• Design & Manufacturing
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• v.17 no.2
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• pp.27-32
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• 2023

Liquid silicon rubber (LSR) has fine thermal compatibility and is widely used in various fields such as medical care and automobiles because it is easy to implement products with good fluidity. With the recent development of flexible sensors, the focus has been on manufacturing conductive elastomers, such as silicone as elastic materials, and carbon black, CNT, and graphene are mainly used as nanomaterials that impart conductive phases. In this study, mechanical behavior and curing behavior were measured and analyzed to manufacture a CB-LSR complex by adding Carbon Black to LSR and to identify properties. As a result of the compression test, the elastic modulus tended to increase as carbon black was added. When the swelling test and the compression set test were conducted, the swelling rate tended to decrease as the content of carbon black increased, and the compression set tended to increase. In addition, DSC measurements showed that the total amount of reaction heat increased slightly as the carbon black content increased. It is considered that carbon black was involved in the crosslinking of LSR to increase the crosslinking density and have a positive effect on oil resistance reinforcement.

• Korean Journal of Mineralogy and Petrology
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• v.35 no.3
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• pp.367-376
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• 2022

This study is a preliminary step to understand the reaction between various liquids and zeolite in the subduction zone environment. Stilbite, NaCa₄(Al₉Si₂₇)O₇₂·28(H₂O), was selected and high pressure study was conducted on compressional behavior by the pressure-transmitting medium (PTM). Water and NaHCO₃ solution that can exist in the subduction zone was used as PTM, and samples were pressurized from ambient to a maximum of 2.5 GPa. Below 1.0 GPa, both experiments show a low linear compressibility in the range of 0.001 to 0.004 GPa^-1 and a high bulk modulus of 220(1) GPa. This is presumably because the structure of the stilbite becomes very dense due to insertion of water molecules or cations into the channel. On the other hand, at 1.0 GPa or higher, the trends of the two experiments are different. In the water run, the linear compressibility of the c-axis is increased to 0.006(1) GPa^-1. In the NaHCO₃ run, the linear compressibility of the b- and c-axis is increased to 0.006(1) GPa^-1. The bulk modulus after 1.0 GPa shows values of 40(1) and 52(7) GPa in water and NaHCO₃ run, respectively, confirming that stilbite becomes more compressible than that before 1.0 GPa. It is caused by the migration of cations and water molecules inside the channel, as the water molecules in the PTM start to freeze and stop to insert toward the channel at 1.0 GPa or more. In the NaHCO₃ run, it is assumed that the distribution of extra-framework species inside the structure is changed by substitution of the Na⁺ cation. It can be expected from tendency of the relative intensity ratio of the (001) and (020) peaks which show a different from that of the water run.

• Geotechnical Engineering
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• v.14 no.3
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• pp.25-46
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• 1998

This paper shows that there are the results of a series of model tests on the behavior of single pipe pile which is subjected to lateral load in, Nak-dong River sand. The purpose of the present paper is to estimate the effect of Non-homogeneity. constraint condition of pile head, lateral load velocity, relative density, and embedded length of pile on the behavior of single pile. These effects can be quantified only by the results of model tests. Also, these are compared with the results of the numerical methods (p-y method, modified Vlasov method; new ${\gamma}$ parameter, Characteristic Load Method'CLM). In this study, a new ${\gamma}$ parameter equation based on the Vlasov method was developed to calculate the modulus of subgrade reaction (E. : nhz.) proportional to the depth. The p-y method of analysis is characterized by nonlinear behavior. and is an effective method of designing deep foundations subjected to lateral loads. The new method, which is called the characteristic load method (CLM). is simpler than p-y analysis. but its results closely approximates p-y analysis results. The method uses dimensional analysis to characterize the nonlinear behavior of laterally loaded piles with respect to be relationships among dimensionless variables. The modulus of subgrade reaction used in p-y analysis and modified Vlasov method obtained from back analysis using direct shear test (DST) results. The coefficients obtained from DST and the modified ones used for the prediction of lateral behavior of ultimate soil reaction range from 0.014 to 0.05. and from 0.2 to 0.4 respectively. It is shown that the predicted numerical results by the new method (CLM), p-y analysis, and modified Vlasov method (new parameter) agree well with measured results as the relative density increases. Also, the characteristic load method established applicability on the Q-Mnu. relationship below y/D=0.2.

• Elastomers and Composites
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• v.49 no.1
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• pp.24-30
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• 2014

3-Amino-1,2,4-triazole (ATA) (2.5 and 5.0 phr) was incorporated into a immiscible maleated ethylene propylene diene rubber(mEPDM)/maleated high density polyethylene(mHDPE) (50 wt%/50 wt%) blend by melt mixing. Effects of the ATA on structure, mechanical and rheological properties of the blend was investigated. FT-IR and DMA results revealed that supramolecular hydrogen bonding interactions between the polymer chains occur by reaction of ATA with maleic anhydride grafted onto the component polymers in the blend, which induces the physical crosslinks in the blend. FE-SEM analysis showed that mEPDM forms a dispersed phase in continuous mHDPE matrix, and the blend with the ATA has finer phase morphology as compared to the blend without the ATA. By the addition of ATA in the blend, there were significant increases in tensile strength, modulus and elongation-at-break as well as elastic recoverability. Melt rheology studies revealed that ATA induced substantial increase in storage modulus and complex viscosity of the blend at the melt state.

• Polymer(Korea)
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• v.26 no.2
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• pp.218-226
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• 2002

For the preparation of high resilience polyurethane (PU) foams with polyether type cell openers which have different ethylene oxide (EO) content, molecular weight and chain structure, the influences of tell opener structure on the kinetics, rheology, structural stability, open cell content and mechanical properties of the obtained foam were investigated. It was observed that urea formation reaction was delayed with the increase of EO content and incorporation of ester linkage in cell opener molecule and was relatively independent on the molecular weight. With the rheological studies, the decreases of viscosity and storage modulus were confirmed for the increase of EO content and molecular weight, so that the resulted foam had low structural stability and high open cell content. The cell opener having ester linkage in molecule exhibited the lowest values of viscosity and storage modulus and the obtained foam has high open cell content. However, the structural stability increased due to the larger intermolecular interaction of ester linkage. The hardness, tensile strength, tear strength and elongation of foam were deteriorated with increase of EO content and molecular weight of tell opener. On the other hand, the cell opener having ester linkage in molecule improved the values of tensile strength, tear strength and elongation.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.371-378
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• 2012

Hydrophilic silica nanoparticles (SNPs) were treated by using 3-glycidoxypropyltrimethoxy silane (GPTMS) and then they were blended with polyurethane-urea (PUU) emulsions to obtain SNPs/PUU nanocomposite films. Thermo-mechanical properties of the nanocomposite films were investigated by varying the grafted amount of GPTMS onto SNPs and the contents of SNPs in the PUU matrix. The thermo-mechanical properties of the nanocomposite films were also compared in terms of the dispersibility of SNPs in the PUU matrix and thermal curing of the GPTMS-grafted SNPs. The maximum amount of grafted GPTMS was $1.99{\times}10^{-6}\;mol/m^2$, and which covered ca. 53% of the total SNP surface area. $^{29}Si$ CP/MAS NMR analyses with the deconvolution of peaks revealed the details of polycondensation degree and patterns of GPTMS in the surface modification of SNPs. The surface modification did not significantly affect colloidal stability of the SNPs in aqueous medium; however, the hydrophobic modification of SNPs offered a favorable effect on the dispersibility of SNPs in the PUU matrix as well as better thermal stability. XRD patterns revealed that GPTMS-grafted SNPs broadened the reduced the characteristic peak of polyol in PUU matrix. The composite films became rigid and less flexible as the SNP content increased from 5 wt.% to 20 wt.%. Particularly, Young's modulus and tensile modulus significantly increased after the thermal curing reaction of the epoxy groups in the SNPs.

• Korean Journal of Materials Research
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• v.21 no.7
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• pp.384-390
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• 2011

Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.1-1
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• 1994

;The electronic state calculations for various types of ceramic materials have beell performed by the use of $DV-X\;{\alpha}$ cluster method. The molecular orbital levels and wave functions for model clusters have been computed to study the electronic properties ami chemical bonding of the ceramics. For ${\beta}-sialon(Si_{6-z}Al_zO_zN_{8-z})$ which is a high temperature structural material based on ${\beta}-Si_3N_4$, we have made model cluster calculations to estimate the strength of chemical bonding between atoms by the Mulliken population analysis. It is found that the covalent bonding between Si and N atoms is very strong in pure ${\beta}-Si_3N_4$, but the covalency around solute atom is considerably weakened when Si atom is substituted by AI. This tendency is enhanced by an additional substitution of oxygen atom for N. The result calculated can well explain the experimental data of changes in mechanical properties such as the reductions of Young's modulus and Vickers hardness with increment of z-value in ${\beta}-sialon$. Various model clusters for transition metal oxides which show many interesting physical and chemical properties have also been calculated. High-valent perovskite-type iron oxides EMFe0_3E(M=Ca and Sr) possess very interesting magnetic and chemical properties. In these oxides, iron exists as $Fe^{4+}$ state, but the experimental measurement of Mossba~er effect suggests that disproportionation $2Fe^{4+}=Fe^{3+}+Fe^{5+}$ takes place for $CaFe0_3$ at low temperatures. The model cluster calculations for these compounds indicated the existence of considerably strong covalent bonding of Fe-O. The calculations of hyperfine interaction at iron neucleus show very good agreement with the experimental Mossbauer measurements. The result calculated also implies that the disproportionation reaction is strongly possible by assuming the quenching of breathing phonon mode at low temperatures.tures.

• Journal of the Korean Geotechnical Society
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• v.28 no.7
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• pp.67-75
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• 2012

This paper addresses the size effect of shallow foundation settlement in very dense weathered granite soil commonly encountered in bridge foundation. Load-settlement curves measured from the plate load tests of 5 different plate sizes in 2 sites were analyzed. The test results showed that the ground beneath the plate was considered not to reach the failure state and the settlement continuously increased proportionately as load increased. The result implies that settlement would govern the stability or serviceability of foundation on very dense weathered soil. The size effect is expressed as a relationship of subgrade reaction modulus to the size of plate. Compared with the previous relationships, the size effect in this result was more prominent and indicated that settlement prediction using the previous method could possibly underestimate the settlement of foundation in dense weathered granite soil.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.12
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• pp.969-976
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• 2011

In this study we aims to evaluate the effects of 1/3 mol% $Co_3O_4$ addition on the reaction, microstructure development, resultant electrical properties, and especially the bulk trap and grain boundary properties of $ZnO-Bi_2O_3-Sb_2O_3$ (Sb/Bi=2.0, 1.0, and 0.5) system (ZBS). The samples were prepared by conventional ceramic process, and characterized by XRD, density, SEM, I-V, impedance and modulus spectroscopy (IS & MS) measurement. In addition of $Co_3O_4$ in $ZnO-Bi_2O_3-Sb_2O_3$ (ZBSCo), the phase development, density, and microstructure were controlled by Sb/Bi ratio. Pyrochlore on cooling was reproduced in all systems. The more homogeneous microstructure was obtained in ZBSCo (Sb/Bi=1.0) system. In ZBSCo, the varistor characteristics were improved drastically (non-linear coefficient ${\alpha}$=23~50) compared to ZBS. Doping of $Co_3O_4$ to ZBS seemed to form $V^{\cdot}_o$(0.33 eV) as dominant defect. From IS & MS, especially the grain boundary of Sb/Bi=0.5 system is composed of electrically single barrier (0.93 eV) and somewhat sensitive to ambient oxygen with temperature.