Polymer-derived SiBCN ceramic and their potential application for high temperature membranes

A novel preceramic polymer suitable to form a SiBCN ceramic was synthesized by hydroboration reaction of 1,3,5-trivinyl-1,3,5-trimethyl-cyclotrisilazane with borane dimethylsulphide. The obtained polymer denoted as poly (borosilazane) was characterised by FT-IR and NMR spectroscopy and its thermal stability was studied by thermal gravimetric analysis in combination with in situ mass spectrometry (TG/MS). The polymer-to-ceramic transformation was achieved at 1050 degrees C in inert argon atmosphere yielding black and X-ray amorphous SiBCN ceramics thermally stable up to 1800 degrees C. Using the dip-coating technique, a SiBCN ceramic thin film was formed on a porous alumina substrate. N-2 sorption isotherm analysis revealed that the thin film contained a small amount of micropores of about 0.6 nm in diameter, as well as mesopores between 2.7 and 6 nm in size. The total pore volume was found to be about three orders of magnitude smaller than that of a hydrogen permselective amorphous silica membrane derived from polysilazane. These results indicated potential application of the SiBCN thin film as a molecular sieve membrane suitable for high-temperature separation of small gas molecules like hydrogen below 0.3 nm in size.