Current Nanoscience (v.10, #1)
Graphical Abstracts: (i-xiii).
Editorial: Proceeding of the 12th International Symposium on Novel and Nano Materials (ISNNM-2012) by Jung-Ho AHN (2-2).
Effect of Micro Ti and TiO2 P-25 Nano Powder Addition on Mechanical Properties of TiO2 Nanopowders by Hyo Young Park, Rumman Md Raihanuzzaman, Han-Jin Ko, Joon-Min Park, Young-Choon Kim, Soon-Jik Hong (3-6).
Sintered bodies of TiO2nanopowders were fabricated by magnetic pulsed compaction (MPC) and subsequent 2 step sinteringin this study and then, the effect of micro Ti and P-25 nano TiO2 powder addition on density, shrinkage and hardness was investigated.The optimum processing conditions in order to find the maximum density, hardness and shrinkage were found to be 0.5~0.7 GPa MPCpressure and 1450oC sintering temperature, with addition of 6% of TiO2 P-25 nanopowder. High pressure and rapid compaction usingmagnetic pulsed compaction (MPC) enhanced the density with increasing MPC pressure up to 0.7 GPa without the formation of surfaceor edge cracks on the consolidates bulks, and significantly reduced the shrinkage rate (about 15 in this case) of the sintered bulks comparedto the general process (about 18%). Overall, most of the properties showed gradual changes with increasing MPC-ed pressure andTiO2 P-25 nanopowder content.
Preparation and Characterization of Copper Nanoparticles via the Liquid Phase Plasma Method by Heon Lee, Sung Hoon Park, Seong-Gyu Seo, Sun-Jae Kim, Sang-Chai Kim, Young-Kwon Park, Sang-Chul Jung (7-10).
Polycrystalline copper nanoparticles were synthesized from copper chloride dihydrate solution using the liquid phase plasmareduction method. A bipolar pulsed power supply with tungsten electrodes was used to generate discharge in the aqueous solutions.While large size of dendrite-shaped copper nanoparticles were mostly observed in the initial stage and particle size decreased with dischargetime. The particles were dispersed with less and less small particles by the addition of CTAB and anisotropic shapes nanoparticleswere mostly observed at long time plasma-treated with high concentration of surfactant. Many spots could be seen in the selected areadiffraction pattern (SADP) for polycrystalline particles.
Separation of Heavy Rare Earth Elements with Extraction Chromatography by Jeong-Gon Kim (11-15).
Used mainly in industries manufacturing secondary battery, display, LED, semiconductor, and other state-of-the-art products,rare earth elements (REEs) remain in demand and such demand has increased drastically. However, due to the lack of alternative materialsand recycling technologies for REEs, many countries encounter difficulty in acquiring REEs.;As part of the efforts to secure REEs, some studies have developed wet process techniques in the material flow process, particularly forscrapping and disposal. Among these techniques, the agent extraction method and liquid/solid separation process allow the separation/refinement of high-quality REEs due to their excellent selection and separation performance. This study used Amberite XAD-7HP asthe solvent impregnated resin and D2EHPA as the agent to separate each REE from the standard sample solution, mixed with heavyREEs (e.g., La and Ba) and light REEs (e.g., Eu, Tb, and Y). Each one of these REEs was about 100ppm in DI water using extractionchromatography.;In this study, the pH change of HCI was between 0.1 and 3N, and the flow speed of the solution was between 0.9 and 2.6ml/min. The extractionresult was analyzed by ICP-AES. Each REE was successfully separated with the HCI pH between 0.1N and 1N, and with thespeed of the HCI between 1.6 and 2.6m/min.
Low Current Resistive Switching Behavior in Semiconductor/Ferroelectric Coupling by Hongsu Park, YoungWoong Moon, DuckKyun Choi (16-19).
Using an a-InGaZnO(amorphous-IGZO) n-type semiconducting material, a vertically operating two terminal metalsemiconductor-ferroelectric-metal (MSFM) non-volatile resistive switching structure has been investigated. PZT thin film of compositionZr/Ti=10/90 was prepared by spin-coating method on the Pt/Ti/SiO2/p-Si(100) substrate, and 50 nm thick a-IGZO semiconductor thinfilm was deposited as a resistive layer by RF sputtering on the PZT layer. The fabricated coupling structure exhibited three orders ofswitching margin. At a reading voltage of 2.5V, the “on” current and “off” current were 2.6 x10-9A and 4.5 x10-12A respectively. Such anextremely low pico-level “on” current is determined by the leakage current of PZT and is attributed to the charge accumulation at the a-IGZO/PZT interface layer. On the other hand, the current level of the "off" state is associated with the charge depletion in the a-IGZOlayer due to the polarity reversal in the PZT layer. The “on” current level observed in this study is about three orders of magnitude lowerthan the reported values of typical ferroelectric devices, indicating read speed might be slow. However, the potential for low power operatingapplications is still promising in the aspect that the increase the leakage current in PZT material is not as much difficult as decreaseit.
Cu based Sputtering Target Materials for Solar Cell Manufactured by Cold Spray Deposition by Kee-Ahn Lee, Myung-Ju Lee, Dong-Yong Park, Hyung-Jun Kim (20-22).
This study attempted to manufacture Cu-In and Cu-Ga coating materials via the cold spray deposition (as a new process forsputtering target material) and to investigate the material's applicability as a sputtering target for solar cell. To examine the microstructuraland property changes made to those coating layers, purity, density, hardness, and porosity were measured. The results showed thatcoating layers of Cu-In and Cu-Ga could be well manufactured via cold spraying under optimal process conditions. With the Cu-In coatinglayer, the pure Cu and intermetallic compounds of Cu7In3 and Cu4In were found to exist inside the layer. In the case of Cu-Ga layer,pure Cu, and Cu3Ga were detected. The value of porosity significantly decreased after annealing heat treatment. A Sputtering test was actuallyconducted using the cold sprayed Cu based materials and it was confirmed that those coating materials could be applied as a sputteringtarget material for solar cell.
Comparative Study between Impact Behaviors of Composites with Aluminum Foam and Honeycomb by Y.C. Kim, J.U. Cho (23-27).
The need for composites has been growing in various industries because it has high mechanical properties for weight as wellas superior stiffness and strength. The composites addressed in this study are multi-pore aluminum foam and honeycomb whose have excellentimpact energy-absorption capability. In this study, impact tests of aluminum foam and honey core sandwich composite with porouscore are conducted in a bid to examine its mechanical properties. Different impact energies such as 50J, 70J, and 100J are applied tothese specimens. The greater the impact energy is the shorter the duration of the maximum load. Maximum load is higher at foam than athoneycomb sandwich. At 50J test, the striker damages on the lower face at honeycomb but it does not damage at foam. At 70J test, itpenetrates the specimen of composite at honeycomb but it does not penetrate at foam. On comparative study between impact behavior resultsof aluminum foam and honey core sandwich composite with porous core, stiffness at aluminum foam sandwich is superior than ataluminum honeycomb sandwich. The stabilities on aluminum foam and honeycomb core composite structure can be predicted by use ofthis experimental result.
Effect of Dysprosium-Compounds Treatment on Coercivity of Nd-Fe-B Sintered Magnets by Dhani Ram Dhakal, Seok Namkung, Min-Woo Lee, Tae-Suk Jang (28-31).
In order to find an effective method to increase the coercivity of Nd-Fe-B magnets using less Dy quantity, an ordinaryprocessedNd-Fe-B sintered magnet was treated with dysprosium-compound suspension in this work. After the magnets were prepared bya normal sintering process, they were cut into the size of 10 x10 x5 mm3 pieces and then dipped in 20 % DyF3 suspension and 20 % DyHxsuspension, for one minute, so that the magnets were coated with the dysprosium compounds. These coated magnets were further subjectedto heat treatment. As a consequence, coercivity of the coated magnets was increased over 255 kAm-1 for Dy-contained one and243 kAm-1 for Dy-free one without noticeable reduction in the remanence and the energy product values. This improvement of the coercivitywas due to Dy diffusion along grain boundaries from the surface of the coated magnets, thereafter, a partial replacement of Nd inNd2Fe14B main grain by Dy had taken place near the grain boundaries, resulting in the increase of anisotropy field in that area.
Microwave Technique: A Powerful Tool for Sintering Ceramic Materials by A. Borrell, M. D. Salvador, M. Miranda, F. L. Penaranda-Foix, J. M. Catala-Civera (32-35).
Microwave sintering has emerged in recent years as a promising technology for faster, cheaper and eco-friendlier processingof a wide variety of materials, which are regarded as significant advantages against conventional sintering procedures. The present investigationdescribes a technique for sintering two different ceramic materials by microwave heating: alumina-15vol.% zirconia and hydroxyapatitenanopowders. The results show that microwave sintering achieves higher density values, excellent mechanical propertiesand a homogeneous microstructure at lower sintering temperatures. The densities of microwave processed samples were close to thetheoretical densities, and the near-net-shape of the green body was preserved without significant dimensional changes. The main advantagesof microwave heating can be summarized as follows: a more flexible process, reduced processing times and production costs, andenvironmental benefits. Thus, microwaves are a clear alternative to conventional heating methods, using up to 70% less energy throughoutthe whole sintering process.
Interface Reactions of Pure Ti Thermal Plasma Spray Coated Mo-Si-B Alloys During Oxidation by Y.H. Song, J.M. Kim, J.S. Park (36-39).
The oxidation behaviors of Ti powder thermal spray coated Mo-Si-B alloys have been investigated in order to identify the underlyingmechanism for the effect of precursor Ti coatings on Mo-Si-B alloys. Pure Ti powder was thermally sprayed on the two phasealloy (Mo (solid solution)+T2(Mo5SiB2)) fabricated by arc melting elemental components. The oxidation tests performed at 1100 °Cshow that the Ti powder was tightly bonded and reacted with the surface of the substrate, and TiO2 layer was formed at the outer surfaceof the coated Ti layer as a result of oxidation exposure. The oxidation behaviors of pure elemental component coated Mo-Si-B alloyshave been discussed in terms of microstructural observations during oxidation tests.
Microstructures and Mechanical Properties of CNT/AZ31 Composites Produced by Mechanical Alloying by Daehwan Kim, Bonghak Seong, Guenho Van, Inshup Ahn, Sugun Lim (40-46).
In this study, the mechanical properties and hot extrusion of carbon nanotubes (CNTs)-reinforced Mg (AZ31) based compositewere investigated. To improve the mechanical properties of the Mg alloy AZ31, CNT /AZ31 composites were fabricated by mechanicalalloying and hot extrusion process. Then, extrudates of these composites were formed using a hot-extrusion process. The conditions toprepare the extruded specimens, which were rod-shaped, were at extrusion temperature of 400 °C, an extrusion ratio of 19:1, and a ramspeed of 1.0 mm/s. A 300 ton press was used for an extrusion. The microstructures were observed using by optical microscopy (OM),scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The characterization of the hot-extruded CNT/AZ31rods was performed through electrical resistance and tensile test. The extruded CNT/ AZ31 rods showed significantly improved ultimatetensile strengths and yield strengths, but the exhibited an elongation of less than 2%. These results were due to the formation MgO betweenMg and the CNTs during themechanical alloying process.
Effects of Partial Phase Transformation on Characteristics of 9Cr Nanostructured Ferritic Alloy by Ji-Hyun Yoon, Yongbok Lee, Suk-Hoon Kang, Thak S. Byun, David T. Hoelzer (47-50).
The core structures of future nuclear systems require tolerance to extreme irradiation, and some critical components, for example,the fuel cladding in Sodium-cooled Fast Reactors (SFRs), have to maintain mechanical integrity to very high doses of 200 - 400 dpaat high temperatures up to 700 °C. The high Cr nanostructured ferritic alloys (NFAs) are under intense research worldwide as a candidatecore material. Although the NFAs have some admirable characteristics for high-temperature applications, their crack sensitivity is veryhigh at high temperatures. The fracture toughness of high strength NFAs is unacceptably low above 300 °C. The objective of this study isto develop processes and microstructures with improved high temperature fracture toughness and ductility. To optimize the afterextrusionheat treatment condition, both the computational simulation technique on phase equilibrium and the basic microstructural andmechanical characterization have been carried out. 9 Cr-NFA was produced by the mechanical alloying of pre-alloyed Fe-9Cr base metallicpowder and yttria particles, and subsequent extrusion. The post-extrusion heat-treatments of various conditions were applied to the asextrudedNFA. The tensile and fracture toughness tests were conducted for as-extruded and heat-treated samples at up to 700°C. Fracturetoughness of the NFA has increased by more than 40% at every testing temperature after heat-treatment in the inter-critical temperaturerange. The increment of fracture toughness of the NFA after post-extrusion heat-treatment is attributed to the increased strength at below500oC, and an increased ductility at 700oC.
Characteristic Analysis of Carburized Quenching Processes for Bevel Gear of Automobile Driving Part by Key-Sun Kim (51-55).
The mechanical properties of automobile bevel gears manufactured by carburized guenching process are evaluated by using afinite elements method. The gear teeth of super, helical, and warm gears typically have constant cross sections and the same module,which results in the same frictional wear and stress. Bevel gears, however, are of a cone shape and thus the cross section of gear toothchange in the axial direction. As a result, the hardness after heat treatment depends on the axial location of the gear tooth. Hardness distributiondue to the non-constant cross section causes gear abrasion or damage. It is difficult, however, to measure the hardness in threedimensionalway through experiments. Hence, this study attempts to simulate the carburized quenching process through a numericalanalysis in order to interpret the three-dimensional heat-treatment effects. The analytical results include variations of each structure,hardness, temperature over various sections depending on the cooling rate. To verify this approach, the gear used in the experiment wasdesigned based on the same condition of the analytical model. The Carburized Quenching was carried out and the characteristics of carbonpenetration, micro-structure and surface hardness were investigated by means of SEM and EPS. The theoretical results were comparedwith experimental results to verify the analytical method for Carburized Quenching.
Characteristics of Machined Surface Layer of Cemented Carbide by Wire Electrical Discharge Machine by Woo-Gun Sim, Joon-Woo Song, Song-Jik Hong, Key-Sun Kim (56-61).
Wire cutting Electrical Discharge Machine (Wire EDM) uses the electrical discharge heat to cut the work piece with thin wireof brass or stainless steel by electrical discharge heat. The electrode and the work piece are melted and the cutting fluid between the electroand the piece is evaporated with burst. The melted material is spread in the shape of very tiny sphere chip. By the abrupt heating andcooling on the cutting surface, residual stress and void occurs on the surface. However the surface of oil Electrical Discharge machiningis in hardening due to carbon in oil, the surface of water-wire cutting is in ductile structure. This ductile phenomenon might be due to thepenetration of the melted wire brass into surface of the work piece. This paper presents the variation of micro structure and hardness ofcemented carbide, cut by Wire cutting EDM with discharge energy. Brass is used for electrode. The mechanical property of the structureis changed by cemented copper from brass. The hardness distribution of the machined surface is evaluated. It is found that the cutting surfacelayer is in ductile structure. Considering the penetration phenomenon of the melting brass wire into Cu and Zn surface layer, thevariation of hardness is investigated. The thickness of WC-Co (material of cemented carbide) ductile layer, generated by WEDM, isevaluated. This result will be useful information for a fine machining.
Mechanical Properties of WC-Co Alloys with Various Mixing and Milling Conditions using High Energy Ball Miller by Joon-Woo Song, Rumman Md. Raihanuzzaman, Soon-Jik Hong (62-65).
This study aims to understand the changes in mechanical properties when WC-7.5wt%Co and WC-12wt%Co compositionswere experimented with various mixing, milling and consolidation conditions. Magnetic Pulsed Compaction (MPC) was used to consolidateWC-7.5wt% Co and WC-12wt% Co powders where high-energy ball milling with varying duration was employed for generatingvarious powder types. Mechanically alloyed milled, non milled and mixed (non milled and milled powders in certain proportions) powderswith compositions of WC-7.5wt% Co and WC-12wt% Co were used, followed by applying high pressures to form the bulks. Maximumdensities for mixed milled and non milled WC-Co bulks after MPC were found to be around 60-65%, which later turned nearly82% after sintering, while a maximum hardness of over 1400 Hv was observed in WC-12wt%Co sample. Density, hardness and othermicrostructural behavior did not illustrate substantial changes when mixed powders were used, although variations were noticed whennon-milled powders were used for consolidation.
Characterization and Cell Performance of Al Paste with an Inorganic Binder of Bi2O3-B2O3-ZnO System in Si Solar Cells by Bit-Na Kim, Do-Hyung Kim, Hyeong-Jun Kim, Heon Lee, Hyo Sik Chang, Sung-Soo Ryu (66-69).
In this study, eco-friendly Pb-free Bi2O3-B2O3-ZnO glass frits were selected as an inorganic additive for the Al paste used inSi solar cells. The effect of glass chemistry on the electrical property of the Al electrode and on the cell performance was investigated.The results showed that as the molar ratio of ZnO to B2O3 increased, the glass transition temperature and softening temperature decreasedbecause of the reduced glass viscosity. In Al screen-printed Si solar cells, as the molar ratio of ZnO to B2O3 increased, the sheet electricalresistance of the Al electrode decreased and the cell efficiency increased. The microstructure of the sintered electrodes showed that theuniformity and thickness of the back-surface field were significantly influenced by the glass chemistry.
Effect of Carbon Addition on the Property of Mechanically Alloyed Ni-Y2O3 by Jung-Ho Ahn, Jinsung Jang, Tae Kyu Kim (70-73).
We synthesized Y2O3-reinforced nickel-matrix nanocomposites by mechanical alloying of Ni-Y2O3, Ni-Y, Ni-NiO-Y and Ni-CuO-Y powders. Mechanical alloying of constituent powder mixtures resulted in a complete dissolution of yttrium or Y2O3 in nickel,forming a nickel-based solid solution. However, undesirable oxides such as NiO easily formed after a prolonged milling and subsequentsintering even in an inert gas atmosphere. The oxidation occurred almost inevitably due to oxygen impurity which remained at the surfaceof starting powders and in an inert gas used for milling or sintering. To solve this problem, we added a small amount of carbon orpolyethylene as process control agents during ball milling. The result showed that the addition of these carbon-based additives, in particularpolyethylene, was very effective to reduce a harmful formation of over-grown oxides during annealing and sintering, while promotingthe oxidation of yttrium to form fine and uniformly distributed Y2O3 from the nickel-based solid solution.
In-situ Monitoring of Micro-scale PWSCC of Ni-based Alloys in a Simulated Primary Water Chemistry of a PWR using an EN-DCPD Technique by Sung-Woo Kim, Yeon-Ju Lee, Seong-Sik Hwang (74-77).
This work was conducted to establish an electrochemical noise (EN) measurement combined with a direct-current potentialdrop (DCPD) method, namely, an EN-DCPD technique, for in-situ monitoring of nano- or micro-scale crack initiation and the propagationof primary water stress corrosion cracking (PWSCC) of nickel based alloys, and to investigate its underlying mechanism. The ENsignals of the potential and current were measured under various conditions of a simulated primary water chemistry of a pressurized waterreactor (PWR), and the amplitude and frequency of the EN signals were analyzed in both the time and frequency domains. From thespectral and stochastic analyses, the effects of such experimental factors as the current application in DCPD, loading condition, temperature,and pressure of the primary water environment were found to be effectively excluded from the EN signals generated from thePWSCC propagation. From a stochastic analysis based on the shot-noise theory, the PWSCC propagation could be distinguished from thegeneral corrosion, by considering the Weibull shape parameter.
Methanol Synthesis from Syngas Produced via Gasification of Municipal Solid Waste by Jong-Ki Jeon, Gwan Hyung Lee, Jong-Wan Lim, Sung Hoon Park, Jae Hoi Gu, Sang Chai Kim, Jong-In Dong, Young-Kwon Park (78-80).
A model gas that mimics the syngas produced from gasification of municipal solid waste was applied, for the first time, to thesynthesis of methanol over commercial Cu-based catalysts. The effects of various operation conditions, such as temperature, pressure,contact time (W/F), and H2/COx and CO/COx ratios, on the methanol yield were investigated. The Cu-based catalysts containing a smallamount of Mg showed a higher activity than that without Mg. The catalysts were characterized by Brunaure-Emmett-Teller, X-ray diffraction,and temperature-programmed reduction. The methanol yield was the highest under the following operational condition: temperature230-250oC, pressure 60 bar, W/F 0.05 g¨l/min, H2/COx ratio 2, and CO/COx ratio 0.8.
Relation between Surface Oxide and SCC of Alloy 600 by Dong-Jin Kim, Hong Pyo Kim, Seong Sik Hwang (81-85).
Stress corrosion cracking (SCC) is one of major threats against the integrity of the structural materials composing a nuclearpower plant (NPP). Lead is deleterious element accelerating the SCC of Alloy 600 used as a steam generator tubing material in an NPP.In the present work, the oxide property grown on an Alloy 600 surface was evaluated as a function of PbO content using electrochemicalimpedance spectroscopy (EIS) and a field-emission transmission electron microscopy, equipped with an energy dispersive X-ray spectroscopy(TEM -EDS) for the specimen prepared using a focused ion beam (FIB). Alloy 600 was immersed in 0.1M NaOH containingPbO in the range of 0-5,000 ppm at 315oC for 2 weeks. The oxide property was compared with SCC susceptibility obtained from a slowstrain rate tension (SSRT) test for Alloy 600 in 0.1M NaOH containing PbO. The impedance value was greatly decreased by adding PbOinto the solution indicating a decrease in passivity. The composition of the oxide was also changed by Pb in an aqueous solution. The duplexoxide layer consisting of outer porous nickel-rich oxide and inner dense chromium-rich oxide is modified to a Pb incorporatednickel-rich oxide layer. Modification of the oxide property induced by lead incorporation caused an obvious increase in SCC susceptibility.It is expected that lead observed at the crack tip of an early cracked pulled Alloy 600TT tube was considerably responsible for SCCacceleration of this tube among numerous sound tubes in an NPP.
A Novel Method for Fabricating Fe-Cr-Al Open-cell Metallic and Alloyed Foams by Luong-Huu Bac, Byoung-Kee Kim, Young-Min Kong (86-88).
A new fabrication process for generating open-cell metallic and alloyed foams was developed by combining electrical explosionof wire (EEW) and electrospray (ESP) techniques. Fe-Cr-Al alloy nano-powders prepared by EEW in ethanol were used as a startingmaterial, and commercial polyurethane (PU) sponges were used as templates. Fe-Cr-Al foams were successfully fabricated with porositiesgreater than 90%. The porosity of the fabricated foams was controlled by spraying time during the ESP process. As spraying time increasedfrom 1 to 5 h, porosity decreased from 97 to 90%. The sintered foam possessed a continuous open-cell structure, which was dependenton the structure of the PU template. The proposed method may be useful in the future as a simple means to fabricate open-cellporous materials.
Corrosion Behavior on Ni-base Alloys Applied with Nano-TiO2 in High Temperature Caustic Water by Kyung-Mo Kim, Eun-Hee Lee, Do-Haeng Hur (89-93).
In Pressurized Water Reactor (PWR) power plants, Alloy 600, a Ni-Cr-Fe alloy, is used for steam generator tube materials.However, these tubes have experienced a lot of corrosion problems during their operation times. Several chemicals have been investigatedfor inhibitors of stress corrosion cracking (SCC) in the tube materials. Titanium dioxide (TiO2), which is sonochemically treated inwater, was tested to evaluate the inhibition effect of SCC using a reverse U-bend specimen of alloy 600 under the condition of a 10%NaOH solution and a temperature of 315o C. The TiO2 particle size was reduced by ultrasonic power, and the morphology of the TiO2powder was observed by a transmission electron microscope (TEM) based on the ultrasonic processing times. The particle size of TiO2affects the SCC rate of the tube materials, and shows an improvement in resistance on SCC when decreasing the particle size of TiO2.When the nano-sized inhibitor is applied, the property of the oxide layer is changed to a more dense composition. The chemical compositionin the oxide layer was analyzed using an X-ray photoelectron spectroscope (XPS) with a variation in the ultrasonic process times,and the difference in the Ti-compound structure between the oxide surface and inner layer of oxide was compared using XPS data.
Effects of Oxygen Concentration on the Size Distribution of Oxide Particles in ODS Steel by Tae Kyu Kim, Chang Hee Han, Suk Hoon Kang, Sanghoon Noh, Jinsung Jang (94-96).
ODS steel normally contains an exceptionally high oxygen concentration owing to oxygen adsorption on the metal powdersurfaces, as well as to the contamination during mechanical alloying and consolidation. In this study, the effect of oxygen concentrationon the size distribution of oxide particles in ODS steel has been investigated. The oxygen concentration in one ODS steel sample wasabout 7000 ppm (sample A), while that in the other was controlled to be about 2500 ppm (sample B) by a hydrogen reduction processprior to consolidation. Sample A revealed a much smaller mean grain size (~10 μ m) than sample B (~25 μ m). Two types of oxide particles,fine YTiO4 (< 30 nm) and coarse Cr-O (>100 nm), were mainly found in both samples. The fine YTiO4 particles in sample Ashowed a larger mean particle size (15 nm) than those (9 nm) in sample B, while their number density was nearly the same. Coarse Cr-Oparticles in sample A revealed a much higher number density than sample B. It is thus concluded that the size distribution and grain sizeof ODS steel can be controlled by a control of the excess oxygen concentration.
Oxidation of Ti3Al0.3Si0.7C2 Compounds at 900-1200oC in Air by Jae Chun Lee, Sang Whan Park, Dong Bok Lee (97-100).
Ti3Al0.3Si0.7C2 compounds were synthesized via the powder metallurgical process, and oxidized isothermally and cyclicallybetween 900 and 1200 oC in air. They had good thermal shock resistance, forming adherent oxide scales during cyclic oxidation. Theyoxidized to rutile-TiO2, α-Al2O3, and amorphous SiO2, together with gaseous escape of carbon. The oxide scales that formed during isothermaland cyclical oxidation were similar in that an outer (TiO2, Al2O3)-mixed scale, a thin intermediate Al2O3 layer, and an inner(TiO2, SiO2)-mixed scale formed. The outer scale formed by the outward diffusion of Ti4+ and Al3+ ions. The intermediate scale formedby the outward diffusion of Al3+ ions. The inner scale formed by the inward diffusion of O2- ions. No selective oxidation occurred fromthe early oxidation period.
Formation of Hollow Copper Oxide by Oxidation of Cu Nanoparticles by J.-G. Lee, R. Nakamura, Y.-S. Choi, J.-H. Yu, C.-J. Choi (101-103).
The formation of hollow Cu oxide nanoparticles through the oxidation process has been studied with Cu nanoparticles producedby the plasma arc discharge method. The initial copper nanoparticles had a size range of 40 - 60 nm and a thin Cu2O layer on thesurface. After oxidation at 100°C, there was no significant change in the particles. After oxidation at 200°C, however, the particles consistedof Cu2O and CuO instead of metallic Cu. By further increasing the temperature up to 300°C, only CuO particles remained. The obtainedCuO particles had a hollow structure which resulted from the Kirkendall effect.
Electrolytic Recovery of Tin from Printed Circuit Boards (PCBs) Disassembled from Waste Liquid Crystal Displays (LCDs): Selection of H2SiF6 + H2SO4 + H2O2 Leaching Solution over Two-stage Leaching in HNO3 and HCl by Sungkyu Lee, Kyoung-Hoon Kang, Jae Layng Park, Myung-hwan Hong, Soo-Young Lee, Sung-Su Cho, Hyun Seon Hong (104-107).
Waste PCBs (Printed Circuit Boards) from LCDs (Liquid Crystal Displays) contain valuable raw materials, Sn, Cu, and othernoble metals. Among these, high purity tin was obtained by electro-winning after appropriate acid leaching of tin. For this, leaching andelectro-winning process parameters were optimized for solution stability, dissolution and electrolytic efficiency. Two aqueous procedureswere developed and tested for electro-winning at mass-production capable basis: (1) HCl leaching after preliminary HNO3 dissolutionwas quite effective in leaching high proportion of Sn as analyzed by ICP (Inductively Coupled Plasma) method. (2) Direct one-stepleaching in H2SiF6 + H2SO4 + H2O2 was also tested and the solution was finally selected as electrolytes in electro-winning due to massproductioncapability. The most efficient recovery of tin was observed after 7h electro-winning in aqueous H2SiF5 + H2SO4 + H2O2 maintainedat 40 oC: 96%-pure tin was obtained with 93.2% recovery rate.
Effects of Aluminum and Strontium Content on the Microstructures and Mechanical Properties of Mg-Al-Ca-Sr Alloys by Byoung-Gi Moon, Bong-Sun You, Yu-Dong Hahn (108-113).
The effects of aluminum and strontium content on an Mg-Al-Ca-Sr alloy were investigated in terms of microstructural andmechanical properties. The addition of up to 2 wt% of strontium to the Mg-5Al-2Ca alloy caused the major interdendritic intermetallicphase to change from Al2Ca to a combination of Mg2Ca, Al4Sr, and Mg17Sr2. Moreover, the addition of 2 wt% of aluminum to the Mg-5Al-2Ca-xSr alloys caused the formation of β -Mg17Al12 phase suppressing the formation of Mg17Sr2. The creep resistance was significantlyimproved by the addition of strontium due to the formation of a thermally stable Al4Sr phase in the interdendritic region. However,the ductility deteriorated as the amount of second phases along the interdendritic boundary increased. Furthermore, an increase in aluminumcontent resulted in a drop of ductility and creep resistance at elevated temperature due to the poor metallurgical stability by the formationof β-Mg17Al12 phase.
Development for Fabrication of Refined Silicon Nanoparticles by Transferred Arc Plasma System by Byungkwon Kim, Jungho Hwang, Jeong Yeol Kim, Dongho Park (114-117).
Refining silicon and silicon nanoparticles are an important research area in solar energy research. These are related with solarcell efficiency. Silicon nanoparticles are also used for thin film solar cell and screen printing technology. We review the synthesis of siliconnanoparticles and refining of silicon. Refined silicon nanoparticles with minimal boron content were fabricated with transferred arcplasma equipped with impactor system. To control the chemical reactions leading to the formation of these compounds, H2O was injectedinto the shield gas line of the plasma torch. The plasma reactive time for boron removal was evaluated. The reactive time was altered bychanging the flow rate of the shield gas of the plasma torch, fixing the powder feed concentration. The removal ratio of boron was alsoevaluated to conform if the boron content in the silicon particles was in the range required for standard solar grade silicon. The sizes andcompositions of the particles were analyzed by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), InductivelyCoupled Plasma (ICP), and X-Ray Diffraction(XRD) analysis.
Microstructure and Thermoelectric Properties of N-type 95%Bi2Te3-5%Bi2Se3 Compound Prepared by High Energy Milling and Hot Extrusion by Hyo-Seob Kim, Soon-Jik Hong (118-122).
Nanocrystalline n-type 95%Bi2Te3-5%Bi2Se3 bulk with prepared by the combined application of high energy milling and hotextrusion processes in this study. The effect of milling time on the microstructure of powders was characterized by scanning electronmicroscopy (SEM). With increasing milling time, powder size quickly decreased, and finally yielded nanocrystalline Bi2Te3 of less than200nm grain size and of spherical morphology, at 90min. Microstructure and thermoelectric properties of the samples after hot-extrusionwere also investigated. The hot-extruded samples observed fine-grains and improved mechanical properties. The maximum power factorof the nanaocrystalline Bi2Te3 bulk sample reaches 4.6x10-5W/mK2 at room temperature, which is lower than the zone-melted one due tohigh impurity and oxidization.
Study of the Evolution of Defects in the Structure of Reactor Pressure Vessel by Rate Theory by Gyeong-Geun Lee, Yong-Bok Lee, Min-Chul Kim, Junhyun Kwon (123-127).
In this work, we implemented a chemical rate theory model for the growth of nano-sized point defect clusters (PDCs) and copper-rich precipitates (CRPs) which can change the mechanical properties in the reactor pressure vessel material of a nuclear power plant.For the calculation of irradiation defect evolution, a number of time-dependent differential equations were established and numericallyintegrated. The concentration of mono-size vacancies and interstitials was saturated at an early stage of irradiation, and it was found thatthe vacancy concentration was higher than the interstitial concentration. The high concentration of vacancies induced a growth of theCRPs at the later stage. The concentration of PDCs and the size of CRPs were used to estimate the mechanical changes, and the calculationresults were compared with the measured changes in yield strength and Charpy V-notch transition temperature shift obtained fromthe surveillance test data of Korean light water reactors (LWRs). It was observed that the estimated values were in fair agreement withthe experimental results in spite of the uncertainty regarding the material property parameters and modeling method.
Effect of Scrap Size on Extraction of Neodymium from Nd-Fe-B Magnet Scrap by Liquid Metal Extraction by Hyun Woong Na, Yong Hwan Kim, Hyeon Taek Son, In Ho Jung, Han Shin Choi, Tae Bum Kim (128-130).
The effects of Nd-Fe-B magnet scrap size on extraction behavior were investigated by liquid metal extraction using moltenMg. The magnet scraps with Mg were placed into a stainless steel crucible and then heated to 1,073K for 10 to 50min. The amount of extractedNd after liquid metal extraction process was increased with an increasing with holding time and scrap size, and the maximum contentsof Nd in Mg were observed to be about 24.2 wt.% in the conditions of the 5mm sized scrap heated for 50min. It was revealed thatNd oxides existing in the magnet scraps prevent the dissolution of Nd into Mg.
Characteristics of Niobium Powder Used Capacitors Produced by Metallothermic Reduction in Molten Salt by Jae-sik Yoon, Gae-hang Lee, Soon-jik Hong, Hyun-seon Hong, Chan-gi Lee, Ji-myon Lee (131-134).
The niobium capacitor shows somewhat more unstable characteristics than the commercial tantalum capacitors, but it will benonetheless considered as an excellent substitute of tantalum capacitors in the future. In this study, niobium powder is fabricated by metallothermicreduction process using K2NbF7 as a raw material, KCl and KF as diluents, and Na as a reducing agent. The niobium particlesize greatly decreases from 0.7 μm to 0.2μ m as the amount of diluent increases. However, when a higher surface area of niobium powderis desired, more amounts of diluents are used in the said method. The niobium powder morphology and particle sizes are very sensitive tothe amount of sodium excess, thus the particle size of niobium powder increases with increases in the amount of sodium excess. Whenmore diluent and sodium are used, the niobium powder is contaminated further by impurities such as Fe, Cr, Ni, and others [1,2].
CFD Simulation of Chemical Vapor Deposition of Silicon Carbide in CH3SiCl3-H2 System by Kyoon Choi, Jun-Woo Kim (135-137).
The CVD apparatus for the uniform coating of silicon carbide was suggested and realized into a 3-dimensional computer-aideddesign (CAD) model. An experimental condition is simulated with a computational fluid dynamic program to obtain temperature andflow distribution in the CVD chamber. The simulated temperature showed the very uniform distribution especially in the hot zone regionand that is thought to be the result of the design of the CVD apparatus. The temperature measured with a thermocouple showed the goodmatching with the simulated one, which reflected the assumption and the boundary conditions during the simulation were plausible.
A Study on the Efficient Recovery and Separation of the Phosphor from CCFLs in End-of-Life LCD Units by Hyun Seon Hong, Hang Chul Jung, Minhye Seo, Sunghyun Uhm, Jae Sik Yoon, Han Gil Suk (138-142).
The effective recovering process that consists of air-jetting, centrifugation and air-classifying was developed for phosphor recyclingfrom flat panel display devices. At the first processing stage of air-jetting, 95% phosphor could be recovered while the recoveryrate was dependent on the dimension of CCFLs. After two subsequent stages of mechanical separation, Blue, Red and Green rich phosphorcould be selectively collected. The recovery of Red phosphor was 61.2% and purity of (Y, Eu)2O3 was 95%.
Recycling of Silicon Sludge and its Optical Properties by Bum-Sung Kim, Woo-Byoung Kim (143-145).
We have developed a mass production process of Si quantum dots using photo-induced chemical etching method with oxidationand etching agents and have investigated its optical properties. Average size of the fabricated Si quantum dots was estimated to be2 nm. Absorption peaks of the fabricated quantum dots were observed in the short wavelength regions, e.g., 200 - 350 nm. On the otherhand, in the case of raw sludge, absorption was not observed in the UV-visible wavelength regions due to the narrow energy band gap(e.g., 1.12 eV). The calculated energy band gap of fabricated Si quantum dots was calculated to be 3.5 eV by the modified Kubelka-Munk function. Blue emission peaks around 475 nm wavelengths were observed due to the quantum confinement effect. When the emissionpeak was fixed, two excitation peaks were observed in 340 nm and 380 nm, respectively, which seemed to be due to the energy bandgap widening and/or surface coating with an ultrathin layer.
The Effect of Sc on the Microstructure and Mechanical Properties of Hypereutectic Al-Si Alloy Fabricated by a Gas Atomization Process by Tae-Haeng Lee, Han-Jin Ko, Tae-Sik Jeong, Soon-Jik Hong (146-150).
In this study, the effect of Sc addition on the microstructure and mechanical properties of Al-20Si alloys fabricated by extrusionof powders was investigated. The Al-Si-(Sc) powders produced by high pressure gas atomization were used in starting materials.The microstructure and structural characterization were performed by optical microscopy (OM), X-ray diffractometry (XRD), scanningelectron microscopy (SEM) and transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDS). Mechanicalproperties of extruded bars were investigated by micro hardness test, tensile test and wear test. With increasing the Sc contentsin Al-Si alloys, mechanical properties were significantly increased. These enhanced mechanical properties can be explained based on therefinement of primary Si due to the suppression of growth of primary Si by the well-surrounded and uniformly distributed Sc.
Evaluation of Microstructure and Mechanical Properties in a Thick Plate of G91 Steel and its Weld for High Temperature Nuclear System by Min-Chul Kim, Sang-Gyu Park, Ki-Hyoung Lee, Sung Ho Kim, Bong-Sang Lee (151-153).
The purpose of this study is to investigate the microstructure and mechanical properties in 9Cr-1Mo-V steel and its weld. A220 mm thick forged plate with a typical composition of G91based on ASME A336 was used. Narrow gap welds were produced by submergedarc welding (SAW) with two different welding speeds. The microstructures in the base metal were typical tempered martensite atall locations, and the sizes of prior austenite grains were increased with the depth from the surface. The yield and tensile strengths tend todecrease with an increase in test temperature, especially at temperatures higher than 500oC. The upper shelf energy of the specimen fromcenter was lower than that from the surface, and it also showed a higher index temperature. The toughness deterioration at the centermight be caused by the larger size of the prior austenite grains and the existence of the delta ferrite. In the case of the weld, the largersizes of the weld beads were observed in the upper region with a lower welding pass speed. There was no significant difference in thestrength of the upper and lower welds, but the elongations of the upper weld were slightly larger than those of the lower weld. In theCharpy impact test, the lower weld showed a better impact toughness than the upper weld caused by the relatively smaller size of theweld beads and finer microstructures owing to a lower heat input by the increased welding speed.
Mechanical Properties of Al2TiO5 Ceramics for High Temperature Application by Dami Kim, Hyeong-Jun Kim, Hyung-Tae Kim, Jung Namkung, Ikjin Kim, Sung-Churl Choi, Sung- Soo Ryu (154-158).
The present work investigated the effects of MgO as a thermodynamic stabilizer and ZrO2 and mullite (3Al2O3¨SiO2) as kineticstabilizers on the mechanical properties of Al2TiO5 at high temperatures. Al2TiO5 was synthesized using reaction sintering at 1500, 1550,and 1600°C for 2 h. The mix-stabilized Al2TiO5 sintered at 1500°C showed the highest mechanical strength (138 MPa) at 1100°C, whilethe mullite-only Al2TiO5 sintered at 1550°C showed a mechanical strength of only 67 MPa at 1200°C. The strength improvementachieved at high temperatures was affected by not only secondary phase mullite to inhibit grain growth of Al2TiO5 and to improvestrength but thermodynamic stabilizer to promote synthesis Al2TiO5. The coefficient of thermal expansion of mix-stabilized Al2TiO5 decreasedwith increase of sintering temperature due to its microcrack, however, that of the mullite-only Al2TiO5 was not changed becauseof large number of pores.
Optical Properties and Thermal Stability of Ultrathin TaNx-Ag-Si Films for Low Emissivity Applications by Sivasankar Reddy Akepati, Chadrasekhar Loka, Ho Tak Yu, Kee-Sun Lee (159-163).
TaNx(1, 3 & 5 nm) films deposited on the Ag(10 nm)/Si(3 nm)/glass show dense microstructure, and this structure was stableeven after annealing at 300 °C in Ar (80%) + O2 (20%) ambient for 5 min. The RMS (Root Mean Square) roughness of the films decreasedwith increasing the TaNx film thickness. The partial oxidation of TaNx was observed in TaNx(3 & 5 nm)/Ag(10 nm)/Si(3nm)/glass at 300 oC annealing temperature, but no Ag diffusion happened at this temperature. It indicates that no outward diffusion of Agoccurred during the annealing. The as deposited and annealed TaNx(1, 3 & 5 nm)/Ag(10 nm)/Si(3 nm)/glass films showed better transmittancethan Ag(10 nm)/glass films in the visible region. The optical data obtained here was in good agreement with simulated predictions.
Microstructures and Electrochemical Properties of Si-Ni-Ti Alloys Mixed with Various Forms of Carbon by Dae Yeong Jeong, Won-Wook Park, Keun Yong Sohn (164-167).
The microstructures and electrochemical properties of rapidly-solidified silicon alloys mixed with various forms of carbonhave been investigated. Rapidly-solidified Si70Ni15Ti15 (at%) alloy (SNT1515) ribbons were prepared by arc-melting, followed by meltspinning process in vacuum. The obtained ribbons were fragmented by ball milling to produce a fine powder of -500mesh. The alloypowder was mixed with various types of carbon: multi-walled carbon nanotubes, hard carbon, soft carbon, and graphite. Each was addedby 2wt% by ball milling for 2 hours. The microstructure of the melt-spun ribbon showed a fine silicon primary phase surrounded bySi7Ni4Ti4 and TiSi2 intermetallic compounds. The additions of carbon to the SNT1515 alloy remarkably improved its cyclic performance.Soft carbon was identified to be the most effective in improving the cycle capacity because of its fine particles and uniform distribution.
Preparation and Characterizations of Lithium Iron Borate Nano-sized Powders via Aerosol and Thermal Process by Kun-Jae Lee, Dong-Wan Kim, Hyun Seon Hong (168-170).
Ultrasonic spray pyrolysis (USP) and thermal reaction were combined to fabricate lithium iron borate compound nanopowderin cost-effective and high throughput manner. This procedure exploits USP process to prepare homogenous precursor nanopowders,thereby imparting improved reaction during post thermal process. It is believed to be a distinguished route to produce a cathode materialin lithium secondary battery.