Single-source-precursor synthesis of novel V8C7/SiC(O)-based ceramic nanocomposites

In the present work, novel V8C7/SiC(O) ceramic nanocomposites were synthesized upon thermal transformation of a polymer-derived single-source-precursor, which was obtained by the chemical modification of a polycarbosilane with vanadyl acetylacetonate. High-temperature treatment of the precursor in argon atmosphere first leads to an amorphous SiVOC single-phase ceramic which subsequently undergoes phase-separation, crystallization and finally converts into V8C7/SiC(O) ceramic nanocomposites. Interestingly, the high-temperature stability of V8C7/SiC(O) was shown to strongly depend on the oxygen content present either in the SiC(O) matrix or in the atmosphere during the annealing process. Thus, larger oxygen contents induce a conversion of the V8C7 phase into V5Si3. The specific surface area (SSA) of the obtained nanocomposite powders depends on the processing temperature: The SSA decreases from 64 to 4 m2/g as the pyrolysis temperature increases from 600 to 1300 °C, respectively. Whereas it increases again to ca. 50 m2/g as the sample is exposed to 1700 °C (6 h annealing), due to the evolution of CO. Preliminary results of the catalytic activity of the V8C7/SiC(O)-based materials show that they are active for the decomposition of the ammonia. The maximum ammonia conversion efficiency was found to be 35% at around 650 °C, which is higher than that of the pure vanadium carbide reported in the literature (ca. 13%).