Synthesis and Characterization of Ceramic Membranes (W-Type Zeolite Membranes) Toraj Mohammadi * Department of Chemical Engineering, South Tehran Branch, Islamic Azad University, P.O. Box 11365-4435, Tehran, Iran Hojjatollah Maghsoodloorad Research Centre for Membrane Separation Processes, Faculty of Chemical Engineering, Iran University of Science and Technology, Narmak, Tehran, Iran In this article, effects of synthesis parameters (synthesis temperature, synthesis time, and number of layers) on W-type zeolite membranes synthesized over flat SUS supports for O 2 /SF 6 gas separation were experimentally investigated. Experiments were carried out at these levels of synthesis temperature: 165°C, 185°C, and 200°C; synthesis time: 6, 12, and 18 h and number of layers: 1 and 2. Permeation measurements, XRD and SEM analysis were used for characterization of the synthe- sized membranes. The results showed that increasing synthesis temperature from 165°C up to 185°C increases separation fac- tor of O 2 /SF 6 , however, further increasing decreases the separation performance. The same trend was observed for synthesis time for the single layer synthesized zeolite W membrane, although for the double layer synthesized zeolite W membrane, separation factor increased with increasing synthesis time. Repetition of layering has a net positive effect on separation factor of O 2 /SF 6 , and negative effect on permeation flux through the membranes. This behavior was attributed to the dual effect of synthesis temperature and synthesis time on selectivity. More zeolite crystals are deposited and larger crystals are formed at higher synthesis temperatures and longer synthesis times. Well W-type zeolite membrane was synthesized at 185°C for 18 h with two repeating layers with a high separation factor of 20.1. *torajmohammadi@iust.ac.ir © 2012 American Ceramic Society Int. J. Appl. Ceram. Technol., 1–11 (2012) DOI:10.1111/j.1744-7402.2011.02749.x