Microstructure dependent ablation behaviour of precursor derived SiOC ceramic foam for high temperature applications

Ablation behaviour of poly(hydridomethylsiloxane) derived open and closed porous structured SiOC ceramic foams was evaluated using oxy-acetylene flame at 1500 °C for various time durations. X-ray diffraction and scanning electron microscopy analyses of ablated SiOC ceramic foams revealed the formation of a thin protective SiO₂ layer inhibiting further oxidation. The closed porous structured SiOC ceramic foams exhibited very low mass ablation rate in contrast to open porous structured SiOC ceramic foams owing to the differences in thermal energy dissipation mechanism. The feasibility of the plausible foam reduction reactions pertaining to the ablation mechanism was further investigated by computing the Gibbs energy and HR-TEM analysis. The study corroborated the significance of tailoring the microporous structured SiOC ceramic foams as potential thermal protection material for high temperature applications.     

Synthesize and crystallization behavior of SiOC/SiC nanocomposites derived from organosilane slurry residue

A route preparing SiOC/SiC nanocomposites directly by pyrolysis of organosilane slurry residue was investigated. Organosilane slurry residue's unique composition, containing both silicon and carbon, offers an intriguing platform for developing advanced ceramic materials. The pyrolysis process is examined comprehensively, revealing the chemical reactions and structural changes leading to SiC crystals formation. The phase evolution at various annealing temperatures was revealed. Crystallization behavior in the process were studied. The results reveal that SiOC matrix was generated at annealed temperature 800°C and SiC nanoparticles were formed at 1300°C. In comparison to phase separation of SiOC, carbothermal reduction of SiO₂ was domain in SiC formation. This research advances the understanding of SiOC/SiC nanocomposites, highlighting the value of repurposing industrial byproducts for sustainable and innovative materials development.     

Single source precursor-derived SiOC/TiOxCy as an anode component for Li-ion batteries

Amorphous silicon oxycarbides are known to be an effective anode material for lithium-ion batteries. Despite their exceptional properties and high charge capacities, however, their practical uses are limited by their significant first-cycle loss, considerable hysteresis, and low cyclic ability. Comparatively, SiOC/metal oxide materials have demonstrated increased rate capability and cyclic stability. This study utilized a liquid precursor-derived ceramic method to modify SiOC with titanium (IV) butoxide precursor to synthesize SiOC/TiO_xC_y. X-ray diffractograms confirmed the amorphous nature of SiOC/TiO_xC_y. The elemental composition and bonding properties were investigated using X-ray photoelectron spectroscopy, and electron microscopy was used to explore morphological features. In the first cycle, the reversible capacity of pyrolyzed SiOC/TiO_xC_y was 520 mAh g⁻¹, which then increased to 736 mAh g⁻¹ for the 1200°C annealed SiOC/TiO_xC_y due to the increased free carbon network and TiC conductive phases. The irreversible capacity of the first cycle was 568 mAh g⁻¹, which was lower than the annealed SiOC irreversible capacity of 695 mAh g⁻¹. Interestingly, the rate stability of the pyrolyzed SiOC/TiO_xC_y performed more stability than the annealed sample. Localized carbothermal reactions between amorphous SiOC/TiO_xC_y and free carbon at annealing temperatures resulted in loss of structure stability.     

Effect of additive structure and size on SiO2 formation in polymer‐derived SiOC ceramics

Silicon oxycarbide (SiOC) ceramics with highly adjustable properties and microstructures have many promising applications in batteries, catalysis, gas separation, and supercapacitors. In this study, additive structures on the nucleation and growth of SiO₂ within SiOC ceramics are investigated by adding cyclic tetramethyl‐tetravinylcyclotetrasiloxane (TMTVS) or caged octavinyl‐polyhedral oligomeric silsesquioxane (POSS) to a base polysiloxane (PSO) precursor. The effects of the 2 additives on the polymer‐to‐ceramic transformation and the phase formation within the SiOC are discussed. POSS encourages SiO₂ nucleation and leads to more SiO₂ formation with significantly increased ceramic yield, which subsequently leads to higher specific surface of 1557 m²/g with a larger pore size of ～1.8 nm for the porous SiOC. High TMTVS content decreases both the specific surface area and pore volume of the resulting porous SiOCs. This study demonstrates a new approach of using Si‐rich additive POSS to increase the SiOC yield while maintaining or even increasing the specific surface area.     

Growth of multi-morphology amorphous silicon oxycarbide nanowires during the laser ablation of polymer-derived silicon carbonitride

Multi-morphology amorphous SiOC nanowires were successfully prepared within the interfacial interstices between the unaffected 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 diffusivity 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 flowing state of the reactant gases, the laser power, and the surface morphology of the SiCN ceramics. Each amorphous SiOC nanowire with specific morphology can be uniformly distributed in separate regions, which makes it possible to control the growth of amorphous SiOC nanowires in different morphologies.     

Silicon oxycarbide ceramics with reduced carbon by pyrolysis of polysiloxanes in water vapor

SiOC ceramics pyrolyzed from polysiloxanes are usually black because of the formation of excess carbon in the ceramic network. Here we show that the pyrolysis of polysiloxanes in water vapor significantly reduces carbon from SiOC and yields a white SiOC ceramic. Chemical analysis shows the amount of carbon in the white ceramic is only half of that in the black one pyrolyzed in argon. ²⁹Si nuclear magnetic resonance spectral (NMR) analysis indicates the reduction of the carbon-rich [SiC₄] and [SiC₂O₂] units with the enhanced formation of the oxygen-rich [SiO₄] and [SiCO₃] units by the water pyrolysis. Importantly, this water pyrolysis resultant carbon reduction is realized in a bulk polysiloxane, and the white SiOC ceramic is obtained in a bulk body with the retained shape of the precursor body. The water pyrolysis can be adopted as an effective mean to tailor the structure of PDCs via the simple introduction of water vapor in pyrolysis.     

In-situ formation of titanium carbide in carbon-rich silicon oxycarbide ceramic for enhanced thermal stability

Silicon oxycarbide (SiOC) ceramic has attracted great attention as fascinating candidate of high-temperature material, however, its thermal stability is significantly limited by the phase separation at high temperature. Here, a TiC/SiOC ceramic was prepared by pyrolysis of a tetrabutyl titanate modified carbon-rich polysiloxane (TBT/PSO) precursor. The TiC phase is in-situ formed by the carbothermal reaction of TBT-derived amorphous TiO₂ phase with excess free-carbon phase during pyrolysis, and its size and amount increase with the pyrolysis temperature. The SiC phase appears at a higher temperature than the TiC phase and is hindered by the increased Ti content in the TBT/PSO precursor. Thus, the TiC/SiOC ceramic exhibits better thermal stability and crystallization resistance than the TiC-free SiOC ceramic under the thermal treatment (1500 °C) in argon atmosphere. The in-situ formation of metal carbide into the carbon-rich SiOC ceramic would further expand its application at high temperature environments.     

Thermodynamic Control of Phase Composition and Crystallization of Metal‐Modified Silicon Oxycarbides

Silicon oxycarbides modified with main group or transition metals (SiMOC) are usually synthesized via pyrolysis of sol‐gel precursors from suitable metal‐modified orthosilicates or polysiloxanes. In this study, the phase composition of different SiMOC systems (M = Sn, Fe, Mn, V, and Lu) was investigated. Depending on the metal, different ceramic phases formed. For M = Mn and Lu, MO_x/SiOC ceramic nanocomposites were formed, whereas other compositions revealed the formation of M/SiOC (M = Sn), MSi_x/SiOC (M = Fe) or MC_x/SiOC (M = V) upon pyrolysis. The different phase compositions of the SiMOC materials are rationalized by a simple thermodynamic approach which generally correctly predicts which type of ceramic nanocomposite is expected upon ceramization of the metal‐modified precursors. Calculations show that the thermodynamic stability of the MO_x phase with respect to that of the C–O system is the most important factor to predict phase formation in polymer‐derived SiMOC ceramic systems. A secondary factor is the relative stability of metal oxides, silicates, carbides, and silicides.     

In-situ pyrolyzed polymethylsilsesquioxane multi-walled carbon nanotubes derived ceramic nanocomposites for electromagnetic wave absorption

Iron acetylacetonate (Fe(acac)₃) modified polymethylsilsesquioxane (PMS), simplified as PMS(Fe), was firstly obtained from PMS and Fe(acac)₃ via the condensation reaction. Multi-walled carbon nanotubes (MWCNTs) were then introduced to fabricate the corresponding MWCNTs/SiC nanocrystals/amorphous SiOC ceramic composites via pyrolyzed process. Owing to the catalytic effect of iron and heterogeneous nucleation promoted by MWCNTs, SiC nanocrystals were separated from SiOC amorphous ceramic matrix under 1400?°C. When the mass fraction of MWCNTs was 9?wt%, the obtained MWCNTs/SiC nanocrystals/amorphous SiOC ceramic composite (C9) demonstrated high microwave-absorbing properties. The minimum reflection loss (RL_min) and effective absorption bandwidth (EBA) of the obtained C9 at X-band (8.2–12.4) reached ?61.8?dB and 2.6?GHz (a thickness of 2.19?mm), respectively. Compared with other polymer-derived ceramics (PDCs), the RL_min was higher and the required thickness was thinner. This excellent microwave-absorbing property was due to the interfacial polarization relaxation generated between nanocrystals (MWCNTs & SiC) and amorphous SiOC, and the formed complete conductive networks inside the ceramic composites.     

Crack healing of ferrosilicochromium-filled polymer-derived ceramic composites

In this study, SiOC/FeSiCr/SiC-ceramics were derived by using polymethylsilsesquioxane as a polymeric precursor and FeSiCr (iron-chromium-silicide) and SiC powders as ceramic fillers in a polymer-extrusion process followed by pyrolytic conversion in a nitrogen atmosphere. The crack healing properties of the ceramic in an oxidising atmosphere were subsequently investigated. The SiOC/FeSiCr/SiC-ceramics showed crack closure and strength recovery behaviour after oxidation treatments in air from 600 to 1300?°C with various holding times from 2 to 1000?min. The crack healing mechanisms at different oxidation temperatures and with various dwell times are discussed.     

3D printed crack-free SiOC(Fe) structures with pyrolysis-induced carbon nanowires for enhanced wave absorption performance

High-performance SiOC(Fe) wave-absorbing ceramics, containing a large number of carbon nanowires, were successfully prepared using a combination of photopolymerization 3D printing technology and the polymer-derived ceramic pyrolysis method. By employing an optimized segmented slow heating scheme with extended holding time, the pyrolysis of SiOC(Fe) ceramics at 1000 °C facilitated the growth of carbon nanowires, Fe₃C and SiO₂ grains. These carbon nanowires were interlaced and interconnected within the samples, forming abundant conductive networks. This highly conducive network efficiently converted electromagnetic energy into thermal energy, effectively dissipating electromagnetic waves, and consequently enhancing the microwave absorption performance of ceramics. Moreover, this approach not only reduced ceramic cracks but also improved the dielectric loss performance of the materials, achieving a minimum reflectivity value of −35.72 dB. The SiOC(Fe) ceramics added with 5 wt% VcFe effectively enhanced the magnetic loss of the material, reduced the difference between the relative complex permeability (μ_r) and the relative complex dielectric constant (ε_r), and improved the impedance matching between the material surface and air, thereby further improving its microwave absorption performance. This resulted in an increase in the maximum effective absorption bandwidth of the material to 12.7 GHz at 5 mm. This study offers a promising solution for the preparation of ceramic matrix composite materials incorporating carbon nanowires, magnetic particles and ceramic precursors, which would be potentially valuable for radar detection and sensor applications.     

Phase content prediction in polymer-derived ceramics with metal additives

In this study, silicon oxycarbide (SiOC) is selected as the base polymer to derive a SiOC ceramic (PDC) matrix, and four transition metals M (M = Ni, Mo, Co, and Zr) are individually introduced into the SiOC base to form various SiOC/M systems. SiOC-Ni, SiOC-MoC_x, and SiOC-CoSi_x are obtained by pyrolysis at 1100°C, whereas SiOC-ZrO_x forms upon pyrolysis at 1400°C. The selected SiOC/M systems encompass four different types of phase separation pathways—pure metal, metal carbide, metal silicide, and metal oxide (SiC-SiO₂-C-Ni, SiC-SiO₂-C-MoC_x, SiC-SiO₂-C-CoSi_x, and SiC-SiO₂-C-ZrO_x). The driving force for crystallization has been analyzed using a Gibbs free energy minimization method and phase fractions of these different PDC systems are calculated based on the lever rule. This work also reveals the energetics related to the quaternary systems and provides guidance to synthesizing metal-containing PDCs with desired phase contents. In addition, we have examined the broad applicability of the phase content prediction method for a variety of other SiOC/M systems.     

Structural Design of Polymer‐Derived SiOC Ceramic Aerogels for High‐Rate Li Ion Storage Applications

SiOC ceramic aerogels with different porosity, pore size, and specific surface area have been synthesized through the polymer‐derived ceramic route by modifying the synthesis parameters and the pyrolysis steps. Preceramic aerogels are prepared by cross‐linking a linear polysiloxane with divinylbenzene (DVB) via hydrosilylation reaction in the presence of a Pt catalyst under highly diluted conditions. Acetone and cyclohexane are used as solvent in our study. Wet gels are subsequently supercritically dried with CO₂ to get the final preceramic aerogels. The SiOC ceramic aerogels are obtained after a pyrolysis treatment at 900°C in two different atmospheres: pure Ar and H₂ (3%)/Ar mixtures. The nature of the solvent has a profound influence of the aerogel microstructure in terms of porosity, pore size, and specific surface area. Synthesized SiOC ceramic aerogels have similar chemical compositions irrespective of processing conditions with ~40 wt% of free carbon distributed within remaining mixed SiOC matrix. The BET surface areas range from 215 m²/g for acetone samples to 80 m²/g for samples derived from cyclohexane solvent. The electrochemical characterization reveals a high specific reversible capacity of more than 900 mAh/g at a charging rate of C (360 mA/g) along with a good cycling stability. Samples pyrolyzed in H₂/Ar atmosphere show a high reversible capacity of 200 mAh/g even at a high charging/discharging rate of 20 C. Initial capacities were recovered after whole cycling procedure indicating their structural stabilities resisting any kind of exfoliations.     

Microwave-absorption properties of SiOC ceramics derived from novel hyperbranched ferrocene-containing polysiloxane

In this contribution, we design a novel strategy to synthesize SiOC ceramics by pyrolysis of hyperbranched ferrocene-containing polysiloxane (HBPSO-VF) which are synthesized by the reaction of polysiloxane (PSO) with 1,1′-Bis(dimethylvinylsilyl)ferrocene (VF). This SiOC ceramics show much lower crystallization temperature because of the capability of HBPSO-VF to incorporate metallic iron into the backbone of PSO. The usage of HBPSO-VF offers enhanced ceramic yield of 83 wt% at 1200 °C due to the deep cross-linking of hydrosilylation. Nano-sized SiC and turbostratic carbons are separated from amorphous SiOC phase when it is annealed at 1100 °C, while crystallization temperature is 1400 °C when PSO is used as polymer precursors. The minimum reflection coefficient (RC_min) of this nanocrystal-containing ceramic reaches −46 dB, exhibiting a promising prospect as a kind of electromagnetic wave (EMW) absorbing materials. This method also can be further extended to develop other functional Si-based polymer derived ceramic (PDC) systems for EMW absorption and shielding applications.     

Macrostructural design of highly porous SiOC ceramic foams by preceramic polymer viscosity tailoring

Highly porous SiOC ceramic foams with gradient or uniform macrostructures were obtained through polymer derived ceramic routes. Precuring of preceramic polymers and introduction of SiO₂ powders were used to tailor precursor viscosity and hence SiOC foam macrostructure. Effects of polymer viscosity on porosity, pore size, pore distribution were investigated by light microscopy and micro-computed tomography techniques. SiOC ceramic foams. Foams from one unmodified precursor, showed pore size gradient with small pores located at bottom and large pores at the top. To address this non-uniformity, the viscosity of the precursor was increased by pre-curing the preceramic polymer, which resulted in decrease of the average pore size and improvement in pore size uniformity. For a different system with a self-foaming preceramic polymer, because of the simultaneous release of foaming gases and rapid increase in viscosity during crosslinking, the foam had non-uniform macrostructure with large pores and thick struts at the bottom. By addition of SiO₂ fillers, the crosslinking reaction rate was reduced leading to homogeneous pore nucleation and uniform small pore size foams.     

SiOC Ceramic Monoliths with Hierarchical Porosity

SiOC glass monoliths possessing hierarchical porosity were produced by a one-pot processing method. Periodic mesoporous organosilica (PMO) particles were embedded into a foamed siloxane preceramic polymer. After pyrolysis at 1000°C in inert atmosphere, open celled, permeable SiOC ceramic monoliths with a high amount of pores, ranging in size from hundred of micrometers to a few nanometers, were obtained. The components possessed a specific surface area of 137 m²/g, indicating the retention of most of the mesopores after the pyrolytic conversion of the PMO precursor particles. These fillers converted to truncated rhombic dodecahedral SiOC mesoporous micron-sized grains, homogeneously distributed throughout the SiOC cellular matrix. The produced porous ceramics possessed compression strength of about 1.7 MPa, which is adequate for their use in several engineering applications.     

Preparation and properties of SiOC ceramic modified carbon fiber needled felt preform composites

SiOC ceramic modified carbon fiber needled felt preform composites (C_f/SiOC) with densities of 0.4 and 0.7 g/cm³ were prepared by precursor infiltration and pyrolysis (PIP) method using methyltrimethoxysilane (MTMS) and dimethyldimethoxysilane (DMDMS) as precursors. The densification behavior was investigated through scanning electron microscopy (SEM) analysis of microstructure of C_f/SiOC composites undergoing different PIP times. The results indicate that with increase of PIP times, a great amount of SiOC ceramic was introduced into the preform, completely covering on the carbon fibers and occupying the open pores. The thermal performance, mechanical properties, and oxidation resistance of the composites were studied via various tests. The results illustrate that after two-time PIP procedure, thermal conductivities of the composites are 0.41–2.54 and 1.28–4.04 W/(m·K) in z direction and x/y plane, respectively, at RT-1500 °C. The compressive strengths of the composite arrive at 2.1 MPa in z direction and 7.8 MPa in x/y plane, which are almost 3.5 times and 6.5 times, respectively, counterparts of the raw preform. The incorporation of SiOC ceramic can remarkably improve anti-oxidation ability of the composites at 600 °C. The oxidation weight loss is merely 2.1 wt% after 60-min oxidation at 600 °C.     

热解含铁聚硅氧烷原位生长硅氧碳纤维制备硅氧碳复合材料

将铁氯化物混入聚硅氧烷前驱体进行交联成型和热解,利用热解中在聚硅氧烷中形成的孔隙和在孔隙中形成的铁颗粒为催化剂,在硅氧碳陶瓷基体中原位生长出硅氧碳纳米纤维,制备出硅氧碳陶瓷和硅氧碳纤维复合材料。用扫描电子显微镜观察材料断面,结果显示：在硅氧碳陶瓷基体中生长出纳米纤维,部分纤维取向分布,纤维紧贴于硅氧碳陶瓷基体,二者呈良好结合;能谱分析显示纤维中含硅、氧和碳,证实其为硅氧碳。所制得的硅氧碳陶瓷和硅氧碳纤维的复合结构不同于通常热解纯聚硅氧烷形成的单相的硅氧碳结构,在硅氧碳基体中的硅氧碳纤维是在聚硅氧烷前驱体中引入的铁催化剂在热解过程中通过催化聚硅氧烷一维生长形成的,该过程可用于发展一步法原位制备纳米纤维前驱体陶瓷复合材料。     

Gas Sensing Behavior of Mesoporous SiOC Glasses

In this study, for the first time, we report the gas sensing behavior of aerogel‐derived silicon oxycarbide (SiOC) glasses. The SiOC glass pyrolyzed at 1400°C has specific surface area of 150 m²/g with pore size in the 2–20 nm range. SiOC sensor shows good response to 5 ppm NO₂ at 300°C. NO₂ response completely disappears at 400°C, and from this temperature SiOC sensor starts respond to H₂. The optimum sensitivity for H₂ is obtained at 500°C. SiOC sensor is very selective; it is not sensitive to other gases such as acetone vapor or CO, even at high concentrations.     

Macroporous polymer-derived SiO2/SiOC monoliths freeze-cast from polysiloxane and amorphous silica derived from rice husk

A freeze-casting route towards macroporous SiOC/SiO₂ ceramic nanocomposites from preceramic polymers was developed. Amorphous SiOC/SiO₂ monolith with pore channels aligned along the freezing direction were obtained from commercially available methyl-phenyl-vinyl-hydrogen polysiloxane (Silres® H62C) and amorphous silica derived from rice husk ash freeze-cast with water or tert-butyl alcohol, crosslinked and pyrolyzed at 1100 °C in nitrogen. The influence of processing parameters such as solvent (tert-butyl alcohol or water), polymer to silica ratio (2:1, 1:1, 1:2), cooling rate (2, 4, 6 °C/min) and pre-crosslinking of polysiloxane on the porosity and structure of the obtained ceramic nanocomposites were assessed by X-ray tomography, XRD, solid state NMR, scanning electron microscopy and mercury porosimetry. The microstructure of SiOC ceramics derived from the Silres H62C polysiloxane was studied as well.