Molecular Dynamics Simulation Studies on Thermal ExpansionBehavior of Siliceous Faujasite

Abstract

We have performed molecular dynamics (MD) simulations including the vibration of the zeolite framework for some siliceous faujasite (Si-FAU) under various temperatures. MD simulation was carried out with MXDTRICL program under NPT ensemble. The calculation well reproduced the structure of Si-FAU after the structural relaxation at 300K. Negative thermal expansion was found over the temperature range of 100 to 1100K. The liner thermal expansion coefficient was estimated as −2.94×10⁻⁶ K⁻¹, and this value was almost the same as the experimental value (−4.2×10⁻⁶ K⁻¹). The changes of ring size of 12-membered ring in Si-FAU against time or temperature was investigated. The average ring size of the 12-membered ring in Si-FAU was almost the same in the temperature range from 100K to 1100K, but the variation of ring size against time became large with increasing temperature. The maximum ring size increased with temperature until 1100 K and it is an interesting finding that the ring size expanded ca. 15% by the thermal vibration.