High temperature ceramics for use in membrane reactors: the development of microporosity during the pyrolysis of polycarbosilanes

The pyrolysis of polycarbosilane (PCS), a ceramic precursor polymer, at temperatures up to 700 degreesC under an inert atmosphere results in the development of amorphous microporous materials which have a number of potential applications, such as gas separation membranes. This paper investigates the development of microporosity during pyrolysis under nitrogen, at temperatures ranging from 300 to 700 degreesC, of both the cross-linked and non-cross-linked starting materials. The products are characterised by nitrogen adsorption, to determine surface areas and pore volumes, solid-state NMR, electron microscopy and FTIR, and their formation is studied using thermal analysis and evolved gas analysis with on-line mass spectrometry. The cross-linked and non-crosslinked PCSs have a maximum micropore volume of 0.2 cm(3) g(-1) at pyrolysis temperatures of between 550 and 600 degreesC. The microporosity is stable in air at room temperature, but is lost in oxidising atmospheres at elevated temperatures.