• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.195-196
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• 2006

In recent years, demands for sintered ferrous material with higher strength are increasing. To satisfy these demands, studies and commercial use of the die wall lubrication method, the warm compaction method and the combination of both methods are widely carried out to achieve high density. The die wall lubrication warm compaction method makes it possible to achieve high density by reducing internal lubricant through die wall lubrication, although the method involves several issues such as prolonged cycle time due to lubricant spraying and difficulty in spraying lubricant in the case of compacting with complicated geometry. Meanwhile, the conventional warm compaction method requiring no die wall lubricant application cannot achieve such a high density as in the case of die wall lubrication warm compaction due to higher volume of internal lubricant. However, this report discloses our study result in which the possibility of improving density is exhibited by using a lubricant type with superior dynamic ejection property that can reduce volume of lubricant additive.

• Composites Research
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• v.30 no.5
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• pp.267-272
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• 2017

In this study, SiC powder was added to twill woven carbon fiber reinforced plastic (CFRP) composites to improve its mechanical properties. An acoustic emission (AE) frequency analysis method was suggested for the prediction of failure behaviors. Tensile tests were conducted and the fracture characteristics of each component of the SiC reinforced composite were evaluated using AE. The results showed that SiC powder improved the strength of twill woven CFRP composites and the fracture behavior of the SiC reinforced CFRP composite and its crack extension could be effectively evaluated on the basis of the specific AE frequency bands which are 100 to 228 kHz and 428 to 536 kHz upon the resin failure and 232 to 424 kHz due to addition of SiC powder and 576 to 864 kHz at the fiber breakage.

• Journal of the Korean Ceramic Society
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• v.31 no.8
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• pp.823-828
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• 1994

Dispersion condition of Si3N4 powder in molten wax was established by comparing relative viscosity of mixture with 20 vol% solids loading, while the evaluation of compression-molded sample was demonstrated as an effective method for developing a binder system for injection molding. The best dispersion of Si3N4 powder in molten wax was achieved when Si3N4 powder was treated with 5% stearic acid, and the critical powder volume fraction was determined to be about 0.51 from density measurement of compression-molded samples. Samples containing polar secondary binder showed markedly improved green strength, higher thermal expansion and increased wicking rate in the early stage.

• Journal of Powder Materials
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• v.25 no.4
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• pp.346-354
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• 2018

Over the last decade, the study of the synthesis of semiconductor colloidal quantum dots has progressed at a tremendous rate. Colloidal quantum dots, which possess unique spectral-luminescent characteristics, are of great interest in the development of novel materials and devices, which are promising for use in various fields. Several studies have been carried out on hot injection synthesis methods. However, these methods have been found to be unsuitable for large-capacity synthesis. Therefore, this review paper introduces synthesis methods other than the hot injection synthesis method, to synthesize quantum dots with excellent optical properties, through continuous synthesis and large capacity synthesis. In addition, examples of the application of synthesized colloid quantum dots in displays, solar cells, and bio industries are provided.

• Applied Microscopy
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• v.32 no.4
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• pp.311-317
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• 2002

There is great requirement on the TEM specimen preparation method with particle size selectivity as a prerequisite for the quantitative structure analysis on the materials such as gibbsite powder, which generally forms a large agglomerate and shows a variation of transition process depending on their sizes. In this experiment, we made an attempt to give a methodology for the TEM specimen preparation of powder with the size selectivity. After mixing 1 wt% gibbsite powder with ethanol solvent, gibbsite suspension was prepared by application of ball-milling and ultrasonification with addition of 0.25 vol% dispersion agent, Darvan C, which was diluted into distilled water by the ratio 1:19. Appling the static sedimentation method to gibbsite suspension after estimation of the sedimentation time by the measurement of accumulative concentration variation, we acquired TEM specimens with well-dispersed and size selected gibbsite particles in nm scale. Overall picture of each sample was taken by SEM and morphology of each dispersed particle was imaged by TEM. Raw and processed gibbsite powders were also examined by XRD to investigate whether they were suffered from phase change during the process or not.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2002.07a
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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.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.9
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• pp.787-792
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• 2015

Recently, 3D printing technology is a hot issue in various industrial fields. According to the user's application, it allows for the free form fabrication method to be utilized in a wide range. The powder based fusion technique is one of the 3D printing methods. When using this method it is possible to apply the various binder jetting techniques such as piezo, thermal bubble jet, dispenser and so on. In this paper, a multi thermal bubble ink jet was integrated for jetting of powder binding material and developing a power fused 3D printing system. For high quality 3D printing parts, it needs an analysis and evaluation of the behavior of the thermal bubble ink jet head. In the experiment, a correlation between jetting binder quantity and layer thickness of powder was investigated, and a 3D part model was fabricated, which was used by measuring the scale factor.

• Advances in nano research
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• v.16 no.2
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• pp.165-173
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• 2024

The production of multipurpose cotton fabrics aimed at elevating the quality of aerobic and dance sportswear is explored in this study. Powder metallurgy, known for its high efficiency in manufacturing technological components with minimal waste, is employed as a method for fabricating brush ferrules for painting. The utilization of iron-copper material, prepared through powder metallurgy, enhances the strength and quality of the brush ferrules. A microscopic analysis reveals a robust interconnection between the particles of each layer achieved through isostatic pressure, resulting in a favorable microstructure. The relative density and strength of parts produced from copper-iron powder exhibit an increase with higher pressure levels. The application of this material in brush ferrules ensures their durability and longevity, thereby supporting the creation of artwork. The evolution of art over time reflects changing ideas and possibilities, and technological advancements have significantly improved artistic tools. The role of tools in artistic expression is paramount, and the integration of powder metallurgy materials in brush ferrules fortifies their artistic importance. In summary, this study underscores the advantages of powder metallurgy in augmenting the quality of art tools and facilitating artistic creation.

• International Journal of Industrial Entomology and Biomaterials
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• v.35 no.2
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• pp.77-82
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• 2017

We studied on improvement method of rutin content using mulberry leaf powder. Mulberry leaves were collected and then hot-air dried and powdered for experiment. As a result, we have developed a pre-treatment method that extracts mulberry leaf powder with water or fermented alcohol with reflux extractor and then increases the rutin content by improving the process. Citric acid (0.1 ~ 1%) and 1000 ml fermented alcohol (50 ~ 95%) or water (10 ~ 50 times) was extracted with 100 g of mulberry leaf powder using a reflux extraction device ($80{\sim}90^{\circ}C$, 1 hour, twice). The extracts were collected, filtered and concentrated. For the recrystallization, the concentrate was dissolved by adding distilled water and allowed to stand at a low temperature. Then, the supernatant was discarded by centrifugation, and only the residue was lyophilized to prepare a final powder. As a result, regardless of the concentration of citric acid added, the content of rutin was higher in 90% fermented alcohol extract. Whereas, in the case of extracting with water, citric acid 0.5% was added to water 25 times as much as the weight of mulberry leaf powder, and 2274.4 (mg / 100g) of rutin content was highest in the case of refluxing twice at $80^{\circ}C$ for 1 hour. The powder with increased rutin content is expected to be applicable to various foods as a food additive. In addition, it can contribute to the improvement of the farm income by promoting consumption of mulberry leaf while satisfying the consumers' desire for functional food intake.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.10
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• pp.346-351
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• 2018

Metal three-dimensional (3D) printing technologies are mainly classified as powder bed fusion (PBF) and direct energy deposition (DED) methods according to the method of application of a laser beam to metallic powder. The DED method can be used to fabricate fine and hard 3D metallic structures by applying a strong laser beam to a thin layer of metallic powder. The PBF method involves slicing 3D graphics to be a certain height, laminating metal powders, and making a 3D structure using a laser. While the DED method has advantages such as laser cladding and metallic welding, it causes problems with low density when 3D shapes are created. The PBF method was introduced to address the structural density issues in the DED method and makes it easier to produce relatively dense 3D structures. In this paper, thin lines were produced by using PBF 3D printers with stainless-steel powder of roughly $30{\mu}m$ in diameter with a galvano scanner and fiber-transferred Nd:YAG laser beam. Experiments were carried out to find the optimal conditions for the width of a line depending on the processing times, laser power, spot size, and scan speed. The optimal conditions were two scanning processes in one line structure with a laser power of 30 W, spot size of $28.7{\mu}m$, and scan speed of 200 mm/s. With these conditions, a minimum width of about $85.3{\mu}m$ was obtained.