• Composites Research
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• v.26 no.2
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• pp.123-128
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• 2013

The PVDF (polyvinylidene fluoride) fibers were prepared using the wet spinning processing. To improve ${\beta}$-phase crystalline which closely related piezoelectric property PVDF wet spun fibers conducted post treatment. Post treatment is consisted of heat stretching and annealing process. The heat stretching and annealing conditions were controlled by changing temperature between glass transition temperature and melting temperature. From these experimental data, the resulting crystal structure of the ${\beta}$-phase crystalline was confirmed by FT-IR and XRD experiments. From these analysis results, optimum stretching and annealing conditions of the wet spun PVDF fibers were founded to increase high ${\beta}$-phase crystalline. Furthermore results showed that thermal processing had a direct effect on modifying the crystalline microstructure and also confirmed that heat stretching and annealing could increase the degree of crystallinity and ${\beta}$-phase crystalline. Finally, piezoelectric constant ($d_{11}$) of the post heat treated PVDF fibers reinforced composite were measured to investigate the feasibility for the sensing materials.

• Journal of Korea Foundry Society
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• v.27 no.4
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• pp.167-172
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• 2007

In the present study, the microstructural evolution and mechanical properties of $Al_{71.6}Ge_{28.4}$ eutectic alloy have been investigated. Stable (fcc ${\alpha}$-Al and diamond cubic ${\beta}$-Ge) and various metastable crystalline (monoclinic, rhombohedral) phases were produced by competitive phase selection during non-equilibrium processing methods i.e. melt spinning and injection casting. The as-injection casted samples containing metastable-equilibrium eutectic (${\alpha}$-Al + monoclinic) structure showed much higher strength than samples with equilibrium eutectic (${\alpha}-Al+{\beta}-Ge$) structure but plasticity disappointingly diminished. In order to endow the enhanced ductility without significant strength drop, the alloys was heat-treated at transition temperature from metastable phase to stable phase. The annealed specimen displayed the phase transformed microstructural evolution and enhanced macroscopic plasticity.

• Journal of Technologic Dentistry
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• v.25 no.1
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• pp.21-28
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• 2003

The purpose of this study was to process bio-active glass ceramic composite, reinforced with sapphire fibers, by hot press. Also to study the interface of the matrix and the sapphire fiber, and the mechanical properties. Glass raw materials melted in Pt crucible at 1300$^{\circ}C$ during 3.5 hours. The melt was crushed in ball mill and then crushed material, ground and sieved to $<40{\beta}{\mu}m$. Sapphire fibers cut (30mm) and aligned. Powder and fibers hot pressed. The micrographs show good bonding between the matrix and the fiber and no porosity in the glass matrix. This means ideal fracture phenomena. Glass is fractured before the fiber. This is indication of good fracture strength. EDXS showing aluminum rich phase and crystalline phase. Bright field image of the matrix showing crystalline phase. Also diffraction pattern of TEM showing the crystalline phase and more than one phase. Strength of the samples was determined by 3 point bend testing. Strength of the 10vol% sample was approximately 69MPa, while strength of the control sample is 35MPa. Conclusions through this study as follow: 1. Micrographs show no porosity in the glass matrix and the interface. 2. The interface between the fiber and the glass matrix show no gaps. 3. Fracture of the glass indicates characteristic fiber-matrix separation. 4. Presence of crystalline phase at high processing temperature. 5. Sapphire is compatible with bioactive glass.

• Applied Microscopy
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• v.45 no.2
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• pp.58-62
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• 2015

Formation of an icosahedral phase in the bulk glass forming $Ti_{40}Zr_{29}Be_{14}Cu_9Ni_8$ alloy during crystallization from amorphous phase and solidification from melt is investigated. The icosahedral phase with a size of 10 to 15 nm forms as a thermodynamically stable phase at intermediate temperature during the transformation from amorphous to crystalline phases such as Laves and ${\beta}$-(Ti-Zr) phases, indicating that the existence of the icosahedral cluster in the undercooled liquid. On the other hand, the icosahedral phase forms as a primary solidification phase even though the Laves phase is stable at high temperature, which is can be explained based on the high nucleation rate of icosahedral phase relative to that of competing crystalline Laves phase due to lower interfacial energy between icosahedral and liquid phases.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.589-589
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• 2012

Indium sulfide thin films have been grown onto glass substrates using radio frequency magnetron sputtering at room temperature. The as-deposited film were annealed in nitrogen atmosphere at different temperatures of 100, 200, 300, 400 and $500^{\circ}C$ with an 1 h annealing time. The effect of annealing temperature on composition, structure, morphology and optical properties of the as-grown In2S3 films has been studied. The XRD results indicate that the as-deposited films are composed by a mixture of both cubic ${\alpha}$ and ${\beta}$ crystalline phases, with some fraction of tetragonal phase. The thermal annealing on the films produces the conversion of the cubic crystalline phases to the tetragonal ${\beta}$ one and a crystalline reorientation of the latter phase. The surface morphological analysis reveals that the films grown at $300^{\circ}C$ have an average grain size of ~ 58 nm. These films show a S/In ratio of 0.99. The optical band gap is found to be direct and the films grown at $300^{\circ}C$ shows a higher optical transmittance of 80% and an energy band gap of 2.52 eV.

• Composites Research
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• v.33 no.1
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• pp.19-24
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• 2020

In this paper, the microwave irradiation process was conducted during the Poly(vinylidene fluoride) (PVDF) nano-composite film fabrication process to analyze how the β-crystalline is increased. TiO₂ was added as a nanoparticle reinforcement to further improve the β-crystalline conformation of the PVDF films by van der Waals force due to the difference of electronegativity between PVDF and the metal oxide nanoparticle. The crystalline conformation of the fabricated films was analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. According to these analysis results, it was confirmed that the microwave irradiation process during the solvent evaporation process increases the crystallinity of the PVDF films, and more β-crystalline can be obtained after additional film stretching process. It was also found that the PVDF nano-composite films with the metal oxide have relatively higher β-crystalline conformation rather than the neat PVDF films.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.858-864
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• 1995

A porous glass-ceramics body was prepared in the phosphate system. The glass composition of 47.2CaO-22.2TiO2-30.6P2O5 (mol%) containing a few weight percent of ZrO2 was suitable for a mother glass of a porous glass-ceramics. The dense glass-ceramics body was made by a two-step heat treatment of the mother glass. The crystalline phases of the glass-ceramics were $\beta$-Ca3(PO4)2 and CaTi4(PO4)6. The $\beta$-Ca3(PO4)2 phase could be selectively leached out with HCl solution and thus a crystalline $\beta$-Ca3(PO4)2 skeleton was remained. The dimension and shape of the porous glass-ceramics were nearly the same as the those of the first formed glass. The specific surface area and average proe radius of the porous glass-ceramics were 19$m^2$/g and 22 nm, respectively.

• Journal of the Korean Ceramic Society
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• v.50 no.4
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• pp.275-279
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• 2013

The purpose of this study was to prepare calcium phosphate cement [CPC] for use in artificial bone. Nano-crystalline calcium phosphate [CaP] was precipitated at $37^{\circ}C$ using highly active $Ca(OH)_2$ in DI water and an aqueous solution of $H_3PO_4$. From the XRD measurements, the nano-CaP powder was close to apatitic TCP phase and the powders fired at $800^{\circ}C$ showed a critical ${\beta}$-TCP phase. A mixture of one mole $CaCO_3$ and two moles di-calcium phosphate was calcined at $1100^{\circ}C$ to make a reference ${\beta}$-TCP material. The nano-CaP powders were added to the normal ${\beta}$-TCP matrix and fired at $900^{\circ}C$ to make a ${\beta}$-TCP block. The sintered block showed improved mechanical strength, which was caused by the solid state interaction between nano-CaP and normal ${\beta}$-TCP.

• Bulletin of the Korean Chemical Society
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• v.12 no.5
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• pp.490-494
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• 1991

The ${\beta} to {\alpha}$ phase transition in silver iodide is studied with the (N, V, E) and (N, P, T) molecular dynamics (MD) method. In experiments, the phase transition temperature is 420 K. Upon heating of ${\beta}$ form, the iodine ions undergo hcp to bcc transformation and silver ions become mobile. MD simulations for the ${\beta}$ and ${\alpha}$ phases are carried out at several temperatures and the radial distribution functions (rdf) are obtained at those temperatures in the (N, V, E) ensemble. But the phase transition is not found in our calculation. Next the phase transition is studied with the (N, P, T) MD and we find some evidences of phase transition. At 3 Kbars and 2 Kbars the phase transition temperatu re is about 300 K. For 3.55 Kbars, the phase transition is higher (420 K) than the low pressure case. The phase transition temperature is somewhat dependent on the pressure in our calculations.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.7
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• pp.550-554
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• 2013

Carbon nanotubes (CNT) / polyvinylidene fluoride (PVDF) piezoelectric composite films for nanogenerator devices were fabricated by spray coating method. When the CNT/PVDF mixture solution passes through the spray nozzle with small diameter by the compressed nitrogen gas, electric charges are generated in the liquid by a triboelectric effect. Then randomly distributed ${\beta}$ phase PVDF film could be re-oriented by the electric field resulting from the accumulated electrical charges, and might be resulted in extremely one-directionally aligned ${\beta}$ phase PVDF film without additional electric field for poling. X-ray diffraction patterns were used to investigate crystal structure of the CNT/PVDF composite films. It was confirmed that they revealed extremely large portion of the ${\beta}$ phase PVDF crystalline in the film. Therefore we could obtain the poled CNT/PVDF piezoelectric composite films by the spray coating method without additional poling process.