Tailoring the micro- and nanostructure of polymer-derived ceramic papers

Through the pyrolysis of cellulose-based paper templates infiltrated with a suitable polymer precursor, ceramic composites exhibiting a paper-like structure can be conveniently prepared. Such polymer-derived ceramic papers (PDCPs) unite the unique morphology of regular cellulose papers with the properties of the ceramic system utilized. Here, two paper templates, made from eucalyptus and cotton, respectively, were infiltrated with two polysilazane-based polymer precursors modified with either Fe, Ni, or Pd and converted into multi-phasic ceramic papers. In addition to the type of paper template, precursor composition, and transition metal used, the present study aims to rationalize the influence of pyrolysis temperature and atmosphere on the morphology, microstructure, and phase composition of the ceramic papers generated. For this purpose, scanning electron microscopy, SEM, and (scanning) transmission electron microscopy, (S)TEM, in conjunction with EDS analyses were used to elucidate the microstructural features of the ceramic composites in great detail. It is shown that the transition metals precipitate as nanosized metallic particles and silicides in the case of Pd and Ni, while the introduction of Fe features oxide and carbide phases in addition to that. Moreover, the metals catalyze both the graphitization of the cellulose fibers and, at higher temperatures, the generation of whisker-like Si-based nanostructures composed of either SiC or Si3N4, depending on the processing atmosphere used.