Mechanism of H₂O Insertion and Chemical Bond Formation in AlPO₄‑54·xH₂O at High Pressure

The insertion of H₂O in AlPO₄-54·xH₂O at high pressure was investigated by single-crystal X-ray diffraction and Monte Carlo molecular simulation. H₂O molecules are concentrated, in particular, near the pore walls. Upon insertion, the additional water is highly disordered. Insertion of H₂O (superhydration) is found to impede pore collapse in the material, thereby strongly modifying its mechanical behavior. However, instead of stabilizing the structure with respect to amorphization, the results provide evidence for the early stages of chemical bond formation between H₂O molecules and tetrahedrally coordinated aluminum, which is at the origin of the amorphization/reaction process.