• Korean Journal of Materials Research
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• v.31 no.10
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• pp.552-561
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• 2021

For the purpose of manufacturing a high efficiency TiO₂ photocatalyst, B-doped TiO₂ photocatalysts are synthesized using a plasma electrolytic oxidation method in 0.5 M H₂SO₄ electrolyte with different concentrations of H₃BO₃ as additive. For the B doped TiO₂ layer fabricated from sulfuric electrolyte having a higher concentration of H₃BO₃ additive, the main XRD peaks of (101) and (200) anatase phase shift gradually toward the lower angle direction, indicating volume expansion of the TiO₂ anatase lattice by incorporation of boron, when compared with TiO₂ layers formed in sulfuric acid with lower concentration of additive. Moreover, XPS results indicate that the center of the binding energy peak of B1s increases from 191.45 eV to 191.98 eV, which suggests that most of boron atoms are doped interstitially in the TiO₂ layer rather than substitutionally. The B doped TiO₂ catalyst fabricated in sulfuric electrolyte with 1.0 M H₃BO₃ exhibits enhanced photocurrent response, and high efficiency and rate constant for dye degradation, which is ascribed to the synergistic effect of the new impurity energy band induced by introducing boron to the interstitial site and the improvement of charge transfer reaction.

• Journal of the Korean Electrochemical Society
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• v.11 no.1
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• pp.42-46
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• 2008

Even though fuel cell have high efficiency when pure hydrogen from gas tank is used as a fuel source, it is more beneficial to generate hydrogen from city gas (mainly methane) in residential application such as domestic or office environments. Thus hydrogen is generated by reforming process using hydrocarbon. Unfortunately, the reforming process for hydrogen production is accompanied with unavoidable impurities. Impurities such as CO, $CO_2$, $H_2S$, $NH_3$, $CH_4$, and $CH_4$ in hydrogen could cause negative effects on fuel cell performance. Those effects are kinetic losses due to poisoning of the electrode catalysts, ohmic losses due to proton conductivity reduction including membrane and catalyst ionomer layers, and mass transport losses due to degrading catalyst layer structure and hydrophobic property. Hydrogen produced from reformer eventually contains around 73% of $H_2$, 20% or less of $CO_2$, 5.8% of less of $N_2$, or 2% less of $CH_4$, and 10ppm or less of CO. This study is aimed at investigating the effect of carbon dioxide on fuel cell performance. The performance of PEM fuel cell was investigated using current vs. potential experiment, long run(10 hr) test, and electrochemical impedance measurement when the concentrations of carbon dioxide were 10%, 20% and 30%. Also, the concentration of impurity supplied to the fuel cell was verified by gas chromatography(GC).

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.377-377
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• 2012

Microprocessor technology now relies on copper for most of its electrical interconnections. Because of the high diffusivity of copper, Atomic layer deposition (ALD) $TaN_x$ is used as a diffusion barrier to prevent copper diffusion into the Si or $SiO_2$. Another problem with copper is that it has weak adhesion to most materials. Strong adhesion to copper is an essential characteristic for the new barrier layer because copper films prepared by electroplating peel off easily in the damascene process. Thus adhesion-enhancing layer of cobalt is placed between the $TaN_x$ and the copper. Because, cobalt has strong adhesion to the copper layer and possible seedless electro-plating of copper. Until now, metal film has generally been deposited by physical vapor deposition. However, one draw-back of this method is poor step coverage in applications of ultralarge-scale integration metallization technology. Metal organic chemical vapor deposition (MOCVD) is a good approach to address this problem. In addition, the MOCVD method has several advantages, such as conformal coverage, uniform deposition over large substrate areas and less substrate damage. For this reasons, cobalt films have been studied using MOCVD and various metal-organic precursors. In this study, we used $C_{12}H_{10}O_6(Co)_2$ (dicobalt hexacarbonyl tert-butylacetylene, CCTBA) as a cobalt precursor because of its high vapor pressure and volatility, a liquid state and its excellent thermal stability under normal conditions. Furthermore, the cobalt film was also deposited at various $H_2/NH_3$ gas ratio(1, 1:1,2,6,8) producing pure cobalt thin films with excellent conformality. Compared to MOCVD cobalt using $H_2$ gas as a reactant, the cobalt thin film deposited by MOCVD using $H_2$ with $NH_3$ showed a low roughness, a low resistivity, and a low carbon impurity. It was found that Co/$TaN_x$ film can achieve a low resistivity of $90{\mu}{\Omega}-cm$, a low root-mean-square roughness of 0.97 nm at a growth temperature of $150^{\circ}C$ and a low carbon impurity of 4~6% carbon concentration.

• Resources Recycling
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• v.26 no.6
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• pp.84-90
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• 2017

The electro-refining process was performed to recovery high purity copper from low grade copper containing sludge in sulfuric acid. The surface morphologies and roughness of electro-refining copper were analyzed with variation of the type and concentration of organic additives, the best surface morphology was obtained 5 ppm of the gelatin type and 5 to 10 ppm of the thiol type organic additive. The crude metal consisted of copper with 86.635, 94.969 and 99.917 wt.%, several impurity metals of iron, nickel, cobalt and tin by pyro-metallurgical process. After electro-refining process, the purity of copper increases to 3N or 4N grade. The impurity concentrations and copper purities of copper crude metals, electrolyte and electro-refining copper were analyzed using ICP-OES, the electro-refining time and purity of copper crude metal to recover 4N grade copper were deduced.

• Resources Recycling
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• v.31 no.2
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• pp.20-32
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• 2022

This study implemented a chelating agent (Ethylenediaminetetraacetic acid, EDTA) in purification to obtain high-purity vanadium pentoxide (V₂O₅) for use in VRFB (Vanadium Redox Flow Battery). V₂O₅ (powder) was produced through the precipitation recovery of ammonium metavanadate (NH₄VO₃) from a vanadium solution, which was prepared using a low-purity vanadium raw material. The initial purity of the powder was estimated to be 99.7%. However, the use of a chelating agent improved its purity up to 99.9% or higher. It was conjectured that the added chelating agent reacted with the impurity ions to form a complex, stabilizing them. This improved the selectivity for vanadium in the recovery process. However, the prepared V₂O₅ powder exhibited higher contents of K, Mn, Fe, Na, and Al than those in the standard counterparts, thus necessitating additional research on its impurity separation. Furthermore, the vanadium electrolyte was prepared using the high-purity V₂O₅ powder in a newly developed direct electrolytic process. Its analytical properties were compared with those of commercial electrolytes. Owing to the high concentration of the K, Ca, Na, Al, Mg, and Si impurities in the produced vanadium electrolyte, the purity was analyzed to be 99.97%, lower than those (99.98%) of its commercial counterparts. Thus, further research on optimizing the high-purity V₂O₅ powder and electrolyte manufacturing processes may yield a process capable of commercialization.

• Resources Recycling
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• v.24 no.6
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• pp.9-16
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• 2015

In a recycling scheme of spent lithium ion batteries, a co-precipitation process for the re-synthesis of precursor is essential after the leaching of lithium ion battery scraps. In this study, the effect of ammonia as impurity during the co-precipitation process was investigated in order to re-synthesize a precursor of Ni-rich cathode active material $LiNi_{0.6}Co_{0.2}Mn_{0.2}O_2$ (NCM 622). As ammonia concentration increases from 1 M (the optimum condition for synthesis of the precursors based on 2 M of metal salt solution) to 4 M, the composition of obtained precursors deviates from the designed composition, most notably for Ni. The Ni co-precipitation efficiency gradually decreases from 100% to 87% when the concentration of ammonia solution increases from 1 M to 4 M. Meanwhile, the morphological properties of the obtained precursors such as sphericity, homogeneity and size distribution of particles were also investigated.

• Resources Recycling
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• v.29 no.1
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• pp.17-24
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• 2020

In this study, rare earth elements (REE) leaching from a refractory REE ore containing goethite as a major gangue mineral was conducted, introducing a two-stage method of chemical decomposition-acid leaching. At the chemical decomposition step, using one of alkaline agent, NaOH, the ore was decomposed, changing NaOH concentration from 20 to 50 wt% at 10% (w/w) of pulp density and the maximum temperature achieved without boiling at each NaOH concentration. With increasing NaOH concentration, light REE (Ce, La and Nd) and iron were concentrated in the solid phase which is the decomposed product, while aluminum (Al) and phosphorus (P) were removed to the liquid phase, and their concentrations in the solid phase were down to 0.96 and 0.17%, respectively. In addition, through XRD analysis, it was found that the crystallinity of goethite was considerably decreased. At the acid leaching step, the product decomposed by 50 wt% NaOH was leached at 3.0 M HCl and 80 ℃ for 3 hr, then the REE leaching efficiency was above 94% (Ce 80%), and the leaching efficiencies of Al and P were decreased to 12 and 0%, respectively. Therefore, in terms of both REE leaching efficiency and impurity removal, those decomposition and leaching conditions were chosen as optimum processing methods of the investigated material. In terms of REE leaching mechanism, because REE and iron leaching efficiencies showed the positive correlation each other, so it can be concluded that decreasing crystallinity of goethite affect the improvement of REE leaching.

• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.1
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• pp.8-11
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• 2012

Purpose : Among quality control items, the radiochemical impurity must be below 10% of total radioactivity. In this regard, as the recently commercialized automatic synthesis module produces a large amount of 18F-FDG, radiolysis of radiopharmaceuticals is very likely to occur. Thus, this study compared the changes in radiochemical purity regarding radiolysis of $^{18}F$-FDG according to automatic synthesis module. Materials and methods : Cyclotron (PETtrace, GE Healthcare) was used to produce $^{18}F$ and automatic synthesis module (FASTlab, Tracerlab MX, GE Healthcare) was used to achieve synthesis into FDG. For radiochemical purity, Radio-TLC Scanner (AR 2000, Bioscan), GC (Gas Chromatograph, Agilent 7890A) was used to measure the content of ethanol included in $^{18}F$-FDG. Glass board applied with silica gel ($1{\times}10cm$) was used for stationary phase while a mixed liquid formed of acetonitrile and water (ratio 19:1) was used for mobile phase. High-concentration and low-concentration $^{18}F$-FDG were produced in each synthesis module and the radiochemical purity was measured every 2 hours. Results : The purity in low-concentration (below 2.59 GBq/mL) was measured as 99.26%, 98.69%, 98.25%, 98.09% in Tracerlab MX and as 99.09%, 97.83%, 96.89%, 96.62% in FASTlab according to 0, 2, 4, 6 hours changes, respectively. The purity in high-concentration (above 3.7 GBq/mL) was measured as 99.54%, 96.08%, 93.77%, 92.54% in Tracerlab MX and as 99.53%, 95.65%, 92.39%, 89.82% in FASTlab according to 0, 2, 4, 6 hours changes, respectively. Also, ethanol was not detected in GC of $^{18}F$-FDG produced in FASTlab, while 100~300 ppm ethanol was detected in Tracerlab MX. Conclusion : Whereas the change of radiochemical purity was only 3% in low-concentration $^{18}F$-FDG, the change was rapidly increased to 10% in high-concentration. Also, higher radiolysis were observed in $^{18}F$-FDG produced in FASTlab than Tracerlab MX. This is because ethanol is included in the synthesis stage of Tracerlab MX but not in the synthesis stage of FASTlab. Thus, radiolysis is influenced by radioactivity concentration than the inclusion of ethanol, which is the radioprotector. Therefore, after producing high-concentration $^{18}F$-FDG, the content must be diluted through saline to lower concentration.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.358-358
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• 2012

The application of BZO (Boron-doped Zinc Oxide) films use as the TCO(Transparent Conductive Oxide) material for display and solar cell industries, where the conductivity of the BZO films plays a critical role for improvement of cell performance. Thin BZO films are deposited on glass substrates by using RF sputter system. Then charging flow rates of O2 gas from zero to 10 sccm, thereby controlling the impurity concentration of BZO. BZO deposited on soda lime glass and RF power was 300 W, frequency was 13.56 MHz, and working pressure was $5.0{\times}10-6$ Torr. The Substrate and glass between distance 200 mm. We measured resistivity, conductivity, mobility by hall measurement system. Optical properties measured by photo voltaic device analysis system. We measured surface build according to oxygen flow rate from XPS (X-ray Photoelectron Spectroscopy) system. The profile of the energy distribution of the electrons emitted from BZO films by the Auger neutralization is measured and rescaled so that Auger self-convolution arises, revealing the detail structure of the valence band. It may be observed coefficient ${\gamma}$ of the secondary electron emission from BZO by using ${\gamma}$-FIB (Gamma-Focused Ion Beam) system. We observed the change in electrical conductivity by correlation of the valence band structure. Therefore one of the key issues in BZO films may be the valence band that detail structure dominates performance of solar cell devices. Demonstrating the secondary electron emission by the Auger neutralization of ions is useful for the determination of the characteristics of BZO films for solar cell and display developments.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3407-3412
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• 2012

The Ti incorporation at Fe-site in the double perovskite lattice of $Sr_2FeNbO_6$ (SFNO) system is studied. The Ti concentration optimization yielded an efficient photocatalyst. At an optimum composition of Ti as x = 0.07 in $Sr_2Fe_{1-x}Ti_xNbO_6$, the photocatalyst exhibited 2 times the quantum yield for photolysis of $H_2O$ in presence of $CH_3OH$, than its undoped counterpart under visible light (${\lambda}{\geq}420nm$). Heavily Ti-doped $Sr_2Fe_{1-x}Ti_xNbO_6$ lattice exhibited poor photochemical properties due to the existence of constituent impurity phases as observed in the structural characterization, as well as deteriorated optical absorption. The higher electron-density acquired by n-type doping seem to be responsible for the more efficient charge separation in $Sr_2Fe_{1-x}Ti_xNbO_6$ (0.05 < x < 0.4) and thus consequently displays higher photocatalytic activity. The Ti incorporated structure also found to yield stable photocatalyst.