• Carbon letters
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• v.14 no.4
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• pp.197-205
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• 2013

Five vapor-grown carbon nanofiber (VGCNF) reinforced vinyl ester (VE) nanocomposite configurations were fabricated, imaged, and mechanically tested in order to obtain information on the influence and the interactions of the role of the microstructure at lower length scales on the observed continuum level properties/response. Three independent variables (the nanofiber weight fraction and two types of nanofiber mixing techniques) were chosen to be varied from low, middle, and high values at equally spaced intervals. Multiple mixing techniques were studied to gain insight into the effect of mixing on the VGCNF dispersion within the VE matrix. The point count method was used for both lower length-scale imaging techniques to provide quantitative approximations of the magnitude and the distribution of such lower length-scale features. Finally, an inverse relationship was shown to exist between the stiffness and strength properties of the resulting nanocomposites under uniaxial quasistatic compression loading.

• Journal of the Korean Ceramic Society
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• v.33 no.3
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• pp.251-258
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• 1996

The reactions between an active metal brazing alloy and interlayers together with the effects of interlayer type on the interfacial microstructure change were investiaged for silicon nitride/stainless steel joint. The bending strengths were measured for joints with Mo, Cu, Ni interlayer type of different thicknesses. It was found that the interlayer with a low yield strength value is effective to improve the bending strength of the Si3N4/stainless steel joint. The maximum joint strength obtained at room temperature for a laminated Cu/Mo interlayer was about 460 MPa. The combined use of Mo and thin Cu layer was found to be effective in enhancing the bending strength for the Si3N4/S.S.316 joint.

• Journal of the Korean Ceramic Society
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• v.27 no.7
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• pp.861-868
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• 1990

Investigation for the preparation of high strength hardened cement paste using ordinary portland cement, hydroxypropyl methyl cellulose(HPMC) with SiC powder was carried out. The cement paste was mixed with 0.1 of water cement ratio by twin roll mill and cured 60 days in humidity chamber. The hydration degree of cement paste cured with W/C=0.1 in 60 days was about 30% and most pores in the paste were found to be existed as gel pores of diameter less than 0.01㎛. The maximum flexural strength of hardened cement paste was about 960kg/㎠. When the SiC powder was added to the paste, the flexural strength was 1000∼1100kg/㎠ and the Young's modulus was 8∼9×105kg/㎠.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.05a
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• pp.109-112
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• 1993

In this paper, We have studied about the microstructure of the piezoceramics PZT that were added with some kinds of additives, such as Niobium(Nb), Iron(Fe) or Manganese(Mn). The grain size of PZT ceramics was decreased with increasing the amounts of additive of Nb or Fe, while increased with increasing Mn. The curie temperature was changed slightly for the PZT ceramics containing $Fe^{3+}$, which is not dependent on the amounts, but $Nb^{5+}$ or $Mn^{2+}$ ion added PZT was lowered. The resistivity was increased with increasing the amounts of $Nb^{5+}$ additive, while decreased for $Mn^{2+}$ additive.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.249-251
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• 2002

It is well known that the interaction and adhesion between the glass fiber(GF) and polymer matrix has a significant effect in determining the properties of fiber-reinforced materials. Therefore, it is one of most important to modify the surface of GF with an appropriate sizing. We investigated the treatment method of GF with coupling agent to improve the interaction of the interfacial regions, and then the correlation between interfacial property and interphase microstructure was examined in an attempt to realize a proper morphology around the GF surface.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.6
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• pp.938-946
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• 2008

Fe-base amorphous alloy and two crystalline phases composite were fabricated. The effect of temperature and strain rate on mechanical properties was evaluated utilizing compression test. Mixture of non-crystalline and crystalline phases were found using X-ray diffraction (XRD) and differential thermal analysis (DTA) tests. Based on glass transition temperature and crystallization temperature. compression tests were performed in the temperature ranging from $560^{\circ}C$ to $700^{\circ}C$ with $20^{\circ}C$ interval. Relationship between microstructure, including fracture surface morphology, and mechanical behavior was studied. The peak stress of Fe-base amorphous alloy was over 2GPa and expected to have a good wear resistance, but it is expected hard to deform because of low ductility. The peak stress and elongation of two crystalline phases composite was over 1GPa and about 20%, therefore it is possible to deform high strength wear resistant materials such as engine valve.

• Journal of Power System Engineering
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• v.11 no.3
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• pp.41-46
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• 2007

The microstructure and electrochemical analysis of welds of electric resistance welding(ERW) pipe were investigated. The direction of metal flow line in HAZ of ERW pipe shifted to the inner(or outer) surface of pipe by plastic deformation during welding. The lowest heat input welds of ERW pipe was showed crack by liquid penetrant testing. Accelerated corrosion test by constant current density of 20mA/$cm^{2}$ developed groove at the welds of ERW pipe and the measured grooving factors were about $1.2{\sim}1.5$. Corrosion potential of base metal obtained by cyclic polarization in artificial sea water(3.5wt.% NaCl solution) was 100mV higher than that of weld metal of ERW pipe.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.7
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• pp.469-476
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• 2009

Most material of engineering interest undergoes solidification process from liquid state. Identifying the underlying mechanism during solidification process is essential to determine the microstructure of material thus the physical properties of final product. In this paper, effect of fluid convection on the dendrite solidification morphology is studied using Level Contour Reconstruction Method. Sharp interface technique is used to implement correct boundary condition for moving solid interface. The results showed good agreement with exact boundary integral solution and compared well with other numerical techniques. Effects of Peclet number and undercooling on growth of dendrite tip of both single and multiple seeds have been also investigated.

• Bulletin of the Korean Chemical Society
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• v.23 no.9
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• pp.1304-1323
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• 2002

Superconducting BiSrCaCu(Ni)O ceramicss have been prepared by the gel method using an aqueous solution containing a tartaric acid. The aqueous solution of metal salts was concentrated without precipitation. The precursor so prepared was homogeneou s and calcined at $825^{\circ}C$ for 24 h to produce superconducting phase. The thermal decomposition of gels, the formation of superconducting phase, and their ceramic microstructure were studied using IR, TGA, XRD, resistance measurements, and SEM. This method is highly reproducible and leads to powders with excellent homogeneity and small particle size for easy sinterability. The nickel dopant substituting for Cu gives rise to the gradual decrease of the Tc. Phase pure 2212 ceramics were obtained at 825 $^{\circ}C$ for 24 h. SEM pictures showed that liquid phase was formed when the samples were sintered temperatures higher than 825 $^{\circ}C$.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.6
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• pp.886-894
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• 1990

Sinterbility, microstructure, mechenical and electrical properties of yttriastabilized zirkconiz (92 mole % ZrO2 + 8 mole % Y2O3) doped with 0.5 mole % SiO2 and 0-2.O mole% Al2O3 were studied as a functin of Al2O3 addition. Sintered density increased with increasing Al2O3 addition up to o.5 mole%but decreased up to 1.0mole% Al2O3. Vickers hardness is proportional to sintered density. The specimen added 0.5mole% Al2O3 and 0.5mole% SiO2 exhibited a maximum conductivity. And the specimen added 0.5 mole % Al2O3 and 0.5 mole% SiO2 was measured a maximum electromotive force for a characteristics of oxyzen partial pressure.