• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.557-558
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• 2006

In all conventional sintered PM products, the pores present are of two types, primary and secondary. Primary pores forming during compaction and latter during sintering, due to penetration of formed liquid through the matrix grain boundary. Effect of carbon addition on diffusion of Cu in SH737-2Cu system was investigated. After compaction and transient liquid phase sintering at $1120^{\circ}C$ and $1180^{\circ}C$, samples were characterized for densification, showing rise in sintering density and reduction in swelling on carbon addition. Quantitative microstructural characterization (shape factor and pore size) revealed bimodal distribution for 0% carbon, more rounded pores for 0.9% carbon and higher sintering temperature, and pore coarsening at higher sintering temperature.

• Advances in nano research
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• 제7권2호
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• pp.125-134
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• 2019

The Origanum vulgare L.-mediated synthesis of Ag nanoparticles was successfully realized within the present study. Various concentrations of the $AgNO_3$ used as a silver precursor (1, 2.5, 5, 10 and 100 mM) were used. Very rapid formation of Ag nanoparticles was observed, as only minutes were necessary for the completion of the reaction. With the increasing concentration, red shift of the surface plasmon resonance peak was observed in the Vis spectra. According to photon cross-correlation spectroscopy results, the finest grain size distribution was obtained for the 2.5 mM sample. The transmission electron microscopy analysis of this sample has shown bimodal size distribution with larger crystallites with 100 nm size and smaller around 10 nm. The antibacterial activity was also the best for this sample so the positive correlation between good grain size distribution and antibacterial activity was found. The in-depth discussion of antibacterial activity with related works from the materials science point of view is provided, namely emphasizing the role of effective nanoparticles distribution within the plant extract or matrix. The antibacterial activity seems to be governed by both content of Ag nanoparticles and their effective distribution. This work contributes to still expanding environmentally acceptable field of green synthesis of silver nanoparticles.

• 열처리공학회지
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• 제5권2호
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• pp.85-94
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• 1992

Microstructural evolution of wrought Inconel 718 superalloy with different heat treatment conditions was studied. Heat treatment was performed via conventional(CHT), modified(MHT), Merrick(MeHT) and modified Merrick (MMeHT) methods. The size of ${\gamma}^{\prime}$ and ${\gamma}^{\prime\prime}$ precipitates which are principal strengthening phases in Inconel 718 superalloy increase in order of CHT, MHT, MeHT. For the case of MMeHT, a coexistence of fine ${\gamma}^{\prime\prime}$ precipitate and very coarse particles due to exess growth of ${\gamma}^{\prime\prime}$, which is called bimodal distribution, was observed. CHT gave the finest grain size. (Ti, Nb)C carbide and needle-like ${\delta}$ phase were formed together at grain boundaries for CHT, and were formed both inside and at boundaries of grains for MHT, MeHT and MMeHT. Morphology of partially serrated grain boundaries was developed in all heat treatment conditions except CHT.

• 한국전기전자재료학회논문지
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• 제18권6호
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• pp.550-553
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• 2005

[ $Pb(Zr_{0.2}Ti_{0.8})O_3$ ] powders, prepared by the sol-gel method, were mixed with an organic vehicle and the PZT thick films were fabricated by the screen-printing techniques on Pt/alumina substrates. The structural and dielectric properties were examined as a function of sintering temperature. The particle size distribution of the powder is bimodal with the mean particle size of about $1.2\;{\mu}m$. The average grain size of the PZT thick films sintered above $1000^{\circ}C$ was about $3.1\;{\mu}m$ and the thickness of the specimens was approximately $41\;{\mu}m$. The relative dielectric constant and dielectric loss of the thick films sintered at $1050^{\circ}C$ were 337 and $1.24\%$, respectively.

• 한국세라믹학회지
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• 제31권7호
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• pp.703-714
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• 1994

Sintering and microstructure of Ce-TZP/Al2O3 composite with $\alpha$-Al2O3 matrix containing dispersed 5~50 vol% ZrO2 were discussed. Sintered density was increased with elevating forming pressure in range of 6~300 MPa and about >99.2% of theoretical density was obtained at 1$600^{\circ}C$ for 2h in case of 300 MPa of 6~300 MPa uniaxially cold-pressed compacts containing 20 vol% ZrO2. All kinds of different batch composition exhibited nearly the same shrinkage behaviour with end-point shrinkage between 20 and 24%, and had the maximum shrinkage rate (0.41~0.54%/min) around 140$0^{\circ}C$. Grain growth was occurred faster in $\alpha$-Al2O3 than in {{{{ gamma }}-Al2O3 starting matrix during sintering at 1$600^{\circ}C$. Bimodal pore size distribution of interaglomerate pores with size of 0.03~0.2 ${\mu}{\textrm}{m}$ and of interaglomerate pores with size of around 60 ${\mu}{\textrm}{m}$ was obtained in Ce-TZP/$\alpha$-Al2O3 composite sintered at 130$0^{\circ}C$. But unimodal pore size distribution with around 0.1 ${\mu}{\textrm}{m}$ was observed in Ce-TZP/{{{{ gamma }}-Al2O3 composite sintered at the same temperature. Microcracks were occurred due to the tlongrightarrowm transformation of ZrO2 on cooling process.

• 한국세라믹학회지
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• 제31권10호
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• pp.1218-1230
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• 1994

In manufacturing process of porous glass-ceramics by the filler method, the sintering behaviour of crystallizable glass powder mixed with various salts was studied and also the effects of precipitated crystal phases on the properties of porous glass-ceramics were investigated. Fine-grained crystallizable glass powder was homogeneously mixed with various slat having grain size 100~200 ${\mu}{\textrm}{m}$ and sintered for densification. After washing out the inorganic salt with distilled water, the porous sintered body was heat treated additionly for crystallization. The MgO-Al2O3-SiO2 base glass was used as crystallizable glass powder and the water soluble salts such as K2SO4 and MgSO4 were used as filler. When K2SO4 was used, leucite crystal phase was formed as a result of the ion exchange and porous glass-ceramics which exhibit high temperature resistance and high thermal expansion coefficient of 17$\times$10-6/$^{\circ}C$ could be obtained. On the contrary, when MgSO4 was used, only slight ion exchange is observed and $\mu$-cordierite and $\alpha$-cordierite crystal phases were formed and porous glass-ceramics which exhibit low thermal expansion coefficient schedule were determined with the results of DTA curves, thermal shrinkage curves and XRD patterns analysis. From DTA curves and thermal shrinkage curves, it was found that the sintering densification have been completed at the temperature range of exothermic peak for crystallization. The pore size distributions and pore diameters were measured by mercury porosimeter. The pore diameter of porous glass-ceramics was 10~15 ${\mu}{\textrm}{m}$ when 100~200${\mu}{\textrm}{m}$ grain size of K2SO4 was used and it was 25~30 ${\mu}{\textrm}{m}$ when the same grain size of MgSO4 was used. The porous glass-ceramics K2SO4 used shows bimodal pore size distribution and its porous skeleton structure was ascertained by SEM observation.

• 한국재료학회지
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• 제10권1호
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• pp.55-61
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• 2000

$UO_2$분말에 PVA-Al(III) 착물과 AlOOH를 각각 0.03~1.0wt%를 첨가하여 소결체를 제조한 후 소결체 특성을 비교하였다. PVA-Al(III) 착물과 AlOOH는 $1000^{\circ}C$의 소소분위기에서 열분해하는 경우 생성상은 $\theta-Al_2O_3$이었다. 순수 $UO_2$분말에 비해 AlOOH가 첨가된 혼합 분말의 곁보기 밀도는 더 높았고, PVA-Al(III) 착물이 첨가된 혼합 분말은 더 낮은 겉보기 밀도를 보였다. AlOOH가 첨가된 소결체의 경우 약 $800^{\circ}C$ 부근에서 치밀화가 시작되었지만, PVA-Al(III) 착물이 첨가된 소결체의 경우에는 약 $900^{\circ}C$에서 치밀화가 시작되었다. 기공 크기 분포는 AlOOH가 첨가된 $UO_2$소결체의 경우에 monomodal 형태로, 그리고 PVA-Al(III) 착물의 첨가된 소결체의 경우에는 bimodal 형태로 나타났다. 결정립 크기는 1wt% 첨가시 AlOOH가 첨가된 $UO_2$소결체의 경우에 약 $13\mu\textrm{m}$이었지만, PVA-Al(III) 착물의 첨가된 소결체의 경우에는 약 $\36mu\textrm{m}$까지 성장하는 현저한 효과를 확인하였다.

• 천문학회지
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• 제12권1호
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• pp.27-34
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• 1979

Temperature history of very small interstellar dust particles is followed under diffuse interstellar radiation. Because of extremely small thermal capacities of these grains with sizes ranging from a few tens to hundred Angstroms in radii, they are to experience strong fluctuations in temperature whenever they are hit by interstellar ultraviolet photons. Fluctuating temperature can inhibit these smaller component of interstellar dust from growing into core-mantle particles of submicron sizes by continuously evaporating atoms and molecules adsorbed on their surface. This is interpreted as a possible physical reason for the bimodal nature in grain size distribution. A brief discussion is also given to the far infrared emission properties of such small grains in diffuse interstellar dust clouds.

• 열처리공학회지
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• 제25권3호
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• pp.138-145
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• 2012

An ${\alpha}$-Ferrite (Fe) powder dispersed with 4 vol.% of $Al_2O_3$ was successfully produced by a simple miling at 210 K with a mixture of $Fe_2O_3$, Fe and Al ingredient powders, followed by 2 step high temperature consolidation: Hot Pressing (HP) at 1323 K and then Hot Isostatic Pressing at 1423 K. The microstructure of the consolidated material was characterized by standard metallographic techniques such as XRD (X-ray Diffraction), TEM and STEM-EDS. The results of STEM-EDS analysis showed that the HIPed materials comprised a mixture of pure Fe matrix with a grain size of ~20 nm and $Al_2O_3$ with a bimodal size distribution of extremely fine (~5 nm) and medium size dispersoids (~20 nm). The mechanical properties of the consolidated materials were characterized by compressive test and micro Vickers hardness test at room temperature. The results showed that the yield strength of the ODS (Oxide Dispersion Strengthened) Fe alloy are as much as $674{\pm}39$ MPa and the improvement of the yield strength is attributed to the presence of the fine $Al_2O_3$ dispersoid.

• 한국분말재료학회지
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• 제2권1호
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• pp.29-35
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• 1995

In this study the calcined condition and characteristic of Cu-Ni-Zn ferrite powder were investigated. The Cu-Ni-Zn ferrite powder has been synthesized by the thermal decomposition of the organic acid salt. This process did not require a strict pH control and provided the uniform composition and fine powder with about 0.3 $\mu\textrm{m}$. The XRD diffraction pattern of this powder showed about 50% spinel phase. The optimum calcination was found to be done at $700^{\circ}C$ for one hour. After the calcination, the amount of spinel increased to 90%. The distribution of the particle size showed bimodal peaks, one was about 0.5 $\mu\textrm{m}$ and the other was about 20 $\mu\textrm{m}$. The large particles of 20 $\mu\textrm{m}$ were the agglomeration of fine Particles. The mean Particle size of the powder was about 0.4 $\mu\textrm{m}$. The powder was compacted under 100 MPa pressure and sintered at 1100~ $1250^{\circ}C$ for one hour in air. The density of ferrites specimen was a function of the sintering temperature. The higher the temperature, the denser the ferrite. The maximum relative density of the sintered ferrite was about 93% at $1250^{\circ}C$. The grain size of sintered specimen at $1200^{\circ}C$ was 5 $\mu\textrm{m}$ and homogeneous.