• Journal of the Korean Ceramic Society
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• v.33 no.8
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• pp.849-854
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• 1996

boehmite which is the by-product in alcohol process contains anions such as $Cl^-,{NO_3}^-.or\; CH_3COO^-$ Influe-nce of these anions was studied on properties of $\alpha$-alumina powders prepared by treating the transformed ${\gamma}$-alumina with the alumina sol and $\alpha$-alumina seeds (d_{50}=0.36\mu\textrm{m}$) Disperal 20/1 and 10/1 containing $Cl^-$ produced spherical powder Disperal 20/2 with ${NO_3}^-$ produced equiaxed powder and Disperal 10/3 with $CH_3$ $COO^-$ irregular shaped and sized powder. All of these $\alpha$-alumina powders were submicron. Although the green density of the alumina powder derived from Disperal 10/1 by calcination at $1200^{\circ}C$/1h. was 53% it did not sinter even at $1550^{\circ}C$ for 2h. which implies that its d50 is greater than $3\mu\textrm{m}$. The others gave green densities in the range of 44~47% but they sintered as well as the AKP-30 at $1500^{\circ}C$/2 h or $1550^{\circ}C$/2 h.

• Journal of Power System Engineering
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• v.17 no.2
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• pp.108-113
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• 2013

In this study, lightweight aggregate was made from basalt stone powder sludge. Clay and glass powder were respectively added from 0 to 20 wt% and from 0 to 100 wt%. The glass powder helped to form glassy phase which trapped generating gas in the materials. $CaCO_3$ helping bloating process was added from 0 to 10 wt%. It was possible to produce lightweight aggregate at range from $1150^{\circ}C$ to $1200^{\circ}C$. The specimen was heated in furnace at 1100, 1150 and $1200^{\circ}C$ for 15 min, respectively, to sinter aggregates. Chemical composition of materials were determined, and characteristics were analyzed, including specific gravity, water absorption. Lightweight aggregate which was heated at $1200^{\circ}C$ had specific gravity of $0.53g/cm^3$, water absorption of 3.08%, and this value satisfied KS L 8551 standard.

• Journal of Industrial Technology
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• v.35
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• pp.3-8
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• 2015

A study has been made on defects which are formed in manufacturing processes of engine bearing and also on fatigue crack growth behavior in each step of bearing metal manufacturing. After the first step(sinter brass powder on steel plate ; Series A) many voids are made on brass surface and its size is decreased by the second step(rolling process of sintered plate ; Series B). After the third step(re-sintering step of brass powder and rolling ; Series C) the number of voids is decreased and its type shows line. The time of fatigue crack initiation and the growth rate of fatigue crack are in order of Series A, Series B, Series C. These reasons are that void fosters the crack initiation and growth, and residual stress made by rolling process effects on the crack growth rate in Series B, C. In forming and machining processes by use of final bearing metal, crack was observed at internal corner of flange and peeling off was observed at junction between steel and brass. Owing to the above crack and peeling off, it is considered that there is a possibility of fatigue fracture during the application time.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.469.2-469.2
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• 2014

All-solid-state solar cell based on Chloride doped organometallic halide perovskite, (CH3NH3)PbIxCl3-x, has achieved a highly power conversion efficiency (PCE) to over 15% [1] and further improvements are expected up to 20% [2]. In this way, solar cells using novel light absorbing perovskite material are actively being studied as a next generation solar cells. However, making solution-process require high temperature up to $500^{\circ}C$ to form compact hole blocking layer and sinter the mesoporous oxide scaffold layer. Because of this high temperature process, fabrication of flexible solar cells on plastic substrate is still troubleshooting. In this study, we fabricated highly efficient flexible perovskite solar cells with PCE in excess of 11%. Atomic layer deposition (ALD) is used to deposit dense $TiO_2$ as hole blocking layer on ITO/PEN substrate. The all fabrication process is done at low temperature below $150^{\circ}C$. This work shows that one of the important blueprint for commercial use of perovskite solar cells.

• Journal of the Korean Society of Visualization
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• v.16 no.2
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• pp.7-15
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• 2018

The fluid-flow characteristics of flue-gas-recirculation (FGR) system can have a significant effect on system efficiency of a sintering plant. The flow characteristics in the system were investigated. A sintering plant with FGR system was modeled. Numerical visualization was performed and flow characteristics were analyzed. Characteristics of the flow distribution of the branch ducts, the inflow of air into the recirculating hood, and the flow in the hood were discussed. Based on the results three suggestions were proposed: (1) distribution of branch duct flowrate upstream, (2) installation of external air ducts in the hood, and (3) installation of baffles at the hood corners. The suggestions were tested numerical and experimental visualization methods. The suggestions were effective and confirmed to be applicable to the actual sinter plant.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.8
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• pp.476-482
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• 2016

Convectional PZT based piezoelectric ceramics have to sinter at high temperature about $1,200^{\circ}C$ for their suitable electrical properties. However, some issues: low temperature sintering piezoelectric ceramic composition and reliable internal electrode, have recently attracted a great deal of interest as a highly efficient multi-layered piezoelectric ceramics. In order to optimize low temperature sintering conditions of thick-film PMN-PZ-PT ceramic, it was investigated sintering and piezoelectric properties according to the change of $LiBiO_2$ contents. Thus, the superior piezoelectric properties were found at the pallet type PMN-PZ-PT optimized with low sintering processing at $925^{\circ}C$ including 7 wt% $LiBiO_2$ sintering aid. Consequentially, we successfully manufactured thick-film PMN-PZ-PT ceramics, which had superior piezoelectric and dielectric properties, with 5 wt% of $LiBiO_2$ sintering aid at temperature of $900^{\circ}C$.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.574-579
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• 2013

The milling and particulate characteristics of Al alloy-$Al_2O_3$ powder mixtures for a reaction-bonded $Al_2O_3$ (RBAO) process were studied. A commercially available prealloyed Al powder with Zn, Mg, Cu and Cr alloying elements (7475 series) was mixed with a calcined sinter-active $Al_2O_3$ powder and then milled in centrifugal milling equipment for ~48 hrs. The Al alloy-$Al_2O_3$ powder mixtures after milling were characterized and evaluated in various ways to reveal their particulate characteristics during milling. The milling efficiency of the Al alloy increased with a longer milling time. Comminution of the Al alloy particles started with its elongation, showing a high aspect ratio. With a longer milling time, the elongated Al alloy particle changed in terms of its shape and size, becoming equiaxially fine particles. Regardless of the milling efficiency of the Al alloy particles, all of the Al alloy particles repeatedly experienced strong plastic deformation during milling, giving rise to higher density of surface defects, such as microcracks, and leading to higher residual microstress within the Al alloy particles. The chemical reactions, oxidation behavior and hydration behavior of the Al alloy particles and the hydrolysis characteristics of their reaction with the environment were also observed during the milling process and during the subsequent powder handling steps.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.808-809
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• 2006

The decrease of the distance between particle centers due to the growth of the sinter necks can be explained by the well known two-particle model. Unfortunately this model fails to provide a comprehensive description of the processes for 3D specimens. Furthermore, there is a significant discrepancy between the calculated and the measured shrinkage because particle rearrangements are not considered. Only the recently developed analysis of the particle movements inside of 3D specimens using micro focus computed tomography $({\mu}CT)$, combined with photogrammetric image analysis, can deliver the necessary experimental data to improve existing sintering theories. In this work, ${\mu}CT$ analysis was applied to spherical copper powders. Based on photogrammetric image analysis, it is possible to determine the positions of all particle centers for tracking the particles over the entire sintering process and to follow the formation and breaking of the particle bonds. In this paper, we present an in-depth analysis of the obtained data. In the future, high resolution synchrotron radiation tomography will be utilized to obtain in-situ data and images of higher resolution.

• Journal of Powder Materials
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• v.6 no.1
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• pp.88-95
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• 1999

The purpose of this study is to investigate the manufacturing feasibility of WC-Co milling inserts via Powder Injection Molding (PIM) process. WC-Co is used in a wide variety of cutting tools due to its high hardness, stiffness, compressive strength and wear resistance properties. WC-Co parts for a high stress application were conventionally produced by the press and sinter method, which were Iimited to 2 dimensional shapes. Manufacturing WC-Co parts for a high stress application by PIM implies that tool efficiency can be highly improved due to increased freedom is design. P30 grade WC powder (WC-Co-TiC-TaC system) was mixed with RIST-5B133 binder and injection molded into milling inserts (Taegu Tech. Model WCMX 06T 308). The mean grain size of the powder was about 0.8$\mu$m. Injection molded specimens were debound by solvent extraction and thermal degradation method at various conditions. The specimens were sintered at 140$0^{\circ}C$ for 1 hr in vacuum. Carbon content, weight loss, dimensional change, and macro defects of the specimen were carefully monitored at each stage of the PIM process. PIMed WC-Co milling inserts reached 100% full density after sinteing. Its mechanical properties and micro-structures were comparable with the press and sintered milling insert. Carbon content of the sintered WC-Co insert was mainly determained by the atmosphere of thermal debinding. By controlling powder loading and injection molding condition, dimensional accuracy could be obtained within 0.4%. We confirm that PIM can not only be an alternative manufacturing method for WC-Co parts economically but also provide a design freedom for more effieient cutting tools.

• Journal of Industrial Technology
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• v.31 no.A
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• pp.45-51
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• 2011

A study has been made on defects which are formed in manufacturing processes of engine bearing and also on fatigue crack growth behavior in each step of bearing metal manufacturing. After the first step (sinter brass powder on steel plate ; Series A) many voids are made on brass surface and its size is decreased at the second step (rolling process of sintered plate ; Series B). After the third step (re-sintering step of brass powder and rolling ; Series C) the number of voids is decreased and its type shows line. The time of fatigue crack initiation and the growth rate of fatigue crack are in order of Series A, Series B, Series C. These reasons are that void fosters the crack initiation and growth, and residual stress made by rolling process affects on the crack growth rate in Series B, C. In forming and machining processes by use of final bearing metal, crack was observed at internal corner of flange and peeling off was observed at interface between steel and brass. Owing to the above crack and peeling off, it is considered that there is a possibility of fatigue fracture during the application time.