Nanoporous Silicon Oxycarbonitride Ceramics Derived from Polysilazanes In situ Modified with Nickel Nanoparticles

Ni-polysilazane precursors were synthesized from polysilazane and trans[bis(2-aminoetanol-N,O)diacetato-nickel(II)]. The Ni-polysilazane precursors are superparamagnetic indicating formation of nanosized nickel particles (similar to 2-3 nm) confirmed by HRTEM as well. The as-obtained Ni-polysilazane precursors were thermolized at 700 degrees C and transformed to ceramic nanocomposites, manifesting a nanoporous structure, revealing a BET surface area of 215 m(2) g(-1), a micropore surface area of 205 m(2) g(-1), and a micropore volume of 0.113 cm(3) g(-1) Although Si-C-N-(O) ceramics derived from the native polysilazane are nonporous, the pronounced development of porosity in the Ni/Si-C-N (O) system was attributed to (i) the stabilizing effect of carbosilane bonds, which prohibit the formation of macropores during thermolysis; (ii) the reduced barrier for heterogeneous pore nucleation as a result of in situ created nickel nanoparticles; and (iii) the reduced viscous flow of the pores due to the presence of nickel nanopartides and turbostratic carbon. The formation of turbostratic carbon is due to the reactions catalyzed by nickel nanoparticles that result in graphene stacking as inferred from the STA-MS studies.