Critical Point Drying Autoclave

The critical point drying autoclave in the AFCAL Lab is used in one way of drying wet sol-gels.  Once the precursor chemicals are combined, they are left alone to sit and gel.  Once the liquid gels, the sol-gel is placed into a methanol bath.  After sitting in the methanol bath, the sol-gel is placed into the autoclave.  It is cooled to 4� C and filled with liquid CO₂.  The CO₂ is drained using a valve and replaced every 8-12 hours for 2-3 days.  This process removes the methanol from the sol-gel and replaces it with CO₂.  After the solvent exchange is complete, the autoclave is heated to about 40� C to raise the CO₂ to its supercritical point.  Once the high temperature is reached, the gasses are slowly released and an aerogel is made.