Effect of calcination and polycrystallinity on mechanical properties of nanoporous MFI zeolites

The mechanical properties of nanoporous pure-silica-zeolite (PSZ) polycrystalline MFI films-both as-synthesized and calcined, and assynthesized PSZ MFI single crystals are studied by nanoindentation using a Berkovich indenter. The indentation modulus and hardness of calcined seeded-growth MFI films are measured to be 3.6% and 21.8% lower than that of the as-synthesized films, respectively. The calcination process demonstrated a much higher influence on the hardness than the indentation modulus of the films. A simple mechanical analysis indicates that the calcined MFI film has a modulus of resilience of 36.6% lower than that of the as-synthesized MFI film. Furthermore, the indentation modulus and hardness of the as-synthesized MFI single crystals are measured to be 27.6% and 30.9% higher than those of the as-synthesized seeded-growth MFI film, respectively. The grain boundaries and interzeolitic defects seem to be the primary reasons for the lower mechanical properties of the polycrystalline films than those of the MFI single crystals. (C) 2006 Elsevier B.V. All rights reserved.