• Composites Research
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• 제20권2호
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• pp.21-26
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• 2007

이 논문은 합성섬유를 이용하여 포틀랜드 시멘트 모르타르를 보강한 복합재료인 ECC(Engineered Cementitious Composite)의 설계 과정과 건설현장에 이 복합재료를 적용할 수 있도록 시공성을 부여한 연구 내용을 정리하였다. 이 연구에서는 다양한 시공성, 즉 자기충전(self·consolidating)과 스프레이 시공성을 갖는 ECC를 제작하기 위하여 단계적인 재료 개발 방법론을 채택하였다. 우선 마이크로역학(micromechanics)과 안정상태균열이론(steady-state cracking theory)을 이용하여 골재와 섬유를 선정한 후, 굳기 전 재료의 레올로지를 제어하는 방법으로 시공성을 구현하였다. 여기서, 굳기 전 재료의 레올로지를 제어하기 위하여 화학첨가제(chemical admixtures)와 광물첨가재(mineral admixtures)의 양을 소량으로 조절하는 방법을 사용하였다. 이러한 방법을 활용함으로써 굳기 전에는 다양한 시공성을 나타내면서, 굳은 후에는 높은 연성(인장변형경화 거동)을 나타내는 실용적인 ECC 복합재료를 개발하였다.

• 한국입자에어로졸학회지
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• 제14권3호
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• pp.65-72
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• 2018

Core-shell structured $Fe_3O_4/graphene$ composites were synthesized by aerosol spray drying process from a colloidal mixture of graphene oxides and $Fe_3O_4$ nanoparticles. The structural and electrochemical performance of $Fe_3O_4/graphene$ were characterized by the field-emission scanning electron microscopy, X-ray diffraction, Raman spectroscopy, cyclic voltammetry, and galvanometric discharge-charge method. Core-shell structured $Fe_3O_4/GR$ composites were synthesized in different mass ratios of $Fe_3O_4$ and graphene oxide. The composite particles were around $3{\mu}m$ in size. $Fe_3O_4$ nanoparticles were encapsulated with a graphene. Morphology of the $Fe_3O_4/graphene$ composite particles changed from a spherical ball having a relatively smooth surface to a porous crumpled paper ball as the content of GO increased in the composites. The $Fe_3O_4/GR$ composite fabricated at the weight ratio of 1:4 ($Fe_3O_4:GO$) exhibited higher specific capacitance($203F\;g^{-1}$) and electrical conductivity than as-fabricated $Fe_3O_4/GR$ composite.

• Korean Chemical Engineering Research
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• 제56권1호
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• pp.42-48
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• 2018

리튬이온전지의 음극재로 높은 이론적인 용량과 낮은 방전 전위 및 무독성을 가진 실리콘이 높은 관심을 받고 있다. 본 연구에서는 리튬이온전지의 고효율 음극재로 활용을 위한 실리콘-탄소나노튜브-탄소(Si-CNT-C) 복합체를 제조하였다. 복합체 제조를 위해서는 에어로졸 자기조립과 후 열처리 공정을 사용하였다. 제조된 Si-CNT-C 복합체는 구형이었으며 평균 입자크기는 $2.72{\mu}m$이었다. 복합체의 크기는 실리콘 및 탄소나노튜브의 농도가 증가할수록 커지는 것을 확인하였다. Si-CNT-C 복합체는 탄소나노튜브와 글루코스에서 탄화된 탄소가 실리콘 입자들을 중심으로 표면에 부착된 형태이었다. 제조된 Si-CNT-C 복합체는 전기화학 분석을 통해 순수한 실리콘보다 우수한 사이클 성능을 보여주고 있음을 확인하였다.

• 한국입자에어로졸학회지
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• 제16권4호
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• pp.95-105
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• 2020

Vanadium Pentoxide (V2O5) has been emerged as alternative electrode materials for supercapacitors due to their low cost, natural abundance, and environmental friendliness. Graphene (GR) loaded with V2O5 can exhibit enhanced specific capacitance. In this study, we present three-dimensional (3D) crumpled graphene (CGR) decorated with V2O5. The V2O5-graphene composites were synthesized from a colloidal mixture of graphene oxide (GO) and Ammonium metavanadate (NH4VO3), via aerosol spray drying and post heat treatment process. The average size of composite was ranged from 1.82 to 4.6 ㎛. Morphology of the composite changed from a crumpled paper ball to spherical ball having relatively smooth surface as the content of V2O5 increased in the composites. The electrochemical performance of the V2O5-graphene composites was examined. The V2O5-graphene composite electrode showed the specific capacitance of 312 F/g. In addition, the device possessed acceptable cyclic stability, with 84% after 2000 cycles at 2 A/g. These outstanding properties are expected to make the composites prepared in this study as promising electrode materials for supercapacitor applications.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2010년도 춘계 학술대회 제22권1호
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• pp.355-356
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• 2010

이 연구에서는 동결융해저항성(KS F 2456) 및 염소이온 침투저항성(NT Build 492) 시험을 통하여 순환형 폐기물이 혼입된 Eco-ECC(Engineered Cementitous Composite)의 내구성능을 평가하였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 The 6th International Symposium of East Asian Resources Recycling Technology
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• pp.315-324
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• 2001

Mechanochemical effects that occurred in the fine grinding process of quartz particles using planetary ball mill was investigated. Quartz particles have been frequently utilized for optical materials, semiconductor molding materials. We determined that grinding for a long time can be create amorphous structures from the crystalline quartz by Mechanochemical effects. But, to be produced nano-composite particles that the critical grinding time reached for composite materials in a short time. Henceforth, a qualitative estimation must be conducted on the filler for EMC(Epoxy molding compound) materials. It can be produced mechanochemically treated composite materials and also an integrated grinding efficiency considering of the nano-composite amorphous structured particles. The mechanochemical characteristics were evaluated based on particle morphology, size distribution, specific surface area, density and the amount of amorphous phase materials into the particle surface. The grinding operation in the planetary ball mill can be classified into three stages. During the first stage, initial particle size was reduced for the increase of specific surface area. In the second stage, the specific surface areas increased in spite of the increase in particle size. The final stage as a critical grinding stage, the ground quartz was considered mechanochemically treated particles as a nano- composite amorphous structured particles. The development of amorphous phase on the particle surface was evaluated by X-ray diffractometry, thermal gravity analysis and IR spectrometer. The amount of amorphous phase of particles ground for 2048 minutes was 85.3% and 88.2% by X-ray analysis and thermal gravity analysis, respectively.

• 치위생과학회지
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• 제23권1호
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• pp.29-38
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• 2023

Background: The purpose of this study was to investigate the effect of salad dressings on the flowable composite resin surface and the erosion-inhibitory effect of calcium. Methods: The experiment included six groups: oriental dressing, balsamic dressing, lemon-garlic dressing, lemon-garlic dressing supplemented with 3% calcium, mineral water as a negative control group, and orange juice as a positive control group. pH and titratable acidity were measured. The prepared specimens were immersed in the experimental solutions for 1, 3, 5, 15, and 30 minutes. The surface microhardness was measured using the Vickers hardness number before and after the treatment, and the surface of the specimens was observed using a scanning electron microscope (SEM). Results: The pH values of the experimental groups in increasing order were as follows: lemon-garlic dressing (2.49±0.03), balsamic dressing (3.12±0.06), lemon-garlic dressing +3% calcium (3.27±0.09), oriental dressing (3.75±0.03), orange juice (3.82±0.02), and mineral water (7.32±0.16). The largest surface hardness reduction value was shown in lemon-garlic dressing (-9.61±1.16), followed by balsamic dressing (-9.17±1.63), oriental dressing (-8.62±1.09), orange juice (-8.19±1.36), lemon-garlic dressing +3% calcium (-6.76±1.23), and mineral water (-1.63±2.47). According to the SEM findings, the experimental and positive control groups showed rough surfaces and micropores, whereas the negative control group showed a smooth surface. Moreover, the lemon-garlic dressing with +3% calcium showed fewer micropores and a smoother surface than the lemon-garlic dressing. Conclusion: The intake of salad dressings at a low pH could weaken the surface microhardness of the flowable composite resin. However, adding calcium to these salad dressings can reduce the risk of microhardness reduction on the flowable composite resin surface.

• 한국광물학회:학술대회논문집
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• 한국광물학회.한국암석학회 2001년도 공동학술발표회 논문집
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• pp.40-40
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• 2001

The sorption behavior of Cs(I), Sr(II), and U(VI) on representative single minerals(oxide and clay) and rocks were comparatively studied by using batch type sorption experiment. The effects of pH, ionic strength and the sorption mechanism were also discussed. It was found that mineral structure played as a main factor governing the sorption characteristics of Cs(I), Sr(II). The sorption of Cs(I) and Sr(II) on minerals showed ionic strength-dependency, which is a indirect sign of weak binding between metal cation and mineral surfaces. However, the sorption behavior of U(VI) was quite different compared with that of Cs(I), and Sr(II). Fe-oxide minerals showed strong tendency for U(VI) sorption, dominating the sorption in the composite/mixture systems. The surface characteristics which arise from mineral structure, and the affinity of metal ions to the sorption sites of minerals are the key to understand the role of minerals in the radionuclide sorption.

• Journal of Forest and Environmental Science
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• 제37권2호
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• pp.116-127
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• 2021

Predicting carbon distribution of soil aggregates is difficult due to complexity in organo-mineral formation. This limits global warming mitigation through soil carbon sequestration. Therefore, knowledge of land use effect on carbon stabilization requires quantification of soil mineral cations. The study was conducted to quantify carbon and base cations on soil mineral fractions in Natural Forest, Plantation Forest and Farm Land. Five 0.09 ha were demarcated alternately along 500 m long transect with an interval of 50 m in Natural Forest (NF), Plantation Forest (PF) and Farm Land (FL). Soil samples were collected with soil cores at 0-15, 15-30 and 30-45 cm depths in each plot. Soil core samples were oven-dried at 105℃ and soil bulk densities were computed. Sample (100 g) of each soil core was separated into >2.0, 2.0-1.0, 1.0-0.5, 0.5-0.05 and <0.05 mm aggregates using dry sieve procedure and proportion determined. Carbon concentration of soil aggregates was determined using Loss-on-ignition method. Mineral fractions of soil depths were obtained using dispersion, sequential extraction and sedimentation methods of composite soil samples and sieved into <0.05 and >0.05 mm fractions. Cation exchange capacity of two mineral fractions was measured using spectrophotometry method. Data collected were analysed using descriptive and ANOVA at α_0.05. Silt and sand particle size decreased while clay increased with increase in soil depth in NF and PF. Subsoil depth contained highest carbon stock in the PF. Carbon concentration increased with decrease in aggregate size in soil depths of NF and FL. Micro- (1-0.5, 0.5-0.05 and <0.05 mm) and macro-aggregates (>2.0 and 2-1.0 mm) were saturated with soil carbon in NF and FL, respectively. Cation exchange capacity of <0.05 mm was higher than >0.05 mm in soil depths of PF and FL. Fine silt (<0.05 mm) determine the cation exchange capacity in soil depths. Land use and mineral size influence the carbon and cation exchange capacity of Gambari Forest Reserve.

• Restorative Dentistry and Endodontics
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• 제26권1호
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• pp.1-8
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• 2001

Dental Caries which has high prevalence rate, accounts for majority of dental diseases. Many treatment and preventive treatment has been developed, thereby reducing the prevalence rate, but in our country, fluoridization has not spread widely yet, so prevention has not been done satisfactorily. When dental caries progresses, irreversible damage of tooth structure occurs. In initial dental caries, demineralizing tooth structure can be remineralized, so restorative treatment is unnecessary. In this study, 20 teeth restored with composite resin without fluoride release were used and divided into two groups. Incipient dental caries were artificially made and demineralization procedure was done for 1 and 2 weeks, for each group. Changes in mineral contents around the margins were analysed with confocal laser scanning microscope. The results were as follow. 1. Both total fluorescence of the lesion and average fluorescence of the lesion of remineralized samples decreased compared to demineralizing state. (p＜0.01) 2. Confocal laser scanning microscopy can be used in quantitative analysis of mineral change. In result, confocal laser scanning microscopy can be used in quantitative analysis of mineral change and it could be used in many different fields of dentistry in the future.