• Title/Summary/Keyword: urea precursor

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A Study on the Fabrication of Hollow Glass Sphere by Using a Liquid-mix Precursor (혼합액상 전구체를 이용한 유리 중공구체의 제조에 관한 연구)

  • Lee, Yong Bin;Kim, Ki Do;Kim, Hee Taik
    • Applied Chemistry for Engineering
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    • v.10 no.8
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    • pp.1186-1191
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    • 1999
  • By using a liquid-mix precursor, we prepared the hollow glass spheres(HGS) as an additive of polymer compound which are used in the field of modifier, promoter, filler, and reinforcement. Liquid-mix precursor is a mixture of 40% sodium silicate aqueous solution, boric acid as a insolubilizing agent, and urea as a blowing agent. To obtain the precursor particles which are fed into a gas flame furnae, the above liquid-mix precursor was dried in oven and crushed with ball mill. We assumed the size of precursor particles ($53{\sim}63{\mu}m$, $63{\sim}180{\mu}m$), temperature of furnace($800{\sim}1200^{\circ}C$), and amount of urea(0~30 g) as the parameters affecting on the properties of HGS. As a result mean particle size of HGS increases with increasing the temperature of furnace and the amount of urea and with decreasing the size of precursor particles. Also, we found that incresing the amount of urea is related to a decrease of the crush strength of HGS.

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Synthesis of Sinter-active $Y_2O_3$ Powders Using Urea (요소를 이용한 활성 이트리아 분말의 합성)

  • 한주환
    • Journal of the Korean Ceramic Society
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    • v.34 no.12
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    • pp.1247-1253
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    • 1997
  • Sinter-active yttria powders were prepared by a solution precipitation with using a self-decomposing precipitation agent NH2CONH2(urea). The cold-pressed powders can be sintered to full density and the microstructure of grains less than 200 nm at a temperature as low as 120$0^{\circ}C$. The activity of the yttria powder has been controlled by varying nucleation conditions during precipitation and by minimizing formation of aggregates. The type of precursor is decisive in preparation of a sinter-active oxide powder, and urea is desirable as a precipitation agent for an active yttrium oxide powder.

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Study on urea precursor effect on the electroactivities of nitrogen-doped graphene nanosheets electrodes for lithium cells

  • Kim, Ki-Yong;Jung, Yongju;Kim, Seok
    • Carbon letters
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    • v.19
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    • pp.40-46
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    • 2016
  • Nitrogen-atom doped graphene oxide was considered to prevent the dissolution of polysulfide and to guarantee the enhanced redox reaction of sulfur for good cycle performance of lithium sulfur cells. In this study, we used urea as a nitrogen source due to its low cost and easy preparation. To find the optimum urea content, we tested three different ratios of urea to graphene oxide. The morphology of the composites was examined by field emission scanning electron microscope. Functional groups and bonding characterization were measured by X-ray photoelectron spectroscopy. Electrochemical properties were characterized by cyclic voltammetry in an organic electrolyte solution. Compared with thermally reduced graphene/sulfur (S) composite, nitrogen-doped graphene/S composites showed higher electroactivity and more stable capacity retention.

Fermentation and Purification of LacZ-Fused Single Chain Insulin Precursor for($B^{30}$-Homoserine) Human Insulin

  • SeungYup Lee;Jeo
    • Biotechnology and Bioprocess Engineering:BBE
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    • v.1 no.1
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    • pp.9-12
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    • 1996
  • In order to produce the single chain precursor of a novel human insulin analogue, (B30-Homoserine) insulin, the fermentative behaviors of Escherichia coli JM103 were studied, which harbors pKBA plasmid carrying a hybrid gene in which the gene for a single chain precursor was fused with lacZ gene under tac promoter. The maximal induction of gene expression was achieved when more than 0.05 mM of isopropyl-$\beta$-D-thiogalactopyranoside(IPTG) was supplemented to fermentation medium after 4 h cultivation of E. coli, and followed by longer than 2-h fermentation. The hybrid protein of the single chain insulin precursor was isolated from cytoplasmic inclusion bodies by dissolving in 8M urea solution, and purified through DEAE-Sephacel and Sephadex G-200 column chromatographies with a recovery of 35%. The finally purified hybrid protein showed a single band on sodium dodecyl sulfate-polyacrylamide gel.

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Fabrication and Characterization of Cf/SiC Composite with BN Interphase Coated by Wet Chemical Process (습식법으로 제조된 BN 중간층을 가진 Cf/SiC 복합재의 제조 및 물성 평가)

  • Koo, Jun-mo;Kim, Kyung Ho;Han, Yoonsoo
    • Journal of the Korean institute of surface engineering
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    • v.50 no.6
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    • pp.523-530
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    • 2017
  • In this study, we developed the h-BN interphase for ceramic matrix composites (CMCs) through a wet chemical coating method, which has excellent price competitiveness and is a simple process as a departure from the existing high cost chemical vapor deposition method. The optimum condition for nitriding an h-BN interphase using boric acid and urea as precursors were derived, and the h-BN interphase coating through a wet method on a carbon preform of 2.5 D was conducted to apply the optimum conditions to the CMCs. In order to control the coating property via the wet coating method, four parameters were investigated such as dipping time of the specimen in the precursor solution, the ratio of boric acid and urea in the precursor, the concentration of solution where the precursor was dissolved, and the cycle of dipping and dry process. The CMCs was fabricated through polymer impregnation and pyrolysis (PIP) processes and a three-point flexural strength test was conducted to verify the role of the coated h-BN interphase.

Study of the Feature of Antimony doped Tin Oxide Using Urea (우레아를 이용한 ATO(Antimony doped Tin Oxide)의 특성 연구)

  • Kim, Jin-Chul;Ahn, Yong-Kwan;Choi, Byung-Hyun;Lee, Mi-Jae;Back, Jong-Hoo;Sim, Kaung-Bo
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.361-362
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    • 2005
  • Antimony doped tin oxide(ATO) nano powders have been synthesized by homogeneous precipitation method using $SnCl_4\cdot5H_2O$ for precursor, $SbCl_3$ as doped material and urea. The hydrolysis of urea and conductive mechanism and Heat treatment was performed at the temperature from $500^{\circ}C$ to $700^{\circ}C$ in air. The ATO nano powders are characterized by means of Thermogravimetry differential thermal analyzer (TG-DTA), X-ray diffraction (XRD), Brunauer, Emmett, and Teller adsorption (BET), Scanning electron microscopy (SEM) ATO nano powders with an average size of nm and the highest surface area 129 $m^2g^{-1}$ are obtained.

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Influence of Urea Precursor on the Electrochemical Properties of Ni-Co-based Metal Organic Framework Electrodes for Supercapacitors

  • Jung, Ye Seul;Jung, Yongju;Kim, Seok
    • Applied Chemistry for Engineering
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    • v.33 no.5
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    • pp.523-531
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    • 2022
  • A NiCo-metal organic framework (MOF) electrode, prepared using urea as a surfactant, was synthesized using a one-pot hydrothermal method. The addition of urea to the NiCo-MOF creates interstitial voids and an ultra-thin nanostructure in the NiCo-MOF, which improves its charge transfer performance. We obtained the optimal metal to surfactant ratio to achieve the best specific capacitance. The NiCo-MOF was employed as the working electrode material in a three-electrode system. Field emission scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy were employed to characterize the microstructures and morphologies of the composites. Cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy curves were employed to quantify the electrochemical properties of the electrodes in a 6 M KOH electrolyte.

Synthesis and Characterization of Fiberous AlN by Electrospinning (전기방사에 의한 섬유상 질화알루미늄 합성 및 특성 평가)

  • Chun, Seung-Yeop;Hwang, Jin-Ah;Chu, Jae-Uk;Chun, Myoung-Pyo
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.30 no.7
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    • pp.441-446
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    • 2017
  • Aluminum nitride fibers were synthesized by carbothermal reduction and nitridation of precursor fibers obtained by electrospinning. The starting materials used to synthesize the AlN fibers were $Al(NO_3)_3{\cdot}9H_2O$ and urea. Polyvinylpyrrolidone with increasing viscidity was used as the carbon source to obtain a composite solution. The mixed solution was drawn into a plastic syringe with a stainless steel needle, which was used as the spinneret and connected to a 20 kV power supply. A high voltage was supplied to the solution to facilitate the formation of a dense net of fibers on the collector. The precursor fibers were dried at $100^{\circ}C$ and then heated to $1,400^{\circ}C$ for 1 h in a microwave furnace under $N_2$ gas flow for the carbothermal reduction and nitridation. X-ray diffraction studies indicated that the synthesized fibers consisted of the AlN phase. Field emission scanning electron microscopy studies indicated that the diameter of the calcined fibers was approximately 100 nm.

Synthesis of Yttrium Iron Garnet Powder by Homogeneous Precipitation and its Crystallization (균일침전법에 의한 Yttrium Iron Garnet 분말의 합성 및 결정화)

  • 안영수;한문희;김종오
    • Journal of the Korean Ceramic Society
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    • v.33 no.6
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    • pp.693-699
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    • 1996
  • YIG precursor powder was obtained by homogeneous precipitation in chloride salt solution by thermal decom-position of urea. It was found that ferric ions precipitated prior to yttrium ions. The precipitate was minute and spherical in shape. The precipitate formed consisted of the mixture of amorphous and ferric oxyhydroxide. Crystallization of YIG was proceeded by solid state reaction of intermediate YFeO3 and Fe2O3 in the temperature range of 85$0^{\circ}C$ to 140$0^{\circ}C$. Single phase of YIG was obtained by heat-treatment of the powder at 140$0^{\circ}C$ for 6 hrs in air. The powder calcined was molded into pellets and sintered in air. The maximum density of 4,92 g/cm3(95.1% of theoretical density) was obtainable for the pellet sintered at 145$0^{\circ}C$ using the powder calcined at 90$0^{\circ}C$.

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Synthesis and Characterization of MoO3 Nano Particle by Controlling Various Growth Conditions in Solution Combustion Method

  • Namhun Kwon;Seyoung Lee;Jaeseok Roh;Kun-Jae Lee
    • Archives of Metallurgy and Materials
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    • v.66 no.4
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    • pp.991-995
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    • 2021
  • In this paper, synthesize MoO3 particles with various particle properties by control growth influence factors was mainly studied. The experimental conditions were established in molar ratio of Mo:urea and pH levels. The plate-type of MoO3 particles were formed without proceeding any established conditions, but the rod-shape particles were formed by adjusting molar ratio of Mo:urea. Also, different ranges of the particle size were formed by adjusting experimental conditions. Through the results, it was confirmed that particles with a size in the range of 300 ~ 400 nm were obtained by adjusting precursor concentration and the micrometer size of particles were formed by increase pH levels. The properties of the particles formed accordingly by setting various factors that can affect the growth process of MoO3 particle was analyzed as variables and the particle growth behavior was also observed.