SiC Foam Research Articles

Effect of SiC layer on microwave absorption properties of novel three-dimensional interconnected SiC foam with double-layer hollow skeleton

To design a lightweight and high-performance absorber, this work introduced a novel three-dimensional interconnected SiC foam with double-layer hollow skeleton (3D-ISF), which was prepared by depositing SiC, pyrolytic carbon, and SiC layer on interconnected carbon foam, followed by oxidation of carbon. SEM results showed the interconnected hollow structure had been successfully synthesized, which was beneficial for microwave absorbing efficiency, and numerous columnar SiC defects were observed and played a critical role in the microwave absorption properties. The electromagnetic performances of 3D-ISF-I and 3D-ISF-II were investigated in depth. With the increase of thickness of SiC layer, 3D-ISF-II exhibited a better microwave absorption property, which could be ascribed to the higher impedance matching ratio (Zr) and attenuation constant (α). The optimum reflection loss value of 3D-ISF-II could reach −45.649 dB while that of 3D-ISF-I was just −32.070 dB. There is no doubt that the prepared materials have tunable microwave absorbing properties, which can promote the development of SiC-based absorbing materials to a certain extent. Finally, it was confirmed that the Zr played a dominant role in 3D-ISF, which provided practical guidance for the design of porous materials.

Hollow SiC foam with a double interconnected network for superior microwave absorption ability

For high-efficiency microwave absorber, it is wise to integrate the porous structure and SiC material. In this work, the hollow SiC foam with a double interconnected network is proposed via a simple chemical vapor deposition and direct oxidation process. The SiC film imparts the foam with excellent mechanical property and microwave absorption performance. As a result, the fabricated SiC foam possesses a superior compressive response of 1.409 MPa at 17.51% strain, which is much higher than the original C foam or SiC reinforced C foam. Besides, SiC foam shows a minimum reflection loss value of −50.75 dB at 4.85 mm at 6.00 GHz. The effective bandwidth frequency and electromagnetic absorption efficiency also prove the superiority of the hollow porous architecture at the specified thickness, followed by a simple interpretation of the microwave absorbing mechanism. Given the excellent characteristics, the SiC foam has the enormous applied potential as a lightweight absorber in complex microwave absorbing conditions, especially for high temperature applications.

Nanowire‐decorated SiC foam from tissue paper and silicon powder by filter‐pressing

AbstractA facile and scalable method for the preparation of low‐density SiC foam from tissue paper and silicon powder is reported. The co‐dispersion of pulp‐containing tissue paper micro‐ribbons and silicon powder is coagulated by adjusting the pH to 3.5. The silicon particles adhere to the tissue paper micro‐ribbons during the coagulation. The coagulated co‐dispersion on filter‐pressing consolidates the silicon particle‐decorated tissue paper micro‐ribbons and orients them perpendicular to the filter‐pressing direction. The filter‐pressed body on drying followed by heat treatment at 1600°C in inert atmosphere produces SiC foam. The tissue paper micro‐ribbons retain their morphology during carbonization as well as high‐temperature reaction with the silicon. The enormous growth of carbon‐rich SiC nanowires is observed on the SiC micro‐ribbons. The random orientation of SiC micro‐ribbons in the X‐Y plane with the hairy nanowires on the surface and their stacking in the Z‐direction produces a porosity of ~94 vol.% with pore sizes in the range of 0.08 to 20 µm. The SiC foam shows a compressive strength and Young's modulus of 0.22 and 5.5 MPa, respectively. The thermal conductivity decreases from 0.11 to 0.07 W m−1 K−1 when temperature increases from 25°C to 350°C.

Thermal analysis of methane hydrate formation in a high-pressure reactor packed with porous SiC foam ceramics

The porous SiC foam ceramic (SFC) packings were recently demonstrated capable of enhancing methane hydrate formation in the hydrate-based separation technologies, while the heat transfer analysis is one of the key requirements for effective implementation of this technology. In this study, the evolution of thermal resistance during hydrate formation was obtained based on hydration heat and gas consumption in experiments, while the effects of the packings’ properties (e.g. quantity, porosity, materials, stacking patterns) on the overall and local thermal resistances were predicted by the conductive heat transfer models. The overall tendency predicted by the model agreed with the experimental data. Results clearly indicated that the SFC packings could maintain the reaction system at a low thermal resistance for a longer time under relative low driving force. It also highlighted the role of the stacking patterns of SFC packings on heat transfer. The overall thermal resistance was reduced by about 39% after rotation of the SFC packings. When the SFC packings were stacked parallel to the reactor bottom, the composites formed by packings and hydrates was the main resistance for heat transfer which accounted for 30–50% of the overall thermal resistance. However, the contribution of this portion was only 13–25% if the SFC packings were stacked perpendicular to the reactor bottom. Overall results from this study were beneficial for better understanding where the main heat transfer resistance was from and how it varied against the packings’ properties when employing the foam packings for enhancing gas hydrate formation.

Preparation and Microwave Absorption Properties of Double-Layer Hollow Reticulated SiC Foam

High-performance microwave absorption and being lightweight have become the foremost crucial factors in the practical application of mordern microwave adsorbers. In view of this, we presented the d...

Absorption and desorption of liquid film flowing over a porous layer

A hybrid multiphase model is used to facilitate modeling mass transfer of liquid film flowing over porous medium. The improved method relies on the combination of the VOF and Eulerian-Eulerian models. However, the coupled model cannot be directly applied to a two-domain situation because the Eulerian-Eulerian framework is found not compatible with computational mesh consisting of multi domains. To increase robustness of the coupled model for flow field of non-uniform spatial properties, several field functions relative to the position and properties of the porous zone are implanted, which keeps fluid domain single in mesh. The resulting model is then used to investigate the mass transfer characteristics of liquid film flowing over a thin compressed SiC foam layer. The gas side and liquid side mass transfer characteristics are investigated respectively by absorption of ammonia from air into water, and desorption of oxygen from water into nitrogen. By comparison with the results of liquid film flowing over a rigid surface, it is found that mass transfer performance degrades when liquid film flows over a porous layer. Besides, for liquid side mass transfer, desorption rate is greatly affected by the properties of the porous layer, and a non-linear relationship between desorption rate and liquid flow rate is observed.

Accelerated formation of methane hydrates in the porous SiC foam ceramic packed reactor

A new approach was proposed to facilitate methane hydrate formation using the porous SiC foam ceramic (SFC) packings without the assistance of mechanical agitation. The performance of regular packings with two different stacking patterns (parallel stacking and perpendicular stacking) and random packings with six different structure parameters (particles size: 3 – 9 mm, pore size: 0.5 – 1.0 mm) were tested. The overall results clearly demonstrated the promotion effects of SFC packings on the kinetics of hydrate formation, which also increased the repeatability of hydrate synthesis especially under low driving force. Compared with the control experiments, the induction time was decreased by up to 88%, the maximum growth rate was increased by up to 95%, while the degree of water conversion to hydrates was increased by up to 1.2-fold (274.6 K, 7.3 MPa). Insignificant decrease was observed in the above performance during the five cycles of cooling-melting experiments, indicating the good reusability of the SFC packings. To the best of our knowledge, the porous SFC materials were for the first time successfully employed for accelerating gas hydrate formation, which provided an alternative method to improve the efficiency of the natural gas storage.

Microcellular SiC foams containing in situ grown nanowires for electromagnetic interference shielding

Microcellular SiC foams (MSiCFs) are produced by thermal setting of dispersions of silicon and NaCl powders in molten sucrose-glycerol solutions in a mould followed by carbonization, NaCl removal and reaction bonding at 1500°C. The acidic silica layer on silicon particle surface catalyses the setting of the pastes by −OH condensation. The SiC nanowires grown in situ by a catalyst-free vapour–solid (VS) mechanism creates web-like architecture within the microcells (cell size −2 to 22μm) of the foams. The MSiCFs with porosity in the range of 86.8–91.1vol.% exhibit thermal conductivity and compressive strength in the ranges of 0.334–0.758Wm−1K−1 and 0.97–2.38MPa, respectively. The MSiCFs show excellent electromagnetic interference (EMI) shielding property in the X-band frequency region enhanced by the in situ grown SiC nanowires within microcells. The EMI shielding effectiveness (45.6dB) and specific shielding effectiveness (137dBg-1cm3) are the highest reported for SiC foams.

Methane hydrate formation in the SiC foam ceramics packed reactor in presence of β-cyclodextrin

Cyclodextrins were used as environmental friendly additives in enhancing the kinetics of gas hydrate formation. Effects of β-Cyclodextrin (Beta-CD) on methane hydrate formation in the SiC foam ceramics packed reactor were evaluated in this paper. To investigate the roles of these additives played in the enhancement of hydrate formation kinetics, different concentrations of Beta-CD and sodium dodecyl sulfate (SDS) mixed solution were used in the gas hydrate formation system. The overall results demonstrated that the addition of Beta-CD promoted the formation of methane hydrate. Compared with the control experiments with only 200 ppm SDS and SFC packings, the induction time for methane hydrate formation was shortened by 97.6 % when 1000 ppm Beta-CD was added, while the maximum gas consumption rate and water conversion rate were increased by up to 284.2 % and 102.0 %, respectively. Results showed that simultaneous usage of Beta-CD, SDS and SFC packings enhanced the methane hydrate formation kinetics.

Flow Pattern of Miscellaneous Liquids with Varied Flow Rates on Structured Corrugation SiC Foam Packing

Although the unique liquid behavior renders structured corrugation SiC foam packing (SCFP-SiC) a great alternative in distillation, the separation efficiency depends heavily on capacity and liquid property. The aim of this work is to discuss the change of flow pattern with miscellaneous liquids at different flow rates in order to explain the performance of SCFP-SiC in a distillation column. The ultraviolet photography and pulse tracer method were used to estimate the effective flow area and the resident time, respectively. The experimental results indicate that the liquid flow pattern on SCFP-SiC consists of streamflow and transfusion flow. The stream flow can be enlarged by the increase of liquid flow rate so that the effective flow area is reduced, resulting in the decrease of separation efficiency at high liquid capacity. What is more, there exists a vast difference of flow pattern between polar liquid (e.g., water and acetic acid) and nonpolar liquid (e.g., cyclohexane). Transfusion flow of the former is much less than that of the latter, causing the poor performance when separating polar system. Therefore, the liquid capacity and type should be evaluated firstly in the use of SCFP-SiC.

Formation of CeO2 coatings on Si–SiC foams by electrophoretic deposition and sintering in air

Abstract We demonstrate that AC-EPD, using an aqueous slurry system followed by sintering in air, is an effective technique to form thick ceramic coatings on porous Si–SiC cellular ceramic substrates. As an example, CeO2 particles with high surface area dispersed in water have been deposited successfully on Si–SiC foams by optimizing the zeta potential and dispersion conditions. Moreover, the parameters for AC-EPD were determined by controlling voltage, frequency, time, and degree of signal asymmetry to minimize water electrolysis in this aqueous system. The microstructure of CeO2 layer has been controlled by adjusting sintering conditions to obtain porous and dense layers at 1200 and 1400 °C, respectively. The grain growth of the CeO2 deposit upon the heat treatment was explained by the diffusion of SiO2 into the CeO2 coating layer, which resulted in a firm joining with the Si–SiC substrate.

SiC foam based structured catalyst for process intensification in oxidative dehydrogenation of 1-butene to butadiene

Oxidative dehydrogenation of butenes to butadiene is a highly exothermic and diffusion-controlled reaction. The problems of high adiabatic temperature rise and pressure drop, low gas velocity and conversion, as well as high consumption of water exist in the conventional reactors. In order to ease these problems, SiC foam supporting ZnFe2O4-α-Fe2O3 (ZnFe2O4-α-Fe2O3/SiC foam) structured catalyst was prepared by a slurry-coating method. Its performance was systematically studied with varied reaction temperature, oxygen/1-butene molar ratio, steam/1-butene molar ratio and 1-butene gaseous hourly space velocity (GHSV), respectively. The results showed that the 1-butene conversion and butadiene selectivity over the structured catalyst could reach about 87% and 91%, respectively, at a 1-butene GHSV of 300 h−1, and even at a 1-butene GHSV of 600 h−1, the conversion could still maintain at 78%, which was much better than that of the particulate catalysts. In addition, compared to the particle packed bed, the structured bed showed lower temperature rise and nearly isothermic, could lower the consumption of water and allowed to be operated with a wider range of O2/1-butene molar ratio and a much higher 1-butene GHSV, due to its better process intensification capacity.

Nanodiamonds @ N, P co-modified mesoporous carbon supported on macroscopic SiC foam for oxidative dehydrogenation of ethylbenzene

A robust monolith catalyst has been fabricated involving the combination of nanodiamonds (NDs) and mesoporous carbon modified by nitrogen and phosphorus (ND@NMC-xP, x = amount of ammonium biphosphate) on a β-SiC foam. The ND@NMC-0.02 P/SiC monolith catalyst with 0.2 at.% of P elements exhibits an excellent catalytic performance for oxidative dehydrogenation of ethylbenzene (EB), delivering 90.2% selectivity to styrene (ST) up to 32.6% conversion. The specific conversion rate of monolith catalyst based on the unit weight of NDs and mesoporous carbons (25.3 mmol gact. phase−1 h−1) is 3-fold higher than that of unsupported NDs. The role of nitrogen is believed to enhance the density of active sites and thus offering a high EB conversion, whereas the addition of phosphorus inhibits deep oxidation of EB to carbon oxides and therefore for a high selectivity to ST. The monolith catalyst not only contributes a high utilization efficiency of NDs but also mitigates the high pressure drop across the catalytic bed, which is potentially suitable for a real industrial process.

Structured ZSM-5 coated SiC foam catalysts for process intensification in catalytic cracking of n-hexane

Structured zeolite/SiC foam catalysts provide alternative solutions to mass and heat transfer limited chemical transformations for process intensification, exemplified by cracking reactions.

Seasonal Thermal Energy Storage with Aqueous Sodium Hydroxide – Development and Measurements on the Heat and Mass Exchangers

A 1 kW closed sorption Thermal Energy Storage (TES) system based on water absorption/desorption in a high-energy density sorbent like sodium hydroxide (sorbent, NaOH) is developed and tested at HSR-SPF. The overall concept of the 1 kW prototype system, based on the tube bundle and falling film model is presented. A modular design was chosen for the absorber/desorber unit with the aim of testing several types of tubes and liquid sorbent modifications. The influence of SiC foams with different porosity on the sorbent mass uptake, thus on the sorbent residence time in the water vapour is presented. The experiments have indicated that, although a better residence time can be obtained for ceramic samples with small pores size, a balance has to be found between ceramic clogging and gas-liquid area to achieve an efficient heat and mass exchange. The improved tube bundles are further tested in the 1 kW prototype.

A comparative study of Ni/Al2O3–SiC foam catalysts and powder catalysts for the liquid-phase hydrogenation of benzaldehyde

In this study, Al2O3-washcoated SiC (Al2O3–SiC) foams and Al2O3 powder were employed as the supports of a Ni catalyst for the liquid-phase hydrogenation of benzaldehyde. A series of Ni/Al2O3–SiC foam catalysts and Ni/Al2O3 powder catalysts with a Ni loading from 10 wt% to 37 wt% of the weight of Al2O3 were first prepared by a deposition–precipitation (DP) method. The catalytic activity and recyclability of both kinds of catalysts were then compared. Although it had a smaller accessible surface area with the reactant, the foam catalyst with a Ni loading of 16 wt% exhibited a slightly higher conversion of benzaldehyde after 6 h (of 99.3%) in comparison with the Ni/Al2O3 catalyst with identical Ni loading (conversion of 97.5%). When the Ni loading increased from 16 wt% to 37 wt%, the reaction rate obtained with the foam catalyst increased significantly from 0.108 to 0.204 mol L−1 h−1, whereas the reaction rate obtained with the powder catalyst increased from 0.106 to 0.123 mol L−1 h−1. Furthermore, the specific activity (moles of benzaldehyde consumed by 1 g min−1 of Ni) of the foam catalyst with a Ni loading above 30 wt% was superior to that of the powder catalyst because of its smaller Ni-particle size and higher mass-transfer rate. The foam catalyst displayed a high recyclability as a function of run times owing to the strong interaction between the Ni component and the Al2O3 coating. The conversion of benzaldehyde over the foam catalyst remained almost unchanged after being used 8 times. In comparison, a drop of 43% in the conversion of benzaldehyde with the powder catalyst was observed after being used 7 times due to the leaching of the Ni component.

Heterogeneous photodegradation of Pyrimethanil and its commercial formulation with TiO2 immobilized on SiC foams

Vine is one of the crops undergoing the most pesticide treatment. Due to the presence of pesticides residues in water and food, and the negative effects on human and wildlife health, it is necessary to develop an effective treatment. Photocatalytic oxidation using semiconductors is one of the advanced oxidation processes for degradation of organic pollutants in water and air. A TiO2 in nanopowder is an excellent photocatalyst that can mineralize a large range of organic pollutants such as pesticides and dyes. In order to eliminate the problems due to TiO2 nanoparticles, we have successfully supported TiO2 on β-SiC foams. The supporting material has been used to degrade Pyrimethanil molecule and its commercial formulation: Scala® a fungicide produced by BASF Company. After 4 h of treatment in our conditions, a 88% and 74% of Pyrimethanil and Scala was removed with a 58 and 47% of mineralization, respectively. These results are very encouraging because there is no need to filter to separate the catalyst from the treated water which is very important for a large-scale use of this process.

Silicon carbide foam supported ZSM-5 composite catalyst for microwave-assisted pyrolysis of biomass

Considering a series of issues facing the application of catalysts in large scale catalytic fast pyrolysis systems, a novel composite catalyst of ZSM-5 coatings on SiC foam supports was developed and tested for ex-situ catalytic upgrading of the pyrolytic vapors. Different configurations of catalysts placement were compared and the results showed the composite catalyst could significantly improve the bio-oil quality without significantly reducing the yield. The effect of catalyst to biomass ratio on the product yields and bio-oil composition was studied and the results showed that increasing catalyst to biomass ratio could improve the quality of bio-oil at the cost of its yield. In addition, the composite catalyst can maintain its activity until a catalyst to biomass ratio of 1/10, outperforming ZSM-5 in other configurations reported in literature. Furthermore, the composite catalysts could be regenerated and reused while well preserving its material properties and catalytic activity after seven reaction-regeneration cycles.

Nickel Sulfides Decorated SiC Foam for the Low Temperature Conversion of H₂S into Elemental Sulfur.

The selective oxidation of H2S to elemental sulfur was carried out on a NiS2/SiCfoam catalyst under reaction temperatures between 40 and 80 °C using highly H2S enriched effluents (from 0.5 to 1 vol.%). The amphiphilic properties of SiC foam provide an ideal support for the anchoring and growth of a NiS2 active phase. The NiS2/SiC composite was employed for the desulfurization of highly H2S-rich effluents under discontinuous mode with almost complete H2S conversion (nearly 100% for 0.5 and 1 vol.% of H2S) and sulfur selectivity (from 99.6 to 96.0% at 40 and 80 °C, respectively), together with an unprecedented sulfur-storage capacity. Solid sulfur was produced in large aggregates at the outer catalyst surface and relatively high H2S conversion was maintained until sulfur deposits reached 140 wt.% of the starting catalyst weight. Notably, the spent NiS2/SiCfoam catalyst fully recovered its pristine performance (H2S conversion, selectivity and sulfur-storage capacity) upon regeneration at 320 °C under He, and thus, it is destined to become a benchmark desulfurization system for operating in discontinuous mode.

Three-dimensional hierarchical porous sludge-derived carbon supported on silicon carbide foams as effective and stable Fenton-like catalyst for odorous methyl mercaptan elimination

The poor reusability of catalysts and secondary pollution are critical issues for sulfur-containing volatile organic compounds (S-VOCs) removal. In this paper, a three-dimensional (3D) hierarchical porous sludge-derived carbon supported on silicon carbide foams (SiC) has been fabricated for deep decomposition of S-VOCs under ambient conditions. The sludge-derived Fenton-like catalyst has been confirmed to be hierarchical 3D porous structure based on detailed characterization by scanning electron microscopy (SEM), X-ray diffraction (XRD), Nitrogen adsorption-desorption measurements and Raman spectroscopy. Significantly, the catalyst after KOH activation (SCFeK-SiC) shows excellent catalytic decomposition of methyl mercaptan (CH3SH) with almost complete CH3SH oxidation into sulfate using hydrogen peroxide as an oxidant under ambient conditions. This catalyst also possesses relative low iron dissolution and excellent cycling performance. The efficient catalytic ability of SCFeK-SiC can be attributed to SiC foam functioned as a stable 3D macroporous skeleton, in which the porous sludge-derived carbon immobilizes the active iron species and promotes the efficient capture of gaseous CH3SH, thus facilitating the decomposition of CH3SH by generating reactive species, specifically ·OH. The reaction mechanism was systematically investigated. Herein, the design of the porous sludge-derived carbonaceous Fenton-like catalyst paves an avenue for efficient VOCs treatment and rational sludge disposal.