• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.29 no.6
• /
• pp.245-250
• /
• 2019

We investigated the post-annealing effect of Sn-incorporated β-Ga₂O₃ (β-Ga₂O₃ : Sn) nanowires (NWs) grown on sapphire (0001) substrates using radio-frequency powder sputtering. The β-Ga₂O₃ : Sn NWs were converted to a porous structure during the vacuum annealing process at 800℃. Host non-stoichiometric Ga₂O_3-x, is transformed into stoichiometric Ga₂O₃, where Sn atoms separate and form Sn nano-clusters that gradually evaporate in a vacuum atmosphere. As a result, the amount of Sn atoms was reduced from 1.31 to 0.27 at%. Pores formed on the sides of β-Ga₂O₃ : Sn NWs were observed. This increases the ratio of the surface to the volume of β-Ga₂O₃ : Sn NWs.

• Composites Research
• /
• v.15 no.1
• /
• pp.53-60
• /
• 2002

Composite ablative tubes required capabilities of ablative and structural characteristics were fabricated through filament winding technique and several experiments were conducted to evaluate the structural performance of composite ablative tubes. For this purpose, manufacturing procedures were briefly described and then resin digestion method was applied to measure the fiber volume fraction and the void content of composite ablative tubes. The configuration of tensile specimen fur composite ablative tubes with not losing the continuity of reinforced fibers was suggested by evaluating mechanical properties of several types of the specimen with different widths. Also, suitable processing variables for composite ablative tubes were determined by evaluating mechanical properties of several types of the specimen with different processing variables. In addition, acoustic emission signals were obtained during the proof test and could be applicable to study the crack initiation and the damage mode of composite ablative tubes. Finally, the structural reliability of composite ablative tubes could be verified to satisfy design requirements through the proof and burst tests.

• The Journal of the Acoustical Society of Korea
• /
• v.6 no.2
• /
• pp.19-29
• /
• 1987

The absorption coefficients of various length bundles of straws simulating perforated material were studied both theoretically and experimentally. For the theoretical predictions Zwikker and Kosten's theory was modified by adapting Biot's theory based on Poiseuille flow. The experimental data were collected using an impedance tube where the attenuation along the length of the tube was considered. The theoretically predicted values agreed very well with the experimentally measured ones for frequencies lower than 700Hz with bundles shorter than 120mm in length placed against the rigid end of the impedance tube. Configurations with an air gap between the end of a bundle and the rigid end were also investigated. Absorption coefficients were higher for 150mm bundles than for those of combined/air gap configurations with a total length of 150mm. Also for the fixed bundle lengths, absorption was found to increase with increasing air gap.

• Journal of Advanced Marine Engineering and Technology
• /
• v.22 no.2
• /
• pp.139-145
• /
• 1998

Filament winding method is widely used for composite fabrications using low viscosity liquid for-mation and processing asymmetrical structures of pressure vessel pipe rocket motor case etc. The filament winding method is affected by several parameters such as pot life of process time viscosi-ty of resin filament winding temperature and schedules curing condition and post curing condi-tion of resin. To develope high functional composite materials the rotation(5, 15, 20, 30rpm) of the winding machine was controlled by D.C motor. And the wiper to give proper tension was equipped between strand and resin bath. The resin is hooked by the design wiper. The adequate cure schedule was found by DSC. NOL ring test is carried out to investigate the basic physical properties such as design technology. The void contents in filament winding is generally higher than that of the prepreg laminated plate. These high contents of void can make a crack in resin in spite of low deformation. These problem was solved by giving tension in processing. To improve the characteristics of fiber volume fraction void contents resin/fiber bonding the winding speedc is changed under constant tension. It was found that resin impregnation was not different from in fiber contents void contents at the range of 0.5~1kg tension but it was found that resin was not impregnated at the above of 1.5kg tension. In burst test a pure PE liner was failed at a nozzle part under the $14kg/\textrm{cm}^2$ pressure but a pressure vessel of CNG was failed at a cylinder part under the $200kg/\textrm{cm}^2$ pressure.

• Membrane Journal
• /
• v.26 no.2
• /
• pp.146-151
• /
• 2016

Sulfonated poly (arylene ether sulfone) (SPAES) random copolymers have merits such as high proton conductivity, relatively low production cost, and thermochemical resistance when applied as polymer electrolyte membranes for fuel cells. However, it is difficult to directly employ SPAES copolymers into practical fuel cell membrane applications owing to their low chemical stability and dimensional instability under harsh operation conditions. A plausible solution is to impregnate SPAES copolymers into support films (e.g., electrospun polyimide support) with interconnected pore structures and high thermochemical toughness. In this study, a SPAES copolymer with a swivel group, which induces high free volume for fast ion transport, is chosen as ionomers to prepare pore-filling membranes (PFMs). The feasibility of the resulting membranes is evaluated via membrane characterizations.

• Composites Research
• /
• v.34 no.1
• /
• pp.1-7
• /
• 2021

Fiber-reinforced thermoplastic composites are applied to transport industries to lightweight of body, and applications will be expanded gradually. In this study, the impregnation and mechanical properties of continuous glass fiber (GF) reinforced polycarbonate (PC) composites were evaluated with different molecular weights of PC. The continuous GF reinforced PC composite were prepared by using GF fabric and PC film via continuous compression molding method. The melting flow index and tensile strength of PC matrix were evaluated with different molecular weights. Mechanical properties (tensile, flexural, and compressive) and pore rate of GF/PC composite were evaluated with different molecular weights of PC. The fracture behavior was analyzed to fracture surface of GF/PC composite using FE-SEM images. As these results, it was condition of representing the best mechanical property that the GF/PC composite was prepared by using PC of 20,000 g/mol as matrix.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.8
• /
• pp.855-861
• /
• 2013

Small-pore Cu-chabazite SCR catalysts with high NOx conversion at low temperatures are of interest for marine diesel engines with exhaust temperatures in the range of 150 to $300^{\circ}C$. Unfortunately, fuels for marine diesel engines can contain a high level of sulfur of up to 1.5% by volume, which corresponds to a $SO_2$ level of 500 ppm in the exhaust gases for an engine operating with an A/F ratio of 50:1. This high level of $SO_2$ in the exhaust may have detrimental effects on the NOx performance of the Cu-chabazite SCR catalysts. In the present study, a bench-flow reactor is used to investigate the effects of sulfur poisoning on the NOx performance of Cu-chabazite SCR catalysts. The SCR catalysts were exposed to simulated diesel exhaust gas stream consisted of 500 ppm $SO_2$, 5% $CO_2$, 14% $O_2$, 5% $H_2O$ with $N_2$ as the balance gas at 150, 200, 250 and $300^{\circ}C$ for 2 hours at a GHSV of 30,000 $h^{-1}$. After sulfur poisoning the low-temperature NOx performance of the SCR catalyst is evaluated over a temperature range of 150-$300^{\circ}C$ to determine the extent of the catalyst deactivation. Desulfation is also carried out at 600 and $700^{\circ}C$ for 30 minutes to determine whether it is possible to recover the NOx performance of the sulfur-poisoned SCR Catalysts.

• Composites Research
• /
• v.36 no.3
• /
• pp.180-185
• /
• 2023

This paper investigates the impact of fiber dispersion on the internal structure and mechanical strength of SiC_f/SiC composites manufactured using spread SiC fibers. The fiber volume ratio of the specimen to which spread SiC fiber was applied decreased by 9%p compared to the non-spread specimen, and the resin slurry impregnated between the fibers more smoothly, resulting in minimal matrix porosity. In order to compare the fiber dispersion of each specimen, a method was proposed to quantify and evaluate the separation distance between fibers in composite materials. The results showed that the distance between fibers in the spread specimen increased by 2.23 ㎛ compared to the non-spread specimen, with a significant 42.6% increase in the distance between fiber surfaces. Furthermore, the 3pt bending test demonstrated a 49.3% higher flexural strength in the spread specimen, accompanied by a more uniform deviation in test data. These findings highlight the significant influence of SiC fiber dispersion on achieving uniform densification of the SiC_f/SiC matrix and increasing mechanical strength.

• Korean Journal of Food Science and Technology
• /
• v.38 no.3
• /
• pp.400-407
• /
• 2006

Twenty six strains of lactic acid bacteria were isolated from Jeung-pyun batter, among which Tetragenococcus halophilus 1-12 showed highest dextransucrase activity at 36.95 DSU/mg, followed by T. halophilus 5-8 (36.87 DSU/mg protein), T. halophilus 2-12 (32.66 DSU/mg protein), T. halophilus 3-3 (31.43 DSU/mg protein), T. halophilus 3-1 (30.73 DSU/mg protein), T. halophilus 5-12 (29.43 DSU/mg protein), and Leuconostoc mesenteroides subsp mesenteroides 2-9 (28.5 DSU/mg protein). L. mesenteroides subsp mesenteroides 2-9, T. halophilus 1-12, and L. mesenteroides subsp dextranicum 5-13, were selected as starters (0.1, 0.5, and 1.0%) for Jeung-pyun manufacturing. Specific volume of Jeung-pyun added with 1.0% L. mesenteroides subsp dextranicum 5-13 was highest at 2.00, and 1.0% T. halophilus 1-12-added Jeung-pyun was lowest at 033. Cross-sectional observation of Jeung-pyun showed Jeung-pyun added with 0.5% L. mesenteroides subsp mesenteroides 2-9 was uniformly formed. Number of air holes of Jeung-pyun increased with increasing amount of added T. halophilus 1-12. Increasing addition of L. mesenteroides subsp dextranicum 5-13 resulted in more uniform air holes and volumes. Hardness, gumminess, and chewiness of Jeung-pyun added with 0.5 and 2.0% L. mesenteroides subsp dextranicum 5-13 decreased significantly in compasion to control groups. Jeung-pyun added with 0.5% L. mesenteroides subsp dextranicum 5-13 showed excelIent overall sensory desirability ranking of 8.500.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.34 no.3
• /
• pp.395-402
• /
• 2005

White layer cakes with 10-50% content of domestic millet and waxy millet were carried out to determine how the content of millet and waxy millet affected Quality and properties of a product. The 10% content of waxy millet resulted in the greatest volume, which decreased with the increase in the content of millet and waxy millet; up to 40% content of millet and waxy millet made no significant difference in weight from the control one. The specific loaf volume decreased with the increase in the content of millet and waxy millet. In terms of crum color, as the content of millet and waxy millet increased, the value of L tended to decrease, making it darker, and there was a significant increase in the value of a and b. As for crust color, the value of L, a, and b tended to increase with the increase in the content of millet and waxy millet, making it darker, but with no significant difference from the control one. In terms of texture, 10% content of millet and 10-20% content of waxy millet made no significant difference in hardness from the control one; as for retrogradation, waxy millet tended to make greater increase in hardness than millet. 5℃ storage resulted more rapidly in retrogradation than 25℃. The sensory evaluation showed that with the increase in the content, waxy millet, millet, and the control in order served to make it darker and harder in terms of external properties, with small pores, uneven texture, and reduced flavor in terms of internal properties. There was no significant difference between the cake with 10-20% content of millet and waxy millet and the control one in making a white layer cake by adding millet and waxy millet.