• Korean Chemical Engineering Research
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• v.57 no.4
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• pp.559-564
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• 2019

Hierarchical $ZnCo_2O_4$ hollow nanofibers were prepared by electrospinning and subsequent heat-treatment process. The spinning solution containing polystyrene (PS) nanobeads was electrospun to nanofibers. During heat-treatment process, PS nanobeads in the composite were decomposed and therefore generated numerous pores uniformly in the structure, which facilitated the heat transfer and gas penetration into the structure. The resulting hierarchical $ZnCo_2O_4$ hollow nanofibers were applied as an anode material for lithium-ion batteries. The discharge capacity of the nanofibers was $815mA\;h\;g^{-1}$ ($646mA\;h\;cm^{-3}$) after the 300th cycle at a high current density of $1.0A\;g^{-1}$. However, $ZnCo_2O_4$ nanopowders showed the discharge capacity of $487mA\;h\;g^{-1}$ ($450mA\;h\;cm^{-3}$) after 300th cycle. The excellent lithium ion storage property of the hierarchical $ZnCo_2O_4$ hollow nanofibers was attributed to the synergetic effects of the hollow nanofiber structure and the $ZnCo_2O_4$ nanocrystals composing the shell. The hierarchical hollow nanofiber structure introduced in this study can be extended to various metal oxides for various applications, including energy storage.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.2
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• pp.127-137
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• 2019

Zr electrorefining is demonstrated herein using Zirlo tubes in a chloride-fluoride mixed molten salt in the presence of $AlF_3$. Cyclic voltammetry reveals a monotonic shift in the onset of metal reduction kinetics towards positive potential and an increase in intensity of the additional peaks associated with Zr-Al alloy formation with increasing $AlF_3$ concentration. Unlike the galvanostatic deposition mode, a radial plate-type Zr growth is evident at the top surface of the salt during Zr electrorefining at a constant potential of -1.2 V. The diameter of the plate-type Zr deposit gradually increases with increasing $AlF_3$ concentration. Scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) analyses for the plate-type Zr deposit show that trace amount of Al is incorporated as Zr-Al alloys with different chemical compositions between the top and bottom surface of the deposit. Addition of $AlF_3$ is effective in lowering the residual salt content in the deposit and in improving the current efficiency for Zr recovery.

• Korean Journal of Heritage: History & Science
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• v.44 no.3
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• pp.62-77
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• 2011

Yi Sunsin's artifacts had been exhibited at Hyeonchungsa in Asan-si, Chungchungnam-do. These artifacts include Janggeom(Long swords), Okno(Jade ornament of Korea traditional hat), Yodae(Waist belt) and Dobae(Peach shaped wine cups) Gudae(Yodae's saucers). These were covered with dust and corroded due to long term display. Condition of these artifacts was examined for a re-opening of Yi Chungmugong Memorial Pavilion on 28 March 2011. Before conservation treatment of the artifacts, scientific analysis was conducted to identify the material of the artifacts. The result showed that the red paint on the hilt of the sword is composed of two layers. Pigments of two layers were found to be hematite and cinnabar mixed with red lead respectively. Mixed layer was assumed to have been applied recently. Also it was found that the blade of the sword was repainted using chrome yellow($PbCrO_4$). Considering the time limit, conservation treatment focused on stabilization of damaged area and prevention of futher risk during display.

• Korean Journal of Heritage: History & Science
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• v.52 no.3
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• pp.160-171
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• 2019

The sword with a ring pommel, which was excavated from the first stone chamber of the ancient tombs of Jeongchon Village in Naju, is a sword with a pentagon undecorated ring pommel consisting of a mother sword and two child swords. The sword with an undecorated ring pommel of Jeongchon comprises a ring pommel, a hilt, a knife, and a knife end decoration. This sword was coated with lacquer. The ring pommel is an iron frame covered with silver plate; however the silver tarnished into a light purple due to silver chloride corrosion, and iron corrosion originated from the inside is visible on the surface. Silver chloride corrosion is produced when silver objects are exposed to water, dissolved salts, and dissolved chloride ions when in a buried state. It changes objects into powder, making it difficult to preserve original shapes. The other silver artifacts found in the Jeongchon ancient tombs show similar signs of corrosion. The results of X-ray irradiation and a CT analysis showed that the sword had a ring at the end of the handle, a T-shaped hilt, and was probably connected to the handle end of a knife. If the shape of the mother sword can be inferred from the child swords, the mother sword had a ring pommel, decorations of the handle, covered with silver plate, and a gold ring and a silver line wound around the handle. It is assumed that the ring pommel was connected to the knife by welding because no holes were observed. The end decoration of the knife was made by using an iron plate formed into a shape, half covered by silk, and the other half decorated with silver plate and a gold ring. The sword with an undecorated ring pommel excavated from the ancient tombs of Jeongchon Village comprises the metals of gold, silver, and iron, and includes features of Baekje, Silla, and Gaya, which highlights the influence of surrounding historic sites and various cultures.

• Journal of Conservation Science
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• v.35 no.3
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• pp.253-258
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• 2019

The gilt bronze statue, Seated Avalokiteshvara with a Thousand Hands, of the Goryeo dynasty, is the only one in Korea of its kind that has undergone a conservation process for the special exhibition entitled GORYEO: The Glory of Korea. For the conservation treatment, first, a component analysis (XRF) was conducted, and a manufacturing technique (CT) was analyzed. The results of the investigation revealed that the statue was alloyed with Cu, Sn, and Pb ternary bronze. Its surface, except for the detached plating layers, was originally plated using the mercury amalgam method. This statue was assembled after separately casting each part of the body, such as the left and right arms and the wrists, including the hands, with objects. In particular, each wrist was cast and fitted with a metal nail to express each object in the hands more precisely. Inside the statue, there were five iron cores: two for the head, one for the left elbow, one for the right flank, and one for the right waist. For the preservative treatment, natural adhesive agents, including vegetable gelatin and glue (20%), were mixed with alcohol to protect the base metal and adhere to the plating layers. Using synthetic resin (CDK 520+SN-sheet) for the damaged parts, the restored parts could be attached and detached to/from the statue. Eventually, the compositional analysis and conservation treatment left the statue in a stable condition and ready for exhibitions and future studies.

• Korean Journal of Heritage: History & Science
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• v.54 no.2
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• pp.216-239
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• 2021

Inlay (入絲), a poetic technique of digging grooves in the surface of crafts and decorating them with metal materials, was used throughout the royal daily routines, ceremonies and government officials of the Joseon Dynasty. The government-owned handicraft industry in the Joseon Dynasty was composed of craftsmen belonging to central and local government offices and was operated mainly by government-owned craftsmen. The inlay craftsman was transferred to the central government office and was in charge of inlay poetry for crafts. The current records of Korean inlay craftsmen are concentrated in the state-owned handicraft industry. In the state-owned handicraft industry, the government offices of inlay craftsmen can be divided into Kongjo (工造), Sangeuiwon (尙衣院), and the military. Here the election of a temporary government office for airspace is added. The government offices and military inlay craftsmen who use inlay crafts are assigned, and the inlay craftsmen are placed separately in the temporary office where the fine division of labor is developed. It can be made by utilizing craftsmen. The operation of these production systems was indispensable in pre-modern Korean society, where crafts had to be produced by hand. In this paper, we investigated the roles and job types of craftsmen in the state-owned handicraft industry during the Joseon Dynasty, focusing on inlay craftsmen. Although the details applied to the characteristics and materials of the field, labor supply and demand, etc. are different, Korea pursued crafts for various purposes through craftsmanship within the framework of the basic state-owned handicraft policy . The institutional equipment for implementation was almost common. We believe that adding and analyzing some literature records and relics will help us to study the crafts of the Joseon era in more detail.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.65-70
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• 2021

In this study, interfacial properties and mechanical properties of joints were reported after Cu pads finished with organic solderability preservative (OSP) on flame retardant-4 (FR-4) printed circuit board (PCB) and electronic components were joined with a Sn-57Bi-1Ag solder paste by using a laser bonding process. The laser bonding process was performed under various bonding conditions with changing a laser power and a bonding time and effects of bonding conditions on interfacial and mechanical properties of joints were analyzed. In order to apply for industry, properties of bonding joints using a reflow bonding process which are widely used were compared. When the laser bonding process were performed, we observed that Cu₆Sn₅ intermetallic compounds (IMCs) were fully formed at the interface although the bonding times were very short about 2 and 3 s. Furthermore, void formations of the joints by using the laser bonding process were suppressed at the joints with comparing to the reflow bonding process and shear strengths of bonding joints were higher than that by using the reflow bonding process. Therefore, in spite of a very short bonding time, it is expected that joints will be stably formed and have a high mechanical strength by using the laser bonding process.

• Resources Recycling
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• v.30 no.4
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• pp.11-19
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• 2021

Arsenic (As) oxidation followed by precipitation from a high-As(III)-containing leaching solution derived from a sulfidic ore was investigated in this study to remove aqueous As from the solution using activated carbon (AC) with air injection as an oxidant. To obtain the initial leaching solution, a domestic sulfidic ore was leached in a sulfuric acid solution at pH 1 and 50℃ for 95 h, and approximately 7 g/L of Fe and 3 g/L of As were leached out. To determine the effect of the oxidative reaction utilizing AC with air injection, the leaching solution was tested under the following five oxidative conditions at an initial pH of 1 and 90℃ for 72 h: air-only injection; air injection with 1, 5, and 10 w/v% of AC addition; and H₂O₂ addition. The tests in the presence of both air and AC revealed that the oxidation kinetics and As removal were improved by the reaction between the metallic species and the surface group formed on the AC surface. In addition, the greater the amount of AC added, the better was the reaction efficiency, removing 93-94% of As with more than 5 w/v% of AC addition. Finally, X-ray diffraction analysis confirmed that the precipitate formed from the oxidative reaction was scorodite (FeAsO₄·2H₂O).

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.175-183
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• 2022

With the expansion of the automobile market, the demand for Nd as an essential rare earth material for automobile motors is rapidly increasing. Research on the calcio-thermic reduction process between Nd₂O₃ and calcium-based alloys has been extensively studied in order to manufacture Nd. In this study, Ca-Cu, as a reducing for Nd₂O₃, was prepared by electrolysis in CaCl₂ molten salt. Cu wire and graphite were employed as a working electrode and a counter electrode for electrolysis reaction, respectively. The reference electrode was manufactured by putting Ag wire in a mixture of AgCl and CaCl₂ at a ratio of 1:99 mol%. The cyclic voltammetry results showed that the deposition of Ca²⁺ on the surface of working electrode was observed from a potential of -1.8 V, and the reduction potential of Ca²⁺ decreased as the reaction temperature increased. The diffusion coefficient of Ca²⁺ calculated by the chronoamperometry experiment was found to be 5.4(±6.8)×10^-6 cm²/s. In addition, Ca-Cu liquid alloy was prepared by applying a constant potential to Cu electrodes. The element ratio of Ca-Cu alloy formed by applying a potential of -2.0 V was found to Ca:Cu=1:4.

• Applied Chemistry for Engineering
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• v.33 no.3
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• pp.302-308
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• 2022

The PdO nanoparticle with large surface area was selected to solve the environmental pollution problem at fire range caused by high energy explosives research department explosive (RDX) and high melting explosive (HMX). By simulating water pollution, RDX and HMX nitramine explosives were dissolved in water, followed by the degradation reaction at 313 K by adding PdO. In order to measure the degradation reaction rate of explosives, ¹H NMR was used, which can monitor the reaction rate without losing sample during reaction, and observe the progress of the reaction through the spectrum. The results showed that the degradation of RDX and HMX by PdO nanoparticles are pseudo-first order reaction. The degradation of explosives compounds were observed via the chemical shift and peak intensity analysis of NMR peaks. The measured rate constants for these reactions of RDX and HMX were 2.10 × 10^-2 and 6.35 × 10^-4 h^-1, respectively. This study showed that the application of PdO nanoparticles for explosives degradation is a feasible option.