• Title, Summary, Keyword: Nano-crystalline

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Advances in liquid crystalline nano-carbon materials: preparation of nano-carbon based lyotropic liquid crystal and their fabrication of nano-carbon fibers with liquid crystalline spinning

  • Choi, Yong-Mun;Jung, Jin;Hwang, Jun Yeon;Kim, Seung Min;Jeong, Hyeonsu;Ku, Bon-Cheol;Goh, Munju
    • Carbon letters
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    • v.16 no.4
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    • pp.223-232
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    • 2015
  • This review presents current progress in the preparation methods of liquid crystalline nano-carbon materials and the liquid crystalline spinning method for producing nano-carbon fibers. In particular, we focus on the fabrication of liquid crystalline carbon nanotubes by spinning from superacids, and the continuous production of macroscopic fiber from liquid crystalline graphene oxide.

Catalytic combustion type hydrogen micro gas sensor using thin film heater and nano crystalline SnO2 (나노 결정 SnO2와 백금 박막히터를 이용한 접촉연소식 마이크로 가스센서의 감응특성 연구)

  • Han, Sang-Do;Hong, Dae-Ung;Han, Chi-Hwan;Chun, Il-Soo
    • Journal of Sensor Science and Technology
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    • v.17 no.3
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    • pp.178-182
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    • 2008
  • Planar type micro catalytic combustible gas sensor was developed by using nano crystalline $SnO_2$ Pt thin film as micro heater was deposited by thermal evaporation method on the alumina substrate. The thickness of the Pt heater was around 160 nm. The sensor showed high reliability with prominent selectivity against various gases(Co, $C_3H_8,\;CH_4$) at low operating temperature($156^{\circ}C$). The sensor with nano crystalline $SnO_2$ showed higher sensitivity than that without nano crystalline $SnO_2$. This can be explained by more active adsorption and oxidation of hydrogen by nano crystalline $SnO_2$ particles. The present planar-type catalytic combustible hydrogen sensor with nano crystalline $SnO_2$ is a good candidate for detection of hydrogen leaks.

Synthesis and Optoelectronic Characteristics of Single-crystalline Si Nanowires

  • Kim, Kyung-Hwan;Keem, Ki-Hyun;Kang, Jeong-Min;Yoon, Chang-Joon;Jeong, Dong-Young;Min, Byung-Don;Cho, Kyoung-Ah;Kim, Hyun-Suk;Kim, Sang-Sig
    • Transactions on Electrical and Electronic Materials
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    • v.6 no.5
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    • pp.198-201
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    • 2005
  • Photocurrent of a single-crystalline Si nanowire is investigated in this paper. Single-crystalline Si nanowires with amorphous $SiO_2$ shells were first synthesized from ball-milled SiO powders by thermal chemical vapor deposition, and then the amorphous $SiO_2$ shells were etched out from the as-synthesized Si nanowires. For a single-crystalline Si nanowire, photocurrent-voltage curves taken in air at room temperature were non-linear, and rapid photoresponses were observed when the light was switched on and off. The photocurrent was not changed in intensity under the illumination. Photocurrent mechanism in the single-crystalline Si nanowire is discussed in this paper.

Use of Wet Chemical Method to Prepare β Tri-Calcium Phosphates having Macro- and Nano-crystallites for Artificial Bone

  • Chang, Myung Chul
    • Journal of the Korean Ceramic Society
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    • v.53 no.6
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    • pp.670-675
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    • 2016
  • Calcium phosphate crystallites were prepared by wet chemical method for use in artificial bone. In order to obtain ${\beta}$-tricalcium phosphate (TCP), nano-crystalline calcium phosphate (CaP) was precipitated at $37^{\circ}C$ and at $pH5.0{\pm}0.1$ under stirring using highly active $Ca(OH)_2$ in DI water and an aqueous solution of $H_3PO_4$. The precipitated nano-crystalline CaP solution was kept at $90^{\circ}C$ for the growth of CaP crystallites. Through the growing process of CaP crystallites, we were able to obtain various sizes of rectangular CaP crystallites according to the crystal growing times. Dry nano-crystalline CaP powders at $37^{\circ}C$ were mixed with dry macro-crystalline CaP crystallites and the shaped mixture sample was fired at $1150^{\circ}C$ to make a ${\beta}-TCP$ block. Several tens of nm powders were uniformly coated on the surface, which was comprised of powders of several tens of ${\mu}m$, using a vibrator. The mixing ratio between the nanometer powders and the micrometer powders greatly affected the mechanical strength of the mixture block; the most appropriate ratio of these two materials was 50 wt% to 50 wt%. The sintered block showed improved mechanical strength, which was caused by the solid state interaction between the nano-crystalline ${\beta}-TCP$ and the macro-crystalline ${\beta}-TCP$.

Synthesis of Amorphous Matrix Nano-composite in Al-Cu-Mg Alloy

  • Kim, Kang Cheol;Park, Sung Hyun;Na, Min Young;Kim, Won Tae;Kim, Do Hyang
    • Applied Microscopy
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    • v.44 no.3
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    • pp.105-109
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    • 2014
  • The microstructure of as-quenched $Al_{70}Cu_{18}Mg_{12}$ alloy has been investigated in detail using transmission electron microscopy. Al nano-crystals about 5 nm with a high density are distributed in the amorphous matrix, indicating amorphous matrix nano-composite can be synthesized in Al-Cu-Mg alloy. The high density of Al nano-crystals indicates very high nucleation rate and sluggish growth rate during crystallization possibly due to limited diffusion rate of solute atoms of Cu and Mg during solute partitioning. The result of hardness measurement shows that the mechanical properties can be improved by designing a nano-composite structure where nanometer scale crystals are embedded in the amorphous matrix.

Neutral Beam assisted Chemical Vapor Deposition at Low Temperature for n-type Doped nano-crystalline silicon Thin Film

  • Jang, Jin-Nyeong;Lee, Dong-Hyeok;So, Hyeon-Uk;Yu, Seok-Jae;Lee, Bong-Ju;Hong, Mun-Pyo
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.52-52
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    • 2011
  • A novel deposition process for n-type nanocrystalline silicon (n-type nc-Si) thin films at room temperature has been developed by adopting the neutral beam assisted chemical vapor deposition (NBa-CVD). During formation of n-type nc-Si thin film by the NBa-CVD process with silicon reflector electrode at room temperature, the energetic particles could induce enhance doping efficiency and crystalline phase in polymorphous-Si thin films without additional heating on substrate; The dark conductivity and substrate temperature of P-doped polymorphous~nano crystalline silicon thin films increased with increasing the reflector bias. The NB energy heating substrate(but lower than $80^{\circ}C$ and increase doping efficiency. This low temperature processed doped nano-crystalline can address key problem in applications from flexible display backplane thin film transistor to flexible solar cell.

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Morphology Control of Single Crystalline Rutile TiO2 Nanowires

  • Park, Yi-Seul;Lee, Jin-Seok
    • Bulletin of the Korean Chemical Society
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    • v.32 no.10
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    • pp.3571-3574
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    • 2011
  • Nano-scaled metal oxides have been attractive materials for sensors, photocatalysis, and dye-sensitization for solar cells. We report the controlled synthesis and characterization of single crystalline $TiO_2$ nanowires via a catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) growth mechanism during TiO powder evaporation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that as grown $TiO_2$ materials are one-dimensional (1D) nano-structures with a single crystalline rutile phase. Also, energy-dispersive X-ray (EDX) spectroscopy indicates the presence of both Ti and O with a Ti/O atomic ratio of 1 to 2. Various morphologies of single crystalline $TiO_2$ nano-structures are realized by controlling the growth temperature and flow rate of carrier gas. Large amount of reactant evaporated at high temperature and high flow rate is crucial to the morphology change of $TiO_2$ nanowire.

Pulsed Electric Current Sintering of Nano-crystalline Iron-base Powders

  • Li, Yuanyuan;Long, Yan;Li, Xiaoqiang;Liu, Yunzhong
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.272-273
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    • 2006
  • A new process of pulsed electric current sintering was developed. It combines compaction with activated sintering effectively and can manufacture bulky nano-crystalline materials very quickly. A nano-structured steel is obtained with high relative density and hardness by this process. The average grain size of iron matrix is 58nm and the carbide particulate size is less than 100 nm. The densification temperature of ball-milled powders is approximately $200^{\circ}C$ lower than that of blended powders. When the sintering temperature increases, the density of as-sintered specimen increases but the hardness of as-sintered specimen first increases and then decreases.

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Rietveld Analysis of Nano-crystalline MnFe2O4 with Electron Powder Diffraction

  • Kim, Jin-Gyu;Seo, Jung-Wook;Cheon, Jin-Woo;Kim, Youn-Joong
    • Bulletin of the Korean Chemical Society
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    • v.30 no.1
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    • pp.183-187
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    • 2009
  • The structure of nano-crystalline $MnFe_2O_4$ was determined and refined with electron powder diffraction data employing the Rietveld refinement technique. A nano-crystalline sample (with average crystal size of about 10.9 nm) was characterized by selected area electron diffraction in an energy-filtering transmission electron microscope operated at 120 kV. All reflection intensities were extracted from a digitized image plate using the program ELD and then used in the course of structure refinements employing the program FULLPROF for the Rietveld analysis. The final structure was refined in space group Fd-3m (# 227) with lattice parameters a=8.3413(7) $\AA$. The reliability factors of the refinement are $R_F$=7.98% and $R_B$=3.55%. Comparison of crystallographic data between electron powder diffraction data and reference data resulted in better agreement with ICSD-56121 rather than with ICSD-28517 which assumes an initial structure model.