• Elastomers and Composites
• /
• v.38 no.3
• /
• pp.235-242
• /
• 2003

A vulcanization reaction characteristics of an isoprene rubber (IR)-modified natural rubber/carbon black (NR/CB) composite was studied using in-situ electrical property measuring technique. Since the electrical conductivity of the sample composite would be changed continuously during the vulcanization reaction by rearranging of the carbon black particles within the sample, volume resistivity (${\rho}$) might be obtained as a function or reaction time. A stabilization time ($t_i$), maximum reaction speed time ($t_p$), and volume resistivity at that time(${\rho}_p$) were defined from the data for the Arrhenius analysis. Volume resistivity ${\rho}$ showed a comparatively high value of ${\sim}10^8$ order before the reaction started, and dramatically decreased to be stabilized within $1{\sim}2$ minutes as soon as the reaction started. As the more time elapsed, thereafter, ${\rho}$ decreased monotonously to a certain constant value through a peak, ${\rho}_p$ at time $t_p$, which was considered as the maximum reaction rate. As a result, while $t_i$ values were comparatively constant as $1{\sim}2$ minutes, $t_p$ values showed to become shorter and shorter as the reaction temperature.

• Korean Journal of Materials Research
• /
• v.2 no.5
• /
• pp.366-374
• /
• 1992

Mechanical and impact properties of stitched S2 glass fiber reinforced polyester woven laminates composites have been studied. Laminates were stitched using Kevlar 49 thread with 1/2, 1, and 2 inch stitch spacing. Tensile and 3-point bending tests haute been performed to evaluate the mechanical properties of stitched and unstitched laminates. Impact tests at applied energy of 234.7J were performed to examine the impact behavior and toughness changes of the specimen. The same specimens were also tested repeatedly at low impact energy level of 110.2J for 3 times to evaluate damage tolerance properties. The tensile and 3-point bending test results showed that one inch spacing specimen had the highest tensile and flexural strength. It also showed the highest energy absorption capability and the best damage tolerance property at the repeated impact test. The half inch spacing specimen showed the lowest tensile strength and energy absorption property at the impact energy level of 234.7J, even though it had the highest frequency of stitching thread.

• Journal of the Korean Magnetics Society
• /
• v.12 no.6
• /
• pp.212-217
• /
• 2002

The pseudo spin valve with a structure of Tl/CoFe(t $\AA$)/Cu(30 $\AA$)/NiFe(50 $\AA$)/Ta, showing giant magnetoresistance properties by utilizing coercivity difference between only two soft ferromagnetic layers were produced by d.c UHV magnetron sputtering system. In pseudo spin valve Ta/CoFe/Cu/NiFe/Ta, the magnetic and magnetoresistance properties with change of CoFe thickness were investigated. When the thickness of CoFe was 60 $\AA$, a typical MR curve of pseudo spin valve structure was obtained, showing MR ratio of 3.8 cio and the coercivity difference of 27.4 Oe with a sharp change of hard layer switching. When the CoFe thickness was varied from 20 to 100 $\AA$, coercivity difference between two layers was increased to 40 $\AA$. and decreased to 100 $\AA$ gradually. It is thought the change in coercivity of hard layer was due to the crystallinity and magnetostriction of thin CoFe layer. In order to improve the MR property in CoFe/Cu/NiFe trier layer structure, CoFe layer with change of 2-20 $\AA$ thick was inserted between Cu and NiFe. When the thickness of CoFe was 10 $\AA$, MR ratio was 6.7％, showing excellent MR property. This indicates 50 ％ higher than that of CoFe/Cu/NiFe pseudo spin valve.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.26 no.1
• /
• pp.39-46
• /
• 2015

In this paper, a gas sensor using a modified $90^{\circ}$ hybrid coupler structure with conducting polymer which operates at 2.4 GHz is represented. Conducting polymers are used to the gas sensing material in proposed sensors. The conducting polymer varies its electrical property, such as work function and conductivity corresponding to the certain gas. To verify this variation of electrical property of conducting polymer at microwave frequencies, the conducting polymer is incorporated with the $90^{\circ}$ hybrid coupler structure, and this proposed sensor operates as reflection type variable attenuator and variable phase shifter. The conducting polymer is employed as impedence-variable transmission lines that cause a impedance mismatching between the general transmission line and conducting polymer. The experiment was conducted with 100 ppm ethanol gas at temperature of $28^{\circ}C$ and relative humidity of 85 %. As a result, the amplitude deviation of $S_{21}$ is 0.13 dB and the frequency satisfying ${\angle}S_{21}=360^{\circ}$ is shifted about 2.875 MHz.

• Korean Chemical Engineering Research
• /
• v.50 no.5
• /
• pp.795-801
• /
• 2012

Nanoparticles have received significant attention because of their unusual characteristics including high surface area to volume ratios. Thiol ligand have been used as stabilizers of metal nanoparticles since Brust et al. They reported the preparation method of ligand capped metal nanoparticles by protecting the nanoparticles with a self-assembled monolayer of dodecanethiolate. In this method, volatile organic compounds (VOCs) were used as sovents. This study was carried out to replace these VOCs with room temperature ionic liquids (RTILs). We used two type of ILs to prepare metal nanoparticles. One is a hydrophobic IL, [BMIM][[$PF_6$] (1-Butyl-3-methylimidazolium hexafluorophosphate) purchased from IL maker, C-Tri from Korea and the other one is a hydrophilic one, [BMIM][Cl] (1-Buthy-3-methylimdazolium chloride) sinthesized by us. In the case of preparing Ag and Au nanoparticles using [BMIM][Cl], we didn't use phase transition reagents and ethanol because it has hydrophilic property and preparing Au, Ag nanoparticles using [BMIM][[$PF_6$] the method is as same as Brust et al.'s except using [BMIM][[$PF_6$] instead of organic solvent because it has hydrophobic property. FT-IR and UV-vis, TEM, TGA analysis have been used in an attempt to determine the particle size and verify functional groups. The particle size obtained from TEM was very similar to those obtained by Brust et al. This is a clear example of ligand capped metal nanoparticles prepared using ionic liquids. And the experimental result demonstrated ionic liquids can act as a highly effective medium for the preparation and stabilization of gold and silver metal nanoparticles.

• Korean Chemical Engineering Research
• /
• v.43 no.2
• /
• pp.305-312
• /
• 2005

Poly(urethane-imide)s were prepared by reaction between crosslinkable endgroup containing soluble polyimide (PI) by chemical imidization and acrylate end-capped polyurethane (PU). Poly (amic acid) was prepared from 2,2'-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 4,4'-oxydianiline (ODA) and then end-capped with maleic anhydride (MA). The PU prepolymers were prepared by the reaction of polycaprolactone diol, tolylene 2,4-diisocyanate and end-capped with hydroxyl ethyl acrylate. The effect of PU content on the residual stress behavior, morphology and thermal property was studied. The poly(urethane-imide)s were characterized by thin film stress analyzer (TFSA), XRD, TGA and DMTA. Low residual stress and slope in cooling curve were achieved by higher PU content. Compared to typical polyurethane, these polymers exhibited better thermal stability due to the presence of the imide groups. Finally the residual stress of poly(urethane-imide)s was strongly affected by the morphological structure.

• Korean Journal of Food Science and Technology
• /
• v.44 no.5
• /
• pp.568-576
• /
• 2012

Baksulgi with various sugar substitutes was prepared and characterized for physicochemical and sensory qualities. The 10% sugar in a control baksulgi was replaced with 16.1% glucose, 13.3% erythritol, 10.2% xylitol, 0.2% stevioside (enzymatically modified stevia 100%), 0.05% aspartame, or 1.2% sucralose. Instrumental and sensory analyses indicated that the baksulgi with glucose was significantly different in color from the others, which was attributed to high susceptibility to browning reaction of the glucose. Baksulgi with aspartame showed significantly lower pH than that of control baksulgi, suggesting that the aspartame might have been hydrolyzed into its constituent amino acids under elevated steaming temperature. A sensory evaluation revealed that baksulgi with sucralose or xylitol was comparable to the control baksulgi in all sensory characteristics. However, the baksulgi with sucralose showed appreciably increased hardness with increased storage time at $4^{\circ}C$, partially due to the anhygroscopic property of sucralose.

• Composites Research
• /
• v.31 no.4
• /
• pp.122-127
• /
• 2018

Sandwich composites of carbon fiber reinforced plastic(CFRP) and polymer foam will be used to automobile and aerospace industry according to increasing importance of light weight. In this study, mechanical and heat resistance properties of sandwich composites were compared with type of polymer foam (polyethylene terephthalate(PET), polyvinylchloride(PVC), epoxy and polyurethane). All types of polymer foams were degraded to 30, 60, 120, 180 minutes in $180^{\circ}C$. After heat degradation, the polymer foams were observed using optical microscope and compressive test was performed using universal testing machine(UTM). Epoxy foam had the highest compressive property to 2.6 MPa and after thermal degradation, the mechanical property and structure of foam were less changed than others. Epoxy foam had better mechanical properties than other polymer foams under high temperature. Because the epoxy foam was post cured under high temperature. As the results, Epoxy foam was optimal materials to apply to structures that thermal energy was loaded constantly.

• Journal of the Korean Society of Food Science and Nutrition
• /
• v.44 no.9
• /
• pp.1407-1413
• /
• 2015

The objective of this study was to investigate the rheological and pasting properties of potato flour dispersions at different concentrations (3, 4, 5, 6, and 7%, w/w). A potato cultivar 'Goun', used in this study, was developed by Highland Agriculture Research Center, RDA. Potato flour dispersions showed shear-thinning behaviors (n=0.44~0.51) at $25^{\circ}C$. Apparent viscosity (${\eta}_{a,100}$), consistency index (K), and yield stress (${\sigma}_{oc}$) significantly increased with an increase in potato flour concentration. Storage modulus (G') and loss modulus (G") significantly increased, whereas complex viscosity (${\eta}^*$) was significantly reduced with increasing frequency (${\omega}$) from 0.63 to 63.8 rad/s. Magnitudes of G' and G" were significantly increased with elevation of potato flour concentration. G' values were considerably greater than G" over the entire range of frequency (${\omega}$) with a high dependence on ${\omega}$. Cox-Merz rule was not applicable to potato flour dispersions. Rapid Visco Analyzer data showed that peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and set back viscosity of samples significantly increased with an increase in potato flour concentration.

• Korean Journal of Materials Research
• /
• v.8 no.11
• /
• pp.1020-1025
• /
• 1998

Irradiation-induced changes in mechanical properties and magnetic parameters were measured and compared to explore possible correlations for Mn-Mo-Ni low alloy steel surveillance specimens which were irradiated to a neutron fluence of $2.3\times10^{19}n/cm^2$(E>1.0MeV) in a typical pressurized water reactor environment at about $288^{\circ}C$. For mechanical property parameters, microvickers hardness, tensile and Charpy impact test were performed and Barkhausen noise amplitude, coercivity, remanence, maximum induction were measured for magnetic parameters. respectively. Results of mechanical property measurements showed an increase in yield and tensile strength, microvickers hardness. 41J indexed $RT_{NDT}$ and a decrease in upper shelf energy irrespective of base and weld metals. However, in the case of tensile properties, the changes in weld metal were negligible compared to the base metal. In the case of magnetic measurements, it is found that magnetic remanence, BN amplitude. BN energy have dropped significantly but coercivity(H,) has increased rapidly after irradiation. In this study. the measurements conducted on surveillance specimens of Mn-Mo-Ni low alloy steel showed that there were strong correlations between mechanical properties and magnetic properties.