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 uC 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 uC, of both the cross-linked and noncross-
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 cm3 g21 at pyrolysis temperatures of between 550
and 600 uC. The microporosity is stable in air at room temperature, but is lost in oxidising atmospheres at
elevated temperatures.