Poly(borosiloxanes) as precursors for carbon fiber ceramic matrix composites

Abstract

Ceramic matrix composites (CMCs), constituted of a silicon boron oxycarbide (SiBCO) matrix and unidirectional carbon fiber rods as a reinforcement phase, were prepared by pyrolysis of carbon fiber rods wrapped in polysiloxane (PS) or poly(borosiloxane) (PBS) matrices. The preparation of the polymeric precursors involved hydrolysis/condensation reactions of alkoxysilanes in the presence and absence of boric acid, with B/Si atomic ratios of 0.2 and 0.5. Infrared spectra of PBS showed evidence of Si-O-B bonds at 880 cm-1, due to the incorporation of the crosslinker trigonal units of BO3 in the polymeric network. X ray diffraction analyses exhibited an amorphous character of the resulting polymer-derived ceramics obtained by pyrolysis up to 1000 °C under inert atmosphere. The C/SiBCO composites showed better thermal stability than the C/SiOC materials. In addition, good adhesion between the carbon fiber and the ceramic phase was observed by SEM microscop

Thermal properties of polymethylvinylborosiloxanes

“…7). It is worthy to stress that quite a large residue after thermooxidative decomposition of PMVBSs (P 800 ) ranged from 22.2 to 33.3 %, and it might be the result of the formation of a ceramic material (a ceramics of a type SiBCO [20,[35][36][37]]-a borosilicate glass and silica). The content of boron in macromolecules of PMVBSs does not affect the mass of the residue after thermooxidative decomposition of the samples; however, the largest mass of the residue characterizes the sample corresponding to the molecular formula of B 6 O 11 T 0 6 D 100 D 25 vi M 14 , with the highest content of boron in the siloxane chain (Table 3).…”

“…The thermal decomposition of the PMVBSs under nitrogen atmosphere begins at T C 140°C, [28][29][30][31][32][33][34]38], in comparison with the heating process under nitrogen atmosphere. A liberation of these products promotes ceramization processes: the formation of the ceramics of the type SiBCO [19,[36][37][38]]-a borosilicate glass and silica. Apparently, these processes occur more intensively under air atmosphere than under nitrogen atmosphere, which leads to the distinctly higher value of the residue after thermooxidative decomposition of PMVBSs (P 800 ), as compared with the residue after thermal decomposition (P 500 ) ( Tables 3, 4).…”

Magnetic nanoparticles functionalized ethane sulfonic acid (MNESA): as an efficient catalyst in the synthesis of coumarin derivatives using Pechmann condensation under mild condition

“…The observed peak at 586 cm -1 is related to Fe-O or Fe-O-Fe bond [59]. Also, the strong peak at 1088 cm -1 corresponds to Si-O-Si bond, which confirms the existence of an SiO 2 layer around magnetic nanoparticles [60].…”

“…The FT-IR transmission spectrum of the MNESA (Fig. 1c) shows the following peaks: characteristic absorption at 3444.8 cm -1 that is associated with the free -OH site on magnetic nanoparticles and -OH of -SO 3 OH group [60], stretching frequency in 2850 cm -1 related to C-C and C-H bond vibrations [58] (this peak confirms the presence of alkyl chain on the magnetic nanoparticles), the medium bond in 624 cm -1 presumably is due to the stretching frequency of S-O bond [60], and two peaks at 1085.5 and 1185.5 cm -1 related to asymmetric and symmetric stretching of O-S-O bond, respectively [57]. The observed peak at 586 cm -1 is related to Fe-O or Fe-O-Fe bond [59].…”

Synthesis of hyperbranched polymethylvinylborosiloxanes and modification of addition‐curable silicone with improved thermal stability

“…These polymers, named polyborosiloxanes (PBSs), contain high‐energy B―O and Si―O bonds with corresponding bond energies of 537.6 and 422.5 kJ mol −1 , respectively . PBSs are widely used as active modifiers for thermosetting resins to improve their thermal stability, non‐halogenated flame retardants, heat‐resistant painting and ceramic precursors . Several methods have been described for the synthesis of PBSs from di‐ and tri‐functional silicon compounds as well as boron‐containing compounds, such as boric acid (BA), boron trioxide, boron trichloride and borate esters .…”