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Open-celled silicon carbide (SiC) foam has been proven of a promising underwater acoustic absorption material. However, further improvement of its sound absorption capacity especially at low frequency is restricted by the acoustic impedance mismatch between the foam material and the water surrounding it. How to tailor the existing SiC foam in order to achieve an optimized impedance match is a key issue. In this work, the underwater acoustic absorption performance of open-celled SiC foam is studied by both analytical and experimental methods. First, based on Zwikker–Kosten’s theory, the modified Johnson–Allard (J–A) model is proposed to analytically predict the absorption performance of liquid-saturated SiC foam. Then three approaches including (i) backing the test samples by a 30-mm-thick air cavity, (ii) enclosing a certain amount of water and (iii) filling the samples with silicon oil are proposed to improve the underwater sound absorption performance of SiC foam. The underwater acoustic absorbency of the silicon oil filled SiC foam is significantly improved, especially in the low frequency band. A sound absorption coefficient near unity is achieved by this manner over a significant portion of the investigated frequency range, eg. 750–4000 Hz. The foam partially filled with water also shows enhanced sound absorbency at low frequency, but the foams backed by air gap and saturated fully by water display degraded sound absorption capacity. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) foam prepared by polymer pyrolysis combined with molten silicon reactive infiltration (MRI) process was experimentally studied for the first time regarding its underwater acoustic absorption coefficient ( α ) mainly over low and middle frequency range (200–4000 Hz). The relationship between α and the pore structure of SiC foam including pore size ( d ) and foam thickness ( t ) was studied. The results indicated that α increased with the decrease of pore size from 3 to 1 mm in most frequencies measured. α also increased with sample thickness at both low and medium frequency, but in general it was more sensitive to pore size than to sample thickness. The existing models built for air-filled porous material under atmospheric circumstance were not valid to describe the underwater acoustic absorption behavior of SiC foam materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] Highly accessible ZSM-5 coatings were grown on SiC foam support. [•] The synthesis processes were optimized for improving the coating adhesion. [•] The obtained composite catalyst showed high stability and yield in MTP reaction. [ABSTRACT FROM AUTHOR]

Abstract: ZSM-5 coatings with controllable morphology, Si/Al ratio, and loading were grown on SiC foam support with zeolite precursor modified surface. A homogeneous coverage of the support (15wt.% zeolite) by ZSM-5 crystals with an average crystal size of about 3.5μm was reached by controlling the amount of NaCl and TPAOH. The surface modification by the zeolite precursor gel layer ensured the strong anchoring and the loading of the zeolite crystals on the SiC support. The ZSM-5/SiC foam composite catalyst showed substantial stability and yield improvement in comparison to zeolite pellets in the methanol to propylene (MTP) reaction. [Copyright &y& Elsevier]

To hinder the deactivation and improve the propylene selectivity in the methanol-to-propylene (MTP) reaction, MFI coating with the intrazeolitic aluminum (acidic) gradient supported on SiC foam support (G-MFI/SiC foam) was proposed. The solid polycrystalline silicon was used in the synthesis of G-MFI/SiC foam catalyst provided a prolonged release of silica nutrient in the liquid phase and suppressed the precipitation phenomena. The resulting MFI coating showed the aluminum gradient along the surface normal direction of SiC foams with ZSM-5 layer (about 20 μm) near the SiC surface followed by the silicalite-1 layer (about 10 μm). The alumina (acidic) gradient in the MFI coating renders a passive outer layer of silicalite-1 with fairly large amount of weak and medium acid sites prevented the coke formation as well as promoted the selectivity to propylene in the MTP reaction. Compared to the conventional ZSM-5/SiC foam catalyst, the G-MFI/SiC foam catalyst showed excellent performance in the MTP reaction with good catalytic longevity (8 h vs. 76 h for >95% methanol conversion) and low coke deposition (6.7 × 10 −3  wt.% h −1 vs. 0.26 wt.% h −1 ), as well as high propylene selectivity ( ca. 36% vs. 46%). [ABSTRACT FROM AUTHOR]

A rotating stirrer reactor using aluminum oxide (Al 2 O 3 ) and platinum (Pt) loaded silicon carbide (SiC) foam as both the stirring blade and active catalyst was applied for selective hydrogenation of cinnamaldehyde (CAL). The variations of the catalyst activity and selectivity against the CAL concentration and rotating speed were studied. The reaction rate increased with the increasing of stirring speed and showed a maximum value at 300 rpm, while the highest selectivity of 75% could be achieved at conversion as high as 90% at 100 rpm. [ABSTRACT FROM AUTHOR]

A hierarchical composite catalyst composed of a ZSM-5 coating on SiC nano-whiskers that grew on SiC foam supports was designed and synthesized to simultaneously improve the zeolite loading and mass transfer of both the reactants and products in the methanol-to-propylene (MTP) reaction. SiC nano-whiskers were first grown on SiC foam supports by a chemical vapor deposition method to construct a hierarchical porous structure on the struts. ZSM-5 type zeolite crystals with high coverage were then hydrothermally grown on the SiC nano-whiskers after their surface was properly modified with zeolite precursor gel. In this way, the mass loading of the zeolite coating and mass transfer property, the two key factors that hinder the catalytic properties of the ZSM-5/SiC foam composite reported in our previous work, were enhanced, which in turn substantially improved the stability and selectivity of the obtained ZSM-5/SiC nano-whisker/SiC foam composites in MTP reaction as compared with those of the ZSM-5/SiC foam composites and ZSM-5 pellets. [ABSTRACT FROM AUTHOR]

Highlights: [•] The structured TiO2–SiC were prepared using a composite sol–gel method. [•] The p-type SiC foam support was used in photocatalysis for the first time. [•] The TiO2–SiC enhanced the photocatalytic efficiency by a synergistic effect. [ABSTRACT FROM AUTHOR]