• Title/Summary/Keyword: nanostructured materials

Search Result 366, Processing Time 0.033 seconds

Effect of Austempering Time on the Microstructure and Mechanical Properties of Ultra-High Strength Nanostructured Bainitic Steels (오스템퍼링 시간에 따른 초고강도 나노 베이나이트강의 미세조직과 기계적 특성)

  • Lee, Ji-Min;Hwang, Byoungchul
    • Korean Journal of Materials Research
    • /
    • v.30 no.2
    • /
    • pp.87-92
    • /
    • 2020
  • This study deals with the effects of austempering time on the microstructure and mechanical properties of ultra-high strength nanostructured bainitic steels with high carbon and silicon contents. The steels are composed of bainite, martensite and retained austenite by austempering and quenching. As the duration of austempering increases, the thickness of bainitic ferrite increases, but the thickness of retained austenite decreases. Some retained austenites with lower stability are more easily transformed to martensite during tensile testing, which has a detrimental effect on the elongation due to the brittleness of transformed martensite. With increasing austempering time, the hardness decreased and then remained stable because the transformation to nanostructured bainite compensates for the decrease in the volume fraction of martensite. Charpy impact test results indicated that increasing austempering time improved the impact toughness because the formation of brittle martensite was prevented by the decreased fraction and increased stability of retained austenite.

CO2 Reduction and C2H4 Production Using Nanostructured Gallium Oxide Photocatalyst (산화갈륨 나노구조 광촉매 특성을 이용한 이산화탄소 저감 및 에틸렌 생성 작용)

  • Seo, Dahee;Ryou, Heejoong;Seo, Jong Hyun;Hwang, Wan Sik
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
    • /
    • v.35 no.3
    • /
    • pp.308-310
    • /
    • 2022
  • Ultrawide bandgap gallium oxide (Ga2O3) semiconductors are known to have excellent photocatalytic properties due to their high redox potential. In this study, CO2 reduction is demonstrated using nanostructured Ga2O3 photocatalyst under ultraviolet (254 nm) light source conditions. After the CO2 reduction, C2H4 remained as a by-product in this work. Nanostructured Ga2O3 photocatalyst also showed an excellent endurance characteristic. Photogenerated electron-hole pairs boosted the CO2 reduction to C2H4 via nanostructured Ga2O3 photocatalyst, which is attributed to the ultrawide and almost direct bandgap characteristics of the gallium oxide semiconductor. The findings in this work could expedite the realization of CO2 reduction and a simultaneous C2H4 production using a low cost and high performance photocatalyst.

An atomistic model for hierarchical nanostructured porous carbons in molecular dynamics simulations

  • Chae, Kisung;Huang, Liping
    • Proceedings of the Korean Vacuum Society Conference
    • /
    • 2016.02a
    • /
    • pp.403.2-403.2
    • /
    • 2016
  • Porous materials play a significant role in energy storage and conversion applications such as catalyst support for polymer electrolyte membrane fuel cell. In particular, hierarchical porous materials with both micropores (poresize, ${\delta}$ < 2 nm) and regularly arranged mesopores (2 nm < ${\delta}$ < 50 nm) are known to greatly enhance the efficiency of catalytic reactions by providing enormous surface area as well as fast mass transport channels for both reactants and products from/to active sites. Although it is generally agreed that the microscopic structure of the porous materials directly affects the performance of these catalytic reactions, neither detailed mechanisms nor fundamental understanding are available at hand. In this study, we propose an atomistic model of hierarchical nanostructured porous carbons (HNPCs) in molecular dynamics simulations. By performing a systematic study, we found that structural features of the HNPC can be independently altered by tuning specific synthesis parameters, while remaining other structures unchanged. In addition, we show some structure-property relations including mechanical and gas transport properties.

  • PDF

The density control of carbon nanotubes using spin-coated nanoparticle and its application to the electron emitter with triode structure

  • Kim, Do-Yoon;Yoo, Ji-Beom;Berdinski, A.S.;Han, In-Taek;Kim, Ha-Jong;Jin, Yong-Wan;Kim, Jong-Min
    • 한국정보디스플레이학회:학술대회논문집
    • /
    • 2005.07b
    • /
    • pp.1016-1019
    • /
    • 2005
  • We studied the density control of carbon nanotubes (CNTs) which were grown on the iron nanoparticles prepared from iron-acetate [$Fe(II)(CH_3COO)_2$] solution using freeze-dry method. The density of CNTs was controlled for the enhancement of field emission. The patterning process of iron-acetate catalyst-layer for the fabrication of electronic device was simply achieved by using alkaline solution, TMAH (tetramethylammonium hydroxide). We applied this patterning process of catalyst layer to formation of the electron emitter with under gate type triode structure.

  • PDF

The density control of carbon nanotubes using spin-coated nanoparticle and its application to the electron emitter with triode structure

  • Kim, Do-Yoon;Yoo, Ji-Beom;Berdinski, A.S.;Han, In-Taek;Kim, Ha-Jong;Jin, Yong-Wan;Kim, Jong-Min
    • 한국정보디스플레이학회:학술대회논문집
    • /
    • 2005.07b
    • /
    • pp.1455-1458
    • /
    • 2005
  • We studied the density control of carbon nanotubes (CNTs) which were grown on the iron nanoparticles prepared from iron-acetate $[Fe(II)(CH_3COO)_2]$ solution using freeze-dry method. The density of CNTs was controlled for the enhancement of field emission. The patterning process of iron-acetate catalyst-layer for the fabrication of electronic device was simply achieved by using alkaline solution, TMAH (tetramethylammonium hydroxide). We applied this patterning process of catalyst layer to formation of the electron emitter with under-gate type triode structure.

  • PDF

CO Gas Sensing Characteristics of Nanostructured ZnO Thin Films (산화아연 나노구조 박막의 일산화탄소 가스 감지 특성)

  • Hung, Nguyen Le;Kim, Hyo-Jin;Kim, Do-Jin
    • Korean Journal of Materials Research
    • /
    • v.20 no.5
    • /
    • pp.235-240
    • /
    • 2010
  • We investigated the carbon monoxide (CO) gas-sensing properties of nanostructured Al-doped zinc oxide thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). The Al-doped ZnO thin film was deposited onto the structure by rf sputtering, resulting in a gas-sensing element comprising a ZnO-based active layer with an embedded Pt/Ti electrode covered by the self-assembled Au nanodots. Prior to the growth of the active ZnO layer, the Au nanodots were formed via annealing a thin Au layer with a thickness of 2 nm at a moderate temperature of $500^{\circ}C$. It was found that the ZnO/Au nanostructured thin film gas sensors showed a high maximum sensitivity to CO gas at $250^{\circ}C$ and a low CO detection limit of 5 ppm in dry air. Furthermore, the ZnO/Au thin film CO gas sensors exhibited fast response and recovery behaviors. The observed excellent CO gas-sensing properties of the nanostructured ZnO/Au thin films can be ascribed to the Au nanodots, acting as both a nucleation layer for the formation of the ZnO nanostructure and a catalyst in the CO surface reaction. These results suggest that the ZnO thin films deposited on self-assembled Au nanodots are promising for practical high-performance CO gas sensors.

Synthesis and Sintering of Nanostructured Mg4Al2Ti9O25 by High-Frequency Induction Heating and Its Mechanical Properties (고주파 유도 가열에 의한 나노구조 Mg4Al2Ti9O25 합성 및 소결과 기계적 성질)

  • Kang, Hyun-Su;Doh, Jung-Mann;Yoon, Jin-Kook;Shon, In-Jin
    • Korean Journal of Materials Research
    • /
    • v.24 no.2
    • /
    • pp.67-72
    • /
    • 2014
  • Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties, including high strength, high hardness, excellent ductility and toughness. In this study, nanopowders of $Al_2O_3$, MgO and $TiO_2$ were prepared as starting materials by high energy ball milling for the simultaneous synthesis and sintering of the nanostructured compound $Mg_4Al_2Ti_9O_{25}$ by high-frequency induction heating process. The highly dense nanostructured $Mg_4Al_2Ti_9O_{25}$ compound was produced within one minute by the simultaneous application of 80MPa pressure and induced current. The sintering behavior, grain size and mechanical properties of the $Mg_4Al_2Ti_9O_{25}$ compound were evaluated.

Synthesis of Nanostructured Ceria Powders for an Oxygen-sensor by Thermochemical Process (열화학적 방법에 의한 산소센서용 세리아 나노분말 합성)

  • Lee Dong-Won;Choi Joon-Hwan;Lim Tae-Soo;Kim Yong-Jin
    • Journal of Powder Materials
    • /
    • v.13 no.3 s.56
    • /
    • pp.192-198
    • /
    • 2006
  • The nanostructured cerium oxide powders were synthesized by spray thermal decomposition process for the use as the raw materials of resistive oxygen sensor. The synthesis routes consisted of 1) spray drying of water based organic solution made from cerium nitrate hydrate ($Ce(NO_3){_3}6H_2O$) and 2) heat treatment of spray dried precursor powders at $400^{\circ}C$ in air atmosphere to remove the volatile components and identically to oxidize the cerium component. The produced powders have shown the loose structure agglomerated with extremely fine cerium oxide particles with about 15 nm and very high specific surface area ($110m^2/g$). The oxygen sensitivity, n ($Log{\propto}Log (P_{O2}/P^o)^{-n}$ and the response time, $t_{90}$ measured at $600^{\circ}C$ in the sample sintered at $1000^{\circ}C$, were about 0.25 and 3 seconds, respectively, which had much higher performances than those known in micron or $100{\sim}200nm$ sized sensors.

Research for Controlled Thermal Conductivity of p-Type Skutterudite Materials (P-type Skutterudite 열전소재의 열전도도 제어 연구)

  • Son, Geon Sik;Choi, Soon Mok
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
    • /
    • v.29 no.11
    • /
    • pp.671-675
    • /
    • 2016
  • Skutterudite materials show PGEC (phonon glass electron crystal) characteristics which is an optimal strategy for designing high performance thermoelectric materials. Now two methods are in parallel to control thermal conductivity of skutterudites, a rattler-atoms doping method and a process for nanostructured bulk materials. Amount of rattler atoms in p-type skutterudite are depends on a Fe/Co ratio of matrix, and the optimal Fe/Co ratio has been reported about from 3:1 to 3.5:0.5 in $R(Fe,Co)_4Sb_{12}$ structure. In this paper, our discussion for rattler doping research was concentrated on double-rattler systems and DD-doped systems in p-type skutterudites. A melt spinning precess combined with high energy ball milling were suggested as a strategy for nanostructured bulk materials with PGEC (phonon glass electron crystal) characteristics in p-type skutterudites.