• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.1
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• pp.6-12
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• 2019

Bonding properties of epoxy-containing solder joints were investigated by a high temperature aging test. Specimens were prepared by bonding an R3216 standard chip resistor to an OSP-finished PCB by a reflow process with two basic types of solder (SAC305 & Sn58Bi) pastes and two epoxy-solder (SAC305+epoxy & Sn58Bi+epoxy) pastes. In all epoxy solder joints, an epoxy fillet was formed in the hardened epoxy, lying around the outer edge of the solder joint, between the chip and the Cu pad. In order to analyze the bonding characteristics of solder joints at high temperatures, a high-temperature aging test at $150^{\circ}C$ was carried out for 14 days (336 h). After aging, the intermetallic compound $Cu_6Sn_5$ was found to have formed in the solder joint on the Cu pad, and the shear stress on the conventional solder joint was reduced by a significant amount. The reason that the shear force did not decrease much, even though in epoxy solder, was thatbecause epoxy hardened at the outer edge of the supported solder joints. Using epoxy solder, strong bonding behavior can be ensured due to this resistance to shear force, even in metallurgical changes such as those where intermetallic compounds form at solder joints.

• Korean Journal of Metals and Materials
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• v.47 no.3
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• pp.175-181
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• 2009

Mechanical properties and precipitation behavior of backward extruded 6061 Al alloy for pressure vessel were investigated using tensile test, transmission electron microscopy (TEM) and differential scanning calorimeter (DSC). In this study, solution heat treatment (SHT) was performed at $535^{\circ}C$ for 30~90 min and aging treatment was conducted at 177 and $190^{\circ}C$ for 1~7 h. Maximum tensile strength of $36.6kgf/mm^2$ and yield strength of $33.29kgf/mm^2$ were achieved at the aging time of 5 h at $190^{\circ}C$. TEM observation showed that fine needle-like ${\beta}^{{\prime}{\prime}}$ phase which has 35~45 nm of length was uniformly distributed in the aged 6061 Al alloy specimen. From tensile test, TEM and DSC analysis, it is expected that aging time of 2~5 h at $190^{\circ}C$ is suitable for the extruded A6061 used as pressure vessels.

• Preventive Nutrition and Food Science
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• v.18 no.1
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• pp.50-59
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• 2013

Black jujube was made by aging dried jujube and its physiochemical characteristics, antioxidant activities and ${\alpha}$-glucosidase inhibitory activities were evaluated. The moisture and sugar contents were increased depending on the period of aging times and the pH was reduced thereby increasing acidity. The color of black jujube extract was changed from red to black resulting in decreases of Hunter color values L, a and b. As the aging progressed, sucrose was decomposed by increasing glucose and fructose, indicating higher contents of the total reducing sugars. Among the six different types of organic acids extracted from dried jujube, the levels of oxalic acid and citric acid were increased as the aging progressed. The total polyphenol contents in ethanol and water extracts of dried jujube were 7.74 and 8.12 mg/g, respectively. The water extract of black jujube aged for 48 hr contained the highest polyphenol contents at 16.82 mg/g. The 5'-hydroxymethylfurfural (5'-HMF) contents of black jujube extract significantly increased by longer aging times, and contained higher contents in the ethanol extract than water extract. The ethanol extract of black jujube showed the highest 5'-HMF content with 338.89 mg% after aging for 3 days. Also, $IC_{50}$ values of black jujube aged for 72 hr evaluated by DPPH and ABTS radical assays were 0.54 and 0.59 mg/mL, respectively. ${\alpha}$-Glucosidase inhibitory activities of black jujube at the concentration of 3.33 mg/mL (ethanol extract) increased from 65 to 80 % after aging for 72 hr.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.3
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• pp.51-57
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• 2019

Post curing effects are estimated by specimen tests. Propellant specimen accelerated aging tests are performed when post curing is estimated to be complete and the coefficients of Arrhenius aging equations are acquired. Simulated motors with cylindrical grain are designed and fabricated to confirm the application. Accelerated aging tests are conducted, and aged properties are measured and estimated for the inner bore, center and bond parts of the grain. The measured aging ratios of the modulus are compared with the ones predicted by the equations. As the results, the accelerated aging equations predict well the propellant aging trends; however, some differences are observed at the bond part. Therefore, the specimen extraction part must be carefully chosen to suit the test purpose when a rocket motor grain is used for the aging test.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.48 no.3
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• pp.80-90
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• 2016

The purpose of this study was to investigate the functional properties of natural dyed Hanji for cultural properties conservation and storage. To estimate functional properties of Hanji, antimicrobial, insect repellent test, and Oddy test were executed. Hanji dyed with 10% Golden thread (Coptis chinensis), a natural dye and silver nitrate mordanting showed the most excellent antifungal activities against A. niger, P. chrysogenum, and Trichoderma sp. before and after aging. The insects repellent test followed didn't indicate significant effects on treated Hanji against Lasioderma serricorne, Sitophilus zeamais, and Tribolium castaneum. According to Oddy test result, Hanji dyed with Golden thread and silver nitrate caused no significant corrosions on copper, silver, and lead after aging 28 days.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.662-668
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• 2013

Reported here are results of the mechanical and electrical properties of both of intact and thermally degraded epoxy-coated copper busducts that are made by fluidized bed process. To elucidate and compare the properties mentioned above, electrical breakdown by thermal and water aging, v-t characteristic, bending test, impact test and cross cut test are carried out. Although the performance of electrical and mechanical properties are gradually decreased in increasing the severe conditions such as temperature, aging time, and so forth, sample C has a better performance in both mechanical and electrical properties.

• Elastomers and Composites
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• v.52 no.2
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• pp.105-113
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• 2017

The curing behavior, mechanical properties, hot-air aging resistance, abrasion properties,thermal properties, etc., of EVM/EPM/APP (ammonium polyphosphate)/DPER (dipentaerythritol)/EG (expandable graphite) and EVM/EPM/ATH (aluminium trihydroxide) flame retarding systems in ethylene vinyl acetate rubber (EVM) blends with EPM (ethylene propylene rubber) were sequentially examined. For both flame retarding systems, the torque values increased with the content of EPM rubber and with the vulcanization time. As the content of EPM rubber increased, the scorch time became shorter, whereas the optimum cure time followed an increasing trend. For the EVM/EPM/APP/DPER/EG flameretarding system, as the content of EPM rubber increased, the hardness did not change,whereas the tensile strength and elongation at break decreased. A hot-air aging resistance test at $150^{\circ}C$ showed that the heat resistance decreased with the EPM content regardless of the kinds and contents of flame retardants. As the EPM content increased, the abrasion rate became higher and the abrasion resistance of the EVM/EPM/APP/DPER/EG flame retarding systems exceeded that of the EVM/EPM/ATH flame retarding counterparts. In comparison with the EVM/EPM/ATH flame retarding systems, the thermal stability of the EVM/EPM/APP/DPER/EG flame retarding system showed an increasing tendency.

• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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• pp.234-240
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• 2007

The electrical properties and dc aging behavior for specified stress state of system, which is composed of quaternary Zn-Pr-Co-Cr, were investigated for different $Dy_2O_3$ addition doping level. As $Dy_2O_3$ doping level increased, the density decreased in the range of 5.51-4.90 $g/cm^3$, reaching maximum at 0.5 mol% and the average ZnO grain size decreased in the range of 17.7-6.0 ${\mu}m$. The incorporation of $Dy_2O_3$ significantly improved the non-ohmic properties, above 30 in non-ohmic coefficient, compared with that of undoped samples. The samples with the best performance of non-ohmic properties were obtained for $Dy_2O_3$ doping level of 1.0 mol%, with 49 in non-ohmic coefficient and 2.6 ${\mu}A/cm^2$ in leakage current. The samples with the highest stability were obtained for $Dy_2O_3$ doping level of 0.5 mol%.

• Polymer(Korea)
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• v.25 no.3
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• pp.359-366
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• 2001

Isothermal physical aging of a glass fiber/epoxy composite was examined at different aging temperatures ($T_a$) and degrees of conversion (monitored by the glass transition temperature, $T_g$) by means of the TBA torsion pendulum technique. The range of aging temperature was from 10 to $130^{\circ}C$ : the conversion was systematically changed from $T_g$=$76^{\circ}C$ to $T_g$=$177^{\circ}C$ (fully crosslinked). The effect of isothermal physical aging was manifested as perturbations of the modulus and mechanical loss vs. temperature in the vicinity of $T_a$ for all conversions. The rate of isothermal physical aging determined from the change of modulus with aging time at fixed aging temperature decreased and then increased with increasing conversion below T$_{a}$=9$0^{\circ}C$. There exists a superposition in aging rate vs. ($T_g$ -$T_a$) by shifting horizontally and vertically. This implies that the physical aging process is independent of the change of chemical structure as conversion proceeds. It has been found that water absorbed at the aging temperature below $70^{\circ}C$ during isothermal physical aging lowers the apparent aging rate. It is due to the absorbed water molecules forming strong polar interactions with hydroxyl group on network chain and reducing the segmental mobility during the physical aging.g.

• Journal of the Korean Ceramic Society
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• v.38 no.12
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• pp.1174-1179
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• 2001

Mn-Co-Ni oxide system has been used as the NTC thermistors for normal temperature applications. Mn-Co-Ni oxide-based thermistors with various compositions were sintered at 1250$^{\circ}C$ for 3 hours and then maintained at 1000$^{\circ}C$ for 3 hours. The electrical properties of the thermistors fabricated were measured. In particular the MCN622 composition (Mn$_3$O$_4$60 wt%, Co$_3$O$_4$20 wt%, NiO 20wt%) exhibited the lowest resistivity and relatively high B constant. The MCN721 composition (Mn$_3$O$_4$70wt%, Co$_3$O$_4$20wt%, NiO 10 wt%) showed the higher resistivity than any other compositions. The aging properties of each composition showed comparatively stable characteristics within ${\pm}$2%.