• Journal of the Korean Ceramic Society
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• v.31 no.12
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• pp.1552-1560
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• 1994

Glasses in K2O-Na2O-MgO-Al2O3-SiO2-F system were crystallized to prepare machinable glass-ceramics. The optimum nucleating and crystal growing temperatures were approximately $700^{\circ}C$ and 1060~112$0^{\circ}C$, respectively for the samples investigated. Crystalline phases of sellaite, norbergite, and fluorphlogopite appeared progressively as heat-treatment temperature was increased. Surface roughness of the crystallized specimens after the machining was similar to that of metal aluminum (2.18 ${\mu}{\textrm}{m}$). Thermal expansion coefficient, Vickers hardness and dielectric constants of the fluorphlogopite glass-ceramics prepared were 7.37~10.21 ($\times$10-6/$^{\circ}C$), 302~456kgf/$\textrm{mm}^2$ and 5.97~16 respectively.

• Journal of the Korean Ceramic Society
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• v.28 no.9
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• pp.683-688
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• 1991

ZnO-P2O5 system glass containing 45 to 60 mol% ZnO has been melted at 120$0^{\circ}C$ and crystallized through heat treatment. Each condition of crystallization was determined by measurement of dilatometric softening point and DTA. The principal crystalline phase was identified as zinc metaphosphate [Zn(PO3)2] in the glasses containing 45~55 mol% ZnO and zinc pyrophosphate (Zn2P2O7) in the sample of 60 mol% ZnO with X-ray diffraction patterns. The crystalline mechanism was investigated by XRD and SEM. As the results, the specimens containing 50~60% ZnO showed the existence of oriented structure due to one-dimensional crystal growth.

• Journal of the Korean Ceramic Society
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• v.29 no.3
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• pp.223-231
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• 1992

CaO and ZnO were added to Al2O3-SiO2 binary system respectively as flux, then ZrO2 and TiO2 were applied as nucleating agent to these CaO-Al2O3-SiO2 and ZnO-Al2O3-SiO2 ternary system glass. The transparency could not be kept in CaO-Al2O3-SiO2 system glass, whereas the transparent glass-ceramics were prepared in ZnO-Al2O3-SiO2 system glass containing ZrO2 as the nucleating agent. At this time the optimum heating temperatures for the nucleation and the crystal growth were 78$0^{\circ}C$ and 97$0^{\circ}C$. The sizes of the precipitated crystals in the transparent glass-ceramics were below 0.1 ${\mu}{\textrm}{m}$, and their light transmissibilities were more than 80%.

• Journal of the Korean Ceramic Society
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• v.30 no.2
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• pp.107-114
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• 1993

Zinc-Borosilicate(ZnO 65.0wt%, B2O3 21.5wt%, SiO2 9.0wt%, PbO or tiO2 4wt%) passivation glasses were studied using differential thermal analysis(DTA), scanning electron microscopy(SEM) observations, X-ray diffraction (XRD) patterns and measurement of thermal expansion coefficients. Passivation glasses containing 4wt% TiO2 and 4wt% PbO had crystallization temperature of 680~73$0^{\circ}C$ and major crystalline phases were identified by X-ray diffraction as $\alpha$-ZnO.B2O3 and $\alpha$-5ZnO.2B2O3. As increasing firing temperature, the size of crystalline phases increased by observation of SEM. The thermal expansion coefficient of crystallized glass frits was smaller than that of unfired glass.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.288-296
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• 1990

Parent glasses for the experiments were prepared to be ratio of Li2O : Al2O3 : SiO2=4.5 : 25 : 70.5 as basic components, and TiO2 and ZrO2 in the mixing ratio of 1 : 1 were added as the nucleating agents, whose contents were increased in each sample. DTA, XRD, SEM, IR were observed, and thermal expansion and transmissivities were measured for the crystallized samples under the controlled heat-treatments. The transformation temperatures and the dilatometric softening temperatures in thermal expansion curves, and also the exothermic peaks in differential thermo-analytical curves were shifted to lower temperature. The crystal phase deposited through the heat-treatment was identified as ${\beta}$-quartz solid solution with XRD and IR analysis. The crystalline phases in oopactified samples were ${\beta}$-spodumene coexiting with ${\beta}$-quartz solid solution. The samples having more than 3% nucleating agents were transparent. The crystallized grain sizes were ranged 0.05 to 0.1$\mu\textrm{m}$. The crystallized transparent samples were exceeded 85% in the transmissivity.

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.521-528
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• 1990

Li2O.2SiO2 glass-ceramics were made from the melt by the nucleation and growth treatment. The optimum nucleation temperature and time were determined from DTA curves of as-quenched and thermally treated glasses, and found to be 44$0^{\circ}C$ and 3hrs. The optical microscopic technique was also used to support this result. The volume fractions of crystals present in the partially crystallized specimens were measured using the optical microscopy and the amorphous X-ray scattering methods. The degree of crystallization increased with increasing the crystallization temperature and time. The crystalline phase identified by X-ray diffraction was lithium disilicate. As the crystallinity increased up to 95%, the transmittance of glass-ceramics was decreased linearly. It was also found that for the same heat treatment condition (575$^{\circ}C$, 30min), a thicker specimen showed higher transmittance, presumably due to less crystallinity.

• Journal of the Korean Ceramic Society
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• v.22 no.3
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• pp.29-34
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• 1985

The IR spectra of he heavy metal fluoride glasses showed peaks at $1, 400cm^{-1}$ or $1, 100cm^{-1}$ due to metal oxyfluoride impurities. The intensity of this band and hence the oxide impurity content of the glass could be reduced considerably by the use of reactive atmosphere melting under $CCl_4$ In comparison with the fundamental IR absorption band of heavy metal oxides the oxide impurity bands observed in the heavy metal fluoride glasses are multiphonon bands due to a 2-phonon absorption process. The envelope of the a vs. v curve beyond thue fundamental region shows the exponential fall off of a with increasing v-typical of intrinsic multiphonon absorption. In the multiphonon region the amount of structure is intermediate between that observed for covalent solids and that for ionic solids.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.829-835
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• 1989

Devitrifing solder glasses in a specific group of glass ceramic materials are extensively used in hermetically sealing alumina electronics packages. Preferred frit glass compositions of this study consist of 37~40wt% PbO, 35~40wt% ZnO, 18~20wt% B2O3, 1~3wt% SiO2, 0~6wt% TiO2. The coated frit glasses crystallize during firing and form a strong hermetic seal. DTA and X-ray diffraction were used to characterize crystallization of the glass frit. Frit seal containing 2wt% TiO2 has crystallization temperature of 550~57$0^{\circ}C$ with surface nucleation. Frit seal containing 6wt% TiO2 has crystallization temperature of 515~5$25^{\circ}C$ with bulk nucleation, and the main crystalline phase was perovskite lead titanate having minus expansion coefficient. The average activation energy for the crystallization calculated from Ozawa equation was 65$\pm$10kcal/mol.

• 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.42 no.11 s.282
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• pp.770-776
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• 2005

Hardening and hydroxyapatite(HAp) formation behavior of the bioactive cements in the system of $CaO-SiO_{2}-P_{2}O_{5}$ glasses and the corresponding glass-ceramics were studied. DCPD (Dicalcium Phosphate Dihydrate: $CaHPO_4{\cdot}2H_2O$) and DCPA (Dicalcium Phosphate Anhydrous: $CaHPO_4$) were developed when the prepared glass and glass-ceramic powders were mixed with three different solutions. The DCPD and DCPA transformed to HAp when the cement was soaked in Simulated Body Fluid (SBF), and this HAp formation strongly depended on the releasing capacity of $Ca^{2+}$ ions from the cements. The glass-ceramic containing apatite showed fast setting, but no HAp formation was observed because no $Ca^{2+}$ ions were released from this glass-ceramics. The compressive strength of the cements increased with reaction time in SBF until all DCPD and DCPA transformed to HAp.