• Journal of the Korean Ceramic Society
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• v.38 no.7
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• pp.643-647
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• 2001

퓨란수지로부터 유리질 탄소를 제조하였다. 유리질 탄소의 제조시, 사용된 수지가 경화 및 탄화 단계에서 많은 양의 가스를 방출하면서 큰 수축이 발생하여 크랙을 형성하고 휨 현상을 일으킨다. 이런 현상을 감소시키기 위하여 본 실험에서는 경화단계에서 압력을 가하고, 가열속도를 매우 느리게 하였다. 또한, 경화단계에서 무게감소와 수축율을 억제하고, 발생하는 가스의 배출을 용이하게 하여 궁극적으로는 시편의 크랙 및 휨 현상을 방지하고자 필러와 알콜을 첨가하였다. 그 결과, 무게감소와 수축을 억제하고 밀도의 증가를 가져왔고 유리질 탄소를 용이하게 제조할 수 있었으나 알코올을 첨가한 경우 필러의 양이 증가할수록 높은 비저항 값과 낮은 강도값을 나타내었다. 이런 현상은 알코올이 경화단계에서 분해 증발하면서 미세한 기포를 형성하고 이것들이 기공으로 전이하여 최종 제품에까지 영향을 주었기 때문이다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.39.2-39.2
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• 2011

7075알루미늄 합금은 기계적 강도가 가장 높은 고강도 합금으로 열처리 공정이 반드시 필요하다. 그러나 열처리 공정 중 재료의 두께에 따른 내부 온도의 차이로 인한 잔류응력이 발생하여 최종 제품의 치수에 변화를 일으켜 제품 생산에 어려움이 있다. 따라서 본 연구에서 극저온 열처리 공정을 통하여 야기되는 7075알루미늄 합금의 기계적 특성 및 미세조직에 관하여 연구하였다. 7075 알루미늄 합금은 석출경화를 통한 강화가 이루어지며, 석출경화를 위해서 용체화 처리를 하여 인공시효를 하는 기존 공정과 비교하여 극저온 열처리 공정은 두 개의 추가적인 단계를 가지고 있다. 첫 번째 단계는 -196도의 액체 질소 속에 샘플을 극저온 ��칭을 하는 단계이고, 두 번째 단계는 샘플의 온도를 급격하게 올리는 up-hill quenching이다. 잔류응력은 X-ray diffraction을 이용한 $sin2{\psi}$ 방법으로 측정되었다. 극저온 열처리 후 기계적 특성을 평가하기 위하여 vickers hardness를 측정하였으며 미세 조직의 특성을 파악하기 위하여 EBSD와 TEM을 이용하여 평가하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.12
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• pp.261-267
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• 2020

The demand for faster, lighter, and thinner portable electronic devices has brought about a change in semiconductor packaging technology. In response, a stacked chip-scale package(SCSP) is used widely in the assembly industry. One of the key materials for SCSP is a die-attach film (DAF). Excellent flowability is needed for DAF for successful die attachment without voids. For DAF with high flowability, two-step curing is often required to reduce a cure crack, but one-step curing is needed to reduce the processing time. In this study, DAF composition was categorized into three groups: cure (epoxy resins), soft (rubbers), hard (phenoxy resin, silica) component. The effect of the composition on a cure crack was examined when one-step curing was applied. The die-attach void and flowability were also assessed. The cure crack decreased as the amount of hard components decreased. Die-attach voids also decreased as the amount of hard components decreased. Moreover, the decrease in cure component became important when the amount of hard component was small. The flowability was evaluated using high-temperature storage modulus and bleed-out. A decrease in the amount of hard components was critical for the low storage modulus at 100℃. An increase in cure component and a decrease in hard component were important for the high bleed-out at 120℃(BL-120).

• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.41-52
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• 2012

Suction drain method can directly apply vacuum pressure to the soft ground through vertical drains so it can make hardening zones around them. These hardening zones make steeply lower the discharge efficiency of the pore water with decreasing permeability. This paper considered a stepped vacuum pressure to minimize a hardening zone which is one of the important parameters that can decrease discharge efficiency. A series of laboratory tests were conducted in order to examine the effect of the hardening zones and to evaluate their effects to the ground improvements with varying durations which applied stepped vacuum pressures(-20kPa, -40kPa, -60kPa and -80kPa) with Busan marine clay. According to strength(CPT), water content test and theoretical investigation indicate a size of the hardening zone within 7cm and the decreasing ratio of permeability about 2.0~4.0. Also, the total settlements are larger for the stepped vacuum pressure than the instant vacuum loading. The application time with vacuum pressure is determined considering the geotechnical properties of the interested clays. Results of numerical analysis show that consolidation behavior is appropriate to measurement for considering hardening zones.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.63-64
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• 2014

In this study, we has a purpose to estimate the joint movement responsiveness performance for the domestic products of one-component structural silicon sealants. For this purpose, we make a comparative study for the four domestic products focused on tensile properties after allowed the cyclic-movements for three days at initial step of curing phase. A joint movement range ±10% and the rate of compression and extension 3.2mm/h were assumed in those tests. As a result, the large space were induced inside the sealant by rupture, and then adhesion and cohesion failures were caused by stress concentration. The tensile properties were reduced by 15~60% in comparison with physical properties. In this case, the generating defect was caused and the service-life was decreased. Thus, further researches as relationship of test condition and products properties on this behavior would be studied.

• Polymer(Korea)
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• v.27 no.2
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• pp.120-128
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• 2003

The effects of catalyst, accelerator and blend composition on the cure behavior of unsaturated polyester resin (UPE), vinyl ester resin (VE) and their blends were studied using differential scanning calorimetry(DSC). The DSC thermograms strongly depend on each variable. The result shows that the small exothermic peak at 115$^{\circ}C$ is due mainly to the UPE component in the UPE/VE blends and the large one at 134~138 $^{\circ}C$ is due mainly to the VE component. The results also indicate that the change of the DSC thermogram measured after each blend was exposed to high temperature 18$0^{\circ}C$ and the fast curing conditions of a few tens seconds provide useful information on understanding the thermal processing of a blend at high speed. The measurements of resin flow time represent that there are three distinct stages of cure in the UPE/VE blends: induction, transition and macro-gelation stages, as similarly reported for UPE by others earlier. The thermal stability and flexural properties of the cured UPE are significantly improved by blending it with the VE, depending on the composition.

• Geotechnical Engineering
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• v.10 no.1
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• pp.103-118
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• 1994

A series of drained triaxial testis was performed on a Band by use of cubical triaxial apparatus, in which three principal stresses could be applied independently. The stress -strain behavior on the same stress path with cubical triaxial test was analyzed with application of the isotropic single hardening constitutive model presented by Lade. The behavior predicted by the constitutive model presented good coincidence with experimental results during poi mary loading. However, the predicted Mo윤ding and reloading behavior wan much different from results of cubical triaxial testy. That is, the softening part of the prediction might result in a rough approximation, since the plastic work parameters of single hardening model were based on the hardening portion of the data.

• Restorative Dentistry and Endodontics
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• v.27 no.2
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• pp.207-211
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• 2002

항균 활성도는 Root canal sealer가 갖추어야 할 필수요소 중 하나이다. 본 연구는 최근 임상술식에 사용되고 있는 8종의 root canal sealer의 근관내 혐기성 세균에 대한 항균효과를 알아보기 위해 시행되었다. 또한 본 연구에서는 혼합직후의 경화되지 않은 sealer와 경화 7일 후 sealer의 항균효과도 비교하였다. 항균효과 측정을 위해 사용된 균주는 최근 실패한 근관치료 증례에서 배양되어 보고된 바 있는 Enterococcus faecalis와 근관내 주요 감염균인 그램음성 혐기성세균인 Staphylococcus aureus를 대상으로 하였고, Agar diffusion test 방법을 사용하였다. 실험방법으로는 2개의 paper disk에 신선하게 혼합한 각각의 sealer를 도포하여 한개의 disk는 즉시 실험에 사용하고 다른 한개의 disk는 일주일간 혐기성 배양기에서 경화시킨 다음 사용한다 각각의 균주를 Brucellar blood agar plate에 접종한 다음, sealer가 도포된 paper disk를 plate상에 올려놓는다. 대조군으로는 식염수에 침윤시킨 disc를 같은 방법으로 각 실험단계에 사용한다. 각 plate를 혐기성 배양기에서 48시간동안 배양한 뒤 실험에 사용한 sealer의 항균효과를 6mm paper-disk를 둘러싼 inhibition zone을 측정하여 평가한다. Fisher's PLSD분석방법 결과 E. faecalis에 대하여 경화 전과 후의 AH26모두 경화 전과 후의 Roth 801, Dentalis, Apexit, AH Plus, RSA그리고 경화 후의 MCS보다 유의성 있게 강한 항균효과를 나타내는 것으로 보고되었으며. 경화 후의 AH26은 경화 전의 AH 26, 경화 전의 Ketac Endo, 경화 전의 MCS보다 통계학적으로 유의성이 있는 항균작용을 하는 것이 관찰되었다 (p＜0.05). 경화 후 Roth 801, 경화전과 후의 Dentalis, AH plus, Apexit, RSA는 E. faecalis에 대한 항균효과를 나타내지 못하였다. S. aureus에 대하여 경화후의 AH26이 경화 전과 후의 Roth 801, Apexit, AH Plus, RSA보다 유의성있는 항균효과를 보이는 것을 발견 할 수 있었고, 경화 전의 AH 26이 경화 후의 AH plus보다 나은 항균효과를 나타냄을 알 수 있었다. 또, 경화 전과 후의 Apexit, 경화 후의 AH Plus, 경화 전과 후의 RSA에서는 S. aureus에 대한 항균작용이 발견되지 않았다. 본 실험의 결과 AH26이 가장 강한 항균 작용을 갖는 것을 알 수 있었으며, 각 sealer의 경화 전과 후의 항균효과는 AH26이 경화 전보다 경화 후에서 더 강한 항균효과를 나타내는 것 이외에는 효과의 차이가 없었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.121-128
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• 2007

The present study evaluates the resistance to sulfate attack of cement matrix with or without silica fume. The main variable was the replacement levels of silica fume. In order to introduce sulfate attack to cement matrix, mortars and pastes was exposed to sodium sulfate solution for 510 days. Visual examination, expansion and compressive strength loss of mortars in addition to characteristics of pore for the paste samples were regularly investigated. From the test results, it was clearly observed that the cement matrix with silica fume was very resistant to sulfate attack irrespective of the replacement levels of silica fume. However, the severe deterioration due to sulfate attack was found in cement matrix without silica fume.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.324-330
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• 2018

In accordance with the amendment of the Industrial Safety and Health Act of 2007, Korea completely prohibited the import, distribution and manufacture of asbestos like Europe and Japan. Accordingly, the current problem of asbestos is the safe maintenance and disposal of asbestos construction material, the disposal of asbestos, and the final disposal of asbestos building materials. In the past, Korea used 100,000 tons of asbestos every year, and the building materials using it exceeded 1 million tons per year. These asbestos building materials continued to be used until 2006, and the Ministry predicted that these materials would continue to be maintained until 2044. When the permeable hardening agent is applied to the asbestos building material installed in the pre-pretreatment step for the harmless treatment of the asbestos waste and the dismantling is carried out, the scattering of the asbestos is suppressed in the disassembling step, detoxification treatment conditions can be improved. Therefore, permeable hardeners should be stably penetrated into asbestos building materials. In this study, it is suggested that pre - pretreatment methods for the harmlessization of waste asbestos building materials with medium density level can be presented. In order to efficiently perform pre - treatment for chemical harmlessness in the future, the mixing ratio of permeable hardener and middle water Optimization is the most important factor.