• Research Paper

    Enhanced Oxygen Evolution in 0.1 % Fe-Doped NiS2 on Carbon Cloth
    Shoupik Mullani, Vaibhav Lokhande, Chihoon Kim, Shital Bachankar, Aditi Kumbhar, Taeksoo Ji
    With increasing globalization and the urgent need for sustainable energy solutions, electrochemical water splitting has emerged as a crucial technology for clean … + READ MORE
    With increasing globalization and the urgent need for sustainable energy solutions, electrochemical water splitting has emerged as a crucial technology for clean energy production. In this study, we report the successful synthesis of 0.1 % Fe-doped NiS2 via a one-step hydrothermal method. The incorporation of Fe into the NiS2 matrix significantly enhances its electrochemical performance, as evidenced by a remarkable reduction in overpotential, to 180 mV at a current density of 10 mA cm-2, compared to 250 mV for undoped NiS2. Additionally, the Fe-doped NiS2 exhibits a reduced Tafel slope, high double layer capacitance, and lower charge transfer resistance than undoped NiS2, indicating improved reaction kinetics for oxygen evolution. These improvements are attributed to the enhanced conductivity and catalytic activity imparted by Fe doping, which facilitates more efficient charge transfer and reaction processes at the electrode surface. The results suggest that Fe-doped NiS2 is a highly promising and robust candidate for applications in electrochemical energy conversion. Moreover, the doping strategy employed here offers a valuable approach for tailoring the properties of other metal sulfides and chalcogenides, paving the way for the design of next generation electrocatalysts that can drive large-scale energy conversion processes with minimal energy loss. - COLLAPSE
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    27 February 2025

  • Research Paper

    Residual Stresses in Shot-Peened Mechanical Structural Carbon Steel Using High-Energy X-Rays
    Chang-Hwan Bae, Seung-In Lim, Chang-Suk Han
    X-ray diffraction is widely used as a non-destructive method for measuring residual stress in crystalline materials, and is particularly useful as a … + READ MORE
    X-ray diffraction is widely used as a non-destructive method for measuring residual stress in crystalline materials, and is particularly useful as a technique for controlling residual stress that has been introduced during the heat treatment or surface treatment of metallic materials. Neutron stress measurement is gaining attention as an internal material measurement method. It complements the demerits of the X-ray method in that it measures stress in a very thin surface layer. The neutron stress measurement method, like the X-ray method, is based on the principle of crystal diffraction, and its penetration depth is about 1,000 times greater than that of the X-ray method and is suitable for measuring the inside of a material. This study investigated the residual stress measurement method using the sin2ψ method using shot-peened mechanical structural carbon steel. The non-destructive measurement using high-energy X-rays was compared with the residual stress measured using conventional laboratory X-rays, and the following results were obtained. The high intensity diffraction angles using high-energy X-rays are low, but can be measured with sufficient precision. Interpreting the three diffractions 633, 552, and 721 as a single diffraction profile allowed stress measurements to be made, and the calculated value was close to the weighted average of the intensity ratios. The results of the high-energy X-ray residual stress measurements were in good agreement with the results from laboratory X-rays, confirming the usefulness of this method as a non-destructive method of assessing stress deep inside materials. - COLLAPSE
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    27 February 2025

  • Research Paper

    Mo Recovery from Waste Hydrotreating Catalyst via Tributyl Phosphate
    Yongyang Bu, Haitao Wu, Kejie Hu, Dazhuang Huang, Tian Ai, Songdong Yao
    This study investigated the process of reclaiming Mo from calcined waste hydrotreating (CWHT) catalysts using tributyl phosphate (TBP) as an extractant with … + READ MORE
    This study investigated the process of reclaiming Mo from calcined waste hydrotreating (CWHT) catalysts using tributyl phosphate (TBP) as an extractant with electron-withdrawing properties. Using inductively coupled plasma (ICP) technology, the optimal operating conditions for Mo recovery were determined based on the metal ion content in different processes. Considering the pH impact on metal species in solution, an acid leaching solution with 6 M sulfuric acid was employed. After 3 h of reaction, 94 wt% of the Mo was transferred from the WHT catalyst to the acid leaching solution. Adjusting the filtrate to a pH of 1.5 allowed the TBP to selectively extract over 98.8 wt% of Mo from the aqueous filter solution into the organic phase. MC-Cabe-Thiele theory predicts that a three-stage countercurrent extraction can reduce Mo to less than 0.2 wt%. Stripping moved approximately 98 wt% of the Mo from the organic to the inorganic phases. The recovered colorless organic tributyl phosphate can be used in the recycled extraction process. - COLLAPSE
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    27 February 2025

  • Research Paper

    Volatilization of Alkali Elements during the Potassium Sodium Niobate Thin Film Deposition Process via RF Magnetron Sputtering
    Je-Yeon Park, Il-Ryeol Yoo, Seong-Hui Choi, Kyung-Hoon Cho
    This study examines the volatilization of alkali elements on the surfaces of ceramic targets and in the deposited films during the deposition … + READ MORE
    This study examines the volatilization of alkali elements on the surfaces of ceramic targets and in the deposited films during the deposition of potassium sodium niobate (KNN) thin films using a ceramic target with the nominal composition K0.55Na0.55NbO3 via a RF magnetron sputtering process. Under a 100 W RF power condition, significant volatilization of alkali elements occurred on the surface of the ceramic target, resulting in the inevitable formation of a Nb-rich secondary phase in the thin films. However, perovskite-phase KNN thin films with excellent reproducibility and without secondary phases were obtained under 50 W RF power and a substrate temperature of 600 °C. When the RF power was reduced to 20 W or the substrate temperature was lowered to 500 °C under 50 W RF power, no crystalline thin films could be obtained. Additionally, when the substrate temperature was raised to 700 °C under 50 W RF power, the niobium-rich secondary phase appeared in the thin films due to the volatilization of alkali elements. The conditions of 50 W RF power and a substrate temperature of 600 °C were found to be optimal for depositing perovskite-phase KNN thin films. However, complete suppression of potassium volatilization from the thin films was not achievable. Consequently, the resulting films had a sodium-rich composition compared to K0.5Na0.5NbO3 and exhibited lower dielectric constants along with relaxor ferroelectric characteristics. This study highlights the importance of monitoring the compositional changes in ceramic targets during the RF sputtering process to ensure high reproducibility in KNN thin film fabrication. - COLLAPSE
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    27 February 2025

  • Research Paper

    Impact of Capping Metal Work Function and Length on Electron Mobility in ZTO TFT

    ZTO TFT의 Capping Metal 종류와 길이에 따른 전기적 특성

    Minseok Choi, Jaeseon Back, Jinwoo Lee, Moonsuk Yi

    최민석, 백재선, 이진우, 이문석

    Zinc tin oxide (ZTO) thin films were deposited using atomic layer deposition (ALD) to ensure precise thickness control and uniformity. However, the … + READ MORE
    Zinc tin oxide (ZTO) thin films were deposited using atomic layer deposition (ALD) to ensure precise thickness control and uniformity. However, the low-temperature processing of ZTO often results in increased defect states, leading to degraded electrical performance. To address this issue, metal capping layers (Al or Au) were added to the ZTO active layer. The capping layers modulate electron energy levels at the interface, increase carrier density, and reduce interface traps, thereby improving electrical properties. Aluminum (Al) and gold (Au) were evaluated for their impact on key performance metrics, including electron mobility (µsat), threshold voltage (VT), subthreshold swing (SS), and on/off current ratio (ION/OFF). Results show that Al-capped ZTO thin-film transistors (TFTs) exhibited enhanced performance due to the lower work function of Al (4.0 eV), which facilitates electron injection and reduces contact resistance. In contrast, Au-capped ZTO TFTs showed decreased performance due to electron depletion caused by the higher work function of Au (5.1 eV). Optical analyses, including UPS and UV-Vis, revealed the band structure and work function of the ZTO thin films. This study concludes that the choice of capping material and its design parameters play a critical role in optimizing TFT performance, offering valuable insights for the development of next-generation high performance TFT devices. - COLLAPSE
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    27 February 2025

  • Research Paper

    Influence of Band Gap Enlargement on Thermoelectric Performance in Cu0.008Bi2Te3

    밴드 갭 증가가 Cu0.008Bi2Te3의 열전 성능에 미치는 영향

    Hyunjin Park, Okmin Park, Changwoo Lee, Young-Woo Kim, Sang-il Kim, Hyun-Sik Kim

    박현진, 박옥민, 이창우, 김영우, 김상일, 김현식

    We investigated the effect of band gap engineering on the thermoelectric properties of n-type Cu0.008Bi2Te3 using the … + READ MORE
    We investigated the effect of band gap engineering on the thermoelectric properties of n-type Cu0.008Bi2Te3 using the two-band (TB) model. The experimental measurements showed a zT of ~0.41 at 300 K and ~0.46 at 520 K, with an optical band gap of ~0.13 eV. While fixing the density-of-state effective mass (md*), deformation potential (Edef), lattice thermal conductivity (κl), and Fermi level based fitted based on experimental data, we varied the band gap (Eg) from 0.1 to 0.3 eV to analyze its impact on the thermoelectric performance. The TB model calculations revealed that the power factor (PF) increased and the thermal conductivity (κ) decreased with increasing Eg at both 300 K and 520 K, leading to an enhancement in zT. The magnitude of this enhancement was more pronounced at 520 K than at 300 K, which can be attributed to the suppressed bipolar effects at higher temperatures. Our findings suggest that increasing the band gap of Cu0.008Bi2Te3 can significantly improve its thermoelectric performance, to an estimated maximum zT of ~0.61 at 520 K for Eg = 0.3 eV. The theoretical maximum zT, considering the optimized hole concentration (nH), was estimated to be ~0.75. We demonstrate that Eg engineering of narrow-bandgap semiconductor thermoelectric materials can significantly enhance thermoelectric performance. - COLLAPSE
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    27 February 2025

  • Research Paper

    High-Temperature Oxy-Acetylene Torch Test of Filament-Wound Cf/SiC-ZrB2 Composite Ring

    필라멘트 와인딩 공법으로 제작한 Cf/SiC-ZrB2 복합체의 고온 산소-아세틸렌 토치 평가

    Yoonjae Cho, Seung Yong Lee, Jung Hoon Kong, Sanghyeon Kim, Jae-Hyeong Choi, Do Kyung Kim

    조윤재, 이승용, 공정훈, 김상현, 최재형, 김도경

    Composites of carbon fiber-reinforced silicon carbide (Cf/SiC) with ultra-high temperature ceramics (UHTCs) exhibit superior resistance to oxidation and ablation under … + READ MORE
    Composites of carbon fiber-reinforced silicon carbide (Cf/SiC) with ultra-high temperature ceramics (UHTCs) exhibit superior resistance to oxidation and ablation under high temperatures. Components in large-scale applications often have complex geometries, making it crucial to understand the oxidation and ablation behaviors of curved and non-uniform surfaces. In this study, a Cf/SiC-ZrB2 composite was fabricated into a 300 mm cylindrical shape using filament winding and liquid silicon infiltration processes. The resulting specimens exhibited a uniform microstructure, with SiC and ZrB2 crystals evenly distributed across the top and bottom surfaces, demonstrating the feasibility of producing large-scale composites. The specimens underwent an oxyacetylene torch test at 2,100 K for 5 min to assess their ablation and oxidation performance. The results revealed significant variation in the oxide layer due to the non-flat surface, with the layer thickness gradually decreasing as the oblique angle was reduced. Additionally, the presence of high-melting-point ZrO2 in the oxide layer near the torch center was attributed to the migration and solidification of molten SiO2. This suggests that large and complex Cf/SiC incorporating UHTCs can effectively form a protective oxide layer, even under conditions where SiO2 displacement occurs. The findings underscore the importance of integrating geometric considerations into the design of ultra-high temperature ceramic composites to achieve the thermal and ablation resistance required for advanced high-temperature applications. - COLLAPSE
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    27 February 2025
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Journal Informaiton Korean Journal of Materials Research Korean Journal of Materials Research
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