• Membrane Journal
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• v.23 no.2
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• pp.151-158
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• 2013

The effect of layered double hydroxides (LDH) on the gas separation properties of ethylene vinyl acetate copolymer was investigated. Mg-Al LDH/EVA nanocomposite membranes were prepared from solution intercalation using organically modified LDH (DS-LDH). Dodecyl sulfate (DS)-LDH was obtained by the intercalation of DS anion in the interlayer. The nanocomposite structure has been elucidated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). XRD pattern clearly shows that the DS-LDH layers are disorderly well dispersed in the EVA matrix. The maximum tensile strength and elongation of the LDH/EVA nanocomposite membrane were found with the LDH content 3 wt%. The thermal properties of nanocompostie membrane were enhanced by the incorporation of LDH in EVA matrix. Gas permeation of LDH/EVA nanocomposite membranes with LDH contents of 1, 3, 5 wt% was studied for $O_2$ and $CO_2$ single gases. The presence of 3 wt% LDH decreased $O_2$ permeability by up to 53% compared to the EVA membrane. In spite of barrier property of nanocomposite membrane, however, the gas permeability for $CO_2$ was increased due to its strong affinity with the residual OH groups on the LDH.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.267-273
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• 2006

We have prepared PP/Ba-ferrite composite fabrics by a melt-blown spinning method and investigated the relationship between the properties of PP/Ba-ferrite composite fabrics and melt-blown processing factors. A PP composite containing Ba-ferrite as a magnetic particulate filler was prepared in the form of pellet from PP resin and Ba-ferrite powder by melt compounding using a single extruder. Screw turning force (rpm), DCD (die-to-collector distance), and Ba-ferrite content were changed. We measured diameters of fiber, mechanical, thermal, and magnetic properties for the composited PP fabrics. The elongation was increased and a fiber diameter and tensile strength were decreased as the spinning distance increased or screw turning force decreased. The crystallinity was increased with increasing spinning distance according to XRD. It was assumed that the orientation of crystalline domain in the neat PP without ferrite was increased by drawing in mechanical direction, however, the orientation in the PP composite was decreased according to XRD analysis. We measured a magnetic property of PP nonwoven fabric containing Ba-ferrite powder. A coercive force, maximum magnetization, and residual magnetization are reduced with the spinning distance. According to the result of TGA measurement, the heat resistance was increased with the Ba-ferrite powder content and with decreasing the spinning distance.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.962-969
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• 1999

Elastic and elasto-plastic stress analyses of AlN/Cu and AlN/W pints produced by active-metal brazing method using Ag-Cu-Ti insert-metal were performed with use of Finite-Element-Method(FEM). The results of stress analyses were compared with those from the pint strength tests and the observations of fracture behaviors. It was shown that a remarkably larger maximum principal stress is built in the AlN/Cu pint compared to the A1N/ W joint. Especially, the stress concentration with tensile component was confirmed at the free surface close to the bonded interface of AlN/Cu. The elasto-plastic analysis under consideration of stress relaxation effect of Ag-Cu-Ti insert possessing a so-called 'soft-metal effect' showed that the insert leads to a lowering of maximum principal stress in AlNiCu pint, even though an increase of the insert thickness above 100$\mu\textrm{m}$ could not bring its further decrease. The maximum pint strengths measured by shear test were 52 and 108 MPa for AlNiCu and AlN/W pints. respectively. Typical fractures of AlN/Cu pints occurred in a form of 'dome' which initiated from the free surface of AlN close to the bonded interface and proceeded towards the AlN inside forming a large angle. AlN/W pints were usually fractured at AlN side along the interface of AlN/insert-metal.

• Journal of the Korean Geotechnical Society
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• v.34 no.12
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• pp.93-103
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• 2018

Behaviors of splices between bolts and welding spliced PHC piles using the tensile strength test were analyzed. The bolts spliced PHC piles, which were tightened over $200N{\cdot}m$ tightening torque, showed straight V shaped line at splices at the lowest 20 N load. Both sides of PHC piles stayed straight, so the full section of bolts spliced piles did not show the unifying behavior, which was the most important performance requirement as pile. Other bolts spliced PHC piles, tightened with $20N{\cdot}m$ loosening torque, also showed the same straight V shaped line at splices for each step of loading. The full section of bolts spliced piles did not return to the initial position after each step of unloading and did not show the elastic material behavior. The splices quality of bolts spliced piles is much lower than that of welding spliced piles with respect to displacement of splices during each step of loadings, residual displacements during each step of unloadings, and failure loads. Results showed that bolts spliced PHC piles, tightened with both over $200N{\cdot}m$ and as low as $20N{\cdot}m$ torque, fell short of performance requirements of spliced PHC pile.

• Korean Journal of Materials Research
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• v.4 no.8
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• pp.906-914
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• 1994

Plastic behavior of two-phase intermetallic compounds based on $LI_{2}$-type $(Al, Cr)_3$ Ti was investigated using compression test at R.T. and 77K. $LI_{2}$ single phase alloys and two-phase alloys consisting of mainly $LI_{2}$ phase and a few or 20% second phases were selected from AI-Ti-Cr phase diagram. In general, compared with Llz single phase, two-phase alloys consisting of 20% second phase showed relatively high yield strength and poor ductility. Among the alloys, however, AI-21Ti-23Cr alloy consisting of 20% $Cr_{2}Al$ phase showed available ductility as well as high yield strength. Plastic behavior of $LI_{2}$ single phase alloys and two-phase alloys consisting of a few% $Cr_{2}Al$ was also investigated. Homogenization of arc melted ingots substantially reduced the amount of second phases but introduced extensive pore. When Cr content increased in $Ll_{2}$ single phase alloys after the homogenization, the volume fraction of pore in the alloys decreased, and no residual pore was observed in two-phase alloys consisting of a few% $Cr_{2}Al$ phase. Environmental effect on the ductility of the alloys was investigated using compression test at different strain rates($1.2 \times 10^{-4}/s$ and $1.2 \times 10^{-2}/s$). Environmental embrittlement was least significant in A1-25Ti-10Cr alloy consisting of LIZ single phase among the alloys tested in this study. However, based on the combined estimation of the pore formation, environmental embrittlement and ingot cast structure, AI-21Ti-23Cr alloy consisting of 20% $Cr_{2}Al$ as the second phase is expected to show the best tensile elongation behavior.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.96-113
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• 1996

It has been found that the misfit dislocations in heavily boron-doped layers originate from wafer edges. Moreover, the propagation of the misfit dislocation into a heavily boron-doped region can be suppressed by placing a surrounding undoped region. Using a surrounding undoped region the disloction-free heavily boron-deoped silicon membranes have been fabricated. The measured surface roughness, fracture strength, and residual tensile stress of the membrane are 20.angs. peak-to-peak, 1.39${\times}$10$^{10}$ and 2.7${\times}$10$^{9}$dyn/cm$^{2}$, while those of the conventional heavily boron-doped silicon membrane with high density of misfit dislocations are 500 peak-to-peak, 8.27${\times}$10$^{9}$ and 9.3${\times}$10$^{8}$dyn/cm$^{2}$ respectively. The differences between these two membranes are due to the misfit dislocations. Young's modulus has been extracted as 1.45${\times}$10$^{12}$dyn/cm$^{2}$ for both membranes. Also, the effective lattice constant of heavily boron-doped silicon, the in-plane lattice constant of the conventional membrane, and the density of misfit dislocation contained in the conventional membrane have been extracted as density of misfit dislocation contained in the conventional membrane have been extracted as density of misfit dislocation contained in the conventional membrane have been extracted as 5.424.angs. 5.426.angs. and 2.3${\times}$10$^{4}$/cm for the average boron concentration of 1.3${\times}$10$^{20}$/cm$^{-23}$ cm$^{3}$/atom. Without any buffer layers, a disloction-free lightly boron-doped epitaxial layer with good crsytalline quality has been directly grown on the dislocation-free heavily boron-doped silicon layer. X-ray diffraction analysis revealed that the epitaxial silicon has good crystallinity, similar to that grown on lightly doped silicon substrate. The leakage current of the n+/p gated diode fabricated in the epitaxial silicon has been measured to be 0.6nA/cm$^{2}$ at the reverse bias of 5V.