Critical path 51-55 heat removal

Since shrinkage and cracking are produced by capillary forces, Kistler [94] reasoned that those problems could be avoided by removing the liquid from the pores above the critical temperature (T ) and critical pressure (P ) of the liquid. As indicated in the phase diagram in Fig. 32, there is no longer any distinction between the liquid and vapor phases the densities become equal, there is no liquid-vapor interface and no capillary pressure. In the process of supercritical (or hypercritical) drying, a sol or wet gel is placed into an autoclave and heated along a path such as the one indicated in Fig. 32. The pressure and temperature are increased in such a way that the phase boundary is not crossed once the critical point is passed, the solvent is vented at a... 

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