ISSN:
1573-4854
Keywords:
sol-gel
;
silica
;
particle size
;
xerogels
;
surface area
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract The acid catalyzed hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the absence of alcohol was studied using cylindrical internal reflectance Fourier transform infrared (CIR-FTIR) spectroscopy at four temperatures. Special attention was given to the low-frequency band around 940 cm-1 and its evolution corresponding to the changing silicic acid concentration. This method compared well with other published methods for studying condensation kinetics. Three different conditions for gelation were used to determine temperature and humidity effects on resultant gels. In addition, effect of reaction temperature on gel porosity and surface area was studied. Sols that were gelled at high humidity (84–96% R.H.) and room temperature, 22–24°C, had a much higher surface area and porosity than those gelled at low humidity (5–50% R.H.) and room temperature, 22–24°C, whereas sols gelled at high humidity (79–98% R.H.) and low temperature, 7–8°C, had an intermediate surface area and porosity. Temperature of hydrolysis and condensation reactions did not have a significant effect on surface area. It is proposed that differences in surface area and porosity are mainly caused by the rate of solvent evaporation. Rapid evaporation of solvent and quick gelation of the low humidity samples results in a close-packed microporous xerogel. This is in contrast to the slow gelation and increased available time for condensation in the higher humidity samples, resulting in a more open structure.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1009682117946
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