• Journal of Technologic Dentistry
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• v.38 no.2
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• pp.69-77
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• 2016

Purpose: This study was to evaluate the shear bond strength of ceramic fused to Ni-Cr alloy(Alophaloy) by heat treatment. Methods: The specimens were divided into 5 groups according to heat treatment conditions prior to porcelain application. Eighteen specimens from each group were subjected to the shear load a universal testing machine using a 0.1mm/min cross-head speed and two specimens from each group were observed with SEM and EDX line profile. Results: The observation of the oxide film on the metal surface by SEM photograph showed a coarsening with an increasing degassing hold time. The diffusion of metal oxide was observed farther from the opaque layer in the heat treated specimen than no heat treated specimen. The shear bond strength measured highest to A5(55.23MPa) in the 10min holding group and measured lowest from A1(24.38MPa) in the no heat treated group, and there was a significant difference(p<0.05). Conclusion: The shear bond strength of Ni-Cr alloy improved in the heat treatment compared to the no heat treatment specimen.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.99-102
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• 2008

The growth of domestic energy demand is rapidly increased for the industrialization and the improvement of the living standards. It is also recognised that the importance of the use of environmentally friendly energy and high efficient equipment. Ground Source heat pumps(GSHP) using earth as heat source or sink are outstanding environmentally friendly energy systems which have high thermal efficiency when compared to conventional heating and cooling system. So government employs a policy and increase investment for expanding renewable energy market volume. Especially is established a system for obligatory usage of renewable energy to achieve 5% renewable energy diffusion rate by 2011. And the market demand for the ground source heat pump is rapidly growing due to its strong advantages. However domestic situation usually have been depended on the import of ground source heat pumps. In this paper, the results of development of a ground source heat pump using refrigerant R410A are reported.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.4
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• pp.381-383
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• 1999

First topic of this paper aims to clarify how oxygen and heat transfer in silicon melt under cusp-shaped magnetic fields. We obtained asymmetric temperature distribution by using time dependent and three-dimensional calculation. Second topic is study on molecular dynamics simulation, which was carried out to estimate diffusion constants of oxygen in silicon melt.

• Magazine of RCR
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• v.19 no.3
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• pp.24-28
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• 2024

• Clean Technology
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• v.26 no.1
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• pp.30-38
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• 2020

The kinetic and thermodynamic parameters of Acid Red 66, adsorbed by granular activated carbon, were investigated on areas of initial concentration, contact time, and temperature. The adsorption equilibrium data were applied to Langmuir, Freundlich, Temkin, Redlich-Peterson, and Temkin isotherms. The agreement was found to be the highest in the Freundlich model. From the determined Freundlich separation factor (1/n = 0.125 ~ 0.232), the adsorption of Acid Red 66 by granular activated carbon could be employed as an effective treatment method. Temkin's constant related to adsorption heat (B_T = 2.147 ~ 2.562 J mol^-1) showed that this process was physical adsorption. From kinetic experiments, the adsorption process followed the pseudo-second order model with good agreement. The results of the intraparticle diffusion equation showed that the inclination of the second straight line representing the intraparticle diffusion was smaller than that of the first straight line representing the boundary layer diffusion. Therefore, it was confirmed that intraparticle diffusion was the rate-controlling step. From thermodynamic experiments, the activation energy was determined as 35.23 kJ mol^-1, indicating that the adsorption of Acid Red 66 was physical adsorption. The negative Gibbs free energy change (ΔG = -0.548 ~ -7.802 kJ mol^-1) and the positive enthalpy change (ΔH = +109.112 kJ mol^-1) indicated the spontaneous and endothermic nature of the adsorption process, respectively. The isosteric heat of adsorption increased with the increase of surface loading, indicating lateral interactions between the adsorbed dye molecules.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1671-1678
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• 1996

In external chemical vapor deposition processes including VAD and OVD the distribution of flame-synthesized silica particles is determined by heat and mass transfer limitations to particle formation. Combustion gas flow velocities are such that the particle diffusion time scale is longer than that of gas flow convection in the zone of particle formation. The consequence of these effects is that the particles formed tend to remain along straight smooth flow stream lines. Silica particles are formed due to oxidation and hydrolysis. In the hydrolysis, the particles are formed in diffuse bands and particle formation thus requires the diffusion of SiCl$\_$4/ toward CH$\_$4//O$\_$2/ combustion zone to react with H$\_$2/O diffusing away from these same zones on the torch face. The conversion kinetics of hydrolysis is fast compared to diffusion and the rate of conversion is thus diffusion-limited. In the language of combustion, the hydrolysis occurs as a Burke-Schumann process. In selected conditions, reaction zone shape and temperature distributions predicted by the Burke-Schumann analysis are introduced and compared with experimental data available. The calculated centerline temperatures inside the reaction zone agree well with the data, but the calculated values outside the reaction zone are a little higher than the data since the analysis does not consider diffusion in the axial direction and mixing of the combustion products with ambient air. The temperatures along the radial direction agree with the data near the centerline, but gradually diverge from the data as the distance is away from the centerline. This is caused by the convection in the radial direction, which is not considered in the analysis. Spatial distribution of silica particles are affected by convection and diffusion, resulting in a Gaussian form in the radial direction.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.6
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• pp.607-615
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• 2009

Analysis of chloride penetration into concrete is performed considering the repeated wetting and drying conditions of tidal zone, by means of the developed finite element program which enables the diffusion-convection analysis to be conducted. Heat conduction and moisture diffusion are also included in the finite element analysis program in order that their effects to chloride penetration may be considered. For the efficiency of calculation, the analyses of temperature, relative humidity and free chloride concentration are conducted successively in that order, by treating the convection of chloride due to moisture diffusion as an source or sink term. By comparing the analysis result from finite element analysis, where main variable is a wetting and drying period, with the chloride profiles from ACI Life-365 method, it is shown that the Life-365 method gives an accurate result for the submerged zone but does not consider the differences of wetting and drying period. To obtain an accurate chloride profile in the tidal zone, it is confirmed that the diffusion-convection finite element analysis should be applied.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.200.1-200.1
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• 2016

Tungsten coatings on the graphite (CX-2320) were successfully deposited using the vacuum plasma spraying (VPS) method. An optimum coating procedure was developed and coating thicknesses of $409{\mu}m$ (without an interlayer) and $378{\mu}m$ (with an interlayer) were obtained with no cracks and no signs of delamination. The mechanical characteristics and microstructure of the tungsten coating layers were investigated using a Vickers hardness tester, FE-SEM, EDS, and XRD. The effect of a titanium interlayer on the properties of the tungsten coating was investigated. It was shown that the titanium interlayer prevented the diffusion of carbon to the tungsten layer, thereby suppressing the formation of tungsten carbide. Vickers hardness data yielded values that were 62.5 ~ 80.46% of those for bulk tungsten, indicating that tungsten coatings on graphite can be utilized as a plasma-facing material. High heat flux tests were performed by using thermal plasma with a maximum flux of $10MW/^2$. Vickers hardness after the heat flux test is performed to see a change in the mechanical properties. The formationof a tungsten carbide and the effect of the titanium interlayer for the diffusion barrier are investigated by using energy dispersion spectroscopy (EDS).

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1464-1469
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• 2000

The effects of SiCl$_4$addition on flame structures have been studied in flame hydrolysis deposition (FHD) processes using Coherent anti-Stokes Raman spectroscopy (CARS) and planar laser induced fluorescence (PLIF) to measure temperatures and OH concentrations, respectively. The results demonstrate that even a small amount of SiCl$_4$ addition can change thermal and chemical structures of H$_2$/O$_2$ diffusion flames. When SiCl$_4$ is added to a flame temperature decreases in non-reacting zone due to the increases in both specific heat and density of the gas mixture, while flame temperature increase in particle formation zone due to the heat release through hydrolysis and oxidation reactions of SiCl$_4$. It is also found that OH concentration decreases dramatically in particle formation zone where temperatures increase. This can be attributed to consumption of oxidative species and generation of HCl during silica formation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1081-1092
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• 2004

The synthesis of Ni-catalyzed multi-walled carbon nanotubes and nanofibers on a catalytic metal substrate, using an ethylene fueled inverse diffusion flame as a heat source, was investigated. When the gas temperature was varied from 1,400K to 900K, approximately, carbon nanotubes with diameters of 20∼60nm were formed on the substrate. In the regions where the gas temperature was higher than 1,400K or lower than 900K, iron nanorods or carbon nanofibers were synthesized, respectively. Based on the quantitative analyses of large amount of SEM and TEM images, the nanotubes formed closer to the flame had a tendency of having larger diameters. HR-TEM images and Raman spectra revealed that carbon nanotubes synthesized had multi-walled structures with some defective graphite layers at the wall. Based on the graphite mode of the Raman spectra, it was believed that the optimal synthesis could be obtained as the substrate was positioned at between 5.5mm and 5.0mm, from the flame axis.