• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 춘계학술대회 논문집
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• pp.135-140
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• 1997

The influences of ZrB$_2$ additions to SiC on microstructural, DDM(Electrical Discharge Machining), mechanical and electrical properties were investigated. composites were prepared by adding 15, 30, 45 vol.% ZrB$_2$particles as a second phase to SiC matrix. SiC-ZrB$_2$ composites obtained by hot pressing for high temperature structural application were fully dense with the relative densities over 99%. The fracture toughness of the composites were increased with the ZrB$_2$contents. In case of composite containing 30vol.% ZrB$_2$, the flexural strength and fracture toughness showed 45% and 60% increase, respectively compared to that of monolithic SiC sample. The electrical resistivities of SiC-ZrB$_2$ composites decreased significantly with the ZrB$_2$ contents. The electrical resistivity of SiC-30vol.% ZrB$_2$ composite showed 6.50$\times$10$^{-4}$ $\Omega$.cm. Cutting velocity of EDM of SiC-ZrB$_2$ composites are directly proportional to duty factor of pulse width. Surface roughness, however, are not all proportional to pulse width. Higher-flexural strength composites show a trend toward smaller crater volumes, leaving a smoother surface; the average surface roughness of the SiC-ZrB$_2$ 15 vol.% composite with the flexural strengthe of 375㎫ was 3.2${\mu}{\textrm}{m}$, whereas the SiC-ZrB$_2$ 30.vol% composite of 457㎫ was 1.35${\mu}{\textrm}{m}$. In the SEM micrographs of the fracture surface of SiC-ZrB$_2$ composites, the SiC-ZrB$_2$ two phases are distinct; the white phase is the ZrB$_2$and the gray phase is the SiC matrix. In the SEM micrographs of the EDM surface, however, these phases are no longer distinct because of thicker recast layer of resolidified-melt-formation droplets present. It is shown that SiC-ZrB$_2$ composites are able to be machined without surface cracking.

• 펄프종이기술
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• 제32권2호
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• pp.16-25
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• 2000

The influence of four process parameters of soft nip calendering including calendering pressure, temperature, moisture content and nip residence time on bulk, smoothness and tensile strength of newsprints has been investigated. In addition, the effect of basis weights on calendering responses has been examined. Bulk of newsprints decreased and smoothness increased with the increase of the calendering pressure, temperature, moisture content of the sheets and nip residence time. Improvement in tensile strength was observed when low calendering pressure and high temperature of heat-ing roll were employed. Tensile strength of the newsprint, however, decreased abruptly when the calendering temperature and pressure increased above certain levels due to the rupture of sheet structure, which has been verified by SEM. SEM micrographs also showed that it would be possible to maintain the inner bulk while densifying the fibers on the outer surface of newsprint by adjusting the soft nip calendering variables properly.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1997년도 춘계학술대회 논문집
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• pp.326-329
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• 1997

The surface of mica/epoxy paper(130${\mu}{\textrm}{m}$) is investigated with SEM(scanning electron microscope). SEM micrographs revealed that thermal aging has a strong influence on aged specimens. The mica/epoxy paper was exposed at 187$^{\circ}C$ in an ordinary electrical oven for 72hour. Stater windings from two generators were measured by tan delta(tan $\delta$)and maximum partial discharge(Qm). The values of tan $\delta$and Qm were fecund to be higher for new generator than old one. The insulation condition of mica/epoxy paper were measured by ac current and tan $\delta$. Test results are observed that the sound specimens are higher than those aged. Model bar coils subjected to various accelerated agings were evaluated by Qm.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2002년도 하계학술대회 논문집 Vol.3 No.2
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• pp.756-759
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• 2002

Nanoparticles of titanium dioxide$(TiO_2)$ were prepared by photochemical synthesis. Surface structure, morphology and particle size of $TiO_2$ thin films were investigated by UV-VIS spectrophotometer, scanning electron microscopy(SEM) and transmission electron microscopy(TEM). All process was prepared at room temperature. The absorption peak of the films was showed at 360nm and $TiO_2$ nanopaticle size was observed at about 20~30nm. Electron diffraction ring patterns of $TiO_2$ nanoparticles and crystallographic spacing were observed by TEM. As a result, crystallographic spacing was about 3.6A in HR-TEM micrographs.

• Carbon letters
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• 제11권2호
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• pp.102-106
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• 2010

In this work, the effect of aminized multi-walled carbon nanotubes (NH-MWNTs) on the mechanical interfacial properties of epoxy nanocomposites was investigated by means of fracture toughness, critical stress intensity factor ($K_{IC}$), and impact strength testing, and their morphology was examined by scanning electron microscope (SEM). It was found that the incorporation of amine groups onto MWNTs was confirmed by the FT-IR and Raman spectra. The mechanical interfacial properties of the epoxy nanocomposites were remarkably improved with increasing the NH-MWNT content. It was probably attributed to the strong physical interaction between amine groups of NH-MWNTs and epoxide groups of epoxy resins. The SEM micrographs showed that NH-MWNTs were uniformly embed and bonded with epoxy resins, resulted in the prevention of the deformation and crack propagation in the NH-MWNTs/epoxy nanocomposites.

• 한국세라믹학회지
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• 제45권10호
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• pp.573-578
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• 2008

In the preparation of hydroxyapatite(HAp)/gelatin(GEL) nanocomposite, GEL matrix was modified by the introduction of chondroitin sulfate(ChS) to obtain a strongly organized composite body. The formation reaction of the HAp/GEL-ChS nanocomposite was then investigated via XRD, DT/TGA, FT-IR, TEM and SEM. The organic-inorganic interaction between HAp nanocrystallites and GEL molecules was confirmed from DT/TGA and FT-IR. According to the DT/TGA results, the exothermal temperature zone between 300 and $550^{\circ}C$ showed an additional peak temperature that indicated the decomposition of the combined organics of the GEL and ChS. From the FT-IR analysis, calcium phosphate(Ca-P) was covalently bound with the GEL macromolecules modified by ChS. From TEM and ED, the matrix of the GEL-ChS molecules was mineralized by HAp nanocrystallites and the dense dried nanocomposite body was confirmed from SEM micrographs.

• 대한기계학회논문집A
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• 제27권12호
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• pp.2055-2060
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• 2003

Striation is a typical pattern observed on the fatigue fracture surface and the spacing is known to correspond to a macroscopic fatigue crack growth rate, and many models for the predict in the formation of such striation have been proposed. However, these theories and methods can't be applied under random loading spectrum. In this study, the fatigue tests were carried out on aluminum alloy under random loading spectrum. The fatigue fracture surfaces were observed in the scanning electron microscope (SEM) and great quantities of SEM micrographs were synthesized and saved in computer system. The space and morphology of several large-scale striations, which are expected to from at the relatively greater load range in loading block, were observed. The crack length for each loading blocks was decided in consideration of regularity and repetition of those striations. It is shown that the applicability of fractographic methods on the fatigue fracture surface under random loading spectrum.

• 분석과학
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• 제20권2호
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• pp.124-130
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• 2007

In this study, we present the preparation and characterization of oxidized fullerene and fullerene dimer [$C_{120}$]. From the XRD data, other weak peaks with pristine fullerene [$C_{60}$] peaks were observed in the X-ray diffraction patterns for fullerene dimer [$C_{120}$]. SEM micrographs for the fullerene dimer [$C_{120}$] indicated that practically all the surface state was shown the drastic morphology changes and its outer surface is clearly visible and resulted in clogging and frost-like formation. From the MALDI-TOF mass spectra, the differences in the spectra recorded on two kinds of fullerene are due to the oxidation including chemical bonding and bridging between the $C_{60}$ molecules. We also obtained additional information from FT-IR spectra on functional component on the chemically modified surface of oxidized fullerene and fullerene dimer [$C_{120}$].

• 분석과학
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• 제13권3호
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• pp.332-337
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• 2000

본 연구에서는 페놀레진으로 부터 유도된 탄소질 수분 흡착제의 질소흡착, 표면 특성 및 수분 흡착량을 통하에 물리화학적인 특성을 제시하였다. 탄소질 수분 흡착제의 질소흡착에 관한 연구로부터 각각의 시료에 대하여 Type II의 흡착등온곡선을 얻었다. 이들 시료에 대한 흡착량은 물을 사용하여 세척한 후에 감소함을 나타내었다. BET식을 사용하여 계산된 $S_{BET}$값은 수세 전에 $648.7m^2/g$를 나타내었고, 수세 후에 $189.3m^2/g$를 나타내었다. SEM 모폴로지의 결과로부터 탄소질 수분 흡착제의 표면구조는 수세 전에 침상구조의 성상을 보였고, 수세 후에는 구형입자의 성상을 관찰 할 수 있었다. 최종적으로 수분흡착 효과를 측정한 결과, 수분 흡착량은 25-63%의 흡착량을 나타내었다. 또한 이들의 효과는 낮은 상대습도에서도 좋은 특성을 보였다.

• Advances in concrete construction
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• 제11권1호
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• pp.73-80
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• 2021

Rice Husk Ash (RHA) geopolymer paste activated by sodium aluminate were characterized by X-ray diffractogram (XRD), scanning electron microscope (SEM), energy dispersion X-Ray analysis (EDAX)and fourier transform infrared spectroscopy (FTIR). Five series of RHA geopolymer specimens were prepared by varying the Si/Al ratio as 1.5, 2.0, 2.5, 3.0 and 3.5. The paper focuses on the correlation of microstructure with hardened state parameters like bulk density, apparent porosity, sorptivity, water absorption and compressive strength. XRD analysis peaks indicates quartz, cristobalite and gibbsite for raw RHA and new peaks corresponding to Zeolite A in geopolymer specimens. In general, SEM micrographs show interconnected pores and loosely packed geopolymer matrix except for specimens made with Si/Al of 2.0 which exhibited comparatively better matrix. Incorporation of Al from sodium aluminate were confirmed with the stretching and bending vibration of Si-O-Si and O-Si-O observations from the FTIR analysis of geopolymer specimen. The dense microstructure of SA2.0 correlate into better performance in terms of 28 days maximum compressive strength of 16.96 MPa and minimum for porosity, absorption and sorptivity among the specimens. However, due to the higher water demand to make the paste workable, the value of porosity, absorption and sorptivity were reportedly higher as compared with other geopolymer systems. Correlation regression equations were proposed to validate the interrelation between physical parameters and mechanical strength. RHA geopolymer shows comparatively lower compressive strength as compared to Fly ash geopolymer.