• 한국세라믹학회지
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• 제44권10호
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• pp.562-567
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• 2007

To precipitate the complex gels of the pH 6, 7, 8, 9 included in a flux and an aluminum hydroxides gel, an aqueous solution of a mixture of $Na_2CO_3\;and\;Na_2PO_4{\cdot}12H_2O$ was added with stirring in an aqueous solution of a mixture of $Al_2(SO_4){_3}{\cdot}18H_2O,\;Na_2SO_4\;and\;K_2SO_4$, and then the complex gels were aged in 20 h at $90^{\circ}C$. As the hydrolysis pH changed, it had an effect on the physical properties such as the crystal structure, crystal morphology and a phase transition temperature of the AlO(OH) gel, and also on the crystal structure, crystal morphology, particle size and particle size distribution of the ${\alpha}-Al_2O_3$ platelets prepared by molten-salt precipitation. Also, in this study, the complex gels were crystallized at $1,200^{\circ}C$ and thereafter dried at $110^{\circ}C$, and then it was investigated to effect of the hydrolysis pH on the crystal structure, morphology and particle size distribution of the ${\alpha}-Al_2O_3$ platelets crystals using XRD, DTA, SEM and particle size analyzer.

• 한국결정성장학회지
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• 제33권6호
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• pp.261-267
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• 2023

마이크로파 유전체 적용을 위해 (Ca, Sr)(Zr, Ti)O₃ (CSZT) 계에서 MgO 첨가에 따른 결정 구조, 미세 구조, 및 유전 특성을 연구하였다. 고상 반응법을 통해 합성된 CSZT 분말은 orthorhombic 단일상을 형성하였다. CSZT의 시편을 각각 1200℃, 1300℃ 및 1400℃에서 소결하였고, 소결 후 모든 시편은 orthorhombic 단일상을 확인하였다. 또한 모든 소결 시편은 온도가 증가함에 따라 입자 크기가 증가하였다. 1 mol% MgO를 첨가한 시편의 경우도 소결 이후에 orthorhombic 구조를 갖는 것을 확인하였다. EDS 분석을 통해 1400℃에서 소결 중에 이차상이 형성된 것을 확인하였다. MgO 첨가된 CSZT의 입자크기분포와 치밀화는 첨가하지 않은 경우와 거의 유사했으나, 입자크기분포가 좁아지며 균일해지는 것을 확인하였다. MgO 첨가된 CSZT는 1 k Hz에서 ε_r = 34.14, tanδ = 0.00047, τ_ε = -3.58 ppm/℃로 우수한 저손실 유전 특성을 가졌다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.351-360
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• 1999

A large NaX type zeolite crystal of a uniform particle size of 20${\mu}{\textrm}{m}$ are grown with various H2O content by hydrothermal reaction and added seed crystal (2~3 ${\mu}{\textrm}{m}$) to reactant solution as a function of different adding seed levels from 3 to 15 %. The result that increased purity of NaX zeolite above 95% and homogeneity of crystal size by increasing adding seed levels, also decreased crystallization time. It was explained that adding seed to synthesis solution leaded out increase of surface area of physical contact reaction and directed growth of seed crystal, so more rapid consumption of reaction gel as increase seeding levels.

• 한국결정성장학회지
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• 제9권4호
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• pp.371-376
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• 1999

A large NaX type zeolite crystal of a uniform particle size of 20$\mu\textrm{m}$ are grown with various {{{{{H}_{2}O}}}} content by hydrothermal reaction and added seed crystal (2~3$\mu\textrm{m}$) to reactant solution as a function of different adding seed levels from 3 to 15%. The result that increased purity of NaX zeolite above 95% and homogeneity of crystal size by increasing adding seed levels, also decreased crystallization time. It was explained that adding seed to synthesis solution leaded out increase of surface area for physical contact reaction and directed growth of seed crystal, so more rapid consumption of reaction gel as increase seeding levels.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.70-73
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• 2000

A finite element analysis model is suggested for analysis of forming process of milli structure whose size is from a few hundreds ${\mu}m$ to a few mm. In this paper, finite element formulation which assemble crystal plasticity theory considering texture development with damage mechanics is developed, since orientation development and growth of micro voids became the primary factors for deformation aspects in large deformation of milli structure. Applying to, extremely, extrusion process of single crystal and extrusion/drawing process of polycrystal milli-size bar, extrusion force, preferred orientation, and damage evolution are examined to understand the characteristics of deformation of milii-size bar.

• 한국군사과학기술학회지
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• 제15권1호
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• pp.81-85
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• 2012

This work is related to study the thermal decomposition of 1,3,5-trinitro-1,3,5-triazacylohexane(RDX) by differential scanning calorimeter and thermo-gravimetry with Kissinger's & Iso-conversional method under nonisothermal conditions, with heating rate from 2 to $8^{\circ}C$/min or given heating rate. We calculated and compared activation energy with these two methods. Iso-conversional method is better than Kissinger's method to study decomposition mechanism. We also investigated activation energy and frequency factor by Kissinger's & Iso-conversional method with the influence of particle size. In case of single crystal, Cl-3(large crystal) has better thermal stability than Cl-5(small crystal). The activation energy increased according to the size of the particle size.

• 한국결정성장학회지
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• 제6권3호
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• pp.392-398
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• 1996

$Si_{3}N_{4}$에 평균입경이 다른 SiC 분말을 0, 10, 20, 30, 40 vol% 첨가하여 고온가압소결법으로 초미립복합재료를 제조하였다. SiC의 첨가량에 따라 $Si_{3}N_{4}$의 결정립성장이 억제되어 원형의 미세한 결정립들이 많아졌다. 이러한 경향은 평균입경이 작은 SiC를 사용한 조성에서 현저하게 나타났다. 이에 따라 파괴강도와 경도는 작은 SiC를 첨가한 시편에서 높은 값을 나타냈으며, 파괴인성은 낮았다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 제2회 단조심포지엄 단조기술의 진보
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• pp.100-123
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• 1995

The relationship between plastic deformation and crystal grain change in warm forging processes of SM100 carbon steel is studied. If the carbon steel is deformed in warm forging temperature (about recrystallization range), the crystal grain and cementite of the internal part are changed, so material properties are changed. Some experimental values, such as the elliptic degree of cementite, the grain size of cementitie and ferrite grain size, are investigated. When the plastic deformation proceeds, the elliptic degree of cementite becomes large, the grain size of cementite particle is small, and the size of ferrite grain appears fine by recrystallization. The elliptic degree of cementite has a considerable effect on formability. The distribution of effective strain in the forging is calculated by the rigid visco-plastic FEM analysis. The effective strain distribution obtained from the FEM simulation is compared with the experimental result. At effective strain 0.3 dynamic recovery and dynamic recrystallization begin, over 2.5 the organization of material has better quality that is suitable for the following cold forming.

• Asian Journal of Atmospheric Environment
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• 제5권3호
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• pp.196-203
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• 2011

The main aim of this study is to establish methods of morphological preservation and elemental quantification for individual snow crystals. Individual snow crystals were collected at a height of 20 m above ground level. To stabilize and preserve the original morphologies of the snow crystals, cyanoacrylate, which has been used to fix liquid droplets, was applied (Kasahara et al., 2000). Several different kinds of snow crystals (dendrite, sectored plate, quasi-sectored plate, and hexagonal plate) were successively stabilized using this method. The stabilized snow crystals were pretreated with acetone, and then the elemental components contained in a whole snow crystal were quantified with the Particle Induced X-ray Emission (PIXE) analytical technique. The snow crystal residual composition determined in the present study was dominated by sulfur and mineral components, and the elemental mass showed an apparent crystal size dependence, where the elemental mass gradually decreased as the crystal size increased.

• 한국재료학회지
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• 제13권5호
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• pp.285-291
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• 2003

The nanosized silver and gold particles are prepared by ERC method in which metal vapors with high temperature is rapidly quenched by coolants such as liquid nitrogen or liquid argon. In order to monitor the crystal structural changes on the internal and the surface of the nanosized noble metal particles, lattice parameter, internal strain and Debye-Waller factor are investigated, and the calculation of X-ray diffraction scattering intensity is performed. The lattice parameters of silver and gold particles agree with those of bulk materials, and crystal internal strain of the metal particles is not changed by rapid cooling. The Debye-Waller factor of gold particles is increased with decreasing particle size because of the surface softening phenomenon of nanosized particles, but the crystal structural change on the surface of the particles is not detected from the comparison the calculated X-ray diffraction profile with the experimental profile on gold particles with the particle size of 4 nm.