• Advances in materials Research
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• v.8 no.3
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• pp.179-196
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• 2019

This paper researches static and dynamic bending behaviors of a crystalline nano-size shell having pores and grains in the framework of strain gradient elasticity. Thus, the nanoshell is made of a multi-phase porous material for which all material properties on dependent on the size of grains. Also, in order to take into account small size effects much accurately, the surface energies related to grains and pores have been considered. In order to take into account all aforementioned factors, a micro-mechanical procedure has been applied for describing material properties of the nanoshell. A numerical trend is implemented to solve the governing equations and derive static and dynamic deflections. It will be proved that the static and dynamic deflections of the crystalline nanoshell rely on pore size, grain size, pore percentage, load location and strain gradient coefficient.

• Macromolecular Research
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• v.11 no.4
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• pp.224-230
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• 2003

The blends of polypropylene (PP) with glass filled thermotropic liquid crystalline polymer (LCP-g) have been prepared by melt mixing techniques at different blend ratios. The thermal, dynamic mechanical, crystalline and morphological characteristics of these blends were investigated. Higher percent crystallinity was observed for 10% level of LCP-g in the blend in comparison to that of other blend ratios. The thermal stability increased with LCP-g concentration in the blend with PP. The variation of storage modulus, stiffness and loss modulus as a function of blend ratios suggested the phase inversion at the 50% level of LCP-g in the blend. The scanning electron microscopy (SEM) photographs showed the creation of voids and destruction of the fiber structures during the dynamic mechanical measurements. Processing behavior of the blends depended on the fiber forming characteristics of LCP-g, which again varied with the molding temperatures.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3571-3574
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• 2011

Nano-scaled metal oxides have been attractive materials for sensors, photocatalysis, and dye-sensitization for solar cells. We report the controlled synthesis and characterization of single crystalline $TiO_2$ nanowires via a catalyst-assisted vapor-liquid-solid (VLS) and vapor-solid (VS) growth mechanism during TiO powder evaporation. Scanning electron microscope (SEM) and transmission electron microscope (TEM) studies show that as grown $TiO_2$ materials are one-dimensional (1D) nano-structures with a single crystalline rutile phase. Also, energy-dispersive X-ray (EDX) spectroscopy indicates the presence of both Ti and O with a Ti/O atomic ratio of 1 to 2. Various morphologies of single crystalline $TiO_2$ nano-structures are realized by controlling the growth temperature and flow rate of carrier gas. Large amount of reactant evaporated at high temperature and high flow rate is crucial to the morphology change of $TiO_2$ nanowire.

• Composites Research
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• v.37 no.1
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• pp.1-6
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• 2024

A liquid crystalline thermosetting epoxy was synthesizes with DGE-DHMS and 1-Methyl Imidazole. To investigate thermal stability, activation energies for thermal decomposition were calculated via Flynn-Wall-Ozawa method and Kissinger method with the data obtained from TGA analysis. The result showed that there were no differences in thermal decomposition behavior between liquid crystalline phases and isotropic phase and also the same thermal decomposition mechanism was applied to the entire process.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2000.04a
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• pp.39-42
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• 2000

• Proceedings of the Korean Society of Potoscience Conference
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• 2005.06a
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• pp.24-24
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• 2005

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.134-134
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• 2009

In this work, we report that crystallization speed as well as the electrical and optical properties about the N-doped $Ge_2Sb_2Te_5$ thin films. The 200-nm-thick N-doped $Ge_2Sb_2Te_5$ thin film was deposited on p-type (100) Si and glass substrate by RF reactive sputtering at room temperature. The amorphous-to-crystalline phase transformation of N-doped $Ge_2Sb_2Te_5$ thin films investigated by X-ray diffraction (XRD). Changes in the optical transmittance of as-deposited and annealed films were measured using a UV-VIS-IR spectrophotometer and four-point probe was used to measure the sheet resistance of N-doped $Ge_2Sb_2Te_5$ thin films annealed at different temperature. In addition, the surface morphology and roughness of the films were observed by Atomic Force Microscope (AFM). The crystalline speed of amorphous N-doped $Ge_2Sb_2Te_5$ films were measured by using nano-pulse scanner with 658 nm laser diode (power : 1~17 mW, pulse duration: 10~460 ns). It was found that the crystalline speed of thin films are decreased by adding N and the crystalline temperature is higher. This means that N-dopant in $Ge_2Sb_2Te_5$ thin film plays a role to suppress amorphous-to-crystalline phase transformation.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.325-332
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• 1998

Crystalline TiO2 ultrafine powders were prepared simply by heating and stirring aqueous TiOCl2 solution with {{{{ {Ti }^{4+ } }} concentration of 0.5 M from room temperature to 10$0^{\circ}C$ under 1 atmoshpere. The crystallinity and the particle shape of TiO2 ultrafine powders obtained by simple precipitation method were analyzed us-ing XRD(X-ray diffractometer). SEM(scanning electron microscopy) and TEM(transmission electron mi-croscopy) TiO2 crystalline precipitate with rutile phases is fully formed at the temperatures of up to $65^{\circ}C$ and then TiO2 crystalline precipitate with anatase phase starts to be formed above temperatures $65^{\circ}C$ showing its full formation at 10$0^{\circ}C$ These behaviors of TiO2 crystalline precipitate directly from an aqueous TiOCl2 solution would be caused due to the existence of {{{{ OMICRON ^2+ }} ions from distilled water which oxydize TiOCl2 to TiO2 not hydrolyzing it to Ti(OH)4 Here thermodynamically stable TiO2 rutile phase generally formed at higher temperature is practically precipitated at lower temperatures in this study This may be due to the precipitation by very slow reaction enough to make TiO2 particles allocated into stable rutile structure.

• Korean Journal of Materials Research
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• v.4 no.3
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• pp.301-311
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• 1994

The growth of amorphous and first crystalline phase, and phase sequence by solid state reaction were examined in Co/Si multilayer thin films by DSC and XRD. The experimental results were compared with the results expected by effective driving force models, PDF and effective heat of formation models.Amorphous phase growth was not observed in Co/Si system and it was consistent with the predicted result by effective driving force. It was observed that the first crystalline phase is CoSi. According to the PDF and effective heat of formation models, the first crystalline phases were CoSi and $CO_2Si$, respectively. The experiemental results were coincident with the PDF model considering structure factors. In case of the atomic concentration ratios of 2Co : 1Si and 1Co : 2Si, the phases sequences were $CoSi\to Co_2Si$ and $CoSi \to Co_2Si \to CoSi \to CoSi_2$, respectively and it was analysized through the effective heat of formation model. The formations of CoSi, $CO_2Si$ and $COSi_2$ in initial stage were controlled by nucleation and the activation energies for the nucleation of three phases were 1.71, 2.34 and 2.79eV.

• Bulletin of the Korean Chemical Society
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• v.28 no.1
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• pp.108-114
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• 2007

The lyotropic behaviors to form the structure of distearoylphosphatidylcholine (DSPC)-based liquid crystal (LC) hydrated by only propylene glycol (PG) without water were examined by differential scanning calorimetry (DSC), X-ray diffractions (XRD), polarized microscope (PM) and transmission electron microscope (TEM). By increasing the amount of PG instead of water, it showed the phase transition to be gradually changed from anisotropic structures to other structures more close to isotropic ones and their appearance to be changed from solid-like states to liquid-like ones with more fluidity. Below 50% w/w PG, the mixtures of DSPC and PG resulted in no direct observation of LC structure through PM because they were very close to solid-states. From 55% w/w to 90% w/w of PG, the dense lamella crystalline structures were observed through PM, and their thickness and area decreased as the content of PG increased. Measured by DSC with heating process, the main phase transition from α -lamella phase to isotropic phase appeared from 52.89 °C to 47.41 °C to show linearly decreasing behaviors because PG affects the hydrophobic region of DSPC-based lamella phase. The repeating distance of the lamella phase and the interlayer distance between bilayers were calculated with XRDs and the average number of bilayers related to the thickness in LC structure was approximately estimated by combining with TEM results. The WAXS and DSC measurements showed that all of PG molecules contributed to swelling both the lipid layer in the edge region of lamella phase close to phosphate groups and the interlayer between bilayers below 90% w/w of PG. The phase and thermal behaviors were found to depend on the amount of PG used by means of dissolving DSPC as a phospholipid and rearranging its structure. Instead of water, the inducement of PG as a polar solvent in solid-lamella phase is discussed in terms of the swelling effect of PG for DSPC-based lamella membrane.