• 한국세라믹학회지
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• 제20권3호
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• pp.211-216
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• 1983

This work aims at characterizing silicon grains and its compacts. In order to remove iron silicon grains were washed with 5N hydrochloride at 60-7$0^{\circ}C$ for 170 hrs, and then followed the chemical analysis by atomic absorption spectrophotometer X-ray diffraction analysis SEM observation and specific surface area determination by B. E. T. Mixtures of graded silicon particles with two or three different sizes were made into packings by mechanical vibration. The mixtures were used to make compacts with 10 mm in diameter and 70mm in length by isostatically pressing at 1, 208 kg/$cm^2$ (20 kpsi) and 4, 255kg/$cm^2$ (60 kpsi) respectively. Bulk densities of packings and compacts were measured. A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$ for the purpose of coating the uniform layer of magnesium oxide on the surface of particles. The results obtained are as follows: (1) About two thirds of iron content could be removed from silicon by washing silicon powders with hydrochloride. (2) Uniform layer of magnesium oxide on the surface of silicon could be prepared by spray-drying suspension and by decomposing it. (3) B. E. T. specific surface area of fine silicon particles was 2, 826.753$m^3$/kg. (4) In the binary system with two sizes of 40-53$\mu\textrm{m}$ particles and <10$\mu\textrm{m}$ particles the maximum bulk density of packing was 55% of theoretical value and that of compacts made at the pressure of 4, 255 kg./$cm^2$ (60 kpsi) was 73% of theoretical value. (5) In the ternary system with three sizes the maximum bulk density of packing was 1.43 g/$cm^3$and that of compacts was 1.80g/$cm^3$which is equivalent to 77.6% of theoretical value. The composition of the closest compact was consisted of 50% of 40-53$\mu\textrm{m}$ particles 20% of 10-30$\mu\textrm{m}$ particles and 30% of <10$\mu\textrm{m}$ parti-cles.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.305-307
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• 1997

Gd-doped $CeO_2$, ultrafine powders were synthesized by the glycine-nitrate process and then their sintering and electrical characteristics were analysed using the dilatometric and AC impedance measurements. In the dilatometric measurements green bodies from the synthesized powders after milling shrinked to about $1470^{\circ}C$ in appearance and then expanded thermally with the increase of the heating temperature, whereas those from the synthesized powders before milling continuously shrinked to the temperatures of $1600^{\circ}C$. It may be due to the change of the packing density of the synthesized powders by milling. In the AC impedance measurements, the electrical resistivity of the Gd-doped $CeO_2$ bodies from the as-milled powders, sintered at $1500^{\circ}C$ with the increase of the sintering time, showed the minimum value at the sintering time of 10h. The minimum total resistivity of the Gd-doped $CeO_2$ bodies sintered at $1500^{\circ}C$ for 10h seems to result from the lowest activation energy by the combination between the activation energies for the resistivities at the grain interior and grain boundary.

• 소성∙가공
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• 제17권7호
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• pp.486-490
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• 2008

This study demonstrates that preloading via the elastostatic compression imposed on amorphous alloys at room temperature induces homogeneous plastic strain associated with structural disordering. This structural disordering causes disorder, which at room temperature creates excess free volume and in turn enhances the plasticity. In this study, we investigated the effects of various parameters, such as stress level, flow rate and preloading time, on the degree of the structural disordering at room temperature. On the basis of the present findings, we proposed a method of enhancing the plasticity of amorphous alloys.

• Nuclear Engineering and Technology
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• 제55권2호
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• pp.749-755
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• 2023

A new approximation method was proposed for treating the non-resonant spatial self-shielding effects of double heterogeneous region such as the double heterogeneous effect of VHTR fuel compact in the thermal energy range and that of BP compact with BISO. The method was developed based on the effective homogenization method and a spherical unit cell model with explicit coated layers and a matrix layer. The self-shielding factor was derived from the relation between the collision probabilities for a double heterogeneous compact and the effective cross section for the homogenized compact. First, the collision probabilities and transmission probabilities for all layers of the spherical model were calculated using conventional collision probability solver. Then, the effective cross section for the homogenized sphere cell representing the homogenized compact was obtained from the transmission probability calculated using the probability density function of a chord length. The verification calculations revealed that the proposed method can predict the self-shielding factor with a maximum error of 2.3% and the double heterogeneous effect with a maximum error of 200 pcm in the typical VHTR problems with various packing fractions and BP compact sizes.

• 한국주조공학회지
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• 제30권2호
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• pp.83-88
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• 2010

Bulk amorphous alloys with reasonable glass forming ability and large plasticity were found in Zr-Cu-Al alloys. Further increase in the GFA and the ductility is expected by appropriately choosing a fourth element. In this study, we select Be as the fourth element and added to the Zr-Cu-Al system to synthesize $(Zr_{57.4}Cu_{38.1}Al_{4.5})_{100-x}Be_x$(x=0~16) alloys and the glass forming ability and the plasticity were measured. With Be addition, the supercooled liquid region (${\Delta}T_x$), the plasticity and GFA as high as $134^{\circ}C$, 20.5%, 7 mm, respectively, can be obtained. Herein, we present the effect of Be addition on the variations of various mechanical properties and thermal characteristics of the $(Zr_{57.4}Cu_{38.1}Al_{4.5})_{100-x}Be_x$ alloys.

• 한국표면공학회지
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• 제29권6호
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• pp.788-796
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• 1996

$TiO_2$ films prepared by RF magnetron sputtering, electron beam evaporation, ion assisted deposition (IAD) and sol-gel method are prepared on c-Si substrate and vitreous silica substrate respectively. From the transmission spectra of $TiO_2$ films on vitreous silica substrate in the spectral region from 190 nm to 900 nm, k($\lambda$) of $TiO_2$ is obtained. Using k($\lambda$) in the interband transition region the coefficients of the quantum mechanical dispersion relation of an amorphous $TiO_2$ and hence n($\lambda$) including the optically opaque region of above fundamental transition energy are obtained. The spectroscopic ellipsometry spectra of $TiO_2$ films in the spectral region of 1.5-5.0eV are model analyzed to get the film packing density variation versus i) substrate material, ii) film thickness and iii) film growth technique. The complex refractive index change of these $TiO_2$ films versus water condensation is also studied. Film micro-structures by SE modelling results are compared with those by atomic force microscopy images and X-ray diffraction data.

• 한국진공학회지
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• 제11권3호
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• pp.141-150
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• 2002

낮은 산소 부분압과 긴 타깃-기판 거리에서 DC 반응이온 마그네트론 스퍼터링(reactive magnetron sputtering ; RMS) 방법으로 $TiO_2$ 박막을 증착하였으며, 증착되는 박막에 end-Hall 이온 소스를 이용하여 아르곤 이온빔 보조 증착을 해 주었다. $TiO_2$ 박막의 광학적 특성은 분광광도계에서 측정된 투과율과 반사율 스펙트럼을 이용하여 분석하였고, 구조적 특성은 AFM과 XRD를 이용하여 분석하였다. 이온빔 보조 RMS 방법으로 증착된 $TiO_2$ 박막은 일반적인 RMS로 증착된 박막보다 조밀도가 높고, 흡수가 낮으며, 표면거칠기가 작았다. 본 연구에서는 이온빔 보조 RMS 방법이 유전체 광학박막 코팅에 적용될 수 있음을 보여준다.

• 한국산학기술학회논문지
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• 제9권1호
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• pp.47-52
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• 2008

소자가 점점 고집적화 됨에 따라, MOS 소자 제조에 있어서 $SiO_2$의 두께가 ${\sim}1nm$로 낮아질 경우 발생하는 터널링전류와 문틱전압 천이를 방지할 수 있는 새로운 게이트용 유전물질을 개발하여 소자의 크기를 줄이는데 주력하고 있다. 본 실험에서는 원자층증착(ALD: atomic layer deposition) 방법으로 증착된 $ZrO_2$ 박막의 물리적, 전기적 특성에 대하여 연구하였다. ALD $ZrO_2$ 박막을 증착한 후 Ar 가스 분위기에서 $800^{\circ}C$, 1 시간동안 열처리한 다음 XRD, TEM, 그리고 C-V plots을 이용하여 $Pt/ZrO_2/Si$ 소자의 형태, 결정화 동역학, 그리고 경계층 특성을 평가한 결과 열처리에 의해 소자의 특성이 크게 향상됨을 알 수 있었다.