A comparative study of fibrous zeolites under pressure

A comparative study on lattice compressibility, structural deformation mechanisms and the role played by the framework (Si/Al distribution, cross-linking of the building unit chains) and extra-framework content on the high-pressure behaviour of fibrous zeolites is reported. The structural analogy in the fibrous zeolite group, due to the 4 = 1 secondary building unit (SBU), induces similar elastic behaviour and a 'fibrous zeolite (FZ) average bulk modulus' can be calculated:K (sub T0) (Ba-FZ) >K (sub T0) (Ca-FZ) > K (sub T0) ((Ca +Na)-FZ) > K (sub T0) (Na-FZ). The experiments on natrolite, scolecite, edingtonite and thomsonite show that the elastic anisotropy, represented by the axial bulk moduli, is strongly influenced by the tetragonal topological symmetry. The high-pressure structural refinements performed show one main deformation mechanism for all these zeolites: the cooperative rotation (anti-rotation) of the SBU. This mechanism greatly reduces the free volume of the eight-membered ring channels, parallel to the SBU-chain direction.