• Advances in concrete construction
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• 제11권5호
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• pp.409-417
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• 2021

The incorporation of non-biodegradable tyre waste in cement-based material has gained more interest towards sustainable construction these days. Crumb rubber (CR) from waste tyre is an alternative for sand replacement in low strength applications. Many researchers have studied CR cement-based materials produced by normal mixing (NM) method and reported a significant decrease in compressive strength due to CR. To compensate this strength loss, this research aims to study the innovative incorporation of CR in cement composite via the preplaced mixing (PM) method. In this investigation, cement composite was produced with NM and PM methods by replacing sand with 0%, 50%, and 100% CR by volume. The test results showed no significant difference in terms of densities of cement composite prepared with both mixing methods. However, cement composite prepared with PM method had lower strength reduction (about 10%) and lowered drying shrinkage (about 20%). In addition, the sound absorption coefficient and noise reduction coefficient of CR cement composite prepared by PM method were in similar range as those prepared with NM method. Overall, the results demonstrate that the PM method is promising, and the maximum replacement level of 50% is recommended for CR in the cement composite.

• 센서학회지
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• 제32권3호
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• pp.159-163
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• 2023

Salt cores have attracted considerable attention for their application to the casting process of electric vehicle parts as a solution to ecological issues. However, the salt core still has low mechanical strength for use in high-pressure die casting. In this study, we investigated the improvements in the bending strength of KCl-based salt cores resulting from the use of reinforcing materials. KCl and Na₂CO₃ powders were used as matrix materials, and glass fiber and carbon fiber were used as reinforcing materials. The effects of carbon fiber and glass fiber contents on the bending strength properties were investigated. Here, we obtained a new fiber-reinforced salt core composition with improved bending strength for high-pressure die casting by adding a relatively small amount of glass fiber (0.3 wt%). The reinforced salt core indicates the improved properties, including a bending strength of 49.3 Mpa, linear shrinkage of 1.5%, water solubility rate of 16.25 g/min·m² in distilled water, and hygroscopic rate of 0.058%.

• 한국건설순환자원학회논문집
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• 제7권4호
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• pp.287-294
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• 2019

고로슬래그 미분말은 뛰어난 염해 저항성 및 내화학성을 가지고 있어 콘크리트에 널리 쓰여왔으나, 고분말도에 따라 수화열과 건조 수축에 의한 균열이 보고되고 있다. 국제 표준에서는 콘크리트에 저분말도 고로슬래그 미분말의 폭 넓은 상용화 및 균열 저감을 위하여 3,000급 저분말도 고로슬래그 미분말이 포함되어 있다. 본 연구에서는 저분말도 고로슬래그 미분말을 치환한 콘크리트(50%의 물-결합재비와 3,000급 고로슬래그 미분말을 60% 치환)와 삼성분계 콘크리트(50% 물-결합재비와 4,000급 고로슬래그 미분말 및 플라이애시를 총 60% 치환)가 고려되었다. 저분말도 고로슬래그 미분말을 치환한 콘크리트와 삼성분계 콘크리트의 강도 차이는 재령 3일차에서 재령 91일차까지 확연한 차이는 없었으며 우수한 염해와 탄산화 저항성을 나타내었다. 또한 적절한 공기량을 함유하여 두 배합 모두 90.0 이상의 높은 내구성 지수를 나타내었다. 배합개선을 통하여 저분말도 GGBFS 콘크리트의 초기강도 개선한다면 낮은 수화열 및 고내구성을 가진 매스 콘크리트를 제조할 수 있으리라 판단된다.

• Food Science and Biotechnology
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• 제17권2호
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• pp.319-323
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• 2008

Mutant rice cv. Goami2 (G2) and Baegjinjoo (BJJ) derived from a high-quality japonica rice cv. Ilpumbyeo (IP) were extruded under different feed moisture (20 and 30%) and barrel temperature (90, 110, and $130^{\circ}C$). Increasing feed moisture at fixed barrel temperature increased extrudate density (ED) in IP and BJJ. Whereas, G2 showed a varied ED depending on extrusion conditions; increasing barrel temperature decreased the ED of G2 extrudate with low feed moisture, but increased with high moisture. Results indicated a positive barrcl temperature effect on volume expansion in IP and G2, but a negative effect on 811, probably due to shrinkage of expanded products containing low-amylose contents. A significant increase of water absorption was found in G2 and BJJ extruded flour, while an increase of water solubility in those from IP. Non-digestible carbohydrates measured by total dietary fiber (TDF) indicated that extrusion increased slightly TDF in IP and BJJ extrudates, but decreased in G2 products, which might be variety-dependent.

• Geomechanics and Engineering
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• 제22권3호
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• pp.227-236
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• 2020

Expansive soils are renowned for their swelling-shrinkage property and these volumetric changes resultantly cause huge damage to civil infrastructures. Likewise, subgrades consisting of expansive soils instigate serviceability failures in pavements across various regions of Pakistan and worldwide. This study presents the use of polypropylene fibers to improve the engineering properties of a local swelling soil. The moisture-density relationship, unconfined compressive strength (UCS) and elastic modulus (E₅₀), California bearing ratio (CBR) and one-dimensional consolidation behavior of the soil treated with 0, 0.2, 0.4, 0.6 and 0.8% fibers have been investigated in this study. It is found that the maximum dry density of reinforced soil slightly decreased by 2.8% due to replacement of heavier soil particles by light-weight fibers and the optimum moisture content remained almost unaffected due to non-absorbent nature of the fibers. A significant improvement has been observed in UCS (an increase of 279%), E₅₀ (an increase of 113.6%) and CBR value (an increase of 94.4% under unsoaked and an increase of 55.6% under soaked conditions) of the soil reinforced with 0.4% fibers, thereby providing a better quality subgrade for the construction of pavements on such soils. Free swell and swell pressure of the soil also significantly reduced (94.4% and 87.9%, respectively) with the addition of 0.8% fibers and eventually converting the medium swelling soil to a low swelling class. Similarly, the compression and rebound indices also reduced by 69.9% and 88%, respectively with fiber inclusion of 0.8%. From the experimental evaluations, it emerges that polypropylene fiber has great potential as a low cost and sustainable stabilizing material for widespread swelling soils.

• 멤브레인
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• 제26권4호
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• pp.310-317
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• 2016

리튬이온 이차전지는 리튬이온이 이동하면서 전기화학적 충방전사이클을 완성하는 에너지변환장치를 의미한다. 리튬이온 이차전지는 높은 에너지밀도와 낮은 자가방전률, 상대적으로 긴 수명주기 등 다양한 장점을 갖는다. 최근 전기차 수요증가는 고용량 리튬이온 이차전지 개발을 촉진하고 있으나 음극에서의 dendrite 형성으로 인한 전기적 단락 현상과 전지 폭발 문제와 같은 심각한 안전문제를 야기한다. 또한, 리튬이온 이차전지 구동시 상승된 온도에서 폴리올레핀계열(예 : 폴리에틸렌과 폴리프로필렌) 격리막의 열수축 문제가 발생한다. 이와 같이 낮은 열 안정성은 리튬이온 이차전지의 성능과 수명의 감소로 이어진다. 본 연구에서는 폴리올레핀계열 함침격리막 제조를 위한 중요한 소재로서 술폰화 폴리아릴렌에테르술폰 랜덤 공중합체를 사용하였으며, 제조된 격리막을 이용하여 dendrite 형성과 관련된 금속이온 흡착 능력과 리튬이온전도성, 열적 내구성이 평가되었다.

• 마이크로전자및패키징학회지
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• 제11권4호
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• pp.37-41
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• 2004

이동 통신 기기의 광대역화에 따라 기존의 인쇄 회로 기판에 비해 양호한 전기적 특성과 수동형 부품을 내장할 수 있는 LTCC(Low Temperature Co-fired Ceramic)에 대한 많은 연구 개발이 진행되고 있으나 불 균일한 수축으로 인해 적용에 한계를 보여 왔다. 본 연구에서는 짧은 시간내에 온도를 균일하게 올릴 수 있는 혼합 가열 방식을 개발하여 하부에서부터 시편의 얇은 층이 순차적으로 소결 되도록 하는 일 방향 소결의 조건을 제공하여 시편 상부 표면의 배선 형상이 종래의 전기로 가열보다 안정적으로 형성되는 결과를 얻었다. 기판의 소결 특성, 배선의 전기적 특성, 그리고 배선의 기계적 특성 등을 비교한 결과, 기판의 소형화와 배선의 고밀도화에 전기로 가열 보다 혼합 가열이 적용 가능성이 높음을 알 수 있었다.

• 한국세라믹학회지
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• 제13권1호
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• pp.35-44
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• 1976

The effect of quartz which exists in clays, especially in kaolin used for the production of chamotte sagger, on the strength of refractory was examined. In this study, a mixture of chamotte 50%, kaolin 25%, plastic clay 25% in ternary component system was selected as a batch composition. To this mixture 1%, 3% and 5% of feldspar and sericite were added respectively. The plastic clay used here was separated under 170 mesh by dry process. Feldspar and sericite were separated under 325 mesh by dry process. Feldspar and sericite were separated under 325 mesh by dry process. In order to change the particle size and the content of quartz, the kaolin was separated under 60, 115, 170 and 325 mesh by wet process, substituted quartz for coarse parts of it. Chamotte was classified into three grades, coarse (5-10mesh): medium (10-20mesh): fine(20-115mesh) and the ratio was 1:1:1. Samples were formed in 0.8xIx10cm size with 12.5% water at 160kg/$\textrm{cm}^2$ pressure, and fired at 130$0^{\circ}C$ for 1 hr. The fired samples were ivnestigated by means of x-ray diffraction analysis and microscopic observation, and the physical properties of them were also examined, such as firing shrinkage, apparent specific gravity and bulk specific gravity, apparent porosity, water absorption and modulus of rupture. The obtained results are as follows: 1. When screened kaolin with low content of quartz was added to fixed chamotte-plastic clay system, the sample lowered modulus of rupture and increased apparent porosity as the size of kaolin became finer. 2. When kaolin under 325 mesh with 7.2-15.81% quartz between 60-325 mesh was added to fixed chamotte-plastic clay system, the sample had higher apparent porosity and lower modulus of ruputure as the size and the amount of quartz became larger. 3. The addition of feldspar and sericite to chamotte-plastic clay system improved apparent porosity and modulus of rupture. The effect of feldspar was better when quartz content was low, although that of sericite was better than quartz content was high.

• 한국세라믹학회지
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• 제36권12호
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• pp.1350-1355
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• 1999

Sintering characteristics and dielectric properties of low temperature sinterable Glass/Ceramic dielectric materials were investigated. The dielectric materials which were developed for microwave frequency applications consist of SiO2-TiO2-Bi2O3-RO system(RO:BaO-CaO-SrO) crystallizable glass and Al2O3 as a ceramic filler. Sintering experiments showed that no more densification occurred above 80$0^{\circ}C$ and bulk density and shrinkage depended on Al2O3 content only. Results of dielectric measurements showed that $\varepsilon$r Q$\times$f and $\tau$f of the material containing 30wt% Al2O3 were 17.3, 600 and +23 ppm respectively. Those values for 45 and 60wt% Al2O3 samples were 11.6, 1400, +0.7 ppm and 7.2, 2000, -8.5 ppm, repectively. The results clearly showed that the Glas/Ceramic materials of present experiment decreased in $\varepsilon$r and increased in $\times$f value and changed from positive to negative value in $\tau$f value with the increasement of Al2O3 content.

• Elastomers and Composites
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• 제58권1호
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• pp.44-56
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• 2023

Additive manufacturing (AM) or three-dimensional (3D) printing of metals has been drawing significant attention due to its reliability, usefulness, and low cost with rapid prototyping. Among the various AM technologies, fused deposition modeling (FDM) or fused filament fabrication is receiving much interest because of its simple manufacturing processing, low material waste, and cost-effective equipment. FDM technology uses metal-filled polymer filaments for 3D printing, followed by debinding and sintering to fabricate complex metal parts. An efficient binder is essential for producing polymer filaments and the thermal post-processing of printed objects. This study involved an in-depth investigation of and a fabrication route for a novel multi-component binder system with steel alloy powder (45 vol.%) ranging from filament fabrication and 3D printing to debinding and sintering. The binder system consisted of polyvinyl pyrrolidone (PVP) as a binder and thermoplastic polyurethane (TPU) and polylactic acid (PLA) as a carrier. The PVP binder held the metal components tightly by maintaining their stoichiometry, and the TPU and PLA in the ratio of 9:1 provided flexibility, stiffness, and strength to the filament for 3D printing. The efficacy of the binder system was examined by fabricating 3D-printed cubic structures. The results revealed that the thermal debinding and sintering processes effectively removed the binder/carrier from the cubic structures, resulting in isotropic shrinkage of approximately 15.8% in all directions. The scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) patterns displayed the microstructure behavior, phase transition, and elemental composition of the 3D cubic structure.