• Korean Journal of Materials Research
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• v.6 no.2
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• pp.210-220
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• 1996

The purpose of this study is to develop the processing techniques of Fiber Reinforced Metal by Liquid Phase Diffusion Bonding method with SiC fiber as a reinforcing material and CP Ti(Commercial Pure) as a matrix. The microstructure and the distribution of elements in reaction and CP Ti(Commercial Pure) as a matrix. The microstructure and the distribution of elements is reaction zone among CP Ti/Ti-15wt%Cu-20wt%Ni(TCN20)/SiC long fiber were investigated by Optical Microscope, SEM/EDX, EPMA, X-ray and AES. The results obtained in this study are as follows. 1) When Ti matrix composite materials are fabricated under the bonding condition of 1273Kx1200sec, the SiC long fiber was the most suitable reinforcing material for Ti matrix composite materials. 2) With SiC long fiber under same condition, a TiC layer(1.0-1.6$\mu\textrm{m}$) was observed on the surface of SiC long fiber. 3) Liquid Phase Diffusion Bonding has shown the feasibility of production of Ti matrix composite materials.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.70-78
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• 1993

An attempt was made to investigate the effect of brazing time on microstructure, microhardness, and corrosion of Zircaloy -4as well as the beryllium diffusion into its sheet. The sheets were coated with beryllium and brazed at $1020^{\circ}C$ for 20-40 minutes in $2{\times}10^{-5}$ torr vacuum atmosphere. 1. Microstructurally the brazed zone was largely divided into three regions: a region of continuous or partially formed of eutectic liquid films along grain boundaries; a region of precipitation in both grains and grain boundaries; a region of elongated wide structure of .alpha.-laths, which was not affected by beryllium. 2. Due to the precipitates, the beryllium-migrated region was hardened and the width of the hardened region increased with increasing brazing time. 3. Beryllium brazed Zircaloy -4 sheets showed a higher corrosion rate than those of as-received and heat-treated at a brazing temperature. 4. Diffusion coefficient of beryllium into Zircaloy -4 at $1020^{\circ}C$ for 30 minutes was $7.67{\times}10^{-7}cm^2/sec.$ It seemed that Be penetrated Zircaloy -4 by forming eutectic liquid films along grain boundaries in the proximity of Be/Zr interface and it, thereafter, diffused into Zircaloy mainly by interstitial solid solution.

• Journal of Korean Society for Atmospheric Environment
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• v.16 no.4
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• pp.339-350
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• 2000

The three-dimensional new corrdinate system over a single hill double hills and complex terrain with a single hill and a rectangular obstacle was generated using a body-fitted coordinate system. Control of the coordinate line distribution in the field was executed by generalizing the elliptic generating system to Poisson equation. ▽2ξ=P. The new coordinate system was well fitted to the surface boundary of single hill and double hills. But in the case of complex terrain with hill and rectangular obstacle there was smoothing tendency around the rectangular obstacle. In order to show the validity of the body-fitted coordinate system the heat diffusion equation was transformed and the temperature distribution was calculated over the various terrain. The results showed the temperature distribution was very symmetrical and stable around hills and obstacle. As a result the couple of a body-fitted coordinate system and the heat diffusion equation were executed successfully. Wind field over complex terrain with hill and rectangular obstacle which represent urban area was simulated stably in body-fitted coordinate system. The qualitative result show the enhancement of wind speed at the upwind direction of a hill and a rectangular obstacle and the recirculation zone at the downwind direction.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.2
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• pp.133-143
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• 1992

The water-quality control for coastal waters is continuously required in view point of the environmental protection. The purpose of this study is to simulate the hydrodynamic process and the dispersion phenomena of several pollutants in Suyeong Bay, Pusan. The present study employs the depth-averaged 2-dimensional model for nemerical simulation of the hydrodynamics and diffusion. The nemerical solution is obtained by ADI(Altenating Direction Implicit) scheme which is frequently used for tidal current and diffusion computations in the coastal zone. To verify the nunlerical results, the field observations of various water quality parameters such as COD, SS and nutrients were performed during the spring tide. In the results of this study, the computed tidal currents show the clockwise flows for ebb tide and counter-clockwise flows for flood tide. In comparison with the water-qualities in ebb tide and flood tide, there seems to be slightly deteriorated in ebb tide and especially near the estuary of Suyeong River. In flood tide, however, the water-quality near Kwangan Beach is deteriorated. The computed distributions of COD and SS are in god agreements with the observed ones, while those of $PO_4\;^{3-}-P\;and\;NO_3\;^--N$ show slight differences due to the complex transformation processes.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.487-498
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• 2015

A proper initial curing is a very simple and inexpensive alternative to improve concrete cover quality and accordingly extend the service life of reinforced concrete structures exposed to aggressive species. A current study investigates the effect of wet curing duration on chloride penetration in plain and blended cement concretes which subjected to tidal exposure condition in south of Iran for 5 years. The results show that wet curing extension preserves concrete against high rate of chloride penetration at early ages and decreases the difference between initial and long-term diffusion coefficients due to improvement of concrete cover quality. But, as the length of exposure period to marine environment increased the effects of initial wet curing became less pronounced. Furthermore, a relationship is developed between wet curing time and diffusion coefficient at early ages and the effect of curing length on time-to-corrosion initiation of concrete is addressed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1101-1109
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• 2004

Experimental measurements of flame structure and soot characteristics were performed fur ethene inverse diffusion flames (IDF). IDF has been considered as the excellent flow field to study the incipient soot because soot particle do not experience the oxidation process. In this study, LIF image clarified the reaction zone of IDF with OH signal and PAH distribution. laser light scattering technique also identified the being of soot particle. To address the degree of soot maturing, C/H ratio and morphology of soot sample were investigated. From these measurements, the effect of flow residence time and temperature on soot inception could be suggested, and more details on soot characteristic in the IDF was determined according to fuel dilution and flame condition. The fuel dilution results in a decrease of temperature and enhancement of residence time, but the critical dilution mole fraction is existed for temperature not to effect on soot growth. Also, the soot inception evolved on the specific temperature and its morphology are independent of the fuel dilution ratio of fuel.

• Journal of the Korean Professional Engineers Association
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• v.20 no.4
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• pp.5-11
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• 1987

The experiment was carried out for the purpose of studying the carburization of pure iron ingot and sintered iron powder by solid carbon in the atmosphere of $N_2$ gas. The velocity of carburization was estimated by the diffusion coefficient D calculated by carburization equation. The results obtained were as follows ; 1. The briqueted sample of iron fine powder which made by higher pressure, carburization depth and carbon concentration were increased as much, and pure iron shelved the maximum value. 2, The higher the carburization temperature, carburization depth and carbon concentration were increased, and the melting zone which had 3.0~3.3%C at the interface of carburization was formed at 130$0^{\circ}C$. As the pure iron ingot was carburized, the diffusion coefficient D of carbon were 0.211$\times$$10^{-6}$$\textrm{cm}^2$ㆍsec$^{-1}$ at 120$0^{\circ}C$ and 0.391$\times$$10^{-6}$$\textrm{cm}^2$ㆍsec$^{-1}$ at 130$0^{\circ}C$, respectively. 4. As the sintered iron powder was carburized at the pressure of 4 ton/$\textrm{cm}^2$, the diffusion coefficient of carbon were 0.157$\times$$10^{-6}$$\textrm{cm}^2$ㆍsec$^{-1}$ at 120$0^{\circ}C$ and 0.103$\times$$10^{-5}$$\textrm{cm}^2$ㆍsec$^{-1}$ at 130$0^{\circ}C$, respectively.

• Journal of Technologic Dentistry
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• v.21 no.1
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• pp.15-26
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• 1999

This study was carried out by observing to composition of oxide on the surface of dental porcelain low gold alloy with various Indium additions according to the degassing and analysing the change composition of additional elements In on diffusion behaviors of Porcelain-matal surface. The specimens used were Au-Pd-Ag alloys by small indium addition. These specimens were treated for 10min at $1000^{\circ}C$ in vacuum condition. To investigate the microsturcture of oxidized alloy surface, SEM and EDAX were used, and EPMA were used to investigate the diffusion behaviors of porcelain-metal surface. X-ray diffraction were used to observe the morphological changes in the oxidation zone. The results of this study were obtained as follows ; 1) The hardness of alloy increased with increasing amount of In addition. 2) The formation of oxidation increased with increasing In content after heat treatment. 3) Diffusion of indium elements increased with increasing In content in metal-porcelain surface after firing. 4) The oxidations of alloy surface were mainly $In_2O_3$.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.2981-2994
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• 1995

In order to elucidate the effects of positive pressure gradient on flame properties, structure and stabilization, an experimental study is made on turbulent diffusion flame stabilized by a circular cylinder in a divergent duct flow. A commercial grade gaseous propane is injected from two slits on the rod as fuel. In this paper, stabilization, characteristics and flame structure are examined by varying the divergent angle of duct. Temperature, ion current and Schlieren photographs were measured. It is found that critical divergent angle is expected to be about 8 ~ 12 degree through blow-off velocity pattern to divergent angle and the positive pressure gradient influences the flame temperature, intensity of ion current and eddy structure behind the rod. With the increase of divergent angle, typical temperature of recirculation zone is low but intensity of ion current is high in shear layer behind rod. Energy distributions of fluctuating temperature and ion current signals turn up low frequency corresponding to large scale eddies but high frequency corresponding to small scale eddies as well as low with the increase of divergent angle. Therefore the flame structure becomes a typical distributed-reacting flame.

• Computers and Concrete
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• v.15 no.4
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• pp.589-606
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• 2015

It is well-documented that the major deterioration of coastal RC structures is chloride-induced corrosion. Therefore, regional investigations are necessary for durability based design and evaluation of the proposed service life prdiction models. In this paper, four reinforced concrete jetties exposed to severe marine environment were monitored to assess the long term chloride penetration at 6 months to 96 months. Also, some accelerated durability tests were performed on standard samples in laboratory. As a result, two time-dependent equations are proposed for basic parameters of chloride diffusion into concrete and then the corrosion initiation time is estimated by a developed probabilistic service life model Also, two famous service life prediction models are compared using chloride profiles obtained from structures after about 40 years in the tidal exposure conditions. The results confirm that the influence of concrete quality on diffusion coefficients is related to the concrete pore structure and the time dependence is due to chemical reactions of sea water ions with hydration products which lead a reduction in pore structure. Also, proper attention to the durability properties of concrete may extend the service life of marine structures greater than fifty years, even in harsh environments.