Sol-gel derived SiO₂ glass objects are of interest because of their high purity. However, cracking of wet gels during drying, or of dried gels during hydrocarbon removal and sintering, are the main obstacles preventing the commercialization of this process. These difficulties can be overcome using gels with high strength and large pores. In this study, gels were prepared using Si(OC₂H₅)₄, C₂H₅OH, H₂O and acidic catalysts. The strength, shear modulus, microstructure, drying and sintering behavior of these gels were investigated as functions of catalyst type and aging time. Experiments indicate that the modulus of rupture must be high enough to overcome drying stresses. In addition, the shear modulus must be high enough so that the gels are sufficiently stiff to prevent bending during drying. Repetitive and reliable drying of relatively large gels (D equals 8 - 10 cm, L equals 40 cm) was achieved within a week. However, to obtain crack-free sintered glasses the xerogels must have larger pores (pore radius > 40 angstrom). This is required for easy removal of organic groups at 200 - 500 degree(s)C and of chemically bonded hydroxyl or silanol groups at 800 - 1200 degree(s)C.

Date Published: 13 October 1994
PDF: 8 pages
Proc. SPIE 2288, Sol-Gel Optics III, (13 October 1994); doi: 10.1117/12.189008

Published in SPIE Proceedings Vol. 2288:
Sol-Gel Optics III
John D. Mackenzie, Editor(s)