On the drying of silica gels.

A procedure described for drying of sol-gel structures without cracking. The addition of a non-ionic surfactant in the material preparation is shown to be crucial to reducing the drying stresses developed by these high strain visco-elastic materials. Experiments are described which illustrate the effect of relative humidity on the drying rate and shrinkage of various samples under isothermal conditions. Surface temperature measurements indicate that evaporation occurs at approximately the wet-bulb temperature of the surrounding atmosphere. Acoustic detection of the internal strain activity during drying leads to the conclusion that control of the sol-gel surface tension is critical.