Molecular Simulation of Thermal Destruction Processes in Aluminophosphates

The thermal destruction process of AlPO₄-5 and VPI-5 was investigated by using molecular dynamics and computer graphic methods. The mobility of atoms in AlPO₄-5 was increased and the framework became unstable as the temperature increased. Finally the framework transformed into an amorphous phase. During this process, bonds between Al and O were frequently broken or formed, P-O bonds were, however, scarcely changed. This indicates that the Al-O bond in the framework is weaker than the P-O bond. AlPO₄-5 has only one T (T = Al or P) site, whereas three crystallographically distinct T sites are located in VPI-5. Thus, we also investigated dynamic differences between Al atoms located in distinct T sites during the thermal destruction process of VPI-5. It was found that Al-O bonds formed by Al atoms at the T 1 site are most apt to be broken.