• Journal of the Korean Ceramic Society
• /
• v.31 no.12
• /
• pp.1459-1466
• /
• 1994

A novel technique for determining the oxygen tracer diffusion coefficients in oxides was developed. After the 16O-18O solid-gas exchange reactions between 16O in the oxides and 18O in the ambient gas, Raman spectra of the cross sections of oxide samples were measured in a spatial resolution of 5 ${\mu}{\textrm}{m}$. From thus obtained Raman spectra, depth profiles of 18O concentration in the oxide samples were calculated. The oxygen tracer diffusion coefficients and the surface exchange coefficients were determined under the assumptions that samples are semi-infinite slab and that the surface exchange reactionsare not negligible. The oxygen tracer diffusion coefficient of 2.8 mol% Y2O3-containing tetragonal ZrO2 polycrystals, 8 mol% Y2O3-containing ZrO2 polycrystals, and 10 mol% Y2O3-containing cubic ZrO2 single crystals (along the a axis) are as follows.

• Journal of the Korean institute of surface engineering
• /
• v.16 no.3
• /
• pp.98-107
• /
• 1983

A study on the improvement of wear resistance of brasses by electroplating and diffusion treatment of tin was carried out. The optimum condition of the treatment obtained was as follows. Plating thickness of tin : 5 - 9 $\mu\textrm{m}$ Condition of diffusion treatment : atmosphere ; fused nitrate bath (KNO3 + NaNO3) temperature and time ; 1st step 320$^{\circ}C$, 60min. and 450$^{\circ}C$, 30min. During the diffusion treatment, internetallic compounds of Cu-Sn were formed and these compounds were identified as η, $\varepsilon$ and $\delta$ phase from the outer tin layer. It was considered that the improvement of wear resistance of brasses by the treatment is because of the formation of intemetallic compounds particalarly $\varepsilon$phase which is very hard, between soft tin layer brass.

• Korean Chemical Engineering Research
• /
• v.57 no.5
• /
• pp.652-665
• /
• 2019

Analytical solutions of the reactant concentration inside porous spherical catalytic particles were obtained from unsteady reaction-diffusion equation by applying eigenfunction expansion method. Various surface concentrations as exponentially decaying or oscillating function were considered as boundary conditions to solve the unsteady partial differential equation as a function of radial distance and time. Dirac delta function was also used for the instantaneous injection of the reactant as the surface boundary condition to calculate average reactant concentration inside the particles as a function of time by Laplace transform. Besides spherical morphology, other geometries of particles, such as cylinder or slab, were considered to obtain the solution of the reaction-diffusion equation, and the results were compared with the solution in spherical coordinate. The concentration inside the particles based on calculation was compared with the bulk concentration of the reactant molecules measured by photocatalytic decomposition as a function of time.

• Journal of Electrochemical Science and Technology
• /
• v.13 no.3
• /
• pp.347-353
• /
• 2022

Agarose hydrogel, a solid electrolyte, was investigated voltammetrically in terms of transport properties and natural convection effects using a ferrocenyl compound as a redox probe. To confirm the diffusion properties of solute on the agarose interface, the diffusion coefficients (D) of ferrocenemethanol in agarose hydrogel were determined by cyclic voltammetry (CV) according to the concentration of agarose hydrogel. While the value of D on the agarose interface is smaller than that in the bulk solution, the square root of the scan rate-dependent peak current reveals that the mass transport behavior of the solute on the agarose surface shows negligible convection or migration effects. In order to confirm the reduced natural convection on the gel interface, scan rate-dependent CV was performed in the solution phase and on the agarose surface, respectively. Slow scan voltammetry at the gel interface can determine a conventional and reproducible diffusion-controlled current down to a scan rate of 0.3 mV/s without any complicated equipment.

• Journal of Conservation Science
• /
• v.26 no.2
• /
• pp.109-120
• /
• 2010

Four gilded bronze objects and a gilded silver object were examined for elemental diffusion between the gilding layer and the mating matrix. The gilded bronzes consist of three objects from three different historical periods, the Korean Three Kingdoms period, the Koryo and the Choseon periods and one from an unknown period. The gilded silver was from the Koryo period. The amalgam process seems to have been the major technique employed for all of them in gilding. The occurrence of substantial diffusion was observed in all but the anonymous object, particularly in the Choseon artifact where evidence was found that the diffusion phenomenon was intentionally utilized in gilding. The gold content in the gilded bronzes decreases gradually from surface to interior while the copper content increases to the interior, making it difficult to locate the boundary between the gilding layer and the matrix. This gradual change in composition must have resulted from elemental diffusion at elevated temperatures. The oxygen content negligible in the gilding layer precludes the possibility of corrosion being responsible for the varying composition. It is observed that non-uniform diffusion caused variation of colors in the surface of gilded bronzes. The change of colors induced by diffusion, which is always accompanied by the unique surface morphology and chemical compositions, is distinguished from the color change by corrosion. In the gilded silver object, diffusion of mercury was observed along with that of gold and silver.

• Journal of the Korean Chemical Society
• /
• v.45 no.4
• /
• pp.351-356
• /
• 2001

Planarization of the free-standing diamond film surface as smooth as possible could be obtained by using the hydrogen plasma etching with the diffusion of the carbon species into the metal alloy (Fe, Cr, Ni). For this process, we placed the free-standing diamond film between the metal alloy and the Mo substrate like a metal-diamond-molybdenum (MDM) sandwich. We set the sandwich-type MDM in a microwave-plasma-enhanced chemical vapor deposition (MPECVD) system. The sandwich-type MDM was heated over ca. 1000 $^{\circ}C$ by using the hydrogen plasma. We call this process as the hydrogen plasma etching with carbon diffusion process. After etching the free-standing diamond film surface, we investigated surface roughness, morphologies, and the incorporated impurities on the etched diamond film surface. Finally, we suggest that the hydrogen plasma etching with carbon diffusion process is an adequate etching technique for the fabrication of the diamond film surface applicable to electronic devices.

• Journal of Welding and Joining
• /
• v.15 no.6
• /
• pp.32-40
• /
• 1997

Solid state diffusion bonding is the joining process performed by creep and diffusion, which is accelerated by heating below melting temperature and proper pressing, in vacuum or shielding gas atmosphere. By this process we can obtain sufficient joint which can't be expected from the fusion welding. For Ti-6Al-4V alloy, the optimum solid state diffusion bonding condition and mechanical properties of the joint were found, and micro void morphology at bond interface was observed by SEM. The results of tensile test showed sufficient joint, whose mechanical properties are similar to that of base metal. 850$^{\circ}$C, 3MPa is considered as the optimum bonding condition. Void morphology at interface is long and flat at the initial stage. As the percentage of bonded area increases, however, small and round voids are found. Variation of void shape can be explained as follows. As for the void shrinkage mechanism, at the initial stage, power law creep is the dominant, but diffusion mechanism is dominant when the percentage of bonded area is increased.

• Journal of Environmental Science International
• /
• v.11 no.7
• /
• pp.679-686
• /
• 2002

Turbulence greatly influence on atmospheric flow field. In the atmosphere, turbulence is represented as turbulent diffusion coefficients. To estimate turbulent diffusion coefficients in previous studies, it has been used constants or 2-level method which divides surface layer and Ekman layer. In this study, it was introduced Smagorinsky method which estimates turbulent diffusion coefficient not to divide the layer but to continue in vertical direction. We simulated 3-D flow model and TKE equation applied turbulent diffusion coefficients using two methods, respectively. Then we showed the values of TKE and the condition of each term to TKE. The results of Smagorinsky method were reasonable. But the results of 2-level method were not reasonable. Therefor, it had better use Smagorinsky method to estimate turbulent diffusion coefficients. We are expected that if it is developed better TKE equation and model with study of computational method in several turbulent diffusion coefficients for reasonably turbulent diffusion, we will able to predict precise wind field and movements of air pollutants.

• Journal of the Korean Institute of Telematics and Electronics
• /
• v.24 no.2
• /
• pp.248-253
• /
• 1987

Boron diffusion into silicon through poly\ulcorneri-SiO2 was carried out for the diffusion with low concentration using CVD-BN. The result of direct boron diffusion from BN into silicon and that of boron diffusion through SiO2 from BN into silicon was compared with the result of boron diffusion through poly-Si-SiO2 from BN into silicon. In the case of boron diffusion through poly Si-SiO2, the low concentration diffusion was obtained, that is the boron surface concentration in silicon Cs=10**16 Cm**-3, and the glassy compounds were not seen.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.394-394
• /
• 2012

We fabricated organic-inorganic superlattice films using molecular layer deposition (MLD) and atomic layer deposition (ALD). The MLD is a gas phase process in the vacuum like to atomic layer deposition (ALD) and also relies on a self-terminating surface reaction of organic precursor which results in the formation of a monolayer in each sequence. In the MLD process, 'Alucone' is very famous organic thin film fabricated using MLD. Alucone layers were grown by repeated sequential surface reactions of trimethylaluminum and ethylene glycol at substrate temperature of $80^{\circ}C$. In addition, we developed UV-assisted $Al_2O_3$ with gas diffusion barrier property better than typical $Al_2O_3$. The UV light was very effective to obtain defect-free, high quality $Al_2O_3$ thin film which is determined by water vapor transmission rate (WVTR). Ellipsometry analysis showed a self-limiting surface reaction process and linear growth of each organic, inorganic film. Composition of the organic films was confirmed by infrared (IR) spectroscopy. Ultra-violet (UV) spectroscopy was employed to measure transparency of the organic-inorganic superlattice films. WVTR is calculated by Ca test. Organic-inorganic superlattice films using UV-assisted $Al_2O_3$ and alucone have possible use in gas diffusion barrier for OLED.