pore collapse during drying.

For some materials, the transition from a colloidal dispersion into a gel happens without the addition of crosslinking materials. For others, crosslinking materials are added to the dispersion to promote the strong interaction of the solid particles in order to form the gel. The gelation time depends heavily on a variety of factors such as the chemical composition of the precursor solution, the concentration of the precursor materials and additives, the processing temperature, and the pH. Many materials may