Abstract
Influence of water addition and catalysts such as HCl and NH4OH on the gel region and the gelation behavior of alkoxide solutions was examined in the B2O3-Na2O system. The resuls are as follows: (1) With the water addition r=0-1, where r=water added/water necessary for complete hydrolysis, gel region was found in the range of B2O3=60-90mol%. With water addition of r>1 gel region was reduced. Crystals precipitated with the addition of HCl. The gel region with NH4OH addition was the same as that observed with water addition. (2) Gelation time was reduced by water addition. No effect on gelation time was found by NH4OH addition. (3) From the measurements of pH and temperature rise in the B(OBu)3-NaOCH3 mixtures, it was inferred that sodium-borate precursors (complex) such as B(OBu)3(ONa) and B(OBu)3-n(ONa)n formed in the B(OBu)3-NaOCH3 mixtures. With water addition, the formation of hydroxide complex such as B(OH)3ONa and B(OH)3-n(ONa)n was also inferred.
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