• Korean Journal of Materials Research
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• v.30 no.9
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• pp.447-452
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• 2020

In this work, α-Fe₂O₃ nanocrystals are synthesized by co-precipitation method and used as adsorbent to remove Cr⁶⁺, Cd²⁺, and Pb²⁺ from wastewater at room temperature. The prepared sample is evaluated by XRD, BET surface area, and FESEM for structural and morphological characteristics. XRD patterns confirm the formation of a pure hematite structure of average particle size of ~ 40 nm, which is further supported by the FESEM images of the nanocrystals. The nanocrystals are found to have BET specific surface area of ~ 39.18 m² g^-1. Adsorption experiments are carried out for the different values of pH of the solutions, contact time, and initial concentration of metal ions. High efficiency Cr⁶⁺, Cd²⁺, and Pb²⁺ removal occur at pH 3, 7, and 5.5, respectively. Equilibrium study reveals that the heavy metal ion adsorption of the α-Fe₂O₃ nanocrystals followed Langmuir and Freundlich isotherm models. The Cr⁶⁺, Cd²⁺, and Pb²⁺ adsorption equilibrium data are best fitted to the Langmuir model. The maximum adsorption capacities of α-Fe₂O₃ nanocrystals related to Cr⁶⁺, Cd²⁺, and Pb²⁺ are found to be 15.15, 11.63, and 20 mg g^-1, respectively. These results clearly suggest that the synthesized α-Fe₂O₃ nanocrystals can be considered as potential nano-adsorbents for future environmental and health related applications.

• Corrosion Science and Technology
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• v.16 no.1
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• pp.1-7
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• 2017

When aiming for an increased and more sustainable use of metals a thorough knowledge of the corrosion phenomenon as function of the local metal microstructure is of crucial importance. In this work, we summarize the information presented in our previous publications[1-3] and present an overview of the different local (electrochemical) techniques that have been proven to be effective in studying the relation between different microstructural variables and their different electrochemical behavior. Atomic force microscopy (AFM)[1], scanning electrochemical microscopy (SECM)[2], and electrochemical scanning tunneling microscopy (EC-STM)[3] were used in combination with electron backscatter diffraction (EBSD). Consequently, correlations could be identified between the grain orientation and grain boundary characteristics, on the one hand, and the electrochemical behavior on the other hand. The grain orientation itself has an influence on the corrosion, and the orientation of the neighboring grains also seems to play a decisive role in the dissolution rate. With respect to intergranular corrosion, only coherent twin boundaries seem to be resistant.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.37 no.4
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• pp.82-89
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• 2014

Recently, the mineral resource protection policies and regulations in production countries of natural resources including rare metals are becoming more stringent. Such environment makes which market has malfunction. In other word, those are not perfect or pure market. Therefore because each market of natural resources have special or unique characters, it is difficult to forecast their market prices. In this study, we constructed several models to estimate prices of natural resources using statistical tools like ARIMA and their business indices. And for examples, Indium and Coal were introduced.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.3
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• pp.557-565
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• 1997

Screw-shaped implants of commercially pure (c.p.) titanium, c.p. niobium, c.p. zirconium, and stainless steel(Sus 304) were inserted in the rabbit tibial bone over 12 weeks of follow-up. New developed torque gauge instrument was used to evaluate the implant holding power and a image analysis program coupled to a microscope was used for histomorphometry. The three best consecutive threads of each implant were measured. Quantitative analyses at 12 weeks revealed a partial bone contact to the four kinds investigated metals. There were no obvious adverse tissue reactions to any of the biomaterials. At 12 weeks the average removal torques for titanium, niobium and zirconium were better than that needed for Sus 304 screws, on the other hand high score of bony contact ratio of titanium and niobium were showed in comparison to those of zirconium and Sus 304. There was no significant differences in the amount of interfacial bone of zirconium and Sus 304 whereas there was significant difference in the torque forces of niobium and Sus 304. Three months after implant insertion, the average removal torque was 6.64 Ncm for the titanium, 6.57 Ncm for the niobium, 6.38 Ncm for the zirconium, and 4.25 Ncm for the Sus 304. On average bone contacts there were 51.24% in the titanium, 48.19% in the niobium, 31.79% in the zirconium, 23.54% in the Sus 304. Biocompatibility of the titanium, niobium and zirconium was acceptable level in comparison to the Sus 304.

• Journal of Welding and Joining
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• v.25 no.4
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• pp.35-41
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• 2007

In kinetic spraying process, the critical velocity is an important criterion which determines the deposition of a feedstock particle onto the substrate. In other studies, it was experimentally and numerically proven that the critical velocity is determined by the physical and mechanical properties and the state of materials such as initial temperature, size and the extent of oxidation. Compared to un-oxidized feedstock, oxidized feedstock required a greater kinetic energy of in-flight particle to break away oxide film during impact. The oxide film formed on the surface of particle and substrate is of a relatively higher brittleness and hardness than those of general metals. Because of its physical characteristics, the oxide significantly affected the deposition behavior and critical velocity. In this study, in order to investigate the effects of oxidation on the deposition behavior and critical velocity of feedstock, oxygen contents of Al feedstock were artificially controlled, individual particle impact tests were carried out and the velocities of in-flight Al feedstock was measured for a wide range of process gas conditions. As a result, as the oxygen contents of Al feedstock increased, the critical velocity increased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.1983-1993
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• 1996

For selected (pure and compound) metallic species effects of saturation ratio, temperature, particle size and number density on condensation mechanisms are first reviewed. The tendencies for vaporization and condensation differ between metallic species because of the significant differences in their saturation pressures. Then particle pressure of a metal vapor species at incineration temperature is calculated by simplifying waste as a compound of methane, chlorine and small amounts of metals and assuming a thermodynamic equilibrium state. Next the condition is assessed for which supersaturation of combustion gases by the species above the critical level for homogeneous condensation may occur, when the gases contain a large number of pre-existing particles such as entrained ashes. Regardless of the presence of chlorine in the waste, the homogeneous condensation of PbO vapors may occur, depending on number density of the pre-existing particles. However, when chlorine exists in the waste, the homogeneous condensation of PbCl$_2$vapors does not occur, which is similar to the case of Cd and Hg vapors. Thus these highly volatile species, PbCl$_2$, Cd, and Hg, may emit to atmosphere as vapor phase. In general, for reducing the emission of hazardous metallic species into the atmosphere, the number density of pre-existing particles has to be increased. For fixed particle number density, the temperature drop rate must be kept in low if the temperature at which a condensable vapor species emits from a incineration system is fixed, while the temperature drop rate must be kept in high if the residence time for which a condensable species stays in the system is fixed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.5
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• pp.500-506
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• 2024

The transparent electrode characteristics of the SnO₂/AgNi/SnO₂ (OMO) multilayer structures prepared by sputtering were investigated according to the annealing temperature. Ni-doped Ag of various compositions was selected as the metal layer and heat treatment was performed at 100~300℃ to evaluate the thermal stability of the metals. The manufactured OMO multilayer structures were heat treated for 6 hours at 400~600℃ in an N₂ atmosphere. The structural, electrical, and optical properties of the OMO structures before and after annealing were evaluated and analyzed using a UV-VIS spectrophotometer, 4-point probe, XPS, FE-SEM, etc. OMO with Ni-doped Ag shows improved performance due to the reduction of structural defects of Ag during annealing, but OMO structure with pure Ag shows degradation characteristics due to Ag diffusion into the oxide layer during high-temperature annealing. The figure of merit (FOM) of SnO₂/Ag/SnO₂ was highest at room temperature and gradually decreased as the heat treatment temperature increased. On the other hand, the FOM value of SnO₂/AgNi/SnO₂ mostly showed its maximum value at high temperature(~550℃). In particular, the FOM value of SnO₂/Ag-Ni (3.2 at%)/SnO₂ was estimated to be approximately 2.38×10^-2 Ω^-1. Compared to transparent electrodes made of other similar materials, the FOM value of the SnO₂/Ag-Ni (3.2 at%)/SnO₂ multilayer structure is competitive and is expected to be used as an alternative transparent conductive electrode in various devices.

• Korean Journal of Heritage: History & Science
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• v.52 no.1
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• pp.4-21
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• 2019

In this paper, 23 Silla gold earrings from the sixth and seventhand centuries, excavated from the Yeongnam region, were analyzed. Based on the silver content of the gold plate, they were classified into three types. The classifications included type I(20-50wt%), type II(10-20wt%) and type III (less than 10wt%). In the analysis process, the composition and morphological differences were identified on the surface of the gold plate. In the case of type I and II earrings, it was observed that the fine holes were concentrated in a relatively higher part of the gold content. The causes of the difference in the surface composition of the gold plate were divided into four categories: 1) surface treatment, 2) thermal diffusivity in the manufacturing process, 3) differences in composition of alluvial gold, and 4) the refining method of gold. It is possible that depletion gilding was attempted to increase the gold content while intentionally removing the other metals from the surface of the gold alloy in the portion where the gold deposit is relatively concentrated on the surface of the gold plating. The highest copper content was detected in the earring with the highest gold content of the analyzed earrings, and it was assumed that thermal diffusion had occurred between the gold plate and the metal rod during the manufacturing process rather than intentional addition. Copper was detected only in the thin ring earring type, and copper was not detected in the thick ring earring type or pendant type. It also proves that this earring has a high degree of tightness at higher temperatures, as there was an invisible edge finish on other earrings and horizontal wrinkles on the gold plate surface. In terms of the material of the gold plate, we examined whether the silver content of the gold plate was natural gold or added by alloy through analyzing the alluvial gold collected in the region. As a result of the analysis, it was found that on average about 13wt% of silver is included. This suggests that type II is natural gold, type III is refined gold, and type I seems to have been alloyed with natural gold. Here, we investigated the refining method introduced in the ancient literature, both at home and abroad, about the possibility of alloying silver after the refining process of type III earrings and then making pure gold. It was found that from ancient refining methods, silver which had been present in the natural gold was removed by reacting and combining with silver chloride or silver sulfide, and long-term efforts and techniques were required to obtain pure gold through this method. Therefore, it was concluded that the possibility of adding a small amount of silver in order to increase strength after making pure gold through a refining process is low.

• Journal of the Korean Vacuum Society
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• v.10 no.3
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• pp.289-297
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• 2001

Highly-porous $SnO_2$thin films were prepared for recognizing and detecting of the inflammable gases, like butane, propane, LPG, carbon monoxide. To obtain sensing films, Sn, Pt/Sn, Au/Sn, and Pt,Au/Sn films were deposited employing a thermal evaporator for Sn film and a sputter for novel metals of Pt or/and Au. These films were annealed for 2 h at $700^{\circ}C$ to form $SnO_2$-based thin films. The films showed the tetragonal structure and also exhibited many defects and porosity, which could give high sensitivity to thin films. The thin films showed high sensitivity and reproductivity to the tested gases(butane, propane, LPG, and carbon monoxide) to even to low gas concentrations in range of workplace environmental standards. Especially, Pt/$SnO_2$film showed the highest sensitivity to butane, LPG, and carbon monoxide. And pure $SnO_2$ film manifested the highest sensitivity to propane. By using the sensing patterns from the films, we could reliably recognize the kinds and the quantities of the tested inflammable gases within the range of the threshold limit values(TLV) and the lower explosion limit(LEL) through the principal component analysis(PCA).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.197-197
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• 2016

Commercially pure titanium (CP Ti) and Ti-6Al-4V alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element, such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}-stabilizer$ and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Manganese(Mn) plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Radio frequency(RF) magnetron sputtering in the various PVD methods has high deposition rates, high-purity films, extremely high adhesion of films, and excellent uniform layers for depositing a wide range of materials, including metals, alloys and ceramics like a hydroxyapatite. The aim of this study is to research the Mn coatings on the micro-pore formed Ti-29Nb-xHf alloys by RF-magnetron sputtering for dental applications. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. Mn coatings was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h at room temperature. The microstructure, phase and composition of Mn coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.