A study of nitridation process of polycarbosilane fibers by solid-state high-resolution NMR

Abstract

Results of the 298i NMR spectroscopy show that the nitridation of polycarbosilane fibers begins at about 500"C and is almost complete at about 7000C. It can be concluded that the C--Si and carbon bonds of polycarbosilane fibers are broken by heat-treatment at 630"C in N H 3 gas flow.Silicon nitride (Si--N) fibers have been prepared by the heat-treatment o f electron irradiation-cure polycarbosilane fibers in NH 3 gas flow [1,2[. The mechanical properties of the Si--N fibers are closely related to the nitridation process of the cured polycarbosilane fibers. Previously, we studied the nitridation process of polycarbosilane fibers without electron irradiation-cure using solid-state 29Si high-resolution NMR [3]. The nit¡ of the polycarbosilane begins from 500~ and is almost completed at 700~The mechanism involves the pyrolysis of polycarbosilane skeleton, OH3[ ' ~-- CH 2Si CH 2

Fabrication and Characterization of Short Silicon Nitride Fibers from Direct Nitridation of Ferrosilicon in N2 Atmosphere

“…Generally, Si 3 N 4 fibers can be commonly fabricated by pyrolysis of polymer precursors such as polysilazane (PSZ), polycarbosilazane (PCSZ) and polycarbosliane (PCS) [ 1 ]. Silicon nitride fibers were synthesized from the PCS by pyrolysis in ammonia gas atmosphere as early as in 1980s [ 7 , 8 ]. Si 3 N 4 fibers, nanowires and nanobelts can also be synthesized via carbothermal reduction and nitridation of diatomaceous earth [ 9 ] or rice husk ash [ 10 ] or silica nanopowders and silica gel [ 11 ], laser assisted chemical vapor deposition (LCVD) process [ 12 ], Ni-catalyzed chemical vapor deposition (CVD) process [ 13 ], directly reaction between silicon and ammonia [ 14 ] or with catalyst assist [ 15 ].…”