Micro‐/Macroporous Ceramics from Preceramic Precursors

Abstract

Porous silicon oxycarbide (SiOC) ceramics in particular bulk and cellular structures are produced via polymer pyrolysis. By using optimal pyrolysis parameters (i.e., heating rate, maximum temperature) the addition of either solid fillers or chemically active additives is efficient in preventing the collapse of pore structure and controlling pore formation through decomposition. Fast pyrolysis can lead to crack formation and a loss of specific surface area at temperatures above 600°C, whereas slow pyrolysis is able to preserve mesopores up to 1200°C combined with high surface areas. These SiOC ceramics with bimodal pore size distribution are potential candidates for adsorption/separation processes under severe conditions.

Investigation of photoluminescence of Si−O−C(−H) ceramics at an early stage of decarbonization by using high energy excitation

“…Increase in SSA is generally observed in pyrolysis process of silicone resin precursors, while a hydrogen atmosphere remarkably accelerates the SSA increase. 10,14 FT-IR spectra of the samples in a range of 4000-420 cm −1 were obtained by KBr pellet method with high sample concentrations. In the range of 2200-440 cm −1 , diffuse reflection method was adopted for samples diluted in KBr powder.…”

Processing of polysiloxane-derived porous ceramics: a review

“…• C combined with high surface areas [83]. The pore size and morphology of the cellular structures change with the addition of template materials.…”

“…The highly reactive nature of Si Cl bond in chlorine-containing polysilanes enables the cross-linking of polycarbosilanes to take place partly in the same temperature range where transformation of polysilanes to polycarbosilanes occurs [127]. Amine-catalyzed condensation of Si OH groups was used in cross-linking of polysiloxanes [80,81,83,84]. Kim et al cross-linked the expanded compacts of polysiloxane/ PMMA [74], extruded blends of polysiloxane/LDPE [69], and CO 2 -foamed blends of polysiloxane/mPE [95,100] by introducing aminoalkylalkoxysilanes as the condensation catalyst and subsequently annealing in air, prior to pyrolysis.…”

“…The foamed mixtures were subsequently pyrolyzed to produce porous ceramics [6,77,80,81]. Thus, SiC, SiOC and SiNC based porous ceramics were developed by direct co-foaming of preceramic polymers (usually silicone resin) mixed with PU precursors (polyols and isocyanates), the latter serve as blowing aids and structural templates [72,[80][81][82][83][84]. This method offers substantial flexibility in fabricating foams with the desired cell size, degree of cell opening, cell morphology, bulk density, thermal, elastic and mechanical properties using different types of PU precursors and ceramic/metallic fillers [6,82].…”

Mesoporous Si-B-N Ceramics from a Single Source Precursor via an Imide Gel

“…27,28 On the other hand, chemical reactions between the functional groups attached to the pore internal surface will generate attractive forces that bring about viscous flow of the polymer and consequent shrinkage of the pore size and therefore effective surface area. 28 As shown in the discussion above, the main processes that occurred at this temperature were the ammonolysis reactions of Si-NMe 2 with ammonia and condensation reactions between Si-NMe 2 , Si-NH 2 , Si-NH and Si-NH-B groups.…”