total compression rate of 40% up to 4 times. The Inconel 706 compression test specimens heated once showed finer grains as the effective strain increased due to the dynamic recrystallization phenomenon. However, as the number of heating increases, grain refinement was observed even in a low effective strain distribution of 0.43 due to static recrystallization during reheating. Moreover, grain growth occurs at a relatively low effective strain of 0.43 when the number of reheating is four or more. Therefore, it was effective to apply an effective strain of 0.43 or more during hot forging to Inconel 706 in order to induce crystallization through grain refinement and improve the properties of forged products. In addition, we could notice that up to three reheating times condition was appropriate to prevent grain growth and maintain fine grain size.

• Journal of Electrochemical Science and Technology
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• v.14 no.3
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• pp.262-271
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• 2023

For electrode stability and the electrochemical performance of the Li-ion cell, it is essential that the active ingredients and unique additives in the polymer binder be well dispersed with the solvent-based slurry. The efficient procedure used to create the slurry affects the rheological characteristics of the electrode slurry. When successively adding different steps of Nmethyl-2-pyrrolidone (NMP) solvent to the cathode composition, it is evenly disseminated. The electrochemical performance of the Li-ion cells and the electrodes made with slurry formed by single step and multiple steps of addition of NMP solvent are examined. To preform rheological properties of cathode electrode slurry on Ni-rich Lithium Nickel-Cobalt-Aluminum Oxide (LiNi_0.80Co_0.15Al_0.05) (NCA). Also, we investigate different step addition of electrode formation and mechanical strength characterization like peel strength. According to the EIS study, a multi-step electrode slurry has lower internal resistance than a single-step electrode slurry, which results in better electrical characteristics and efficiency. Further, microstructure of electrodes is obtained electrochemical performance in the 18650 cylindrical cells with targeted capacity of 1.5 Ah. The slurry of electrodes prepared by single step and multiple steps of addition of NMP solvent and its effect on the fabrication of 1.5 Ah cells. A three-step solvent addition on slurry has been found to be a lower internal resistance than a single-step electrode slurry as confirmed by the EIS analysis, yielding improved electrical properties and efficiency.

• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.1
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• pp.33-39
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• 2024

In this study, the basic properties of cement paste with varying replacement ratio of micro-silica and fumed silica were analyzed to determine the suitability of nanomaterials for use as concrete admixtures. Referring to the ultra-high strength mix, the fluidity of cement paste was evaluated according to the nanomaterial replacement rate and the compressive strength characteristics were compared and analyzed. The related properties of the reactive nanomaterials to the cement hydrate were analyzed using SEM and EDS to observe the microstructure and identify the components of the hydration product. The reactive nanomaterials used in this study had tap densities between 0.061 and 0.264 g/cm³, which were lower than SF. Micro silica exhibited excellent compressive strength properties with increasing replacement ratio, but fumed silica, unlike micro white, obtained excellent compressive strength at replacement ratio of 0.01~0.1 %. The same trend was observed in the hydration characterization.

• Journal of the Korea Institute of Building Construction
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• v.24 no.3
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• pp.285-295
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• 2024

This study investigated the impact of accelerated carbonation on Ordinary Portland Cement(OPC) paste that had undergone steam curing at 500℃·hr. Two carbonation environments were examined: atmospheric carbonation(1atm, 20% CO₂) and pressurized carbonation(5atm, 99% CO₂). Chemical analysis using X-ray diffraction(XRD) and Fourier-Transform Infrared spectroscopy(FT-IR) were conducted, along with physical characterization via scanning electron microscopy(SEM) and compressive strength testing. Results indicated that atmospheric carbonation with 20% CO₂ concentration significantly densified the internal microstructure of the OPC paste, leading to enhanced compressive strength. Conversely, pressurized carbonation at 5atm with 99% CO₂ concentration resulted in rapid densification of the surface structure, which hindered CO₂ diffusion into the sample. This limited the extent of carbonation and prevented the improvement of physical properties.

• Journal of Powder Materials
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• v.31 no.3
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• pp.243-254
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• 2024

High-entropy alloys (HEAs) have been reported to have better properties than conventional materials; however, they are more expensive due to the high cost of their main components. Therefore, research is needed to reduce manufacturing costs. In this study, CoCrFeMnNi HEAs were prepared using metal injection molding (MIM), which is a powder metallurgy process that involves less material waste than machining process. Although the MIM-processed samples were in the face-centered cubic (FCC) phase, porosity remained after sintering at 1200℃, 1250℃, and 1275℃. In this study, the hot isostatic pressing (HIP) process, which considers both temperature (1150℃) and pressure (150 MPa), was adopted to improve the quality of the MIM samples. Although the hardness of the HIP-treated samples decreased slightly and the Mn composition was significantly reduced, the process effectively eliminated many pores that remained after the 1275℃ MIM process. The HIP process can improve the quality of the alloy.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2444-2451
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• 2024

This work demonstrates a new sol-gel approach for synthesizing PbO₂-doped zirconia using zircon mineral precursors. The streamlined methodology enables straightforward fabrication of the doped zirconia composites. Comprehensive materials characterization was performed using XRD, SEM, and TEM techniques to analyze the crystal structure, microstructure, and morphology. Quantitative analysis of the XRD data provided insights into the nanoscale crystallite sizes achieved, along with their relationship to lattice imperfections. Furthermore, the gamma-ray shielding capacity for the PbO₂-doped zirconia samples was estimated by the Monte Carlo simulation, which proves an increase in the gamma ray shielding properties by raising the Pb concentration. The linear attenuation coefficient increased between 0.467 and 0.499 cm^-1 (at 0.662 MeV) by increasing the Pb content between 11 and 21 wt%. By increasing the Pb content to 21 wt%, the synthesized composites' lead equivalent thickness reaches 2.49 cm. The radiation shielding properties for the synthesized composites revealed a remarkable performance against low and intermediate γ-ray photons, with radiation shielding capacity of 37.3 % and 21.4 % at 0.662 MeV and 2.506 MeV, respectively. As a result, the developed composites can be employed as an alternative shielding material in hospitals and radioactive zones.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3608-3615
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• 2024

This study introduces a lead-free alternative for enhanced radiation protection. While lead aprons effectively attenuate ionizing radiation, concerns regarding flexibility, weight, and environmental hazards persist. In response, the present research is focused on producing an innovative sheet shielding comprised of carefully selected dense metal oxide microparticles (DMOs-MPs) and liquid silicone rubber (LSR). To evaluate the efficacy of the LSR samples, the current study uses rigorous testing procedures, such as microstructure characterization using EDX and FESEM. Furthermore, the study investigated key attenuation parameters within the LSR samples. Radiation protection was greatly and effectively supplied using DMOs-MPs filler (Bi-1 to Bi-7) in LSR samples; this protection reached 99.9% in the X-ray energy range. Due to the unique characteristics of the Bi-7, the results demonstrated that the samples' shielding efficiency improved with the addition of high atomic number and high-density fillers. It had the greatest attenuation coefficient and density. At 60 keV, Bi-7's density was 2.980 gcm^-3, and its LAC and MAC were 19.2621 cm^-1 and 6.4638 cm²/g, respectively. It also had the lowest half-value layer values in the energy range of 60-120 keV. The LSR samples showed effective radiation absorption for different energy levels, indicating that LSR can enhance the flexibility and comfort of the apron while providing adequate radiation protection. The incorporation of the DMOs-MPs with LSR represents an effective contribution and a noteworthy stride to enhance the safety and well-being of medical professionals routinely exposed to ionizing radiation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.2
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• pp.92-97
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• 2011

Landfill is the main treatment method for bottom-ash because it has not only an irregular particle size and ingredients but also not proper recycling treatment. The aim of this study is to raise recycling rate of bottom-ash(nonplasticity pulverulent) and for the purpose of alternatives of clay to investigate the properties of Bottom-ash (B/A)-Hard Clay (H/C) bodies with controlled interfacial chemistry properties. After investigating the sedimentation height of suspensions with controlled pH, it was discovered that there was no hetero-polar aggregation for mixed slips because hard clay and bottom-ash had similar interfacial chemistry properties. Also, bulk density, water absorption, and microstructure properties of each pellet was observed that made by silp casting method and manufactured at $50^{\circ}C$ intervals between $1000{\sim}1250^{\circ}C$. As a result, dispersed slip of clay and bottom ash are possible for slip casting and plastic forming process because they exhibit Bingham plastic behavior. Products that made by slip with dispersed clay and bottom ash are not only suitable for KS L 4201 and KS L 1001 at $1250^{\circ}C$ but it is also possible to apply for ceramic and sanitary ware because specific gravity was about 15 % lighter than general ceramic materials.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.6
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• pp.245-251
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• 2015

We have applied mechanical alloying (MA) to produce soft magnetic composite material using a mixture of elemental $Fe_2O_3$-Mg powders. An optimal milling and heat treatment conditions to obtain soft magnetic ${\alpha}$-Fe/MgO composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that ${\alpha}$-Fe/MgO composite powders in which MgO is dispersed in ${\alpha}$-Fe matrix are obtained by MA of $Fe_2O_3$ with Mg for 30 min. The saturation magnetization of ball-milled powders increases with increasing milling time and reaches to a maximum value of 69.5 emu/g after 5 h MA. The magnetic hardening due to the reduction of the ${\alpha}$-Fe grain size by MA was also observed. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at $800{\sim}1000^{\circ}C$ under 60 MPa. X-ray diffraction result shows that the average grain size of ${\alpha}$-Fe in ${\alpha}$-Fe/MgO nanocomposite sintered at $800^{\circ}C$ is in the range of 110 nm.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.6 no.6
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• pp.457-460
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• 2005

Nano-sized titanium oxide and zirconium oxide powders were synthesized by hydrolysis of titanium isopropoxide $[Ti(OC_3H7)_4]$ and zirconium tetrachloride ($ZrC1_4$) via a sol-gel technique. Lead titanate powders were prepared by mixing $TiO_2$ precursors with PbO slurry made with dilute $NH_4OH$. Lead zirconate titanate powders were, then, synthesized by mixing $PbTiO_3$ with $ZrO_2$ powders. The goal of this research was to obtain the $PbZrTiO_3(PZT)$ powders and sintering these powders at low temperature. The $PbTiO_3$ and PZT powders after firing were analyzed by X-ray diffraction(XRD) and transmission electron microscopy(TEM) was utilized to observe the shape and size of the synthesized nano-particles. In the XRD pattern, the well-crystallized PZT phase could be obtained in consequence of firing at $900^{\circ}C$. SEM micrographs also showed that grains of PZT were relatively well grown with the size of the range of $2{\~}4{\mu}m$. The densified perovskite structure of $PbZrTiO_3$ could be obtained by sintering at temperature as low as $900^{\circ}C$. Characterization of the samples showed improved piezoelectric properties.