Changes in structure and in mechanical properties during the pyrolysis conversion of crosslinked polymethylsiloxane and polymethylphenylsiloxane resins to silicon oxycarbide glass

Mechanical and Surface-Chemical Properties of Polymer Derived Ceramic Replica Foams

“…At temperatures higher than 600 °C there are two further weight loss steps resulting from the split off of the phenyl- (maximum rate at ~600 °C) and methyl-groups (maximum rate at ~750 °C) from the SILRES® H62 C and SILRES® MK resin, respectively. These results are in good accordance with the literature as described above [9]. The pyrolytic gases consist mainly of benzene or methane, respectively [12].…”

“…These steps can be correlated to specific reactions that occur during the pyrolytic polymer-to-ceramic transformation in inert gas of crosslinked poly-organosiloxanes with methyl-, ethyl-, phenyl- or ethoxy-side groups. According to the literature these reactions are listed below [7,8,9,10,11,12,13,14,15,16,17]: < 400 °C: Formation and release of water and ethanol due to remained crosslinking active groups like Si–OH and/or Si–OC 2 H 5 ~550–1000 °C: Redistribution reactions involving the exchange of Si-O, Si-H and Si-C bonds with the release of volatile silicon compounds (e.g., Me 3 SiOSiMe 3 );~600–700 °C: Possible release of small amounts of higher linear or cyclic polysiloxanes and/or tetramethylsilanesRadical reactions and release of gaseous products with formation of an open porous network.In dependence of the bonded groups the following temperature steps are ascertainable: ~300–700 °C: Cleavage of Si–(C 6 H 5 ) bonds and release of benzene (for PhSiO 1.5 )~600–900 °C: Cleavage of Si–(CH 3 ) bonds and release of methane (for MeSiO 1.5 )~600–1100 °C: Dehydrogenation > 800 °C: Formation of aromatic carbon/ free carbon> 1000 °C–1600 °C: Enrichment of SiO 4 - and SiC 4 -units and precipitation of nanocrystals of SiO 2 and SiC due to further chemical bond redistribution> 1200 °C–1500 °C: Carbothermal reduction of SiO 2 and C according to the following reaction equations [16]:SiO 2 + 3 C → SiC + 3 COIf y > 1 + x: SiO x C y → SiC + x CO + (y − x − 1) CIf y < 1 + x: SiO x C y → [(x + y − 1)/2] SiC + [(x + y −1)/2 CO + (x – y + 1) SiC> 1550 °C: Graphitization/ crystallization of the carbon and crystallization of SiC…”

“…The course from precursor to the polymer derived ceramic has been examined by many researchers analyzing the changes of typical properties such as pyrolysis weight losses, density and porosity changes and sample shrinkage [8]. The pyrolysis process was also studied by analyzing the changes in mechanical [9] and electric [7] properties as a function of conversion temperature, respectively. Ceramic microstructure, phase composition and crystallization behavior were investigated with respect to process conditions [10,11,12,13,14,15,16,17].…”

Potential of Glass, Basalt or Carbon Fibres for Reinforcement of Partially Pyrolysed Composites With Improved Temperature and Fire Resistance

“…Another advantage is its excellent oxidation resistance in a pyrolysed state at high temperatures. The properties of the partially and fully pyrolysed states of this resin have been previously studied with respect to the evolution in time of its weight loss, density, volume shrinkage, elasticity, and hardness during pyrolysis [31]. The pyrolytic properties of the resin used are shown in Table 1.…”

“…The third reason for the decrease in strength can be the internal stresses arising from the shrinkage of the pyrolysed matrix [31]. This reason appears to be the most likely because at 650 °C, the nominal temperature used for pyrolysis, only the basalt fibres exhibit tension relaxation, as shown in Figure 9.…”