• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.16 no.2
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• pp.203-209
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• 2018

To correctly predict the neutron behavior based on diffusion calculations, it is necessary to adopt well-specified boundary conditions using suitable diffusion approximations to transport boundary conditions. Boundary conditions such as the zero net-current, the Marshak, the Mark, the zero scalar flux, and the Albedo condition have been used extensively in diffusion theory to approximate the reflective and vacuum conditions in transport theory. In this paper, we derive and analyze these conditions to prove their mathematical validity and to understand their physical implications, as well as their relationships with one another. To show the validity of these diffusion boundary conditions, we solve a sample problem. The results show that solutions of the diffusion equation with these well-formulated boundary conditions are very close to the solution of the transport equation with transport boundary conditions.

• Journal of Surface Science and Engineering
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• v.37 no.6
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• pp.350-359
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• 2004

Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at $1050^{\circ}C$ for 1hr and $650^{\circ}C$ for 5 hr. The samples for SCC were shot-peened using $\Phi$0.6 mm steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of$ 288^{\circ}C$, 90 kgf pressure, water with 8 ppm dissolved oxygen, and $8.3xl0^{-7}$/s strain rate. After the corrosion and see test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot- peened specimen. Stress corrosion cracking strength decreased with the increase of the Ti/C ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.374-375
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• 2006

This paper describes anodic bonding characteristics of MCA to Si-wafer using evaporated Pyrex #7740 glass thin-films for MEMS applications. Pyrex #7740 glass thin-films with the same properties were deposited on MCA under optimum RF sputter conditions (Ar 100 %, input power $1\;W/cm^2$). After annealing at $450^{\circ}C$ for 1 hr, the anodic bonding of MCA to Si-wafer was successfully performed at 600 V, $400^{\circ}C$ in $110^{-6}$ Torr vacuum condition. Then, the MCA/Si bonded interface and fabricated Si diaphragm deflection characteristics were analyzed through the actuation and simulation test. It is possible to control with accurate deflection of Si diaphragm according to its geometries and its maximum non-linearity being 0.05-0.08 %FS. Moreover, any damages or separation of MCNSi bonded interfaces did not occur during actuation test. Therefore, it is expected that anodic bonding technology of MCNSi-wafers could be usefully applied for the fabrication process of high-performance piezoelectric MEMS devices.

• Tribology and Lubricants
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• v.20 no.3
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• pp.145-151
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• 2004

A modified surface layer by ion implantation is very thin (under 1 $\mu\textrm{m}$) but has superior mechanical characteristics. therefore ion implantation has been used successfully as a surface treatment technology to improve the wear, fatigue, and corrosion resistances of materials. MEVVA which is a kind of ion beam apparatus has merits of low cost and is usable to various metals, but occurs a droplet ranging from micron to tens of micron on the implanted surface at ion implantations. wear is a dynamic phenomenon on interacting surfaces with rotative motion. Since wear changes in condition of the surface, we should control to surface. In order to improve a wear resistance of Ti ion implanted 1C-3Cr steel(material for roller in the cold working process), it is essential to investigate the effect of the droplets on the wear characteristics. In this study, we investigate the effect of the droplets on the wear characteristics of 1C-3Cr steel using SEM Tribosystem as in-situ system. Results show that the droplet occurred at ion implantation becomes the cause of severe wear. Therefore, the ion-implanted surface should be removed the droplet to improve wear resistance.

• Applied Science and Convergence Technology
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• v.26 no.6
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• pp.179-183
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• 2017

The direct growth method is simplified manufacturing process used to avoid damages and contaminants from the graphene transfer process. In this paper, graphene nano-walls (GNWs) were direct synthesized using electron cyclotron resonance (ECR) plasma by varying the $CH_4/H_2$ gas flow rate on the copper foil at low temperature (without substrate heater). Investigations were carried out of the changes in the morphology and characteristic of GNWs due to the relative intensity of hydrocarbon radical and molecule in the ECR plasma. The results of these investigations were then discussed.

• Journal of Welding and Joining
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• v.17 no.2
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• pp.104-111
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• 1999

The interfacial microstructure and bond strength were examined for WC-Co/Cu/SM45C steel join using a nickel-plated copper in vacuum at 1323K for 0.6ks∼3.6ks. After bonding, microstructure in bonding interface was observed by OM(Optical Microscopy), SEM(Scanning Electron Microscopy) and EPMA(Eelectron Probe Micro Analyzer). The oil cooling was carried out at 353K, the cooling rate in air and furnace was 22K/s and 4.4K/s. respectively. It was found that dendritic widths increased with the content of cobalt and bonding times at 1323K. As a whole, bond strength values at the same bonding condition decreased in this order: WC-13wt.%Co/SM45Csteel. WC-8wt.%Co/SM45Csteel and WC-4wt.%Co/SM45Csteel. The bond strength of WC-13wt.%Co/S45C steel joint in oil cooling was 273MPa. This value was greatly higher than those of 125MPa in furnace cooling and 93MPa in air cooling at 1323K for 0.6ks. The bond strength values were found to be closely associated with the content of cobalt in WC-Co and cooling rate.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.89-97
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• 2001

A microgyroscope, which vibrates in two orthogonal axes on the substrate plane, is designed and fabricated. The shuttle mass of the vibrating gyroscope consists of two parts. The one is outer shuttle mass which vibrates in driving mode guided by four folded springs attached to anchors. And the other is inner shuttle mass which vibrates in driving mode as the outer frame does and also can vibrate in sensing mode guided by four folded springs attached to the outer shuttle mass. Due to the directions of vibrating mode, it is possible to fabricate the gyroscope with simplified process by using polysilicon on insulator structure. Fabrication processes of the microgyroscope are composed of anisotropic silicon etching by RIE, gas-phase etching (GPE) of the buried sacrificial oxide layer, metal electrode formation. An eletromechanical model of the vibrating microgyroscope was modeled and bandwidth characteristics of the gyroscope operates at DC 4V and AC 0.1V in a vacuum chamber of 100mtorr. The detection circuit consists of a discrete sense amplifier and a noise canceling circuit. Using the evaluated electromechanical model, an operating condition for high performance of the gyroscope is obtained.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.9
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• pp.946-957
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• 2012

The objective of this paper is to investigate into the development of a thin flat panel photo-bioreactor case with characteristics shapes. The thin flat panel photo-bioreactor case was designed to be manufactured from a plastic thermoforming process. A proper design with a relatively high rigidity was obtained through the structural analyses for different designs of the photo-bioreactor case. The thermoforming analyses were performed. From the results of the thermoforming analyses, a proper forming condition and the formability of the designed plastic photo-bioreactor case were estimated. The thermoforming moulds for the flat panel photobioreactor cases were manufactured. The thermoforming experiments were performed to examine the manufacturability of the designed flat panel photo-bioreactor cases. From the results of the thermoforming experiments, it was shown that thin flat panel photo-bioreactor cases with characteristic shapes can be manufactured from the designed thermoforming mould and process.

• Journal of Surface Science and Engineering
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• v.33 no.5
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• pp.319-328
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• 2000

Silver is known to have such characteristics as low shear strength, good transfer-film forming tendency, and good corrosion resistance. Silver thin films have been prepared by ion plating of physical vapour deposition (PVD) using both argon gas pressure and bias voltage of processing condition. After the silver films were prepared, the properties in them were examined by gas pressure and bias voltage of substrate. Their morphology and crystal orientation were investigated by scanning electron microscopy (SEM) and X-ray diffractor. The properties of film were, also, studied to relate with morphology, X-ray diffraction pattern, and friction coefficient at vacuum ambient. The friction coefficient was stabilized remarkably on deposited films with increasing argon pressure for deposition. Also, the effect of increasing of the bias voltage for deposition resulted in lower friction coefficient and stability in $1.7$\times$10^{-4}$ torr. On the contrary, behavior of friction coefficient was stabilized on deposited films with decreasing the bias voltage in $1.7$\times$10^{-5}$ torr for deposition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.87-91
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• 2004

It is definitely required to control dispersion of the rocket engine performance in order to accomplish the mission of launch vehicle successfully. We performed the dispersion analysis of gas generator cycle LRE (liquid rocket engine) accompanied with ANASYN. As a result, the vacuum thrust dispersion of the engine was $+5.34\%,\;-5.27\%$ and the mixture ratio deviated $+9.07\%,\;-9.82\%$ from the nominal value due to the errors of components and engine inlet condition of propellants. By applying the gas generator regulator only, the dispersion of the engine performance increases. Error in turbine efficiency is the most influential factor to the dispersion of engine performance.