• Journal of Korean Society on Water Environment
• /
• v.33 no.6
• /
• pp.736-743
• /
• 2017

In this study, 4-nonylphenol (4-NP), an endocrine disrupting chemical, was removed by ozone treatment processes under the various experimental conditions including UV irradiation, $TiO_2$ addition. The ozone flow rate and concentration were maintained at $1.0L{\cdot}min^{-1}$ and $70{\pm}5mg{\cdot}L^{-1}$. The pH, COD and TOC of the samples were obtained every 10 minutes for 60 minutes in laboratory scale batch reactor. We found that the combination of UV irradiation and $TiO_2$ addition for ozonation improves the removal efficiency of COD and TOC in 4-NP aqueous solution. In case of the $O_3/UV/TiO_2$ system, COD and TOC were greatly reduced to 85.3 ~ 94.0% and 89.2 ~ 97.2%, respectively. 4-NP degradation rate constants, $k_{COD}$ and $k_{TOC}$, were calculated based on the COD and TOC values. Significantly, $k_{COD}$ and $k_{TOC}$ were improved in the $O_3/UV/TiO_2$ treatment process compared with single $O_3$ process, because the oxidation and the mineralization of 4-NP were increased by generating of the hydroxyl radical. The $k_{COD}$ and $k_{TOC}$ were obtained to be $5.81{\times}10^{-4}{\sim}10.8{\times}10^{-4}sec^{-1}$ and $11.9{\times}10^{-4}{\sim}19.4{\times}10^{-4}sec^{-1}$ in the $O_3/UV/TiO_2$ process. Activation energy ($E_a$) of ozone oxidation reaction based on $k_{COD}$ and $k_{TOC}$ were increased in order of $O_3/UV/TiO_2$ < $O3/UV$ < $O_3/TiO_2$ < $O_3$ process. It was confirmed that the addition of $TiO_2$ and UV irradiation to the ozone oxidation reaction significantly reduced the $E_a$ value and the degradation of 4-NP.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.10
• /
• pp.1289-1295
• /
• 2012

A process heat exchanger (PHE) in a nuclear hydrogen system is a key component for transferring the considerable heat generated in a very high temperature reactor (VHTR) to a chemical reaction that yields a large quantity of hydrogen. A performance test on a small-scale PHE prototype made of Hastelloy-X is underway in a small-scale gas loop at the Korea Atomic Energy Research Institute. Previous research on the high-temperature structural analysis of the small-scale PHE prototype had been performed using base material properties. In this study, a high-temperature structural analysis considering the mechanical properties in the weld zone was performed, and the obtained results were compared with those of the previous research.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.148-149
• /
• 2012

This paper reports doping of carbon atoms in GaN layer, which based on dimethylhydrazine (DMHy) and growth temperature. It is well known that dislocations can act as non-radiative recombination center in light emitting diode (LED). Recently, many researchers have tried to reduce the dislocation density by using various techniques such as lateral epitaxial overgrowth (LEO) [1] and patterned sapphire substrate (PSS) [2], and etc. However, LEO and PSS techniques require additional complicated steps to make masks or patterns on the substrate. Some reports also showed insertion of carbon doped layer may have good effect on crystal quality of GaN layer [3]. Here we report the growth of GaN epitaxial layer by inserting carbon doped GaN layer into GaN epitaxial layer. GaN:C layer growth was performed in metal-organic chemical vapor deposition (MOCVD) reactor, and DMHy was used as a carbon doping source. We elucidated the role of DMHy in various GaN:C growth temperature. When growth temperature of GaN decreases, the concentration of carbon increases. Hence, we also checked the carbon concentration with DMHy depending on growth temperature. Carbon concentration of conventional GaN is $1.15{\times}1016$. Carbon concentration can be achieved up to $4.68{\times}1,018$. GaN epilayer quality measured by XRD rocking curve get better with GaN:C layer insertion. FWHM of (002) was decreased from 245 arcsec to 234 arcsec and FWHM of (102) decreased from 338 arcsec to 302 arcsec. By comparing the quality of GaN:C layer inserted GaN with conventional GaN, we confirmed that GaN:C interlayer can block dislocations.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.23 no.2
• /
• pp.199-207
• /
• 2015

Solid materials of ammonia sources with SCR have been considered for the application of lean NOx reduction in automobile industry, to overcome complex problems of liquid urea based SCR. These solid materials produce ammonia gas directly with proper heating and can be packaged by compact size, because of high volumetric ammonia density. Among ammonium salts and metal ammine chlorides, calcium ammine chloride was focused on this paper due to low decomposition temperature. In order to make calcium ammine chloride in lab-scale, simple reactor and glove box was designed and built with ammonium gas tank, regulator, and sensors. Basic test conditions of charging ammonia gas to anhydrous calcium chloride are chosen from equilibrium vapor pressure by Van't Hoff plot based on thermodynamic properties of materials. Synthetic method of calcium ammine chloride were studied for different durations, temperatures, and pressures with proper ammonia gas charged, as a respect of ammonia gas adsorption rate(%) from simple weight calculations which were confirmed by IC. Also, lab-made calcium ammine chloride were analyzed by TGA and DSC to clarify decomposition step in the equations of chemical reaction. To understand material characteristics for lab-made calcium ammine chloride, DA, XRD and FT-IR analysis were performed with published data of literature. From analytical results, water content in lab-made calcium ammine chloride can be discovered and new test procedures of water removal were proposed.

• Journal of Powder Materials
• /
• v.23 no.2
• /
• pp.91-94
• /
• 2016

High-quality colloidal CdSe/ZnS (core/shell) is synthesized using a continuous microreactor. The particle size of the synthesized quantum dots (QDs) is a function of the precursor flow rate; as the precursor flow rate increases, the size of the QDs decreases and the band gap energy increases. The photoluminescence properties are found to depend strongly on the flow rate of the CdSe precursor owing to the change in the core size. In addition, a gradual shift in the maximum luminescent wave (${\lambda}_{max}$) to shorter wavelengths (blue shift) is found owing to the decrease in the QD size in accordance with the quantum confinement effect. The ZnS shell decreases the surface defect concentration of CdSe. It also lowers the thermal energy dissipation by increasing the concentration of recombination. Thus, a relatively high emission and quantum yield occur because of an increase in the optical energy emitted at equal concentration. In addition, the maximum quantum yield is derived for process conditions of 0.35 ml/min and is related to the optimum thickness of the shell material.

• Journal of Energy Engineering
• /
• v.15 no.2 s.46
• /
• pp.107-117
• /
• 2006

The status of water splitting thermochemical cycle for hydrogen production was reviewed in this article. Mass production of hydrogen could be possible using the thermochemical process which is similar to the concept of conventional chemical reaction system if the high temperature heat source is available. The mediators (chemicals and reagents) should be used to split chemically stable water, and should be recycled in a closed cycle in order to be environmentally acceptable. Though there is no process to reach commercial stage, IS cycle, two-step cycles based on metallic oxide such as ZnO/Zn, $Fe_3O_4/FeO$ and the associated cycles are attracted due to their possibilities of application. Development of materials for high temperature and/or corrosive conditions during thermochemical process is still important topic in some thermochemical processes.

• Applied Chemistry for Engineering
• /
• v.10 no.2
• /
• pp.231-236
• /
• 1999

Several series of morphologically controlled $MoO_3$/$SiO_2$ catalysts were prepared, characterized, and tested for hydrodesulfurization (HDS) of dibenzothiophene (DBT) activity. Molybdenum surface loaded with 4.0 atoms $Mo/nm^2$ was prepared as sintered hexagonal and sintered orthorhombic, as well as a novel "well dispersed hexagonal" phase. Characterization by XRD, Raman, and $O_2$ chemisorption results reveals that the dispersion of $MoO_3$ over silica depends on the final $MoO_3$ phase in the order of; sintered hexagonal < sintered orthorhombic < dispersed hexagonal phase. Temperature programmed reduction (TPR) results show that both bulk and dispersed microcrystalline of $MoO_3$ reduce to $MoO_2$ at $650^{\circ}C$ and to Mo metal at $1000^{\circ}C$. HDS of DBT was performed in a differential reactor at 30 atm over the temperature range $350{\sim}500^{\circ}C$. Activity of $MoO_3$/$SiO_2$ toward HDS of DBT is proportional to dispersion.

• Applied Chemistry for Engineering
• /
• v.17 no.5
• /
• pp.547-551
• /
• 2006

In the reactor following the American standard test method (ASTM) D5757-95 and lab-scale fluidized bed combustor, the attrition characteristics of sand and ash of Korean anthracite were investigated. The attrition characteristics, such as particle size distribution of fly ash, attrition rate, and attrition ratio etc, were studied with variation of gas velocities. The particle attrition of ash was more active than sand which was generally used as a fluidized material and also the attrition index of ash taken by ASTM D5757-95 was 5 times higher than that of sand. The formation of fine particles continuously occurred due to particle attrition with increasing gas velocities. The following equation has been suggested for attrition rate of ash. $$\frac{dW}{dt}=-3.18{\times}10^{-7}(U-U_{mf})W$$.

• Journal of the Korean institute of surface engineering
• /
• v.44 no.4
• /
• pp.131-136
• /
• 2011

A kinetic study has been made for the growth of nanocrystalline diamond (NCD) particles to a continuous thin film on silicon substrate in a microwave plasma chemical vapor deposition reactor. Parameters of deposition have been microwave power of 1.2 kW, the chamber pressure of 110 Torr, and the Ar/$CH_4$ ratio of 200/2 sccm. The deposition has been carried out at temperatures in the range of $400\sim700^{\circ}C$ for the times of 0.5~16 h. It has been revealed that a continuous diamond film evolves from the growth and coalescence of diamond crystallites (or particles), which have been heterogeneously nucleated at the previously scratched sites. The diamond particles grow following an $h^2$ = k't relationship, where h is the height of particles, k' is the particle growth rate constant, and t is the deposition time. The k' values at the different deposition temperatures satisfy an Arrhenius equation with the apparent activation energy of 4.37 kcal/mol or 0.19 eV/ atom. The rate limiting step should be the diffusion of carbon species over the Si substrate surface. The growth of diamond film thickness (H) shows an H = kt relationship with deposition time, t. The film growth rate constant, k, values at the different deposition temperatures show another Arrhenius-type expression with the apparent activation energy of 3.89 kcal/mol or 0.17 eV/atom. In this case, the rate limiting step might be the incorporation reaction of carbon species from the plasma on the film surface.

• Journal of the Korean institute of surface engineering
• /
• v.47 no.3
• /
• pp.99-103
• /
• 2014

The encapsulation method of flexible organic light emitting devices (OLEDs) was investigated for the structure of ITO / 2-TNATA / NPB / $Alq_3$ : Rubrene (1 vol.%) / $Alq_3$ / LiF / Al / $Alq_3$ / LiF / Al (OLED #1), on which $SiN_x$ thin film was deposited and metal film was attached to protect the damage of OLED from oxygen and moisture. The $SiN_x$ thin film was deposited by plasma enhanced chemical vapor deposition (PECVD) method using $SiH_4$ of 20 sccm and $N_2$ of 15~35 sccm as reactor gases. The optimum $SiN_x$ deposition condition was found to be 20 sccm $SiH_4$ and 20 sccm $N_2$ from the Ca test of the fabricated $SiN_x$ thin film. The life time of OLED #1, OLED #1 / $SiN_x$ 200 nm, OLED #1 / $SiN_x$ 400 nm and OLED #1 / $SiN_x$ 400 nm / metal film was 7, 12, 25, and 45 hours, respectively. In conclusion, it has been shown that the lifetime of OLEDs can be improved more than 6 times by $SiN_x$ film and a metal film encapsulation.