Drying Behavior of Colloidal Silica Gels

Observations of the drying behavior of thick-wall colloidal silica gel structures are reported. Various techniques are examined to prevent cracking during the drying of these highstrain viscoelastic materials. Experiments are described which illustrate the effect of relative humidity on the drying rate and on the 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 in the material preparation is crucial to reducing the interior stresses.