• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.224-230
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• 1999

Agglomeration of colloidal alumina particles in a suspension is simulated. Particles in a suspension have potential energies between them and move to decrease the summation of all the potential energies between particles. The effects of various types of potential curves on particle agglomeration were checked. Strong short range attractive energy without repulsive energy barrier makes small strong clusters with disordered network structure but weak short-range force with big repulsive energy barrier makes big agglomerates with a close packing structure. As particles are agglomerated the potential energy with strong repulsive energy barrier between agglomerates gradually decreases the importance of the repulsive energy barrier and induces a different type of agglomeration behavior.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.7-11
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• 1997

직경 3.5 cm, 길이 1.5 m 의 석영관 내에서 염화제1철 증기를 수소로 환원하여 철 초미립자를 제조하였다. 염화제1철의 증발조건, 염화제1철 증기와 수소의 혼합방법, 반응물의 예비가열온도, 반응온도, 염하제1철의 농도, 반응기내 체류시간이 생성된 철 입자의 크기 및 크기분포에 미치는 영향을 조사하였다. 철 입자의 평균직경은 40-88 cm 이고, 기하표준편차는 1.4 정도로 나타났다. 철 입자들은 자기적 성질에 의해 서로 연결되어 체인을 형성하였으며, 전자회절분석 결과 단결정이었다. 평균입경 55nm 철 입자들의 항자력은 900 Oe, 포화자화값은 130 emu/g 이었다.

• Journal of the Korean Ceramic Society
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• v.38 no.3
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• pp.267-273
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• 2001

Bayer process는 보오크사이트로부터 수산화알루미늄을 추출시키는 가장 일반적인 방법으로서 공정 조건에 따라 수산화알루미늄의 1차입자경, 입도분포도 및 생산효율 등이 달라지게 된다. 이러한 수산화알루미늄의 특성에 영향을 미치는 석출인자로는 석출시간, 석출온도차($\Delta$T), 종자 첨가시 함께 투입되는 공정순환액(spent liquor) 및 종자크기 등이 있다. 본 실험에서는 이러한 각각의 인자들이 수산화알루미늄 석출시 입자성장에 미치는 영향을 연구하였다. 그 결과 석출시간이 길수록, 정온석출 보다는 냉각석출의 경우가, 또한 공정순환액이 첨가되지 않을수록 석출율은 증가하나 입자크기에는 영향을 주지 않았으며 입자성장에 가장 큰 영향력을 미치는 인자는 투입 종자크기로 나타났다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.2
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• pp.69-73
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• 2018

Crystal growth of ${\alpha}-Fe_2O_3$ nanosized particles of 80~90 nm in size, which were hydrothermally prepared from 0.03 M $FeCl_3$ solution at $100^{\circ}C$, was investigated in Pb-containing and Pb-free frit. By heating ${\alpha}-Fe_2O_3$ nanosized particles in two frits at $800^{\circ}C$, the average diameter of particles in frits was increased to 200~210 nm and 150~160 nm, respectively, and the crystal growth due to the aggregation and sintering of several ${\alpha}-Fe_2O_3$ particles was observed. Formation ratios of larger particles over 100 nm in diameter were 54 % in Pb-free frit and 85 % in Pb-containing frit. After heating ${\alpha}-Fe_2O_3$ particles in frits at $800^{\circ}C$, 7~9 nm in average diameter of pores were formed in particles. Theses pores were derived from the porous structure of original ${\alpha}-Fe_2O_3$ particles and confined in particles during sintering.

• Journal of the Korean Vacuum Society
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• v.2 no.3
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• pp.346-354
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• 1993

The diamond particles and films were deposited on Si and qurtz substrate for $CH_4-H_2$ mixed gas by using RF plasma CVD. The temperature of substrate and the thinkness of films deposited on Si substrate were uniformly kept up by inserting metal plate between substrate and substrate holder. On increasing the reaction pressure in the same discharge power, the morphologies of films were changed from well-defind films to micro-crystal or ball-like. When diamond films were deposited on Si substrate from $CH_4-H_2$ mixed gas, we obtained well-defined diamond films at lower concentration than 0.5 vol% of $CH_4/H_2$. The deposited diamond films were indentified by SEM, XRD and Raman spectroscopy.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.10a
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• pp.21-25
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• 1997

우수한 세라믹스 제조를 위해서는 작은 입자지름, 좁은 입도분포, 구형의 입자형태, dopant와 matrix가 균일한 고용체를 갖고, 응집입자가 없으며 고순도인 원료 분말의 제조가 선행되어야 한다. 이를 위하여 본 연구에서는 수열 합성법을 이용하여$\alpha$-Al$_2$O$_3$, $\alpha$-SiO$_2$, PZT, PSZT, BTO등의 미세분말을 제조하는 공정에서 반응온도, 광화제의 양과 종류, 반응시간, 출발물질의 양과 종류, 전처리공정, 교반공정 등이 평균입자지름과 결정성 및 입도분포에 미치는 영향을 조사하였다. 그결과 미세분말의 종류에 관계없이 반응온도, 반응시간, 성장기질의 농도, 종자결정의 농도 등이 증가할수록 평균입경은 커지며, 광화제의 농도가 증가할수록 평균 입자지름이 작아지고, 광화제의 농도가 종자결정의 농도가 증가할수록 입도분포가 좁아짐을 알 수 있었다. 특히 $\alpha$-SiO$_2$에 대해 수열합성실험으로부터 평균입자지름과 수열합성의 조업변수간의 특성방정식을 얻었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.23-29
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• 2000

The agglomeration of titania particles with 30 nm in radii was simulated based on the colloidal stability. For surface potential increase from 4.5 to 16.8 mV the height of energy barrier increased. This tendency may explain the experimentally observed aggregation behavior where particles with smaller size and higher potential exhibited higher stability but form bigger and harder agglomerates with irregular shapes after drying.

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.101.2-101
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• 2002

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.54-61
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• 1991

YBCO films deposited on MgO(100) and Si(100) by rf-magnetron sputtering using stoichiometric single target were annealed under oxygen atmosphere at $880^{\circ}C$ for 1 hr. The microstructure and superconducting properties of YBCO thin films depended on the composition of pre-annealed thin films. Basal planesuperconducting particles grown on MgO(100) substrate had small and rod-like shade due to preferred orientation, while superconducting film grown on the basal plane-superconducting particles showed round-shape particles. If pre-annealed thin film had nonstoichiometric composition, liquid phase was formed during the heat treatment, which made it easy for particles to grow in the preferred orientation and thus to form textured structure. But the thin films with the textured structure did not show good superconducting properties, especially $T_c$, since the liquid phase transformed into second phase in the grain boundary during the cooling. The effect of the second phase on $T_{c, \;zero}$ was greater than that on $T_{c, \;on}$.

• Korean Journal of Materials Research
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• v.1 no.1
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• pp.37-45
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• 1991

In order to control the microstructures, the sintering behavior and abnormal grain growth with Ba/Ti ratio variation of $BaTiO_3$were investigated. The $BaTiO_3$powders used in this study were prepared by conventional calcination of $BaCO_3$ and $TiO_2$. The onset temperatures of the sintering were lowered and the densification was enhanced with increasing amounts of $TiO_2$ excess. These results are because of decrease of calcined particle sizes. A eutectic melt above temperature of $1320^{\circ}C$ did not assist the densification. Grain growth was strongly inhibited with increasing amounts of $TiO_2$ excess. The inhibition of grain growth caused abnormal grain growth due to inhomogeneous distribution of Ti-rich second phase.