솔-젤법에 의한 석영유리의 제조-II. 초임계 건조 및 소결

임재곤; 고영표; 이건흥; 이시우

HWAHAK KONGHAK, Vol.31, No.1, 45-53, February, 1993

Export Citation

솔-젤법에 의한 석영유리의 제조-II. 초임계 건조 및 소결

Manufacture of Silica Glass by Sol-Gel Process II. Supercritical Drying and Sintering

임재곤, 고영표, 이건흥, 이시우

초록

2단계 sonogel공정에 의하여 제조된 젤을 초임계 건조하여 에어로젤을 만들고 이것을 소결하여 석영유리를 제조하였으며, 젤의 미세구조와 공정변수들 간의 상호관계들을 조사하였다. 초임계 건조의 용매로는 에탄올을 사용하였으며, 조업조건은 300℃, 1500psi로 고정하였다. 소결은 150℃, 300℃, 400℃, 600℃, 900℃ 및 1100℃에서 등온을 유지하며 진행하였으며, 분위기 가스로는 질소(<300℃), 산소(300℃-600℃) 및 헬륨(>600℃)를 사용하였다. 초임계 건조에는 약 8시간, 소결에는 약 17시간이 소요되었다. 에탄올을 사용한 초임계 건조는 젤의 표면을 소수성으로 만들어 물의 흡착을 최소화함으로 소결에 유리하였다. 너무 높은 초임계 건조온도는 입자의 수축을 가져와 오히려 소결에 불리하므로, 최적 초임계 건조온도가 존재하였다. 소결시 발생하는 부풀음을 방지하기 위해서는 150℃에서 수분을 충분히 제거해 주어야 하였다. 소결시 젤의 부피 변화는 1070℃까지는 완만하였으며, 1100℃에서 급격히 기공이 닫히며 소결이 완결되었다. 초임계 건조가 불완전하거나, 낮은 pH에서 제조된 젤은 소결에 의하여 결정이 생기는 것을 관찰하였다. 초임계 건조를 채택한 경우에는 wet젤의 구조가 소결의 조건에 큰 영향을 주었다.

Aerogels were manufactured by supercritical drying of the wet gel which was made using 2-step sonogel process and silica glass was obtained by sintering of these aerogels. Effect of the microstructure of aerogels on process variables was investigated. Ethanol was chosen as a supercritical drying solvent, and the operating condition was set to 300℃ and 1500psi. Sintering was performed with isothermal stags at 150℃, 300℃, 400℃, 600℃, 900℃ and 1100℃, and gaseous atmosphere was changed from nitrogen(<300℃) to oxygen(300-600℃) and helium(>600℃). It took about 8 hours in supercritical drying, and 17 hours in sintering. Supercritical drying with ethanol made the surface of aerogels hydrophobic, resulting in minimum adsorption of water on the surface. Since reduction of particles occurred due to high temperature during supercritical drying, optimum supercritical drying temperature must exist. Long isothermal stage at 150℃ eliminated bloating of sintered sample. The volume of aerogels reduced slowly up to 1070℃, but the pores were closed suddenly at 1100℃. Incomplete supercritical drying and low gelation pH produced crystals in sintering. The structure of wet gel had strong effect on the sintering conditions.

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[1] 고영표, 석사논문, 포항공과대학, 포항, Korea (1992)

[2] Zarzycki J, Prassas M, Phalippou J, J. Mater. Sci., 17, 3371 (1982)

[3] Hench LL, Ulrich DR, "Science of Ceramic Chemical Processing," John Wiley & Sons, New York, p. 52 (1986)

[4] Mizuno T, Nagata H, Manabe S, J. Non-Cryst. Solids, 100, 236 (1988)

[5] Lim JG, Koh YP, Lee KH, Rhee SW, HWAHAK KONGHAK, 30(6), 657 (1992)

[6] 이건홍, 이시우, 김춘호, 서항석, 에너지 R&D, 13, 197 (1991)

[7] Onorato PIK, Su SR, Am. Ceram. Bull., 64, 1342 (1985)

[8] Brinker CJ, Clark DE, Ulrich DR, "Better Ceramics through Chemistry II," North-Holland, New York, p. 237 (1986)

[9] Kennedy GC, Econ. Geol., 45, 629 (1950)

[10] Fricke J, "Aerogels," Springer-Verlag, Berlin, p. 57 (1986)

[11] Iura J, Kawaguchi T, Revue de Physique Appliquee, 24, 53 (1989)

[12] Laudish RA, Johnson DW, J. Non-Cryst. Solids, 79, 155 (1986)

[13] Brinker CJ, Clark DE, Ulrich DR, "Better Ceramics through Chemistry," North-Holland, New York, p. 47 (1986)

[14] Brinker CJ, Clark DE, Ulrich DR, "Better Ceramics through Chemistry," North-Holland, New York, p. 71 (1986)

[15] Paulaitis ME, Penninger JML, Gray RD, Davidson P, "Chemical Engineering at Supercritical Fluid conditions," Ann Arbor Science, Ann Arbor, p. 445 (1983)

[16] Boonstra AH, Baken JME, J. Non-Cryst. Solids, 109, 1 (1989)

[17] Hench LL, Ulrich DR, "Ultrastructure Processing of Ceramics, Glasses, and Composites," John Wiley & Sons, New York, p. 70 (1984)

[18] Ruvolo EC, Bellinetti HL, Aegerter MA, J. Non-Cryst. Solids, 121, 244 (1990)

[19] Kawaguchi T, Hishikura H, Iura J, Kokubu Y, J. Non-Cryst. Solids, 63, 61 (1984)

[20] Brinker CJ, Scherer GW, "Sol-Gel Science," Academic Press, Boston, p. 518 (1990)

[21] Yamane M, Inoue S, Yasumori A, J. Non-Cryst. Solids, 63, 13 (1984)

[22] Klein LC, "Sol-Gel Technology for Thin Films, Fibers, Preforms, Electronics, and Specialty Shapes," Noyes Publications, Park Ridge, p. 247 (1988)

[23] Aksay IA, Dabbs DM, Sarikaya M, J. Am. Ceram. Soc., 74, 2343 (1991)