The Effect of Impregnation of Boric Acid on the Formation of Silica Structure
1994 Volume 67 Issue 4 Pages 217-222
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1994 Volume 67 Issue 4 Pages 217-222
In order to find the effect of boron impregnation on the formation of three dimensional network in the silica structure, silica sol containing boron was synthesized by hydrolysis of tetraethyl ortho silicate, and the viscosity of the sol was measured as a function of the passage of time. The viscosity of the sol containing boron was enhanced in a shorter time than that of the boron-free sol. It was indicated that the rate of polycondensation in the sol was accelerated by the presence of proton and borate ions which were formed boric acid [B (OH) 3].
Thin silica films were prepared on metal substrates from the differently aged sols, and FT-IRAS of those films was measured. An absorption band at 1400 cm-1, which is assigned to asymmetric B-O-B stretching vibration of trigonal boron, was observed in the boron-containing silica films. The intensity of the band was proportional to the boron concentration. On the other hand, an absoption band at 1065 cm-1, which was related to the formation of skeletal structure of silica, was not affected at all by the presence of boron. It was suggested that boron in the polycondensed silica formed some borates, such as diborate, tetraborate, and boroxol, which would stay independent of the silica skeletal structure.
A boiling treatment of the films in hydrochloric acid (pH 2) or water promoted pores in such films.
