A simple process for synthesizing SiOC foams with low density (45–115 kg/m3) and high porosity (95–98%) is reported here. The process involves the impregnation of a flexible polyurethane foam with a ...preceramic polymer solution and pyrolysis in the inert atmosphere. SEM analysis showed that the resultant SiOC foam had a fully open interconnected porous structure with dense struts. N2 adsorption test performed on the as-pyrolyzed SiOC foams showed very low surface area, which can be increased by leaching out the SiO2-rich network by HF, leaving behind a mesoporous C-rich SiOC foam. The remarkably high surface area up to 147 m2/g (7350 m2/liter) has been reached after 24 h etching. HF etching leads to a decrease of the compressive strength. However, a good combination of compressive strength (∼80 kPa), porosity (95%) and surface area (7315 m2/liter) of the foam has been obtained and it makes the SiOC foam a potential candidate for specific applications.
A method is described here for preparing lightweight and low cost polymer-derived silicon carbide foam by impregnation of preceramic polymer in polyurethane foam. A series of silicon carbide foams ...with various density (0.035–0.35g/cm3), porosity (87–98%) and thermal conductivity (0.05–0.12W/m·K) were prepared using allylhydropolycarbosilane as a base material. Surface analysis shows that the resultant foams have an open and interconnected porous structure. Phase analysis shows that it has cubic crystal structure. There was no evidence of cracks or damage even after treating the silicon carbide foam with concentrated hydrofluoric acid for 12days. From the oxidation resistance experiment, it can be concluded that the silicon carbide foam is stable up to 1500°C in air and 2000°C in argon.
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•Lightweight and low cost silicon carbide foam is prepared by polymer derived ceramic route.•Silicon carbide foam shows interconnected open cell structure made of solid strut.•It has good structural stability at very high temperature.•It is stable in reactive environments.
Silicon oxycarbide (SiOC) aerogels have been synthesized from preceramic polymers via pyrolysis in inert atmosphere at 1200 and 1300°C. The as synthesized materials have a typical colloidal ...microstructure with mesoporosity in the range 10–50nm and no microporosity. HF acid attack of the SiOC aerogels dissolves preferentially the SiO2-rich phase and creates micro-and (small)mesopores (<10nm) in the aerogels microstructure finally leading to a materials with hierarchical porosity. The HF post-pyrolysis treatment is more efficient for the SiOC aerogels pyrolyzed at the maximum temperature, i.e. 1300°C, leading to a maximum value of specific surface area of 530m2/g and total porosity of 0.649cc/g.
SiOC ceramic aerogels with different porosity, pore size, and specific surface area have been synthesized through the polymer‐derived ceramic route by modifying the synthesis parameters and the ...pyrolysis steps. Preceramic aerogels are prepared by cross‐linking a linear polysiloxane with divinylbenzene (DVB) via hydrosilylation reaction in the presence of a Pt catalyst under highly diluted conditions. Acetone and cyclohexane are used as solvent in our study. Wet gels are subsequently supercritically dried with CO2 to get the final preceramic aerogels. The SiOC ceramic aerogels are obtained after a pyrolysis treatment at 900°C in two different atmospheres: pure Ar and H2 (3%)/Ar mixtures. The nature of the solvent has a profound influence of the aerogel microstructure in terms of porosity, pore size, and specific surface area. Synthesized SiOC ceramic aerogels have similar chemical compositions irrespective of processing conditions with ~40 wt% of free carbon distributed within remaining mixed SiOC matrix. The BET surface areas range from 215 m2/g for acetone samples to 80 m2/g for samples derived from cyclohexane solvent. The electrochemical characterization reveals a high specific reversible capacity of more than 900 mAh/g at a charging rate of C (360 mA/g) along with a good cycling stability. Samples pyrolyzed in H2/Ar atmosphere show a high reversible capacity of 200 mAh/g even at a high charging/discharging rate of 20 C. Initial capacities were recovered after whole cycling procedure indicating their structural stabilities resisting any kind of exfoliations.
Synthesis and characterization of polymer-derived SiCN aerogels are reported. The wet pre-ceramic gels are synthesized via hydrosilylation reaction of a polysilazane with divinylbenzene as ...cross-linker using cyclohexane as solvent. Subsequently, the wet polymeric gels are dried using supercritical carbon dioxide for the removal of the solvent. The SiCN ceramic aerogels are obtained through pyrolysis in N2 at 1000 and 1500°C. The ceramic aerogels show a low density (<0.1g/cm3), high porosity (>90%), high specific surface area (>150m2/g) and display a hierarchical pores size distribution which ranges from micropores to mesopores and small macropores.
A new approach for forming aerogels with various silicon‐based compositions and hybrids between ceramics and carbon has been developed by combining efficient hydrosilylation as the ...hybridization‐crosslinking approach associated with gelation in the presence of solvent and followed by supercritical drying techniques. Highly porous carbon‐enriched SiC/C aerogels with adequate mechanical durability have been synthesized, pyrolyzed, and characterized. The “wet” gels were obtained by crosslinking a commercial polycarbosilane with divinylbenzene via Pt‐catalyzed hydrosilylation reaction in highly diluted condition (90 vol% of solvent). A supercritical drying was performed after exchanging the solvent (cyclohexane) with liquid CO2 forming undamaged aerogels. A subsequent pyrolysis and heat treatment (up to 1500 °C) in argon flow converted the polymeric aerogel into a SiC/C‐based material with bulk density of 166 kg m−3, SSA of 444 m2 g−1, a micro‐meso pore volume of 0.79 cm3 g−1, total porosity above 90 vol% and ultimate compressive strength of 1.6 MPa. The final product was compared to its cured gel and intermediates obtained during the pyrolysis process.
A new method to obtain SiC/C aerogels is proposed. Preceramic aerogels made of polycarbosilane crosslinked with divinylbenzene are obtained by means of Pt catalyzed hydrosilylation reaction in highly diluted condition. Supercritical drying is performed with liquid CO2 and after pyrolysis monolithic SiC/C aerogels are obtained.
Polymer derived ceramic (PDCs) aerogels belonging to the Si–O–C–N system are synthesized by crosslinking a preceramic polymer in a diluted solution followed by supercritical or atmospheric drying and ...pyrolysis in inert (N2) or reactive (NH3/CO2) atmosphere. Accordingly, aerogels with hierarchical porosity ranging from some microns to few nanometers together with high specific surface area in the range 30–400 m2 g−1 have been obtained. Moreover, their surface contains a broad range of moieties (Si–OH, Si–NH, C=O, etc.) that can interact and bind metal ions thanks to electrostatic interactions. This combination of hierarchical porosity, high SSA, and broad range of chemical functionalities makes these PDCs aerogels interesting candidates for water purification. In this work, SiOC and SiCN aerogels have been tested as adsorbents for Cr(III)/(VI) ions from aqueous solutions with promising results for the SiOC aerogel pyrolyzed in N2 and the SiCN treated in NH3. Correlations and similarities among the Cr(VI)/(III) adsorption capacity with the main features of the porous substrates (SSA, N2 TPV, amount of free C, bulk density, isoelectric point, main IR peaks (Si–OH, OH, NH, C=O, C=C, Si–O, C–N, Si–N) have been investigated by applying the Principal Component Analysis (PCA).
Polymer derived SiOC and SiCN aerogels are produced, starting from preceramic aerogels, through a pyrolysis process with reactive atmospheres (Ar, CO2, NH3) and are characterized for the adsorption of Cr(VI/III) from aqueous solutions. Results show that SiOC and SiCN aerogels pyrolyzed in inert N2 and reactive NH3 flow, respectively, display a good adsorption capacity for Cr(VI) (30 and 20 mg g−g, respectively, after 1 h contact time).
•A novel simple synthesis route to Si3N4 nanofelts has been developed.•The nanofelts can be easily shaped in large and complex componenets.•The thermal conductivity of the nanofelts is as low as 11 ...mW m−1 K−1 in Ar.•The thermal stability of the nanofelts is excellent up to 1000°C in air.•Flexible nanofelts can be obtained.
Nowadays, the best thermal insulators are aerogel-based materials. However, their industrial application is constrained by a complex synthesis route (requiring supercritical drying) and by their fragility. Moreover, the most common aerogels, based on amorphous SiO2, have a poor thermal stability. In this work, a fast and simple synthesis route to ultra-highly-insulating Si3N4 nanofelts is developed. The process is based on a specific treatment of SiOC polymer-derived ceramics in N2 atmosphere. The obtained nanofelts possess porosity as high as 99.7% (10 kg m−3) and thermal conductivity down to 11 mW m−1 K−1 in Ar atmosphere, which is among the lowest ever measured. The new material surpasses aerogels in terms of flexibility and temperature resistance. Moreover, it can be easily shaped in physical objects of industrial interest. Thus, it offers a unique combination of intriguing properties such as thermal insulation, lightweight, temperature resistance and flexibility. These, combined with the simple manufacturing process, could lead to far-reaching implications in multiple technological fields.
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Si
OC
ceramic aerogels with different porosity, pore size, and specific surface area have been synthesized through the polymer‐derived ceramic route by modifying the synthesis parameters and the ...pyrolysis steps. Preceramic aerogels are prepared by cross‐linking a linear polysiloxane with divinylbenzene (
DVB
) via hydrosilylation reaction in the presence of a Pt catalyst under highly diluted conditions. Acetone and cyclohexane are used as solvent in our study. Wet gels are subsequently supercritically dried with
CO
2
to get the final preceramic aerogels. The Si
OC
ceramic aerogels are obtained after a pyrolysis treatment at 900°C in two different atmospheres: pure Ar and H
2
(3%)/Ar mixtures. The nature of the solvent has a profound influence of the aerogel microstructure in terms of porosity, pore size, and specific surface area. Synthesized Si
OC
ceramic aerogels have similar chemical compositions irrespective of processing conditions with ~40 wt% of free carbon distributed within remaining mixed Si
OC
matrix. The
BET
surface areas range from 215 m
2
/g for acetone samples to 80 m
2
/g for samples derived from cyclohexane solvent. The electrochemical characterization reveals a high specific reversible capacity of more than 900 mAh/g at a charging rate of C (360 mA/g) along with a good cycling stability. Samples pyrolyzed in H
2
/Ar atmosphere show a high reversible capacity of 200 mAh/g even at a high charging/discharging rate of 20 C. Initial capacities were recovered after whole cycling procedure indicating their structural stabilities resisting any kind of exfoliations.
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