• Journal of the Korean Ceramic Society
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• v.46 no.4
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• pp.413-418
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• 2009

Glass systems based on Ca, Sr, Ba, and Zn modified alumino-boro silicates were investigated in order to improve the dielectric and mechanical properties of a typical LTCC (low temperature co-fired ceramic) which was developed for high frequency highly-integrated modules. The glass was prepared by a typical melting procedure and then mixed with cordierite fillers to fabricate glass/ceramic composite-type LTCC materials. The amount of cordierite filler was fixed at 50 volumetric%. For an optimal glass composition of 7.5% CaO, 7.5% BaO, 5% ZnO, 10% $Al_2O_3$, 30% $B_2O_3$, and 40% $SiO_2$ in mole ratio, the resultant LTCC composite showed a dielectric constant of 5.8 and a dielectric loss ($tan{\delta}$) of 0.0009 after firing at $900^{\circ}C$. An average bending strength of 160MPa was obtained for the optimal composition.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2003.04a
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• pp.60-60
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• 2003

• Korean Journal of Materials Research
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• v.22 no.12
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• pp.669-674
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• 2012

Yellow phosphor dispersed color conversion glasses are promising phosphor materials for white LED applications because of their good thermal durability, chemical stability, and anti-ultraviolet property. Six color conversion glasses were prepared with high Tg and low Tg specimens of glass. Luminous efficacy, luminance, CIE (Commission Internationale de l'Eclairage) chromaticity, CCT (Correlated Color Temperature), and CRI (Color Rendering Index) of the color conversion glasses were analyzed according to the PL spectrum. Color conversion glasses with high Tg glass frit, sintered at higher temperature, showed better luminous properties than did color conversion glasses with low Tg glass frit. The characteristics of the color conversion glass depended on the glass composition rather than on the sintering temperature. The XRD peaks of the YAG phosphor disappeared in the color conversion glass with major components of $B_2O_3$-ZnO-$SiO_2$-CaO and, in the XRD results, new crystalline peaks of $BaSi_2O_5$ appeared in the color conversion glass with major components of $Bi_2O_3$-ZnO-$B_2O_3$-MgO. The characteristics of CIE chromaticity, CCT, and the CRI of low Tg color conversion glasses showed worse color properties than those of high Tg color conversion glasses. However, these color characteristics of low Tg glasses were improved by thickness variation. So color conversion glasses with good characteristics of both luminous and color properties were attained.

• Korean Journal of Materials Research
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• v.24 no.12
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• pp.710-714
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• 2014

The effect of titanium dioxide ($TiO_2$) on the properties of color conversion glasses was examined for glasses based on $BaO-ZnO-B_2O_3-SiO_2$. One glass sample, containing 25 mol% of each component, was used as a reference; the other three glass samples contained 1, 3, and 5 mol% $TiO_2$, respectively. The four color conversion glass samples were prepared by sintering a mixture of glass frits and a $YAG:Ce^+$ phosphor. The characteristics of the color conversion glass samples, such as luminous efficacy, luminance, CIE (Commission International de I'Eclairage) chromaticity, CCT (Correlated Color Temperature), and CRI (Color Rendering Index) were analyzed according to the PL spectrum. The refractive index of the glass samples was found to increase with the titanium dioxide content. In conclusion, luminous efficacy of color conversion glasses increased as the content of $TiO_2$ was raised in the glass matrix.

• Journal of the Korean Ceramic Society
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• v.36 no.12
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• pp.1350-1355
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• 1999

Sintering characteristics and dielectric properties of low temperature sinterable Glass/Ceramic dielectric materials were investigated. The dielectric materials which were developed for microwave frequency applications consist of SiO2-TiO2-Bi2O3-RO system(RO:BaO-CaO-SrO) crystallizable glass and Al2O3 as a ceramic filler. Sintering experiments showed that no more densification occurred above 80$0^{\circ}C$ and bulk density and shrinkage depended on Al2O3 content only. Results of dielectric measurements showed that $\varepsilon$r Q$\times$f and $\tau$f of the material containing 30wt% Al2O3 were 17.3, 600 and +23 ppm respectively. Those values for 45 and 60wt% Al2O3 samples were 11.6, 1400, +0.7 ppm and 7.2, 2000, -8.5 ppm, repectively. The results clearly showed that the Glas/Ceramic materials of present experiment decreased in $\varepsilon$r and increased in $\times$f value and changed from positive to negative value in $\tau$f value with the increasement of Al2O3 content.

• The Journal of Advanced Prosthodontics
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• v.8 no.1
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• pp.43-52
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• 2016

PURPOSE. This study was conducted to evaluate the effects of full-coverage all-ceramic zirconia, lithium disilicate glass-ceramic, leucite glass-ceramic, or stainless steel crowns on antagonistic primary tooth wear. MATERIALS AND METHODS. There were four study groups: the stainless steel (Steel) group, the leucite glass-ceramic (Leucite) group, the lithium disilicate glass-ceramic (Lithium) group, and the monolithic zirconia (Zirconia) group. Ten flat crown specimens were prepared per group; opposing teeth were prepared using primary canines. A wear test was conducted over 100,000 chewing cycles using a dual-axis chewing simulator and a 50 N masticating force, and wear losses of antagonistic teeth and restorative materials were calculated using a three-dimensional profiling system and an electronic scale, respectively. Statistical significance was determined using One-way ANOVA and Tukey's test (P<.05). RESULTS. The Leucite group ($2.670{\pm}1.471mm^3$) showed the greatest amount of antagonist tooth wear, followed by in decreasing order by the Lithium ($2.042{\pm}0.696mm^3$), Zirconia ($1.426{\pm}0.477mm^3$), and Steel groups ($0.397{\pm}0.192mm^3$). Mean volume losses in the Leucite and Lithium groups were significantly greater than in the Steel group (P<.05). No significant difference was observed between mean volume losses in the Zirconia and Steel groups (P>.05). CONCLUSION. Leucite glass-ceramic and lithium disilicate glass-ceramic cause more primary tooth wear than stainless steel or zirconia.

• Journal of Powder Materials
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• v.27 no.6
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• pp.498-502
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• 2020

We investigate the effects of Yb2O3 and calcium aluminosilicate (CAS) glass as sintering additives on the sintering behavior of AlN. The AlN specimens are sintered at temperatures between 1700℃ and 1900℃ for 2 h in a nitrogen atmosphere. When the Yb2O3 content is low (within 3 wt.%), an isolated shape of secondary phase is observed at the AlN grain boundary. In contrast, when 3 wt.% Yb2O3 and 1 wt.% CAS glass are added, a continuous secondary phase is formed at the AlN grain boundary. The thermal conductivity decreases when the CAS glass is added, but the sintering density does not decrease. In particular, when 10 wt.% Yb2O3 and 1 wt.% CAS glass are added to AlN, the flexural strength is the highest, at 463 MPa. These results are considered to be influenced by changes in the microstructure of the secondary phase of AlN.

• Journal of the Korean Ceramic Society
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• v.29 no.12
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• pp.956-962
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• 1992

The predominant sintering mechanisms of low firing temperature ceramic substrate which consists of borosilicate glass containing alumina as a filler are the rearrangement of alumina particles and the viscous flow of glass powders. In this system, sintering condition depends on the volume ratio of alumina to glass and on the particle size. When the substrate contains about 35 vol% alumina filler and the average alumina particle size is 4 $\mu\textrm{m}$, the best firing condition is obtained at the temperature range of 900∼1000$^{\circ}C$. The extensive rearrangement behavior occurs at these conditions, and the optimum sintering condition is attained by smaller size of glass particles, too. The formation of cristobalite during sintering causes the difference of thermal expansion coefficient between the substrate and Si chip. This phenomenon degradates the capacity of Si chip. Therefore, the crystallization should be prevented. In the alumina filled borosilicate glass system, the crystallization does not occur. This effect may have some relation with aluminum ions in alumina. For aluminum ions diffuse into glass matrix during sintering, functiong as network former.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.177-177
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• 2009

이동통신 시스템의 소형화 경량화 다기능화 추세에 따라 세라믹 모듈의 정밀도 및 집적도가 중요한 요소로 부각되고 있다. 이러한 모듈의 고집적화 추세에 대응하기 위하여 세라믹 소성시 수축율 제어가 필수적인 요소로 부각되고 있으며, 이에 따라 X, Y축의 소성 수축율을 0에 근접하게 제어하는 무수축 소성 기술이 요구되고 있다. 선행연구를 통하여 $Al_2O_3$/Glass/$Al_2O_3$ 구조의 glass infiltration법에 의한 무수축 소성 기술 구현 가능성을 확인하였으나, 아직 해결해야 할 문제점들이 있다. glass가 $Al_2O_3$층으로 infiltration되는 과정에서 glass층이 de-lamination 되는 결함이 발견되었으며 이는 유전체 기판의 Q값을 낮추고 기판의 신뢰성에 악영향을 줄 수 있어 이에 대한 개선이 필요한 실정이다. 본 연구에서는 $Al_2O_3$/Glass/$Al_2O_3$ 구조의 glass infiltration법에 의한 선행 실험에서 관찰된 기판 내부의 de-lamination 현상에 대한 원인을 규명하고 해결책을 제시하고자 하였다. glass 유동과 바인더 burn-out이 동시에 진행됨에 따라 기공이 생성되며 glass가 점성유동함에 따라 이 기공이 glass층으로 모이게 되어 de-lamination 현상이 발생하는 것으로 사료된다. 이를 해결하기 위하여 de-lamination층에 $Al_2O_3$의 tamping을 시도하여 glass층의 기공이 빠져 나갈 수 있는 channel 을 형성하고, 남아있는 기공을 $Al_2O_3$로 채우는 효과를 얻을 수 있었다. 이에 따라 기판의 밀도와 Quality factor 값이 향상되었으며 미세구조가 치밀한 무수축 기판을 제작할 수 있었다.

• Journal of the Korean Ceramic Society
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• v.36 no.6
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• pp.583-589
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• 1999

In the fabrication of ceramic chip couples for high frequency application such as the mobile communication equipment the formation of electrode lines and Ag diffusion were investigated with heat treatment conditions for removing organic binders. The deformation and densification of the electrode line greatly depended on the binder burnout process due to the overlapped temperature zone near 400$^{\circ}C$ of the binder dissociation and the solid phase sintering of the silver electrode. Ag ions were diffused into the glass ceramic substrate. The Ag diffusion was led by the glassy phase containing Pb ions rather than by the crystalline phase containing Ca ions. The fact suggests that the Ag diffusion could be controlled by managing the composition of the glass ceramic substrate.