Current Nanoscience - Volume 10, Issue 1, 2014

Sintered bodies of TiO2nanopowders were fabricated by magnetic pulsed compaction (MPC) and subsequent 2 step sintering in 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 MPC pressure and 1450°C sintering temperature, with addition of 6% of TiO2 P-25 nanopowder. High pressure and rapid compaction using magnetic pulsed compaction (MPC) enhanced the density with increasing MPC pressure up to 0.7 GPa without the formation of surface or edge cracks on the consolidates bulks, and significantly reduced the shrinkage rate (about 15 in this case) of the sintered bulks compared to the general process (about 18%). Overall, most of the properties showed gradual changes with increasing MPC-ed pressure and TiO2 P-25 nanopowder content.

Polycrystalline copper nanoparticles were synthesized from copper chloride dihydrate solution using the liquid phase plasma reduction 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 discharge time. The particles were dispersed with less and less small particles by the addition of CTAB and anisotropic shapes nanoparticles were mostly observed at long time plasma-treated with high concentration of surfactant. Many spots could be seen in the selected area diffraction pattern (SADP) for polycrystalline particles.

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 materials and 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 for scrapping 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 as the solvent impregnated resin and D2EHPA as the agent to separate each REE from the standard sample solution, mixed with heavy REEs (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 extraction chromatography. 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 extraction result was analyzed by ICP-AES. Each REE was successfully separated with the HCI pH between 0.1N and 1N, and with the speed of the HCI between 1.6 and 2.6m/min.

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 composition Zr/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 thin film was deposited as a resistive layer by RF sputtering on the PZT layer. The fabricated coupling structure exhibited three orders of switching margin. At a reading voltage of 2.5V, the “on” current and “off” current were 2.6x10-9A and 4.5x10-12A respectively. Such an extremely 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-IGZO layer due to the polarity reversal in the PZT layer. The “on” current level observed in this study is about three orders of magnitude lower than the reported values of typical ferroelectric devices, indicating read speed might be slow. However, the potential for low power operating applications is still promising in the aspect that the increase the leakage current in PZT material is not as much difficult as decrease it.

This study attempted to manufacture Cu-In and Cu-Ga coating materials via the cold spray deposition (as a new process for sputtering target material) and to investigate the material’s applicability as a sputtering target for solar cell. To examine the microstructural and property changes made to those coating layers, purity, density, hardness, and porosity were measured. The results showed that coating layers of Cu-In and Cu-Ga could be well manufactured via cold spraying under optimal process conditions. With the Cu-In coating layer, 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 actually conducted using the cold sprayed Cu based materials and it was confirmed that those coating materials could be applied as a sputtering target material for solar cell.

The need for composites has been growing in various industries because it has high mechanical properties for weight as well as superior stiffness and strength. The composites addressed in this study are multi-pore aluminum foam and honeycomb whose have excellent impact energy-absorption capability. In this study, impact tests of aluminum foam and honey core sandwich composite with porous core are conducted in a bid to examine its mechanical properties. Different impact energies such as 50J, 70J, and 100J are applied to these specimens. The greater the impact energy is the shorter the duration of the maximum load. Maximum load is higher at foam than at honeycomb sandwich. At 50J test, the striker damages on the lower face at honeycomb but it does not damage at foam. At 70J test, it penetrates the specimen of composite at honeycomb but it does not penetrate at foam. On comparative study between impact behavior results of aluminum foam and honey core sandwich composite with porous core, stiffness at aluminum foam sandwich is superior than at aluminum honeycomb sandwich. The stabilities on aluminum foam and honeycomb core composite structure can be predicted by use of this experimental result.

In order to find an effective method to increase the coercivity of Nd-Fe-B magnets using less Dy quantity, an ordinaryprocessed Nd-Fe-B sintered magnet was treated with dysprosium-compound suspension in this work. After the magnets were prepared by a normal sintering process, they were cut into the size of 10 x10 x5 mm3 pieces and then dipped in 20 % DyF3 suspension and 20 % DyHx suspension, for one minute, so that the magnets were coated with the dysprosium compounds. These coated magnets were further subjected to heat treatment. As a consequence, coercivity of the coated magnets was increased over 255 kAm-1 for Dy-contained one and 243 kAm-1 for Dy-free one without noticeable reduction in the remanence and the energy product values. This improvement of the coercivity was due to Dy diffusion along grain boundaries from the surface of the coated magnets, thereafter, a partial replacement of Nd in Nd2Fe14B main grain by Dy had taken place near the grain boundaries, resulting in the increase of anisotropy field in that area.

Microwave sintering has emerged in recent years as a promising technology for faster, cheaper and eco-friendlier processing of a wide variety of materials, which are regarded as significant advantages against conventional sintering procedures. The present investigation describes a technique for sintering two different ceramic materials by microwave heating: alumina-15vol.% zirconia and hydroxyapatite nanopowders. The results show that microwave sintering achieves higher density values, excellent mechanical properties and a homogeneous microstructure at lower sintering temperatures. The densities of microwave processed samples were close to the theoretical densities, and the near-net-shape of the green body was preserved without significant dimensional changes. The main advantages of microwave heating can be summarized as follows: a more flexible process, reduced processing times and production costs, and environmental benefits. Thus, microwaves are a clear alternative to conventional heating methods, using up to 70% less energy throughout the whole sintering process.

The oxidation behaviors of Ti powder thermal spray coated Mo-Si-B alloys have been investigated in order to identify the underlying mechanism for the effect of precursor Ti coatings on Mo-Si-B alloys. Pure Ti powder was thermally sprayed on the two phase alloy (Mo (solid solution)+T2(Mo5SiB2)) fabricated by arc melting elemental components. The oxidation tests performed at 1100 °C show that the Ti powder was tightly bonded and reacted with the surface of the substrate, and TiO2 layer was formed at the outer surface of the coated Ti layer as a result of oxidation exposure. The oxidation behaviors of pure elemental component coated Mo-Si-B alloys have been discussed in terms of microstructural observations during oxidation tests.

In this study, the mechanical properties and hot extrusion of carbon nanotubes (CNTs)-reinforced Mg (AZ31) based composite were investigated. To improve the mechanical properties of the Mg alloy AZ31, CNT /AZ31 composites were fabricated by mechanical alloying and hot extrusion process. Then, extrudates of these composites were formed using a hot-extrusion process. The conditions to prepare the extruded specimens, which were rod-shaped, were at extrusion temperature of 400 °C, an extrusion ratio of 19:1, and a ram speed 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/AZ31 rods was performed through electrical resistance and tensile test. The extruded CNT/ AZ31 rods showed significantly improved ultimate tensile strengths and yield strengths, but the exhibited an elongation of less than 2%. These results were due to the formation MgO between Mg and the CNTs during themechanical alloying process.

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 dpa at high temperatures up to 700 °C. The high Cr nanostructured ferritic alloys (NFAs) are under intense research worldwide as a candidate core material. Although the NFAs have some admirable characteristics for high-temperature applications, their crack sensitivity is very high at high temperatures. The fracture toughness of high strength NFAs is unacceptably low above 300 °C. The objective of this study is to develop processes and microstructures with improved high temperature fracture toughness and ductility. To optimize the afterextrusion heat treatment condition, both the computational simulation technique on phase equilibrium and the basic microstructural and mechanical characterization have been carried out. 9 Cr-NFA was produced by the mechanical alloying of pre-alloyed Fe-9Cr base metallic powder and yttria particles, and subsequent extrusion. The post-extrusion heat-treatments of various conditions were applied to the asextruded NFA. The tensile and fracture toughness tests were conducted for as-extruded and heat-treated samples at up to 700°C. Fracture toughness of the NFA has increased by more than 40% at every testing temperature after heat-treatment in the inter-critical temperature range. The increment of fracture toughness of the NFA after post-extrusion heat-treatment is attributed to the increased strength at below 500°C, and an increased ductility at 700°C.

The mechanical properties of automobile bevel gears manufactured by carburized guenching process are evaluated by using a finite 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 tooth change in the axial direction. As a result, the hardness after heat treatment depends on the axial location of the gear tooth. Hardness distribution due to the non-constant cross section causes gear abrasion or damage. It is difficult, however, to measure the hardness in threedimensional way through experiments. Hence, this study attempts to simulate the carburized quenching process through a numerical analysis 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 was designed based on the same condition of the analytical model. The Carburized Quenching was carried out and the characteristics of carbon penetration, micro-structure and surface hardness were investigated by means of SEM and EPS. The theoretical results were compared with experimental results to verify the analytical method for Carburized Quenching.

Wire cutting Electrical Discharge Machine (Wire EDM) uses the electrical discharge heat to cut the work piece with thin wire of brass or stainless steel by electrical discharge heat. The electrode and the work piece are melted and the cutting fluid between the electro and the piece is evaporated with burst. The melted material is spread in the shape of very tiny sphere chip. By the abrupt heating and cooling on the cutting surface, residual stress and void occurs on the surface. However the surface of oil Electrical Discharge machining is in hardening due to carbon in oil, the surface of water-wire cutting is in ductile structure. This ductile phenomenon might be due to the penetration of the melted wire brass into surface of the work piece. This paper presents the variation of micro structure and hardness of cemented carbide, cut by Wire cutting EDM with discharge energy. Brass is used for electrode. The mechanical property of the structure is changed by cemented copper from brass. The hardness distribution of the machined surface is evaluated. It is found that the cutting surface layer is in ductile structure. Considering the penetration phenomenon of the melting brass wire into Cu and Zn surface layer, the variation of hardness is investigated. The thickness of WC-Co (material of cemented carbide) ductile layer, generated by WEDM, is evaluated. This result will be useful information for a fine machining.

This study aims to understand the changes in mechanical properties when WC-7.5wt%Co and WC-12wt%Co compositions were experimented with various mixing, milling and consolidation conditions. Magnetic Pulsed Compaction (MPC) was used to consolidate WC-7.5wt% Co and WC-12wt% Co powders where high-energy ball milling with varying duration was employed for generating various powder types. Mechanically alloyed milled, non milled and mixed (non milled and milled powders in certain proportions) powders with compositions of WC-7.5wt% Co and WC-12wt% Co were used, followed by applying high pressures to form the bulks. Maximum densities for mixed milled and non milled WC-Co bulks after MPC were found to be around 60-65%, which later turned nearly 82% after sintering, while a maximum hardness of over 1400 Hv was observed in WC-12wt%Co sample. Density, hardness and other microstructural behavior did not illustrate substantial changes when mixed powders were used, although variations were noticed when non-milled powders were used for consolidation.

In this study, eco-friendly Pb-free Bi2O3–B2O3–ZnO glass frits were selected as an inorganic additive for the Al paste used in Si 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 decreased because of the reduced glass viscosity. In Al screen-printed Si solar cells, as the molar ratio of ZnO to B2O3 increased, the sheet electrical resistance of the Al electrode decreased and the cell efficiency increased. The microstructure of the sintered electrodes showed that the uniformity and thickness of the back-surface field were significantly influenced by the glass chemistry.

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 subsequent sintering even in an inert gas atmosphere. The oxidation occurred almost inevitably due to oxygen impurity which remained at the surface of starting powders and in an inert gas used for milling or sintering. To solve this problem, we added a small amount of carbon or polyethylene as process control agents during ball milling. The result showed that the addition of these carbon-based additives, in particular polyethylene, was very effective to reduce a harmful formation of over-grown oxides during annealing and sintering, while promoting the oxidation of yttrium to form fine and uniformly distributed Y2O3 from the nickel-based solid solution.

This work was conducted to establish an electrochemical noise (EN) measurement combined with a direct-current potential drop (DCPD) method, namely, an EN-DCPD technique, for in-situ monitoring of nano- or micro-scale crack initiation and the propagation of primary water stress corrosion cracking (PWSCC) of nickel based alloys, and to investigate its underlying mechanism. The EN signals of the potential and current were measured under various conditions of a simulated primary water chemistry of a pressurized water reactor (PWR), and the amplitude and frequency of the EN signals were analyzed in both the time and frequency domains. From the spectral 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 the PWSCC propagation. From a stochastic analysis based on the shot-noise theory, the PWSCC propagation could be distinguished from the general corrosion, by considering the Weibull shape parameter.

A model gas that mimics the syngas produced from gasification of municipal solid waste was applied, for the first time, to the synthesis 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 small amount 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: temperature 230-250oC, pressure 60 bar, W/F 0.05 g·l/min, H2/COx ratio 2, and CO/COx ratio 0.8.

Stress corrosion cracking (SCC) is one of major threats against the integrity of the structural materials composing a nuclear power 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 electrochemical impedance 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 containing PbO in the range of 0-5,000 ppm at 315oC for 2 weeks. The oxide property was compared with SCC susceptibility obtained from a slow strain rate tension (SSRT) test for Alloy 600 in 0.1M NaOH containing PbO. The impedance value was greatly decreased by adding PbO into the solution indicating a decrease in passivity. The composition of the oxide was also changed by Pb in an aqueous solution. The duplex oxide layer consisting of outer porous nickel-rich oxide and inner dense chromium-rich oxide is modified to a Pb incorporated nickel-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 SCC acceleration of this tube among numerous sound tubes in an NPP.

A new fabrication process for generating open-cell metallic and alloyed foams was developed by combining electrical explosion of wire (EEW) and electrospray (ESP) techniques. Fe-Cr-Al alloy nano-powders prepared by EEW in ethanol were used as a starting material, and commercial polyurethane (PU) sponges were used as templates. Fe-Cr-Al foams were successfully fabricated with porosities greater than 90%. The porosity of the fabricated foams was controlled by spraying time during the ESP process. As spraying time increased from 1 to 5 h, porosity decreased from 97 to 90%. The sintered foam possessed a continuous open-cell structure, which was dependent on the structure of the PU template. The proposed method may be useful in the future as a simple means to fabricate open-cell porous materials.

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 investigated for inhibitors of stress corrosion cracking (SCC) in the tube materials. Titanium dioxide (TiO2), which is sonochemically treated in water, 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 315°C. The TiO2 particle size was reduced by ultrasonic power, and the morphology of the TiO2 powder was observed by a transmission electron microscope (TEM) based on the ultrasonic processing times. The particle size of TiO2 affects 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 composition in 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.

ODS steel normally contains an exceptionally high oxygen concentration owing to oxygen adsorption on the metal powder surfaces, as well as to the contamination during mechanical alloying and consolidation. In this study, the effect of oxygen concentration on the size distribution of oxide particles in ODS steel has been investigated. The oxygen concentration in one ODS steel sample was about 7000 ppm (sample A), while that in the other was controlled to be about 2500 ppm (sample B) by a hydrogen reduction process prior to consolidation. Sample A revealed a much smaller mean grain size (~10 μm) than sample B (~25 μm). 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 A showed a larger mean particle size (15 nm) than those (9 nm) in sample B, while their number density was nearly the same. Coarse Cr-O particles in sample A revealed a much higher number density than sample B. It is thus concluded that the size distribution and grain size of ODS steel can be controlled by a control of the excess oxygen concentration.

Ti3Al0.3Si0.7C2 compounds were synthesized via the powder metallurgical process, and oxidized isothermally and cyclically between 900 and 1200 °C in air. They had good thermal shock resistance, forming adherent oxide scales during cyclic oxidation. They oxidized to rutile-TiO2, α-Al2O3, and amorphous SiO2, together with gaseous escape of carbon. The oxide scales that formed during isothermal and 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 formed by the outward diffusion of Al3+ ions. The inner scale formed by the inward diffusion of O2- ions. No selective oxidation occurred from the early oxidation period.

The formation of hollow Cu oxide nanoparticles through the oxidation process has been studied with Cu nanoparticles produced by the plasma arc discharge method. The initial copper nanoparticles had a size range of 40 - 60 nm and a thin Cu2O layer on the surface. After oxidation at 100°C, there was no significant change in the particles. After oxidation at 200°C, however, the particles consisted of Cu2O and CuO instead of metallic Cu. By further increasing the temperature up to 300°C, only CuO particles remained. The obtained CuO particles had a hollow structure which resulted from the Kirkendall effect.

Waste PCBs (Printed Circuit Boards) from LCDs (Liquid Crystal Displays) contain valuable raw materials, Sn, Cu, and other noble metals. Among these, high purity tin was obtained by electro-winning after appropriate acid leaching of tin. For this, leaching and electro-winning process parameters were optimized for solution stability, dissolution and electrolytic efficiency. Two aqueous procedures were developed and tested for electro-winning at mass-production capable basis: (1) HCl leaching after preliminary HNO3 dissolution was quite effective in leaching high proportion of Sn as analyzed by ICP (Inductively Coupled Plasma) method. (2) Direct one-step leaching in H2SiF6 + H2SO4 + H2O2 was also tested and the solution was finally selected as electrolytes in electro-winning due to massproduction capability. The most efficient recovery of tin was observed after 7h electro-winning in aqueous H2SiF5 + H2SO4 + H2O2 maintained at 40°C: 96%-pure tin was obtained with 93.2% recovery rate.

The effects of aluminum and strontium content on an Mg-Al-Ca-Sr alloy were investigated in terms of microstructural and mechanical properties. The addition of up to 2 wt% of strontium to the Mg-5Al-2Ca alloy caused the major interdendritic intermetallic phase 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 significantly improved 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 aluminum content resulted in a drop of ductility and creep resistance at elevated temperature due to the poor metallurgical stability by the formation of β-Mg17Al12 phase.

Refining silicon and silicon nanoparticles are an important research area in solar energy research. These are related with solar cell efficiency. Silicon nanoparticles are also used for thin film solar cell and screen printing technology. We review the synthesis of silicon nanoparticles and refining of silicon. Refined silicon nanoparticles with minimal boron content were fabricated with transferred arc plasma equipped with impactor system. To control the chemical reactions leading to the formation of these compounds, H2O was injected into the shield gas line of the plasma torch. The plasma reactive time for boron removal was evaluated. The reactive time was altered by changing the flow rate of the shield gas of the plasma torch, fixing the powder feed concentration. The removal ratio of boron was also evaluated to conform if the boron content in the silicon particles was in the range required for standard solar grade silicon. The sizes and compositions of the particles were analyzed by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), Inductively Coupled Plasma (ICP), and X-Ray Diffraction(XRD) analysis.

Nanocrystalline n-type 95%Bi2Te3-5%Bi2Se3 bulk with prepared by the combined application of high energy milling and hot extrusion processes in this study. The effect of milling time on the microstructure of powders was characterized by scanning electron microscopy (SEM). With increasing milling time, powder size quickly decreased, and finally yielded nanocrystalline Bi2Te3 of less than 200nm grain size and of spherical morphology, at 90min. Microstructure and thermoelectric properties of the samples after hot-extrusion were also investigated. The hot-extruded samples observed fine-grains and improved mechanical properties. The maximum power factor of the nanaocrystalline Bi2Te3 bulk sample reaches 4.6x10-5W/mK2 at room temperature, which is lower than the zone-melted one due to high impurity and oxidization.

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 numerically integrated. The concentration of mono-size vacancies and interstitials was saturated at an early stage of irradiation, and it was found that the vacancy concentration was higher than the interstitial concentration. The high concentration of vacancies induced a growth of the CRPs at the later stage. The concentration of PDCs and the size of CRPs were used to estimate the mechanical changes, and the calculation results were compared with the measured changes in yield strength and Charpy V-notch transition temperature shift obtained from the surveillance test data of Korean light water reactors (LWRs). It was observed that the estimated values were in fair agreement with the experimental results in spite of the uncertainty regarding the material property parameters and modeling method.

The effects of Nd-Fe-B magnet scrap size on extraction behavior were investigated by liquid metal extraction using molten Mg. 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 extracted Nd after liquid metal extraction process was increased with an increasing with holding time and scrap size, and the maximum contents of 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 that Nd oxides existing in the magnet scraps prevent the dissolution of Nd into Mg.

The niobium capacitor shows somewhat more unstable characteristics than the commercial tantalum capacitors, but it will be nonetheless considered as an excellent substitute of tantalum capacitors in the future. In this study, niobium powder is fabricated by metallothermic reduction process using K2NbF7 as a raw material, KCl and KF as diluents, and Na as a reducing agent. The niobium particle size greatly decreases from 0.7μm to 0.2μm as the amount of diluent increases. However, when a higher surface area of niobium powder is desired, more amounts of diluents are used in the said method. The niobium powder morphology and particle sizes are very sensitive to the amount of sodium excess, thus the particle size of niobium powder increases with increases in the amount of sodium excess. When more diluent and sodium are used, the niobium powder is contaminated further by impurities such as Fe, Cr, Ni, and others [1,2].

The CVD apparatus for the uniform coating of silicon carbide was suggested and realized into a 3-dimensional computer-aided design (CAD) model. An experimental condition is simulated with a computational fluid dynamic program to obtain temperature and flow distribution in the CVD chamber. The simulated temperature showed the very uniform distribution especially in the hot zone region and that is thought to be the result of the design of the CVD apparatus. The temperature measured with a thermocouple showed the good matching with the simulated one, which reflected the assumption and the boundary conditions during the simulation were plausible.

The effective recovering process that consists of air-jetting, centrifugation and air-classifying was developed for phosphor recycling from flat panel display devices. At the first processing stage of air-jetting, 95% phosphor could be recovered while the recovery rate was dependent on the dimension of CCFLs. After two subsequent stages of mechanical separation, Blue, Red and Green rich phosphor could be selectively collected. The recovery of Red phosphor was 61.2% and purity of (Y, Eu)2O3 was 95%.

We have developed a mass production process of Si quantum dots using photo-induced chemical etching method with oxidation and etching agents and have investigated its optical properties. Average size of the fabricated Si quantum dots was estimated to be 2 nm. Absorption peaks of the fabricated quantum dots were observed in the short wavelength regions, e.g., 200 - 350 nm. On the other hand, 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 emission peak was fixed, two excitation peaks were observed in 340 nm and 380 nm, respectively, which seemed to be due to the energy band gap widening and/or surface coating with an ultrathin layer.

In this study, the effect of Sc addition on the microstructure and mechanical properties of Al-20Si alloys fabricated by extrusion of 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), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with an energy dispersive X-ray spectroscopy (EDS). Mechanical properties of extruded bars were investigated by micro hardness test, tensile test and wear test. With increasing the Sc contents in Al-Si alloys, mechanical properties were significantly increased. These enhanced mechanical properties can be explained based on the refinement of primary Si due to the suppression of growth of primary Si by the well-surrounded and uniformly distributed Sc.

The purpose of this study is to investigate the microstructure and mechanical properties in 9Cr-1Mo-V steel and its weld. A 220 mm thick forged plate with a typical composition of G91based on ASME A336 was used. Narrow gap welds were produced by submerged arc welding (SAW) with two different welding speeds. The microstructures in the base metal were typical tempered martensite at all locations, and the sizes of prior austenite grains were increased with the depth from the surface. The yield and tensile strengths tend to decrease with an increase in test temperature, especially at temperatures higher than 500°C. The upper shelf energy of the specimen from center was lower than that from the surface, and it also showed a higher index temperature. The toughness deterioration at the center might 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 larger sizes of the weld beads were observed in the upper region with a lower welding pass speed. There was no significant difference in the strength of the upper and lower welds, but the elongations of the upper weld were slightly larger than those of the lower weld. In the Charpy impact test, the lower weld showed a better impact toughness than the upper weld caused by the relatively smaller size of the weld beads and finer microstructures owing to a lower heat input by the increased welding speed.

The present work investigated the effects of MgO as a thermodynamic stabilizer and ZrO2 and mullite (3Al2O3·SiO2) as kinetic stabilizers 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, while the mullite-only Al2TiO5 sintered at 1550°C showed a mechanical strength of only 67 MPa at 1200°C. The strength improvement achieved at high temperatures was affected by not only secondary phase mullite to inhibit grain growth of Al2TiO5 and to improve strength but thermodynamic stabilizer to promote synthesis Al2TiO5. The coefficient of thermal expansion of mix-stabilized Al2TiO5 decreased with increase of sintering temperature due to its microcrack, however, that of the mullite-only Al2TiO5 was not changed because of large number of pores.

TaNx(1, 3 & 5 nm) films deposited on the Ag(10 nm)/Si(3 nm)/glass show dense microstructure, and this structure was stable even after annealing at 300 °C in Ar (80%) + O2 (20%) ambient for 5 min. The RMS (Root Mean Square) roughness of the films decreased with increasing the TaNx film thickness. The partial oxidation of TaNx was observed in TaNx(3 & 5 nm)/Ag(10 nm)/Si(3 nm)/glass at 300 °C annealing temperature, but no Ag diffusion happened at this temperature. It indicates that no outward diffusion of Ag occurred during the annealing. The as deposited and annealed TaNx(1, 3 & 5 nm)/Ag(10 nm)/Si(3 nm)/glass films showed better transmittance than Ag(10 nm)/glass films in the visible region. The optical data obtained here was in good agreement with simulated predictions.

The microstructures and electrochemical properties of rapidly-solidified silicon alloys mixed with various forms of carbon have been investigated. Rapidly-solidified Si70Ni15Ti15 (at%) alloy (SNT1515) ribbons were prepared by arc-melting, followed by melt spinning process in vacuum. The obtained ribbons were fragmented by ball milling to produce a fine powder of -500mesh. The alloy powder was mixed with various types of carbon: multi-walled carbon nanotubes, hard carbon, soft carbon, and graphite. Each was added by 2wt% by ball milling for 2 hours. The microstructure of the melt-spun ribbon showed a fine silicon primary phase surrounded by Si7Ni4Ti4 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.

Ultrasonic spray pyrolysis (USP) and thermal reaction were combined to fabricate lithium iron borate compound nanopowder in 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 material in lithium secondary battery.