Accurate measurement of the thermal expansion of MFI zeolite membranes by in situ HTXRPD

Template removal by calcination of MFI type membranes is often accompanied by crack formatìon. The thermal behavior of MFI type membranes, synthesized with and without masking, was studied to understand the mechanìsm. Masking prevents growth of zeolite in thè interior of the support during membrane synthesis. Rietveld refìnements of powder diffraction data collected in situ at high temperature allowed to accurately determine the change in thermal expansion of thè MFI film and thè porous a-alumìna support. During heating, a relatively large contraction of the celi volume during template removal occurred in thè zeolite powder and in thè film of thè membrane prepared with masking. The much smaller decrease in thè non-masked sample indicates that this membrane is under stress during heating and as a consequence, cracks are formed. The stress imposed in the membrane prepared without masking may be due to the opposite thermal behavior of the substrate in combination with strong bonds between thè membrane and thè support.