• 한국재료학회지
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• 제22권2호
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• pp.78-81
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• 2012

$Y_2O_3$ nanomaterials have been widely used in transparent ceramics and luminescent devices. Recently, many studies have focused on controlling the size and morphology of $Y_2O_3$ in order to obtain better material performance. $Y_2O_3$ powders were prepared under a modified solvothermal condition involving precipitation from metal nitrates with aqueous ammonium hydroxide. The powders were obtained at temperatures at $250^{\circ}C$ after a 6h process. The properties of the $Y_2O_3$ powders were studied as a function of the solvent ratio. The synthesis of $Y_2O_3$ crystalline particles is possible under a modified solvothermal condition in a water/ethylene glycol solution. Solvothermal processing condition parameters including the pH, reaction temperature and solvent ratio, have significant effects on the formation, phase component, morphology and particle size of yttria powders. Ethylene glycol is a versatile, widely used, inexpensive, and safe capping organic molecule for uniform nanoparticles besides as a solvent. The characterization of the synthesized Y2O3 powders were studied by XRD, SEM (FE-SEM) and TG/DSC. An X-ray diffraction analysis of the synthesized powders indicated the formation of the $Y_2O_3$ cubic structure upon calcination. The average crystalline sizes and distribution of the synthesized $Y_2O_3$ powders was less than 2 um and broad, respectively. The synthesized particles were spherical and hexagonal in shape. The morphology of the synthesized powders changed with the water and ethylene glycol ratio. The average size and shape of the synthesized particles could be controlled by adjusting the solvent ratio.

• Advances in Energy Research
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• 제5권1호
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• pp.13-29
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• 2017

The roles of Na, Mn, W and silica, and the synergistic effects between each metal in the $MnNa_2WO_4/SiO_2$ catalyst have been investigated for oxidative coupling of methane (OCM). The crystallisation of amorphous silica during calcination at $900^{\circ}C$ was promoted primarily by Na, but Mn and W also facilitated this process. The interaction between Na and Mn tended to increase the extent of conversion of $Mn_3O_4$ to $Mn_2O_3$. The formation of $Na_2WO_4$ was dependent on the order in which Na and W were introduced to the catalyst. The impregnation of W before Na resulted in the formation of $Na_2WO_4$, but this did not occur when the impregnation order was reversed. $MnWO_4$ formed in all cases where Mn and W were introduced into the silica support, regardless of the impregnation order; however, the formation of $MnWO_4$ was inhibited in the presence of Na. Of the prepared samples in which a single metal oxide was introduced to silica, only $Mn/SiO_2$ showed OCM activity with significant oxygen conversion, thus demonstrating the important role that Mn plays in promoting oxygen transfer in the reaction. The impregnation order of W and Na is critical for catalyst performance. The active site, which involves a combination of Na-Si-W-O, can be formed in situ when distorted $WO_4^{2-}$ interacts with silica during the crystallisation process facilitated by Na. This can only occur if the impregnation of W occurs before Na addition, or if the two components are introduced simultaneously.

• 분석과학
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• 제10권3호
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• pp.203-208
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• 1997

출발물질로 $BaCl_2$와 $TiCl_4$를 사용하고 침전제로 dimethyl oxalate(DMO)를 사용하여 균일침전법에 의해 barium titanyl oxalate(BTO)를 제조하였다. 반응조건을 변화시켜 가면서 실험을 수행한 결과 반응 온도가 높을수록, [DMO]/[$Ba^{2+}+Ti^{4+}$]의 비율이 증가할수록 핵 형성시간이 단축되었으며 BTO 입자가 unimodal에서 bimodal을 거쳐 넓은 범위의 unimodal로 전환하는 속도가 빨랐다. 균일침전법으로 얻은 BTO를 $900^{\circ}C$에서 하소하여 얻은 barium titanate(BT)의 입자 크기는 통상의 공침법으로 합성한 BT 입자보다 큰 형태를 나타냈으며, 결정상은 tetragonal이었다. 또한 교반이 BTO 및 BT 분말의 특성에 큰 영향을 줌을 발견하였다.

• 공업화학
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• 제10권7호
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• pp.1020-1027
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• 1999

헤테로폴리산(HPW)을 표면적이 서로 다른 담체인 $SiO_2$ MCM-41, MCM-48에 담지농도와 소성온도를 달리하며 담지시켰다. X-선 회절분석, 질소 흡착법, 적외선 흡수 스펙트럼, $^{31}P$ 고체 핵자기 공명을 통해서 이 담지촉매의 특성을 조사하였다. IR과 NMR의 결과로부터 HPW가 담체안에서 케긴 구조를 유지하면서 존재함을 확인할 수 있었다. MCM-41의 경우에는 35 wt %, MCM-48의 경우에는 65 wt %로 담지시킨 경우에도 X-선 회절패턴에서 HPW 고유의 피크가 나타나지 않았으며, 이와 같은 특성을 통해서 HPW가 고분산 되어 있음을 알 수 있었다. Di, bis, tri-pentaerythritol의 가수분해 반응에서 이들 담지 촉매는 높은 촉매 활성을 보였으며 HPW, $HPW/SiO_2$보다 HPW/MCM-41, 48의 촉매 활성이 더 우수하였다.

• 한국수소및신에너지학회논문집
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• 제21권6호
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• pp.500-506
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• 2010

The metal monolith catalyst coated with 15wt% Ni/$MgAl_2O_4$ is applied to the natural gas steam reforming for hydrogen production. To address the improvement of adherence between metal monolith and catalyst coating layer, the pre-calcination temperature as well as the coating conditions of $Al_2O_3$ sol are optimized. When the Fe-Cr alloy monolith is pre-calcined at $900^{\circ}C$ for 6 h, $Al_2O_3$ layer was formed uniformly on the entire surface of the metal substrate. It is seen that the formation of $Al_2O_3$ layer on the monolith surface is essential for the uniform coating of $Al_2O_3$ sol onto the monolith substrate. The monolith catalyst coated with 10wt% $Al_2O_3$ sol shows high $CH_4$ conversion and good thermal stability as compared with the monolith catalyst without $Al_2O_3$ sol coating under severe reaction conditions with high GHSV of 30,000 $h^{-1}$ at $700^{\circ}C$. In addition, the metal monolith catalyst shows higher catalytic activity and better thermal conductivity than 15wt% Ni/$MgAl_2O_4$ pellet catalyst.

• 한국토양비료학회지
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• 제41권6호
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• pp.369-373
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• 2008

Mg-Al LDH를 이용하여 수용액중 비소와의 반응특성을 규명하고 비소 제거제로서 활용가능성을 규명하기 위하여 비소의 흡착특성, 제거효율 및 제거기작에 대한 조사를 하였다. Mg-Al LDH는 소성(calcination)에 의한 탈수로 Mg oxide 형태를 나타내었고 비소를 흡착시킨 결과 반응 22시간 이후에 흡착평형에 도달하였으며 흡착량은 약 530 mmol/kg정도였다. 반응농도별 LDH의 등온흡착은 L-type의 흡착반응을 나타내었다. 소성된 Mg-Al LDH는 용액중에서 재수화(rehydration) 될 때 비소가 LDH의 구조의 복구과정(reconstruction)에서 이온교환 반응에 의해 층간삽입이 일어나는 것으로 나타났다. LDH에 대한 arsenate와 phosphate, arsenate와 sulfate의 경쟁흡착 결과 arsenate와 phosphate의 선택성은 비슷한 편이었고, arsenate는 sulfate에 비해 선택성이 우수하였다. 따라서 calcined Mg-Al LDH는 비교적 높은 비소 제거효율을 나타내므로 비소 제거제로서 사용 가능성이 매우 높은 것으로 판단된다.

• 센서학회지
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• 제27권5호
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• pp.345-351
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• 2018

We employed an unprecedented technique to synthesize porous $WO_3@SnO_2$ nanofibers exhibiting core-shell and fiber-in-tube configurations. Firstly, 2-methylimidazole was uniformly incorporated in as-spun nanofibers containing ammonium metatungstate hydrate and the sacrificial polymer (polyacrylonitrile). Secondly, the 2-methylimidazole on the surfaces of nanofibers was complexed with tin(II) chloride ($SnCl_2$) via simple impregnation of the as-spun nanofibers in ethanol containing tin(II) chloride dihydrate ($SnCl_2{\cdot}2H_2O$). The presence of vacant p-orbitals in tin (Sn) and the nucleophilic nitrogen on the imidazole ring allowed for the reaction between $SnCl_2$ and 2-methylimidazole, forming adducts on the surfaces of the as-spun nanofibers. The calcination of these nanofibers resulted in porous $WO_3@SnO_2$ nanofibers with a higher surface area ($55.3m^2{\cdot}g^{-1}$) and a better response to 1-5 ppm of acetone than pristine $SnO_2$ NFs synthesized using a similar method. An improved response to acetone was achieved upon functionalization of the $WO_3@SnO_2$ nanofibers with catalytic palladium nanoparticles. This work demonstrates the potential application of $WO_3@SnO_2$ nanofibers as sensing layers for chemiresistive sensory devices for the detection of acetone in exhaled breath.

• 한국분말재료학회지
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• 제23권1호
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• pp.38-42
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• 2016

$BaTiO_3$-coated Fe nanofibers are synthesized via a three-step process. ${\alpha}-Fe_2O_3$ nanofibers with an average diameter of approximately 200 nm are first prepared using an electrospinning process followed by a calcination step. The $BaTiO_3$ coating layer on the nanofiber is formed by a sol-gel process, and a thermal reduction process is then applied to the core-shell nanofiber to selectively reduce the ${\alpha}-Fe_2O_3$ to Fe. The thickness of the $BaTiO_3$ shell is controlled by varying the reaction time. To evaluate the electromagnetic (EM) wave-absorbing abilities of the $BaTiO_3@Fe$ nanofiber, epoxy-based composites containing the nanofibers are fabricated. The composites show excellent EM wave absorption properties where the power loss increases to the high frequency region without any degradation. Our results demonstrate that the $BaTiO_3@Fe$ nanofibers obtained in this work are attractive candidates for electromagnetic wave absorption applications.

• 자원리싸이클링
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• 제24권5호
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• pp.3-14
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• 2015

청정석탄발전기술 중 하나인 순환유동층보일러(CFBC) 기술의 고도화에 따라 국내외 로내탈황 기술개발 현황과 국내외 유동층보일러용 석회석의 탈황특성 연구현황을 조사하였다. 석회석계 탈황제는 고온탈황특성이 우수한 원소 중 하나로 $850-950^{\circ}C$ 내외에서 최적의 탈황특성을 가지고 있다. 그리고, 탈황시험방법에 따라 흡수제 표면의 격막의 확산반응, 입자의 크기, 기공의 수량, 크기 및 구조에 의한 탈황공정의 효율성을 결정할 수 있다. 2015년 이후 대형 순환유동층형발전소의 본격적인 가동에 따라 석회석의 광상학적, 결정학적 특성 및 소성특성과 연계된 추가적인 연구가 필요한 것으로 사료된다.

• 한국재료학회지
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• 제26권10호
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• pp.561-569
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• 2016

$SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ phosphorescent phosphors were synthesized using the polymerized complex method. Generally, phosphorescent phosphors synthesized by conventional solid state reaction show a micro-sized particle diameter; thus, this process is restricted to applications such as phosphorescent ink and paint. However, it is possible to synthesize homogeneous multi-component powders with fine particle diameter by wet process such as the polymerized complex method. The characteristics of $SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ powders prepared by polymerized complex method with one and two step calcination processes were comparatively analyzed. Temperatures of organic material removal and crystallization were observed through TG-DTA analysis. The crystalline phase and crystallite size of the $SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ phosphorescent phosphors were analyzed by XRD. Microstructures and afterglow characteristics of the $SrAl_2O_4$: $Eu^{2+}$ and $Dy^{3+}$ phosphors were measured by SEM and spectrofluorometry, respectively.