• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3483-3485
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• 2011

• 한국세라믹학회:학술대회논문집
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• 한국세라믹학회 2003년도 추계총회 및 연구발표회 초록집
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• pp.237.2-237
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• 2003

• 대한치과기공학회지
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• 제5권1호
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• pp.13-17
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• 1983

The experimental investication wax performed to study fitness of casting crowns with various investment widely used in Korea. 36 wax patterns were invested and casted according to the regular casting method. The result were as follow : 1. Casting with cristobalite investments of Shofu were seen apart, 0.04mm the tightest space in the linguo and bucco-cervical margin. And the largest deviation, 0.1mm was shown in the central groove 0.1mm was shown in the central groove area of occlusal surface(Jensen Metal) 2. Casting with cristobalite investments of kerr were seen apart, 0.04mm the tightest space in the linguo and bucco-cervical margin And the largest deviation, 0.09 was shown in the central groove area of occlusal surface(Jensen Metal) 3. Casting with Quartz investments of G-C were seen apart, 0.04mm the tightest space in the linguo-cervical margin, And the largest deviation, 0.1mm was shown in the central groove area of occlusal surface(Jensen Metal) 4. Casting with cristobalite investments of shofu were seen apart, 0.01mm the tightest space in the linguo-cervical margin, And the largest deviation, 0.03mm was shown in the central groove of occusal surface(Bo-sung A type gold alloy) 5. Casting with cristobalite investments of kerr showed the best fintness in linguo-cervical margin. And the largest deviation, 0.02mm was shown in the central groove area of occlusal surface(Bosung A type gold alloy) 6. Casting with Quartz investments of G-C were Seen apart, 0.02mm the tightest space in the linguo-cervical margin, And the largest deviation, 0.04mm was shown in the central groove area of occlusal surface(Bo-sung A type gold alloy) 7. Casting with cristobalite investments of shofu were seen apart, 0.01mm the tightest space in the linguo-cervical margin. And the largest deviation, 0.08mm was shown in the buccal cusp area of occlusal surface(Bo-sung B type gold alloy) 8. Casting with cristobalite investments of kerr shown the best fitness in linguo-cervical margin. And the largest deviation, 0.04mm was shown in the central groove atea of occlusal surface(Bosung B type gold alloy) 9. Casting with Quartz investments of G-C were seen apart, 0.03mm the tightest space in the linguo-cervical margin. And the largest deviation, 0.04mm was shown in the central groove area of occlusal surface(Bo-sung B type gold alloy) 10. Casting with cristobalite investments of kerr shown the best fitness and Bo-sung A type gold alloy showed the best fitness.

• 한국결정성장학회지
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• 제28권3호
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• pp.99-105
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• 2018

본 연구에서는 단결정 실리콘 제조수율에 영향을 미치는 것으로 알려진 석영도가니 표면의 불균일한 결정화를 피하기 위해, 결정화촉진제로 Ba이 포함된 코팅용액을 제조하여 분무열분해법으로 코팅 후, 열처리에 따른 석영도가니 표면의 결정화를 조사하였고, 다음과 같은 결과를 얻었다. 코팅하지 않은 도가니의 경우 온도가 상승함에 따라 $1350^{\circ}C$에서부터 결정화가 진행되는 것을 알 수 있었으며, $1450^{\circ}C$가 되어서야 균일하게 결정화가 되는 것을 확인하였으며, 결정상은 ${\beta}$-cristobalite로 확인되었다. Ba이 코팅된 도가니는 $1000^{\circ}C$부터 결정화가 진행되고 $1300^{\circ}C$에서 전체적으로 도가니 표면에 균일하게 결정화가 진행되는 것을 알 수 있었다. Ba이 코팅된 도가니는 결정상으로 ${\alpha}$-cristobalite와 침상 결정의 $BaSi_2O_5$이 생성되었다가 소멸하며, ${\beta}$-cristobalite 상이 최종적으로 균일한 결정상으로 남는 것을 알 수 있다.

• 한국세라믹학회지
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• 제17권4호
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• pp.197-202
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• 1980

The oxidation mechanism of the not sintered pellets and sintered bodies of $Si_3N_4$ was investigated. in air over the temperature range of 800~130$0^{\circ}C$. The $\beta$-cristobalite was instantaneously formed and covered the particles of powder packed in the not sintered and weakly sintered porous $Si_3N_4$ bodies by molecular diffusion of oxygen through the porous Si3N4 bodies and an immediate oxidation. The diffusion of oxygen ion through the formed $\beta$-cristobalite surface layer is assumed to control the further oxidation of the $Si_3N_4$ particles of the porous $Si_3N_4$ bodies. The diffusion coefficients and activation energies of oxygen ion through the $\beta$-cristobalite layer were obtained by the use of a derived equation.

• 자원환경지질
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• 제32권4호
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• pp.399-409
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• 1999

Mullitization of kaolinite and dickite was examined with special attention to the influence of polytypism and impurities on the phase transformation. The phase transformation sequence in dickite is identical with that in kaolinite except that cristobalite is crystallized at $50^{\circ}C$ higher temperature in dickite. Difference in phase transformation above $1000^{\circ}C$ in kaolin minerals is attributed to the different crystal structures of metadickite and metakaolinite on the effect of impurities. A part of quartz is transformaed into cristobalite. Spinel-type phase produced in disordered kaolins including illite occurs over a short range of temperatures. Primary mullite is transformed into orthorhombic mullite at higher temperature as well. These results sustain the idea that disintegration of methkaolin and the spinel-type phase supplies extra sillica and promotes the growth of mullite cristobalite.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.521-526
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• 2007

Density functional calculations have been performed for the reactions of perfluoroalkylsilane and alkylsilane with silica surfaces. The (100) and (111) surfaces of ${\beta}-cristobalite$ are used as two possible models of the hydroxylated amorphous silica surface. This is the crystalline phase of silica with density and refractive index closest to those of amorphous silica. Moreover, two ${\beta}-cristobalite$ surfaces have the two types of silanol groups, namely the single silanols and the geminal silanols. We investigate the possible adsorption structure and formation energy of perfluoroalkylsilane and alkylsilane molecules with two type of silanol groups. The results will be compared with cluster and slab model.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권9호
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• pp.641-647
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• 1999

The paper provides the results of microstructure analysis and dielectricproperties of porcelain suspension insulators. The evaluation of characteristics was also made as a function of the manufacturers and fabricated years for the experimental specimens which had been used in real distribution lines. Even though the series A contained higher alumina contents than the series B, the densification of series A was lower than that of series B, resulting from much porosity. The microstructure investigation confirmed that series A had much porosity than series B. The series A contained quartz $(SiO_2),\; mullite\; (Al_6Si_2O_{13}),\; corundum(Al_2O_3),\; and cristobalite\; (SiO_2)$ phases. However, the series B had no cristobalite phase which had very high thermal expansion coefficient. Also, the tan$\delta$of series A was more abruptly increased than that of series B as increasing temperature. The elevated temperature may make much expansion of cristobalite crystal than other crystals, resulting in crack and puncture inside cap during the summer days.

• 한국세라믹학회지
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• 제32권5호
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• pp.626-634
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• 1995

SiC를 51.9wt% 함유한 SiC-자기질 혼합 분말이 자기 코아의 표면연마 공정에서 부산물로 발생한다. 이 원료 분말을 SiC질 세라믹스를 제조하기 위한 출발물질로 하였다. 원료자체로 성형 $1350^{\circ}C$에서 열처리하면 SiC, $Al_{2}O_{3}$, cristoblite, mullite 결정상이 존재하면 미세구조는 SiC 입자를 유리질 매트릭스가 덮고 있고 구형 기공이 존재한다. 원료 성형체를 열처리시 시편 무게 증가에 의해 판단되는 SiC의 산화는 600~$800^{\circ}C$ 범위에서 시작하나 XRD 분석에 의해서는 $1000^{\circ}C$ 열처리에 이르러서야 $SiO_{2}$의 cristobalite 결정상을 확인하였다. 예비 열처리 후에 소성한 시편은 mullite화 반응이 촉진되는데, $1000^{\circ}C$의 예비 열처리 후 $1350^{\circ}C$에서 소성한 시편은 SiC, cristobalite, mullite가 결정상으로 존재하며, 밀도 2.24g/$cm^{3}$, 흡수율 11.73%이고 유리상이 적고 다공성인 미세구조를 갖는다. 원료 자체에서 51.9wt%이던 SiC 함량은 $1350^{\circ}C$ 소성시편에서는 예비 열처리 조건에 따라 약 37~22%로 감소한다.

• 한국자원리싸이클링학회:학술대회논문집
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• 한국자원리싸이클링학회 2004년도 춘계임시총회 및 제23회 학술대회
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• pp.155-158
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• 2004

본 연구에서는 공냉(空冷)된 화력발전소 바닥재의 입도분포, 화학조성, 광물상 등 기초 특성과 압축강도비에 의해 포졸란 반응성을 측정하였다. 바닥재의 주요 성분은 $SiO_2$, $Al_2O_3,\;Fe_2O_3$로 이들의 합계가 91.2wt.%였으며, 주요 광물상은 mullite, quartz, cristobalite, tridymite, hematie 등이었다. 입도별 화학조성 변동은 거의 없었으나, 입도가 커짐에 따라 $SiO_2$는 quartz에서 cristobalite로 존재하는 비율이 증가하였다. 분쇄된 바닥재(blame 비표면적 $7,540cm^2/g$)의 양생 28일에서의 활성도 지수는 101을 나타내었다.