Polymer-derived Silicon Oxycarbide Ceramics Research Articles

SiCO Ceramics as Storage Materials for Alkali Metals/Ions: Insights on Structure Moieties from Solid-State NMR and DFT Calculations.

Polymer-derived silicon oxycarbide ceramics (SiCO) have been considered as potential anode materials for lithium- and sodium-ion batteries. To understand their electrochemical storage behavior, detailed insights into structural sites present in SiCO are required. In this work, the study of local structures in SiCO ceramics containing different amounts of carbon is presented. 13 C and 29 Si solid-state MAS NMR spectroscopy combined with DFT calculations, atomistic modeling, and EPR investigations, suggest significant changes in the local structures of SiCO ceramics even by small changes in the material composition. The provided findings on SiCO structures will contribute to the research field of polymer-derived ceramics, especially to understand electrochemical storage processes of alkali metal/ions such as Na/Na+ inside such networks in the future.

In Vitro Cytocompatibility Assessment of Ti-Modified, Silicon-oxycarbide-Based, Polymer-Derived, Ceramic-Implantable Electrodes under Pacing Conditions.

Polymer-derived ceramics (PDC) have recently gained increased interest in the field of bioceramics. Among PDC's, carbon-rich silicon oxycarbide ceramics (SiOC) possess good combined electrical and mechanical properties. Their durability in aggressive environments and proposed cytocompatibility makes them an attractive material for fabrication of bio-MEMS devices such as pacemaker electrodes. The aim of the present study is to demonstrate the remarkable mechanical and electrical properties, biological response of PDCs modified with titanium (Ti) and their potential for application as pacemaker electrodes. Therefore, a new type of SiOC modified with Ti fillers was synthesized via PDC route using a Pt-catalyzed hydrosilylation reaction. Preceramic green bodies were pyrolyzed at 1000 °C under an argon atmosphere to achieve amorphous ceramics. Electrical and mechanical characterization of SiCxO2(1-x)/TiOxCy ceramics revealed a maximum electrical conductivity of 10 S cm-1 and a flexural strength of maximal 1 GPa, which is acceptable for pacemaker applications. Ti incorporation is found to be beneficial for enhancing the electrical conductivity of SiOC ceramics and the conductivity values were increased with Ti doping and reached a maximum for the composition with 30 wt % Ti precursor. Cytocompatibility was demonstrated for the PDC SiOC ceramics as well as SiOC ceramics modified with Ti fillers. Cytocompatibility was also demonstrated for SiTiOC20 electrodes under pacing conditions by monitoring of cells in an in vitro 3D environment. Collectively, these data demonstrate the great potential of polymer-derived SiOC ceramics to be used as pacemaker electrodes.

Role of polysiloxanes in the synthesis of aligned porous silicon oxycarbide ceramics

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 to 160 m2/g and a total pore volume ranging from 0.18 to 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.

Flash pyrolysis of polymer-derived SiOC ceramics

For the first time, flash pyrolysis was carried out to fabricate polymer derived silicon oxycarbide (SiOC) ceramics. With the application of a DC electric field at a furnace temperature of only 780 °C, the SiOC ceramics exhibit characteristics that usually have to be pyrolyzed at ∼1300 °C. Both electric field and current density accelerate the SiOC microstructure development, causing carbon and SiC phases to form at >520 °C lower pyrolysis temperatures than conventional within the SiOC matrix. With higher electric fields, the samples experience greater mass loss and linear shrinkage, while also forming more SiC and a more ordered carbon phase. The SiC formation inversely impacts the carbon content, causing a decrease in electrical conductivity. Further, reducing current density results in significant carbon precipitation without SiC formation. The fundamentals can be explained based on increased nucleation rate by the electrical field, accompanied by Joule heating and electromigration. This work is the first to demonstrate the great potential of flash pyrolysis on accelerated phase separation of polymer derived SiOC.

Polymer-Derived Silicon Oxycarbide Ceramics as Promising Next-Generation Sustainable Thermoelectrics.

We demonstrate the potential of polymer-derived ceramics (PDC) as next-generation sustainable thermoelectrics. Thermoelectric behavior of polymer-derived silicon oxycarbide (SiOC) ceramics (containing hexagonal boron nitride (h-BN) as filler) was studied as a function of measurement temperature. SiOC, sintered at 1300 °C exhibited invariant low thermal conductivity (∼1.5 W/(m·K)) over 30-600 °C, coupled with a small increase in both Seebeck coefficient and electrical conductivity, with increase in measurement temperature (30-150 °C). SiOC ceramics containing 1 wt % h-BN showed the highest Seebeck coefficient (-33 μV/K) for any PDC thus far.

29Si and13C Solid-State NMR Spectroscopic Study of Nanometer-Scale Structure and Mass Fractal Characteristics of Amorphous Polymer Derived Silicon Oxycarbide Ceramics

Polymer derived silicon oxycarbide ceramics (SiOC-PDCs) with widely different carbon contents have been synthesized, and their structures have been studied at different length scales using high-resolution 13C and 29Si magic-angle-spinning (MAS) NMR spectroscopic techniques. The data suggest that the structure of these PDCs consists of a continuous mass fractal backbone of corner-shared SiCxO4-x tetrahedral units with “voids” occupied by sp2-hybridized graphitic carbon. The oxygen-rich SiCxO4-x units are located at the interior of this backbone with a mass fractal dimension of ∼2.5 while the carbon-rich units display a slightly lower dimensionality and occupy the interface between the backbone and the free carbon nanodomains.