Modification of perhydropolysilazane with aluminum hydride: Preparation of poly(aluminasilazane)s and their conversion into Si-Al-N-C ceramics

Perhydropolysilazane (PHPS) was modified with trimethylamine-alane adduct, AlH₃·NMe₃, with two nominal Si/Al molar ratios (1 and 5), and the resulting poly(aluminasilazane)s were pyrolyzed under an N₂ atmosphere. Poly(aluminasilazane) with a nominal Si/Al molar ratio of 5 (PAS5) was insoluble because of the formation of cross-link points via dehydrocoupling. In the system with a nominal Si/Al molar ratio of 1 (PAS1), on the contrary, AlH₃·NMe₃ cleaved the Si-N bonds in addition to forming Al-N bonds, drastically modifying the Si-N backbone of PHPS. In addition, a large portion of aluminium was lost in the PAS1 preparation. Thermogravimetric analysis revealed that PAS5 exhibited a ceramic yield of 78% up to 900 °C, while the ceramic yield for PAS1 was 61%. The XRD patterns of the pyrolyzed residues from PAS1 and PAS5 suggest the formation of a 2H wurtzite-type compound and silicon nitride.