J. Sjoblom et al., REACTION BETWEEN ALUMINUM NITRATE NONAHYDRATE AND TETRAETHOXYSILANE IN ETHANOL, Journal of dispersion science and technology, 16(1), 1995, pp. 31-50
The reaction between aluminum nitrate nonahydrate and tetraethoxysilan
e in ethanol was followed by NMR of the Si-29 nucleus. The results sho
wed the initial hydrolysis and condensation to be fast to an extent th
at no monomeric species of the silicon compounds were found after mixi
ng for three minutes. In addition, the results showed the condensation
reaction to be fast compared to the hydrolysis. This fact was demonst
rated by the extremely high ratio of ethoxy groups to OH groups in the
different specia (SiO)y Si(OH)x (OC2H5)4-x-yThe reaction proceeded wi
thout added acid and gave gels of silica with colloidally dispersed al
uminum nitrate. The protons to catalyze the reaction emanated from the
hydrated aluminum salt; titration by sodium hydroxide revealed the hy
drate to be a strong acid in ethanol with a titration point showing th
ree moles of base per mole of aluminium salt.