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1.
Ki-Won Kim Pyeong-Seok Cho Jong-Heun Lee Seong-Hyeon Hong 《Journal of Electroceramics》2006,17(2-4):895-898
A new method for preparing SnO2 whiskers by the decomposition of SnC2O4 is suggested. A Whisker-like morphology of a SnC2O4 precipitate was attained via the gradual addition of an oxalic acid solution to a hot SnCl2 aqueous solution (T > 50∘C). In comparison, when the solution temperature was either lower than 50∘C or when ethanol was used as the solvent, the SnC2O4 precipitate showed an angular and relatively isotropic morphology. The morphology of the SnC2O4 precipitate remained even after its thermal decomposition into SnO2 at 400∘C indicating that SnC2O4 precipitation is a key step in preparing the whiskers. The formation mechanism of SnO2 whiskers was explained by the supersaturation during the precipitation of SnC2O4. 相似文献
2.
Reactive dicalcium silicate (Ca2 SiO4 ) has been synthesized by the Pechini process, and hydration kinetics studied. With increasing calcination temperature, the amorphous product first crystallizes to α'L -phase and subsequently to the ß- and γ-phases. The specific surface area, ranging from 40 to 1 m2 /g, strongly depends on the calcination temperature of 700°-1200°C for 1 h. Samples with a high surface area have a high water demand; a water/cement ratio >2.0 is required to produce formable pastes in some instances. Hydration kinetics are determined by XRD, 29 Si magic-angle spinning nuclear magnetic resonance (MAS NMR), and differential scanning calorimetry/thermogravimetry (DSG/TG). The hydration rate depends only on the surface area, not on the polymorph. Complete hydration occurs in as early as 7 d. Very little calcium hydroxide (Ca(OH)2 ) is formed in the most reactive specimens (calcined at 700° and 800°C), which indicates the Ca/Si ratio in C-S-H gels is ∼2.0, but more Ca(OH)2 forms from samples calcined at higher temperature. The silicate structure of the hydrated Ca2 SiO4 pastes is investigated using 29 Si MAS NMR spectroscopy and trimethylsilylation analysis. 相似文献
3.
Soon-Ho Kwon Youn-Ki Jun Seong-Hyeon Hong In-Seop Lee Hyoun-Ee Kim Ye Yeon Won 《Journal of the American Ceramic Society》2002,85(12):3129-3131
Porous bioceramics, such as hydroxyapatite (HA), tricalcium phosphate (TCP), and biphasic HA/TCP, were fabricated using the polyurethane sponge technique. The porosity of the ceramics was controlled by a multiple coating of the porous body. When a porous body was produced by a single coating, the porosity was ∼90%, and the pores were completely interconnected. When the sintered body was coated five times after the porous network had been made, the porosity decreased to 65%. As the porosity decreased, the strength increased exponentially. The TCP exhibited the highest dissolution rate in a Ringer's solution, and the HA had the lowest rate. The biphasic HA/TCP showed an intermediate dissolution rate. 相似文献
4.
Won-Hoon Song Hyun Sam Ryu Seong-Hyeon Hong 《Journal of the American Ceramic Society》2005,88(9):2642-2644
Ca-containing, particularly CaTiO3 , titania films were prepared by micro-arc oxidation (MAO) of Ti in an electrolytic solution containing calcium acetate monohydrate (CA), and their apatite-inducing ability was evaluated in a simulated body fluid (SBF). The phase, Ca content, and morphology of the films were found to be strongly dependent on the applied voltage. The CaTiO3 -embedded titania was obtained at higher voltages (>300 V). When immersed in SBF, no apatite was induced in all the MAO specimens irrespective of the presence of CaTiO3 , which has been claimed to be an apatite inducer. However, after a hydrothermal treatment at 250°C, apatite was formed on the surfaces of the CaTiO3 -embedded titania after 28 days, which was closely related to the formation of amorphous Ca(OH)2 and presumably surface Ti–OH groups. 相似文献
5.
Ju-Hwan Han Jin-Myung Choi Seong-Hyeon Lee Woojin Jeon Jin-Seong Park 《Ceramics International》2018,44(17):20890-20895
Silicon nitride (Si3N4) films have received great attention not only as dielectric materials for the gate dielectric of transistors and the insulator of capacitors, but also as a buffer layer and etch-stop layer for the semiconductor industry. As the applications of Si3N4 film increase, the necessity of investigating a novel deposition process applicable at low temperature has emerged. In this regard, the plasma-enhanced atomic layer deposition (PEALD) technique is attractive as a promising process; however, the Si3N4 film deposition process at growth temperatures less than 150?°C using PEALD has not been investigated. In this work, the growth behavior and chemistry of SiNx (x?<?1.33) film deposited by the PEALD process at various growth temperatures were developed. Insufficient thermal energy from low growth temperature induces an unstable chemical state of deposited film due to the remaining unreacted ligand of adsorbed precursors. This state results in a further chemical reaction to SiO2 formation by air exposure. Other chemical effects depending on chemical composition and electrical property were also examined in detail. 相似文献
6.
Jun-Young Cho Tae-Ho An Soo Young Shin Hwang Sun Kim Young Seok Kim Hyunick Shin Sung-Hwan Bae Miyoung Kim Seong-Hyeon Hong Chan Park 《Bulletin of Materials Science》2018,41(6):157
The effects of sintering conditions on the microstructure and mechanical properties of the sintered SiC prepared using the SiC powder recovered from the kerf loss sludge were investigated. The recovered SiC powders were consolidated by spark plasma sintering (SPS) and conventional sintering methods. The effects of sintering temperature, time and methods (SPS and conventional sintering) on the phase, grain size and density of SiC were systematically studied. The Vickers hardness of spark plasma-sintered (SPSed) samples was higher than that of conventional sintered samples due to small grain size. When holding time was increased from 10 to 30 min, the grain size and relative density of SPSed samples were also increased, which lead to the almost constant Vickers hardness by competing effects of grain size and relative density. When holding time was over 30 min, no appreciable change of the relative density and grain size were observed, which can lead to similar values of Vickers hardness. SPS process can be used to make SiC with high density and hardness at relatively low temperature compared with the conventional sintering process. 相似文献
7.
Chul-Ho Jung Do-Hoon Kim Donggun Eum Kyeong-Ho Kim Jonghyun Choi Jongwon Lee Hyung-Ho Kim Kisuk Kang Seong-Hyeon Hong 《Advanced functional materials》2021,31(18):2010095
Ni-rich layered LiNixCoyMn1−x−yO2 (LNCM) with Ni content over >90% is considered as a promising lithium ion battery (LIB) cathode, attributed by its low cost and high practical capacity. However, Ni-rich LNCM inevitably suffers rapid capacity fading at a high state of charge due to the mechanochemical breakdown; in particular, the microcrack formation has been regarded as one of the main culprits for Ni-rich layered cathode failure. To address these issues, Ni-rich layered cathodes with a textured microstructure are developed by phosphorous and boron doping. Attributed by the textured morphology, both phosphorous- and boron-doped cathodes suppress microcrack formation and show enhanced cycle stability compared to the undoped cathode. However, there exists a meaningful capacity retention difference between the doped cathodes. By adapting the various analysis techniques, it is shown that the boron-doped Ni-rich layered cathode displays better cycle stability not only by its ability to suppress microcracks during cycling but also by its primary particle morphology that is reluctant to oxygen evolution. The present work reveals that not only restraint of particle cracks but also suppression of oxygen release by developing the oxygen stable facets is important for further improvements in state-of-the-art Li ion battery Ni-rich layered cathode materials. 相似文献
8.
Seong-Hyeon Hong Doh-Yeon Kim Hyun-Min Park Young-Min Kim 《Journal of the American Ceramic Society》2007,90(7):2118-2121
Pure and Nb-substituted CaCu3 Ti4− x Nb x O12+ x /2 (CCTO, x =0, 0.02, 0.1, 0.2, 0.4) ceramics were prepared by a conventional solid-state sintering, and their electric and dielectric properties were investigated using an impedance analyzer. A single-phase CCTO was obtained up to x =0.2 Nb substitution and the lattice parameter increased with Nb substitution concentration. While the grain size decreased with Nb substitution, the resistivity of the grain boundary decreased. The dielectric constant increased with Nb substitution, and the highest value of ∼420 000 was observed in the x =0.2 Nb-substituted specimen at 10 kHz. The obtained electric and dielectric properties in Nb-substituted CCTO were discussed in terms of the internal barrier layer capacitor model, particularly focusing on a ratio of thickness of the grain boundary region to grain size. 相似文献
9.
Jae-Young Lee Seong-Hyeon Hong Jong-Heun Lee Yong Kyun Lee Jae-Young Choi 《Journal of the American Ceramic Society》2005,88(2):303-307
A uniform BaTiO3 nano layer was coated on spherical Ni particles for multilayer ceramic capacitor applications via a Ti-hydroxide coating using the controlled hydrolysis of a TiCl4 butanol solution containing (C2 H5 )2 NH (diethylamine, DEA) and its subsequent hydrothermal reaction at various [Ba(OH)2 ], residual [DEA], and hydrothermal temperatures. The hydrothermal conversion was successful at [Ba(OH)2 ]≥0.065 M (Ba/Ti≥1.3) and T ≥150°C, and the residual DEA in the Ti-hydroxide coating layer not only affected the formation of the BaTiO3 phase but also resulted in a rough surface morphology. When a minimal amount of DEA was involved in the formation of Ti-hydroxide, a uniform BaTiO3 coating with a clean surface morphology could be attained, which was confirmed by elemental mapping of the coated powder and the observation of hollow spheres after removing the Ni core. The BaTiO3 coating was very effective not only in preventing Ni oxidation but also in shifting the starting point of Ni densification to a higher temperature. 相似文献
10.
Won-Taek Moon Youn-Ki Jun Hyun-Su Kim Won-Sik Kim Seong-Hyeon Hong 《Journal of Electroceramics》2009,23(2-4):196-199
Unadded and 0.5 mol% Pd-added ZnO bulk and thin films were prepared by sintering and sputtering, respectively, and their CO gas sensing properties were investigated. The effects of Pd addition, sensing temperature (100–500 °C), and humidity on the CO gas response were discussed. In the bulk sensors, Pd-addition lowered the temperature for the maximum CO gas response (sensitivity) from 400 to 300 °C, whereas the thin film sensors (unadded and Pd-added) exhibited maximum gas response at 200 °C. The Pd-addition enhanced the CO gas response in thin film sensors, and it was also effective for reducing the interference from humidity in both bulk and thin film sensors. 相似文献