Abstract
In this work, the formation of transient microporosity during the polymer-to-ceramic conversion in polymer-derived ceramics was studied using a commercially available poly(vinyl)silazane precursor which was modified with divinylbenzene (DVB) as linker molecule during crosslinking. After pyrolysis treatments between 400 and 700 °C, the resulting materials not only showed distinct changes in elemental composition and structural features upon introduction of the linker molecule, but also a shift in micropore size, e.g. shifting from 0.84 nm to 0.70 nm after pyrolysis at 600 °C. Due to hindrance of transamination reactions in the low-temperature region, the nitrogen content in linker-containing samples was significantly higher, leading to a different composition of micropore-forming entities and, in case of the system studied, to smaller pores. These findings are a first step towards the clarification of the mechanisms leading to the pore formation in PDCs during pyrolytic conversion, which is essential for their use in prospective applications.
Highlights
Since environmental challenges have become more urgent and a central topic of public awareness in the last years, the need for more sustainable, energy-saving processes as well as the use of renewable energy have raised increasing public and industrial interest
In combi nation with Raman data, these results suggest that carbon clusters in PSZ-DVB materials are already present at temperatures ≤ 600 ◦C
A straightforward modification of the initial PSZ precursor network structure was successfully conducted through a hydrosilylation reaction using an overstoichiometric amount of DVB as linker, which was confirmed by elemental analysis as well as IR spectroscopy
Summary
Since environmental challenges have become more urgent and a central topic of public awareness in the last years, the need for more sustainable, energy-saving processes as well as the use of renewable energy have raised increasing public and industrial interest. A particular focus has been set on the development of new and well-tailored sepa ration and catalysis processes, accompanied by increasing technological requirements placed on the materials used. Ceramics fulfil these re quirements to a great extent, exhibiting superior chemical and hightemperature mechanical properties compared to conventionally used polymers or metals. Porous ceramics are promising candidates for ap plications as membrane or catalyst supports, where polymer- or metalbased structures are unsuitable due to the process conditions such as high temperature or harsh chemical environments. In sepa ration processes employing porous membranes, it is crucial to have a well-defined pore size in order to guarantee reliable and satisfactory selectivity. For an application in gas separation, the pore size has to be below 2 nm (and - per IUPAC definition – microporous [1]) to move from the low-selectivity Knudsen diffusion regime to micropore diffusion, yielding higher selectivities [2]
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