• 연구논문집
• /
• s.25
• /
• pp.175-184
• /
• 1995

Mechanical properties of the gas nitrocarburized product depend on the surface compound layer and the diffusion zone formed. The compound layer improves the wear resistance, and the corrosion resistance. Though phase composition, pore layer and growth rate of the compound layer varies according to the treatment time, temperature and the kind of the steel substrate, they are strongly influenced by the environmental gas composition. In the current study, the growth behavior of the compound layer and diffusion zone of the carbon steel and the alloy steel upon nitrocarburizing treatment at $570^{\circ}C$, and the phase composition and the variation in the growth rate of the compound layer according to the variation of the gas environment which was the medium of the nitriding and carburizing reaction were investigated.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.73-78
• /
• 2003

The InP thin films grown by metalorganic chemical vapor deposition (MOCVD) are widely used to optoelectronic devices such as laser diodes, wave-guides and optical modulators. Effects of various parameters controlling film growth rate such as gas-phase reaction rate constant, surface reaction rate constant and mass diffusivity are numerically investigated. Results show that at the upstream region where film growth rate increases with the flow direction, diffusion including thermal diffusion plays an important role. At the downstream region where the growth rate decreases with flow direction, film deposition mechanism is revealed as a mass-transport limited. Mass transport characteristics are also studied using systematic analyses.

• Journal of the Korean Society of Combustion
• /
• v.3 no.2
• /
• pp.29-40
• /
• 1998

Flame structures and NOx formation characteristics in the flame lets of coflow and counterflow diffusion flame are numerically studied. Calculations were carried out twice with the $C_2-Full$ and $C_2-Thermal$ Mechanism for each flame. Mixture fractions and scalar dissipation rates are used as the parameters to compare the flame let structures and NOx formation characteristics quantitatively. It was found that there is a similarity in flame temperature and stable species profiles except radical profiles between two flamelets. And there are some differences in NOx concentration and production rates. These results imply that the flow effects must be considered in calculations for NOx formation of turbulent flames using Laminar Flamelet Model.

• Journal of Power System Engineering
• /
• v.3 no.3
• /
• pp.29-35
• /
• 1999

The purpose of study is to investigate the flame stability and structure of turbulent diffusion flame behind the hollowed flame holder, which is located on the waste gas coming out from the test furnace. PDFs and Power Spectra technique of fluctuating temperature and ion current measurement were needed for this purpose. We discussed that the three types of stabilized flames were found as the result of post study. In this paper, we established the stability mechanism near the flame holder.

• Transactions of Materials Processing
• /
• v.13 no.2
• /
• pp.174-179
• /
• 2004

The effect of grain refinement on the plastic deformation behaviour of nanocrystalline metallic materials is investigated. A phase mixture model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. For the grain interior phase two concurrent mechanisms are considered: dislocation glide and mass transfer by diffusion. The proposed constitutive model was implemented into a finite element code (DEFORM) using a semicoupled approach. The finite element method was applied to simulating room temperature tensile deformation of Cu down to the nanoscale grain size in order to investigate the pre- and post-necking behaviour.

• Journal of Surface Science and Engineering
• /
• v.38 no.2
• /
• pp.83-87
• /
• 2005

We enhanced the color of blue sapphires and rubies successfully by using a oxygen-propane torch flame annealing, which had not been employed so far. We confirmed that about 1 mm-thick de-coloring of the corundum samples were available with 60 minutes flame annealing through eye evaluation, color coordination characterization, and methylene iodide immersion observation. We also suggest that the color centers such as $[Fe_{Al}^{\cdot}]$ may transform into transparent $[Fe_{Al}^{x}],\;[Cr_{A1}^{x}]$ sites with $[V_o^']$ generation at the elevated temperature in oxygen-rich atmosphere by diffusion mechanism. Our results implied that the longer diffusion time and the higher oxygen partial pressure might lead to the better de-coloring enhancement in corundum gem stones.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2012.11a
• /
• pp.58-59
• /
• 2012

Surface hardening mechanism of H13 steel was investigated when ion niriding after shot peening process was applied. Severe plastic deformation induced nanocrystallized grains at surface region. Higher nitrogen concentration was achieved in ion nitrided specimen with shot peening treatment than in single nitrided specimen. The elemental mapping on chromium and nitrogen by TEM-EELs showed chromium dissolved in matrix enhanced bulk nitrogen diffusion at surface region. Higher nitrogen diffusion also caused lattice distortion. Nano-sized grains, higher nitrogen concentration, and lattice diffustion contributed to the surface hardening.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.11
• /
• pp.3391-3398
• /
• 2013

The carboxylated multiwall carbon nanotubes (MWCNT-COOH) and functionalized with isatin derivative (MWCNT-isatin) have been used as efficient adsorbents for the removal of lead (Pb) from aqueous solutions. The influence of variables including pH, concentration of the lead, amount of adsorbents and contact time was investigated by the batch method. The adsorption of the lead ions from aqueous solution by modified MWCNTs was studied kinetically using different kinetic models. The kinetic data were fitted with pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The sorption process with MWCNT-COOH and MWCNT-isatin was well described by pseudo-second-order and pseudo-first-order kinetics, respectively which it was agreed well with the experimental data. Also, it involved the particle-diffusion mechanism. The values of regression coefficient of various adsorption isotherm models like Langmuir, Freundlich and Tempkin to obtain the characteristic parameters of each model have been carried out. The Langmuir isotherm was found to best represent the measured sorption data for both adsorbent.

• Journal of Power System Engineering
• /
• v.4 no.4
• /
• pp.54-58
• /
• 2000

The complete joining method for dissimilar hot die punch materials and its real-time evaluation method are not available at present. Brazing method has been used for joining them, but it is known that the welded joint by the brazing has the lower bonding efficiency and reliability than the diffusion welding. The friction welding with a diffusion mechanism in bonding was applied in this study. So, this work was carried out to determine the optimal friction welding conditions and to analyze mechanical properties of friction welded joints of hot die punch materials (STD61 for the blade part of hot die punch) to alloy steel (SCM440 for the shank part of hot die punch) such as plunger. In addition, acoustic emission test was carried out during friction welding to evaluate the weld quality.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.2
• /
• pp.232-240
• /
• 1986

Extinction characteristics of the two interacting premixed flames are analyzed for the effects of flame stretch and preferential diffusion using large activation energy asymptotic analysis by adopting counterflow system as a model problem. Results show that the flammable limit of the thermally interacting premixed flames is extended compared to the single flame, and the extinction mechanism is classified into weak and strong interactions. As the lewis number of the deficient species increases, the region of strong interaction diminishes which can explain the different characteristics of the extinction boundaries of the lean (rich) methane/air and butane/air flames. The influence of the flame stretch to the interaction boundaries is also studied.