Sodium faujasites, hydrated

Figure 4.7 The number of Al atoms per unit cell and the Si AI ratio versus a for hydrated sodium faujasites (from Dempsey [21]).

D. H. Olson (Mobil Research Development Corp., Princeton, N. J.) In view of the fact that the BF data for dehydrated Ca-exchanged faujasites show breaks agreeing with the position of the breaks shown by DKO for hydrated sodium faujasites, I think the suggestion that resiting of cations is responsible for the breaks can be ruled out. 

It is of interest to compare this figure with the heat of immersion of aluminum-rich faujasite. For a compound with composition NaggAlggSij 20384 one calculates -122.5 kJ/mol (4), which is mainly hydration energy of intra-channel sodium ions. 

When sodium is predominant, the faujasite structure crystallizes when potassium is the major cation, a zeolite of chabazite structure (ZK-14) is formed. Both of these structures can be built from hexagonal prisms as the only building blocks. Apparently the presence of the presumably smaller hydrated potassium ions allows a denser structure (chabazite) to crystallize. 

Faujasites are of particular importance for industrial catalysis. As do all zeolites, they exhibit ionic conductivity, by motion of the cations in the internal channel structure. The cationic mobility is considerable, as shown by Table IX. The conductivity of zeolites is greater than that of most other crystals. At a temperature of 25°C the diffusion coefficient of the sodium ion in hydrated zeolite is only three orders of magnitude smaller than that of simple ions in aqueous solution. The conductivity increases with temperature at 335°C the conductivity of the anhydrous zeolite is greater than that of the... 

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