In-situ small angle X-ray scattering (SAXS) – A versatile tool for clarifying the evolution of microporosity in polymer-derived ceramics

While conventional structural characterization techniques such as gas physisorption have been highly useful in gaining important insights into the general evolution of transient microporosity during the pyrolytic conversion of polymer-derived ceramic materials, they are quite limited in delivering information on the state of ongoing processes, and are prone to biases introduced by external factors; furthermore, systematic investigations to evaluate effects of various processing parameters are generally highly time-consuming. In this work, in-situ small angle X-ray scattering (in-situ SAXS) is employed as a methodological tool for monitoring and clarifying the structural evolution of polymer-derived ceramic materials during the actual polymer-to-ceramic conversion process, focusing on obtaining new insights into the emergence, transformation, and collapse of transient microporosity within these materials. In addition to presenting an experimental setup suitable for SAXS investigations up to 900 °C in inert (N2) or reactive (NH3) atmosphere, a mathematical model for extracting structural descriptors from SAXS data is applied, allowing for the monitoring of micropore size, micropore quantity, and other structural features as a function of temperature and environment during the actual pyrolytic conversion process. The feasibility of this approach for investigating the conversion of polymer-derived ceramics is demonstrated using two polysilazane-based model systems, in-situ SAXS delivering fundamental insights into the respective state of microporosity during the pyrolytic conversion. The results of in-situ experiments are consequently compared to conventionally obtained ex-situ data, the findings being in good agreement. The method presented shows significant potential in gaining further fundamental insights into processes taking place not only within the model systems used here, but is generally suited to achieve a better understanding of precursor-derived materials systems and their respective structural changes during pyrolytic conversion processes.