%0 Journal Article
%T Structural evolution of silica sols modified with formamide
%A Lenza R.F.S.
%A Vasconcelos W.L.
%J Materials Research
%D 2001
%I ABM, ABC, ABPol, SBCC, SBCr, SBMM, SBPMat
%X In this work we investigated the influence of formamide on the acid-catalyzed sol-gel process by Fourier transform infrared spectroscopy (FTIR). Three silica sols were studied: Sol catalyzed with nitric acid without formamide, sol catalyzed with nitric acid containing formamide and sol catalyzed with a mixture of nitric acid and hydrofluoric acid and modified with formamide. Following the time evolution of both the Si-(OH) stretching vibration at around 950 cm-1 and the Si-O-(Si) vibration between 1040 cm-1 and 1200 cm-1 we were able to describe the structural evolution of each sol. The curve of evolution of Si-(OH) stretching vibration corresponding to sol A has a simple asymptotic evolution. In the case of formamide containing sol, we observed a two-step structural evolution indicating that for the system containing formamide the polymerization goes through a temporary stabilization of oligomers, which can explain the non-variation of the Si-O(H) bond wavenumber for a certain time. Gelation times were of several days for gels without formamide and few hours for gels containing additive. The presence of additive resulted in a highly interconnected gel.
%K sol-gel
%K formamide
%K FTIR
%K structural evolution
%U http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392001000300006