• Title/Summary/Keyword: Homogeneous precipitation process

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Dynamic Precipitation and Substructure Stablility of Cu Alloy during High Temperature Deformation

  • Han, Chang-Suk;Choi, Dong-Nyeok;Jin, Sung-Yooun
    • Korean Journal of Materials Research
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    • v.29 no.6
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    • pp.343-348
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    • 2019
  • Structural and mechanical effects of the dynamical precipitation in two copper-base alloys have been investigated over a wide range of deformation temperatures. Basing upon the information gained during the experiment, also some general conclusion may be formulated. A one concerns the nature of dynamic precipitation(DP). Under this term it is commonly understood decomposition of a supersaturated solid solution during plastic straining. The process may, however, proceed in two different ways. It may be a homogeneous one from the point of view of distribution and morphological aspect of particles or it may lead to substantial difference in shape, size and particles distribution. The effect is controlled by the mode of deformation. Hence it seems to be reasonable to distinguish DP during homogeneous deformation from that which takes place in heterogeneously deformed alloy. In the first case the process can be analyzed solely in terms of particle-dislocation-particle interrelation. Much more complex problem we are facing in heterogeneously deforming alloy. Deformation bands and specific arrangement of dislocations in form of pile-ups at grain boundaries generate additional driving force and additional nucleation sites for precipitation. Along with heterogeneous precipitation, there is a homogeneous precipitation in areas between bands of coarse slip which also deform but at much smaller rate. This form of decomposition is responsible for a specially high hardening rate during high temperature straining and for thermally stable product of the decomposition of alloy.

Formation Mechanism of Ultrafine $TiO_2$ Powders from Aqueous $TiOCl_2$ Solution by Homogeneous Precipitation Process at Low Temperature (저온 균일침전법으로 $TiOCl_2$ 수용액에서 얻은 $TiO_2$ 초미분체의 형성기구)

  • 김선재;이희균;박순동;전치중;이창규;김흥회;이은구
    • Journal of the Korean Ceramic Society
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    • v.37 no.5
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    • pp.473-478
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    • 2000
  • The TiO2 powder with the values of the large specific surface area more than 150$m^2$/g has been prepared with the homogeneous precipitation process below 5$0^{\circ}C$ and its formation mechanism was investigated using the SEM, TEM and Raman Spectroscopy. With the spontaneous hydrolysis of aqueous TiOCl2 solutions, all the precipitates were fully and homogeneously crystallized with the rutile TiO2 phase simply by heating, which as transformed to the anatase TiO2 phase as increasing the addition of SO42- ions to the aqueous TiOCl2 solution. The precipitates were formed with spherical secondary particles which consisted of acicular, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It can be thought that the formation and phase determination of crystalline TiO2 powders even at ambient temperature would be related with the existence of the capillary force. This force might be varied depending on the shape change of the primary particles.

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Synthesis and luminescence characteristics of nano-sized YAG : Ce phosphors by homogeneous precipitation method (Homogeneous precipitation method를 통한 나노 YAG : Ce 형광체 합성과 광학 특성)

  • Lee, Chul Woo;Kwon, Seok Bin;Ji, Eun Kyung;Song, Young Hyun;Jeong, Byung Woo;Kim, Eun Young;Jung, Mong Kwon;Yoon, Dae-Ho
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.27 no.1
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    • pp.18-21
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    • 2017
  • In this study, spherical monodispersed cerium-doped yttrium aluminum garnet (YAG : $Ce^{3+}$) phosphor particles were synthesized via homogeneous precipitation method using the mixed solution of yttrium nitrate, cerium nitrate, aluminum nitrate, ammonium aluminum sulfate, and urea as a precipitant. During the process of precursors of monodispersed YAG : $Ce^{3+}$, aluminum ions which form spherical aluminum compounds precipitated first and yttrium compounds precipitated onto the surface of the existing spherical aluminum compounds. Drying process using lyophilization could obtain monodispered spherical YAG : $Ce^{3+}$ particles compare to using oven. The thermal calcination process of YAG : $Ce^{3+}$ precursors under the temperature of $1200^{\circ}C$ for 6 h was enough to obtain 400~500 nm sized YAG particles with pure YAG phase.

Preparation of Hydrated Basic Aluminum Salts by Homogeneous Precipitation Method and Their Thermal Decomposition (균일침전법에 의한 수화 염기성 알루미늄염의 합성 및 열분해)

  • 박홍채;김주석;이승호;오기동
    • Journal of the Korean Ceramic Society
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    • v.26 no.1
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    • pp.132-138
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    • 1989
  • High purity(99.99%) spherical particles of hydrated Basic Aluminum Salts(BAS) were prepared by a homogeneous precipitation process utilizing the urea decomposition reaction and characterized by XRD, SEM, TG-DTA, IR and PSA methods. Amorphous hydrated BAS was precipitated in the range of pH 4~6. The molar ratio [Al3+]/[SO42-] for the precipitate particles was about 3.7. With increasing the concentration of aluminum sulfate the precipitation of the hydrated BAS occurred slowly and the precipitate particles with a narrow size distribution were fine(1-2${\mu}{\textrm}{m}$ in diameter). At temperatures in the range 400$^{\circ}$to 95$0^{\circ}C$, desulfurization and dehydroxylization resulted in weight loss with 22%. When the precipitate particles were thermally treated, the crystlline ${\gamma}$-Al2O3 was identifited by XRD at 50$0^{\circ}C$ and ${\gamma}$-Al2O3 particles were transformed into $\alpha$-Al2O3 at 100$0^{\circ}C$. A vermicular network was produced by calcining at 125$0^{\circ}C$ for 30min.

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Preparation and Properties of Disc Type CuO Catalyst Impregnated Ceramic Filters (디스크형 산화구리 촉매담지 세라믹필터의 제조와 물성)

  • Hong Min-Sun;Moon Su-Ho;Lee Jae-Chun;Lee Dong-Sub;Lim Woo Taik
    • Journal of Korean Society for Atmospheric Environment
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    • v.20 no.2
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    • pp.185-193
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    • 2004
  • A catalyst with CuO ceramic filter for simultaneous treatment of dust and HAP was prepared and characterized. Catalytic ceramic filter can not only potentially achieve the substantial savings in energy but provide with effective optimization and integration of process for simultaneous removal of SO$_2$, NO$_{x}$ and particulates from flue gases. Catalytic ceramic filters remove simultaneously particulates on exterior surface of filters and reduce NO to $N_2$ and $H_2O$ by SCR (Selective Catalytic Reduction) process. Preparation of catalyst impregnated ceramic filter with disk shape (Ψ 50) follow the processing of alumino-silicate ceramic filter, support impregnation and catalyst impregnation (copper oxide). Preparation routes of alumino-silicate catalyst carrier suitable for production of catalytic filters practically were studied and developed using the sol-gel and colloidal processing, homogeneous precipitation and impregnation method. Characterization of the catalyst, catalyst carrier catalytic filter materials have been performed the using various techniques such as BET, XRD, TGA, SEM. Combination of the sol-gel and colloidal processing and impregnation method is recommended to prepare catalyst carriers economically for catalytic filter applications.s.

Dispersion Properties and Photocatalytic Activities of TiO2 Powders Obtained by Homogeneous Precipitation Process at Low Temperature in a Acrylic Resin (저온균일침전법으로 제조된 TiO2 분말의 아크릴레진에서의 분산특성 및 광분해 효과)

  • Woo S. H.;Kim W. W.;Rhee C. K.
    • Journal of Powder Materials
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    • v.11 no.6 s.47
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    • pp.503-509
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    • 2004
  • Dispersion stabilities and photocatalytic activities of rutile $TiO_{2}$ powders with unique nano-structure synthesized by homogeneous precipitation process at low temperature(HPPLT) have been investigated in the acrylic resin containing fluorostyrene in the range of 0~0.16 mole. Isoelectric point of $TiO_{2}$ in the acrylic resin placed in the neutral region whereas that of $TiO_{2}$ in the water placed in the acidic region, indicating that zeta potential and agglomeration of $TiO_{2}$ powder is strongly dependent on the pH and the type of solvent. To prepare an adhesion, an acrylic resin containing fluorostyrene was synthesized by a radical polymerization. The adhesion of coating layer was increased with increasing fluorostyrene's contents without changing the dispersion stabilities and degrading photocatalytic properties.

Effect of Water Wash and Dry Temperature in Homogeneous Precipitation Method on the Manufacture of Mn-added Barium Hexaaluminates (균일용액침전법에서 수세여부와 건조온도가 망간이 첨가된 바륨헥사알루미네이트의 제조에 미치는 영향)

  • Park, Ji Yun;Kim, Seo Young;Rhee, Young Woo
    • Korean Chemical Engineering Research
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    • v.59 no.3
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    • pp.435-442
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    • 2021
  • Mn-added Barium hexaaluminates were manufactured by homogeneous precipitation method using Urea. The effects of water wash and dry temperature were analyzed by thermal weight analysis, X-ray diffraction analysis, and scanning electron microscopy. Catalysts that went through the filtration step only produced pure hexaaluminate images compared to those that went through the water wash step. During the drying process, it seems that the remaining urea helps dehydration of the precursor and affects the phase shift of gibbsite to boehmite, which is easy to convert to pure hexaaluminate. The catalyst WO200 gave the best performance in the methane combustion reaction, and NOx was not emitted in the reaction for all catalysts. Hexaaluminates were found to affect reducing the highest CO emissions.

Preparation of Ce0.8Gd0.2O1.9 Powder by Milling of CeO2 Slurry and Oxalate Precipitation (CeO2 슬러리 분쇄와 옥살산 침전을 이용한 Ce0.8Gd0.2O1.9 분말의 합성)

  • Sim, Soo-Man
    • Journal of the Korean Ceramic Society
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    • v.47 no.2
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    • pp.183-188
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    • 2010
  • $Ce_{0.8}Gd_{0.2}O_{1.9}$(GDC20) powder was synthesized by milling of $CeO_2$ slurry and Gd oxalate precipitation. The mixture of $CeO_2$ powder and Gd precipitates calcined at $600^{\circ}C$ for 2 h showed the particle size distribution similar to that of $CeO_2$ powder, which had been milled during the synthesis process. Attrition milling of the calcined powder with an average particle size of $0.36\;{\mu}m$ for 2 h resulted in a decrease in the particle size to $0.24\;{\mu}m$. Although the milled powder consisted of small particles(<$1\;{\mu}m$), a small amount of fine platy $Gd_2O_3$ particles, which had been survived in the milling process, was observed. Sintering of the powder compacts for 4 h showed relative densities of 80.7% at $1300^{\circ}C$ and 97% at $1400^{\circ}C$, respectively. Densification was found to almost complete at $1500^{\circ}C$, resulting in a dense and homogeneous microstructure with a relative density of 99.5%.