• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2003.05a
• /
• pp.14-14
• /
• 2003

Silicon carbide (SiC)는 높은 power 영역과 높은 온도영역에서도 작동 가능한 우수한 반도체 물질이다. 또한 우수한 열적 화학적, 안정성을 가지고 있어 가흑한 조건에서의 소자로써도 사용 가능하다. 현재 SiC 적용분야로는 우수한 전기적, 기계적 성질을 이용한 미세소자(MEMS)와 GaN 와 거의 유사한 격자상수를 가지는 것을 이용한 GaN epitaxial 성장의 기판으로도 사용되어진다. 그러나 SiC 는 기존의 습식식각 용매에 대해 화학적 안정성을 가지고 있기 때문에 전자소자의 제작에 있어서 플라즈마를 이용한 건식식각의 중요성이 대두되어지고 있다. 소자제작에 있어 이러한 건식식각시 식각 단면의 제어, 이온에 의한 낮은 손상 정도, 매끄러운 식각 표면, 그리고 고속의 식각 속도둥이 요구되어진다. 본 실험에서는 식각 속도의 증가와 수직한 식각 단면둥을 획득하기 위하여 SF6 플라즈마에서 Source power, dc bias voltage, 그리고 외부에서 인가되는 자속의 세기를 변화시쳐가며 식각 속도, 식각 마스크와의 식각 션택비, 식각 단면둥과 같은 SiC 의 식각 특성을 관찰하였다. 식각 후 식각 단면은 주사전자 현미경(SEM)을 통해 관찰하였다. 본 실험에서의 가장 높은 식각 속도는 분당 1850n 로써 이때의 공정조건은 1400W 의 inductive power, -600V 의 dc bias voltage, 20G 의 외부자속 세기이었다. 또한, 높은 inductive power 조건과 낮은 dc bias voltage 조건에서 Cu는 $SF_6$ 플라즈마 내에서 식각부산물의 증착으로 인해 SiC 와 무한대의 식각선택비를 보였다. 이러한 Cu 마스크를 사용한 SiC 의 식각에서는 식각 후 수직한 식각 단변을 관찰할 수 있었다. 것올 알 수 있다. 따라서, 기존의 pve 보다 세라믹 기판의 경우가 수분 흡수율이 높아 더 오랫동안 전류를 흐르게 하여 방식성이 개선된 것으로 판단된다.을 통해 경도가 증가한 시편의 경우 석출상의 크기가 5nm 이하로 매우 작고 대체로 기지와 연속적인 계면을 형성하나, 열처리가 진행될수록 석 출상의 크기가 커지고 임계크기 이상에 이르면 연속적인 계면은 거의 발견되지 않고, 대부 분 불연속적이고 확연한 계면을 형성함을 관찰 할 수 있었다. 알루미나(${\alpha}-Al_2O_3$) 기판 위에 증착한 $(Ti_{1-x}AI_{x})N$ 피막은 마찬가지로 (200) 우선 방위를 나타내었으나, 그 입자의 크기가 수십 nm로 고속도강위에 증착한 피막에 비해 상당히 크게 형성되었다. 또한 열처리 후에 AIN의 석출이 진행됨에도 불구하고 경도 증가는 나타나지 않고, 열처리가 진행됨에 따라 경도가 감소하는 양상만을 나타내었다. 결국 $(Ti_{1-x}AI_{x})N$ 피막이 열처리 전후에 보아는 기계적 특성의 변화 양상은 열역학적으로 안정한 Wurzite-AlN의 석출에 따른 것으로 AlN 석출상의 크기에 의존하며, 또한 이러한 영향은 $(Ti_{1-x}AI_{x})N$ 피막에 존재하는 AI의 함량이 높고, 초기에 증착된 막의 업자 크기가 작을 수록 클 것으로 여겨진다. 그리고 환경의 의미의 차이에 따라 경관의 미학적 평가가 달라진 것으로 나타났다.corner$적 의도에 의한 경관구성의 일면을 확인할수 있지만 엄밀히 생각하여 보면 이러한 예의 경우도 최락의 총체적인 외형은 마찬가지로 $\ulcorner$순응$\lrcorner$의 범위를 벗어나지 않는다. 그렇기 때문에

• Korean Journal of Veterinary Pathology
• /
• v.2 no.1
• /
• pp.17-24
• /
• 1998

This is the first report of c-Jun protein expression and mRNA in a pancreatic islet in a nonobese diabetic(NOD) state mice. In this experiment NOD mice with insulin-dependent diabetes mellitus type I at age 16 weeks(n=7) just before death(n=4) were used. The control group consist of prediabetic NOD(8 weeks n=7) and ICR(8 weeks n=7 and 16 weeks n=7) mice. c-Jun positive cells in the pancreatic islet of NOD mice were localized in the same positions as a-glucagon producing cells. immunoreactivity was negative in the prediabetic NOD(8 weeks) and ICR(8 weeks and 16 weeks) mice. The number of c-Jun positive cells in mice with severe diabetic state just before death were significantly decreased when compared to NOD(16 weeks) mice. Expression of c-Jun in mRNA level was assessed by RT-PCR method. The levels of mRNA in NOD(16 weeks) mice group were elevated in total pancreatic tissues. The present results suggest that the induction of proto-oncogene protein may be of significance in assessing cell specific injury and may play a functional role between pancretic islet $\alpha$-cells and $\beta$-cells in the diabetic state.

• Economic and Environmental Geology
• /
• v.47 no.4
• /
• pp.441-453
• /
• 2014

Thermal and physical properties were measured on 206 Jurassic granite samples obtained from three boreholes in the central part of Korea. Thermal conductivity(${\lambda}$), thermal diffusivity(${\alpha}$), and specific heat(Cp) were measured in a laboratory; the average values are ${\lambda}$=2.813 W/mK, ${\alpha}=1.296mm^2/sec$, and Cp=0.816 J/gK, respectively. In addition, porosity(${\phi}$), and dry and saturated density(${\rho}$) were measured in the laboratory; the average values are ${\phi}$=0.01, ${\rho}(dry)=2.662g/cm^3$ and ${\rho}(saturated)=2.67g/cm^3$, respectively. Thermal diffusivity of 10 granite samples were measured with increasing temperature from $25^{\circ}C$ to $200^{\circ}C$. In this study, we found that thermal diffusivity at $200^{\circ}C$ is about 30% lower than thermal diffusivity at $25^{\circ}C$. In correlation analysis, thermal conductivity increases with increasing thermal diffusivity. However, thermal conductivity does not show good correlation with porosity and density. Consequently, we know that thermal conductivity of granite would be more influenced by mineral composition than by porosity. We also derived ${\rho}=-2.393{\times}{\phi}+2.705$ from density and porosity data. XRD and XRF analysis were performed to investigate effects of mineral and chemical composition on thermal conductivity. From those results, we found that thermal conductivity increases with increasing quartz and $SiO_2$, and decreases with increasing albite and $Al_2O_3$. Regression analysis using those mineral and chemical composition were carried out ; we found $K=0.0294V_{Quartz}+1.93$ for quartz, $K=0.237W_{SiO_2}-14.09$ for $SiO_2$, and $K=0.053W_{SiO_2}-0.476W_{Al_2O_3}+6.52$ for $SiO_2$ and $Al_2O_3$. Specific gravities were measured on 10 granite samples in the laboratory. The measured specific gravity depends on chemical compositions of granite. Therefore, specific gravity can be estimated by the felsic-mafic index(F) that is calculated from chemical composition. The estimated specific gravity ranges from 2.643 to 2.658. The average relative error between measured and estimated specific gravities is 0.677%.

• Polymer(Korea)
• /
• v.29 no.2
• /
• pp.156-160
• /
• 2005

$\alpha,\omega-Vinyl$ poly (dimethyl-methylphenyl) siloxane prepolymer (VPMPS ) was prepared by the equilibrium polymerization of octamethylcyclotetrasiloxane $(D_4)$, 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane $(D_3^{Me,Ph)$, and 1,1,3,3-tetramethyl-1,3-divinyldisiloxane (MVS). And also, of $\alpha,\omega-hydrogen$ poly(dimethyl-methyl)siloxane prepolymer (HPDMS) as end blocker was prepared from octamethylcyclotetrasiloxane $(D_4)$, 1,3,5-trimethylcyclotrisiloxane $(D_3^:Me,H})$, and 1,1,3,3-tetramethyldisiloxane (MS). Nickel ferrite nanoparticles having spinel magnetic material was prepared by the sol-gel method using PAA as a chelating agent. Poly(organosiloxane) rubber nanocomposite containing silica and nickel ferrite ultrafine powder modified with 1,3-divinyltetramethyldisilazane (VMS) was prepared by compounding VPMPS, HPDMS, and catalyst in high speed dissolver. The mechanical properties, heat dissipating away characteristics, and volume resistivities for POX-30 and POX-50 were measured.

• Korean Journal of Materials Research
• /
• v.2 no.1
• /
• pp.27-34
• /
• 1992

Tantalum silicide films are prepared from a composite $TaSi_{28}$ target source and subjected to rapid thermal annealing($500-1100^{\circ}C$, 20sec) in Ar ambient. The formation and the properties of tantalum silicides have been investigated by using 4-point probe, x-ray diffraction, scanning electron microscope(SEM), Auger electron spectroscope(AES), and ${\alpha}$-step. It has been found that the sample annealed above $700^{\circ}C$ forms a polycrystalline $TaSi_2$ phase, and grains grow in granular form regardless of the kind of substrates. The mechanism of the formation of tantalum silicide is the nucleation and growth by Ta-Si short range reaction. The tantalum silicide film has the relatively low resistivity($70-72.5{\mu}{\Omega}-cm$) and smooth surface roughness.

• Korean Journal of Materials Research
• /
• v.14 no.9
• /
• pp.670-675
• /
• 2004

Glasses in the $Bi_{2}O_3-SiO_2-ZnO$ glasses system were examined as a potential replacement for lead-oxide glass frits with low firing temperature ($500\sim600^{\circ}C$) for the dielectric layer of a plasma display panel (PDP). The glasses were evaluated for glass transition temperature($T_{g}$) and thermal expansion coefficient(${\alpha}$). After forming transparent thick films by a screen-printing method, it was evaluated for the optical properties. The transmittance of thick films fired at $500-600^{\circ}C$ showed above $80\%$, which was not dependent on the firing temperature. As a result, many pores were observed at samples fired at low temperature, while the number of pores from samples prepared at high temperature decreased and the pores size increased.

• Korean Journal of Materials Research
• /
• v.14 no.11
• /
• pp.821-827
• /
• 2004

Titanium oxide thin films were prepared on Si(100) substrates by R.F. magnetron reactive sputtering at $30\sim200watt$ R.F power range, and annealed at $600^{\circ}C\sim800^{\circ}C$ for 1 hour. The properties of $TiO_2$ thin films were analyzed using x-ray, ${\alpha}-step$, ellipsometer, scanning electron microscopy, and FT-IR spectrometer. Upon in-situ depositions, the initial phase of $TiO_2$ thin film showed non-crystalline phase at R.F. power $30\sim100$ watt. The crosssection of $TiO_2$ thin films were sbserved to be the columnar structure. With the increasing R.F power and annealing temperature, the grain size, crystallinity, refractive index, and void size of titanium oxides showed a tended to increase. The FT-IR transmittance spectra of titanium oxide thin films have the obsorption band of Ti-O bond, Si-O bond, Si-O-Ti bond and O-H bond. With the increase of R.F. power and annealing temperature, these films have the stronger bond structures. It is considered that such a phenomena is due to phase transition and good crystallinity

• Korean Journal of Metals and Materials
• /
• v.50 no.8
• /
• pp.575-582
• /
• 2012

Medium carbon steel was aluminized by hot dipping into molten Al or Al-1 at% Si baths. After hot-dipping in these baths, a thin Al-rich topcoat and a thick alloy layer rich in $Al_5Fe_2$ formed on the surface. A small amount of FeAl and $Al_3Fe$ was incorporated in the alloy layer. Silicon from the Al-1 at% Si bath was uniformly distributed throughout the entire coating. The hot dipping increased the microhardness of the steel by about 8 times. Heating at $700-1000^{\circ}C$, however, decreased the microhardness through interdiffusion between the coating and the substrate. The oxidation at $700-1000^{\circ}C$ in air formed a thin protective ${\alpha}-Al_2O_3$ layer, which provided good oxidation resistance. Silicon was oxidized to amorphous silica, exhibiting a glassy oxide surface.

• Membrane and Water Treatment
• /
• v.10 no.5
• /
• pp.353-360
• /
• 2019

ZSM-5 membrane was prepared on tubular macroporous ${\alpha}$-alumina support using a different synthesis route. The effects of organic template agent and Si/Al ratio of the synthesis gel on morphology, structure, and separation performance of the ZSM-5 membrane used for dehydration of isopropanol were investigated. High water perm-selectivity ZSM-5 membrane with a thickness of about $3.0{\mu}m$ and a low Si/Al ratio of 10.1 was successfully prepared from organotemplate-free synthesis gel with a molar composition of $SiO_2$ : $0.050Al_2O_3$ : $0.21Na_2O$ : NaF : $51.6H_2O$ at $175^{\circ}C$ for 24 h. The ZSM-5 membrane exhibited high pervaporation performance with a flux of $3.92kg/(m^2{\cdot}h)$ and corresponding separation factor of higher than 10,000 for dehydration of 90 wt.% isopropanol/water mixture at $75^{\circ}C$.

• Korean Chemical Engineering Research
• /
• v.55 no.3
• /
• pp.436-442
• /
• 2017

Fischer-Tropsch synthesis is the technology of converting a syngas (CO+$H_2$) derived from such as coal, natural gas and biomass into a hydrocarbon using a catalyst. The catalyst used in the Fischer-Tropsch synthesis consists of active metal, promoter and support. The types of these components and composition affect the reaction activity and product selectivity. In this study, we manufactured an iron catalyst using ${\gamma}-Al_2O_3/SiO_2$ mixed support (100/0 wt%, 75/25 wt%, 50/50 wt%, 25/75 wt%, 0/100 wt%) by an impregnation method to investigate how the composition of ${\gamma}-Al_2O_3/SiO_2$ mixed support effects on the reaction activity and product selectivity. The physical properties of catalyst were analyzed by $N_2$ physical adsorption and X-Ray diffraction method. The Fischer-Tropsch synthesis was conducted at $300^{\circ}C$, 20bar in a fixed bed reactor for 60h. According to the results of the $N_2$ physical adsorption analysis, the BET surface area decreases as the composition of ${\gamma}-Al_2O_3$ decreases, and the pore volume and pore average diameter increase as the composition of ${\gamma}-Al_2O_3$ decreases except for the composition of ${\gamma}-Al_2O_3/SiO_2$ of 50/50 wt%. By the results of the X-Ray diffraction analysis, the particle size of ${\alpha}-Fe_2O_3$ decreases as the composition of ${\gamma}-Al_2O_3$ decreases. As a result of the Fischer-Tropsch synthesis, the CO conversion decreases as the composition of ${\gamma}-Al_2O_3$ decreases, and the selectivity of C1-C4 decreases until the composition of ${\gamma}-Al_2O_3$ was 25 wt%. In contrast, the selectivity of C5+ increases until the composition of ${\gamma}-Al_2O_3$ is 25 wt%.