(307d) Fabrication of SiC-Type Films Using Low-Energy Plasma Enhanced Chemical Vapor Deposition (PECVD) and Subsequent Pyrolysis for Membrane Gas Separation Applications

The ability to efficiently separate hydrogen (H₂) under high temperature and pressure steam reforming (SR) conditions is important for the further development of clean energy sources. Nanoporous silicon carbide (SiC) materials have been shown to possess excellent H₂ separation properties, and unlike conventional polymeric membranes, they are able to function under the extreme SR conditions. In addition, Si-based membranes do not have H₂ embrittlement and sulfur (S) poisoning issues that plague competitive Pd-based metallic membranes. Solution-phase techniques have long been used to deposit precursor films prior to pyrolysis into SiC, but they tend to face difficulties with substrate compatibility and the use of toxic solvents. In this study, we introduce a solventless synthesis route for fabricating SiC-type films by depositing an organosilicon copolymer poly(vinylphenyldimethylsilane-co-divinylbenzene) (p(VPDMS-co-DVB)) film using low-energy plasma chemical vapor deposition (PECVD) followed by subsequent pyrolysis. We have selected in our studies a monomer (VPDMS) and a crosslinking agent (DVB) for preparing the pre-ceramic polymer materials with no oxygen in their structure, which makes them appropriate to use to fabricate SiC-type films upon pyrolysis. The chemical structure of the film was systematically studied in-situ during pyrolysis as a function of temperature using Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS). The majority of the functional groups were found to have disappeared by a temperature of 800 °C, with most of the mass loss occurring between 350 °C and 520 °C. Thermogravimetric Analysis (TGA) was used to measure the loss of mass as the pyrolysis temperature was increased, and the observed pyrolysis rates were compared to estimates of such rates from the DRIFTS analysis. A flat support composed of silicon carbide powders was tested for membrane preparation. Our proposed synthesis route provides a scalable and solventless method of producing SiC-type ceramic films for such applications as high-temperature sensors and membranes.

Keywords: Silicon Carbide, Chemical Vapor Deposition, Pyrolysis, Hydrogen separation