• Korean Journal of Materials Research
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• v.9 no.12
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• pp.1196-1204
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• 1999

We have carried out copper MOCVD(metalorganic chemical vapor deposition) onto the reactive sputtered PVD-TiN and rapid thermal converted RTP-TiN substrates using direct liquid injection for effective delivery of the (hfac)Cu(vtmos) [$C_{10}H_{13}O_{5}CuF_{6}$Si: 1,1,1,5,5,5-hexafluoro-2,4- pentadionato (vinyltrimethoxysilane) copper (I)] precursor. Especially, the influences of deposition conditions and the substrate type on growth rate, crystal structure, microstructure, and electrical resistivity of copper deposits have been discussed. It is found that the film growth with 0.2ccm precursor flow rate become mass-transfer controlled up to Ar flow rate of 200sccm and pick-up rate controlled at a vaporizer above 1.0Torr reactor pressure. The surface-reaction controlled region from 155 to 225$^{\circ}C$ at 0.6Torr reactor pressure results in the apparent activation energies of 12.7~14.1kcal/mol, and above 224$^{\circ}C$ the growth rate with $H_2$ addition could be improved compared to the pure Ar carrier. The Cu/RTP-TiN structures which have high copper nucleation density in initial stage of growth show more pronounced (111) preferred orientations and lower electrical resistivities than those on PVD-TiN. The variation of electrical resistivity with substrate temperature reflects the three types of film microstructure changes, showing the lowest value for the deposit at 165$^{\circ}C$ with small grains of good contacts.

• The Korean Journal of Mycology
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• v.26 no.3 s.86
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• pp.380-386
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• 1998

To obtain basic data for mass production of Isaria japonica, cultural characteristics of japonica were investigated by using liquid, solid media and silkworms pupa. Mycelia grew favorably at the temperature of $23{\sim}28^{\circ}C$ on MYG medium with pH 7.0. The fruiting-body of I. japonica was induced below $20^{\circ}C$ in MYG liquid medium (Malt yeast glucose) under fluorescent light. In MYG basal medium mixed with pupal powder of silkworms, the fresh weight of fruiting-bodies was increased with increasing concentration of pupal powder. The highest yield of fruiting bodies was obtained in carbon-rich medium supplemented with pupal powder of silkworm. Also, fruiting-bodies of I. japonica were produced massively on the silkworm pupa placed on the stainless tray in the shortest time. The structure and shape of fruiting-bodies were coral-like, many-branched types with numerous conidiospores.

• Polymer(Korea)
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• v.36 no.1
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• pp.76-87
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• 2012

Three kinds of hydroxypropyl cellulose (HPC) derivatives, [6-{4-(4-cyanophenylazo)phenoxy}]hexyloxypropyl celluloses (CAHPCs) with degree of etherification (DET) ranging from 0.4 to 3, fully substituted acrylic acid esters of HPC (HPCA) and CAHPCs (CAHPCAs) were synthesized. The crosslinked HPCA (HPCAG) and CAHPCAs (CAHPCAGs) were also prepared by exposing thermotropic mesophases of HPCA and CAHPCAs to UV light. Both CAHPCs and CAHPCAs with DET ${\leq}$ 1.2, as well as HPC and HPCA, formed enantiotropic cholesteric phases whose optical pitches(${\lambda}_m$'s) increase with temperature, wheras both CAHPCs and CAHPCAs with DET ${\geq}$ 1.4 showed monotropic nematic phases. CAHPCAGs with DET ${\leq}$ 1.2, as well as CAHPCAs with DET ${\leq}$ 1.2, exhibited reflection colors in a wide temperature range. On the other hand, CAHPCAGs with DET ${\geq}$ 1.4, as well as CAHPCAs with DET ${\geq}$ 1.4, showed Schileren textures typical of nematic phase, indicating that the liquid crystalline structure is virtually locked upon photocrosslinking. The isotropization temperatures($T_i$'s) of both CAHPCAs and CAHPCAGs decreased with increasing DET. The $T_i$ of CAHPCAG, however, was higher than that of CAHPCA at the same DET. Moreover, the temperature dependence of ${\lambda}_m$ of CAHPCAGs was much weaker than that of CAHPCAs.

• Korean Journal of Materials Research
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• v.4 no.5
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• pp.600-607
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• 1994

Optimum exper~mental conditions were established for the growth of heteroepitaxial GaAs layers on InP using liquid phase epitaxy (LPE) technique. Results showed that the optimum growth temperature was $720^{\circ}C$ at a cooling rate of $0.5^{\circ}C$/min. Surface morphology of the grown layers significantly improved by addition of about 0.005wt% Se to the Ga growth melt, which effectively suppressed melt-back of InP substrates into the melt during the initial stage of growth. It was observed that the quality of GaAs layers also improved substantially when the substrates patterned with grating structure were used, as determined by the (400) double crystal X-ray diffraction. The transmission electron microscopy observation indicated t.hat the misfit dislocations interact with each other at the grating region, resulting in a lower dislocation density in the upper GaAs layer.

• Polymer(Korea)
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• v.32 no.5
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• pp.446-457
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• 2008

Three kinds of hydroxypropyl cellulose (HPC) derivatives: 6- (cholesteryloxycarbonyl) pentoxypropyl celluloses(CHPCs) with degree of esterification(DE) ranging from 0.6 to 3, 6-[4-{4'-(nitrophenylazo)phenoxycarbonyl}] pentoxypropyl celluloses (NHPCs) with DE ranging from 0.4 to 3, and fully 6-(cholesteryloxycarbonyl) pentanoated NHPCs (CNHPCs) were synthesized, and their thermotropic liquid crystalline properties were investigated. All the CHPCs and NHPCs with $DE{\leq}1.7$ formed enantiotropic cholesteric phases, whereas CNHPCs with 6-(cholesteryloxycarbonyl) pentanoyl DE(DEC) more than 1.6 exhibited monotropic cholesteric phases. On the other hand, NHPCs with $DE{\geq}2.4$ and CNHPCs with $DEC{\leq}1.3$ showed monotropic nematic phases. NHPCs with $DE{\leq}l$, as well as HPC, formed right-handed helices whose optical pitches (${{\lambda}_m}'s$) increase with temperature, while all the CHPCs formed left-handed helices whose ${{\lambda}_m}'s$ decrease with temperature. In contrast with these derivatives, NHPCs with $1.4{\leq}DE{\leq}1.7$ and CNHPCs with $DEC{\geq}1.6$ did not display reflection colors over the full cholesteric range, suggesting that the helical twisting power of the cellulose chain and the cholesteryl group highly depends on the chemical structure and DE of mesogenic group.

• Korean Journal of Optics and Photonics
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• v.19 no.4
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• pp.294-301
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• 2008

We have performed modeling and simulations of optical characteristics for a cholesteric liquid crystal (CLC) color filter. Berreman's $4{\times}4$ matrix method was used for the calculation of reflectance spectra of the CLC color filter with respect to the incident angle. The results were employed as input parameters for a user-defined coating property of an illumination design software based on the ray-tracing method, LightTools. Color shift characteristics of a planar transmission-type CLC color filter were simulated using LightTools. The results were compared with the results obtained with Berreman's $4{\times}4$ matrix method. It was found that color shift characteristics of the CLC color filter could be simulated to a reasonable accuracy when the reflectance spectra with less than 5 degrees of incremental incidence-angle were used as the input data for the user-defined coating property of LightTools. We have simulated color shift characteristics of a reflection-type CLC color filter having hemi-spherical patterns. The simulation method reported in this paper has been found to be also used for a non-planar CLC color filter structure.

• Clean Technology
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• v.25 no.1
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• pp.14-18
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• 2019

In general after the etching process, waste etching solution contains metals. (ex. Nickel (Ni), Chromium (Cr), Zinc (Zn), etc.) In this work, we proposed a recycling process for waste etching solution and refining from waste liquid contained nickel to make nickel metal nano powder. At first, the neutralization agent was experimentally selected through the hydrolysis of impurities such as iron by adjusting the pH. We selected sodium hydroxide solution as a neutralizing agent, and removed impurities such as iron by pH = 4. And then, metal ions (ex. Manganese (Mn) and Zinc (Zn), etc.) remain as impurities were refined by D2EHPA (Di-(2-ethylhexyl) phosphoric acid). The nickel powders were synthesized by liquid phase reduction method with hydrazine ($N_2H_4$) and sodium hydroxide (NaOH). The resulting nickel chloride solution and nickel metal powder has high purity ( > 99%). The purity of nickel chloride solution and nickel nano powders were measured by EDTA (ethylenediaminetetraacetic) titration method with ICP-OES (inductively coupled plasma optical emission spectrometer). FE-SEM (field emission scanning electron microscopy) was used to investigate the morphology, particle size and crystal structure of the nickel metal nano powder. The structural properties of the nickel nano powder were characterized by XRD (X-ray diffraction) and TEM (transmission electron microscopy).

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.1
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• pp.1-11
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• 2021

POGO is a dynamic axial instability phenomenon that occurs in liquid-propelled rockets. As the natural frequencies of the fuselage and those of the propellant supply system become closer, the entire system will become unstable. To predict POGO, the propellant (oxidant and fuel) tank in the first stage is modeled as a shell element, and the remaining components, the engine and the upper part, are modeled as mass-spring, and structural analysis is performed. The transmission line model is used to predict the pressure and flow perturbation of the propellant supply system. In this paper, the closed-loop transfer function is constructed by integrating the fuselage structure and fluid modeling as described above. The pogo suppressor consists of a branch pipe and an accumulator that absorbs pressure fluctuations in a passive manner and is located in the middle of the propellant supply system. The design parameters for its design optimization to suppress the decay phenomenon are set as the diameter, length of the branch pipe, and accumulator. Multiple-objective function optimization is performed by setting the energy minimization of the closed loop transfer function in terms of to the mass of the pogo suppressor and that of the propellant as the objective function.

• Applied Chemistry for Engineering
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• v.22 no.3
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• pp.277-285
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• 2011

Polysulfone (PSf) membranes were prepared via the phase inversion process. Polyvinylpyrrolidone (PVP) was added as a nonsolvent additive in the casting solution containing a mixture of PSf and n-methylpyrrolidone. The added PVP played a role of enhancing liquid-liquid phase separation of the casting solution, and significantly reduced the solution fluidity. When prepared via the diffusion-induced process using water as a precipitation nonsolvent, the solidified membranes revealed a typical asymmetric structure irrespective of the addition of PVP. With 5 wt% PVP content, the finger-like cavities were more developed in the membrane sublayer compared to that of the membranes prepared without PVP. In contrast, with more than 10 wt% of PVP, the formation of finger-like cavities was suppressed, and the thickness of polymer nodule layer was increased. The surface porosity was also increased with the PSf content in the casting solution. The water permeability curve as a function of PVP addition revealed the inflection point. The maximum water permeability for 12 wt% PSf membrane was obtained with 5 wt% PVP content, and that for 18 wt% PSf membrane with 15 wt% PVP.

• Clean Technology
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• v.27 no.1
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• pp.69-78
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• 2021

Vegetable oils, such as palm oil and cashew nut shell liquid (CNSL), are used as major raw materials for bio-diesel in transportation and bio-heavy oil in power generation in South Korea. However, due to the high unsaturation degree caused by hydrocarbon double bonds and a high content of oxygen originating from the presence of carboxylic acid, the range of applications as fuel oil is limited. In this study, hydrotreating to saturate unsaturated hydrocarbons and remove oxygen in mixed bio-oil containing 1/1 v/v% palm oil and CNSL on monometallic catalysts (Ni and Cu) and bimetallic catalysts (Ni-Zn, Ni-Fe, Ni-Cu Ni-Co, Ni-Pd, and Ni-Pt) was perform under mild conditions (T = 250 ~ 400 ℃, P = 5 ~ 80 bar and LHSV = 1 h-1). The addition of noble metals and transition metals to Ni showed synergistic effects to improve both hydrogenation (HYD) and hydrodeoxygenation (HDO) activities. The most promising catalyst was Ni-Cu/��-Al2O3, and in the wide range of the Ni/Cu atomic ratio of 9/1~1/4, the conversion for HYD and HDO reactions of the catalysts were 90-93% and 95-99%, respectively. The tendency to exhibit almost constant reaction activity in these catalysts of different Ni/Cu atomic ratios implies a typical structure-insensitive reaction. The refined bio-oil produced by hydrotreating (HDY and HDO) had significantly lower iodine value, acid value, and kinetic viscosity than the raw bio-oil and the higher heating value (HHV) was increased by about 10%.