• Korean Journal of Mineralogy and Petrology
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• v.33 no.1
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• pp.29-39
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• 2020

A series of struvite (MgNH₄PO₄·6H₂O) was synthesized and dried at various temperatures (15-60℃). Crystallization of struvite and its structural properties were significantly influenced by synthetic and drying temperature. Struvite was favorably formed at synthetic temperatures ≤30℃ with an inverse relationship between the crystallinity and synthetic temperature. The crystallinity of struvite was also significantly reduced by an increase in drying temperature from 45℃ to 60℃ due to the loss of structural water molecules and ammonium ions by the facilitated thermal decomposition. However, struvite formed at lower synthetic temperature showed higher crystallinity, and its amorphization by thermal decomposition was inhibited. These results demonstrate that struvite formed at low temperature with an stable condition thermodynamically through favorable crystallization shows high crystallinity and stability with respect to the structural and thermal resistance.

• Journal of the Mineralogical Society of Korea
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• v.29 no.3
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• pp.131-139
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• 2016

Detailed knowledge on maskelynite, a glassy phase of plagioclase found in shocked meteorites and impact craters, is essential to understand a shock metamorphism. Here, we explore an inhomogeneous shock metamorphism in the lunar meteorite Mount DeWitt (DEW) 12007 with an aim to understand the formation mechanism of maskelynite. Most plagioclase grains in the DEW 12007 partially amorphized into maskelynite with a unidirectional orientation. Back-scattered electron (BSE) images of maskelynite show a remnant of planar deformation fracture possibly indicating that the maskelynite would be formed by solid-state transformation(i.e., diaplectic glass). Plagioclase with flow texture is also observed along the rim of maskelynite, which would be a result of recrystallization of melted plagioclase. Results of Raman experiments suggest that shock pressure for plagioclase and maskelynite in the DEW 12007 is approximately 5-32 GPa and 26-45 GPa, respectively. The difference in shock pressures between plagioclase and maskelynite can be originated from 1) external factors such as inhomogeneous shock pressure and/or 2) internal factors such as chemical composition and porosity of rock. Unfortunately, Raman spectroscopy has a limitation in revealing the detailed atomic structure of maskelynite such as development of six- or five-coordinated aluminum atom upon various shock pressure. Further studies using nuclear magnetic resonance spectroscopy are necessary to understand the formation mechanism of maskelynite under high pressure.

• Journal of the Korean Vacuum Society
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• v.21 no.6
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• pp.348-353
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• 2012

We investigated chemical states of a $Sb_2Te_3$ thin film with the polycrystalline phase by using high-resolution x-ray photoelectron spectroscopy with synchrotron radiation. The $Sb_2Te_3$ thin film was formed by sputtering. The rhombohedral phase was confirmed by x-ray diffraction. To remove the surface oxide, we performed $Ne^+$ ion sputtering for 1 hour with the beam energy of 1 kV and post-annealing at $100^{\circ}C$ for 5 min in ultra-high vacuum. We obtained the Te and Sb 4d core-levels spectra with the peaks at the binding energies of 40.4 and 33.0 eV, respectively. The full-width of half maximum of both the Te and Sb $4d_{5/2}$ core-levels is 0.9 eV. The Te and Sb core-levels only show a single chemical state, and we also confirmed the stoichiometry of approximately 2 : 3.

• Proceedings of the Korea Crystallographic Association Conference
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• 2003.05a
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• pp.26-26
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• 2003

산업 폐기물로서 전량 매립되고 있는 styrene monomer (SM) 공정에서 발생되는 산화철 폐촉매를 사용하여 NiZn-페라이트를 합성하였고, 그 자기적 특성을 조사하였다. 평균입경 0.5㎛로 미분쇄된 산화철 폐촉매에 NiO 및 ZnO를 혼합하여 900℃에서 하소한후 1230℃에서 5시간 동안 소결하여 스핀넬형 페라이트 소결체를 얻었다. Ni/sub x/Zn/ub 1-x/Fe₂O₄(x=0.36, 0.50, 0.66) 및 (Ni/sub 0.5/Zn/sub 0.5/)/sub 1-y/Fe/sub 2+y/O₄(y=-0.02, 0, 0.02) 조성에 대하여 초투자율을 측정하였다. S-parameter를 측정하여 반사 감쇄량을 계산하였다. Ni/sub 0.5/Zn/sub 0.5/fe₂O₄ 조성의 경우 밀도 5.38 g/㎤ kHz에서의 초투자율이 59인 특성을 얻었다. 산화철 폐촉매를 이용하여 X-band 주파수 영역에서 높은 전자파 흡수능을 갖는 전파흡수체를 제조할 수 있음을 확인하였다. Ni/sub 0.5/Zn/sub 0.5/Fe₂O₄ 조성에 대하여 1100℃에서 하소한 분말을 사용하여 실리콘 고무에 복합시킨 후 전파흡수능을 측정하였다. 폐촉매에는 산화철 이외에 CeO₂가 주된 첨가물로 함유되어 있어서 페라이트의 합성 후에도 2차상으로서 존재하였다. 출발 원료인 산화철 폐촉매에 존재하는 K₂O 및 CeO₂를 제거하기 위하여 산처리와 분산제를 이용한 CeO₂ 분리과정을 행하였다. 정제된 산화철 폐촉매에 NiO 및 ZnO를 혼합하여 900℃에서 하소하여 스핀넬형 페라이트를 합성하고 1325℃에서 5시간 소결하였다. 위와 마찬가지로 Ni/sub x/Zn/sub 1-x/Fe₂O₄(x=0.36, 0.50, 0.66)과 (Ni/sub 0.5/Zn/sub 0.5/)/sub 1-y/Fe/sub 2+y/O₄(y=-0.02, 0, 0.02) 조성에 대하여 자기적 특성을 조사하였다.화된 중성자빔으로 측정하였다 BPC-Si를 구부려 슬랩의 곡률반경을 변화시키면서 단색기-시료-검출기가 평행파 반평행배치일 때 Cu(111), (200), (220), (311), (331), (420)면의 회절선을 측정하여 각 조건에서 분해능과 강도를 평가하였다.료의 가시적 변화를 통해 illumination angle 1.25mrad(Dose rate : 334 × 10³ e/sup -//sec·n㎡)일 경우 약 3초 이내에 비정질화가 시작됨을 알 수 있었고 이는 약 1 × 10/sup 6/ e/sup -//sec·n㎡ 의 전자선량에 해당되며 이를 기준으로 각각의 illumination angle에 대한 임계전자선량을 평가할 수 있었다. 실질적으로 Cibbsite와 같은 무기수화물의 직접가열실험 시 전자빔 조사에 의해 야기되는 상전이 영향을 배제하고 실험을 수행하려면 illumination angle 0.2mrad (Dose rate : 8000 e/sup -//sec·n㎡)이하로 관찰하고 기록되어야 함을 본 자료로부터 알 수 있었다.운동횟수에 의한 영향으로써 운동시간을 1일 6시간으로 설정하여, 운동횟수를 결정하기 위하여 오전, 오후에 각 3시간씩 운동시키는 방법과 오전부터 6시간동안 운동시키는 두 방법을 이용하여 품질을 비교하였다. 각 조건에 따라 운동시킨 참돔의 수분함량을 나타낸 것으로, 2회(오전 3시간, 오후 3시간)에 나누어서 운동시키기 위한 육의 수분함량은 73.37±2.02%를 나타냈으며, 1회(6시간 운동)운동시키기 위한 육은 71.74±1.66%을 나타내었다. 각각의 운동조건에서 양식된 참돔은 사육초기에는 큰 변화가 없었으나, 사육 5일 이후에는 수분함량이 증가하여 15일에는 76.40±0.14, 75.62±0.98%의 수분함량을 2회와 1회 운동시킨 참돔의 육에서 각각 나타났다. 운동횟수에 따른 지질함량은 2회 운동시킨 참돔은 5.83±2.08, 1회 운

• Journal of the Mineralogical Society of Korea
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• v.32 no.3
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• pp.201-211
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• 2019

The particle size and crystallinity of fault gouge generally decreases with slip. Phyllosilicates including talc are known to be present in fault gouge and play an important role in fault weakening. In particular, the coefficient of friction varies depending on the presence of a water molecule on the surface of mineral. The purpose of this study is to investigate the effect of talc on fault weakening by changing the water content and dehydration behavior of talc before and after grinding, which systematically varied particle size and crystallinity using high energy ball mill. Infrared spectroscopy and thermal analysis show that the as-received talc is hydrophobic before grinding and the water molecule is rarely present. After grinding up to 720 minutes, the particle size decreased to around 100 ~300 nm, and in talc, where amorphization proceeded, the water content increased by about 8 wt.% and water molecule would be attached on the surface of talc. As a result, the amount of vaporized water by heating increased after grinding. The dihydroxylation temperature also decreased by ${\sim}750^{\circ}C$ after 720 minutes of grinding at ${\sim}950^{\circ}C$ before grinding due to the decrease of particle size and crystallinity. These results indicate that the hydrophobicity of talc is changed to hydrophilic by grinding, and water molecules attached on the surface, which is thought to lower the coefficient of friction of phyllosilicates. The repeated slip throughout the seismic cycle would consistently lower the coefficient of friction of talc present in fault gouge, which could provide the clue to the weakening of matured fault.

• Journal of the Korean Vacuum Society
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• v.22 no.4
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• pp.188-192
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• 2013

Many studies have been conducted for preventing from diffusion between silicon wafer and metallic thin film due to a decrease of line-width and multi-layer thin film for miniaturization and high integration of semiconductor. This paper has focused on the nano-mechanical property of diffusion barrier which sample is prepared for various gas flow rate of nitrogen with tungsten (W) base from 2.5 to 10 sccm. The deposition rate, resistivity and crystallographic properties were measured by a ${\beta}$-ray back-scattering spectroscopy, 4-point probe and x-ray diffraction (XRD), respectively. We also has investigated the nano-mechanical property using the nano-indenter. As a result, the surface hardness of W-N thin film was increased rapidly from 10.07 to 15.55 GPa when the nitrogen gas flow was increased from 2.5 to 5 sccm. And the surface hardness of W-N thin film had 12.65 and 12.77 GPa at the nitrogen gas flow of 7.5 and 10 sccm respectively. These results were decreased by the comparison with the W-N thin film at nitrogen gas flow of 5 sccm. It was inferred that these severe changes were caused by the stoichiometric difference between the crystalline and amorphous state in W-N thin film. In addition, these results were caused by increased compressive stress.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.31-31
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• 2009

PECVD를 이용하여 제조된 미세결정질 p-i-n 실리콘 박막 태양전지에서, p 층은 태양전지의 윈도우 역할 및 그 위에 증착될 i ${\mu}c-Si:H$ 층의 'seed'층 역할을 수행하기 때문에, p층의 구조적 및 전기적, 광학적 특성은 태양전지의 전체 성능에 큰 영향을 미칠 수 있다. 본 연구에서는 $SiH_4$ 농도를 변화시켜 각기 다른 결정 특성을 갖는 p ${\mu}c-Si:H$층을 제조하고 그 위에 i ${\mu}c-Si:H$ 층을 증착하여 p층의 결정 특성변화와 그에 따른 i ${\mu}c-Si:H$ 층 및 'superstrate' p-i-n 미세결정질 실리콘 박막 태양전지의 특성 변화를 조사하였다. P층의 경우, $SiH_4$ 농도가 증가함에 따라 결정분율 (Xc)이 감소하여 비정질화되었으며 그에 따라 dark conductivity가 감소하는 경향을 나타내었다. 각기 다른 결정분율을 가지는 p 'seed' 층 위에 증착된 태양전지는, p 'seed' 층의 결정분율이 증가함에 따라 개방전압, 곡선인자, 변환효율이 경향적으로 감소하였다. 이는 p 층 결정분율 변화에 따른 p/i 계면특성 저하 및 그 위에 증착되는 i ${\mu}c-Si:H$ 층의 결함밀도 증가 등에 따른 태양전지 특성 감소 때문인 것으로 판단되며, 이를 분석하기 위하여 i ${\mu}c-Si:H$ 층의 전기적, 구조적 특성 분석 및 태양전지의 dark I-V 특성 등을 분석하고자 한다.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.678-684
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• 1998

By means of constant- pressure molecular dynamics simulations, we studied the liquid- glass- crystalline transition of a system composed of Lennard- Jones particles with periodic boundary conditions. Atomic volume and enthalpy were calculated as functions of temperature during heating and cooling processes. The Wendt- Abraham ratio derived from radial distribution function and the angular distribution function characterizing short range order were analyzed to distinguish between liquid, glass and crystalline states. A liquid phase resulting from a slow heating of an initial fee crystal amorphized on fast quench, but it crystallized on slow quench. When slowly heated, the amorphous phase from fast quench crystallized into an fee structure. A system with free surface was shown to melt from the surface inward at a lower temperature than bulk system and to have a strong tendency for crystallization even during a fast quench from a liquid state.

• Korean Journal of Materials Research
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• v.10 no.8
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• pp.569-574
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• 2000

To improve the ductility of $Al_3Hf$ and $Al_3Ta$ intermetallic compounds, which are the potential temperature structural materials, the mechanical alloying behaviour and the effect of ternary additions on the $Ll_2$ phase formation were investigated. During the mechanical alloying by the SPEX mill, the $Ll_2$ $Al_3Hf$ intermetallic compound was formed after 6 hours of milling in AL-25%Hf system. In AL-25%Ta system, however, only the $D0_{22}$ $Al_3Ta$ intermetallic compound was formed until 30 hours of milling and the $Ll_2$ phase was not observed. In AL-12.5%M-25%Ta(M=Cu, Zn, Mn, Fe, Ni) systems, the additions of Cu and Zn had no effect on the $D0_{22}$ structure of the binary $Al_3Hf$ and the additions of Mn, Fe and Ni produced the amorphous phase. Therefore it was considered that these ternary additions could not overcome the energy difference between $Ll_2$ and $D0_{22}$ structures in the $Al_3Hf$ intermetallic compound. In AL-12.5%M-25%Hf(M=Cu, Zn, Mn, Fe, Ni)systems, the additions of Cu and Zn did not affect the $Ll_2$ structure of the binary $Al_3Hf$ but the additions of oMn, Fe and Ni produced the amorphous phase as they did in AL-12.5%M-25%Ta systems. Therefore, it was considered that the Ni, Mn and Fe additions promote the formation of amorphous phase in $Al_3X$ intermetallic compounds.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.5
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• pp.213-217
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• 2013

The GaN layer was typical III-V nitride semiconductor and was grown on the sapphire substrate which cheap and convenient. However, sapphire substrate is non-conductivity, low thermal conductivity and has large lattice mismatch with the GaN layer. In this paper, the poly GaN epilayer was grown by HVPE on the metallic compound graphite substrate with good heat dissipation, high thermal and electrical conductivity. We tried to observe the growth mechanism of the GaN epilayer grown on the amorphous metallic compound graphite substrate. The HCl and $NH_3$ gas were flowed to grow the GaN epilayer. The temperature of source zone and growth zone in the HVPE system was set at $850^{\circ}C$ and $1090^{\circ}C$, respectively. The GaN epilayer grown on the metallic compound graphite substrate was observed by SEM, EDS, XRD measurement.