A Spectroscopic Study of an Anhydrous Tetraethyl Orthosilicate-Boric Acid-Ethanol System |
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Authors: | Zha Congji Atkins GR Masters AF |
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Institution: | (1) Australian Photonics Cooperative Research Centre, Optical Fibre Technology Centre, The University of Sydney, Australian Technology Park, Eveleigh, NSW 1430, Australia;(2) School of Chemistry, The University of Sydney, NSW 2006, Australia |
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Abstract: | Hydrolysis and condensation reactions in an anhydrous sol-gel system comprising tetraethyl orthosilicate (TEOS, Si(OC2H5)4), boric acid (H3BO3) and ethanol have been studied using X-ray diffraction and NMR spectroscopy, and similarities and differences with the more traditional aqueous system are discussed. Boric acid is able to hydrolyse TEOS directly, and subsequent condensation reactions form borosiloxane (=B–O–Si) and siloxane (Si–O–Si) linkages. In an aqueous system, borosiloxanes are unstable to hydrolysis and are formed only upon heat treatment of the gel, a restriction avoided with anhydrous conditions. The anhydrous mixture is stable indefinitely against gelation, but can be readily gelled by addition of NaOH in ethanol. This system may be useful for preparing borosilicate glasses at lower temperatures with good homogeneity. |
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Keywords: | borosilicate sol-gel anhydrous system hydrolysis mechanism |
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