• Title/Summary/Keyword: Hexagonal particle

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Influence of Crystal Structure on the Chemical Bonding Nature and Photocatalytic Activity of Hexagonal and Cubic Perovskite Compounds

  • Lee, Sun-Hee;Kim, In-Young;Kim, Tae-Woo;Hwang, Seong-Ju
    • Bulletin of the Korean Chemical Society
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    • v.29 no.4
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    • pp.817-821
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    • 2008
  • We have investigated the influence of the crystal structure on the chemical bonding nature and photocatalytic activity of cubic and hexagonal perovskite A[$Cr_{1/2}Ta_{1/2}$]O3 (A = Sr, Ba) compounds. According to neutron diffraction and field emission-scanning electron microscopy, the crystal structure and particle size of these compounds are strongly dependent on the nature of A-site cations. Also, it was found that the face-shared octahedra in the hexagonal phase are exclusively occupied by chromium ions, suggesting the presence of metallic (Cr-Cr) bonds. X-ray absorption and diffuse UV-vis spectroscopic analyses clearly demonstrated that, in comparison with cubic Sr[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase, hexagonal Ba[$Cr_{1/2}Ta_{1/2}$]$O_3$ phase shows a decrease of Cr oxidation state as well as remarkable changes in interband Cr d-d transitions, which can be interpreted as a result of metallic (Cr-Cr) interactions. According to the test of photocatalytic activity, the present semiconducting materials have a distinct activity against the photodegradation of 4-chlorophenol. Also the Srbased compound was found to show a higher photocatalytic activity than the Ba-based one, which is attributable to its smaller particle size and its stronger absorption in visible light region.

Hexagonal Shape Characteristics according to the Change in Standoff Distance during Fine Particle Blasting (미세입자 분사가공 시 분사높이 변화에 따른 육각형 가공형상 특성)

  • Lee, Hyoung-Tae;Lee, Sea-Han;Wang, Duck Hyun
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.20 no.9
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    • pp.76-83
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    • 2021
  • This study examines the characteristics of spraying conditions based on the change in standoff distance during fine particle spraying while measuring the surface roughness, maximum depth, and maximum width of the sprayed surface. The processing shape of the sprayed surface is analyzed to understand the effects of injection pressure, nozzle diameter, standoff distance, processing shape, processing cycle, processing speed, and injection particles, which are the main factors of fine particle injection processing. Based on the derived characteristics, we attempt to determine the interrelationships of these major factors. The standoff distance is set as a variable factor and a spray machining experiment using a hexagonal shape (from among polygons) instead of square and circular shapes is conducted. Results reveal that research on the characteristics of spraying conditions could be expanded based on changes in the shapes of workpieces.

Optical Properties of Mid-infrared Transparent ZnS Ceramics with Different Molar Ratio of S/Zn (S/Zn의 몰비에 따른 중적외선 투과용 ZnS 세라믹스의 소결과 광학적 특성)

  • Yeo, Seo-Yeong;Park, Buem-Keun;Kim, Chang-Il;Paik, Jong-Hoo
    • Journal of Sensor Science and Technology
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    • v.28 no.4
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    • pp.256-261
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    • 2019
  • In this study, mid-infrared transparent zinc sulfide (ZnS) ceramics were fabricated through hydrothermal synthesis with different molar ratios of S/Zn (S/Zn = 0.8, 1.0, 1.2, 1.4, and 1.6). The ZnS ceramics were sintered at a relatively low temperature of $850^{\circ}C$ to prevent the occurrence of the hexagonal phase featuring optical anisotropy. The phase composition, microstructure, and optical properties of the ZnS ceramics were subsequently investigated by employing X-ray diffraction, scanning electron microscopy, and Fouriertransform infrared spectroscopy. The results obtained indicate that the ZnS nanoparticles feature the cubic phase, without the hexagonal phase. Moreover, with increasing S, the crystallinity and particle size of the ZnS nanoparticles increased. The crystallinity and density of the ZnS ceramics improved when the molar ratio of S was higher than the molar ratio of Zn, thereby enhancing the transmittance. Furthermore, the ZnS ceramic with an S/Zn value of 1.2 was found to exhibit the highest transmittance of approximately 69% owing to the reduced occurrence of the hexagonal phase and a high density of 99.8%.

A Study on Packing of Regular Particles - Preparation of Dense Sintered Silicon Carbide (1) - (규칙입자의 충전 -치밀된 탄화규소 소결체의 제조(제 1 보)-)

  • 문병훈;남건태;최상욱
    • Journal of the Korean Ceramic Society
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    • v.31 no.9
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    • pp.989-994
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    • 1994
  • This study aims at finding the closest packings of regular shape particles such as sphere, circle rod and hexagonal rod type. As the ratio of particle size to container lowered to less than 1/10, the wall effect decreased gradually. The tap density of spherical particles with almost orthorhombic arrangement was 59.5%, while those of circle rod and hexagonal rod type particles were 63.5% and 63.0% respectively. And it was decreased with increasing the aspect ratio of regular particles. The tap density of binary mixtures was larger than that corresponding to the monosized particles packing by about 15%. The tap density of ternary mixtures was larger than that of corresponding to the packing of binary mixtures by about 9%. This work employed the binary mixture of 60% coarse particles and 40% fine particles with size ratio of 1.0 to 1/10 and the ternary mixture of 60% coarse particles, 20% medium and 20% fine particles with size ratio of 1:1/10:1/400 respectively.

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Synthesis of $Ni_2Y$ magnetic particles by coprecipitation method (공침법에 의한 $Ni_2Y$ 자성 분말의 합성)

  • 김한근;사공건
    • Electrical & Electronic Materials
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    • v.9 no.9
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    • pp.906-910
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    • 1996
  • Ferroxplana N $i_{2}$Y(B $a_{2}$N $i_{2}$F $e_{12}$ $O_{22}$ ) magnetic particles, which is one of the hexagonal ferrite were synthesized by a coprecipitation method. The coprecipitates were prepared by adding aqueous solution of BaC $I_{2}$ - 2 $H_{2}$O, NiC $I_{2}$ - 6 $H_{2}$O and FeC $I_{3}$ - 6 $H_{2}$O(of which the mole ratio is $Ba^{+2}$ : N $i^{+2}$ : F $e^{3+}$= 1 : 1 : 6) to a mixture of NaOH and N $a_{2}$C $O_{3}$. The shape of Ferroxplana N $i_{2}$Y magnetic particles obtained at 1, 100(.deg. C) was hexagonal plate-like, average particle size and aspect ratio were 2(.mu.m) and 7, respectively.y.

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Synthsis of Ferroxplana Y-type($Ni_2Y$) Magnetic Particles (Ferroxplana Y-type($Ni_2Y$) 자성(磁性) 분체의 합성)

  • Park, S.H.;Kim, H.G.;SaGong, G.
    • Proceedings of the KIEE Conference
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    • 1993.07b
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    • pp.1140-1142
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    • 1993
  • It has been prepared by a coprecipitation method for Ferroxplana $Ni_2Y\;(Ba_2Ni_2Fe_{12}O_{22}$ magnetic particles, which is one of the Hexagonal ferrite. The coprecipitates were synthesized by adding aqueous solution of $BaCl_2{\cdot}2H_2O,\;NiCl_2{\cdot}6H_2O\;and\;FeCl_2{\cdot}4H_2O$ (of which the mole ratio is $Ba^{2+}:Ni^{2+}:Fe^{2+}$=1:1:6) to a mixture of NaOH and $Na_2CO_3$ solution. The shape of Ferroxplana $Ni_2Y$ magnetic particles obtained at the calcined temperature 1,100($^{\circ}C$) was hexagonal plate-like, average particle size was 2(${\mu}m$), and aspect ratio was more than 7.

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Effect of Molar Ratio of $Fe_2O_3$ and BaO Addition on the Characteristics of Sr-Ferrite ($Fe_2O_3$몰비 및 B\ulcorner첨가가 Sr-Ferrite 특성에 미치는 영향)

  • 문기훈;심영재;조성걸
    • Journal of the Korean Ceramic Society
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    • v.34 no.5
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    • pp.453-460
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    • 1997
  • Sr-ferrite having magnetoplumbite structure is similar to Ba-ferrite in magnetic characteristics, but better magnetic characteristics for using motor application. To improve remanence magnetic flux density(Br) and coercive force(iHc), it is necessary that sintered ferrites must have high density and grain size less than 1 $\mu$m. By varying n values in SrO.nFe2O3 basic composition, calcination temperature, and BaO addition, Sr-ferrite powder and sintered specimen was prepared. The n values, calcination temperature, and BaO addition affected secondary phase formation, particle size, and particle shape. BaO addition enhanced Fe2O3 secondary phase and hexagonal shape particle. Fe2O3 phase reduced sintered density which greatly decreased Br.

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Fabrication of various Si particle by Pulsed Laser Ablation (PLA법에 의한 Si 미립자 제작)

  • Kim, M.S.;Yoshimoto, Mamoru;Koinuma, Hideomi
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11b
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    • pp.121-125
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    • 2001
  • We study the feasibility of synthesizing Si particles using PLA method. In the previous studies, it was possible to control the size of Si nanoparticles by the He gas pressure. In this study, we fabricated sub-micron size Si particles with various shapes such as conical, hexagonal, and ring by controlling not only the ambient gas pressure but also the laser energy density. Furthermore, we found that the conical Si particles were uniform-sized and had step shape when observed from FE-SEM and AFM. The conical Si particle has the same crystal structure as the bulk single crystalline Si by the analysis of the Raman scattering. It is shown that the relationship between the laser energy density and the He gas pressure inside the chamber affects the shape of the Si particle.

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Fabrication of various Si particle by Pulsed Laser Ablation (PLA법에 의한 Si 미립자 제작)

  • ;Mamoru Yoshimoto;Hideomi Koinuma
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11a
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    • pp.121-125
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    • 2001
  • We study the feasibility of synthesizing Si particles using PLA method. In the previous studies, it was possible to control the size of Si nanoparticles bythe He gas pressure. In this study, we fabricated sub-micron size Si particles with various shapes such as conical, hexagonal, and ring by controlling not only the ambient as pressure but also the laser energy density. Furthermore, we found that the conical Si particles were uniform-sized and had step shape when observed from FE-SEM and AFM. The conical Si particle has the same crystal structure as the bulk single crystalline Si by the analysis of the Raman scattering. It is shown that the relationship between the laser energy density and the He gas pressure inside the chamber affects the shape of the Si particle.

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Preparation of corundum ($\alpha$-Al_{2}O_{3}$) by hydrothermal growing process : I. A study on the effects of reaction temperature and seed crystal (수열성장법에 의한 코런덤($\alpha$-Al_{2}O_{3}$) 제조 : I. 반응온도와 종자결정의 영향에 관한 연구)

  • 반종성;이기정;서경원;목영일;이철경
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.6 no.2
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    • pp.129-140
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    • 1996
  • In this study, we have prepared corundum ($\alpha$-Al_{2}O_{3}$) single crystals from aluminum hydroxides by hydrothermal growing process and have investigated the reaction conditions. The hydrothermal conditions were mainly affected by reaction temperature, seed crystal and reaction time. Especially, seed crystal has strong effects on the particle size and crystallity of products. By adding seed crystal in Japanese gibbsite solution as the nutrient, hydrothermal reaction was performed for 2 hours at the reaction temperature of $460^{\circ}C$, to produce corundum powders which had weight mean particle diameter of $11\;\mu\textrm{m}$ with hexagonal crystal, Without adding seed crystal in Russian gibbstite solution, corundum powders that have weight mean particle diameter of $6\;\mu\textrm{m}$ with hexagonal crystals were also formed after 2 hours operation at the reaction temperature of $420^{\circ}C$.

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