• Title/Summary/Keyword: Ceramic oxides

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Synthesis and Properties of Multimetal Oxide Nanopowders via Nano-explosive Technique

  • Vasylkiv, Oleg;Sakka, Yoshio;Skorokhod, Valeriy
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.152-153
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    • 2006
  • We demonstrate the methodology of engineering the multi-component ceramic nanopowder with precise morphology by nanoblast calcinations decomposition of preliminary engineered nanoreactors. Multiple explosions of just melted $C_3H_6N_6O_6$ embedded into preliminary engineered nanoreactors break apart the agglomerates due to the highly energetic impacts of the blast waves. Also, the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during each nano-explosion in surrounding area. This methodology was applied for production of agglomeratefree nano-aggregates of $Gd_{20}Ce_{80}O_{1.95}$ with an average size of 42 nm and $LaSrGaMgO_{3-x}$ nanopowder with an average aggregate size of 83 nm.

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Surface Modification of a Mild and Stainless Steel by Alumina Spraying (아루미나 용사에 의한 연강 및 스테인레스강의 표면개질)

  • 배종규;박승옥;정인상
    • Journal of the Korean institute of surface engineering
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    • v.22 no.4
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    • pp.185-196
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    • 1989
  • The surface modification of a mild and stainless steel by alumina sprayed coating were studied. The effects of surface roughness and bond coating layer on the adhesive strengthy and durability of sprayed specimens were also investiated. The adhesive strength of ceramic coating was affected by surface roughness and bond coating layer thinkness. That showed excellent undergrit blast time and bond coating layer; 60 sec and 0.15-0.33mm, respectively. The adhesive strength and densification of sprayed coating with air pressure were superior to those of without and fracture was mainly occured at alumina-bond coating interface. Under ambient atmosphere at $800^{\circ}C$, the oxides existed within bond coating layer promote diffusion of oxygen to lower durability of sprayed specimens. In this case, fracure was occured at sudstrate-bond coating interface.

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A Study on Bond Strength of Procelain with Non Precious Alloy (도재전장관용 비귀금속합금과 도재의 융착결합에 관한 연구)

  • Kang, Sung-Hyun
    • The Journal of Korean Academy of Prosthodontics
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    • v.18 no.1
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    • pp.49-57
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    • 1980
  • The adhesive mechanisms on the metal-ceramic restorations have been reported to be mechanical interlocking, chemical bonding, compressive force, and Van der Waal's force, etc. Of these, the mechanical interlocking and chemical bonding forces are thought to affect the adhesive force between Ni-Cr alloy and porcelain. This study investigates the adhesion of Ni-Cr alloy to porcelain according to surface treatment. For this purpose, the following experiments were made; The compositions of Ni-Cr alloy as cast by emission spectrograph, and the oxides produced on Ni-Cr alloy during degassing at $1850^{\circ}F$ for 30 minutes in air and in vacuum were analyzed by X-ray diffractograph. The metal phases of Ni-Cr alloy were observed according to porcelain-baking cyclic heat treatment by photo microscope and the distribution and the shift of elements of Ni-Cr alloy and porcelain and the failure phases between Ni-Cr alloy and porcelain by scanning electron microscope. The adhesive force between Ni-Cr alloy and porcelain was measured according to surface treatment with oxidization and roughening by Instron Universal Testing Machine. Results were as follows; 1. The metal phases of Ni-Cr alloy as cast and degassing state showed the enlarged and fused core, but when subjected to porcelain-baking cyclic heat treatment, showed a dendrite growing. 2. The kinds of metal oxides produced on Ni-Cr alloy during degassing were found to be NiO and $Cr_2O_3$. 3. The distribution of elements at the interface of Ni-Cr alloy and porcelain in degassing state showed demarcation line, but in roughening state, showed mechanical interlocking phase. 4. The shift of elements at the interface occurred in both states, but the shift amount was found to be larger in roughening than in degassing. 5. The adhesive force between Ni-Cr alloy and porcelain was found to be $3.45{\pm}0.93kg/mm^2$, in degassing and $3.82{\pm}0.99kg/mm^2$, in roughening. 6. The failure phase between Ni-Cr alloy and porcelain showed the mixed type failure.

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A review of smart exsolution catalysts for the application of gas phase reactions (기상 반응용 스마트 용출 촉매 연구 동향)

  • Huang, Rui;Kim, Hyung Jun;Han, Jeong Woo
    • Ceramist
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    • v.23 no.2
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    • pp.211-230
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    • 2020
  • Perovskite-type oxides with the nominal composition of ABO3 can exsolve the B-site transition metal upon the controlled reduction. In this exsolution process, the transition metal emerges from the oxide lattice and migrates to the surface at which it forms catalytically active nanoparticles. The exsolved nanoparticles can recover back to the bulk lattice under oxidation treatment. This unique regeneration character by the redox treatment provides uniformly dispersed noble metal nanoparticles. Therefore, the conventional problem of traditional impregnated metal/support, i.e., sintering during reaction, can be effectively avoided by using the exsolution phenomenon. In this regard, the catalysts using the exsolution strategy have been well studied for a wide range of applications in energy conversion and storage devices such as solid oxide fuel cells and electrolysis cells (SOFCs and SOECs) because of its high thermal and chemical stability. On the other hand, although this exsolution strategy can also be applied to gas phase reaction catalysts, it has seldomly been reviewed. Here, we thus review recent applications of the exsolution catalysts to the gas phase reactions from the aspects of experimental measurements, where various functions of the exsolved particles were utilized. We also review non-perovskite type metal oxides that might have exolution phenomenon to provide more possibilities to develop higher efficient catalysts.

Mineralogical and Geochemical Characteristics of Ancient Field Soil in Jeongdongri as Ceramic Raw Materials of the Baekje Kingdom (백제 와전재료로서 정동리 고토양의 광물 및 지구화학적 특성)

  • Jang, Sung-Yoon;Lee, Chan-Hee
    • Economic and Environmental Geology
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    • v.43 no.6
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    • pp.543-553
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    • 2010
  • This study was focused on the mineralogical and geochemical characteristics of field soil of the Baekje Kingdom from K wongbawigol site in Jeongdongri, Buyeo and whether the bricks from Songsanri Tombs and Muryung's Royal Tomb were made of soil from this site. Soil samples show the similar size fraction as a silt loam and acidic soil, whereas some samples have the enrichment of organic matter, P and S. Also, they have similar geochemical behavior of elements and similar mineral phases consisting of quartz, plagioclase, orthoclase, vermiculite, mica and kaolinite. The enrichment of iron oxide is found in some soil layer, including the iron oxide mottling and precipitation along plant roots and they are attributed to repeat oxidation and reduction environments due to flooding and drainage of field soil. It's anthropogenic alteration by human activity. Especially, it is assumed that the concentration of the iron oxides found in bricks from Muryung's Royal Tomb and Songsanri Tombs is the additional evidence that soil in this study is probably the raw materials of those bricks.

Electrical Properties and Phase Transition Behavior of Lead-Free BaTiO3-Modified Bi1/2Na1/2TiO3-SrTiO3 Piezoelectric Ceramics (BaTiO3 첨가에 따른 Bi1/2Na1/2TiO3-SrTiO3 무연 압전 세라믹스의 전기적 특성 및 상전이 거동 연구)

  • Kang, Yubin;Park, Jae Young;Devita, Mukhllishah Aisyah;Duong, Trang An;Ahn, Chang Won;Kim, Byeong Woo;Han, Hyoung-Su;Lee, Jae-Shin
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.35 no.5
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    • pp.516-521
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    • 2022
  • We investigated the microstructure, crystal structure, dielectric, and elecromechanical strain properties of lead-free BaTiO3 (BT)-modified (Bi1/2Na1/2)TiO3-SrTiO3 (BNT-ST) piezoelectric ceramics. Samples were prepared by a conventional ceramic processing route. Temperature dependent dielectric properties confirmed that a phase transition from a nonergodic relaxor to an ergodic relaxor was induced when the BT concentration reached 1.5 mol%, interestingly, where the average grain size reached a maximum value of 4.5 ㎛. At the same time, enhanced electromechanical strain (Smax/Emax = 600 pm/V) was obtained. It is suggested that the induced ferroelectric-relaxor phase transition by the BT modification is responsible for the enhancement of electromechanical strain in 1.5 mol% BT-modified BNT-ST ceramics.

Crystal Structure Analysis of Uranium Oxides (산화우라늄의 결정구조 분석)

  • 김정석;최용남;이창희;김시향;이영우
    • Journal of the Korean Ceramic Society
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    • v.38 no.11
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    • pp.967-972
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    • 2001
  • The crystal and defect structures of U $O_{x}$(x=2.0, 2.03, 2.14, 2.19, 2.20 and 2.26) were analysed by rietveld refinement and the results were compared to the U-O phase diagram. Neutron diffraction data were collected in the temperature range of RT~100$0^{\circ}C$. The specimens of x=2.14, 2.19, and 2.20 consisted of two phase: $UO_{2+x}$(Fm3m, a≒5.4$\AA$) and $U_4$$O_{9}$(I43d, a≒21.8$\AA$). The proportion of the $UO_{2+x}$(Fm3m) phase increased with increasing the temperature. The variation of the proportion of the two phases with temperature in the U $O_{2.2}$ and U $O_{2.18}$ samples showed some deviation from the expected values from the phase diagram especially at the high temperature range. The phase transitions ${\gamma}$longrightarrow$\beta$longrightarrow$\alpha$ of $U_4$$O_{9}$ were discussed in relation with the phase separation.eparation.ion.

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Effects of Nitrate Electrolyte as the MAO process for Ceramic Coating treatments of AZ31 alloy (MAO법을 이용한 산화피막처리에서 질산염 전해액성분 첨가에 따른 AZ31합금의 표면코팅 특성)

  • Cho, Young-Hee;Jang, Kyong-Soo;Park, Sei-He;Lee, Ho-Jeong;Lee, Tae-Haeng
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.10
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    • pp.4365-4370
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    • 2012
  • AZ31 Mg alloy were coated by Macro Arc Oxidation(MAO) with 3 types of electrolyte and various coating times at 4A/$cm^2$. The Surface morphology of coatings became lager pores and surface crack initiated as the coating time increased. The thickness and micro-hardness of coatings increased as the coating time increased. also. The phase of coatings on AZ31 alloy consisted of MgO, $Mg_2SiO_4$ and $MgAl_2O_4$ oxides. The salt spray corrosion resistance of coated AZ31 alloys revealed excellent corrosion resistance in 5% NaCl solution for 168hr.

Molecular Orientation of Intercalants Stabilized in the Interlayer Space of Layered Ceramics: 1-D Electron Density Simulation

  • Yang, Jae-Hun;Pei, Yi-Rong;Piao, Huiyan;Vinu, Ajayan;Choy, Jin-Ho
    • Journal of the Korean Ceramic Society
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    • v.53 no.4
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    • pp.417-428
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    • 2016
  • In this review, an attempt is made to calculate one-dimensional (1-D) electron density profiles from experimentally determined (00l) XRD intensities and possible structural models as well in an effort to understand the collective intracrystalline structures of intercalant molecules of two-dimensional (2-D) nanohybrids with heterostructures. 2-D ceramics, including layered metal oxides and clays, have received much attention due to their potential applicability as catalysts, electrodes, stabilizing agents, and drug delivery systems. 2-D nanohybrids based on such layered ceramics with various heterostructures have been realized through intercalation reactions. In general, the physico-chemical properties of such 2-D nanohybrids are strongly correlated with their heterostructures, but it is not easy to solve the crystal structures due to their low crystallinity and high anisotropic nature. However, the powder X-ray diffraction (XRD) analysis method is thought to be the most powerful means of understanding the interlayer structures of intercalant molecules. If a proper number of well-developed (00l) XRD peaks are available for such 2-D nanohybrids, the 1-D electron density along the crystallographic c-axis can be calculated via a Fourier transform analysis to obtain structural information about the orientations and arrangements of guest species in the interlayer space.

Effect of Pulse Frequency on the Properties of ZnO:Al Thin Films Prepared by Pulsed DC Magnetron Sputtering (펄스 DC 마그네트론 스퍼터링법에 의한 ZnO:Al 박막 증착시 펄스 주파수의 영향)

  • 고형덕;이충선;태원필;서수정;김용성
    • Journal of the Korean Ceramic Society
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    • v.41 no.6
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    • pp.476-480
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    • 2004
  • AZO (Al-doped ZnO) thin films were deposited on glass by pulsed magnetron sputtering method, and their structural, electrical and optical properties were investigated. XRD patterns showed that a highly c-axis preferred AZO film was grown in perpendicular to the substrate when pulse frequency of 30 ㎑ was applied to the target. Microstructure of thin films showed that the fibrous grain of tight dome shape was grown. The deposition rate decreased linearly with increase of pulse frequency, and the lowest resistivity was 8.67${\times}$10$\^$-4/ $\Omega$-cm for the film prepared at pulse frequency of 30 ㎑. The optical transmittance spectra of the films showed a very high transmittance of 85∼90%, within visible wavelength region and exhibited the absorption edge of about 350 nm. The characteristics of the low electrical resistivity and high optical transmittance of AXO films suggested a possibility for the application to transparent conducting oxides.