• Title/Summary/Keyword: Rapid grain growth

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Abnormal grain growth of ZnO ceramics (ZnO 세라믹스 거대입성장)

  • Kim, Young Jung
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.29 no.6
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    • pp.251-256
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    • 2019
  • In the process of ZnO ceramic sintering at a temperature of 1385℃, higher than the normal sintering temperature, some grains were growth up to mm scale. When sintered at 1400℃ for 8 hours, the size of the grains that are not involved in the abnormal growth is as large as 30~40 ㎛, but the size of the abnormal grown grain reaches 1,000 ㎛, which is more than 10,000 times bigger in volume than the normal one within 8 hr growth. As a cause of rapid and abnormal grain growth, primary particle size distribution, compaction density variation within sample and doping of impurities could be considered. The primary particle size distribution could be considered main reason for abnormal grain growth but no solid evidence was obtained. Through the observation of the microstructure, it is presumed that the giant grains grow absorbing the neighbor grains through a grain rotation process.

Abnormal Grain Growth Behaviors of $BaTiO_3$ Ceramics with Controlling of Particle Size Distributjion of Calcined Powder (하소분체의 입도조절에 따른 $BaTiO_3$ 요업체의 비정상 입성장거동)

  • 이태헌;김정주;김남경;조상희
    • Journal of the Korean Ceramic Society
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    • v.32 no.2
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    • pp.147-154
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    • 1995
  • Abnormal grain growth behavior of BaTiO3 ceramics with controlling of particle size distribution of calcined powder was investigated. The particle size distribution was controlled by changing the calcining temperature or by using of classification and regrinding process. With broadening of the normallized size distribution in calcined powder, it showeda normal grain growth behavior in sintered body due to an increase of volume fraction of seed grain in the calcined powder. It was supposed that the seed grains could easily contact each other for the rapid grain growth during sintering process and resulted in fast switching-over from abnormal to normal grain growth stage.

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Densification Behavior of $BaTiO_3$ Ceramics with Grain Growth ($BaTiO_3$ 요업체에서 입성장에 따른 치밀화 거동)

  • 이태헌;김정주;김남경;조상희
    • Journal of the Korean Ceramic Society
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    • v.32 no.1
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    • pp.51-56
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    • 1995
  • Variation of sintered density of BaTiO3 powder calcined at 120$0^{\circ}C$ and 135$0^{\circ}C$ was investigated with respect to the grain growth behavior. It was found that BaTiO3 powder, which was calcined at 120$0^{\circ}C$, showed abnormal grain growth behavior during sintering process. At initial stage of sintering process, the densification rate of specimen was accelerated with rapid grain growth caused by the abnormal grain growth. But with the increase of sintering time, abnormally grown grain met each other and the density of specimen decreased drastically due to coalescence of pores located in triple junction. On the contrary, BaTiO3 powder calcined at 135$0^{\circ}C$ showed normal grain growth behavior and gradually densified with the increase of sintering time.

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Comparison of Yield and Growth Characteristics of Korean High Yielding Cultivars and IRRI's New Plant Type Rice Line

  • Lee, Byun-Woo;Ha, Jong-Ryuk
    • KOREAN JOURNAL OF CROP SCIENCE
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    • v.44 no.1
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    • pp.59-63
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    • 1999
  • Yield and growth characteristics were compared for five rice cultivars; a new Tongil-type, so called "super-rice", Dasanbyeo, an old Tongil-type Milyang 23, two japonicas Dongjinbyeo and Ilpumbyeo, and a new plant type (NPT)line IR65600-27-1-2. The objective of this stusy was to clarify the high yielding capacity of Dasanbyeo in terms of growth characteristics. The average grain yield (9 t/ha) of Dasanbyeo was higher than that of Milyang 23 by ca. 9% that of japonicas by 20 to 30%, and that of NPT line by ca. 100%. The higher grain yield of Dasanbyeo was attributable not only to the greater dry matter production but also to the higher harvest index (HI). Dasanbyeo showed the greatest dry matter at harvest owing not only to the rapid leaf expan-sion at early growth stage and the resulting high LAI through the entire growth stage but also to the high NAR despite the high LAI. The rapid leaf expansion of Dasanbyeo at early growth stage seemed to be related in part to the profuse tillering capacity. HI was 0.53 in Dasanbyeo, 0,51 in Milyang 23, 0.41 in japonicas, and 0.35 in NPT line. Dasanbyeo was indebted for its higher HI to the relatively high grain filling ratio in spite of a much greater sink size than the other cultivars. Dasan had a greater source to sink ratio during grain ripening as measured by LAD/spikelet and dry matter production/spikelet which showed positove correlations with the grain ripening ratio. New plant type (NPT) line showed the lowest grain yield owing to the small sink size and the low grain filling ratio which seemed to have resulted from the abundant occurrence of weak-strength spikelets. The weak sink strength, in turn, seemed to have suppressed photosynthesis during the grain ripening stage.

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Densification and rain Growth of Alumina Heated by Microwave (Microwave로 가열한 알루미나의 소결 및 입성장 거동)

  • 김도형;오성록;김종희
    • Journal of the Korean Ceramic Society
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    • v.29 no.4
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    • pp.305-311
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    • 1992
  • As compared with conventional sintering, rapid heating in microwave system could enhance sinterability and final properties of alumina with a very short sintering time. In this study microwave sintering was performed using zirconia brick as a reaction chamber which was positioned in a 2.45 GHz(700 W) multimode microwave cavity. Microwave-sintered alumina showed high density and smaller grain size than conventionally sintered alumina because the ratio of densification rate/grain growth rate was increased by rapid heating.

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Effects of Ti Underlayer on Microstructure in Cu(B)/Ti/SiO2 Structure upon Annealing (Cu(B)/Ti/SiO2 구조를 열처리할 때 일어나는 미세구조 변화에 미치는 Ti 하지층 영향)

  • Lee Jaegab
    • Korean Journal of Materials Research
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    • v.14 no.12
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    • pp.829-834
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    • 2004
  • Annealing of $Cu(B)/Ti/SiO_2$ in vacuum has been carried out to investigate the effects of Ti underlayer on microstructure in $Cu(B)/Ti/SiO_2$ structures. For comparison, $Cu(B)/Ti/SiO_2$ structures was also annealed in vacuum. Three different temperature dependence of Cu growth can be seen in $Cu(B)/Ti/SiO_2$; B precipitates- pinned grain growth, abnormal grain growth, normal grain growth. The Ti underlayer having a strong affinity for B atoms reacts with the out-diffused B to the Ti surface and forms titanium boride at the Cu-Ti interface. The formation of titanium boride acts as a sink for the out-diffusion of B atoms. The depletion of boron in grain boundaries of Cu films, as results of the rapid diffusion of B along the grain boundaries and the insufficient segregation of B to the grain boundaries, induces grain boundaries to migrate and causes the abnormal grain growth. The increased bulk diffusion coefficient of B within Cu grains can be responsible for the normal grain growth occurring in the annealed $Cu(B)/Ti/SiO_2\;at\;600^{\circ}C$. In contrast, the $Cu/SiO_2$ structures show only the abnormal growth of grains and their sizes increasing as the temperature increases above $400^{\circ}C$.

Effects of Additives and Atmospheres on the Grain Growth of TiO2 Ceramics (분위기와 첨가제가 TiO2 세라믹스의 입자성장에 미치는 영향)

  • 박정현;최헌진;박한수
    • Journal of the Korean Ceramic Society
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    • v.25 no.4
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    • pp.390-398
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    • 1988
  • Effects of atmospheres and adidtives on the grain growth of TiO2 ceramics were investigated. In the range of 1300~140$0^{\circ}C$, grain growth was increased in CO2 as compared with O2 atmosphere and the grain boundary migration activation energy was lower than the diffusion activation energy of oxygen ion in TiO2. Also, in the case of addition of oxides, the grain growth was increased by oxides acting as a acceptor andinhibited by oxides acting as a donor. From the above results, when the oxygen vacancy concentration was increased, the intrinsic grain boundary mobility was increased and the pore drag force was decreased due to the rapid densification. Also it seems that the pore was migrated by the surface diffusion rather than lattice diffusion.

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Fabrication and Mechanical Properties of Porous Silicon Carbide Ceramics from Silicon and Carbon Mixture (실리콘과 카본을 이용한 다공질 탄화규소의 제조와 기계적 특성)

  • Kim, Jong-Chan;Lee, Eun Ju;Kim, Deug-Joong
    • Journal of the Korean Ceramic Society
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    • v.50 no.6
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    • pp.429-433
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    • 2013
  • Silicon, carbon, and B4C powders were used as raw materials for the fabrication of porous SiC. ${\beta}$-SiC was synthesized at $1500^{\circ}C$ in an Ar atmosphere from a silicon and carbon mixture. The synthesized powders were pressed into disk shapes and then heated at $2100^{\circ}C$. ${\beta}$-SiC particles transformed to ${\alpha}$-SiC at over $1900^{\circ}C$, and rapid grain growth of ${\alpha}$-SiC subsequently occurred and a porous structure with elongated plate-type grains was formed. The mechanism of this rapid grain growth is thought to be an evaporation-condensation reaction. The mechanical properties of the fabricated porous SiC were investigated and discussed.

Microstructural Characterization of Hot Extruded Al-Zn-Mg-Cu Alloys Containing Sc (Sc을 첨가한 Al-Zn-Mg-Cu 합금 압출재의 열처리에 따른 미세구조 변화)

  • 이혜경;서동우;이상용;이경환;임수근
    • Transactions of Materials Processing
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    • v.13 no.1
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    • pp.53-58
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    • 2004
  • The microstructural changes of Al-Zn-Mg-Cu alloy containing Sc during hot extrusion and post heat treatment were investigated. Two kinds of Al-Sc alloys with different alloying elements (B1, B2) were hot extruded to make T-shape bars at extrusion temperature of $380^{\circ}C$, then the bars were solution treated at $480^{\circ}C$ for 2hrs followed by artificial aging at $120^{\circ}C$ for 24hrs. The interior microstructure of as extruded bar consisted of elongated grains, however, fine equiaxed grains were also observed around surface. The microstructural gradient suggested that different restoration process could proceed during the hot extrusion. For B1 and B2, different grain growth behaviors were found around the surface during the post heat treatment. Rapid grain growth behavior was observed for B1 around the surface, however, it was not observed for B2. Orientation pinning, which was related with the evolution of preferred orientation, and precipitation were thought to be responsible for the rapid grain growth.

Influence of Sintering Atmosphere on Abnormal Grain Growth Behaviour in Potassium Sodium Niobate Ceramics Sintered at Low Temperature

  • Fisher, John G.;Choi, Si-Young;Kang, Suk-Joong L.
    • Journal of the Korean Ceramic Society
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    • v.48 no.6
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    • pp.641-647
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    • 2011
  • The present study aims to identify the effect of sintering atmosphere [$O_2$, 75$N_2$-25 $H_2$ (mol%) and $H_2$] on microstructural evolution at the relatively low sintering temperature of 1040$^{\circ}C$. Samples sintered in $O_2$ showed a bimodal microstructure consisting of fine matrix grains and large abnormal grains. Sintering in 75 $N_2$ - 25 $H_2$ (mol %) and $H_2$ caused the extent of abnormal grain growth to increase. These changes in grain growth behaviour are explained by the effect of the change in step free energy with sintering atmosphere on the critical driving force necessary for rapid grain growth. The results show the possibility of fabricating $(K_{0.5}Na_{0.5})NbO_3$ at low temperature with various microstructures via proper control of sintering atmosphere.