• 공업화학
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• 제10권8호
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• pp.1186-1191
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• 1999

고분자 화합물의 첨가제로서 개질제, 물성 향상제, 충진제, 강화제 등의 용도로 사용되고 있는 유리 중공구체를 혼합액상 전구체를 사용하여 제조하였다. 혼합액상 전구체는 40% 규산나트륨($Na_2O:SiO_2$= 1:2) 수용액에 불용제인 붕산과 팽창제인 요소를 혼합한 용액이며, 이 용액을 오븐에 건조시킨 후, 볼밀로 분쇄시켜 기체 화염로에 투입될 원료 입자를 제조하였다. 유리 중공구체의 물성에 영향을 미치는 인자로서는 로에 투입될 원료 입자의 크기($53{\sim}63{\mu}m$, $63{\sim}180{\mu}m$)와 로 내부의 온도($800{\sim}1200^{\circ}C$), 그리고 요소의 변화량(0~30 g)을 택하여 실험하였으며, 실험 결과 유리 중공구체의 평균 입경은 원료 입자의 크기가 작을수록, 로 내부의 온도가 클수록, 그리고 요소의 조성이 증가할수록 증가하는 결과를 보여 주었다. 또한, 유리 중공구체의 파쇄 강도는 요소의 양이 증가할수록 감소하는 경향을 나타내었다.

• 한국세라믹학회지
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• 제34권12호
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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.

• Carbon letters
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• 제19권
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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.

• Biotechnology and Bioprocess Engineering:BBE
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• 제1권1호
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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.

• 한국표면공학회지
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• 제50권6호
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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.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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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.

• 공업화학
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• 제33권5호
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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.

• 한국전기전자재료학회논문지
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• 제30권7호
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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.

• 한국세라믹학회지
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• 제33권6호
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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$0^{\circ}C$.

• 한국분말재료학회지
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• 제8권1호
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• pp.13-19
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• 2001

Ni and NiO particles were made by a combustion synthesis process. The characteristics of synthesized powders were investigated with various kinds and amounts of fuels such as urea, citric acid and glycine. Ni phase particles without NiO phase were obtained through combustion synthesis process in air atmosphere with-out further calcinations process, when the content of glycine was 2.44 times of the stoichiometric ratio in the precursor solution. Primary particle sizes of synthesized Ni and NiO particles were about 20∼30 nm.