• Journal of the Korean Chemical Society
• /
• v.48 no.6
• /
• pp.561-567
• /
• 2004

The influence of ultrasound frequency, dissolved gases, and initial concentration on the decomposition of sodium dodecylbenzene sulfonate(DBS) aqueous solution was investigated using ultrasound generator with 200 W ultrasound power. The decomposition rates at three frequencies(50, 200, and 600 kHz) examined under argon atmosphere were highest at 200 kHz. The highest observed decomposition rate at 200 kHz occurred in the presence of oxygen followed by air and argon, helium, and nitrogen. The effect of initial concentration of DBS on the ultrasonic decomposition was decreased with increasing initial concentration and would depend upon the formation of micelle in aqueous solution. It appears that the ultrasound frequency, dissolved gases, and initial concentration play an important role on the sonolysis of DBS. Sonolysis of DBS mainly take place at the interfacial region of cavitation bubbles by both OH radical attack and pyrolysis to alkyl chain, aromatic ring, and headgroup.

• Advanced Composite Materials
• /
• v.17 no.2
• /
• pp.157-166
• /
• 2008

In this study, multiwalled carbon nanotubes (MWCNTs) were compounded with the poly($\varepsilon$-caprolactone) (PCL) matrix at the solution state using chloroform. For homogeneous dispersion of MWCNTs in polymer matrix, oxygen-containing groups were introduced on the surface of MWCNTs. The mechanical properties of the PCL/MWCNTs composites were effectively increased due to the incorporation of MWCNTs. The composites were characterized using scanning electron microscopy in order to obtain information on the dispersion of MWCNT in the polymeric matrix. In case of 1.2 wt% of MWCNTs in the matrix, strength and modulus of the composite increased by 12.1% and 164.3%, respectively. In addition, the dispersion of MWCNTs in the PCL matrix resulted in substantial decrease of the electrical resistivity of the composites as the MWCNTs loading was increased from 0 to 2.0 wt%. Furthermore, thermal stability of the PCL and PCL/MWCNTs-COOH composites were investigated using the data acquired from the thermogravimetric analysis. The detailed kinetics of the thermal degradation of the composites was investigated by analyzing their thermal behavior at different heating rates in a nitrogen atmosphere. Activation energy of thermal degradation was determined by using the equations proposed by Kissinger and Flynn-Wall-Ozawa. The apparent activation energy of PCL/MWCNTs-COOH composite was considerably higher than that of neat PCL.

• Elastomers and Composites
• /
• v.34 no.1
• /
• pp.3-10
• /
• 1999

Kinetics of solution photopolymerization of acrylonitrile(AN) with sensitizer, such as $NaSCN,\;KSCN,\;Ba(SCN)_2,\;NH_4SCN,\;ZnCl_2$ and $Na_2SeO_3$, were studied using UV crosslinker at various monomer concentrations($1.8{\sim}7.58mo1/1$), sensitizer concentrations($10{\sim}60%$), reaction temperature($10{\sim}70^{\circ}C$), energy intensities($1,000{\sim}9,900{\mu}J/cm^2$) at isothermal condition under nitrogen atmosphere. Under the irradiation of high pressure mercury lamp(${\lambda}=365nm$). High conversion and uniform molecular weight were obtained compare to thermal polymerization at reaction temperature of $50^{\circ}C$, reaction time of 3hr and 50% NaSCN without any initiator. Their kinetic model was as follows : $R_p=0.0142[M]^{0.82}[I]^{0.49}[S]^{0.52}$ exp(-1.33/RT).

• Journal of Adhesion and Interface
• /
• v.2 no.2
• /
• pp.11-19
• /
• 2001

The phase-transfer catalyzed radical polymerization of styrene was carried out using tricaprylylmethylammonium chloride as a phase-transfer catalyst in a two-phase system of an aqueous $Na_2S_2O_8$ solution and toluene at $60^{\circ}C$ under nitrogen atmosphere. The initial rate of radical polymerization was expressed as the combined terms of concentrations of quaternary onium cation and peroxydisulfate anion in the aqueous phase rather than the fed concentrations of catalyst and $Na_2S_2O_8$. The observed initial rate of radical polymerization was used to analyze the radical polymerization mechanism with a cycle phase-transfer initiation step in the heterogeneous liquid-liquid system. The viscosity average molecular weight of polystyrene was inversely proportional to concentration of $Na_2S_2O_8$ expressed as $[Q^+]([S_2O{_8}^{2-}]{\alpha}_2)^{1/2}$ derived by the radical polymerization mechanism.

• Journal of the Korean Ceramic Society
• /
• v.40 no.3
• /
• pp.249-254
• /
• 2003

AI, AIN and additives such as Li$_2$CO$_3$, Y$_2$O$_3$ and CaCO$_3$ which promoted nitridation were mixed, formed and heat-treated in nitrogen atmosphere. The effect of solvent, additive and temperature on nitridation of AI-AIN system was studied. When ethanol containing 1 wt% oleic acid was used as a mixing solvent, the formation of oxide was minimized due to surface modification of AI and AIN particles. The addition of Li$_2$CO$_3$ or CaCO$_3$ as an additive extremely diminished the formation of oxide which formed during heat treatment for nitridation compared with the addition of Y$_2$O$_3$.

• Journal of the Korean Ceramic Society
• /
• v.24 no.1
• /
• pp.70-76
• /
• 1987

The effect of C12A7 and OH group on the synthesis of C3A by the sol-gel process using aluminum-sec-butoxide and calcium nitrate was studied. C3A by sol-gel method was compared with C3A obtained by the conventional method with respect to their reactivity of formation and crystal size. The sol-gel process for initial formation of C12A7 and C3A at lower temperature (1100, 1200$^{\circ}C$) was superior, but that for complete crystallization of C3A at higher temperature (1300, 1400$^{\circ}C$) was inferior to oxide mixture process. When heat treated under the atmosphere oxygen-free dried nitrogen eliminate the influence of OH group in C12A7, the reactivity of C3A from sol-gel sample incorporated OH group were poor, whereas that from oxide mixture sample showed remarkable effect. The poor crystallization of C3A at higher temperature is presumed to be due to the fact that incorporated OH group in C12A7 formed at lowr temperature might interrupt the diffusion of CaO to C12A7 to from C3A. The crystal size and the hydration characteristics of both C3A obtained by different processes exhibited almost the same results.

• Journal of the Korean institute of surface engineering
• /
• v.49 no.2
• /
• pp.202-210
• /
• 2016

This study was intended to investigate the effect of the amount of magnesium addition and heat treatment in the Al-Mg coating film in order to improve corrosion resistance of aluminum coating. Al-Mg alloy films were deposited on cold rolled steel by physical vapor deposition sputtering method. Heat treatment was fulfilled in an nitrogen atmosphere at the temperature of $400^{\circ}C$ for 10 min. The morphology was observed by SEM, component and phase of the deposited films were investigated by using GDLS and XRD, respectively. The corrosion behaviors of Al-Mg films were estimated by exposing salt spray test at 5 wt.% NaCl solution and measuring polarization curves in deaerated 3 wt.% NaCl solution. With the increase of magnesium content, the morphology of the deposited Al-Mg films changed from columnar to featureless structure and particle size was became fine. The x-ray diffraction data for deposited Al-Mg films showed only pure Al peaks. However, Al-Mg alloy peaks such as $Al_3Mg_2$ and $Al_{12}Mg_{17}$ were formed after heat treatment. All the sputtered Al-Mg films obviously showed good corrosion resistance compared with aluminum and zinc films. And corrosion resistance of Al-Mg film was increased after heat treatment.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.29 no.9
• /
• pp.552-558
• /
• 2016

Goethite, ${\alpha}$-FeOOH have various applications such as absorbent, pigment and source for magnetic materials. Goethite particles were synthesized in a two step process, where $Fe(OH)_2$ were synthesized in nitrogen atmosphere using $FeSO_4$ as a raw material in the first process, and after that acicular goethite particles were obtained in an air oxidation process of $Fe(OH)_2$ in highly alkaline aqueous solution. Their phase and microstructure were investigated with XRD and FE-SEM. It was found that the morphology of goethite and the ratio of length-to-width (aspect ratio) of acicular goethite are dependent on the some factors such as R value ($OH^-/Fe^{2+}$), air flow rate and pH conditions. In particular, R value has the strongest influence on the synthesized goethite morphology. It is considered that the optimal value R is 4.5 because X-ray diffraction peaks of goethite have the highest intensity at that value. Morphology of goethite particles was controlled by air flow rates, showing that their size and aspect ratio are getting smaller and decrease, respectively as air flow rate increases. The largest goethite particle obtained is about 1,500 nm in length and 150 nm in diameter.

• Korean Journal of Materials Research
• /
• v.16 no.11
• /
• pp.681-686
• /
• 2006

Plasma nitrocarburising and plasma post oxidation were performed to improve the wear and corrosion resistance of S45C and SCM440 steel by a plasma ion nitriding system. Plasma nitrocarburizing was conducted for 3h at $570^{\circ}C$ in the nitrogen, hydrogen and methane atmosphere to produce the ${\varepsilon}-Fe_{2-3}$(N, C) phase. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of $500^{\circ}C$ for 1 hour. The very thin magnetite ($Fe_3O_4$) layer $1-2{\mu}m$ in thickness on top of the $15{\sim}25{\mu}m$ ${\varepsilon}-Fe_{2-3}$(N, C) compound layer was obtained by plasma post oxidation. A salt spray test and electrochemical testing revealed that in the tested 5% NaCl solution, the corrosion characteristics of the nitrocarburized compound layer could be further improved by the application of the superficial magnetite layer. Throttle valve shafts were treated under optimum plasma processing conditions. Accelerated life time test results, using throttle body assembled with shaft treated by plasma nitrocarburising and post oxidation, showed that plasma nitrocarburizing and plasma post oxidation processes could be a viable technology in the very near future which can replace $Cr^{6+}$ plating.

• The Korean Journal of Nuclear Medicine
• /
• v.24 no.1
• /
• pp.101-107
• /
• 1990

To develop $^{131}I-labelled$ m-iodobeneylguanidine $(^{131}I-MIBG)$, various experiments such as synthesis of MIBG, establishment of labelling conditions, determination of radiochemical purity, and examination of stability were carried out. 1) m-Iodobenzylguanidine (MIBG) sulfate was synthesized with a total yield of 62.4% by the condensation of m-iodobenzylamine hydrochloride with cyanamide via MIBG bicarbonate. Its physical properties, IR, $^1H-NMR$, and elemental analysis data were nearly identical to those of literature. 2) Freeze-dried or vacuum-dried kit vials were prepared from the mixture so as to contain MIBG (2 mg), ascorbic acid (10 mg), copper (II) sulfate (0.14 mg), and tin (II) sulfate (0.5 mg) per vial. Copper ( I ) catalyzed radioiodination of MIBG was carried out using kit vials and 0.01 M $H_2SO_4$ as solvent at $100^{\circ}C$ for 30 min under nitrogen atmosphere (optimal conditions). Labelling yield was 98% and radiochemical purity was 99.5%, respectively. 3) Solid-phase radioiodination of MIBG was carried out at $155^{\circ}C$ for 30 min using the prepared vials to contain MIBG (2 mg) and ammonium sulfate (10 mg). Duplicate reactions under the same conditions showed labelling yield of 95% and radiochemical purity of 99.5%. 4) $^{131}I-MIBG$ prepared either by catalytic or by solid-phase exchange method showed radio-chemical purity of 99% even after 3 days storing at room temperature.