• Restorative Dentistry and Endodontics
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• v.27 no.3
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• pp.239-248
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• 2002

이 연구의 목적은 와동의 형태가 굴곡강도와 탄성계수 등 복합레진의 물리적 성질에 미치는 영향을 평가하는 것이다. 복합레진은 Clearfil$^{TM}$ AP-X(Kuraray, Japan)와 Esthet-X$^{TM}$(Dentsply, USA)가 이용되었으며, 상아질 접착제는 Clearfil$^{TM}$ SE Bond(Kuraray, Japan)와 Prime & Bond NT$^{TM}$(Dentsply, USA)를 사용하였다. 대조군의 시편은 split steel mold(25mm$\times$2mm$\times$2mm) 내에 상기 2종류의 복합레진을 충전하여 2개의 대조군 시편을 제작하였으며, 2.4 및 3.4의 C-factor를 부여하기 위한 유리 모형와동을 제작하고, 와동 내에 상기 2종류의 복합레진을 충전하기 전 유리와동의 내면은 sandblasting 처리하고 각각의 복합레진과 동일회사 제품의 상기 상아질 접착제로 처리한 후, 복합 레진을 각각 충전하여 4개의 실험군을 제작하였다. 제작된 실험군 시편은 저속 diamond saw로 충전된 복합레진 부위의 중심부를 통과하도록 절단하여 레진기둥(25mm$\times$2mm$\times$2mm)이 되도록 제작하였다. 제작된 시편을 37$^{\circ}C$의 증류수에 24시간 동안 보관 후, 만능시험기(EZ Test, Shimadzu, Japan)를 이용하여 분당 1mm의 crosshead speed로 3점 굴곡강도를 측정하였다. 또 Linometer(R&B, Korea)를 이용하여 복합레진의 중합수축량을 측정하였으며 굴곡강도측정 후 시편의 파단면은 주사전자현미경(S-2300, Hitachi, Japan)을 이용하여 관찰하였다. 실험결과의 통계분석은 95% 수준의 one-way ANOVA/Tukey's test를 이용하여 결과를 얻었다. 실험에 이용된 2종류 복합레진의 굴곡강도와 탄성계수는 C-factor치 증가에 따라 감소하였으며, 파단면 또한 C-factor의 증가에 따라 더 불규칙해지는 양상을 나타내었다. 본 실험의 결과 hybrid형 복합레진이 micro-hybrid형 복합레진에 비해 C-factor의 영향을 더 많이 받는 것으로 나타났으며, 와동의 C-factor증가가 굴곡강도나 탄성계수와 같은 복합레진의 물리적 성질을 저하시킨다는 것을 의미하였다.

• Elastomers and Composites
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• v.40 no.3
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• pp.196-203
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• 2005

In this work, the engine oil resistant evaluation and breakdown analysis of room temperature vulcanizing silicone adhesives were performed through the surface properties, thermal stabilities, adhesive strength, and morphology measurements. As a result, the permeation of engine oil into adhesive specimens was carried out from surface to center in the specimens. And the oil content in the adhesive specimens was increased and the Si-O-Si bond of the adhesives was decomposed with increasing the aging time. The TGA results indicated that the thermal degradation was mainly occurred at under and surfaces of the specimens. The tensile strength, elongation, and adhesive strength of the adhesives were significantly decreased after the engine oil resistant tests, which could be attributed to the initial lose of adhesive properties resulting from the engine oil absorption and thermal aging. And the failure mode of the adhesive specimens was changed from cohesive failure to interfacial failure.

• Journal of Adhesion and Interface
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• v.17 no.1
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• pp.1-6
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• 2016

In this study, to replace a complicated process such as in the rubber component used in the adhesive of the shoe buffing, pretreatment with primers, we studied mechanical properties and adhesive properties with rubber compound added propanamine and 1,6-Hexanediamine. The adhesive properties rubber specimen added propanamine did not occurrence, but The adhesive properties rubber specimen added 1,6-Hexanediamine was occurrence. Also, the contact angle was decreased compared to not added NBR. And rubber compound added 6-Hexanediamine was smaller than the contact angle was evaluated in comparison to the added propanamine. $NH_2$ group on the rubber surface were confirmed with a peak at $1450{\sim}1550cm^{-1}$ in FT-IR spectrum. Rubber compound added propanamine and 1,6-Hexanediamine was reduced mechanical properties and decreased NBS resistance.

• Composites Research
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• v.26 no.2
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• pp.141-145
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• 2013

The mode II interlaminar fracture toughness was evaluated for CFRP laminates with different types of nonwoven tissues and the source of increased mode II interlaminar fracture toughness was examined by SEM analysis in this paper. The interlaminar fracture toughness in mode II is obtained by an end notched flexure test. The experiment is performed using three types of non-woven tissues: 8 $g/m^2$ of carbon tissue, 10 $g/m^2$ of glass tissue, and 8 $g/m^2$ of polyester tissue. On the basis of the specimen with no non-woven tissue, interlaminar fracture toughness on mode II at specimens inserted with non-woven carbon and glass tissues and polyester tissues increases as much as 166.5% and 137.1% and 157.4% respectively. The results show that mode II interlaminar fracture toughness of CFRP laminates inserted with nonwoven tissues increased due to the fiber bridging, fiber breakage, and hackle etc. by SEM analysis.

• Journal of the Korean Ceramic Society
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• v.36 no.5
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• pp.555-563
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• 1999

Impregnation of phosphorous additiers into graphite bulk was studied with the goal of enhancing the effectiveness of oxidationprotection. In addition graphite acid washing was carried out prior to the impregnation further to improve oxidation resistance. Observation of the oxidation rate for raw graphite(Raw) impregnated graphite with tri-butyl phsophate on raw block(RP) and impregnated graphite on acid-treated graphite(AP) in air are reported. The phsophorus residue adsorbed on the graphite surface at active sites was determined by FTIR, XRS, TGA techniques. AP with tri-butyl phosphate was found to result in both 30% reduction in oxidation rate at 1000$^{\circ}C$ compared to Raw and increase of 120$^{\circ}C$ in oxidation temperature From the samples of oxidation rate of each specimen in Arrhenius plot it can be said that the present oxidation resistance origninates from the change of chemical reaction modesw neigther by acid-washing treatment nor phsophate impregnation

• Composites Research
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• v.23 no.6
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• pp.61-66
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• 2010

In this paper, the variation of mechanical properties of T800 carbon/epoxy composites according to the forming pressure, which was referred to previous studies on a filament winding process, were investigated. The specimens of all the tests were fabricated by an autoclave de-gassing molding process controlling forming pressure (absolute pressures of 0.1MPa, 0.3MPa, 0.7MPa including vacuum) and water jet cutting after fabricating composite laminates. Various tensile tests were performed for in-plane properties and interlaminar properties were also measured by using Iosipescu test jig. Fiber volume fraction was measured to correlate the property variation and the forming pressure. This properties are expected to be utilized in the design of Type III pressure vessel for hydrogen vehicles which uses the same carbon fiber (T800 carbon fiber) for the filament winding process.

• Polymer(Korea)
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• v.36 no.2
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• pp.137-144
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• 2012

The surface of polyethylene (PE) was modified through Ar atmospheric pressure plasma treatment and subsequent grafting of glycidyl methacrylate (GMA). Optimum plasma treatment conditions were determined through analyzing the surface free energies calculated from the contact angles between PE samples and three probe liquids, which were RF-power of 200 W, plasma treatment time of 600 sec, Ar flow rate of 5 LPM, and sample-holder moving speed of 20 mm/sec. To introduce the maximum amount of GMA on PE surface treated under the conditions, graft copolymerization conditions such as GMA concentration, temperature, and time were carefully controlled. Grafting degree (GD) was obtained through weight difference analysis of PE film before and after graft copolymerization. A maximum GD was achieved at the GMA concentration of 20 vol%, the temperature of $80^{\circ}C$, and the treatment time of 4 hr.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.71-79
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• 1993

Positron annihilation characteristics and microhardness of 25% cold worked and isochronally annealed hafnium specimens were measured to study recovery and recrystallization stages of hafnium specimens. The annihilation lifetime of positrons in hafnium has been measured for the distinct cases of annihilation in the annealed lattice and annihilation after trapping at lattice defects generated by cold deformation at room temperature. The annihilation lifetime in the annealed lattice was 187 $\pm$3.7 psec, whereas it was 217 $\pm$ 4.2 psec for positrons trapped at deformation-induced defects (mostly dislocations). The changes in Doppler broadening and hardness showed similar trend in the recrystallization range, however, the measured value of Doppler broadening variation were quite sensitive to changes in the recovery region in which the variation in hardness value was completely insensitive. Recovery of cold worked hafnium initiated at about 623 K and recrystallization occurred at around 1023 K.

• Journal of the Korean Geotechnical Society
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• v.32 no.5
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• pp.49-55
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• 2016

This study aims to present the practical Nitrogen monoxide (NO) removal capacity of cement mortar with Titanium dioxide ($TiO_2$) which is one of the paving materials by considering the environment of pavement in urban areas. NO removal capacity test under designated conditions of humidity of inflow gas and the test with variation of the degree of saturation of specimen were conducted. In the test for humidity, dry specimen is subject to the test and NO removal ratio was observed. Humidity-NO removal ratio curve is a log normal distribution in shape, and the maximum NO removal ratio appears at specific humidity. NO removal capacity test relying on the degree of saturation was carried out with wet specimen to reflect the unsaturated pavement by rainfall and domestic sewage. Wet specimen presents less NO removal capacity than dry specimen and the recovering evolution of NO removal capacity follows evaporation. Moreover, $TiO_2$ under the specific depth of specimen hardly contributes to NO removal capacity.

• Applied Microscopy
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• v.29 no.1
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• pp.67-73
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• 1999

It is practically hard to prepare good TEM specimens from powders which are embedded in epoxy materials for ion milling, because the milling rate difference between powders and epoxy is quite large. In order to overcome this problem, we tried to find methods to increase the density of powders in the embedding epoxy without loosing the adhesive strength between them. Powder density was considerably increased by employing a centrifuge for embedding, compared to the result by a conventional vacuum embedding. In addition, mixing powders of different sizes after sieving also enhanced the final density by allowing smaller particles filling in the gaps of larger particles. Ion milling of powders embedded by these methods resulted in thin specimens good enough for normal TEM works. TEM specimens from spherical, platy and fibrous powders of submicron size were successfully prepared by this centrifuging method.