• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.128-130
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• 2017

$NaBH_4$ was added to improve the water reactivity of aluminum powder as a solid propellant for underwater propulsion. Aluminum powders showed different combustion characteristics depending on the amount of $NaBH_4$ added. When $NaBH_4$ was added, it was burned by reaction with water even at a temperature much lower than the boiling point. In this study, it was confirmed that $NaBH_4$ is an effective additive to accelerate the vapor reaction with Al powder.

• Korean Journal of Materials Research
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• v.21 no.6
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• pp.327-333
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• 2011

Nanostructured cobalt materials have recently attracted considerable attention due to their potential applications in high-density data storage, magnetic separation and heterogeneous catalysts. The size as well as the morphology at the nano scale strongly influences the physical and chemical properties of cobalt nano materials. In this study, cobalt nano particles synthesized by a a polyol process, which is a liquid-phase reduction method, were investigated. Cobalt hydroxide ($Co(OH)_2$), as an intermediate reaction product, was synthesized by the reaction between cobalt sulphate heptahydrate ($CoSO_4{\cdot}7H_2O$) used as a precursor and sodium hydroxide (NaOH) dissolved in DI water. As-synthesized $Co(OH)_2$ was washed and filtered several times with DI water, because intermediate reaction products had not only $Co(OH)_2$ but also sodium sulphate ($Na_2SO_4$), as an impurity. Then the cobalt powder was synthesized by diethylene glycol (DEG), as a reduction agent, with various temperatures and times. Polyvinylpyrrolidone (PVP), as a capping agent, was also added to control agglomeration and dispersion of the cobalt nano particles. The optimized synthesis condition was achieved at $220^{\circ}C$ for 4 hours with 0.6 of the PVP/$Co(OH)_2$ molar ratio. Consequently, it was confirmed that the synthesized nano sized cobalt particles had a face centered cubic (fcc) structure and with a size range of 100-200 nm.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.251.2-251.2
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• 2010

Plant biomass has been proposed to be an alternative source for petroleum-based chemical compounds. Especially, phenolic chemical compounds can be obtained from lignin by chemical depolymerization processes because lignin consists of complex aromatic polymer such as trans-p-coumaryl, coniferyl and sinapyl alcohols, etc. Phenolic chemical compounds from lignin were usually produced in super critical water. However, we applied Near-critical water (NCW) system because NCW is known as a good solvent for lignin depolymerization. Organic matter like lignin can be solved in NCW system and the system has a unique acid-base property without conventional non-eco-friendly chemicals such as sulfuric acid and sodium hydroxide. In this work, we tried to optimize the NCW depolymerization system by adjusting the processing variables such as reaction time, temperature and pressure. Moreover, the amount of additional phenol was optimized by changing the molar ratio between water and phenol. Phenol was used as capping agent to prevent re-polymerization of active fragment such as formaldehyde. Alkali-lignin was used as a starting material and characterized by a Solid State 13C-NMR, FT-IR and EA (Elemental Analysis). GC-MS analysis confirmed that o-cresol, p-cresol, anisole and 4-hydroxyphathalic acid were the main product and they were quantitatively analyzed by HPLC.

• Resources Recycling
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• v.27 no.4
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• pp.57-64
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• 2018

Water leaching of tungsten(W) and vanadium(V) was researched from their oxides through mechanochemical (MC) reaction with alkali compounds. Intensive grinding for the mixture of tungsten/vanadium oxide and alkali compounds (NaOH, $Na2CO_3$) was carried out with change of their mixing ratios and grinding duration. Water soluble compounds, $Na_2WO_4$ and $NaVO_3$, were synthesized through MC reaction and their solubilities increased in proportion to the mixing ratio of sodium compound and grinding times. Whereas vanadium leachability was less affected by the mixting ratio and grinding times. The leachabilities of 99.0% were accomplished by a short period of MC treatment, W (30 min.) and V (5 min.). This process enable us to extract W and V from their oxides via a water leaching, and can be applied to the selective recovery of W and V from $DeNO_x$ spent catalysts.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.84-91
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• 2021

Effervescent tablets generate gas bubbles when chemical reaction occurs between water and tablets. Most of previous studies have been focused on pharmaceutical characteristics of tablets. However, for their applications in disinfectants, cleaners, and pesticides, physical characteristics of bubbles released from the effervescent tablets when they are in water are important. In this study, we experimentally investigated the characteristics of microbubbles generated by an effervescent tablet made of sodium bicarbonate and tartaric acid using PDPA and high-speed camera. Microbubbles were generated using different weights of effervescent tablet as well as in different water temperature. The experimental study shows increase in reaction time, bubble concentration and rise velocity as the weight of effervescent tablet increases from 1 to 20 g. The decrease in average bubble diameter was observed when the temperature of water increased from 25 to 45 ℃. Further, reaction time varies inversely with increase in water temperature, while bubble rise velocity is directly proportional to increase in water temperature. Effervescent table continuously generates the bubble with approximately constant diameter (235 ㎛) in the water. However, bubble concentration and bubble rise velocity decreased over time.

• Textile Coloration and Finishing
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• v.13 no.5
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• pp.24-24
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• 2001

Kinetics and mechanism for alkaline hydrolysis of C. I. Disperse Blue 79(B-79) which is 4-N, N-diacetoxyethyl-2-acylamino-5-ethoxy -2′-bromo-4′,6′-dinitroazobenzene were investigated. The color strength of B-79 in acetone/water solutions of various NaOH concentrations decreased continuously. The hydrolysis rate of B-79 increased with increasing alkali concentration and appeared following first order reaction. The observed rate constants for various concentrations of B-79 showed similar values, and B-79 was hydrolyzed by first order reaction for dye concentration. Therefore, it was confirmed that the overall reaction follow second order kinetics and proceed via S/sub n/2 reaction. From the study on kinetics and spectrometric analysis, it was proposed that the rate determining step of the hydrolysis reaction of B-79 is the nucleophilic substitution reaction - that is the reaction of the rapid attack of $OH^{-}$ on the carbon atom, which is in acceptor ring, adjacent to azo group to break the C-N bond. And it was also found that the final hydrolysis products of B-79 include both the acceptor ring in the form of sodium salt and the donor ring possessing 4-N,N-dihydroxyethyl group converted from 4-N,N-diacetoxyethyl group.

• Textile Coloration and Finishing
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• v.13 no.5
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• pp.312-319
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• 2001

Kinetics and mechanism for alkaline hydrolysis of C. I. Disperse Blue 79(B-79) which is 4-N, N- diacetoxyethyl -2- acylamino-5-ethos y -2'-bromo-4',6'-dinitroazobenzene were investigated. The color strength of B-79 in acetone/water solutions of various NaOH concentrations decreased continuously. The hydrolysis rate of B-79 increased with increasing alkali concentration and appeared following first order reaction. The observed rate constants for various concentrations of B-79 showed similar values, and B-79 was hydrolyzed by first order reaction for dye concentration. Therefore, it was confirmed that the overall reaction follow second order kinetics and proceed via $S_N2$ reaction. From the study on kinetics and spectrometric analysis, it was proposed that the rate determining step of the hydrolysis reaction of B-79 is the nucleophilic substitution reaction - that is the reaction of the rapid attack of OH- on the carbon atom, which is in acceptor ring, adjacent to auto group to break the C-N bond. And it was also found that the final hydrolysis products of B-79 include both the acceptor ring in the form of sodium salt and the donor ring possessing 4-N,N-dihydroxyethyl group converted from 4-N, N-diacetoxyethyl group.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.32 no.1
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• pp.33-40
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• 2000

The effectiveness of silica-based microgels prepared through the reaction of sulfuric acid and sodium silicate as a component of Compozil system has been evaluated . Silica based microgels with better performance in retention and drainage than a commercial colloidal silica sol have been successfully prepared. Silica gels with the highest charge density were obtained when product pH was controlled to 9. And highly charged silica-based microgels showed greater retention and freeness performance than a commerical product. In particular the difference in retention, turbidity , and freeness between these microgels and a commercial product was eminent at low addition rate. The effects of reaction conditions including reaction temperature, process water quality and feeing rate on product efficiency in improving retention and drainage were also investigated and discussed.

• Journal of Korea Foundry Society
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• v.4 no.2
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• pp.102-107
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• 1984

The variations of the mold compression strength were studied by varing the contents of the silicon powder and water glass, silion purities, and molecule rates of the water glass, when domestic JA EUN DO sand is mixed with water glass (sodium silicate) and metallic silicon or ferro - silicon powder by the self - hardening N - PROCESS method. The results obtained from this experiment are as follows; 1) The compression strength of the mold used with metalic powder was higher and more stable than to be used ferro - silicon powder. 2) 6% water glass of 2.8 molecule rate and 1.5% of ferro - silicon of 75% purity for the N - PROCESS used with JA EUN DO sand was suitable mixing rate. 3) The compression strength increased with self - hardening time, and the PH values of the mixture of silicon powder and water glass did not change after 2 hours, but the compression strength increased steadily due to the reaction of remained silicon. 4) It is recommended to take 24 hours for self - hardening time at least.

• Journal of Life Science
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• v.11 no.4
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• pp.321-327
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• 2001

The purpose of this study was to investigate the nitrite scavenging activity of the ethanol and water extracts obtained from Hizikia fusiforme and Sargassum fulvelum using sodium nitrite under different pH conditions. The nitrite scavenging activity was appeared in all the extracts examined and it showed the highest value at pH 1.2 The ethanol extract of Hizikia fusiforme provided higher activity than the water extract of that. Ohterwise, the nitrite scavenging activity of Sargassum fulvelum ethanol extract was similar to that Sargassum fulvelum water extract. There was significant difference among concentration of extracts Hizikia fusiforme and Sargassum fulvelum. Also, nitrite scavenging activity of the extracts Hizikia fusiforme and Sargassum fulvelum decreased with higher pH condition. In addition, the activity was increaed with higher concentration of extracts Hizikia fusiforme and Sargassum fulvelum in the course of reaction time 30 minute to 3 hour.