• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.231-237
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• 2004

Vacuum carburizing continues to gain acceptance as an alternative to atmosphere carburizing particularly in the car industry. The advantages of low-pressure carburization over atmospheric gas carburization is not only the creation of a surface entirely free of oxide and the environmentally friendly nature of these methods but also an improvement in deformation behaviour achieved by combining carburization with gas quenching, a reduction in batch times by increasing the carburization temperature, low gas and energy consumption and the prevention of soot to a large extent. In present study, an improved vacuum carburizing method is provided which is effective to deposit carbon in the surface of materials and to reduce cycle time. Also LPC process simulator was made to optimize to process controls parameters such as pulse/pause cycles of pressure pattern, temperature, carburizing time, diffusion time. The carburizing process was simulated by a diffusion calculation program, where as the model parameters are proposed with help the experimental results and allows the control of the carburizing process with good accordance to the practical results. Thus it can be concluded that LPC process control method based on the theoretical simulation and experimental datas appears to provide a reasonable tool for prototype LPC system.

• 한국세라믹학회지
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• 제49권6호
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• pp.637-641
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• 2012

Due to its high production cost and relatively high energy consumption during the Siemens process, poly-silicon makers have been continuously and eagerly sought another silicon route for decades. One candidate that consumes less energy and has a simpler acidic and metallurgical purification procedure is upgraded metallurgical-grade (UMG) silicon. Owing to its low purity, UMG silicon often requires special steps to minimize the impurity effects and to remove or segregate the metal atoms in the bulk and to remove interfacial defects such as precipitates and grain boundaries. A process often called the 'gettering process' is used with phosphorus diffusion in this experiment in an effort to improve the performance of silicon solar cells using UMG silicon. The phosphorous gettering processes were optimized and compared to the standard POCl process so as to increase the minority carrier lifetime(MCLT) with the duration time and temperature as variables. In order to analyze the metal impurity concentration and distribution, secondary ion mass spectroscopy (SIMS) was utilized before and after the phosphorous gettering process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.332-335
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• 2007

The superplastic forming (SPF) has been widely used in the automotive and aerospace industry because it has great advantages to produce very light and strong components. Finite element method (FEM) is used to model the process of superplastic forming/diffusion bonding (SPF/DB), to predict the pressure-time curve and to analyze the process parameter. In this study, process design of SPF/DB is carried out a 3-sheet sandwich part. SPF/DB process with pressure control was analyzed by using finite element method. For obtaining proper shape, step-by-step pressurization is proposed. The first step of SPD/DB process is obtained by applying of pressure in patches. From the next step it applied pressure to all regions (between inner sheets, between inner and face sheets). By using the proposed pressurization scheme, deficit in part shape is found to be eliminated.

• 한국경영과학회지
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• 제37권2호
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• pp.113-125
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• 2012

The logistic model and the Bass model have diverse names and formulae in diffusion theory. This diversity makes users or readers confused while it also contributes to the flexibility of modeling. The method of handling the integration constant, which is generated in process of deriving the closed form solution of the differential equation for a diffusion model, results in two different 'actual' models. We rename the actual four models and propose the usage of the models with respect to the purpose of model applications. The application purpose would be the explanation of historical diffusion pattern or the forecasting of future demand. Empirical validation with 86 historical diffusion data shows that misuse of the models can draw improper conclusions for the explanation of historical diffusion pattern.

• Journal of Welding and Joining
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• 제18권1호
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• pp.70-76
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• 2000

A rolled steel for structural parts and lead bronze alloy were bonded each other by a new semi-solid diffusion bonding process to investigate the effect of the process parameters, for example bonding temperature and bonding time, on the interface characteristics, and bonding behavior. It can be possible that manufacture of the bonded steel/lead bronze which has a cylindrical shape with inserted the lead bronze alloy into the steel ring by the diffusion bonding process under the semi-solid condition of the lead bronze alloy without any pressure and flux. It has been know that the control of the amount of the liquid phase in semi-solid lead bronze alloy was very important to obtain soundness interface, since the shear strength of the bonded steel/lead bronze at 850℃ for 60 minutes under the condition of about 40% of the liquid phase in the lead bronze alloy shows maximum value, 210 MPa. The shear strength increases with an increase in bonding time and show maximum value, and then decreases.

• International Journal of Aeronautical and Space Sciences
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• 제15권3호
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• pp.320-334
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• 2014

Over the last two decades, numerous experimental and numerical efforts have examined physical phenomena in plasma discharge devices. The physical mechanisms that govern the anomalous electron diffusion from the cathode to the anode in the Hall Effect Thruster (HET) are not fully understood. This work used 1-D numerical method to improve our understanding and gain insight into the effect of the anomalous electron diffusion in the HET. To this end, numerical solutions are compared with various experimental HET performance measurements and the effects of anomalous electron diffusion are analyzed. The relationships between the anomalous electron diffusion and important parameters of the HET are also studied quantitatively. The work identifies the cathode mass flow rate fraction, radial magnetic field distribution, and discharge voltage as significant factors that affect anomalous electron diffusion. Additionally, the study demonstrates a computational process to determine the radial magnetic field distribution required to achieve specific thruster performance goals.

• Journal of the Korean Statistical Society
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• 제24권1호
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• pp.141-147
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• 1995

A diffusion model for a system subject to random shocks is introduced. It is assumed that the state of system is modeled by a Brownian motion with negative drift and an absorbing barrier at the origin. It is also assumed that the shocks coming to the system according to a Poisson process decrease the state of the system by a random amount. It is further assumed that a repairman arrives according to another Poisson process and repairs or replaces the system i the system, when he arrives, is in state zero. A forward differential equation is obtained for the distribution function of X(t), the state of the systme at time t, some boundary conditions are discussed, and several interesting characteristics are derived, such as the first passage time to state zero, F(0,t), the probability of the system being in state zero at time t, and F(0), the limit of F(0,t) as t tends to infinity.

• 한국진공학회지
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• 제4권S2호
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• pp.79-82
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• 1995

$N^+$ beam modified diffusion barriers have been proposed for Cu metallization . The crystalline phases of W and Ti thin films change from polycrytalline to amorphous phase by the N ion implantation of 1~$3\times 10^{17}$atoms/$\textrm{cm}^2$. The comparison between these amorphized diffusion barriers and the conventional W and TiN films shows that the amorphized W and Ti diffusion barriers are superior to the conventional w and TiN for protecting the Cu diffusion barriers are superior to the conventional W and TiN for protecting the Cu diffusion at the annealing temperature range $600^{\circ}C$~$800^{\circ}C$ for 30min. This is a worldwidely new and excellent result on the high temperature thermal stability of diffusion barrier.

• Transactions on Control, Automation and Systems Engineering
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• 제1권1호
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• pp.75-86
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• 1999

An air-data estimator for generic air-breathing hypersonic vehicles (AHSVs) is developed and demonstrated with an example vehicle configuration. The AHSV air-data estimation strategy emphasized improvement of the angle of attack estimate accuracy to a degree necessitated by the stringent operational requirements of the air-breathing propulsion. the resulting estimation problem involves highly nonlinear diffusion process (propagation); consequently, significant distortion of a posteriori conditional density is suspected. A simulation based statistical analysis tool is developed to characterize the nonlinear diffusion process. The statistical analysis results indicate that the diffusion process preserves the symmetry and unimodality of initial probability density shape state variables, and provide the basis for applicability of an Extended Kalman Filter (EKF). An EKF is designed for the AHSV air-data system and the air data estimation capabilities are demonstrated.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권10호
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• pp.451-457
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• 2003

The silicon wafer is stable status at room temperature, but it is weak at high temperatures which is necessary for it to be fabricated into a power semiconductor device. During thermal diffusion processing, a high temperature produces a variety thermal stress to the wafer, resulting in device failure mode which can cause unwanted oxide charge or some defect. This disrupts the silicon crystal structure and permanently degrades the electrical and physical characteristics of the wafer. In this paper, the electrical characteristics of a single oxide layer due to high temperature diffusion process, wafer resistivity and thickness of polyback was researched. The oxide quality was examined through capacitance-voltage characteristics, defect density and BMD(Bulk Micro Defect) density. It will describe the capacitance-voltage characteristics of the single oxide layer by semiconductor process and device simulation.