Compressibility, pressure-induced amorphisation and thermal collapse of zeolites

High-pressure powder diffraction is used to follow the collapse of zeolite-A at ambient temperature and this is compared with the exotherms obtained from differential scanning calorimetry, when collapse at ambient pressure is induced at high temperatures, Constraint theory is discussed in relation to these zeolitic densification processes and a simple model introduced. The fraction of floppy modes created during collapse is linked to the heat released when the zeolite collapses. It is argued that the pressure or temperature of collapse of the crystalline structure coincides with the rigidity percolation threshold and that amorphisation follows constraint reassembly.