Journal of Sol-Gel Science and Technology

, Volume 8, Issue 1–3, pp 165–171 | Cite as

Interaction of Formic Acid with the Silica Gel Network

  • Kenneth G. Sharp
  • George W. Scherer


Silica gels can be made by direct reaction of formic acid with tetraethyl orthosilicate. We have characterized wet gels of this type using a beam-bending technique that yields the elastic modulus, Poisson's ratio, viscoelastic relaxation function, and permeability. When the experiment is performed in ethyl formate, the silica network behaves in an elastic fashion; the permeability is low (<1 nm2), indicating a pore radius of <4.3 nm. The capillary pressure generated in such small pores is estimated to be sufficient to cause collapse of the pores during drying, which would account for the observed ultramicropores in this type of gel. When the pore liquid contains formic acid, viscoelastic relaxation is relatively rapid. Studies of cyclosiloxane compounds indicate that formic acid can attack only the strained siloxane bonds of the network, which would account for the relaxation behavior. Aging in formic acid causes rapid initial shrinkage, because formic acid accelerates condensation of silanols, which drives syneresis; the modulus increases and the permeability decreases monotonically, so there is no indication of coarsening during aging in formic acid, even at 70°C.

aging syneresis shrinkage formic acid viscoelasticity permeability pore size modulus 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    K.G. Sharp, J. Sol-Gel Sci. Tech. 2, 35–41 (1994).Google Scholar
  2. 2.
    G.W. Scherer, J. Sol-Gel Sci. Tech. 2(1/2/3), 199–204 (1994).Google Scholar
  3. 3.
    G.W. Scherer, J. Non-Cryst. Solids, 142(1/2), 18–35 (1992).Google Scholar
  4. 4.
    G.W. Scherer, J. Sol-Gel Sci. Tech. 1, 169–175 (1994).Google Scholar
  5. 5.
    G.W. Scherer, Bending of Gel Beams: Effect of Deflection Rate and Hertzian Indentation, accepted for publication in J. Non-Cryst. Solids.Google Scholar
  6. 6.
    TAPP Thermochemical and Physical Properties (ES Microware, 2234 Wade Court, Hamilton, OH 45013, USA).Google Scholar
  7. 7.
    G.W. Scherer, Relaxation in Glass and Composites (Wiley, New York, 1986; Krieger, Malabar, FL, 1992), pp. 41–43.Google Scholar
  8. 8.
    S. Hæreid, J. Anderson, M.A. Einarsrud, D.W. Hua, and D.M. Smith, J. Non-Cryst. Solids 185, 221–226 (1995).Google Scholar
  9. 9.
    G.W. Scherer, J. Sol-Gel Sci. Tech. 2(1/2/3), 199–204 (1994).Google Scholar
  10. 10.
    R.K. Iler, The Chemistry of Silica (Wiley, New York, 1979) p. 42.Google Scholar
  11. 11.
    J.L. Dandurand and J. Schott, J. Solution Chem. 16(3), 237–256 (1987).Google Scholar
  12. 12.
    K.G. Sharp, U.S. Patent 5,412,016, issued to DuPont Co., May 2, 1995.Google Scholar
  13. 13.
    J. Happel and H. Brenner, Low Reynolds Number Hydrodynamics (Martinus Nijhoff, Dordrecht, 1986).Google Scholar
  14. 14.
    G.W. Scherer, J. Sol-Gel Sci. Tech. 1, 285–291 (1994).Google Scholar
  15. 15.
    D.M. Smith, G.W. Scherer, and J.M. Anderson, J. Non-Cryst. Solids 188, 191–206 (1995).Google Scholar
  16. 16.
    G.W. Scherer, D.M. Smith, X. Qiu, and J.M. Anderson, J. Non-Cryst. Solids 186, 316–320 (1995).Google Scholar
  17. 17.
    G.W. Scherer, S. Hæreid, E. Nilsen, and M.-A. Einarsrud, Shrinkage of Silica Gels Aged in TEOS (to be published).Google Scholar

Copyright information

© Kluwer Academic Publishers 1997

Authors and Affiliations

  • Kenneth G. Sharp
  • George W. Scherer

There are no affiliations available

Personalised recommendations