Young Ku Yoon

Ultrasonic inspection of long steel pipes using Lamb waves

Abstract An ultrasonic inspection technique using Lamb waves was evaluated to detect and determine the exact location of flaws present in long steel pipes. Since multiple modes of Lamb waves are generated due to their dispersive characteristics in the inspected pipes, the selection of a specific Lamb wave mode is very important for inspection of flaws. Experimental studies of flaw detectability with the use of each Lamb wave mode, namely, the A 0 S 0 , A 1 , and S 1 modes and their ultrasonic attenuation characteristics were conducted. The experimental results showed that the A 0 mode is the most effective for detection and exact determination of the location flaws. A lucite wedge containing a water column that generates the A 0 Lamb wave mode was developed and used in the present inspection study. It was found that the ultrasonic beam divergence after wrapping around the inspected pipe once interferes with exact determination of the location of flaws and that the maximum reflection signals are obtained when the transducer is offset axially from the straight line with the position of the flaw. The present study showed feasibilities of ultrasonic inspection with the use of Lamb waves for detection of flaws in insulated or inaccessible steel pipes.

Characteristics of acoustic emission during stress corrosion cracking of Inconel 600 alloy

It is possible to detect by use of the acoustic emission (AE) technique the dynamic processes in stressed materials. In this study, the AE technique is applied to SCC of Inconel 600 due to depletion of chromium at grain boundaries to investigate the AE capability of detecting crack growth and to obtain the relation between AE characteristics and crack mechanisms such as fracture mode and crack growth rate during SCC. In addition, the generation of initial cracks was detected, and minimum crack size detectable with AE was determined to assess the potential of AE as a non-destructive method.

Thermodynamic study on the (U1-yEry)O2±x solid solutions

Abstract The oxygen potentials of (U 1− y Er y )O 2± x solid solutions were measured by means of a thermogravimetric method in the range of 1200 ∼ 1500°C and 10 −13 ≤ p o 2 ≤ 10 −4 atmosphere for y = 0.06 and y = 0.20, respectively. The lattice parameters of the stoichiometric (U 1− y Er y )O 2± x were also measured by the least-squares method in the range of y = 0.01 to y = 0.33. The lattice parameter decreases linearly with an increase in the erbium concentration. The change of the lattice parameter can be expressed in a linear equation of y as a( A ) = 5.4695 − 0.220y for 0 ≤ y ≤ 0.33. The Δ G O 2 has been found to undergo an abrupt increase in the range of −270 to −360 kJ/mol for y = 0.06 and −220 to −320 kJ/mol for y = 0.20 respectively in the temperature range of 1200 ∼ 1500°C. Both Δ S O 2 and Δ H O 2 for (U 1− y Er y )O 2± x showed sharp maxima at about the O M ratio of 2.005, irrespective of erbium content, but the minimum peaks of the Δ S O 2 and Δ H O 2 were shown only for y = 0.20 at O M = 1.995 .

Electrical and optical properties of amorphous BaTiO3 thin films grown by metalorganic chemical vapor deposition on indium tin oxide-coated glass

In order to fabricate insulating films for a full-color thin-film electroluminescent display, an amorphous BaTiO3 thin film was deposited on an indium tin oxide-coated soda lime glass substrate at a low substrate temperature by metalorganic chemical vapor deposition with use of Ba(tmhd)2, Ti(OC3H7)4 and N2O. Scanning electron microscopy of the tilted surface of the as-grown BaTiO3 film showed a surface morphology of granular-like micrograins without defects such as pinholes and clusters. The thickness of the as-deposited film was approximately 1400 A as confirmed by cross-sectional transmission electron microscopy. The formation of an interface film between the as-grown film and the indium tin oxide was not observed. Room-temperature frequency dependence of capacitance and dissipation factor was clearly indicated those typically exhibited by the amorphous BaTiO3 capacitor deposited on the conducting substrates having a metal-insulator-metal (MIM) structure. Optical transmittance measurements showed that the amorphous BaTiO3 film deposited at 400°C on the indium tin oxide-coated glass substrate has the transparency of about 80% in the visible wavelength range. Furthermore, the value of the optical band gap was approximately 4.71 eV. These results indicate that the amorphous BaTiO3 thin film grown on the indium tin oxide-coated glass can be used for thin-film flat panel electroluminescent display applications.

Surface Morphologies of BaTiO3 Thin Films by Atomic Force Microscopy.

Surface morphologies of BaTiO3 thin films have been studied by atomic force microscopy (AFM). The films on (111)InSb, indium tin oxide (ITO)-coated glass and (100)Si substrates are deposited by in-situ metalorganic chemical vapor deposition (MOCVD) at different deposition temperatures of 300°C, 400°C and 600°C, respectively. AFM under ambient conditions showed that the BaTiO3 film deposited on the ITO-coated glass had a smooth surface consisting of large hemispherical grains, while the film on (100)Si had a slightly rough surface with textured rectangular grains. As-grown film on the (111)InSb substrate was in the amorphous phase except near the interface, resulting in a rough surface. Our results of dependence on the kind of substrates and growth temperature suggest that the surface morphology of the as-grown films is strongly influenced by the crystallinity and growing characteristic of the film. For low-temperature growth below the deposition temperature of 600°C, surface roughness of the BaTiO3 film is strongly dependent on growth temperature rather than crystallinity of the films related to substrates.

The structure of bis[(o-hydroxyphenoxy)ethoxy]ethane monohydrate

The title compound (C18H22O6·H2O) crystallizes in space groupP212121 witha=25.909(5),b=8.542(3),c=8.187(3) Å,Z=4. The structure was determined from 1538 X-ray diffractometer data and refined toR=8.05%. The polyether adopts an annular structure with the water molecule at the center, and is slightly folded like the wings of a butterfly. As usual, all torsion angles about C−O aretrans and about C−C aregauche. This complex displays 3 three-center (bifurcated) and 1 two-center hydrogen bonds, between phenolic hydroxyl and water oxygen. The latter is involved in an infinite homodromic chain O(1)−H...OW−H...O(1)−H...

Analysis of the formation of BaTiO3 island deposited on (111) InSb by metalorganic chemical vapor deposition at low temperature

Abstract Islands of BaTiO 3 in a thin film deposited on a (111) InSb substrate by metalorganic chemical vapor deposition at a temperature of 300°C were investigated. Refractive index measured by ellipsometer using a He-Ne laser was 1.95, which is nearly the same value as that of amorphous BaTiO 3 with microcrystals. X-ray diffraction peaks showed the deposit to be mostly amorphous and partly crystalline having the 〈110〉BaTiO 3 direction normal to the (111) InSb. Transmission electron microscopy results showed that partially epitaxial BaTiO 3 islands with periodic misfit dislocations had been formed at the interface between amorphous BaTiO 3 thin layer and the (111) InSb substrate. These BaTiO 3 islands on the (111) InSb substrate formed at a low growth temperature were three-dimensional nuclei which were closely associated with surface irregularities of the (111) InSb substrate.

A computer model for predicting transient fission gas release from UO2 fuel

In this paper, the KFGR-T computer model is developed to predict transient fission gas release from UO{sub 2} fuel with an emphasis on the nonequilibrium behavior of fission gas bubbles. It takes into account the relevant physical processes generally considered by other workers, as well as migration of fission gas bubbles through channels formed by the extension of dislocations to grain boundaries during the transient heatup stage, grain growth/grain-boundary sweeping during the iso-thermal annealing stage at high temperatures, and gas release through intergranular cracking. This computer model is applied to calculate transient fission gas releases, and the calculated values are compared with the results of out-of-pile experiments performed with UO{sub 2} fuel base-irradiated or burnups in the range of 18 to 35 MW {center dot} d/kg U. The absolute values and the trends of the fission gas releases calculated with the KFGR-T model are in good agreement with the experimental data. A parametric study is also done to investigate the sensitivity of the model to variables such as initial grain size, heating rate, temperature gradient, and initial gas concentration, and these results are compared with the sensitivity of other models.