• 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.

• Animal Bioscience
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• v.36 no.5
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• pp.797-809
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• 2023

Objective: Many scientists have investigated solutions to reduce microbiological risks in dry-aged meat after the dry-aging technology was revived for high quality and value-added premium meat product in the market. This study aimed to investigate the effect of scoria powder in onggi (Korean earthenware) on the meat quality of pork loins during 21 days of dry aging and to elucidate its mechanism of action. Methods: The pork loins were randomly divided into three groups: aged in vacuum-packaging, onggi containing red clay only (OR), and onggi containing 30% red clay and 70% scoria powder (OS). Microbial analyses (total plate count and Lactobacillus spp.) and physicochemical analyses (pH, shear force, volatile basic nitrogen [VBN], water activity, 2-thiobarbituric acid reactive substances, water content, water holding capacity, cooking loss, and color analysis) of aged meat were conducted. Far-infrared ray emission, quantification of immobilized L. sakei and microstructure of onggi were investigated to understand the mechanism. Results: On day 21, the meat aged in OS exhibited lower pH, shear force, VBN, and water activity than those aged in OR, along with an increase in the number of Lactobacillus spp. OS had a smaller pore diameter than OR, implying lower gas permeability, which could promote the growth of L. sakei. Conclusion: OS improved the microbiological safety and storage stability of pork loin during dry aging by increasing number of Lactobacillus spp. possibly due to low permeability of OS.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.168-179
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• 2022

Microbiologically Influenced Corrosion (MIC) occurring in underground buried pipes of API 5L X65 steel was investigated. MIC is a corrosion phenomenon caused by microorganisms in soil; it affects steel materials in wet atmosphere. The microstructure and mechanical properties resulting from MIC were analyzed by OM, SEM/EDS, and mapping. Corrosion of pipe cross section was composed of ① surface film, ② iron oxide, and ③ surface/internal microbial corrosive by-product similar to surface corrosion pattern. The surface film is an area where concentrations of C/O components are on average 65 %/16 %; the main components of Fe Oxide were measured and found to be 48Fe-42O. The MIC area is divided into surface and inner areas, where high concentrations of N of 6 %/5 % are detected, respectively, in addition to the C/O component. The high concentration of C/O components observed on pipe surfaces and cross sections is considered to be MIC due to the various bacteria present. It is assumed that this is related to the heat-shrinkable sheet, which is a corrosion-resistant coating layer that becomes the MIC by-product component. The MIC generated on the pipe surface and cross section is inferred to have a high concentration of N components. High concentrations of N components occur frequently on surface and inner regions; these regions were investigated and Na/Mg/Ca basic substances were found to have accumulated as well. Therefore, it is presumed that the corrosion of buried pipes is due to the MIC of the NRB (nitrate reducing bacteria) reaction in the soil.

• Journal of the Korean Society for Heat Treatment
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• v.35 no.2
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• pp.74-81
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• 2022

This study aims to mitigate the microstructural heterogeneity arising from the manufacture of magnesium alloy plates using the twin roll casting (TRC) process. Homogenization was introduced through hot rolling and heat treatment, followed by confirmation of observed changes in the microstructure. Following the TRC process, the hot rolled 2mm plate exhibited a dendritic cast structure tilted in the roll rotation direction, while central segregation were developed. This nonuniform structure and central segregation disappeared upon heat treatment, followed by recrystallization to form uniform and fine grains. Abnormal grain growth (AGG) was observed over the course of heat treatment; grains exhibiting AGG occupied up to 75% of the total area after having held the sample at 400℃ for 64 h. The formation of coarse grains was also observed during heat treatment at 340℃ over a relatively long duration, though the maximum grain size was significantly smaller than that corresponding to the heat treatment at 400℃. AGG in the 400℃ heat treatment occurred because of movement of the grain boundary, which had been fixed prior as a result of the grain boundary fixing effect of the precipitation phase. The re-dissolution of the Ca₂Mg₅Zn₅ precipitated phase over the long duration of the high-temperature annealing process caused the surrounding grains to disappear and regrow.

• Korean Journal of Materials Research
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• v.32 no.3
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• pp.132-138
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• 2022

Zintl phase Mg₃Sb₂ is a promising thermoelectric material in medium to high temperature range due to its low band gap energy and characteristic electron-crystal phonon-glass behavior. P-type Mg₃Sb₂ has conventionally exhibited lower thermoelectric properties compared to its n-type counterparts, which have poor electrical conductivity. To address these problems, a small amount of Sn doping was considered in this alloy system. P-type Mg₃Sb₂ was synthesized by controlled melting, pulverizing, and subsequent vacuum hot pressing (VHP) method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to investigate phases and microstructure development during the process. Single phase Mg₃Sb₂ was successfully formed when 16 at.% of Mg was excessively added to the system. Nominal compositions of Mg_3.8Sb_2-xSn_x (0 ≤ x ≤ 0.008) were considered in this study. Thermoelectric properties were evaluated in terms of Seebeck coefficient, electrical conductivity, and thermal conductivity. A peak ZT value ≈ 0.32 was found for the specimen Mg_3.8Sb_1.994Sn_0.006 at 873 K, showing an improved ZT value compared to intrinsic one. Transport properties were also evaluated and discussed.

• Transactions of Materials Processing
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• v.31 no.3
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• pp.160-166
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• 2022

The purpose of this study is to investigate the effects of combined addition of Ca and Y on the precipitation and age-hardening behavior of an extruded AZ91 alloy by conducting the aging treatment at 200 ℃ for hot-extruded AZ91 and AZ91-0.3Ca-0.2Y alloys. In the AZ91 alloy, many Mg₁₇Al₁₂ discontinuous precipitate (DP) bands formed during air cooling immediately after extrusion are present, whereas in the AZ91-0.3Ca-0.2Y alloy, a few DP bands and numerous Al₂Y, Al₈Mn₄Y, and Al₂Ca phase particles are distributed along the extrusion direction. The peak-aging time of the AZ91-0.3Ca-0.2Y alloy is 16 hours, twice that of the AZ91 alloy. Although both alloys have similar hardness before aging treatment, the hardness after peak-aging treatment (i.e., peak hardness) of the AZ91-0.3Ca-0.2Y alloy is higher than that of the AZ91 alloy, as 93.1 and 88.7 Hv, respectively. The microstructures of both peak-aged alloys comprise DPs and continuous precipitates (CPs). However, the peak-aged AZ91-0.3Ca-0.2Y alloy has a smaller amount of DPs and a larger amount of CPs than the peak-aged AZ91 alloy. Additionally, the inter-particle spacings of DPs and CPs in the former are significantly narrower than those in the latter. These results demonstrate that the addition of small amounts of Ca and Y to a commercial AZ91 alloy considerably affects the formation rate, size, and amount of CPs and DPs during aging and resultant age-hardening behavior.

• Korean Journal of Materials Research
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• v.33 no.5
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• pp.214-221
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• 2023

As a filler metal for lowering the melting point of Ag, many alloy metal candidates have emerged, such as cadmium, with zinc, manganese, nickel, and titanium as active metals. However, since cadmium is known to be harmful to the human body, Cd-free filler metals are now mainly used. Still, no study has been conducted comparing the characteristics of joints prepared with and without cadmium. In addition, studies have yet to be conducted comparing the typical characteristics of brazing filler metals with special structures, and the joint characteristics of brazing filler metals with available frames. In this study, the characteristics of junctions of silver-based intercalation metals were compared based on the type of filler metal additives, using a special structure, a filler metal sandwich structure, to protect the internal base metal. The general filler metal was compared using the structure, and the thickness of the filler metal according to the thickness was reached. A comparison of the characteristics of the junction was conducted to identify the characteristics of an intersection of silver-based brazing filler metal and the effect on joint strength. Each filler metal's collective tensile strength was measured, and the relationship between joint characteristics and tensile joint strength was explored. The junction was estimated through micro strength measurement, contact angle measurement with the base metal when the filler metal was melted, XRD image observation, composition analysis for each phase through SEM-EDS, and microstructure phase acquisition.

• Fisheries and Aquatic Sciences
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• v.26 no.9
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• pp.535-547
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• 2023

Sea cucumbers (Holothuria scabra), also known as beche-de-mer, are highly valued as a luxurious food item and have been utilized as a traditional tonic food in various Asian countries for centuries. The body walls of sea cucumbers are the main edible part, which are primarily composed of glycosaminoglycan (GAG). The rehydration of dried sea cucumber is a crucial step prior to further processing. The aim of this study was to assess the impact of ultrasound-assisted rehydration (UAR) on the quality of dried sea cucumbers. The experiment used four different rehydration methods, including conventional methods at 27℃ (KV27℃) and 15℃ (KV15℃), as well as a combination of ultrasound at 27℃ with conventional at 15℃ (UAR27 + KV15℃) and ultrasound at 15℃ with conventional at 15℃ (UAR15 + KV15℃). Results indicated that the rehydration rate (RR) was significantly affected by both the rehydration method and the temperature used (p < 0.05). UAR27 + KV15℃ was identified as the most effective method in terms of rehydration behavior and quality characteristics of dried sea cucumber, with a RR of 0.58 ± 0.53 gH₂O/hour and reduced rehydration time of up to 28 hours. Moreover, the UAR27 + KV15℃ method demonstrated superior rehydration potential, nutritional value (proximate composition and sulfate content), color, lower energy, and microstructure properties compared to the other methods. The sulfate content and yield of sulfated GAGs were determined to be 89.4 mg/g and 52.8 ㎍/g, respectively. Confirmation of the absorption band of the sulfate group showed the presence of 3-N-acetyl galactosamine at a wavelength of 1,269 cm^-1 and C-O-S at 860 cm^-1. The sea cucumbers treated with UAR exhibited a GAG content approximately 2.9 times higher than those rehydrated with the conventional method. Eventually, the combination of UAR at 27℃ with conventional at 15℃ methods can significantly accelerate the rehydration of sea cucumber without negatively affecting its physical quality properties.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_3
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• pp.1289-1295
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• 2023

Polyurethane foam insulation required for storing and transporting cryogenic liquefied gas is already widely used as a thermal insulation material for commercial LNG carriers and onshore due to its stable price and high insulation performance. These polyurethane foams are reported to have different mechanical performance depending on the density, and the density parameter is determined depending on the amount of the blowing agent. In this study, density-dependent polyurethane foam was fabricated by adjusting the amount of blowing agent. The mechanical properties of polyurethane foam were analyzed in the room temperature and cryogenic temperature range of -163℃ at 1.5 mm/min, which is a quasi-static load range, and the cells were observed through microstructure analysis. The characteristics of linear elasticity, plateau, and densification, which are quasi-static mechanical behaviors of polyurethane foam, were shown, and the correlation between density and mechanical properties in a cryogenic environment was confirmed. The correlation between mechanical behavior and cell size was also analyzed through SEM morphology analysis. Polyurethane foam with a density of 180 kg/m³ had a density about twice as high as that of a polyurethane foam with a density of 96 kg/m³, but yield strength was about 51% higher and cell size was about 9.5% smaller.

• Journal of Powder Materials
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• v.31 no.2
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• pp.152-162
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• 2024

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150℃ under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10^-2/m²) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.