Articles & Issues

Conflict of Interest: In relation to this article, we declare that there is no conflict of interest.

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

All issues

솔-젤법에 의한 석영유리의 제조-I. 초음파를 이용한 젤의 제조

Manufacture of Silica Glass by Sol-Gel Process-I. Manufacture of Sonogels

임재곤 고영표 이건흥 이시우

Lim JG Koh YP Lee KH Rhee SW

HWAHAK KONGHAK, December 1992, 30(6), 657-663(7), NONE

Download PDF

Abstract

초음파를 사용한 2단계 솔-젤 공정을 사용하여 젤을 제조하고, 공정 변수들이 젤화시간 및 젤의 미세구조에 미치는 영향들을 조사하였다. 본 연구에서 얻어진 최적 조건은 다음과 같다:pH2.7로 유지된 TEOS 1몰과 H₂O 10몰의 혼합용액에 500J/ml의 초음파를 10분간 가한 후, NH₄OH를 첨가하여 pH4.7로 만들어 주어 약 6분만에 균일하고 투명한 젤을 얻었다. pH의 편차가 지나치게 클 때에는 촉매의 편재에 의하여 젤에 균일이 발생하였다. 중압반응의 pH가 증가하면 젤화시간은 감소하며, pH5.4 이상에서는 10초 이하의 젤화시간이 관찰되었다. H₂O와 TEOS의 몰비가 10이 될 때까지는 젤화시간이 감소하나, 그 이상에서는 희석효과에 의하여 젤화시간이 증가하였다. 초음파에너지의 증가는 젤의 입자와 평균기공의 크기를 감소시켰다. Sonogel은 normal gel보다 입자 및 기공의 크기가 작으며, 좁은 기공크기 분포를 나타내었다. 증발건조는 부피의 감소와 미세구조의 변화를 수반하는데 반하여, 초임계건조는 wet 젤의 구조를 유지하며 건조할 수 있게 하므로 wet젤의 미세구조 관찰을 위해서는 초임계 건조된 샘플을 사용하여야 한다.

Gels were manufactured by the 2-step sol-gel process with ultrasonic wave mixing. The effects of process variables on the gelation time and the microstructure of gels were investigated. The optimum process conditions obtained were : solution of 1mole TEOS and 10 mole H₂O, hydrolysis pH=2.7, condensa-tion pH=4.7, ultrasonic energy=500J/ml, ultrasonic mixing time of 10 minutes, and gelation time of 6 minutes. Cracks on the gels occured when the difference on pHs of hydrolysis and condensation steps was too large due to the localization of catalysts. Increase of the pH in condensation step decreased the gelation time, and less than 10 seconds of gelation time was observed above pH 5.4. The gelation time decreased up to 10 of H₂O/TEOS mole ratio, but it increased thereafter due to the dilution effect of water. The increase of ultrasonic energy reduced the size of particles and pores in the gel. Compared with normal gels, sonogels had smaller particles, smaller average pore size, and narrower pore size distribution. Since supercritical drying retains the microstructure of wet gels while evaporation drying significant changes the volume and microstructure of them, supercritically dried samples are recommended for observation of microstructures of wet gels.

Keywords

References

임재곤, 이건홍, 이시우, 요업재료의 과학과 기술, 5, 113 (1990)
Hench LL, Ulrich DR, "Ultrastructure Processing of Ceramics, Glasses, and Composites," John Wiley & Sons, New York, p. 15 (1984)
Hench LL, Ulrich DR, "Science of Ceramic Chemical Processing," John Wiley & Sons, New York, p. 52 (1986)
Mizuno T, Nagata H, Manabe S, J. Non-Cryst. Solids, 100, 236 (1988)
Brinker CJ, Clark DE, Ulrich DR, "Better Ceramics through Chemistry," North Holland, New York, p. 301 (1984)
Boonstra AH, Bernards TNM, J. Non-Cryst. Solids, 105, 207 (1988)
Boonstra AH, Mulder CAM, J. Non-Cryst. Solids, 105, 201 (1988)
Brinker CJ, J. Non-Cryst. Solids, 100, 30 (1988)
Tarasevich M, Am. Ceram. Bull., 63, 500 (1984)
Ramirez-del-Solar M, de la Rosa-Fox N, Esquivias L, Zarzycki J, J. Non-Cryst. Solids, 121, 40 (1990)
Mason TJ, "Chemistry with Ultrasound," Elsevier, Amsterdam, p. 6 (1990)
Iler RK, "The Chemistry of Silica," John Wiley & Sons, New York (1979)
de la Rosa-Fox N, Esquivias L, Craievich AF, Zarzycki J, J. Non-Cryst. Solids, 121, 211 (1990)
Aegerter MA, Jafelicci M, Souza DF, Zanotto ED, "Sol-Gel Science and Technology," World Scientific, Singapore, p. 153 (1989)
Strazhesko DN, "Adsorption and Adsorbents," John Wiley & Sons, New York, p. 55 (1973)
Hench LL, Ulrich DR, "Ultrastructure Processing of Ceramics, Glasses and Composites," John Wiley & Sons, p. 43 (1984)