Polymer-derived Silicon Research Articles

Polymer-Derived Silicon Oxycarbide/Graphene Oxide Porous Ceramic Monoliths Obtained from Pickering Emulsions: Application as Active Electrodes for Lithium-Ion Batteries

Polymer-Derived Silicon Oxycarbide/Graphene Oxide Porous Ceramic Monoliths Obtained from Pickering Emulsions: Application as Active Electrodes for Lithium-Ion Batteries

Preparation and electromagnetic wave absorption properties of PDC–SiC/Si3N4 composites using selective laser sintering and infiltration technology

Polymer-derived silicon carbide/silicon nitride (PDC–SiC/Si3N4) composites were prepared by additive manufacturing and infiltration technology. The composite green bodies were prepared using selective laser sintering (SLS) three-dimensional (3D) printing technology. Carbon-rich PDC–SiC was generated via precursor infiltration and pyrolysis (PIP) to increase the dielectric constant and enhance the electromagnetic wave (EMW) attenuation ability of the composites. Low-dielectric materials, including Al2O3, TiO2, and AlPO4, were introduced by sol infiltration to improve the impedance-matching characteristics of the composites. The results showed that the EMW absorption ability of the PDC–SiC/Si3N4 composites enhanced after two and four PIP cycles, whereas it degraded with further increasing the PIP cycle number. Among all the samples, the PDC–SiC/Si3N4 composite after four PIP cycles displayed an excellent EMW absorption ability with the minimal reflection loss of −46.79 dB, whereas its effective absorption bandwidth was narrow. Comparing to the sample without infiltration, the effective absorption bandwidth of the samples after the infiltration treatment with TiO2 or Al(H2PO4)3 sol increased from 1.44 GHz to 4.08 GHz and 3.52 GHz, respectively. These results demonstrate that the PIP process and infiltration with TiO2 or Al(H2PO4)3 sol resulted in a 3D-printed PDC–SiC/Si3N4 ceramic that is a promising EMW absorption material suitable for high-temperature environments.

Study on effect of structure and surface/ physical characteristics of a silicon oxycarbide by hydrofluoric acid etching

ABSTRACT In this study, polymer-derived porous silicon oxycarbide (SiOC) ceramic was synthesised by considering various polymer precursors such as polymethylhydrosiloxane, polydimethylsiloxane and cyclic 2,4,6,8-tetramethyl-2,4,6,8tetravinlycyclotetrasiloxane in various proportions. The pyrolysis temperature of 1000°C was fixed to obtain the amorphous nature of SiOC, which is considered to be favourable for use in anode material for the Li ion batteries. Further, to enhance surface properties viz porosity, pore volume of these pyrolysed SiOC ceramics, hydro fluoric acid etching was performed. In order to establish effect of etching on the SiOC ceramic, various structural and physical/surface characterisations such as Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, Brunauer–Emmet–Teller and Barrett–Joyner–Halenda analysis were conducted. The results showed that specific surface area improved from 164 to 474 m2 g−1 before and after etching, respectively.

Complex impedance study on polymer-derived amorphous silicon carbonitride

Abstract Polymer-derived amorphous-SiCN pyrolyzed at 1200 °C was studied by impedance spectroscopy at different frequencies and temperatures. Obtained impedance spectra were analyzed by using equivalent circuit method. Results revealed that two relaxation effects were involved over the entire studied temperature range, which corresponded to free carbon phase at high frequency and the interface at low frequency. The impedance spectroscopy could be well-fitted by two parallel RC circuits in series. Interface behavior dominated the polarization relaxation process, which was controlled by the resistance as well as the capacitance of interface. All processes performed a 1/T1/4 behavior, which follows a three-dimensional (3D) random hopping mechanism. This paper further found that amorphous-SiCN ceramic materials underwent an interfacial charge polarization process over a frequency range from 0.05 Hz to 10 MHz at different temperatures from −50 to 300 °C.

Synthesis and Microstructural Characterization of Barium Titanate Nanoparticles Decorated SiCN-MWCNT Nanotubes – “nanoNecklace”

In this paper, we report synthesis and characterization of flexible polymer-derived ceramic silicon carbon nitride nanotubes decorated with barium titanate (BTO) nanoparticles where multi-walled carbon nanotubes act as a template. The synthesis was achieved by controlled pyrolysis of polyurea (methylvinyl) silazane and BTO metal-organic precursor. Structural characterization by advanced microscopy techniques revealed 10–50 nm BTO nanoparticles uniformally covering the nanotubes. X-ray photoelectron spectroscopy was used to confirm the BTO perovksite phase. Possible application of this novel structure—nanoNecklace—is in nanocapacitors (NCs) where high dielectric material BTO is arranged on SiCN layer.