Degas Options For Micropore Samples

A degas study was conducted to determine the effectiveness of flow versus vacuum degas. An amorphous silica-alumina and a microporous zeolite were prepared by both techniques and then nitrogen isotherms were collected for both materials. The resulting isotherms established equivalence between vacuum versus flow degas.

Typical degas options include vacuum or flowing degas. The basic concept of degas is quite simple. The sample material is placed in an inert environment. This inert environment exploits chemical potential and creates a favorable state for an adsorbed molecule - perhaps water or carbon dioxide to shift from an adsorbed state to the inert environment. We can justify this theory by assuming a finite concentratio n of adsorbed molecules on the surface versus zero concentration in the inert environment. This assumption allows us to use Le Chatelier’s principle which establishes that the equilibrium must shift. Hence the adsorbed molecules will change concentration (desorb) to reach a new chemical equilibrium.

To assist the shift from the adsorbed molecule to an inert environment, the temperature of the surface may be increased. Increasing temperature will increase the rate of desorption. This establishes two key requirements of degassing:
1. Inert environment - shift from adsorbed phase to inert
2. Heat - increase the rate