Boron nitride by pyrolysis of the melt-processable poly[tris(methylamino)borane]: Structure, composition and oxidation resistance

Evolution of structure and composition of the melt-processable polytris(methylamino)borane] (PTMB) during its conversion to ceramics was studied by TGA, FTIR, Raman, XRD, XPS and elemental analysis (EA). The results show that the ceramic yield was greatly improved from 60.22 to 74.4 wt% at 900 °C by curing in NH₃ prior to pyrolysis. The carbon impurity in the precursor can be removed effectively in NH₃ whereas no similar result occurred in N₂. In NH₃, 93 wt% of carbon was removed at 600 °C and the carbon content in the pyrolyzed product at 900 °C was only 0.37 wt%. At the same time, the conversion from polymer to ceramics was almost completed at 900 °C. Moreover, the sample acquired at 900 °C was amorphous boron nitride (BN), while that of further annealing at 1600 °C showed characteristic of turbostratic BN (t-BN). Additionally, the BN with nearly stoichiometric composition exhibited good oxidation resistance even up to 900 °C in air.