During tire last fifteen years the unique properties of a group of crystalline aluminosilicates have attracted increasing attention in scientific circles and in the chemical process industry. The synthesis and commercial manufacture of these crystalline aluminosilicates, called zeolites, constitutes one of the more sophisticated utilizations of crystallography in molecular science and chemical engineering.type A based on skeletal tetrahedra. Individual cations (Na+) are shown.
The new synthetic zeolite. Type A, is cubic, a" -12.32 A., and X-ray data are consistent with space group 01-Pm.'lni.The unit cell composition is Mei2/" ](A102)i2(Si02)i2]-fVH20 where Me is an exchangeable cation of charge n, and N varies from 20 to 30, The unit cell dimension varies slightly with the cation present. The aluminosilicate framework consists of 24(Si,Al)A), tetrahedra which are joined to form 8-membered oxygen rings in the faces and distorted 6-membeved rings on the 3-fold axes. A large cavity 11.4 A. in diameter occupies the center of the cell and smaller 6.6 A. cavities are located on the 3-fold axes.Probable positions of the cations in the lithium, sodium, thallium and calcium forms are indicated, and correlation of the structure with the adsorptive and ion-exchange properties of the Type A zeolite is discussed.
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