• Title, Summary, Keyword: Carbothermal reduction

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Synthesis and characterization of AlN nanopowder by the microwave assisted carbothermal reduction and nitridation (CRN)

  • Chun, Seung-Yeop;Chun, Myoung-Pyo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.27 no.5
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    • pp.223-228
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    • 2017
  • Aluminum nitride (AlN) powder was successfully synthesized at low temperature via carbothermal reduction and nitridation (CRN) assisted by microwave heating. The synthesis processes of AlN powder were investigated with X-ray diffraction, FE-SEM, FT-IR and TGA/DSC. Aluminum nitrate was used as an oxidizer and aluminum source, urea as fuel, and glucose as carbon source. These starting materials were mixed with D.I water and reacted in a flask at $100^{\circ}C$ for 20 minutes. After the reaction was finished, black foamy intermediate product was formed, which was considered to be an amorphous $Al_2O_3$ particles through intermediate product obtained by solution combustion synthesis (SCS) at the results of X-ray diffraction patterns and FT-IR. This intermediate product was nitridated at temperatures of $1300^{\circ}C$ and $1400^{\circ}C$ in $N_2$ atmosphere by a microwave heating furnace and then decarbonated at $600^{\circ}C$ for 2 hours in air. It should be noticed from FE-SEM images that as nitridated particles, identified as AlN from X-ray diffraction patterns, are covered with carbon residues. After decarbonating the nitridated powders, the spherical pure AlN powders were obtained without alumina and their particle sizes were dependent on the nitridating temperature with high temperature of $1400^{\circ}C$ giving large particles of around 70~100 nm.

Crystallographic Etching in Double-Layer Graphene on $SiO_2$ Substrates

  • Park, Min-Gyu;Ryu, Sun-Min
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.209-209
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    • 2013
  • 그래핀(graphene)의 가장자리(edge)는 결정구조의 배향성에 따라 지그재그(zigzag)와 안락의자(armchair) 형태로 구분되는데, 나노미터 크기의 그래핀의 전자적 성질은 이러한 가장자리의 배향성에 의해 크게 영향을 받는다고 알려져 있다. 단일층 그래핀 가장자리 사이에서 일어나는 산화실리콘($SiO_2$)의 carbothermal reduction은 선택적으로 지그재그 형태의 가장자리를 생성한다고 알려져 있다. 본 연구에서는 라만 분광법과 원자 현미경(atomic force microscopy)을 이용하여 기계적 박리법으로 만들어진 이중층 그래핀에서 일어나는 carbothermal reaction을 연구하였다. 고온 산화 방법으로 이중층 그래핀에 원형 식각공(etch pit)을 만들고 Ar 기체 속에서 700도 열처리를 진행한 후, 원형 식각공이 육각형으로 확장된 것을 관찰하였다. 이것은 이중층 그래핀도 산화실리콘의 carbothermal reduction을 유발한다는 사실을 보여준다. 그러나 이중층 그래핀의 반응속도는 단일층보다 5배 정도 느린 것이 확인되었는데, 이는 이중층 그래핀의 탄소원자와 산화제로 작용하는 산화실리콘 간의 평균 거리가 단일층보다 더 크다는 사실로 설명할 수 있다. 또한 단일층과 이중층 그래핀 모두 1 기압 Ar 분위기에서보다 진공상태에서 반응속도가 현저히 작다는 사실이 관찰되었다. 진공도와 온도에 따른 반응속도로부터 반응 메커니즘 및 활성화 에너지에 대해 고찰하고자 한다.

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Facile Synthesis of Highly Dispersed Ultra-fine ZrC Powders by Carbothermal Reduction Method Using Nanosized ZrO2 and Nanosized Graphite Powder Mixtures (나노크기의 ZrO2와 Graphite 분말 혼합체의 열탄소환원법에 의한 고분산 초미립 ZrC 분말의 합성)

  • Lee, Wha-Jun;Ryu, Sung-Soo
    • Journal of Korean Powder Metallurgy Institute
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    • v.20 no.2
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    • pp.100-106
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    • 2013
  • Ultra-fine zirconium carbide (ZrC) powder with nano-sized primary particles was synthesized by the carbothermal reduction method by using nano-sized $ZrO_2$ and nano-sized graphite powders mixture. The synthesized ZrC powder was well dispersed after simple milling process. After heat-treatment at $1500^{\circ}C$ for 2 h under vacuum, ultra-fine ZrC powder agglomerates (average size, $4.2{\mu}m$) were facilely obtained with rounded particle shape and particle size of ~200 nm. Ultra-fine ZrC powder with an average particle size of 316 nm was obtained after ball milling process in a planetary mill for 30 minutes from the agglomerated ZrC powder.

Characteristics of Silicon Carbide Nanowires Synthesized on Porous Body by Carbothermal Reduction

  • Kim, Jung-Hun;Choi, Sung-Churl
    • Journal of the Korean Ceramic Society
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    • v.55 no.3
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    • pp.285-289
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    • 2018
  • We synthesized silicon carbide (${\beta}-SiC$) nanowires with nano-scale diameter (30 - 400 nm) and micro-scale length ($50-200{\mu}m$) on a porous body using low-grade silica and carbon black powder by carbothermal reduction at $1300-1600^{\circ}C$. The SiC nanowires were formed by vapor-liquid-solid deposition with self-evaporated Fe catalysts in low-grade silica. We investigated the characteristics of the SiC nanowires, which were grown on a porous body with Ar flowing in a vacuum furnace. Their structural, optical, and electrical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). We obtained high-quality SiC single crystalline nanowire without stacking faults that may have uses in industrial applications.

Synthesis of $\beta$-Sialon Powder from Fly Ash (Fly Ash를 이용한$\beta$-Sialon 분말합성)

  • 최희숙;노재승;서동수
    • Journal of the Korean Ceramic Society
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    • v.33 no.8
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    • pp.871-876
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    • 1996
  • It is believed that fly ash could be suitable for preparing the sialon by carbothermal reduction method because the total amount of SiO2 and Al2O3 is above 80% and the unburned residual carbon is above 5% within the fly ash. The effects of reaction temperature (1350, 1400, 145$0^{\circ}C$) reaction time (1, 5, 10 hours) and the amount of carbon additions (C/SiO2=2, 3, 4 mole) on the $\beta$-sialon synthesis were obserbed, It was conformed that $\beta$-sialon (Z=2.15~2.18) was formed as major phase under all of the synthesis conditions and small amount of Si2ON2 SiC, AlN and Si3N4 was formed depending on the synthesis conditions. FeSix intermetal-lic compound was formed above 140$0^{\circ}C$ reaction temperature due to the large amount of iron oxides within the raw fly ash.

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Silicon Carbide Coating on Graphite and Isotropic C/C Composite by Chemical Vapour Reaction

  • Manocha, L.M.;Patel, Bharat;Manocha, S.
    • Carbon letters
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    • v.8 no.2
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    • pp.91-94
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    • 2007
  • The application of Carbon and graphite based materials in unprotected environment is limited to a temperature of $450^{\circ}C$ or so because of their susceptibility to oxidation at this temperature and higher. To over come these obstacles a low cost chemical vapour reaction process (CVR) was developed to give crystalline and high purity SiC coating on graphite and isotropic C/C composite. CVR is most effective carbothermal reduction method for conversation of a few micron of carbon layer to SiC. In the CVR method, a sic conversation layer is formed by reaction between carbon and gaseous reagent silicon monoxide at high temperature. Characterization of SiC coating was carried out using SEM. The other properties studied were hardness density and conversion efficiency.