• 한국분말재료학회지
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• 제1권1호
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• pp.72-78
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• 1994

Two kinds of $U_3Si$ powders and $U_3Si$ dispersed nuclear fuel meats have been prepared by conventional comminution process and a newly developed rotating disk atomization process. In contrast to angular shape and broad size distribution of the conventionally processed powder, the atomized powder was spherical and showed narrow size distribution. For the atomized powder, the heat treatment time for the formation of $U_3Si$ by a peritectoid reaction was reduced to about one tenth, thanks to microstructure refinement by rapid cooling of about 5$\times$104 K/s. The extruding pressure of atomized $U_3Si$ powder and Al powder mixture was lower than that of comminuted $U_3Si$ and Al powder mixture. The elongation of the atomization processed fuel meats was much higher than that of the comminution processed fuel meats and remained over 10% up to 80wt.% of $U_3Si$ powder fraction in the fuel meats. It appears therefore that the loading density of $U_3Si$ in fuel meat can be increased by using atomized $U_3Si$ powder. The atomized spherical particles were randomly distributed, while the comminuted particles with angular and longish shape were considerably aligned along the extrusion direction. Along the transverse direction of the extraction the electrical conductivity of the atomization processed fuel meats was appreciably higher than that of comminution processed fuel meats. This tendency became pronounced as $U_3Si$ content increased. Because the thermal conduction which is believed to be proportioned to the electrical conduction in the nuclear fuel meats occurs in radial direction, the atomization processed fuel can be better used in research reactors where high thermal conductivity is required.

• 한국재료학회지
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• 제33권12호
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• pp.530-536
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• 2023

The theoretical capacity of silicon-based anode materials is more than 10 times higher than the capacity of graphite, so silicon can be used as an alternative to graphite anode materials. However, silicon has a much higher contraction and expansion rate due to lithiation of the anode material during the charge and discharge processes, compared to graphite anode materials, resulting in the pulverization of silicon particles during repeated charge and discharge. To compensate for the above issues, there is a growing interest in SiO_x materials with a silica or carbon coating to minimize the expansion of the silicon. In this study, spherical silica (SiO₂) was synthesized using TEOS as a starting material for the fabrication of such SiO_x through heating in a reduction atmosphere. SiO_x powder was produced by adding PVA as a carbon source and inducing the reduction of silica by the carbothermal reduction method. The ratio of TEOS to distilled water, the stirring time, and the amount of PVA added were adjusted to induce size and morphology, resulting in uniform nanosized spherical silica particles. For the reduction of the spherical monodisperse silica particles, a nitrogen gas atmosphere mixed with 5 % hydrogen was applied, and oxygen atoms in the silica were selectively removed by the carbothermal reduction method. The produced SiO_x powder was characterized by FE-SEM to examine the morphology and size changes of the particles, and XPS and FT-IR were used to examine the x value (O/Si ratio) of the synthesized SiO_x.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2004년도 International Symposium on Powder Materials and Processing
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• pp.62-62
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• 2004

• 한국산업보건학회지
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• 제25권3호
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• pp.294-300
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• 2015

Objectives: The aim of this study is to identify physicochemical properties such as chemical composition, size, shape and crystal structure of powder byproducts generated from a metallization process and its 1st scrubber in the semiconductor industry. Methods: Powder samples were collected from inner chambers during maintenance of the W-plug process equipment (using tungsten hexafluoride as a precursor material) and its 1st scrubber. The chemical composition, size and shape of the powder particles were determined by field emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive spectroscope (EDS). The crystal structure of the powders was analyzed by X-ray diffraction (XRD). Results: From the SEM-EDS and TEM-EDS analyses, O and W were mainly detected, which indicates the powder byproducts are tungsten trioxide ($WO_3$), whereas Al, F and Ti were detected as low peaks. The powder particles were spherical and nearly spherical, and the particle size collected from the process equipment and its 1st scrubber showed 10-20 nm (agglomerates: 55-90 nm) and 16-20 nm (agglomerates: 80-120 nm) as primary particles, respectively. The XRD patterns of the yellow powder byproducts exhibit five peaks at $23.8^{\circ}$ $33.9^{\circ}$ $41.74^{\circ}$ $48.86^{\circ}$ and $54.78^{\circ}$ which correspond to the (200), (220), (222), (400), and (420) planes of cubic $WO_3$. Conclusions: We elucidated the physicochemical characteristics of the powder byproducts collected from W-plug process equipment and its 1st scrubber. This study should provide useful information for the development of alternative strategies to improve the working environment and workers' health.

• 한국분말재료학회지
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• 제19권5호
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• pp.348-355
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• 2012

Cold spray deposition using Titanium powder was carried out to investigate the effects of powder morphology and powder preheating on the coating properties such as porosity and hardness. The in-flight particle velocity of Ti powder in cold spray process was directly measured using the PIV (particle image velocimetry) equipment. Two types of powders (spherical and irregular ones) were used to manufacture cold sprayed coating layer. The results showed that the irregular morphology particle appeared higher in-flight particle velocity than that of the spherical one under the same process condition. The coating layer using irregular morphology powder represented lower porosity level and higher hardness. Two different preheating conditions (no preheating and preheating at $500^{\circ}C$) were used in the process of cold spraying. The porosity decreased and the hardness increased by conducting preheating at $500^{\circ}C$. It was found that the coating properties using different preheating conditions were dependent not on the particle velocity but on the deformation temperature of particle. The deposition mechanism of particles in cold spray process was also discussed based on the experimental results of in flight-particle velocity.

• 한국분말재료학회지
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• 제24권3호
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• pp.202-209
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• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

• 콘크리트학회논문집
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• 제12권4호
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• pp.103-111
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• 2000

The influence of the improvement of grain shape of the coarse aggregate to the unit powder content of concrete and the fine aggregate ratio for the increase of the flowability and segregation resistance of high performance concrete was examined. According to the experimental results, flowability and compacting of concrete presents best states in the S/a which has the smallest 패야 ratio. The coarse aggregate after improvement of grain shape, that has changed from the 0.68 of spherical rate of disk shape to 0.73, led fine aggregate ratio to be down 6% (i.e from 47% to 41%). The improvement of grain shape of the coarse aggregate also led the lowest unit powder content to be down 60kg/㎥ (ie from 530kg/㎥ to 470kg/㎥). And approximate 10% of unit water content has been reduced as unit powder content was down. However, the compressive strength after the improvement of grain shape of the coarse aggregate decreased to 5% due to decrease of adhesiveness of the aggregate and cement paste.

• 대한금속재료학회지
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• 제47권1호
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• pp.21-25
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• 2009

The reduction of $Ni(OH)_2$ by hydrazine-sodium phosphinate in water and water-diethylene glycol solutions for the preparation of spherical nickel particles has been studied at room temperature. The effect of reaction conditions on the size and morphology of Ni powder was revealed using SEM and XRD analysis technique. It was shown that in the presence of sodium phosphinate the reduction process become activated and a formation of Ni particles was completed within several minutes at room temperature. As a desired result spherical Ni powders with particles size from 0.07 to 2.0 mm were obtained.

• 한국세라믹학회지
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• 제25권5호
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• pp.473-478
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• 1988

In order to obtain the high purity $\beta$-SiC powder that possesses the excellent sinterability and is close to the spherical shape, the carbon black was mixed into the composition of Si(OC2H5)4-H2O-NH3-C2H5OH which the monodispersed spherical fine particles is formed the hydrolysis of Ethylsilicate and the mixture was carbonized under an argon atmosphere. Particle shpae, size and the yield of $\beta$-SiC powder were investigated according to the molar ratio of carbon/alkoxide and variations of reaction temperature and reaction time. The results of this study are as follow ; 1) The yield of $\beta$-SiC gained from the reaction for one hour at 150$0^{\circ}C$ almost got near 100% and the particle size of $\beta$-SiC from the reaction for 15 hrs at 150$0^{\circ}C$ was 0.2${\mu}{\textrm}{m}$ on the average and close to the spherical shape agglomerate state. 2) When the molar ratio carbon/alkoxide is over 3.1 and the reaction occurs at 145$0^{\circ}C$ for 5hrs, the carbon content has not an effect on the kind of crystal of product.

• 한국세라믹학회지
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• 제28권10호
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• pp.757-766
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• 1991

These powder properties were investigated and prepared of ultrafine Mn-Zn ferrite powder by Direct-wet process from variation of oxidation condition. H2O2 oxidation the products were ultrafine spherical particles of about 400${\AA}$ in diameter and superparamagnetics. H2O2 and Air oxidation, Coexistance ultrafine spherical particles of about 400${\AA}$ and cubic particles of about 1000${\AA}$. The products were constructed of superparamagnetic and ferromagnetic particles, and Magnetization were about 30 emu/g. Air Oxidation, Above 6 hr Air 120 ι/hr and 4 hr of Air 180 ι/hr were uniform cubic particles of above 1000${\AA}$. The products were ferromagnetic particles and Magnetization of above 45 emu/g.