• Research Paper

    Preparation and Evaluation of Optical and Physical Properties of Layered Gradient Zirconia for Aesthetic Dental Applications
    Kyu-Do Choi, Yong-Chan Kwon, Sang-Jin Lee
    Zirconia possesses excellent mechanical, thermal, and chemical properties, and is being widely utilized as a dental ceramic material. To improve the aesthetic … + READ MORE
    Zirconia possesses excellent mechanical, thermal, and chemical properties, and is being widely utilized as a dental ceramic material. To improve the aesthetic appearance of artificial teeth, research has been actively conducted to incorporate various colorants onto zirconia surfaces. Recently, studies have focused on achieving color and translucency comparable to those of natural teeth using zirconia materials alone. In this study, three types of zirconia powders with different yttria stabilizer contents were employed, and the color expression resulting from various combinations of these powders, along with the physical property data obtained from the sintering of each powder, was systematically collected. Based on these data, layered zirconia sintered bodies were fabricated to achieve a gradient effect. In this process, the powders were granulated to achieve high densification through increased green density. Translucency was enhanced by controlling grain size using adjustments in sintering temperature. Consequently, a multi-layered gradient zirconia dental block that successfully reproduces the natural tooth shade while maintaining excellent translucency and aesthetics was fabricated, exhibiting a flexural strength of approximately 635 MPa and a coefficient of thermal expansion of approximately 9.3 × 10-6 /°C. - COLLAPSE
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    27 October 2026

  • Research Paper

    Comparison of Hydrogen Embrittlement in Commercial Cr-Mo Low-Alloy Steels with Different Steel Grades and Tempering Conditions

    강종 및 템퍼링 조건에 따른 상용 Cr-Mo계 저합금강의 수소취성 비교

    Chulmin Kim, Sang-Gyu Kim, Byoungchul Hwang

    김철민, 김상규, 황병철

    This study investigated the combined effects of steel grade and tempering condition on the microstructure, mechanical properties, low-temperature impact toughness, and hydrogen … + READ MORE
    This study investigated the combined effects of steel grade and tempering condition on the microstructure, mechanical properties, low-temperature impact toughness, and hydrogen embrittlement resistance of three commercial Cr-Mo low-alloy steels. After austenitizing at 880 °C and water quenching, AISI 4140 (Steel A) was tempered at 550, 600, and 650 °C, while AISI 4340 (Steel B) and AISI 4330VM (Steel C) were tempered at 650 °C. Scanning electron microscopy of Steel A showed progressive fragmentation and spheroidization of carbides with increasing tempering temperature. In Steel A, the tensile strength decreased from 1,197 to 998 MPa, while the relative notch tensile strength (RNTS) increased from 0.63 to 0.81 as the tempering temperature increased from 550 to 650 °C. At 650 °C, Steels A, B, and C exhibited tensile strengths of 998, 1,118, and 1,172 MPa and RNTS values of 0.81, 0.78, and 0.71, respectively. At comparable tensile-strength levels, Steel B and Steel C showed higher RNTS values than Steel A tempered at lower temperatures. Fractographic examination revealed that the fraction of brittle or quasi-cleavage-like fracture increased with tensile strength under hydrogen-charged conditions. Charpy impact energy at -40 °C and RNTS improved concurrently with tempering temperature in Steel A, although no one-to-one correlation was observed across all grades. These results demonstrate that steel-grade composition and tempering condition should be jointly optimized to balance strength, impact toughness, and resistance to hydrogen embrittlement. - COLLAPSE
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    27 October 2026

  • Research Paper

    Dielectric Properties of Cellulose Nanofibril Films and Environmental Response of Composite Insulating Paper

    목질계 CNF 필름의 유전 특성과 복합 절연지의 온･습도 응답

    Byeong Woon Lee, Wooseok Kim, Doyoung Kim, Yu Jin Lee, Sang Min Won

    이병운, 김우석, 김도영, 이유진, 원상민

    Cellulose nanofibril (CNF) films exhibit dielectric properties that are influenced by both their porous structure and environmental conditions. In this study, wood-derived … + READ MORE
    Cellulose nanofibril (CNF) films exhibit dielectric properties that are influenced by both their porous structure and environmental conditions. In this study, wood-derived hardwood pulp-based CNF films were prepared using CNF dispersion-to-water weight ratios of 1:1, 1:3, and 1:5. Relative permittivity was measured in air and after insulating-oil impregnation, and a series two-phase model was used to estimate the solid-phase permittivity and porosity. As water content increased, the measured permittivity decreased from 2.925 to 2.231, while the estimated solid-phase permittivity remained within 3.819-4.104 and the estimated porosity increased from 0.109 to 0.270. Composite insulating papers containing 0, 5, and 10 wt% CNF were also evaluated under varying temperature and relative humidity conditions. CNF-containing samples showed smaller increases in permittivity at high temperature and humidity, while tensile strength showed a non-monotonic dependence on humidity. These results highlight the importance of considering pore structure and environmental dependence when evaluating CNF-based insulating materials. - COLLAPSE
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    27 October 2026
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Journal Informaiton Korean Journal of Materials Research Korean Journal of Materials Research
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