• Nuclear Engineering and Technology
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• 제31권4호
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• pp.365-374
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• 1999

A nuclear design of fission moly production targets for a research reactor, HANARO was peformed. It was found that the use of MCNP-4A, ORIGEN-2 code was reliable for the analysis of production characteristics of $^{99}$ Mo in a target fuel at an irradiation holes. A parametric study was done for the optimization of target location, target dimension, target shape and fuel materials. It was shown that a fuel thickness was the most sensitive parameters and electro-deposited target gave the highest 99Mo yield ratio. A pellet target with vibro-compaction powder, however, showed the largest production capacity and better engineering feasibility even with less yield ratio. Ten kinds of optimized target design for both LEU and HEU satisfied all the given design constraints. The most favorable design was the HEU ring-shaped electro-deposited target, considered the safety limit, production yield, chemical process easiness, yield ratio, and amount of radioactive waste.

• 열처리공학회지
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• 제31권3호
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• pp.126-134
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• 2018

In this research, we produced polycrystalline n-type $Bi_2Te_{2.7}Se_{0.3}$ powder using water atomization. To obtain full benefit through water atomized powder, we have implemented spark plasma sintering and hot extrusion for powder compaction. The microstructure and thermoelectric properties were investigated and compared. The average grain size of SPS and extruded bulks were 3.08 and $3.86{\mu}m$ respectively. The extruded material microstructure contains layered grains with less grain boundaries and its counter-part SPS displays dense packed grains with high grain boundaries. Among both bulks, extrusion sample exhibited high power factor (PF) of $2.96{\times}10^{-3}Wm^{-1}K^{-2}$ which is 38% higher than SPS ($2.14{\times}10^{-3}$) bulk sample. Due to variations in grain size and grain boundaries, the SPS bulk shows low thermal conductivity than extruded bulk. However, the extruded bulk sample exhibited a peak ZT of 0.69 at 400 K, which is 19% higher than SPS bulk sample, due to its higher power factor.

• 한국세라믹학회지
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• 제50권3호
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• pp.218-225
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• 2013

The densification behavior and strength of sintered reaction bonded silicon nitrides (SRBSN) that contain $Lu_2O_3-SiO_2$ additives were improved by the addition of fine Si powder. Dense specimens (relative density: 99.5%) were obtained by gas-pressure sintering (GPS) at $1850^{\circ}C$ through the addition of fine Si. In contrast, the densification of conventional specimens did not complete at $1950^{\circ}C$. The fine Si decreased the onset temperature of shrinkage and increased the shrinkage rate because the additive helped the compaction of green bodies and induced the formation of fine $Si_3N_4$ particles after nitridation and sintering at and above $1600^{\circ}C$. The amount of residual $SiO_2$ within the specimens was not strongly affected by adding fine Si powder because most of the $SiO_2$ layer that had formed on the fine Si particles decomposed during nitridation. The maximum strength and fracture toughness of the specimens were 991 MPa and $8.0MPa{\cdot}m^{1/2}$, respectively.

• 한국분말재료학회지
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• 제14권6호
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• pp.354-361
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• 2007

The bi-materials with Al-Mg alloy and its composites reinforced with SiC and $Al_2O_3$ particles were prepared by conventional powder metallurgy method. The A1-5 wt%Mg and composite mixtures were compacted under $150{\sim}450\;MPa$, and then the mixtures compacted under 400 MPa were sintered at $773{\sim}1173K$ for 5h. The obtained bi-materials with Al-Mg/SiCp composite showed the higher relative density than those with $Al-Mg/Al_2O_3$ composite after compaction and sintering. Based on the results, the bi-materials compacted under 400 MPa and sintered at 873K for 5h were used for mechanical tests. In the composite side of bi-materials, the SiC particles were densely distributed compared to the $Al_2O_3$ particles. The bi-materials with Al-Mg/SiC composite showed the higher micro-hardness than those with $Al-Mg/Al_2O_3$ composite. The mechanical properties were evaluated by the compressive test. The bi-materials revealed almost the same value of 0.2% proof stress with Al-Mg alloy. Their compressive strength was lower than that of Al-Mg alloy. Moreover, impact absorbed energy of bi-materials was smaller than that of composite. However, the bi-materials with Al-Mg/SiCp composite particularly showed almost similar impact absorbed energy to $Al-Mg/Al_2O_3$ composite. From the observation of microstructure, it was deduced that the bi-materials was preferentially fractured through micro-interface between matrix and composite in the vicinity of macro-interface.

• Geomechanics and Engineering
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• 제18권5호
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• pp.535-543
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• 2019

Building on/with expansive soils with no treatment brings complications. Compacted expansive soils specifically fall short in satisfying the minimum requirements for transport embankment infrastructures, requiring the adoption of hauled virgin mineral aggregates or a sustainable alternative. Use of hauled aggregates comes at a high carbon and economical cost. On average, every 9m high embankment built with quarried/hauled soils cost $12600MJ.m^{-2}$ Embodied Energy (EE). A prospect of using mixed cutting-arising expansive soils with industrial/domestic wastes can reduce the carbon cost and ease the pressure on landfills. The widespread use of recycled materials has been extensively limited due to concerns over their long-term performance, generally low shear strength and stiffness. In this contribution, hydromechanical properties of a waste tyre sand-sized rubber (a mixture of polybutadiene, polyisoprene, elastomers, and styrene-butadiene) and expansive silt is studied, allowing the short- and long-term behaviour of optimum compacted composites to be better established. The inclusion of tyre shred substantially decreased the swelling potential/pressure and modestly lowered the compression index. Silt-Tyre powder replacement lowered the bulk density, allowing construction of lighter reinforced earth structures. The shear strength and stiffness decreased on addition of tyre powder, yet the contribution of matric suction to the shear strength remained constant for tyre shred contents up to 20%. Reinforced soils adopted a ductile post-peak plastic behaviour with enhanced failure strain, offering the opportunity to build more flexible subgrades as recommended for expansive soils. Residual water content and tyre shred content are directly correlated; tyre-reinforced silt showed a greater capacity of water storage (than natural silts) and hence a sustainable solution to waterlogging and surficial flooding particularly in urban settings. Crushed fine tyre shred mixed with expansive silts/sands at 15 to 20 wt% appear to offer the maximum reduction in swelling-shrinking properties at minimum cracking, strength loss and enhanced compressibility expenses.

• 콘크리트학회논문집
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• 제12권2호
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• pp.99-107
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• 2000

This research investigates experimentally an effect on the properties of the high flowing concrete to be poured in the under-ground slurry wall of Inchon LNG receiving terminal(#213,214-TK) according to variations of concrete materials. Variables for sensitivity test were selected items as followings. 1) Concrete temperature (3cases), 2) Unit water (5cases), 3) Fineness modulus of fine aggregate (5cases), 4) Particle size of lime stone powder (3cases), 5) Replacement ratio of blast-furnace slag (4cases) and 6) Addition ratio of high range water reducing agent (5cases). And fresh conditions of the super flowing concrete should be satisfied with required range including slump flow(65$\pm$5cm), 50cm reaching time of flow(4~10sec), V-lot flowing time(10~ 20sec), U-box height(min. 300mm) and air content(4$\pm$1%). As results for sensitivity test, considered flow-ability, self-compaction and segregation resistance of the high flowing concrete, material variations and conditions of fresh concrete should be satisfied with the range as follwings. 1) Concrete temperature are 10~2$0^{\circ}C$(below 3$0^{\circ}C$), 2) Surface moisture of fine aggregate is within $\pm$ 0.6%, 3) Fineness modulus of fine aggregate is 2.6$\pm$0.2, 4)Replacement ratio of blast-furnace slag is 45~50% and 5) Addition ratio of high range water reducing agent is within 1%. Based on the specification for quality control, we successfully finished concrete pouring on the under-ground slurry wall having 75,000㎥(#213,214-TK) and accumulated real date in site.

• Geomechanics and Engineering
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• 제28권6호
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• pp.547-557
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• 2022

Dune sands are poorly graded collapsible soils lacking fines. This experimental study explored the technical feasibility of sustainable invigoration of fine waste materials to improve the geotechnical properties of dune sand. The fine waste considered in this study is fine marble waste. The fine waste powder was mixed with dune sand at different contents (5, 10,15, 20, 25, 50%), where the gradation, void ratio, compaction, and shear strength characteristics were assessed for each fine marble waste -dune sand blend. The geotechnical properties of the dune sand-fine marble waste mix delineated in this study reveal the enhancement in compaction and gradation characteristics of dune sand. According to the results, the binary mixture of dune sand with 20% of fine marble waste gives the highest maximum dry density and results in shear strength improvement. In addition, a numerical study is conducted for the practical application of the binary mix in the field and tested for an isolated shallow foundation. The elemental analysis of the fine marble waste confirms that the material is non-contaminated and can be employed for engineering applications. Furthermore, the numerical study elucidated that the shallow surface replacement of the site with the dune sand mixed with 20% fine marble waste gives optimal performance in terms of stress generation and settlement behavior of an isolated footing. For a sustainable mechanical performance of the fine marble waste mixed sand, an optimum dose of 20% fine marble waste is recommended, and some correlations are proposed. Thus, for improving dune sand's geotechnical characteristics, the addition of fine marble waste to the dune sand is an environment-friendly solution.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2002년도 제3회 최신 분말제품 응용기술 Workshop
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• pp.25-37
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• 2002

The most important industrial application of gamma radiation in characterizing green compacts is the determination of the density. Examples are given where this method is applied in manufacturing technical components in powder metallurgy. The requirements imposed by modern quality management systems and operation by the workforce in industrial production are described. The accuracy of measurement achieved with this method is demonstrated and a comparison is given with other test methods to measure the density. The advantages and limitations of gamma ray densitometry are outlined. The gamma ray densitometer measures the attenuation of gamma radiation penetrating the test parts (Fig. 1). As the capability of compacts to absorb this type of radiation depends on their density, the attenuation of gamma radiation can serve as a measure of the density. The volume of the part being tested is defined by the size of the aperture screeniing out the radiation. It is a channel with the cross section of the aperture whose length is the height of the test part. The intensity of the radiation identified by the detector is the quantity used to determine the material density. Gamma ray densitometry can equally be performed on green compacts as well as on sintered components. Neither special preparation of test parts nor skilled personnel is required to perform the measurement; neither liquids nor other harmful substances are involved. When parts are exhibiting local density variations, which is normally the case in powder compaction, sectional densities can be determined in different parts of the sample without cutting it into pieces. The test is non-destructive, i.e. the parts can still be used after the measurement and do not have to be scrapped. The measurement is controlled by a special PC based software. All results are available for further processing by in-house quality documentation and supervision of measurements. Tool setting for multi-level components can be much improved by using this test method. When a densitometer is installed on the press shop floor, it can be operated by the tool setter himself. Then he can return to the press and immediately implement the corrections. Transfer of sample parts to the lab for density testing can be eliminated and results for the correction of tool settings are more readily available. This helps to reduce the time required for tool setting and clearly improves the productivity of powder presses. The range of materials where this method can be successfully applied covers almost the entire periodic system of the elements. It reaches from the light elements such as graphite via light metals (AI, Mg, Li, Ti) and their alloys, ceramics ($AI_20_3$, SiC, Si_3N_4, $Zr0_2$, ...), magnetic materials (hard and soft ferrites, AlNiCo, Nd-Fe-B, ...), metals including iron and alloy steels, Cu, Ni and Co based alloys to refractory and heavy metals (W, Mo, ...) as well as hardmetals. The gamma radiation required for the measurement is generated by radioactive sources which are produced by nuclear technology. These nuclear materials are safely encapsulated in stainless steel capsules so that no radioactive material can escape from the protective shielding container. The gamma ray densitometer is subject to the strict regulations for the use of radioactive materials. The radiation shield is so effective that there is no elevation of the natural radiation level outside the instrument. Personal dosimetry by the operating personnel is not required. Even in case of malfunction, loss of power and incorrect operation, the escape of gamma radiation from the instrument is positively prevented.

• 한국재료학회지
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• 제25권2호
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• pp.68-74
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• 2015

The porous $Mg_3Sb_2$ based compounds with 60~70% of relative density were prepared by powder compaction at room temperature and reactive liquid phase sintering at 1023 K for 4hrs. The stoichiometric $Mg_3Sb_2$ compounds were synthesized from elemental Sb and Mg powder in the mixing range of 61~63 at% Mg. The increased scattering effect due to the micro-pores reduced the mobility of the charge carrier and the phonon, which caused the electrical conductivity and the thermal conductivity to decrease, respectively. But the scattering effect was greater for the electrical conductivity than for the thermal conductivity. Excess Mg alloyed in the $Mg_3Sb_2$ compounds decreased the electrical conductivity, but had no effect on the thermal conductivity. On the other hand, the large increase of the Seebeck coefficient was the result of a decrease in the charge carrier density due to the excess Mg. Dimensionless figure of merit of the porous $Mg_3Sb_2$ compound reached a maximum value of 0.28 at 61 at% Mg. The obtained value was similar to that of $Mg_3Sb_2$ compounds having little pores.

• 한국분말재료학회지
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• 제17권4호
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• pp.319-325
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• 2010

Electrical discharge machining (EDM) is an attractive machining technique but it requires electrically conductive ceramic materials. In this study, Alumina matrix composites reinforced with CNTs were fabricated through CNT purification, mixing, compaction and spark plasma sintering (SPS) processes. $Al_2O_3$ nanocomposites with the different CNT concentrations were synthesized. The mechanical and electrical characteristics of $Al_2O_3$/CNTs composites were examined in order to apply the materials to the EDM process. In addition, micro-EDM using wire electrical discharge grinding (WEDG) was conducted under the various EDM parameters to investigate the machining characteristics of machined hole by Field Emission Scanning Electron Microscope (FE-SEM). The results show that $Al_2O_3$/CNTs 10%Vol. was more suitable than the other materials because high conductivity and large discharge energy caused violent sparks resulting in bad machining accuracy and surface quality.