Silicon Oxycarbide Ceramics Research Articles

Modulation of Free Carbon Structures in Polysiloxane-Derived Ceramics for Anode Materials in Lithium-Ion Batteries.

Polymer-derived silicon oxycarbide (SiOC) ceramics have garnered significant attention as novel silicon-based anode materials. However, the low conductivity of SiOC ceramics is a limiting factor, reducing both their rate capability and cycling stability. Therefore, controlling the free carbon content and its degree of graphitization within SiOC is crucial for determining battery performance. In this study, we regulated the free carbon content using divinylbenzene (DVB) and controlled the graphitization of free carbon with the transition metal iron (Fe). Through a simple pyrolysis process, we synthesized SiOC ceramic materials (CF) and investigated the impact of Fe-induced changes in the carbon phase and the amorphous SiOC phase on the comprehensive electrochemical performance. The results demonstrated that increasing the DVB content in the SiOC precursor enhanced the free carbon content, while the addition of Fe promoted the graphitization of free carbon and induced the formation of carbon nanotubes (CNTs). The electrochemical performance results showed that the CF electrode material exhibited a high reversible capacity of approximately 1154.05 mAh g-1 at a low current density of 100 mA g-1 and maintained good rate capability and cycling stability after 1000 cycles at a high current density of 2000 mA g-1.

Multiscale design and digital light processing preparation of high-strength SiOC ceramic metastructures for tuning microwave absorption properties

Silicon oxycarbide (SiOC) ceramics have been used to fabricate microwave-absorbing metastructures, demonstrating impressive absorption capabilities. However, SiOC ceramic metastructures with excellent performance require simple fabrication processes and appropriate mechanical and electromagnetic properties. In this study, a solvent-free photosensitive polysiloxane preceramic was developed by blending methoxy/hydroxy polysiloxanes with acrylates, with a ceramic yield of over 60% after curing using a novel two-step ultraviolet (UV)/thermal method. The composition and microstructure of SiOC ceramics can be designed by controlling the preceramic composition. Dense, crack-free gyroid-shellular shaped triple periodic minimal surface (GS-TPMS) electromagnetic metastructures were fabricated using digital light processing (DLP) 3D printing technology. By designing the porosity of the GS-TPMS structure to 51%, an effective absorption bandwidth that covers the X-band can be achieved at a thickness of 3.1 mm. The honeycomb structure, with a geometric density of 0.69 g/cm3, exhibited a high compressive strength of 107.05 MPa. This paper presents an efficient approach for the prompt and customized fabrication of lightweight ceramic metastructures with outstanding microwave absorption properties.

Lightweight aerogel-like silicon oxycarbide ceramics with directionally honeycomb-like structure for high temperature environments

Ceramic aerogels are considered promising thermal protection materials for their excellent thermal insulation performance and high-temperature stability. Lightweight aerogel-like silicon oxycarbide (SiOC) was prepared from polyhydromethylsiloxane (PHMS) as precursor and divinylbenzene (DVB) as crosslinker through solvothermal, freeze casting/drying and pyrolysis. The aerogel-like SiOC ceramic can achieve a low density of 0.087 g·cm−3 under the optimized mass ratio of DVB:PHMS of 1.5:1, with a directionally honeycomb-like structure induced by cyclohexane ice-crystals during the freeze casting. The unique porous structure endows the aerogel-like SiOC with low effective thermal conductivity (0.051–0.057 W·m−1·K−1) and good compressive strength (0.30–0.34 MPa). Moreover, the aerogel-like SiOC maintains structural and property stability after heat treatment (1400 °C in argon or 800 °C in air) for good thermal stability and oxidation resistance, which sheds light on the preparation of high-performance SiOC thermal insulation materials for high-temperature environments.

Preparation of polymer-derived SiOC-Cu ceramic composites and their tribological performance

Cu-containing silicon oxycarbide (SiOC) ceramic composites have been prepared by thermal pyrolysis of polymeric precursors and subsequent spark plasma sintering at 1600 °C. The resulting composites consist of SiO2, SiC, free carbon, and Cu-Si alloys. The microstructure of the composites has been identified via optical microscope and SEM. The mechanical properties, including the Vickers hardness, nano-indentation hardness, and Young’s modulus, of the SiOC composites have been assessed via indentation methods. The effects of Cu content on the tribological properties of the composites have additionally been investigated under different sliding frequencies against Al2O3 spheres at room temperature. It is shown that the introduction of the Cu-Si alloys is effective in reducing the friction coefficient of the material system, which decreases linearly from 0.27 of monolithic SiOC to 0.15 of SiOC with 7 wt% Cu content at 1 Hz. Raman spectroscopy has highlighted the friction-driven evolution of the free carbon phase in the SiOC ceramics. Finally, a correlation between the sliding frequency, Cu-Si content, and tribological properties of SiOC is established.

Toward High-Performance Piezoresistive Polymer Derived SiOC Ceramics through Masked Stereolithography 3D Printing with β-Silicon Carbide Nanopowder Reinforcement.

Enhancing the piezoresistivity of polymer-derived silicon oxycarbide ceramics (SiOCPDC ) is of great interest in the advancement of highly sensitive pressure/load sensor technology for use in harsh and extreme working conditions. However, a facile, low cost, and scalable approach to fabricate highly piezoresistive SiOCPDC below 1400°C still remains a great challenge. Here, the fabrication and enhancement of piezoresistive properties of SiOCPDC reinforced with β-SiC nanopowders (SiCNP ) through masked stereolithography-based 3D-printing and subsequent pyrolysis at 1100°C are demonstrated. The presence of free carbon in SiCNP augments high piezoresistivity in the fabricated SiCNP -SiOCPDC composites even at lower pyrolysis temperatures. A gauge factor (GF) in the range of 4385-5630 and 6129-8987 with 0.25 and 0.50wt% of SiCNP , respectively is demonstrated, for an applied pressure range of 0.5-5MPa at ambient working conditions. The reported GF is significantly higher compared to those of any existing SiOCPDC materials. This rapid and facile fabrication route with significantly enhanced piezoresistive properties makes the 3D-printed SiCNP -SiOCPDC composite a promising high-performance material for the detection of pressure/load in demanding applications. Also, the overall robustness in mechanical properties and load-bearing capability ensures its long-term stability and makes it suitable for challenging and severe environment applications.

Phenol Adsorption Performance of Nitrogen-Doped Porous Carbon Derived from Silicon Oxycarbide Ceramics

Phenol Adsorption Performance of Nitrogen-Doped Porous Carbon Derived from Silicon Oxycarbide Ceramics

Additive Manufacturing of Silicon Oxycarbide Ceramics with Minimal Surface Structures

The traditional ceramic powder sintering forming method severely limits the performance of the fabricated parts. Many new solutions have been achieved by precursor derived ceramics (PDC). Silicon oxycarbide ceramics as one of them has many performance advantages such as excellent mechanical properties, low density, excellent thermal stability, low thermal conductivity, and resistance to thermal shock and corrosion. In this paper, a photosensitive polysiloxane resin (PPR) with excellent light curing properties was prepared, which has high precision in the process of additive manufacturing. In addition, samples with minimal surface features in different porosity were fabricated. The compressive strength of the structure with 85%, 75%, and 65% porosity was about 9.51 MPa, 13.76 MPa, and 21.69 MPa, respectively. These porous silicon oxycarbide ceramics are likely to have a wide range of potential applications in aerospace, aviation, and other fields.

Biomimetic porous silicon oxycarbide ceramics with improved specific strength and efficient thermal insulation

Considering the challenge of aerodynamic heating, the development of high-performance insulating ceramic materials with lightweight and low thermal conductivity is crucially important for aerospace vehicles to achieve flight at high speed for a long time. In this work, macro-porous silicon oxycarbide (SiOC) ceramics with directional pores (DP-SiOC) (mean pore size of 88.1 μm) were prepared using polysiloxane precursors via freeze casting and photocrosslinking, followed by pyrolysis. The DP-SiOC samples were lightweight (density ∼0.135 g cm–3) with a porosity of 90.4%, which showed good shapability through the molding of polysiloxane precursors. The DP-SiOC samples also exhibited an ultra-low thermal conductivity of 0.048 W(m K)–1 at room temperature, which can also withstand heat treatment at 1200 °C for 1 h. In addition, scaffolds with triply periodic minimal surfaces (TPMS) were fabricated using digital light processing (DLP) printing, which was further filled with polysiloxane precursors for increasing the strength of DP-SiOC. The TPMS scaffolds filled with macro-porous SiOC ceramics (TPMS-DP-SiOC) showed good integration between TPMS and macro-pore structures, which had a porosity ∼75% and high specific strength of 9.73 × 103 N m kg–1. The thermal conductivity of TPMS-DP-SiOC samples was 0.255 W(m K)–1 at room temperature. The biomimetic TPMS-DP-SiOC ceramics developed in this study are likely used for thermal protection systems.

Molecular Aggregation Strategy for Pore Generation in SiOC Ceramics Induced by the Conjugation Force of Phenyl.

Porous silicon oxycarbide (SiOC) ceramics with tailorable microstructure and porosity were fabricated using phenyl-substituted cyclosiloxane (C-Ph) as a molecular-scale porogen are analyzed in this study. A gelated precursor was synthesized via the hydrosilylation of hydrogenated and vinyl-functionalized cyclosiloxanes (CSOs), followed by pyrolysis at 800-1400 °C in flowing N2 gas. Tailored morphologies, such as closed-pore and particle-packing structures, with porosities in the range 20.2-68.2% were achieved by utilizing the high boiling point of C-Ph and the molecular aggregation in the precursor gel induced by the conjugation force of phenyl. Moreover, some of the C-Ph participated in pyrolysis as a carbon source, which was confirmed by the carbon content and thermogravimetric analysis (TGA) data. This was further confirmed by the presence of graphite crystals derived from C-Ph, as determined by high-resolution transmission electron microscopy (HRTEM). In addition, the proportion of C-Ph involved in the ceramic process and its mechanism were investigated. The molecular aggregation strategy for phase separation was demonstrated to be facile and efficient, which may promote further research on porous materials. Moreover, the obtained low thermal conductivity of 27.4 mW m-1 K-1 may contribute to the development of thermal insulation materials.

Electrochemical Performance of Polymer-Derived Silicon-Oxycarbide/Graphene Nanoplatelet Composites for High-Performance Li-Ion Batteries.

Amorphous polymer-derived silicon-oxycarbide (SiOC) ceramics have a high theoretical capacity and good structural stability, making them suitable anode materials for lithium-ion batteries. However, SiOC has low electronic conductivity, poor transport properties, low initial Couloumbic efficiency, and limited rate capability. Therefore, there is an urgent need to explore an efficient SiOC-based anode material that could mitigate the abovementioned limitations. In this study, we synthesized carbon-rich SiOC (SiOC-I) and silicon-rich SiOC (SiOC-II) and evaluated their elemental and structural characteristics using a broad spectrum of characterization techniques. Li-ion cells were fabricated for the first time by pairing a buckypaper composed of carbon nanotubes with SiOC-I or SiOC-II as the anode. When mixed with graphene nanoplatelets, the SiOC-II/GNP composites exhibited improved electrochemical performance. High specific capacity (average specific capacity of 744 mAh/g at a 0.1C rate) was achieved with the composite anode (25 wt % SiOC-II and 75% GNP), which was much better than that of monolithic SiOC-I, SiOC-II, or GNPs. This composite also exhibited excellent cycling stability, achieving 344 mAh/g after 260 cycles at a 0.5C rate and high reversibility. The enhanced electrochemical performance is attributed to better electronic conductivity, lower charge-transfer resistance, and short ion diffusion length. Due to their superior electrochemical performance, SiOC/GNP composites with CNT buckypaper as a current collector can be considered a promising anode material for LiBs.

Highly Microporous Nitrogen-Doped Carbon Derived from Silicon Oxycarbide Ceramics for Supercapacitor Application

Highly Microporous Nitrogen-Doped Carbon Derived from Silicon Oxycarbide Ceramics for Supercapacitor Application

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.

Understanding SiOC atomic structures via synchrotron X-ray and reactive force field potential studies

Silicon oxycarbide (SiOC) is a unique system that can generate various compositions and microstructures via different polymeric precursors and pyrolysis conditions. However, understanding of the atomic structure evolution, such as cluster formation, phase evolution, and atomic coordination, is lacking. In this study, cluster evolution and atomic coordination for different SiOC ceramics pyrolyzed at 1200 °C and 1500 °C were investigated by high energy X-ray diffraction (HE-XRD) and radial distribution function (RDF) analysis. A new Reactive Force Field (ReaxFF) molecular dynamics modeling approach was developed to understand nanocluster separation and early-stage atomic radial coordination. For the first time, we demonstrate that orthorhombic SiO2 forms and converts to growth resistant amorphous SiO2. Cubic β-SiC also forms at lower temperatures than reported, along with a minor amount of hexagonal SiC that has never been reported. The RDF data support such phase evolution understanding. ReaxFF simulation provides direct data on atomic mixing, elemental separation, and effects of precursor molecular structures and compositions, especially in the early stage of the pyrolysis. The simulated RDF data complement the experimental data, revealing the significant presence of C–H bonds along with Si–O and C–C bonds.

Polymer-derived SiOC ceramics: A potential catalyst support controlled by the sintering temperature and carbon content

A series of silicon oxycarbide ceramics with varying carbon content from ca. 10 wt% to ca. 40 wt% were prepared by thermal pyrolysis of four commercially available polysiloxanes and subsequent spark plasma sintering (SPS) at 1200 °C, 1400 °C, and 1600 °C. The results showed that the high carbon content led to a porous microstructure, and for SiOC with ca. 40 wt% carbon content, its porosity and specific surface area at 1600 °C reached 34% and 262 m2/g, respectively. The electrochemical behavior of materials was evaluated. It was shown that SiOC has a certain degree of electrocatalytic activity, and the sample with 10 wt% carbon content obtained at 1200 °C exhibited an overpotential of 450 mV vs. RHE at 10 mA·cm−2 in acid medium. Finally, it was analyzed that the electrochemical behavior of SiOC is closely related to the phase composition and microstructure of the resulting ceramics.

Influence of polymer synthesis route and organic fraction content on structure and porosity of silicon oxycarbide ceramics

This paper describes the structural and textural characteristics of silicon oxycarbide ceramics obtained from three different hybrid polymers by varying pyrolysis temperature. The first polymer was prepared by hydrosilylation between poly(hydromethylsiloxane) and divinylbenzene in stoichiometric proportions; the second was similarly obtained, but with excess of divinylbenzene (60 wt.%) and the third was also synthesized with 60 wt.% divinylbenzene, involving simultaneously hydrosilylation and radical reactions. Precursors were pyrolysed under argon at 1000, 1200 and 1500?C to produce silicon oxycarbide-based ceramics. Silicon carbide phase development and devitrification resistance were influenced by the disordered and ordered residual carbon fraction, which was directly related to the polymer structure. High specific surface area and pore volume values were obtained in C-richer ceramics at 1500?C derived from poly(divinylbenzene) network-containing precursor. Silicon oxycarbide matrices, derived from hybrid polymers containing graphitic carbon and silicon carbide phases together with different amount of porosity, revealed desirable features for electrochemical applications and adsorbent systems.

Analyzing the effect of composition, density, and the morphology of the “free” carbon phase on elastic moduli in silicon oxycarbide ceramics

We perform atomistic simulations to model structures and calculate elastic properties of silicon oxycarbide ceramics. We explore individual parameters – composition, density, carbon content – to disentangle mutual dependencies that are difficult to separate in experimental studies. Each parameter is studied through dynamic simulations at finite temperatures for a wide range of temperatures. With multi-million atom models in simulation boxes as large as 40 nm, we reveal a hitherto “hidden” parameter: the morphology of the “free” carbon phase. Embedding, distribution, and interconnection of the carbon phase inside the amorphous matrix of SiCO severely impact the material's mechanical properties. As a consequence, we call for the development of new characterization techniques that will quantify the morphology of carbon in this and similar systems.

Hydrogen storage in graphene nanoplatelet incorporated silicon oxycarbides

AbstractHighly porous materials having high specific surface areas are strong candidate materials for hydrogen storage by physisorption. However, the development of suitable adsorbents for hydrogen storage having chemical stability is still a challenge. Micro and mesoporous silicon oxycarbide (SiOC) ceramics due to their excellent chemical stability can overcome this constraint. Contrary with our expectations, the addition of graphene nanoplatelets (GNP) to SiOC ceramics resulted in a lower gravimetric density. A maximum gravimetric storage density of 1.58 wt.% was observed at 6 bar after adding 0.3 wt.% of GNP, whereas the pristine SiOC ceramic showed a gravimetric capacity of 2.07 wt.% at 6 bar. We have proposed a theoretical framework to quantify these phenomena in line with the existing structural model. We show that the addition of GNP results in an increase in the size of the silica nanodomain leading to an overall reduction in hydrogen uptake. Furthermore, we hypothesize that the addition of GNP beyond 3 wt.% could lead to an increase in the coordination of mixed bonds in the interface and subsequent loss of porosity in the composite. Our study confirms that the pore sizes are crucial in determining the hydrogen uptake in these composites.

The structure evolution of hollow SiOC ceramic microspheres prepared with solvothermal method

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.

Impact of blending with polystyrene on the microstructural and electrochemical properties of SiOC ceramic

AbstractIn this work, we present the electrochemical behavior and microstructural analysis of silicon oxycarbide (SiOC) ceramics influenced by an addition of polystyrene (PS). Polymer‐derived ceramics were obtained by pyrolysis (1000°C, Ar atmosphere) of different polysiloxanes prepared by sol–gel synthesis. This method is very effective to obtain desired composition of final ceramic. Two alkoxysilanes phenylthriethoxysilane and diphenyldimethoxysilane were used as precursors. Before pyrolysis polysiloxanes were mixed with PS using toluene as a solvent. Blending with PS affects the microstructure and free carbon content in the final ceramic material. Free carbon phase has been confirmed to be a major lithium storage host. Nevertheless, we demonstrate here that capacity does not increase linearly with increasing carbon content. We show that the amount of SiO4 units in the SiOC microstructure increases the initial capacity but decreases the cycling stability and rate capability of the material. Furthermore, the microstructure of the free carbon influences the electrochemical performance of the ceramic: More ordered graphitic clusters favor better rate capability performance.

Preparation of silicon oxycarbide (SiOC) anodes for high performance Li-ion batteries using competitive relationship between crosslinking and polymerization

SiOC anode is considered as a candidate for the next generation of lithium ion batteries, because of its appealing specific capacity and relative small volume expansion. However, the inherent inferior electron conductivity blocks its development. Recently, controlling the amount of free carbon domains is adopted to modify the performance, ignoring the influence of free C on the SiOC phases change and their synergistic effect on the performance. The crosslinking and polymerization competition between divinylbenzene and polymethylsilsesquioxane was coordinated to regulate the free carbon and phase composition of SiOC ceramics, and a durable SiOC anode with high ceramic yield was prepared. The result is that, keeping the proportion of free C about 10% and increasing the SiO3C and SiO2C2 phases ratios can obtain good anode within limited cycle life (440 cycle in this work), and increasing free C amount further is necessary for durable long cycle life. Herein, S-DVB-2 anode with 12% free C delivers 698.7 mAh g−1 at a current density of 100 mA g−1 after 100 cycles, and S-DVB-1 anode with 20.6% free C shows excellent stable long cycle performance at the current density of 0.5 A g−1, the remaining capacity is 476 mAh g−1 after 500 cycles.