Firing membranes

Thermal processing is commonly employed to alter the chemistry and microstructure of membrane layers. It can shape, strengthen, and give functionality to a membrane. A good understanding of the processes taking place during the thermal processing of a membrane material allows for optimization and tuning of the membrane properties. This thesis reports on the analysis of a broad array of thermal processing steps applied to typical membrane materials. The processing steps are tailored to the different inorganic, organic, and hybrid materials included in this study. For silicon carbide, a treatment at very high temperatures of over 2000 °C was determined to be crucial for obtaining fibers with sufficient mechanical strength for application as a membrane or membrane support. For glassy silica and organosilica materials, it is shown that the inorganic material is more prone to fracturing than its hybrid counterpart. If fracturing during drying can be prevented, however, it has been demonstrated that these films can be calcined rapidly, decreasing the processing time for these microporous membranes by over a factor 20. A kinetic analysis of this thermal processing step aids in explaining the phenomenon taking place during thermal processing, and allows for describing and predicting the effects of a generic temperature program on these materials. An optimized temperature calibration method for thermo-ellipsometric analysis allowed for studying reactions in thin films of sulfonated poly(ether ether ketone) (SPEEK) and poly(POSS imide)s. For SPEEK, it has been found that prolonged exposure to elevated temperatures causes desulfonation and degradation reactions to take place. The onset of this process was found at lower temperatures than previously known. The thermal imidization of poly(POSS-imide)s has been assessed and was found to follow a kinetic pathway distinct from their organic counterparts. By varying the length of the organic linker groups, changes in the structure of the material can be tuned. In the end, some general rules are given to offer guidance on the different approaches that can be followed to study the thermal processing of membrane materials.