• Fibers and Polymers
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• 제2권3호
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• pp.135-140
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• 2001

Organic-inorganic hybrid composites consisting of poly(vinylidene fluoride) (PVDF) and SiO$_2$ were prepared through a sol-gel process and the crystallization behavior of PVDF in the presence of $SiO_2$ networks was investigated by spectroscopic, thermal and x-ray diffraction measurements. The hybrid composites obtained were relatively transparent, and brittleness increased with increasing content of tetraethoxysilane (TEOS). It was regarded from FT-lR and DSC thermal analyses that at least a certain interaction existed between PVDF molecules and the $SiO_2$ networks. X-ray diffraction measurements showed that all of the hybrid samples had a crystal structure of PVDF ${\gamma}$-phase. Fresh gel prepared from the sol-gel reaction showed a very weak x-ray diffraction peak near 2$\theta$=$21^{\circ}$ due to PVDF crystallization, and Intensity increased grade-ally with time after gelation. The crystallization behavior of PVDF was strongly affected by the amount of $SiO_2$ networks. That is, $SiO_2$ content directly influenced preference and disturbance fur crystallization. In polymer-rich hybrids, $SiO_2$ networks had a favorable effect on the extent of PVDF crystallization. In particular, the maximum portent crystallinity of PVDF occurred at the content of 3.7 wt% $SiO_2$ and was higher than that of pure PVDF. However. beyond about 10 wt% $SiO_2$, the crystallization of PVDF was strongly confined.

• 반도체디스플레이기술학회지
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• 제6권2호
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• pp.15-18
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• 2007

Effects of $O_2$ flow during deposition on Si crystallization at low substrate temperature were studied. Silicon thin films were prepared on $SiO_2$ substrates in a low-pressure chemical vapor deposition chamber using a mixture of $SiH_4$ and $H_2$. In some cases $O_2$ was intentionally introduced during deposition. Growth of poly silicon was observed at the substrate temperature as low as $480^{\circ}C$ when $O_2$ was flowed during deposition implying that crystallization of Si was enhanced by $O_2$ flow. On the other hand, $O_2$ flow did not show any significant effects at higher substrate temperature, where deposition rate is relatively fast. Enhancement mechanism of Si crystallization by $O_2$ flow was suggested from these results.

• 한국세라믹학회지
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• 제32권12호
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• pp.1331-1336
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• 1995

The glass-ceramics for ferro-electric were made from compositions of 70PbO.16TiO2.8SiO2.4B2O3.2AlPO4 (wt%) and 67.5PbO.20TiO2.8.5SiO2.2B2O3.2AlPO4 (wt%). The crystallization kinetics for PbTiO3 crystalline phase formation from glass was studied using non-isothermal DSC techniques. The values of activation energy, ΔE using variables of heating rate and temperature were calculated at various reaction fractions obtained from peak area over DSC. The results indicated that activation energy was lowest at 60% reaction fractions and the activation energy of glass containing 20.0 wt% TiO2 is higher than that of glass containing 16.0 wt% TiO2. The crystallization mechanism was three dimensional growth (n=4).

• ETRI Journal
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• 제19권1호
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• pp.26-35
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• 1997

The substrate effects on solid-phase crystallization of amorphous silicon (a-Si) films deposited by low-pressure chemical vapor deposition (LPCVD) using $Si_2H_6$ gas have been extensively investigated. The a-Si films were prepared on various substrates, such as thermally oxidized Si wafer ($SiO_2$/Si), quartz and LPCVD-oxide, and annealed at 600$^{\circ}C$ in an $N_2$ ambient for crystallization. The crystallization behavior was found to be strongly dependent on the substrate even though all the silicon films were deposited in amorphous phase. It was first observed that crystallization in a-Si films deposited on the $SiO_2$/Si starts from the interface between the a-Si and the substrate, so called interface-interface-induced crystallization, while random nucleation process dominates on the other substrates. The different kinetics and mechanism of solid-phase crystallization is attributed to the structural disorderness of a-Si films, which is strongly affected by the surface roughness of the substrates.

• 한국결정성장학회지
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• 제6권2호
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• pp.275-285
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• 1996

The effect of heat-treatment on catalytic crystallization in $LI_2O-Al_2O_3-SiO_2$ glass system over its glass transition temperature was investigated. Glass composition $4Li_2O{cdot}22AL_2O_3{cdot}66SiO_2{cdot}2TiO_2{cdot}2.5ZrO_2{cdot}1.5P_2O_5{cdot}1.0Na_2O{cdot}1.0As_2O_3$ (wt%) was selected and heat-treated at different heating conditions to obtain transparent glass-ceramic. Nucleation and crystallization behaviour of this composition were estimated by differential thermal analysis (DTA) and X-ray diffractometer (XRD) and its thermal expansion coefficients were measured by Dilatometer. As a result, glass transition temperature was $730^{\circ}C$ and two maximum nucleation temperatures were estimated at $730^{\circ}C$ and 82$0^{\circ}C$ using JMA(Johson-Mehl-Avrami) equation by DTA. $ZrTiO_4$ $\beta$-Quartz solid solution and $\beta$-Spodumene crystals were identified by XRD. The optimum crystallization temperature was 92$0^{\circ}C$ and three step heating schedule was expected to be useful to obtain transparent glass-ceramic.

• 대한의용생체공학회:의공학회지
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• 제15권2호
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• pp.189-194
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• 1994

Effects of ${AI_2O_3}/{P_2O_5}$ ratio on the crystallization of a series of glasses with the nominal composition of 41.4wt % $SiO_2$, 35.0wt % CaO, 20.6wt % (${P_2O_5}$+${AI_2O_3}$) and 3.0wt% MgO were investigated with DTA, XRD and SEM. The major crystalline phases are apatite and anorthite. The glass transition temperature ($T_g$) and the softening point ($T_s$) are shifted to the upper temperature by increasing $AI_2O_3$ content. The temperature of apatite crystallization ($T_{p1}$) is increased by $AI_2O_3$ content, but the tempera¬ture of anorthite crystallization ($T_{p2}$) is not affected significantly. With increased of $AI_2O_3$, the apatite crystallization is decreased, but anorthite crystallization is increased.

• Journal of Information Display
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• 제10권3호
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• pp.117-120
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• 2009

A new crystallization method for amorphous silicon, called selective area heating (SAH), was proposed. The purpose of SAH is to improve the reliability of amorphous silicon films with extremely low thermal budgets to the glass substrate. The crystallization time shortened from that of the conventional solid-phase crystallization method. An isolated thin heater for SAH was fabricated on a quartz substrate with a Pt layer. To investigate the crystalline properties, Raman scattering spectra were used. The crystalline transverse optic phonon peak was at about 519 $cm^{-1}$, which shows that the films were crystallized. The effect of the crystallization time on the varying thickness of the $SiO_2$ films was investigated. The crystallization area in the 400nm-thick $SiO_2$ film was larger than those of the $SiO_2$ films with other thicknesses after SAH at 16 W for 2 min. The results show that a $SiO_2$ capping layer acts as storage layer for thermal energy. SAH is thus suggested as a new crystallization method for large-area electronic device applications.

• 한국세라믹학회지
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• 제37권1호
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• pp.50-56
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• 2000

Precursor gels with the composition of xZrO2·(100-x)SiO2 systems (x=10, 20 and 30 mol%) were prepared by the sol-gel method. Kinetic parameters, such as activation energy, Avrami's exponent, n, and dimensionality crystal growth value, m, have been simultaneously calculated from the DTA data using Kissinger and Matusita equations. The crystallite size dependence of tetragonal to monoclinic transformation of ZrO2 was investigated using XRD, in relation to the fracture toughness. The crystallization of tetragonal ZrO2 occurred through 3-dimensional diffusiion controlled growth(n=m=2) and the activation energy for crystallization was calculated using Kissinger and Matusita equations, as about 310∼325±10kJ/mol. The growth of t-ZrO2, in proportion to the cube of radius, increased with increasing heating temperature and hteat-treatment time. It was suggested that the diffusion of Zr4+ ions by Ostwald ripening was rate-limiting process for thegrowth of t-ZrO2 crystallite size. The fracture toughness of xZrO2·(100-x)SiO2 systems glass ceramics increased with increasing crystallite size of t-ZrO2. The fracture toughness of 30ZrO2·70SiO2 system glass ceramics heated at 1,100℃ for 5h was 4.84 MPam1/2 at a critical crystaliite size of 40 nm.

• 한국세라믹학회지
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• 제53권2호
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• pp.139-144
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• 2016

The dependence of the microwave dielectric properties of the glass-ceramic composite $0.9CaMgSi_2O_6-0.1MgSiO_3$ on the crystallization behaviour was investigated as functions of the $TiO_2$ content and heat-treatment temperature. The crystallization behaviour of the specimens was evaluated via a combination of the Rietveld and reference-intensity ratio methods. For specimens with a $TiO_2$ content of up to 1 wt.%, a monoclinic diopside phase was formed, whereas a secondary $TiO_2$ phase was formed with further increases in the $TiO_2$ content. The quality factor (Qf) of the specimens was strongly dependent on the degree of crystallization. The highest Qf value was obtained with a $TiO_2$ content of 0.5 wt.%, which was improved by increasing the heat-treatment temperature. The dielectric constant (K) was affected by the size of the crystallites and the $TiO_2$ content. The temperature coefficient of the resonant frequency (TCF) was nearly constant for all of the specimens, regardless of the $TiO_2$ content or heattreatment temperature.

• 대한치과기공학회지
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• 제21권1호
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• pp.5-14
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• 1999

Glass ceramics for dental crown prosthesis were prepared by crystallization of CaO-MgO-SiO2-$P_2O_5-TiO_2$ glasses. Their crystallization behaviors have been investigated as a function of heattreatment temperature, holding time and chemical composition in relation to mechinical properties. Crystallization peak temperatures were determined by differential thermal analysis(DTA). Crystalline phases and mircostructures of heat-treated sample were determined by the means of powder X-ray diffraction(XRD) and scanning electron microscopy(SEM). The final crystalline phase assemblages and the microstructures of the samples were found to be dependent on glass compositions, heattreatment temperature, and holding time. 1st crystallization peak temperature(TP), affected strongly by apatite, was found to be increased or decreased. From the experiment, the following results were obtained : 1. The crystallization peak temperature($T_P$) formed by apatite increased until adding up to 9wt% $TiO_2$ to base glass composition, then decreased above that. 2. Apatite($Ca_{10}P_6O_{25}$), whitlockite(${\beta}-3CaO-P_2O_5$), $\beta$-wollastonite($CaSiO_3$), magnesium tianate($MaTiO_3$) and diopside(CaO-MgO-$2SiO_2$) crystal phase were precipitated in MgO-CaO-$SiO_2-TiO_2-P_2O_5$ glass system containing 9wt% and 11wt% of $TiO_2$ 3. Vickers hardness of samples increased with increasing heat-treatment temperature and Vickers hardness of S415T9 samples heat-treated at 1075 was approxi-mately 813Kg $mm^{-2}$ as maximum value. 4. Vickers hardness of samples increased due to precipitation of apatite, whitlockite, $\beta$-wollastonite, magnesium titanate, and diopside crystal phases within glass matrix.