• Korean Journal of Metals and Materials
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• v.48 no.1
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• pp.49-56
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• 2010

This study investigated how the surface of Al-12wt.%Si alloy modified by the plasma electrolytic oxidation process (PEO). The PEO process was performed in an electrolyte with sodium hexametaphsphate as a conducting salt, and the effect of ammonium metavanadate on variations in the morphology of electrochemically generated oxide layers on the alloy surface was investigated. It is difficult to form a uniform passive oxide layer on Al alloys with a high Si content due to the differences in the oxidation behavior of the silicon-rich phase and the aluminum-rich phase. The oxide layer covered the entire surface of the Al-12WT.%Si alloy uniformly when ammonium metavanadate was added to the electrolyte. The oxide layer was confirmed as a mixture of $V_2O_3$ and $V_2O_5$ by XPS analysis. In addition, the oxide layer obtained by the PEO process with ammonium metavanadate exhibited a black color. Application of this surface modification method is expected to solve the problem of the lack of uniformity in the coloring of oxide layeres caused by different oxidation behaviors during a surface treatment.

• Polymer(Korea)
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• v.27 no.2
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• pp.129-134
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• 2003

It has been known that the intercalation of long alkyl chains in montmorillonites (MMT) increased the hydrophobicity as well as gallery spacing of UT, which has influenced on the exfoliation behavior of various polymers. A series of organophilic MMTs were synthesized from the water/isopropyl alcohol solution of MMT with ammonium salts of various alkyl amines. The properties of obtained MMTs such as thermal decomposition temperature, gallery spacing as well as hydrophobic property were investigated. The X-ray diffraction experiments on organophilic montmorillonite demonstrated that the increase of length of alkyl substituent resulted in increase in the spacing between silicate layers, which was ranged from 13.1 to 29.4 $\AA$. On the other hand, introduction of (di-, tri-) alkyl substituents in ammonium salts decreased water absorption of organophiplic montmorillonite to 2.7%.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.783-792
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• 1995

Sol-Gel derived ferroelectric PZT thin films were fabricated on ITO/Glass and Si/SiO2 substrates. In order to investigate the effect of catalysts on the densification and crystallization of PZT thin films, a nitric acid or ammonium hydroxide was added to the PZT stock solution at the state of partial hydrolysis reaction. The measured pH for a stable PZT sol was 5.2~9.3. In case of an acid-catalyzed PZT sol, a highly condensed particulate PZT sol was formed by accelerating the hydrolysis reaction. But weakly branched polymeric PZT sol was formed with a base-catalyzed condition. The difference in densification behavior was not found in the pH range of added catalyst, but the refractive index of PZT thin film was increased rapidly as the annealing temperature increased. The PZT thin film annealed at 54$0^{\circ}C$ for 10 min was fully densified and its refractive index was above 2.4. When the annealing temperature increased, the transition from the pyrochlore phase to perovskite appeared at 54$0^{\circ}C$. The base-catalyzed PZT thin film suppressed to form the pyrochlore phase and proceeded effectively to convert the perovskite phase. This was due to the formation of polymeric molecular structure by controlling the hydrolysis and condensation reaction through the additiion of the ammonium hydroxide.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1334-1339
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• 2018

Spherical nickel ferrite nanoparticles were synthesized using the thermal decomposition method and coated with cetyl trimethyl ammonium bromide (CTAB) after the synthesis. Transmission electron microscopy images showed that the average diameter of the particles was 9.40 nm. The status of the CTAB-coating on the surface of the particles was checked using Fourier-transform infrared spectroscopy. Their hysteresis curve showed that the particles exhibited a superparamagnetic behavior. The $T_1$ and the $T_2$ relaxations of the nuclear spins were observed in aqueous solutions of the particles with different particles concentrations by using a magnetic resonance imaging (MRI) scanner, which showed that the $T_1$ and the $T_2$ relaxivities of the particles in water were $0.57mM^{-1}{\cdot}s^{-1}$ and $10.42mM^{-1}{\cdot}s^{-1}$, respectively. In addition, using an induction heating system, we evaluated their potentials for magnetic hyperthermia applications. The aqueous solution of the particles with a moderate concentration (smaller than 6.5 mg/mL) showed a saturation temperature larger than the hyperthermia target temperature of $42^{\circ}C$. These findings show that the CTAB-coated nickel ferrite particles are suitable for applications as $T_2$ contrast agents in MRI and heat generators in magnetic hyperthermia.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.4
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• pp.36-42
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• 2021

In this study, the impregnation of Lyocell fabrics was performed using phosphoric acid, ammonium phosphate, diammonium hydrogen, triammonium phosphate as phosphorus flame retardant, to fabricate continuous graphite fabrics using lyocell fiber. The physical and chemical structure changes were investigated by thermogravimetric, Fourier-transform infrared spectroscopy, C-nuclear magnetic resonance, X-ray diffraction, and weight analyses, By analyzing the thermal behavior of phosphorus flame retardant, conditions for the temperature, gas, and residual time of the pyrolysis process were set. Graphite fabrics with a tensile strength of 1,007.19±11.47 N/5 cm and yield of 25.3% were fabricated using continuous pyrolysis, carbonization and graphitization process.

• Journal of the Korean Chemical Society
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• v.27 no.1
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• pp.24-30
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• 1983

The polarographic behavior of 1-(2-pyridylazo)-2-naphthol (PAN) in acetonitrile as an aprotic solvent has been investigated. The reduction of PAN in $10^{-2}$ molarity of tetraethyl-ammonium perchlorate acetonitrile solution proceeds along two one-electron steps to give the corresponding hydrazo compound. Every reduction wave was diffusion controlled and considerably reversible. The reduction mechanism of PAN in acetonitrile is estimated as follows;

• Bulletin of the Korean Chemical Society
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• v.30 no.5
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• pp.1097-1100
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• 2009

New types of conducting polyaniline-polymannuronate (PANI-PM) composites were synthesized by in situ deposition techniques in an aqueous media. By dissolving different weight percentage of polymannuronate (PM) (5, 10, 15, and 25%), the oxidative polymerization of aniline was carried out using ammonium per sulfate as an oxidant. The obtained composites were studied for their thermal stability and electrochemical behavior. The thermal stability of PANI-PM composites is lower than PANI, which supports a strong interaction between PANI and PM. However, the composites show an appreciable electrochemical behavior. Based on these observation the PANI-PM composites can be explored in different fields such as electric devices, sensors, functional coatings, etc.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.4
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• pp.460-465
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• 2007

In this study, the removal characteristic of ammonia nitrogen and behavior of nitrogen was investigated using Leclercia adecarboxylata, which was derived from the culture contaminated by ammonia nitrogen of high concentration. The method of ammonia nitrogen removal was not biological nitrification and denitrification but elimination of nutrient salt with internal synthesis of microorganisms which use ammonia nitrogen as substrate. L. adecarboxylata(one of ammonia synthesis microorganisms) was highly activated and showed the most high removal efficiency in free salt condition but the removal efficiency decreased badly in salt concentration of more than 4%. About 80 mg/L of $NH_3-N$ was mostly removed within 20 hours and 500 mg/L of $NH_3-N$ showed less then removal efficiency of 50% because carbon source was not enough. However, ammonium nitrogen concentration was decreased again when the carbon source was inserted additionally thus, ammonium nitrogen removal efficiency by L. adecarboxylata, was related to amount of carbon source. pH decreased from 8.0 to 6.36 according to growth of L. adecarboxylata. Concentration of nitrite nitrogen and nitrate nitrogen did not increase and TKN concentration showed no variation while ammonia nitrogen was removed by L. adecarboxylata. In addition to, when content of protein in organic nitrogen was measured, protein was not detected at the beginning of microorganism synthesis but protein of 193.1 mg/L was detected after 48 hours. Hence, ammonium nitrogen was not decomposed as nitrate nitrogen and nitrite nitrogen but synthesized by L. adecarboxylata, which has excellent ability of nitrogen synthesis and can threat ammonia nitrogen of high concentration in wastewater.

• Journal of the Korean Wood Science and Technology
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• v.42 no.6
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• pp.682-690
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• 2014

In order to improve the thermal stability of wood plastic composites (WPC), thermal degradation behavior of WPC in this study was investigated by the addition of wood flour and fire retardant after hybridization of wood flour and ammonium polyphosphate (APP) into polypropylene (PP) matrix. Thermal degradation behavior of all formulations was analyzed with thermogravimetric analyzer under nitrogen environment at heating rate of $10^{\circ}C/min$. As the thermal degradation temperature of wood flour is lower than that of PP, char layer formed by the wood flour decreases the speed of heat transfer to PP. In addition, the char layer increases the 2nd thermal degradation temperature and decreases the 2nd thermal degradation speed. The WPC treated with APP increases the 1st and 2nd degradation temperatures. In the case of WPC with high loading level of wood flour, the 1st thermal degradation temperature and 2nd thermal degradation rate were increased by the addition of APP, and then the amount of remnants at high temperature was increased by the increase of the APP loading level. In the case of WPC treated with APP, the amount of the remnants at high temperature was increased with the increase of wood flour content from 10 wt% to 50 wt%, indicating that char formation of the APP and wood flour occurred at the same time, resulting in high thermal stability effect by the increase of wood flour content.

• Korean Journal of Food Science and Technology
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• v.47 no.3
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• pp.293-298
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• 2015

This study aimed at characterizing the rheological properties and molecular weight of tara gum fractionated with ammonium sulfate. Tara gum was separated into six fractions (F1-F6) at different concentrations of ammonium sulfate, ranging from 12.21 to 28.67% (w/w). The yield of the tara gum fractions ranged between 4.98 and 17.47%, and their intrinsic viscosity ranged from 9.38 to 12.44 dL/g. The highest values of Huggins coefficient (k') and viscosity-molecular mass were observed in fraction F3. The shear viscosity of the tara gum fractions was measured by a cone-plate viscometer, clearly showing shear thinning behavior. Size-exclusion chromatography results showed that the molecular weight ranged between 635.42 and 776.71 kg/mol, and the F3 fraction exhibited higher values of molecular weight.