Silicon Oxycarbide Materials Research Articles

Synthesis of size-controlled SiOC ceramic materials by silicone oil-based emulsion method for anodes in lithium-ion batteries

A submicron spherical silicon oxycarbide (SiOC) material for lithium-ion battery anodes was successfully synthesized by employing a facile synthetic strategy that used economical silicone oil as a starting material, an emulsion method, and the subsequent pyrolysis of silicone oil emulsion at 900 °C. Although most previous studies concerning silicone-oil-based SiOC exhibited irregular and uncontrollable size after synthesis, the developed emulsion-driven SiOC preparation achieved regular submicron spherical particles. Furthermore, the emulsifier used herein formed a thin carbon coating layer after the synthesis procedure and contributed to the electrochemical performance during battery operation. The spherical submicron size-controlled SiOC material had superior capacity retention compared to pristine SiOC obtained without the emulsion method, owing to the suppressed micro-cracks induced by accumulation of mechanical stress during repeated cycles and prevention of direct contact with the electrolyte by the thin carbon-coating layer.

Silicon Oxycarbide Coatings Consisting of Defined Bottom-Up-Grown Nanostructures.

Silicon oxycarbide (SiOC) materials have arisen in the past few decades as a promising new class of glasses and glass-ceramics thanks to their advantageous chemical and thermal properties. Many applications, such as ion storage, sensing, filtering, or catalysis, require materials or coatings with high surface area and might benefit from the high thermal stability of SiOC. This work reports the first facile bottom-up approach to textured high surface area SiOC coatings obtained via direct pyrolysis of polysiloxane structures of well-defined shapes, such as nanofilaments or microrods. This work further investigates the thermal behavior of these structures by means of FT-IR, SEM, and EDX up to 1400 °C. The rods shrink in volume by ≈30% while their aspect ratio remains unaffected by pyrolysis until at least 1100 °C. The nano-sized filaments show signs of viscous flow already at a comparably low temperature of 900 °C which is very probably due to the nano-size effect. This might open a way to experimentally study the size-effect on the glass transition temperature of oxide glasses, an experimentally unexplored but very relevant topic. These structures have great potential, for example, as ion storage materials and supports in high temperature catalysis and CO2 conversion.

A materials informatics approach for composition and property prediction of polymer-derived silicon oxycarbides

Polymer-derived silicon oxycarbide (SiOC) materials enable the formation of homogeneous microstructures and high temperature stable properties. However, the relationships between the processing parameters and microstructures/properties have not been clearly understood. In this study, a materials informatics approach was employed to the SiOC materials to analyze and estimate the relationships. Datasets were constructed from results of previously reported literature about SiOC. The correlation analysis provided processing parameter ranking regarding the corresponding influences on the properties and microstructures. Such an understanding can be utilized for desired material fabrication. Machine learning models with high accuracy were proposed using the ranked features obtained from the correlation analysis. In addition, important points on the data collection, correlation analysis, and machine learning as well as limitations of the current dataset were discussed. The proposed workflow for the SiOC materials can be extended to different types of polymer-derived ceramics by incorporating various features and targets involved in the processing variables, microstructures, and properties.

A review of silicon oxycarbide ceramics as next generation anode materials for lithium-ion batteries and other electrochemical applications

The present review outlines a comprehensive overview of the research on silicon oxycarbide (SiOC) materials, which are synthesized by various synthetic routes and are investigated as alternatives to crystalline silicon anodes.

Mechanical response of silicon oxycarbide materials processed by spark plasma sintering

Nano- and micro-indentation experiments have been used to evaluate the mechanical properties of dense silicon oxycarbide (SiOC) derived materials obtained by spark plasma sintering (SPS). The sintering temperature varied from 1300 to 1700 °C, with a pressure of 40 MPa. The relationship between the mechanical properties and densification, porosity, evolution of the composition, structure and crystallization depending on the SPS sintering temperature has been determined. The SiOC sample obtained at 1400 °C shows the highest values of hardness (12 GPa) and elastic modulus (95 MPa) in both nano- and micro-indentation tests. The SPS treatment produces a neat densification of the material without promoting the phase separation of the Si–O–C matrix. In terms of the elasto-plastic behaviour, hf/hmax >0.5 and Wel/Wtot <0.7, in conjunction with AFM images, highlight the negligible formation of pile-ups. The elastic recovery is quite high, and is probably due to the flexible segregated carbon phase. The Vickers indentation patterns show the Hertzian cones typical of anomalous glasses. Some minor radial cracks can also be seen, and can be attributed to the presence of both stiffer Si–C bonds which reduce the propagation of cracks, and to carbon, which reduces the brittleness of the SiOC derived materials.

WS2 Nanosheet Loaded Silicon-Oxycarbide Electrode for Sodium and Potassium Batteries

Transition metal dichalcogenides (TMDs) such as the WS2 have been widely studied as potential electrode materials for lithium-ion batteries (LIB) owing to TMDs' layered morphology and reversible conversion reaction with the alkali metals between 0 to 2 V (v/s Li/Li+) potentials. However, works involving TMD materials as electrodes for sodium- (NIBs) and potassium-ion batteries (KIBs) are relatively few, mainly due to poor electrode performance arising from significant volume changes and pulverization by the larger size alkali-metal ions. Here, we show that Na+ and K+ cyclability in WS2 TMD is improved by introducing WS2 nanosheets in a chemically and mechanically robust matrix comprising precursor-derived ceramic (PDC) silicon oxycarbide (SiOC) material. The WS2/SiOC composite in fibermat morphology was achieved via electrospinning followed by thermolysis of a polymer solution consisting of a polysiloxane (precursor to SiOC) dispersed with exfoliated WS2 nanosheets. The composite electrode was successfully tested in Na-ion and K-ion half-cells as a working electrode, which rendered the first cycle charge capacity of 474.88 mAh g-1 and 218.91 mAh g-1, respectively. The synergistic effect of the composite electrode leads to higher capacity and improved coulombic efficiency compared to the neat WS2 and neat SiOC materials in these cells.

Helium ion irradiation effects on microstructure evolution and mechanical properties of silicon oxycarbide

In this study, silicon oxycarbide (SiOC) was fabricated by pyrolysis of a polysiloxane precursor at 1000 °C and 1500 °C in an Ar atmosphere and evaluated as a new nuclear fuel coating material. The 1000 °C pyrolyzed SiOC is fully amorphous while the 1500 °C sample contains crystalline β-SiC nanodomains, a turbostratic carbon network, and an amorphous SiOC matrix. After 100 keV He ion irradiation, no detectable microstructural changes are observed for the 1000 °C pyrolyzed SiOC. However, the 1500 °C pyrolyzed SiOC shows amorphization of crystalline phases. Neither sample has He bubbles, elemental segregation, or voids after irradiation. Irradiation induced hardening is observed for all the samples. Both hardness and elastic modulus values increase with irradiation. These high temperature stable and amorphous phase dominant SiOC materials are promising systems for the development of irradiation-tolerant fuels for advanced nuclear reactors.

Estudio del envejecimiento acelerado bajo radiación solar concentrada de vidrios de oxicarburo como receptores de alta temperatura

Solar energy and especially concentrated solar power systems (CSP) need materials that can tolerate the demanding working conditions. In this sense, the receivers are exposed to large fluxes of solar radiation that produce very high temperatures. In addition, due to the operational conditions of receivers large temperature variations occur during day and night, or on cloudy days being these the main aging factors. However, other factors such as humidity, salines environments or pollutans in industrial zones can not be ruled out. Silicon oxycarbide glasses (SiOC) are composite materials formed by a SiOC glass phase (matrix phase) and a C phase (reinforcing phase) homogeneously dispersed and they can be very promising candidates for this type of applications due to their excellent intrinsic properties like their high resistante against to both oxidation and very aggressive environments, good mechanical properties, etc. In this work we have focused in the evaluation of the composite materials (SiOC porous and dense) against thermal shock produced by Frenel lens that concentrated solar radiation more than 2600 times. In every cycle materials they have been heated (32 oC s-1) an cooled (27 oC s-1) at very high rates from room temperature to 1000 oC. This process has been repeated 100 times or lesser in the case of catastrophic material damage. The evolution of material surface during thermal shock cycles has been followed by several techniques such confocal and electronic microscopies and Raman, Infrarred and UV-Visible spectroscopies. Porous silicon oxycarbide materials experiencied a rapid and severe degradation during the first cycles but dense one tolerates quite well the exposure againts concentrated solar radiation.

Chemical Structure and Microstructure Characterization of Ladder-Like Silsesquioxanes Derived Porous Silicon Oxycarbide Materials.

The aim of this work was to synthesize porous ceramic materials from the SiOC system by the sol-gel method and the subsequent pyrolysis. The usage of two types of precursors (siloxanes) was determined by Si/C ratio in starting materials. It allows us to control the size of the pores and specific surface area, which are crucial for the potential applications of the final product after thermal processing. Methyltrimethoxysilane and dimethyldiethoxysilane were mixed in three different molar ratios: 4:1, 2:1, and 1:1 to emphasize Si/C ratio impact on silicon oxycarbide glasses properties. Structure and microstructure were examined both for xerogels and obtained silicon oxycarbide materials. Brunauer-Emmett-Teller (BET) analysis was performed to confirm that obtained materials are porous and Si/C ratio in siloxanes precursors affects porosity and specific surface area. This kind of porous ceramics could be potentially applied as gas sensors in high temperatures, catalyst supports, filters, adsorbents, or advanced drug delivery systems.

Porous and ultrahigh surface area SiOC ceramics based on perhydropolysilazane and polysiloxane

Abstract Micro-/meso-porous ceramics with ultrahigh surface areas are highly desired in high-temperature applications. In this work, formation of porous silicon oxycarbide (SiOC) is studied based on perhydropolysilazane (PHPS) and polysiloxane (PSO) precursors. The PHPS can be chemically anchored to the PSO by hydrosilylation reaction, due to the extensive Si–H bonds from the PHPS. The presence of water vapor during pyrolysis not only accelerates the hydrolysis of the PHPS additive, but also facilitates the Si–O–Si bond formation within the SiOC. The resulting SiOC material has the highest specific surface area (SSA) of ~2000 m2/g with an average pore size of 1.72 nm. The effects of the PHPS additive on the phase evolution and the resulting porous SiOC after hydrogen fluoride (HF) etching are investigated. 3D view of pore distributions qualitatively illustrates the PHPS effect on the SiO2 nanocluster formation in the SiOC. The difference between the experimental and calculated SSAs is explained based on the etchability and wall thickness of the SiO2 domains.

Physical and Thermal Studies of Carbon-Enriched Silicon Oxycarbide Synthesized from Floating Plants

In the present study, amorphous mesoporous silicon oxycarbide materials (SiOC) were successfully synthesized via a low-cost facile method by using potassium hydroxide activation, high temperature carbonization, and acid treatment. The precursors were obtained from floating plants (floating moss, water cabbage, and water caltrops). X-ray diffraction (XRD) results confirmed the amorphous Si–O–C structure and Raman spectra revealed the graphitized carbon phase. Floating moss sample resulted in a rather rough surface with irregular patches and water caltrops sample resulted in a highly porous network structure. The rough surface of the floating moss sample with greater particle size is caused by the high carbon/oxygen ratio (1: 0.29) and low amount of hydroxyl group compared to the other two samples. The pore volumes of these floating moss, water cabbage, and water caltrops samples were 0.4, 0.49, and 0.63 cm3 g−1, respectively, resulting in thermal conductivities of 6.55, 2.46, and 1.14 Wm−1 K−1, respectively. Floating plants, or more specifically, floating moss, are thus a potential material for SiOC production.

Highly micro- and mesoporous oxycarbide derived materials from HF etching of silicon oxycarbide materials

Abstract Highly micro-mesoporous silicon oxycarbide-derived carbon materials (SiOC-DC) with elevated specific surface area up to 895 m 2 g -1 and high pore volumes of mesopores (0.3 cm 3 g -1 ) and micropores (0.2 cm 3 g -1 ) have been obtained by direct etching of SiOC with HF. Initial organic-inorganic hybrids were synthesized by the sol-gel method employing triethoxysilane and polydimethylsiloxane (PDMS) of different molecular weights (550, 1750 and 4200 gmol -1 ). These hybrids were pyrolyzed from 1100 to 1400 °C. Short PDMS chains (550 gmol -1 ) within the hybrid structure rendered dense SiOC materials after pyrolysis, however long PDMS chains (1750 and 4200 gmol -1 ) produced highly micro-mesoporous SiOC materials up to 1300 °C. The etching of SiOC employing HF produced the selective removing of silica nano-domains and as a result highly micro-mesoporous SiOC-DC materials were created. In dense SiOC the HF attack is favored at the highest temperatures (1400 °C) when the SiOC is more phase separated. On the other hand, in porous SiOC there is an agreement between the pyrolysis temperature and the porosity and, therefore the SiOC materials are etched easier at 1200 °C. SiOC-DC materials are composed by a porous glassy network enriched with carbon (graphene-like carbon and turbostratic carbon) and SiC which present an incipient crystallization.

Influence of molecular architecture of Si-containing precursors and HF chemical treatment on structural and textural features of silicon oxycarbide (SiOC) materials

Silicon oxycarbide (SiOC) ceramics were obtained from two polymeric precursors to investigate the influence of pyrolysis temperature and HF chemical treatment on their structures and textural features. DVDH polycyclic polymer was prepared from 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, and 2,4,6,8-tetramethylcyclotetrasiloxane, whilst PMFV linear from poly [dimethylsiloxane-co-diphenylsiloxane] divinyl terminated. SiOC-based ceramics were obtained by pyrolysis under argon at 1000 and 1500 °C and also etched in HF solution. FT-IR, TG, XRD, N2 gas physisorption at 77 K and elemental analyses were used to characterize the obtained materials. The results revealed information about controlling chemical structure of SiOC ceramics through the combination of adequate precursor, thermal and chemical treatment. The study demonstrated the dependence of the polymeric precursors structure over the ceramic yield and Cgraphitic and β-SiC crystalline phases produced. HF etching allowed the fabrication of porous materials containing carbon conducting and SiC semiconducting phases more exposed into SiOC matrices, thus revealing potentialities to future electrochemical investigations.

Effects of different polymer precursors on the characteristics of SiOC bulk ceramics

Silicon oxycarbide (SiOC) is a material with a number of advantageous properties that strongly depend on its structure. In this study, bulk SiOC ceramics are prepared from polymer precursors with different side groups (Si–H, Si–CH3, Si–CH=CH2, and Si–C6H5) to understand the influence of the C content and network on the structures and properties of the resulting SiOC ceramics. The influence of the side groups on the thermophysical characteristics, phase evolution, oxidation resistance, and electrical conductivity of the SiOC materials is systematically studied. The SiOC samples show superior thermal stability in the air atmosphere up to 690–860 °C. The highest electrical conductivity is 705.3 S m−1 at 403 °C, the highest to date for this family of materials and 3.5 times that of other reported studies. A new concept of free C connectivity is created to correlate with the electrical conductivity. This new conducting behavior with high thermal stability presents promising application potentials in high-temperature semi-conducting components.

A SiOC anode material derived from PVA-modified polysiloxane with improved Li-storage cycling stability

A silicon oxycarbide (SiOC) material was prepared by high-temperature pyrolysis of polyvinyl alcohol (PVA)-modified polysiloxane using phenyltriethoxysilane (PhTES) as raw material and PVA as a composition-modifying additive via sol–gel route, and characterized as an anode material for Li-ion batteries. This modified SiOC material demonstrates superior electrochemical performance to the pristine SiOC material in terms of reversible specific capacity, rate performance, and cycling stability, especially for the significantly improved cycling stability. Long-term cycling test result shows that the initial reversible charge specific capacity delivered at the current density of 100 mA g−1 is 515.2 mAh g−1. After 150 cycles, a capacity of 504.6 mAh g−1 is still remained, giving capacity retention of 97.9%. The improved electrochemical performance is attributed to the increased carbon content and enhanced electrical conductivity as well as the changed morphology of the modified material due to the composition modification of the polymer pre-ceramics.

Heat treatment of commercial Polydimethylsiloxane PDMS precursors: Part I. Towards conversion of patternable soft gels into hard ceramics

The commercially available polydimethylsiloxane (Sylgard®184) is a commonly known material in microelectronic and microfluidic industries as flexible substrates, device packing elements, lab-on-a-chip, or stamps. Recently, PDMS derived materials have attracted much interest in the development of broadband electromagnetic absorbers in the terahertz and microwave regions. When exposed to high temperature (T > 900 °C) PDMS undergoes profound transformations leading to derived solid nanocomposites made of graphitic phase embedded into silicon oxycarbide structure.In this work, we discuss the PDMS thermal changes that have been evaluated using different analytical techniques (thermogravimetry-coupled mass spectrometry, and Raman spectroscopy). The pyrolysis of cross-linked gels in an inert atmosphere gave 50.94 wt% of solid residue at 1500 °C. It was observed that the presence of Si–H bonds in the curing agent promotes cross-linking between the siloxane backbones containing vinyl groups (Si–C2H3) through hydrosilylation reaction. However, excessive addition of curing agent impedes ceramic yield down to 20%. Above 1000 °C, Raman spectra show the formation of disordered sp2 carbon that subsequently organizes with the heat-treatment temperature. These carbon-rich silicon oxycarbide materials are remarkably resistance to oxidation even at 1500 °C.

Bio-templated fabrication of MnO nanoparticles in SiOC matrix with lithium storage properties

Silicon oxycarbide (SiOC) materials are considered as a promising high capacity anode for next-generation Li-ion batteries. However, the rapid capacity fading and poor cycling stability often occur in the SiOC materials with high Si content. In this work, an effective and facile strategy is reported to construct nanocomposites of MnO/SiOC, in which SiOC acts as buffer agent and conductive matrix, while MnO contributes to the major reversible capability. Microalgae (Chlorella) serves as both biological template and carbon source to synthesize SiOC microspheres with the assistance of supercritical CO2 fluid, then rice-like MnO nanoparticles are tightly embedded in the SiOC matrix through the heavy metal ion bio-sorption behavior of Chlorella. As anode materials for Li-ion batteries, the C/MnO/SiOC composites exhibit high reversible capacity of 770 mAh g−1 after 200 cycles at a current density of 100 mA g−1 with excellent cycling stability and great rate capability. This work provides a novel strategy to fabricate SiOC-based high capacity anode materials for advanced Li-ion batteries.

Evaluation of thermal shock resistance of silicon oxycarbide materials for high-temperature receiver applications

Materials used as solar receivers in concentrated solar power technology must withstand severe operational conditions caused by concentrated solar radiation. For this solar technology several ceramic material candidates (silicon carbide, porous and dense silicon oxycarbide) have been subjected to thermal shock resistance test by using Fresnel lens, the equipment available, that concentrates the solar radiation more than 2600 times. Fast heating (37 °C s−1) and cooling rates (28 °C s−1) from 100 to 1200 °C and dwelling time of 10 min are employed. The evolution of materials surface has been evaluated during test by spectroscopic methods and both confocal and electronic microscopies. It has been obtained the surface map of each analyzed sample in order to evaluate the effect of the concentrated solar radiation on the surface and the relationship with their durability. The absorptance values were also determined before and after the ageing test using normal direction between 400 and 1100 nm. Concentrated solar radiation facilitates the decomposition of tested materials producing the formation of gaseous species (mainly CO and CO2) and a dense SiO2 layer which is formed over the material surface. SiC and porous silicon oxycarbide materials fail the thermal shock resistance test. SiC experiences a catastrophic break and in the case of porous silicon oxycarbide, gases generated can evolve easily through the pores producing a severe degradation of the material surface. However, dense silicon oxycarbide resists 100 cycles at 1200 °C due to the formation of a protective SiO2 layer over the material surface and its dense microstructure that slow down the diffusion of the gases preventing bulk material from being degraded. The surface studies confirm the formation of a crystalline SiO2 phase all over the surface. Furthermore, the very similar coefficients of thermal expansion of silicon oxycarbide and silica (≈0.4 × 10−6 °C), protects material against catastrophic failure. Finally, the absorptance values remain fairly constant before and after thermal shock test (94.78 to 95.96–96.09%). The high resistance of dense silicon oxycarbide materials to thermal shock under concentrated solar radiation makes these materials suitable candidates of being used as high temperature solar receivers.

Surface modification of silicon oxycarbide films produced by remote hydrogen microwave plasma chemical vapour deposition from tetramethyldisiloxane precursor

The motivation for this contribution is the search for thin-film silicon oxycarbide (SiOC) materials suitable for modern electronics with good chemical/thermal stability, good barrier properties and conformal coverage, which can be deposited on rigid and flexible substrates, and whose surface can be organically functionalized. Two types of thin SiOC films of very different nature, such as polymer-like and ceramic-like, were fabricated by means of remote hydrogen microwave plasma chemical vapour deposition (RP-CVD) from 1,1,3,3–tetramethyldisiloxane (TMDSO). The RP-CVD coatings deposited on a silicon substrate were then modified by treatment with a direct radiofrequency (RF) plasma process induced in a mixture of argon and water vapour (Ar/H2O), which resulted in the surface activation through the formation of highly reactive silanol groups (SiOH). In this process a silicon oxide layer (SiOx) was also formed, and its growth was examined by FTIR, XPS and ellipsometry. The growth of the SiOx structure reduces the film thickness of silicon oxycarbide. Activation of the film surface is completed in <10 s. In the next modification step, the RP-CVD films were silanized by immobilizing (3-aminopropyl)triethoxysilane (APTES). Attachment of APTES molecules to the activated surface of SiOC films was observed with the development of an additional layer of SiOx on the surface. The silanization with APTES vapour under nitrogen allowed the formation of 10 nm-thick condensate. The AFM microscopic examination showed that the deposited APTES layers are homogeneous without aggregates specific for conventional silanization from the solution. The final modification of RP-CVD films was achieved by functionalization with an organic fluorescent probe, which involves the covalent attachment of pyrene to amino group of APTES using hydroxyimide ester linkage (PyNHS). The results of the present study proved that the chemical functionalization of thin silicon oxycarbide films was achieved.

Template‐Derived Submicrometric Carbon Spheres for Lithium–Sulfur and Sodium‐Ion Battery Electrodes

AbstractHighly microporous submicrometric carbon spheres were synthesized by etching a sol–gel derived silicon oxycarbide (SiOC) material with aqueous hydrofluoric acid solution. The resulting material shows a large total pore volume of 0.63 cm3 g−1 and thus acts as an ideal host for elemental sulfur. Melt impregnation was used to synthesize a carbon–sulfur composite (50:50 wt %) as a cathode for lithium–sulfur batteries. Characterization by electron microscopy clearly showed that the sulfur is homogeneously distributed within the carbon particles. Electrodes prepared from the composite show good cyclic stability at higher specific currents (e.g., at 500 mA g−1); capacities (related to the active material content) as high as 241 mAh g−1 were retained after 100 cycles and coulombic efficiencies quickly reached values close to 100 %. The material was also tested as an anode in sodium‐ion batteries. Compared to the SiOC precursor, the carbon shows significantly improved electrochemical performance. For instance, at a specific current of 100 mA g−1, a capacity as high as 89 mAh g−1 was retained after 100 cycles, whereas SiOC showed a lower capacity of approximately 70 mAh g−1.