• 제목/요약/키워드: Grains

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Selective Carbonization and Nitridation of Titanium in (ZrTi)O2 Powders Synthesized by Copreciptation Method

  • Shin Soon-Gi
    • 한국재료학회지
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    • 제15권10호
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    • pp.662-666
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    • 2005
  • Solid solutions of $(Zr/Ti)O_2$ were prepared in powder form by the coprecipitation technique. After mixing with carbon or exposing to nitrogen gas at elevated temperature, titanium cations selectively diffused out from the oxide compound to form titanium carbide (TiC) or titanium nitride (TiN), respectively. TiN formed strong interfacial contacts between the oxide grains. In contrast, TiC formed as small crystallites on oxide grains but did not bind the matrix grains together. TiN therefore played a role in strengthening the interparticle bonding, but TiC weakened the bonding between grains. Partial diffusion of titanium cations also led to nanolayered structure being formed between the oxide grains, which provided weak interfacial layers that fractured in a step-wise fashion.

2차 seed grain을 사용한 ZnO varistor의 특성 연구 (Properties of ZnO varistor using secondary seed grains)

  • 김형주;마재평;백수현
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 1989년도 춘계학술대회 논문집
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    • pp.87-92
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    • 1989
  • We fabricated primary and secondary seed grains. Primary seed grains having larger grain size were obtained under the conditions that were 2.0m/o BaCO$_3$ and 10 hours sintering. The amount of primary seed grain to yield the largest secondary seed grains were choosed as 3 w/o and we fabricated the low voltage varistors which were joined the low voltage-oriented ZnO varistor system made by conventional method with the secondary seed grains. As a result, ZnO varistor showed appoximately 10V/mm of nonlinear resistance and 15-22 of nonlinear exponent.

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YIG 소결시 나타나는 비정상입성 장 현상과 그의 억제 (Suppression of the abnormal grain growth in the sintering of YIG)

  • 김동영;한진우;전동석;이상석
    • 한국전기전자재료학회:학술대회논문집
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    • 한국전기전자재료학회 2002년도 하계학술대회 논문집
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    • pp.466-469
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    • 2002
  • In the sintering of YIG, abnormal grain growth phenomena was observed. This abnormal grain growth is related to the sintering temperature in this experiment. In the sintering below 145$0^{\circ}C$., the sintered body showed narrow size distribution. However, in the sintering at 145$0^{\circ}C$, a few grains grew rapidly with respect to other grains, and bimodal size distribution was appeared. Liquid phase was not observed far from the abnormally grown large grains, but only near the large grains. This means that the abnormal grain growth was caused by the nonuniform distribution of liquid phase which promote the grains growth. This nonuniform distribution of liquid phase was thought to be due to the nonuniform mixing of the starting materials. This abnormal grain growth was suppressed by enhance the compositional uniformity by multiple calcination.

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DUST GRAINS IN THE ENVELOPES OF INFRARED CARBON STARS

  • Suh, Kyung-Won
    • Journal of Astronomy and Space Sciences
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    • 제9권2호
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    • pp.183-192
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    • 1992
  • We have investigated the properties of dust grains in the envelopes of infrared carbon stars by testing various radiative transfer model spectra with different stellar and enveloped parameters. We have deduced a new opacity pattern for the dust grains reflecting both the experimental data and the model fitting with recent infrared observations. The best pattern we find is very similar to amorphous carbon with a slight modification that could be attributed to some unknown dust grain materials. Unlike oxygen-rich dust grains, the optical properties of carbon grains do not show any reasonable tendency of temperature dependence. We find that the Planck mean values of radiation pressure efficiency factors for the modified amorphous carbon are much larger than those for graphite.

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화분표면형질의 기능적 의의에 관한 연구 (Studies on the Functioanl Significance of Pollen Surface Characters)

  • 이상태
    • Journal of Plant Biology
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    • 제22권1_2호
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    • pp.45-51
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    • 1979
  • From 32 angiosperm species, pollen surface characters such as sculpture pattern, roughness, oil abundance and stickiness were subjectively scored, and compared with size and weight of the grains, and pollination mechanisms. There was a linear relationship between size and weight of the grains. Animal-pollinated grains showed significantly higher roughness, oil abundance and stickiness than wind-pollinated grains. In the former, the grain size was highly correlated with roughness and oil abundance. No such relationship was found in the latter. It was suggested, therefore, that the large the animal-pollinated grains, the greater is the stickiness required, where the stickiness depends on the surface soil abundance and roughness. No functional significance of the sculpture pattern could not be detected in this study.

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Growth Behavior and Mechanisms in Cemented Carbides

  • Yoon, Byung-Kwon;Kang, Suk-Joong L.
    • 한국분말야금학회:학술대회논문집
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    • 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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    • pp.891-892
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    • 2006
  • To test the correlation between grain shape and growth behavior we prepared WC-TiC-Co samples with rounded (Ti, W)C grains and faceted WC grains. The growth of rounded (Ti, W)C grains was normal. In contrast, the growth of faceted WC grains was abnormal or suppressed depending on the initial size of WC particles. These observations were explained using growth theories of crystals in a liquid and were also confirmed by a simulation using their growth equations. The present results thus demonstrate that the growth behavior of carbide grains in a liquid is governed only by their shape, irrespective of the presence of another phase.

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Seed 입자 첨가에 따른 $BaTiO_3$ 요업체의 비정상 입성장거동 (Abnormal Grain Growth Behavior of $BaTiO_3$ Ceramics with Addition of Seed Grains)

  • 이태헌;김정주;김남경;조상희
    • 한국세라믹학회지
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    • 제32권5호
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    • pp.587-593
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    • 1995
  • Abnomal grain growth behavior of BaTiO3 ceramics was investigated with addition of seed grains. It was foudn that the nucleation rate of abnormal grain was constant and growth of abnormal grain was linearly increased with sitnering time, regardless of amount of seed grains. These facts were also confirmed by fitting of the volume fraction of abnormal grain vs. sintering time using Avrami type equation (n=4). It was suggested that seed grains did not change the nucleation rate or growth mechanism of abnormal grain but increase the number of abnormal grains at initial stage of sintering and then it led to fine microstructure of BaTiO3 ceramics.

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Three-dimensional Refractive-index Distributions of Individual Angiosperm Pollen Grains

  • Park, Chansuk;Lee, SangYun;Kim, Geon;Lee, SeungJun;Lee, Jaehoon;Heo, Taehyun;Park, Yoonjeong;Park, YongKeun
    • Current Optics and Photonics
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    • 제2권5호
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    • pp.460-467
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    • 2018
  • Three-dimensional (3D) refractive-index (RI) imaging and quantitative analyses of angiosperm pollen grains are presented. Using optical diffraction tomography, the 3D RI structures of individual angiosperm pollen grains were measured without using labeling or other preparation techniques. Various physical quantities including volume, surface area, exine volume, and sphericity were determined from the measured RI tomograms of pollen grains. Exine skeletons, the distinct internal structures of angiosperm pollen grains, were identified and systematically analyzed.

출발상 제어에 의한 자기복합화 미세구조의 탄화규소 세라믹스 제조 (Preparation of Silicon Carbide Ceramics with Self-reinforced Microstructure by the Control of Starting Phases)

  • 이종국;강현희;이은구;김환
    • 한국세라믹학회지
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    • 제34권12호
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    • pp.1240-1246
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    • 1997
  • Silicon carbides with self-reinforced microstructure which hore a small grain matrix and dispersed large grains with rod-like type were prepared by the liquid-phase sintering and the control of starting phases of raw materials. The specimens with self-reinforced microstructure could be obtained from the compacts with mixed compositions of $\alpha$-SiC and 10-50 % $\beta$-SiC powders and by the pressureless sintering at 185$0^{\circ}C$ for 5h. Large grains with rod or plate-like types were 4H-SiC and small grains with equi-axed type were 6H-SiC. Fracture grains with rod or plate-like types were 4h-SiC and small grains with equi-axed type were 6H-SiC. Fracture toughness of specimens with self-reinforced microstructure was increased by the crack deflection and formation of microcracking due to the existence of rod-like large grains during crack propagation.

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Investigation of Streaky Mark Defect on Hot Dip Galvannealed IF Steel

  • Xinyan, Jin;Li, Wang;Xin, Liu
    • Corrosion Science and Technology
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    • 제9권3호
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    • pp.109-115
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    • 2010
  • Interstitial-free (IF) steels are widely used for car body material. However, a few types of streaky mark defect are commonly found on hot dip galvannealed (GA) IF steel sheets. In the present study, both the phase structure of a streaky mark defect and the microstructure of the substrate just below it were characterized by optical microscopy (OM) and scanning electron microscopy (SEM). It was found that the bright streaky mark area was composed of ${\delta}$ phase while the dark normal area was full of craters. More than half of the grains at the uppermost surface of the substrate just below the streaky mark defect are unrecrystallized grains which could result from lower finish rolling temperature during hot rolling and be kept stable during the annealing process, while almost all the grains in the normal area are equiaxed grains. In order to confirm the effect of the unrecrystallized grains on the coating morphology, hot dip galvannealing simulation experiments were carried out in IWATANI HDPS. It is proved that the unrecrystallized grains accelerate the Fe-Zn reaction rate during galvannealing and result in a flatter coating surface and an even coating thickness. Finally, a formation mechanism of the streaky mark defect on the hot dip galvannealed IF steel sheet was discussed.