• Transactions of Materials Processing
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• v.28 no.6
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• pp.361-367
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• 2019

Microstructure evolution and tensile properties of Al-8mass%Mg alloy casting billet by biaxial alternative forging were investigated in this study. An alternative forging system tailored in this study was used to allow continuous strain accumulations on the alloy workpiece. A finite element (FE) simulation results revealed that the strain was mainly concentrated in the core and that the shear bands developed into a form with an X shape in the cross-section of workpiece after the alternative forging using octangular rod shaped dies. With increasing the forging passes, it was observed that the Al-8mass%Mg alloy workpieces were significantly deformed, and cracks began to form and propagate on the both ends of the forged workpieces after five passes at room temperature. In as-forged microstructures taken by microscopes, twins, clustering of dislocations, and fine subgrains were found. Tensile strengths of the forged specimens showed significant increases depending on the number of forging passes, and a trade-off relationship was observed between the elongation and strength. At room temperature and 100℃ the workpieces showed similar behaviors in microstructural evolution and tensile properties depending on forging passes, while the increase range in strength was reduced at 200℃.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.4
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• pp.189-194
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• 2013

Single phase crystalline powders of $Mg_3Sb_2$ and $Mg_3Bi_2$ were prepared by mechanical alloying Mg, Sb and Bi metals with planetary ball milling for 24~48 h. The compositions of starting raw materials for single phase $Mg_3Sb_2$ and $Mg_3Bi_2$ were 3Mg : 1.8Sb and 3Mg : 1.6Bi, respectively. Two types of mechanically alloyed powders obtained were mixed at some ratios for the fabrication of $Mg_3Sb_2-Mg_3Bi_2$ composites and then hot pressed under uniaxial pressure of 70 MPa at 723 K for 1 h. The main phase of composites was a stable phase similar to $Mg_3Bi_2$ phase with a small amount of Bi phase. The distributions of Sb and Bi elements on EDS mapping images were discontinuous and their compositional contours were clear, which means that the hot pressed specimens were composites composed of two compounds of $Mg_3Sb_2$ and $Mg_3Bi_2$.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.233-239
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• 2002

Reflection properties of $SiO_2$/ITO (Indium Tin Oxide) thin films coated for electromagnetic shielding, anti-static and anti-reflection on the front surface in CRT were studied. The behavior of reflectance as a function of thickness of $SiO_2$/ITO was investigated and applied to theoretical anti0reflection model of double layers and three layers. As the thickness of ITO layer increased, the deviation from theoretical value increased because uniformity of film deteriorated by pore. Because of the effect of mixed layer of $SiO_2$ and ITO, experimental reflectance showed better acceptance to the three layer antireflection model of $SiO_2$/$SiO_2$+ITO/ITO than the two layer model. Based on the theoretical antireflection design, the double layer whose thickness of $SiO_2$ and ITO were 90, 65 nm, respectively appear 2.5% in reflectance at standard wavelength, 550 nm. This phenomenon was similar to theoretical reflectance in visual range.

• The Journal of the Korean dental association
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• v.53 no.10
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• pp.743-750
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• 2015

Objectives: This study compared the mechanical efficacy of sonic activated and passive ultrasonic irrigation for removing intracanal medicament from a simulated root canal under controlled conditions. Materials and Methods: Thirty simulated root canal in resin blocks were randomly divided into 3-groups. The canals were enlarged using ProTaper files and K3XF (#30/0.06). After cleaning and drying, canals were filled with Calcipex. Overfilled materials were wiped out and measured their weight to the unit of 1/10mg. After one week storage in 100% humidity $37^{\circ}C$ temperature, canals were irrigated using 20mL of saline with one of following methods according to the designated groups (n = 10). For group-NI, 30-gauge nickel-titanium irrigation needle was used. During irrigation with every 5mL, needle was moved in-and-out with 4-mm amplitudes. EndoActivator and ultrasonic tip were used for group-EA and group-UT respectively for 20 seconds after every 5mL irrigation using needle. Then the weight was measured again to calculate the weight of residual remnants. The data were analyzed by one-way ANOVA and Duncan's post-hoc test at a significance level of 95%. Results: The weight of the residual medicaments were $3.62{\pm}0.81mg$, $2.84{\pm}0.28mg$, and $2.73{\pm}0.90mg$ for group-NI, -EA, and -UT, respectively. Group-EA and group-UT had no significant differences to remove intracanal medicament and left significantly less amount of paste than group-NI (p < 0.05). Conclusions: Under the controlled conditions of this study, the sonic activation and PUI have similar mechanical efficacy for removing intracanal medicament.

• Journal of the Korean Geotechnical Society
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• v.21 no.4
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• pp.13-20
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• 2005

In this study, consolidation test and numerical analysis were performed with the aim of investigating the characteristics of consolidation behavior of mixed soil with the amount and particle shape of inserted materials. Mixed soil was made up of matrix (dredged clay) and inserted material (crashed oyster shell and/or sand). The concept of stress share ratio was introduced to evaluate the consolidation characteristics of mixed soils. And the finite differential numerical analysis was carried out by applying the Mikasa's consolidation theory. From the results of experiments and numerical analysis, it was verified that mixed soil consolidation behavior is affected by changes in inserted material. When a similar amount of granular material was inserted, the compressibility of the clay matrix of oyster shell mixed soil was smaller than that of sand mixed soil.

• Journal of Environmental Science International
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• v.21 no.1
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• pp.11-21
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• 2012

This study investigated the characteristics of selected volatile organic compounds(VOCs) in newly-finished residential buildings, before the occupants moved in. This investigation was carried out by measuring the indoor and outdoor concentrations of selected VOCs before the occupants moved in and by utilizing an indoor mass balance model. Among 25 target VOCs, five aromatics(benzene, ethyl benzene, toluene, m,p-xylene, and o-xylene) were detected in all samples of both indoor and outdoor air. Toluene was most abundant VOC in the indoor air of new apartments, with a median value of 168 mg $m^{-3}$. Unlike other VOCs, halogenated compounds would not be significantly emitted from building materials. The indoor air concentrations of all selected VOCs, except for 1,3,5-trimethyl benzene, exhibited significant correlations each other, while for outdoor air concentrations, five aromatics only were significantly correlated between them. The emission rate of toluene was higher for the current study(median value, 76.8 mg $m^{-2}\;h^{-1}$) than for a previous study, while the emission rates of limonene, a-pinene and b-pinene(geometric means of 2.4, 13.8 and 9.6 mg $m^{-2}\;h^{-1}$, respectively) were lower and the emission rates of m,p-xylene and 2-butanone(geometric means of 10.9 and 21.3 mg $m^{-2}\;h^{-1}$, respectively) were similar. Although there were a few exceptions, the emission strengths are likely proportional to indoor temperature, and appear to reversely proportional to air exchange rate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.243-249
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• 2016

The present work is for an evaluation of resistance to corrosion in steel coated with cementitious repair material, so that 3 cases of steel plate(Normal, Welding, Welding & coating case) are subjected to ICM(Impressed Current Method) for acceleration of corrosion for 7days. Tested and estimated corrosion ratio through Faraday's Law are compared, and the related flexural strength are evaluated. In Normal and Welding cases, similar level of corrosion ratio(70%) is evaluated, however only 17% level of corrosion ratio is evaluated in the Welding & coating case, which indicates that cementitious repair material is effective to anti-corrosion due to a block of chloride penetration. The flexural test results are consistent with those in accelerated corrosion test, which shows a significant flexural strength in Welding & coating case by 3.4times greater than the others. The cementitious material repair coating is evaluated to be effective to anti-corrosion in welding of steel plate.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.5
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• pp.626-639
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• 2003

Statement of problem : Recently, in attempts to reinforce the acrylic resin and to reduce the polymerization shrinkage, it has been reported that adding vinyloligo-silsesquioxane (vinyl-POSS) to PMMA significantly compensates for polymerization shrinkage and somewhat increases the fracture resistance. Purpose : There haven't been any studies on abrasion that can affect the adaptation of the denture in long-term use. In this study abrasion resistance was compared between acrylic resin with vinyl-POSS and commercialized acrylic resin for denture base. In addition, the difference in abrasion resistance according to molding methods was compared. Material and method : Using PaladentR 20 including vinyl-POSS. PaladentR 20, Lucitone 199R, SR IvocapR, denture bases were fabricated using compression molding technique and continuous-pressure injection technique. Surface hardness and abrasion were measured for each group, and the worn surfaces were observed under a scanning electron microscope. Results : 1. When surface hardness was measured for each material and molding technique, there was no statistically significant difference among the materials. (p<0.05) 2. When same denture base material and molding technique were used, the abrasion due to toothpaste solution was 5 times as severe as the abrasion due to soap solution. 3, When toothpaste solution was used, the abrasion decreased in the order of PaladentR20, PaladentR 20 including vinyl-POSS, SR IvocapR, and Lucitone 199R. However statistically significant difference was seen only among PaladentR 20, SR IvocapR, and Lucitone 199R. (p<0.05). 4. When soap solution was used, the abrasion was more severe in PaladentR 20 and including vinyl-POSS PaladentR 20 groups than in SR IvocapR and Lucitone 199R groups. (p<0.05). Conclusion : Addition of vinyl-POSS doesn't improve the abrasion resistance, and the abrasion resistance was similar to those of existing materials. Additional studies under different conditions are needed. For clinical application of vinyl-POSS, further investigations with different requirements and conditions are necessary.

• The Journal of Advanced Prosthodontics
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• v.2 no.3
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• pp.81-87
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• 2010

PURPOSE. The purpose of this study was to compare the linear sintering behavior of presintered zirconia blocks of various densities. The mechanical properties of the resulting sintered zirconia blocks were then analyzed. MATERIALS AND METHODS. Three experimental groups of dental zirconia blocks, with a different presintering density each, were designed in the present study. Kavo $Everest^{(R)}$ ZS blanks (Kavo, Biberach, Germany) were used as a control group. The experimental group blocks were fabricated from commercial yttria-stabilized tetragonal zirconia powder (KZ-3YF (SD) Type A, KCM. Corporation, Nagoya, Japan). The biaxial flexural strengths, microhardnesses, and microstructures of the sintered blocks were then investigated. The linear sintering shrinkages of blocks were calculated and compared. RESULTS. Despite their different presintered densities, the sintered blocks of the control and experimental groups showed similar mechanical properties. However, the sintered block had different linear sintering shrinkage rate depending on the density of the presintered block. As the density of the presintered block increased, the linear sintering shrinkage decreased. In the experimental blocks, the three sectioned pieces of each block showed the different linear shrinkage depending on the area. The tops of the experimental blocks showed the lowest linear sintering shrinkage, whereas the bottoms of the experimental blocks showed the highest linear sintering shrinkage. CONCLUSION. Within the limitations of this study, the density difference of the presintered zirconia block did not affect the mechanical properties of the sintered zirconia block, but affected the linear sintering shrinkage of the zirconia block.

• Preventive Nutrition and Food Science
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• v.12 no.3
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• pp.167-172
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• 2007

This study was conducted to determine the effect of hygienic processing (HP) on the reduction of microorganisms during manufacturing of saengshik with two vegetables (carrots and cabbage) and two grains (barely and glutinous rice) compared to general processing (GP). For GP, distilled water was used for washing raw materials and equipment. For HP, aqueous ozone (3 ppm) in combination with 1% citric acid and 70% alcohol were used for washing raw materials and the equipment, respectively. In carrots, after cutting, total aerobic bacteria (TAB), yeast and mold (YM) and coliforms were significantly increased to 5.19, 8.04 and 2.08 ($log_{10}$ CFU/g), respectively (p<0.05). Washing effectively reduced the increased microorganisms from cross contamination during cutting, but cross contamination increased with subsequent GP drying and milling procedures to 8.56, 8.27 and 3.71 ($log_{10}$ CFU/g) for TAB, YM and coliforms, respectively (p<0.05). On the other hand, HP washing of carrots with 3 ppm ozone in combination with 1% citric acid showed higher antimicrobial effect than GP washing, significantly decreasing the number of microorganisms (p<0.05). Further cross contamination did not occur through drying and milling due to cleaning the equipments with 70% alcohol prior to processing. After milling, the number of TAB, YM and coliforms were significantly decreased to 3.89, 4.47 and not detectable level ($log_{10}$ CFU/g), respectively (p<0.05). Similar results were observed in cabbage and grains. During storage for two months at different temperatures (22 or $4^{\circ}C$), there were no changes in numbers of spoilage microorganisms in the packaged saengsik after either processing. This suggests the importance of HP for the reduction of microorganisms during saengsik production, and demonstrates the effectiveness of disinfection at each processing stage in minimizing contamination levels to enhance microbial safety of saengshik products.