共查询到20条相似文献,搜索用时 15 毫秒
1.
《Journal of the European Ceramic Society》2020,40(3):594-602
The incorporation of a thermally insulating secondary phase can significantly increase the interfacial thermal resistance attributed to its low intrinsic thermal conductivity and the creation of multiple phonon scattering interfaces between adjacent SiC particles. The newly developed porous SiC-33 wt% SiO2 composites with SiO2 as a thermally insulating secondary phase exhibited a very low thermal conductivity (0.047 Wm−1 K−1, 72.4 % porous), which is an order of magnitude lower than the previously reported lowest thermal conductivity (0.14 Wm−1 K−1, 76.3 % porous) for powder processed porous SiC ceramics and is even lower than the thermal conductivity (0.060 Wm−1 K−1, 87.9% porous) of SiO2 aerogel. The porous SiC-(16–73 wt%) SiO2 composites processed from nano β-SiC and a 40 wt% carbon template exhibited a hierarchical (meso-/macro-porous) pore structure that transformed to a trimodal (micro-/meso-/macro-porous) porous structure when polysiloxane was added and sintering was performed at 600–1000 °C in air. 相似文献
2.
《Ceramics International》2015,41(7):8809-8813
Magnesiothermal synthesis of nanosized SiC has been successfully achieved from a mixture of the natural zeolite clinoptilolite and a high-surface area mesoporous carbon CMK-1, synthesized by impregnating a mesoporous silica template MCM-48 with sucrose, followed by carbonization in argon and removal of the silica template. Magnesium powder was used to initiate the self-combustion reaction. Removal of the alkaline and alkaline earth exchangeable cations from the clinoptilolite by ion exchange with NH4+ was essential for a good yield of product, which is also dependent on the use of excess of carbon. TEM confirmed the nanostructure and size of the 15–25 nm SiC product crystallites. 相似文献
3.
Chularat Wattanakit Chompunuch Warakulwit Piboon Pantu Boonruen Sunpetch Metta Charoenpanich Jumras Limtrakul 《加拿大化工杂志》2012,90(4):873-880
In this work, we are reporting for the first time the synthesis of hierarchical micro‐ and mesoporous zeolite using silica–carbon (SiO2/C) composites prepared by pyrolysis of carbonaceous gases in the presence of silica gel. The pyrolysis effectively yielded carbon deposited onto the raw silica material. The obtained SiO2/C composites were utilised as a bifunctional material, mesoporous template and silica source, for the zeolite synthesis. Tetrapropylammonium hydroxide (TPAOH) was used as a microporous template. The combination of the obtained composites and the TPAOH for the hydrothermal synthesis resulted in the formation of hierarchical micro‐ and mesoporous ZSM‐5. The results from the SEM, TEM, and N2 adsorption/desorption isotherms, and 27Al MAS NMR characterisations of the synthesised samples obtained after the removal of the templates confirmed the successful formation of the micro‐ and mesoporous zeolites. The mesoporosity of the zeolites could be controlled by adjusting the carbon content in the SiO2/C composites while the carbon content could be controlled by varying the deposition time and the concentration of the carbonaceous gases used. This controllable and efficient synthesis method is considered to be a promising method for creating hierarchical micro‐ and mesoporous zeolites. © 2011 Canadian Society for Chemical Engineering 相似文献
4.
Synthesis and characterization of monolithic carbon/silicon carbide composite aerogels 总被引:2,自引:0,他引:2
Yong Kong Ya Zhong Xiao-dong Shen Sheng Cui Junjun Zhang Meng Yang 《Journal of Porous Materials》2013,20(4):845-849
Resorcinol–formaldehyde/silica composite (RF/SiO2) aerogels were synthesized using sol–gel process followed by supercritical CO2 drying. Monolithic carbon/silicon carbide composite (C/SiC) aerogels were formed from RF/SiO2 aerogels after carbothermal reduction. X-ray diffraction and transmission electron microscopy demonstrate that β-SiC was obtained after carbothermal reduction. Scanning electron microscopy and nitrogen adsorption/desorption reveal that the as-prepared C/SiC aerogels are typical mesoporous materials. The pore structural properties were measured by nitrogen adsorption/desorption analysis. The resulting C/SiC aerogels possess a BET surface area of 564 m2/g, a porosity of 95.1 % and a pore volume of 2.59 cm3/g. The mass fraction of SiC in C/SiC aerogels is 31 %. 相似文献
5.
A high performance and low cost C/C–SiC composite was prepared by Si–10Zr alloyed melt infiltration. Carbon fiber felt was firstly densified by pyrolytic carbon using chemical vapor infiltration to obtain a porous C/C preform. The eutectic Si–Zr alloyed melt (Zr: 10 at.%, Si: 90 at.%) was then infiltrated into the porous preform at 1450 °C to prepare the C/C–SiC composite. Due to the in situ reaction between the pyrolytic carbon and the Si–Zr alloy, SiC, ZrSi2 and ZrC phases were formed, the formation and distribution of which were investigated by thermodynamics. The as-received C/C–SiC composite, with the flexural strength of 353.6 MPa, displayed a pseudo-ductile fracture behavior. Compared with the C/C preform and C/C composite of high density, the C/C–SiC composite presented improved oxidation resistance, which lost 36.5% of its weight whereas the C/C preform lost all its weight and the high density C/C composite lost 84% of its weight after 20 min oxidation in air at 1400 °C. ZrO2, ZrSiO4 and SiO2 were formed on the surface of the C/C–SiC composite, which effectively protected the composite from oxidation. 相似文献
6.
MnO2 with novel mesoporous structure has been firstly synthesized via a simple in situ reduction process by using different carbon materials as sacrificed template and reducing agent. The morphology and microstructure of as-synthesized mesoporous MnO2 were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption and desorption experiments. The results demonstrate that porous MnO2 prepared using mesoporous carbon as template has very large specific surface area and uniform pore-size distribution. The electrochemical measurements showed that novel porous MnO2 have higher capacity (221 F g−1) with excellent rate and higher capacity retention as electrochemical capacitors (ECs) electrode materials, which may be attributed to the unique nanostrcture of porous MnO2. These all imply that MnO2 with novel mesoporous structure has been attractive for practical and large-scale applications in mobile equipment. 相似文献
7.
Hierarchical porous nitrogen-doped carbon (HPNC) materials are synthesized through one-step carbonization of polyimide using triblock copolymer P123 as mesoporous template. The microstructure, chemical composition and CO2 adsorption behaviors are investigated in detail. The results show that HPNC materials have hierarchical micro-/mesopore structures, high specific surface area of 579 m2/g, large pore volume of 0.34 cm3/g, and nitrogen functional groups (5.2 %). HPNC materials exhibit high CO2 uptake of 5.56 mmol/g at 25 °C and 1 bar, which is higher than those of previously reported nitrogen-doped porous carbon materials. After 5 cycles the value of CO2 adsorption uptakes is 5.28 mmol/g, which is approximately 95 % of the original adsorption capacity. The estimated CO2/N2 selectivity of HPNC materials is 17, revealing great promise for practical CO2 adsorption and separation applications. The efficient CO2 uptake and enhanced CO2/N2 selectivity are due to the combination of nitrogen-doped and hierarchical porous structures of HPNC materials. 相似文献
8.
Kuikui Xiao Qunli Tang Zheng Liu Aiping Hu Shiying Zhang Weina Deng Xiaohua Chen 《Ceramics International》2018,44(4):3548-3555
3D interconnected mesoporous C/Si/SiO2 composite was synthesized via two facile processes (including magnesiothermic reduction and CVD method) with the SBA-15 as Si source and CH4 as carbon precursor. The micro/mesopores inside the Si/SiO2 particles greatly increase the specific surface area, thus shortening the diffusion distance of lithium ions, electron and guaranteeing fast penetration of electrolyte. Raman spectra shows that the CVD derived carbon is partly graphitized, thus largely enhancing its conductivity. Si/SiO2 coated with two-track carbon (both longitudinal and transverse) and Si/SiO2 coated with single-track carbon are formed by only changing the experiment order. Such two-track C/Si/SiO2 electrode for lithium-ion battery exhibits 63% higher capacity than the single-track C/Si/SiO2 electrode at high-rate performance, attributed to the fast electrochemical reaction kinetics and electron transport rendered by the conductive 3D interconnected structure. This functional structure can effectively accommodate the volume expansion of Si/SiO2 and maintain the electrical connection between electrode and active materials, improving the cycling stability of active materials. 相似文献
9.
The introduction of multiple heterogeneous interfaces in a ceramic is an efficient way to increase its thermal resistance. Novel porous SiC–SiO2–Al2O3–TiO2 (SSAT) ceramics were fabricated to achieve multiple heterogeneous interfaces by sintering equal volumes of SiC, SiO2, Al2O3, and TiO2 compacted powders with polysiloxane as a bonding phase and carbon as a template at 600 °C in air. The porosity could be controlled between 66% and 74% by adjusting the amounts of polysiloxane and the carbon template. The lowest thermal conductivity (0.059 W/(m·K) at 74% porosity) obtained in this study is an order of magnitude lower than those (0.2–1.3 W/(m·K)) of porous monolithic SiC, SiO2, Al2O3, and TiO2 ceramics at an equivalent porosity. The typical specific compressive strength value of the porous SSAT ceramics at 74% porosity was 3.2 MPa cm3/g. 相似文献
10.
《Ceramics International》2023,49(3):4082-4090
Hollow silicon oxycarbide (SiOC) ceramic microspheres were synthesized through solvothermal process of vinyltriethoxysilane in NaOH solution with subsequent pyrolysis at high temperature. Increasing the synthesis temperature not only reduces the Si–C bond and C content in SiOC ceramics, but also transforms the amorphous SiOC ceramics into cristobalite SiO2 after carbonization. The rearrangement reaction of oxygen-enriched structural units results in the increase of SiO2C2 unit. No phase separation occurs at 1400 °C, and SiC nanocrystals are mainly come from the carbothermal reduction reaction of SiO2 with free C. The size change of SiO2 nanograins were further investigated by HF etching. The porous carbon is obtained after removal of SiO2, while HF etching has no effect on the structure of free C. The C content affects the structure evolution of SiOC ceramics significantly. Although the size of SiO2 grows as increase of pyrolysis temperature, the high C content inhibits the crystallization and growth of SiO2 during the pyrolysis process. 相似文献
11.
Direct fabrication of mesoporous carbons using in-situ polymerized silica gel networks as a template
Sangjin Han 《Carbon》2003,41(8):1525-1532
Mesoporous carbons were synthesized by in-situ polymerized silica gel networks as a template. The co-condensation of carbon precursor (sucrose) and silica precursor (sodium silicate) followed by heat treatment generated a carbon/silica nanocomposite. After etching the silica template, mesoporous carbons were obtained. Under optimum synthesis conditions a mesoporous carbon with a high surface area of >800 m2/g and a narrow pore size distribution centered at 3 nm was produced. The three-dimensionally interconnected silica structures effectively functioned as the template for the porous carbon materials. 相似文献
12.
《Journal of the European Ceramic Society》2007,27(4):2095-2102
An in situ reaction bonding technique was developed to fabricate mullite-bonded porous silicon carbide (SiC) ceramics in air from SiC and α-Al2O3, using graphite as the pore-former. Graphite is burned out to produce pores and the surface of SiC is oxidized to SiO2 at high temperature. With further increasing the temperature, the amorphous SiO2 converts into cristobalite and reacts with α-Al2O3 to form mullite (3Al2O3·2SiO2). SiC particles are bonded by the mullite and oxidation-derived SiO2 to obtain porous SiC ceramics. The reaction bonding behavior, open porosity, pore size distribution and mechanical strength of porous SiC ceramics were investigated as a function of the sintering temperature, forming pressure and graphite content. In addition, the phase composition and microstructure were also studied. 相似文献
13.
Synthesis of resorcinol-formaldehyde/silica composite aerogels and their low-temperature conversion to mesoporous silicon carbide 总被引:1,自引:0,他引:1
Ke ChenZhihao Bao Ai DuXiurong Zhu Guangming WuJun Shen Bin Zhou 《Microporous and mesoporous materials》2012,149(1):16-24
Resorcinol-formaldehyde/silica composite (RF/SiO2) gels were acid-catalyzed formed in one pot at 27 °C within 60 min, and then dried to aerogels with supercritical fluid CO2. After carbonization in nitrogen atmosphere and a magnesiothermic reaction at 700 °C, RF/SiO2 aerogels were successfully converted to monolithic mesoporous silicon carbide (SiC aerogels). The starting RF/SiO2 aerogels had an interpenetrating organic/inorganic network and the resulting SiC products preserved monolithic mesoporous morphology similar to the original templates. The as-synthesized SiC aerogels consisted of nanocrystalline β-SiC, possessed a BET surface area of 232 m2/g and showed sufficient mesoporosity. They had a direct band gap of about 3.2 eV (less than that of bulk β-SiC) and showed photoluminescence at room temperature. The mechanisms about the formation of RF/SiO2 gels and the conversion to SiC aerogels were discussed. Potentially, the reported method can be used to convert many metal or semimetal oxide/carbon composite aerogels to carbide aerogels at relatively low temperature for many catalytic, electronic, photonic and thermal applications. 相似文献
14.
Resorcinol–formaldehyde/silica composite (RF/SiO2) aerogel was synthesized by sol–gel process followed by supercritical drying (SCD). Monolithic SiC aerogel was obtained from RF/SiO2 aerogel after carbothermal reduction. The evolution of physical property, crystal structure, morphology and pore structure from RF/SiO2 to SiC aerogel was investigated by different methods, such as X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and N2 adsorption/desorption. The as-synthesized SiC aerogel presented typical mesoporous structure and possessed high porosity (91.8%), high surface area (328 m2/g) and large pore volume (2.28 cm3/g). Carbothermal reduction mechanism was also discussed based on the experiment and characterization results. 相似文献
15.
Elham Kamali Heidari Ehsan Marzbanrad Cyrus Zamani Babak Raissi 《Nanoscale research letters》2010,5(2):370-373
Ultrafine WO3 nanoparticles were synthesized by nanocasting route, using mesoporous SiO2 as a template. BET measurements showed a specific surface area of 700 m2/gr for synthesized SiO2, while after impregnation and template removal, this area was reduced to 43 m2/gr for WO3 nanoparticles. HRTEM results showed single crystalline nanoparticles with average particle size of about 5 nm
possessing a monoclinic structure, which is the favorite crystal structure for gas sensing applications. Gas sensor was fabricated
by deposition of WO3 nanoparticles between electrodes via low frequency AC electrophoretic deposition. Gas sensing measurements showed that this
material has a high sensitivity to very low concentrations of NO2 at 250°C and 300°C. 相似文献
16.
In the present work, mesoporous carbon monoliths with worm-hole structure had been synthesized through hydrothermal reaction by using amphiphilic triblock copolymer F127 and P123 as templates and resole as carbon precursor. Synthesis conditions, carbonization temperature and pore structure were studied by Fourier transform infrared, thermogravimetric analysis, transmission electron microscopy and N2 adsorption–desorption. The results indicated that the ideal pyrolysis temperature of the template is 450 °C. The organic ingredients were almost removed after further carbonized at 600 °C and the mesoporous carbon monoliths with worm-hole structure were obtained. The mesoporous carbon synthesized with P123 as single template exhibited larger pore size (6.6 nm), higher specific surface area (747 m2 g?1), lower pore ratio (45.9 %) in comparison with the mesoporous carbon synthesized with F127 as single template (with the corresponding value of 4.9 nm, 681 m2 g?1, 49.6 %, respectively), and also exhibited wider pore size distribution and lower structure regularity. Moreover, the higher mass ratio of template P123/resole induced similar pore size, larger specific surface area and lower pore ratio at the same synthesizing condition. It was also found that the textural structure of mesoporous carbon was affect by calcination atmosphere. 相似文献
17.
Nitrogen-doped porous graphitic carbons (NPGCs) with controlled structures were synthesized using cheap nano-CaCO3 as template, melamine-formaldehyde resin as carbon precursor, and dilute HCl as template removing agent. In addition to its use as a template, the nano-CaCO3 acted as an internal activating agent to produce micro- and mesopores, as an adsorbent to remove the released hazardous gases (i.e. HCN, NH3), and as a mild graphitization catalyst. The obtained NPGCs with hierarchical nanopores contained as high as 20.9 wt% of nitrogen, had surface areas of up to 834 m2 g–1, and also exhibited high thermal stability with respect to oxidation. Using carbohydrate or phenolic resin as the carbon precursor, this simple approach was also capable of producing hierarchical porous graphitic carbons with high surface area (up to 1683 m2 g–1) and extremely large pore volumes (>6 cm3 g–1). X-ray diffraction and infrared spectroscopy suggested that the intermediate CaCN2 or CaC2 generated during the carbonization plays a critical role in the formation of the graphitic structure. 相似文献
18.
Copper oxide doped mesoporous KIT-6 materials were synthesized by ultrasonication as impregnation method. The highly ordered nature of mesoporous CuO-KIT-6 materials analyzed by low angle X-ray diffraction. The high surface area, pore diameter and mesoporous nature of synthesized materials were confirmed by BET surface area analysis. Si–O–Si, Si–OH and Cu–O–Si bonds in the framework of CuO-KIT-6 were verified by FTIR spectroscopy. The Cu2+ ← O2? charge-transfer transitions and d–d transitions of dispersed Cu2+ on ordered mesoporous KIT-6 were identified by DRS UV–Vis spectroscopy. The morphology of the synthesized CuO-KIT-6 materials was analyzed by HR-SEM. The 3D ordered nature of CuO-KIT-6 confirmed by TEM analysis. The highly ordered 3D mesoporous CuO-KIT-6 materials are excellent catalyst for benzene hydroxylation reaction through C-H activation and styrene epoxidation reaction with 30 % aqueous H2O2. The catalyst CuO-KIT-6 itself showed a good conversion towards both reactions. 相似文献
19.
Sung‐Woo Park Jae‐Chan Kim Byung‐Kook Kim Dong‐Wan Kim 《Journal of the American Ceramic Society》2016,99(6):1885-1888
SiC nanocrystals were prepared using waste poly(vinyl butyral) sheet as a carbon source. SiO2/poly(vinyl butyral) mixtures are converted to SiO2/pyrolytic carbon composites via pyrolysis at low temperatures (500°C) in an Ar atmosphere. Subsequently, low‐temperature magnesiothermic reduction and purification processes result in the formation of tiny SiC nanocrystals. The size of the synthesized SiC nanocrystals ranged from 3 to 12 nm, i.e., they are smaller than the SiO2 precursor offering large specific surface area of 175.76 m2/g and are single phase as 3C–SiC. Hence, 3C–SiC nanocrystals were successfully synthesized using waste poly(vinyl butyral) through this simple, inexpensive, and scalable process, which will be a new application in the recycling industry. 相似文献
20.
Micro/mesoporous SiOC bulk ceramics with the highest surface area and the narrowest pore size distribution were prepared by water‐assisted pyrolysis of polysiloxane in argon atmosphere at controlled temperatures (1100°C–1400°C) followed by etching in hydrofluoric acid (HF) solution. Their pyrolysis behaviors, phase compositions, and microstructures were investigated by DSC, FTIR, XRD, and BET. The Si–O–Si bonds, SiO2‐rich clusters, and SiO2 nanocrystals in the pyrolyzed products act as pore‐forming species and could be etched away by HF. Water injection time and pyrolysis temperature have important effects on phase compositions and microstructures of the porous SiOC bulk ceramics, which have a maximum‐specific surface area of 2391.60 m2/g and an average pore size of 2.87 nm. The porous SiOC ceramics consist of free carbon phase, silicon carbide, and silicon oxycarbide. 相似文献