• 한국세라믹학회지
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• 제36권6호
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• pp.655-661
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• 1999

${\beta}$-SiC formation mechanism in Si melt-C-SiC system with varying in size of carbon source was investigated. A continuous reaction sintering process using Si melt infiltration method was adopted to control the reaction sintering time effectively. It was found that ${\beta}$-SiC formation mechanism in Si melt-C-SiC system was directly affected by the size of carbon source. In the Si melt-C-SiC system with large carbon source ${\beta}$-SiC formation mechanism could be divided into two stages depending on the reaction sintering time: in early stage of reaction sintering carbon dissolution in Si melt and precipitation of ${\beta}$-SiC was occurred preferentially and then SIC nucleation and growth was controlled by diffusion of carbon throughy the ${\beta}$-SiC layer formed on graphite particle. Furthmore a dissolution rate of graphite particles in Si melt could be accelerated by the infiltration of Si melt through basal plane of graphite crystalline.

• 한국의류산업학회지
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• 제3권1호
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• pp.42-47
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• 2001

The hardening system of polyurethanes has usually caused by air pollution. bad working condition and fire hazard according to using orgarnic solvents. Therefore there have been researched on emulsion, water soluble and colloid-dispersion based water soluble instead of using organic solvents recently. This study synthesized polyurethane dispersing particle by means of mixing precursor and neutralized emulsion method. In the first step, polyurethane was preparated from isophorone diisocyanate and poly (ethylene-adipate) glycol, and got precursor by introducing dimethyl propionic acid as a hydrophilic group. Synthesized polyurethane was bonded to the surface of fiber and crosslinked as a anti-static agent, and then looked for the change of color and softening property.

• Steel and Composite Structures
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• 제32권5호
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• pp.559-569
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• 2019

The bond strength between composite laminates and concrete is a key factor that controls the behavior of concrete members strengthened with fiber reinforced polymer (FRP) sheets, which can be affected by several parameters such as thermal stresses and surface preparation. This article presents the result of an experimental study on the bond strength between FRP sheets and concrete at ambient temperature after specimens had been exposed to elevated temperatures of up to $200^{\circ}C$. For this purpose, 30 specimens of plain concrete with dimensions of $150{\times}150{\times}350mm$ were prepared. Three different conventional surface preparation methods (sandblasting, wire brushing and hole drilling) were considered and compared with a new efficient method (fiber implantation). Deformation field during each experiment was monitored using particle image velocimetry. The results showed that, the specimens which were prepared by conventional surface preparation methods, preserved their bond integrity when exposed to temperature below glass transition temperature of epoxy resin (about $60^{\circ}C$). Beyond this temperature, the bond strength and stiffness decreased significantly (about 50%) in comparison with control specimens. However, the specimens prepared by the proposed method displayed higher bond strengths of up to 32% and 90% at $25^{\circ}C$ and $200^{\circ}C$, respectively.

• 대한치과기공학회지
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• 제38권3호
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• pp.135-142
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• 2016

Purpose: The aim of this research was to evaluate the influence of different surface treatments on the shear bond strength of zirconia ceramic to composite resin. Methods: Seventy two cylinder-shape (diameter: 5 mm; height: 12 mm) blocks of experimental industrially manufactured Y-TZP ceramic were abraded with $125{\mu}m\;Al_2O_3$ particles and randomly divided into 4 groups. All the materials were categorized as group Gc(control group - composite resin veneering on zirconia surface), Gr - composite resin veneering after surface treatment of Rocatec system (3M ESPE, Seefeld, Germany) group; Gz - composite resin veneering after surface treatment of Zirconia primer (Z-primer, Bisco, U.S.A) group; Gm - composite resin veneering after surface treatment of zirconia primer (Monobond plus, ivoclar vivadent AG, Liechtenstein) group. Two different zirconia primers and Rocatec system were used to zirconia cylinders (n=16) onto the zirconia surface. Zirconia specimens, polished and roughened, were pretreated and composite bilayer cylinders bonded using conventional adhesive techniques. Results: Shear bond strengths were analyzed using single-factor ANOVA(p<0.05). Bond strength values achieved after airbone particle abrasion and zirconia surface pre-treatments(p<0.05). Conclusion: Shear bond strength tests denmonstrated that zirconia primer is a viable method to improved bond strength between zirconia ceramic core and veneering composites.

• 지질공학
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• 제29권4호
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• pp.383-391
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• 2019

Bio-grouting based on microbial-induced calcite precipitation (MICP) is recently emerging as a novel and environmentally friendly technique for improvement of coarse-grained ground. To date, the mechanical behaviour of bio-grouted coarse-grained soil with different calcite contents and grain sizes still remains poorly understood. The primary objective of this study is to investigate the influence of calcite content on the mechanical properties of bio-grouted coarse-grained soil with different grain sizes. This is achieved through an integrated study of uniaxial loading experiments of bio-grouted coarse-grained soil, 3D digitization of the grains in conjunction with discrete element modelling (DEM). In the DEM model, aggregates were represented by clump logic based on the 3D morphology digitization of the typical coarse-grained aggregates while the CaCO₃ was represented by small-sized bonded particle model. The computed stress-strain relations and failure patterns of the bio-grouted coarse-grained soil were validated against the measured results. Both experimental and numerical investigation suggest that aggregate sizes and calcite content significantly influence the mechanical behaviour of bio-cemented aggregates. The strength of the bio-grouted coarse-grained soil increases linearly with calcite content, but decreases non-linearly with the increasing particle size for all calcite contents. The experimental-based DEM approach developed in this study also offers an optional avenue for the exploring of micro-mechanisms contributing to the mechanical response of bio-grouted coarse-grained soils.

• 한국태양에너지학회 논문집
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• 제32권6호
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• pp.93-99
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• 2012

A nanofluid is a fluid containing suspended solid particles, with sizes on the order of nanometers. Especially graphene nanoparticle that has the high thermal conductivity properties among the various nanoparticles added to the nanofluid is receiving attention. Graphene is a flat monolayer of $sp^2$-bonded carbon atoms tightly packed into a honeycomb lattice. And are known to have very high thermal conductivity. Therefore, we compared thermal conductivity with viscosity of graphene M-5 nanofluids and graphene M-15 nanofluids. Graphene M-5 and graphene M-15 have different average particle diameters and the other properties are the same. Two kinds of graphene nanofluids was examined by measuring thermal conductivity via transient hot-wire method. And the viscosity was measured by using a rotational digital viscometer. As a result, graphene M-5 nanofluids exhibited better thermal conductivity and viscosity than graphene M-15 nanofluids.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
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• pp.234-235
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• 2007

Transparent nanosized $TiO_2$ sol has been made by sol-gel method, using Titanium(IV) isopropoxide precursor. To promote hydrolysis for titania is needed excess water, Oil bath and temperature about $80^{\circ}C$. $TiO_2$ sol is peptized ranging from pH 1 to 1.5 using hydrochloric acid for the stability of sol during a condensation reaction. The average particle size of $TiO_2$ sol was approximately 20nm. $TiO_2$-sillane sol was synthesized by surface treatment using MTMS to the $TiO_2$ sol. TEM analysis has been used to check the degree of dispersion and FT-IR analysis has been used to see if the sillane has been chemically bonded on the surface of $TiO_2$.

• 한국지반공학회논문집
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• 제28권9호
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• pp.85-95
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• 2012

유기산 재료를 이용한 지반 개량은 미생물을 배양하여 지반의 고결화로 인해 친환경적으로 지반의 강도를 증대시키는 방법으로 다양한 토질 성상에 대해 유기산 재료를 혼합 후 미생물 증식으로 강도 증대효과를 규명한 바가 있으나, 현재까지 현장 적용성을 평가한 바가 없다. 본 논문에서는 유기산재료를 이용하여 지반의 미생물 증식으로 인한 지반 고결화에 대해 연구를 실시하였으며, 이를 위해 재령 56일까지 동평판재하시험, 동적콘관입시험, 들밀도시험, SEM-EDS분석을 통해 지반강도의 변화에 대해 규명하였다. 시험 결과, 유기산 재료를 첨가한 지반의 강도와 강성은 증가하는 경향을 나타냈으며, SEM-EDS로부터 탄산칼슘의 증가를 규명할 수 있었다. 향후 유기산 재료를 활용한 친환경적인 지반개량 공법의 지속적인 연구와 관심이 필요하다고 사료된다.

• 한국재료학회지
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• 제9권1호
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• pp.8-13
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• 1999

$ZrB _2$ was prepared from a mixture of $ZrO_2$, $B_2$$O_3$and Mg by SHS method. The combustion products were successfully obtained from a mixture of $Zro_2$:$B_2$$O_3$:Mg=1:2.0:8.5(molar ratio). MgO, by-product, was removed to 92.7% by leaching with 1M HCl solution at 9$0^{\circ}C$, for 10 hours. After leaching, the mean particle size of the resultant $ZrB_2$powders was 23.6$\mu\textrm{m}$. $ZrB_2$-ZrC composite was suitably obtained from a mixture of C/Zr=1.2 molar ratio by arc-melting method. The density of arc-melted specimen increased by adding excess zirconium content(x). The bulk density was 6.17g/㎤ for x=0, and 6.37g/㎤ x=4. Vickers hardness of arc-melted specimen was /$1290kg\textrm{mm}^2$ for x=0, and fracture toughness increased to 4.2MPa.m\ulcornerforx=4 compared to 3.4MPa.m\ulcornerfor x=0.

• Carbon letters
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• 제8권4호
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• pp.326-334
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• 2007

In this study, graphite composites were fabricated by warm press molding method to realize commercialization of PEM fuel cells. Graphite composites have been considered as alternative economic materials for bipolar plate of PEM fuel cells. Graphite powder that enables to provide electrical conductivity was selected as the main substance. The graphite powder was mixed with phenolic resin and the mixture was pressed using a warm press method. First of all, the graphite powder was pulverized with a ball mill for the dense packing of composite. As the ball milling time increases, the average size of particles decreases and the size distribution becomes narrow. This allows for improvement of the uniformity of graphite composite. However, the surface electrical resistivity of graphite composite increases as the ball milling time increases. It is due to that graphite particles with amorphous phase are generated on the surface due to the friction and collision of particles during pulverizing. We found that the contact electrical resistivity of graphite particles increases as the particle size decreases. The contact electrical resistivity of graphite powders was reduced due to high molding pressure by warm press molding. This leads to improvement of the mechanical properties of graphite composite. Hydrogen gas impermeability was measured with the graphite composite, showing a possibility of the application for bipolar plate in fuel cell. And, I-V curves of the graphite composite bipolar plate exhibit a similar performance to the graphite bipolar plate.