Page "Gel" Paragraph 31

A xerogel () is a solid formed from a gel by drying with unhindered shrinkage.

Xerogels usually retain high porosity ( 15-50 %) and enormous surface area ( 150 – 900 m < sup > 2 </ sup >/ g ), along with very small pore size ( 1-10 nm ).

When solvent removal occurs under hypercritical ( supercritical ) conditions, the network does not shrink and a highly porous, low-density material known as an aerogel is produced.

Heat treatment of a xerogel at elevated temperature produces viscous sintering ( shrinkage of the xerogel due to a small amount of viscous flow ) and effectively transforms the porous gel into a dense glass.