• 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.7
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• pp.2584-2594
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• 2024

A novel approach to incorporating oxide formers into ferritic ODS production has been developed using the co-precipitation technique. This method enables the tailored design of complex nano-oxides, integrated during Mechanical Alloying (MA) and precipitated during Spark Plasma Sintering (SPS) consolidation. Findings illustrate that co-precipitation effectively produces nano-powders with customised compositions, enriching Y, Ti, and Zr in the ferritic grade to condition subsequent oxide precipitation. While the addition of Y-Ti-Zr-O nano-oxides did not prevent the formation of Y-Al-O and Al-containing nano-oxides, these were refined thanks to the presence of well-dispersed Zr. Additionally, the Spark Plasma Sintering (SPS) parameters were optimised to tailor the bimodal grain size distribution of the ODS steels, aiming for favourable strength-to-ductility ratios. Comprehensive microstructural analyses were performed using SEM, EDS, EBSD, and TEM techniques, alongside mechanical assessments involving microtensile tests conducted at room temperature and small punch tests carried out at room temperature, 300 ℃, and 500 ℃. The outcomes yielded promising findings, showcasing similar or better performance with conventionally manufactured ODS steels. This reinforces the effectiveness and success of this innovative approach.

• Applied Microscopy
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• v.50
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• pp.2.1-2.7
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• 2020

Electron energy loss spectroscopy (EELS) is an analytical technique that can provide the structural, physical and chemical information of materials. The EELS spectra can be obtained by combining with TEM at sub-nanometer spatial resolution. However, EELS spectral information can't be obtained easily because in order to interpret EELS spectra, we need to refer to and/or compare many reference data with each other. And in addition to that, we should consider the different experimental variables used to produce each data. Therefore, reliable and easily interpretable EELS standard reference data are needed. Our Electron Energy Loss Data Center (EELDC) has been designated as National Standard Electron Energy Loss Data Center No. 34 to develop EELS standard reference (SR) data and to play a role in dissemination and diffusion of the SR data to users. EELDC has developed and collected EEL SR data for the materials required by major industries and has a total of 82 EEL SR data. Also, we have created an online platform that provides a one-stop-place to help users interpret quickly EELS spectra and get various spectral information. In this paper, we introduce EEL SR data, the homepage of EELDC and how to use them.

• Nanomaterials
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• v.12 no.4
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• pp.680-690
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• 2022

Phase-pure ZnMn₂O₄ nanopowders and their aggregated microsphere powders for use as anode material in lithium-ion batteries were obtained by a simple spray drying process using zinc and manganese salts as precursors, followed by citric acid post-annealing at different temperatures. X-ray diffraction (XRD) analysis indicated that phase-pure ZnMn₂O₄ powders were obtained even at a low post-annealing temperature of 400 ℃. The post-annealed powders were transformed into nanopowders by simple milling process, using agate mortar. The mean particle sizes of the ZnMn₂O₄ powders post-treated at 600 and 800 ℃ were found to be 43 and 85 nm, respectively, as determined by TEM observation. To provide practical utilization, the nanopowders were transformed into aggregated microspheres consisting of ZnMn₂O₄ nanoparticles by a second spray drying process. Based on the systematic analysis, the optimum post-annealing temperature required to obtain ZnMn₂O₄ nanopowders with high capacity and good cycle performance was found to be 800 ℃. Moreover, aggregated ZnMn₂O₄ microsphere showed improved cycle stability. The discharge capacities of the aggregated microsphere consisting of ZnMn₂O₄ nanoparticles post-treated at 800 ℃ were 1235, 821, and 687 mA h g^-1 for the 1st, 2nd, and 100th cycles at a high current density of 2.0 A g^-1, respectively. The capacity retention measured after the second cycle was 84%.

• Nanomaterials
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• v.12 no.12
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• pp.1956-1965
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• 2022

The electrode concept of graphite and silicon blending has recently been utilized as the anode in the current lithium-ion batteries (LIBs) industry, accompanying trials of improvement of cycling life in the commercial levels of electrode conditions, such as the areal capacity of approximately 3.3 mAh/cm² and volumetric capacity of approximately 570 mAh/cm³. However, the blending concept has not been widely explored in the academic reports, which focused mainly on how much volume expansion of electrodes could be mitigated. Moreover, the limitations of the blending electrodes have not been studied in detail. Therefore, herein we investigate the graphite blending electrode with micron-sized SiO_x anode material which is one of the most broadly used Si anode materials in the industry, to approach the commercial and practical view. Compared to the silicon micron particle blending electrode, the SiO_x blending electrode showed superior cycling performance in the full cell test. To elucidate the cause of the relatively less degradation of the SiO_x blending electrode as the cycling progressed in full-cell, the electrode level expansion and the solid electrolyte interphase (SEI) thickening were analyzed with various techniques, such as SEM, TEM, XPS, and STEM-EDS. We believe that this work will reveal the electrochemical insight of practical SiO_x-graphite electrodes and offer the key factors to reducing the gap between industry and academic demands for the next anode materials.

• Journal of Korean Society of Forest Science
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• v.86 no.2
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• pp.186-199
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• 1997

The soils derived from granite gneiss occupy almost one third of the land area in Korea. The soils under forest vegetation, formed on granite gneiss, in Sun chon-shi, Chollanam-do in southern part of Korea, were studied to evaluate the weathering and the transformation of primary minerals into secondary minerals, clay minerals. The studied soils contained large amounts of ferromagnesian minerals, weathered biotites and were well weathered, strongly acid and low in organic matters and in ration exchange capacity. The clay contents in the Bt horizon were almost two times higher than those in the C horizon. The O horizon had a thin layer which consisted of a little decomposed plant components with a granic fabric and high porosity, and showed the micromorphological characteristics of moder humus. The related distribution pattern of the E horizon were enaulic and large amounts of silts and small amounts of sand grains were another characteristics of the E horizon. The most striking micromorphological features were multilaminated clay coating and infillings in the voids in the Bt and C horizons, and generally limpid ferriargillans ejected from the biotites and imparted red color to the soils in the Bt horizon. High clay contents in the Bt horizon was not only due to clay translocation, but also due to intensive in situ mineral weathering in this horizon. The most significant pedogenic process, revealed by the petrographic microscope and SEM, was the formation of iron oxides from biotites, the formation of tubular halloysites and the weathering models of biotites; wedge weathering and layer weathering. The thick coating on the weathering biotites showed the characteristics of the weathering process and the synthetic hematites were revealed in clays by TEM. Total chemical analysis of clays revealed extensive loss of Ca, and Na and the concentration of Fe and Al. Mineralogical studies of clays by XRD showed that micas were almost completely weathered to kaolinite, vermiculite-kaolinite intergrade, hematite, gibbsite, while halloysites from other primary minerals. Some dioctahedral mica appeared to be resistant in the soils. Parent rock of the soils contained a considerable amounts of biotites and this forest soils showed especially a dominant characteristics of biotite weathering.

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.313-320
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• 2013

The $AlAs_xSb_{1-x}$ step-graded buffer (SGB) layer was grown on the Silicon (Si) substrate to overcome lattice mismatch between Si substrate and $Al_{0.3}Ga_{0.7}As$/GaAs multiple quantum wells (MQWs). The value of root-mean-square (RMS) surface roughness for 5 nm-thick GaAs grown on $AlAs_xSb_{1-x}$ step-graded buffer layer was ~1.7 nm. $Al_{0.3}Ga_{0.7}As$/GaAs MQWs with AlAs/GaAs short period superlattice (SPS) were formed on the $AlAs_xSb_{1-x}$/Si substrate. Photoluminescence (PL) peak at 10 K for the $Al_{0.3}Ga_{0.7}As$/GaAs MQW structure showed relatively low intensity at ~813 nm. The RMS surface roughness of the $Al_{0.3}Ga_{0.7}As$/GaAs MQW structure was ~42.9 nm. The crystal defects were observed on the cross-sectional transmission electron microscope (TEM) images of the $Al_{0.3}Ga_{0.7}As$/GaAs MQW structure. The decrease of PL intensity and increase of RMS surface roughness would be due to the formation of the crystal defects.

• Korean Journal of Materials Research
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• v.11 no.7
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• pp.556-561
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• 2001

We prepared a new a SOS(silicon-on-silicide) wafer pair which is consisted of Si(100)/1000$\AA$-NiSi Si (100) layers. SOS can be employed in MEMS(micro- electronic-mechanical system) application due to low resistance of the NiSi layer. A thermally evaporated $1000\AA$-thick Ni/Si wafer and a clean Si wafer were pre-mated in the class 100 clean room, then annealed at $300~900^{\circ}C$ for 15hrs to induce silicidation reaction. SOS wafer pairs were investigated by a IR camera to measure bonded area and probed by a SEM(scanning electron microscope) and TEM(transmission electron microscope) to observe cross-sectional view of Si/NiSi. IR camera observation showed that the annealed SOS wafer pairs have over 52% bonded area in all temperature region except silicidation phase transition temperature. By probing cross-sectional view with SEM of magnification of 30,000, we found that $1000\AA$-thick uniform NiSi layer was formed at the center area of bonded wafers without void defects. However we observed debonded area at the edge area of wafers. Through TEM observation, we found that $10-20\AA$ thick amourphous layer formed between Si surface and NiSix near the counter part of SOS. This layer may be an oxide layer and lead to degradation of bonding. At the edge area of wafers, that amorphous layer was formed even to thickness of $1500\AA$ during annealing. Therefore, to increase bonding area of Si NiSi ∥ Si wafer pairs, we may lessen the amorphous layers.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.1
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• pp.15-26
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• 2017

Cobalt ferrocyanide (CoFC) or nickel ferrocyanide (NiFC) magnetic nanoparticles (MNPs) were fabricated for efficient removal of radioactive cesium, followed by rapid magnetic separation of the absorbent from contaminated water. The $Fe_3O_4$ nanoparticles, synthesized using a co-precipitation method, were coated with succinic acid (SA) to immobilize the Co or Ni ions through metal coordination to carboxyl groups in the SA. CoFC or NiFC was subsequently formed on the surfaces of the MNPs as Co or Ni ions coordinated with the hexacyanoferrate ions. The CoFC-MNPs and NiFC-MNPs possess good saturation magnetization values ($43.2emu{\cdot}g^{-1}$ for the CoFC-MNPs, and $47.7emu{\cdot}g^{-1}$ for the NiFC-MNPs). The fabricated CoFC-MNPs and NiFC-MNPs were characterized by XRD, FT-IR, TEM, and DLS. The adsorption capability of the CoFC-MNPs and NiFC-MNPs in removing cesium ions from water was also investigated. Batch experiments revealed that the maximum adsorption capacity values were $15.63mg{\cdot}g^{-1}$ (CoFC-MNPs) and $12.11mg{\cdot}g^{-1}$ (NiFC-MNPs). Langmuir/Freundlich adsorption isotherm equations were used to fit the experimental data and evaluate the adsorption process. The CoFC-MNPs and NiFC-MNPs exhibited a removal efficiency exceeding 99.09% for radioactive cesium from $^{137}Cs$ solution ($18-21Bq{\cdot}g^{-1}$). The adsorbent selectively adsorbed $^{137}Cs$, even in the presence of competing cations.

• Korean Journal of Materials Research
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• v.8 no.7
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• pp.621-627
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• 1998

The formation of Co-silicide between Co/Zr bilayer on the amorphous and crystalline Si substrates has been investigated. The films of Zr(50$\AA$) and Co(l50$\AA$) were deposited with e-beam evaporation system and were heattreated with the rapid thermal annealing system at the temperatures between 50$0^{\circ}C$ and 80$0^{\circ}C$ with 10$0^{\circ}C$ increments for 30 seconds. The phase identification of Co-silicide was carried out by XRD and the chemical analysis was examined by AES and RBS. The interface morphologies of Co/Zr bilayer films were investigated by cross sectional TEM and HRTEM. $CoSi_2$ was formed epitaxially on the crystalline Si substrate above $700^{\circ}C$ while polycrystalline $CoSi_2$ was grown on the amorphous Si substrate. The formation temperature of Co-silicide on the amorphous Si substrate was about 100 C lower than that on the crystalline Si. The COzSi phase was not identified on the both Si substrates. The formation temperature of first phase of Co-silicide on ColZr bilayer was higher than that on Co mono layer. CoSizlayer formed on the amorphous Si substrate exhibits better uniformity compared to the CoSiz formed on the crystalline substrate. The sheet resistance of CoSiz layer on crystalline Si was lower than that on the amorphous Si at high temperatures.tures.