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Role of polysiloxanes in the synthesis of aligned porous silicon oxycarbide ceramics
摘要： The present work focuses on establishing the role of polysiloxane precursors in the synthesis of aligned porous polymer derived silicon oxycarbide ceramics. The precursors used for the synthesis are, polymethylhydrosiloxane, vinyl terminated polydimethylsiloxane and cyclic tetramethyl-tetravinlycyclotetrasiloxane. Hydrotalcite is used for attaining aligned macroporosity during the crosslinking stage itself. Subsequently, pyrolysis of the sample has been carried out to synthesize the ceramics. The evolution of pore structure in these PDCs during the crosslinking and pyrolysis is co-related to the thermal decomposition behaviour. The pore morphology, structure and the size were analyzed using SEM, X-ray computed tomography and BET. Our studies confirm the presence of bimodal porosity in these PDCs. These PDCs have a specific surface area ranging from 77 - 160 m2/g and a total pore volume ranging from 0.18 - 0.29 cm3/g. These results could be significant for achieving a controlled synthesis process of porous materials suitable for various applications like adsorption, filtering and electrochemical storage.
关键词： Mesoporous,X-Ray computed tomography,Pyrolysis,Polymer derived ceramics,Specific surface area
更新于2025-09-23 15:22:29
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Fabrication of grooves on polymer-derived SiAlCN ceramics using femtosecond laser pulses
摘要： In this study, grooves were fabricated on the surface of fully dense polymer-derived SiAlCN ceramics. Industrial femtosecond laser source was used at wavelength of 1030 nm with pulse duration of 290 fs and repetition rate of 100 kHz. Moreover, comprehensive study was carried out to evaluate the influence of scan speed and energy fluence on grooves quality, including the heat-affected zone around the laser-machined grooves, microstructures of laser-irradiated surface, and cross-section morphology of grooves. A series of grooves with width in the range of 30–80 μm and depth below 280 μm was successfully fabricated using femtosecond laser pulse. Laser parameters were optimized to obtain grooves with satisfying surface quality. Furthermore, formation and disappearance of laser-induced periodic surface structures were systematically investigated. This study proposes fabrication of grooves on SiAlCN ceramics via laser processing, which provides precise method for fabrication of microstructure with fascinating properties.
关键词： Laser-induced periodic surface structures,Polymer-derived ceramics,Femtosecond laser pulse,Groove
更新于2025-09-19 17:13:59
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Growth of multi-morphology amorphous silicon oxycarbide nanowires during the laser ablation of polymer-derived silicon carbonitride
摘要： Multi-morphology amorphous SiOC nanowires were successfully prepared within the interfacial interstices between the una?ected SiCN ceramic and the bracket during the laser ablation of polymer-derived SiCN ceramic in a low-pressure argon atmosphere. Laser irradiation experiments were performed using a continuous-wave CO2 laser, and the gas source for the growth of amorphous SiOC nanowires was provided by the laser ablation of the SiCN ceramic. X-ray photoelectron spectroscopy shows that the amorphous SiOC nanowires possess a SiO2 dominated nanostructure, and the formation of amorphous SiOC nanowires is attributed to the good di?usivity of CO in SiO2. The morphologies of the amorphous SiOC nanowires include straight nanowires, beaded nanowires, helical nanowires, and branched nanowires, and these are determined by the ?owing state of the reactant gases, the laser power, and the surface morphology of the SiCN ceramics. Each amorphous SiOC nanowire with speci?c morphology can be uniformly distributed in separate regions, which makes it possible to control the growth of amorphous SiOC nanowires in di?erent morphologies.
关键词： Laser ablation,SiOC,Polymer-derived ceramics,Amorphous nanowires,Multi-morphology
更新于2025-09-12 10:27:22
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Femtosecond laser pulse ablation characteristics of polymer-derived SiAlCN ceramics
摘要： Polymer-derived ceramics (PDCs) are promising high-performance materials for various applications, yet their brittleness represents major drawback in their machining. Femtosecond laser pulse ablation is non-contact rapid processing method used in precision machining of PDCs. Herein, two laser parameters (laser energy fluence and rotational speed) were investigated to achieve laser–material interactions and machining characteristics via machine single circular lines, blind holes, and through-holes in polymer-derived SiAlCN ceramics. With the decrease in rotational speed, the morphology of single circular lines gradually roughened and heat-affected zone was produced. Varying ablation rates were obtained at different energy fluences. For blind holes, three different ablation regions were observed. As the energy fluence increased, blind holes gradually transformed into through-holes. Through-holes with near-cylindrical profiles and minimal collateral damage were obtained. Ablation debris deposited around through-holes were indicative of N release, breaking of Si-N and C-C bonds, and formation of SiOx. Laser ablation of PDCs led to the formation of laser-induced surface structures, bubble pits, stripe structures, molten materials, and sphere-like particles.
关键词： femtosecond laser pulse,ablation characteristics,polymer-derived ceramics,energy fluence
更新于2025-09-12 10:27:22
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Low-frequency dielectric dispersion in polymer-derived amorphous silicon carbonitride ceramics
摘要： Dielectric response of polymer-derived amorphous silicon carbonitride (PDC-SiCN) material was studied over a wide frequency range from 1 mHz to 10 MHz. Apart from presenting a relaxation process over 105–0.03 Hz frequency range, the material showed a strong low-frequency dielectric dispersion (LFDD), which resulted in extremely high permittivities (up to 105) at frequencies lower than 0.03 Hz. It is identified that this LFDD resulted from relaxation process was not induced by conductivity. Therefore, PDC-SiCN material showed two relaxation processes. Based on its microstructure, two polarization mechanisms were proposed for PDC-SiCN: a mechanism based on polarons generated by unpaired electrons present in the material and an interfacial polarization mechanism as a result of different properties of SiCxN4-x matrix and free-carbon clusters. Interfacial polarization process was simulated based on a parallel plate model involving two different materials. The result indicated that the relaxation time of an interfacial polarization can be distributed over a broad time range in the material.
关键词： polaron,polymer-derived ceramics,low-frequency dielectric dispersion,interfacial polarization
更新于2025-09-10 09:29:36