Polymer-derived SiOC Research Articles

Influence of layer thickness and exposure on mechanical properties of additively manufactured polymer-derived SiOC ceramics

One significant hurdle in additively manufacturing polymer-derived ceramics lies in reconciling the lower mechanical properties of additively manufactured parts compared to traditionally manufactured ceramics and PDCs. Here, a methodology is presented for evaluating the influence of layer thickness and exposure on polymer-derived ceramics within the constraints of commercially available software and hardware. Maximizing exposure within printable limitation of DLP processes, produced green bodies with the highest conversion, and resulted in improved pyrolysis outcomes, manufacturability, and most importantly ceramic strengths comparable to traditionally manufactured SiOC PDCs. Decreasing layer thickness and increasing total dwell time had a dramatic impact on mechanical properties, increasing flexural strength by more than 6x from 18 MPa at 100 μm layer thickness to 111 MPa at 10 μm layer thickness. Density of resultant ceramic also increased from 1.62 ± 0.03 g/cc to 2.3 ± 0.05 g/cc. This represented a large increase in mechanical strengths of PDCs produced via DLP in literature.

Corrosion-Resistant Polymer-Derived SiOC Membrane for Effective Organic Removal via Synergistic Adsorption and Peroxymonosulfate Activation

Corrosion-Resistant Polymer-Derived SiOC Membrane for Effective Organic Removal via Synergistic Adsorption and Peroxymonosulfate Activation

Layered composites made of polymer derived SiOC/ZrB2 reinforced by ZrO2/SiO2 fibers with simultaneous microwave absorption and thermal insulation

To simultaneously improve the microwave absorption and thermal insulation properties of the ceramic materials for stealth high-speed vehicles, layered composites made of polymer-derived SiOC/ZrB2 reinforced by ZrO2/SiO2 fibers were reported in this work. The composites possess a continuous multilayer structure, which was fabricated via the precursor impregnation assisted by hot press curing and pyrolysis using the transparent ZrO2/SiO2 fibers and polymer-derived SiOC and nano ZrB2. The layered composites show an effective absorption band (EAB) of 4.2 GHz at a thickness of 2.9 mm and a minimum reflection loss of –59.34 dB. The exceptional electromagnetic (EM) wave attenuation capability is ascribed to the impedance matching as well as massive EM wave loss caused by the multilayers in which the nano ZrB2 provides interfacial polarization and electrical conduction loss. With a design of the multi-curvature arch structure, a remarkable reduction of radar cross section can be achieved. Besides, the layered composites exhibit good oxidation resistance and thermal insulation when exposed to the dynamic heating environment, demonstrating the potential application in harsh environments used for multifunctional electromagnetic absorbing materials.

Synthesis and characterization of polymer-derived nanocrystal SiOC powders via high temperature XRD method

In the study, polymer-derived SiOC powders was synthesized by sol-gel method. The resulting composites consists of β-SiO2, SiC and free carbon. Tetraethylorthosilicate (TEOS) and Polydimethylsiloxane (PDMS) were selected as starting materials to obtain organic-inorganic structure. After the gelling process, the powders were heat treated at 1100°C in Argon medium to obtain the desired phases. Scanning Electron Microscopy (SEM), Differential Thermal Analysis (DTA) and Fourier Transform Infrared Spectroscopy (FT-IR) analyses were used for characterization. In addition, instant phase changes were determined by high-temperature XRD in powders subjected to heat treatment up to 1500 °C in a helium environment. The effect of temperatures on the transformation in SiOC synthesis, the transformation temperatures of α-cristobalite to β-cristobalite were sharply determined and the SiC formation temperature was revealed. The effect of temperature on crystal size was also obtained as a result of the study.

Vat photopolymerization 3D printing of polymer-derived SiOC ceramics with high precision and high strength

Polymer-derived ceramic (PDC) combined with 3D printing technology allows for the fabrication of various complex 3D structures and components that cannot be achieved through conventional ceramic preparation methods. However, current 3D printing PDC technologies suffer from low accuracy, poor mechanical and low ceramic yield, which severely limit their application values. Here, we report a polysiloxane-based preceramic polymer (PCP) precursor capable of producing high-precision and high-strength SiOC ceramics with ceramic yield as high as 56.9% after pyrolysis at 1100℃ in vacuum. Adding butyl acrylate into the precursor significantly improves printing resolution. Through special material design and printing parameter optimization, we fabricate various complex structures with overall sizes ranging from submillimeters to centimeters and printing resolution as high as 5 μm via vat photopolymerization 3D printing. The compressive strength of SiOC ceramic with I-WP structure reaches up to 240MPa while its density is only 0.367g/cm3, corresponding to a specific strength as high as 6.54 × 105N·m/kg. The printing resolution, specific strength and ceramic yield are all at the top level compared with previously reported works. The proposed approach will greatly promote the industrial application of 3D printing PDC technology in engineering fields and extreme environments.

Correction: Strong, lightweight, thermally stable, and hydrophobic sustainable structural composites produced from coal-based waste and polymer-derived SiOC ceramics

Correction: Strong, lightweight, thermally stable, and hydrophobic sustainable structural composites produced from coal-based waste and polymer-derived SiOC ceramics

Design and Performance Comparison of Polymer-Derived Ceramic Ambigels and Aerogels.

This work reports the synthesis and characterization of preceramic- and polymer-derived SiOC aerogels obtained from a commercial siloxane resin. The preceramic aerogels were obtained by ambient pressure drying (ambigels) and CO2 supercritical drying. Despite different drying processes, the final ceramic ambi/aerogels have very similar microstructural features in density, porosity, pore size, and specific surface area. Both materials have shown promising results for oil sorption and water cleaning. Supercritically dried-SiOC aerogel had low thermal conductivity with 0.046 W·m-1·K-1 at RT and 0.073 W·m-1·K-1 at 500 °C. These results suggest that substituting the rather complicated and expensive CO2-SC drying with the more friendly and cheap ambient pressure drying can be done without having to accept significant microstructural/property degradation.

Strong, lightweight, thermally stable, and hydrophobic sustainable structural composites produced from coal-based waste and polymer-derived SiOC ceramics

Recycling coal-based waste (CBW) into composites suitable as a building material might be a necessary response to combat its risk to the environment. Therefore, the objective of this study was to investigate the microstructure and performance of coal composites produced from CBW and polysiloxane polymer (SPR-212). Four types of CBW that differ in physicochemical properties were examined. Fourier transform infrared spectroscopy results indicated that the higher the intensity of the C=C bonds in the CBW, the higher the pyrolysis mass loss and shrinkage experienced by the composites during pyrolysis. The continuous operating temperature of the composites is up to 600 °C. However, at temperatures above 600 °C, composites containing carbon content greater than 36% manifested dramatic degradation. Pyrolysis mass loss in the range of 5.28 to 29.62% was obtained for all the composites. The density range of the composites is between 1.5 and 1.9 g per cubic centimetre. The water absorption of all the composites is within the range of 0 to 25% and is comparable to many building materials. Notably, the composites containing total carbon less than 10% registered a water contact angle greater than 90°, indicating the low wettability of their surface. Furthermore, composites that embodied the highest total carbon (63%) displayed the worst structural property. The findings of this study lay the foundation for further development of high-quality structural coal composites from CBW and the SPR-212 preceramic polymer through optimisation of the processing conditions.Graphical abstractAssessment of structural composites produced from coal-based waste and polymer-derived SiOC ceramics

In-situ polymer-derived SiOC strengthened aluminum sheets: Investigations on its manufacturing and structure-property correlations

Ceramic nanoparticles are used to strengthen metals/alloys but their agglomeration within the matrix, weak particle-matrix interface, and high cost are concerning issues. Polymer-derived ceramics could overcome these problems. Pyrolyzed SiOC was obtained from poly(methylhydrosiloxane) (PMHS) in-situ within an Al matrix. Before pyrolysis, PMHS was fragmented and distributed in the nano and sub-micron scale by accumulative roll bonding (ARB). In the mid-section/central region of the composite along the thickness, a multimodal grain size distribution with a combination of large elongated and fine equiaxed grains (recrystallized grains) was observed. However, near the surface, only the latter was present. The PDC-containing specimen exhibited an improvement in strength by ∼ 8.5 times compared to the parent material. Whereas, the improvement compared to a similarly processed specimen but without the polymer-derived SiOC particles was by ∼ 6 times. Fractography revealed ductile fracture with sheet debonding in the composite.

Effect of ultra-fast pyrolysis on polymer-derived SiOC aerogels and their application as anodes for Na-ion batteries

In the last decade, Sodium-Ion-Batteries (SIB) started to gain interest as a possible complementary candidate to support the overburdened lithium technology, but the manufacturing of a proper anode material is one of the challenging factors for the development of performing SIB. Among others, porous polymer-derived ceramics have been widely explored as suitable anodes despite the production of such materials being time and energy-consuming. In this work, we investigate the feasibility of adopting a low-cost ultra-fast high-temperature pyrolysis for the ceramic conversion of a polymer-derived SiOC aerogel to be employed as anode material. A comprehensive study including N2 physisorption, 29Si MAS NMR and Raman spectroscopy provides the insights of the effect of ultra-fast and conventional heating rates (i.e., 200 °C·s−1 vs. 5 °C·min−1) on the microstructural features and ceramic yield of the SiOC aerogels. As a consequence of the ultra-fast heating rate, a compositional drift towards oxygen-rich SiOC is observed and discussed. The electrochemical performance of both ceramics has been tested and related to the observed compositional differences, revealing a stable capacity of 103 mAh·g−1 for the ultra-fast pyrolyzed SiOC anode, and 152 mAh·g−1 for SiOC ceramized at 5 °C·min−1.

Polymer-derived SiOC as support material for Ni-based catalysts: CO2 methanation performance and effect of support modification with La2O3.

In this study, we investigated Ni supported on polymer-derived ceramics as a new class of catalyst materials. Catalysts have to withstand harsh reaction conditions requiring the use of a support with outstanding thermal and mechanical stability. Polymer-derived ceramics meet these requirements and bring the additional opportunity to realize complex porous structures. Ni-SiOC and La-modified Ni-SiOC catalysts were prepared by wet impregnation methods with target concentrations of 5wt% for both metal and oxide content. Polymer-derived SiOC supports were produced using a photoactive methyl-silsesquioxane as preceramic polymer. Catalysts were characterized by N2-adsorption-desorption, XRD, SEM, H2-TPR, and in-situ DRIFTS. CO2 methanation was performed as a test reaction to evaluate the catalytic performance of these new materials at atmospheric pressure in the temperature range between 200°C and 400°C. XDR, H2-TPR, and in-situ DRIFTS results indicate both improved dispersion and stability of Ni sites and increased adsorption capacities for CO2 in La-modified samples. Also, modified catalysts exhibited excellent performance in the CO2 methanation with CO2 conversions up to 88% and methane selectivity >99% at 300°C reaction temperature. Furthermore, the pyrolysis temperature of the support material affected the catalytic properties, the surface area, the stability of active sites, and the hydrophobicity of the surface. Overall, the materials show promising properties for catalytic applications.

Microstructural evolution and microwave transmission/absorption transition in polymer-derived SiOC ceramics

Herein, we present the structural evolution of polymer-derived SiOC ceramics with the pyrolysis temperature and the corresponding change in their microwave dielectric properties. The structure of the SiOC ceramics pyrolyzed at a temperature lower than 1200 °C is amorphous, and the corresponding microwave complex permittivity is pretty low; thus, the ceramics exhibit wave transmission properties. The Structural arrangement of free carbon in the SiOC ceramics mainly happens in the temperature range of 1200 °C-1300 °C due to the separation from the Si–O–C network and graphitization, while the structural arrangement of the Si-based matrix mainly occurs in the range of 1300 °C-1400 °C owing to the separation of SiC4 from the Si–O–C network to form nanocrystalline SiC. In pyrolysis temperature range of 1200 °C-1400 °C, the microwave permittivity of SiOC shows negligible change. At a pyrolysis temperature exceeding 1400 °C, the carbothermal reaction of free carbon and the Si–O backbone becomes significant, leading to the formation of crystalline SiC. The as-formed SiC and residual defective carbon improve the polarization loss of SiOC ceramics. In this case, the SiOC ceramics show significantly increased complex permittivity, exhibiting electromagnetic absorption characteristics. These characteristics promote the application of polymer-derived SiOC ceramics to high-temperature electromagnetic absorption materials.

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.

Polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2 for excellent and stable high-temperature microwave absorption (up to 900 °C)

Microwave absorbing materials for high-temperature harsh environments are highly desirable for aerodynamically heated parts and engine combustion induced hot spots of aircrafts. This study reports ceramic composites with excellent and stable high-temperature microwave absorption in air, which are made of polymer-derived SiOC reinforced with core–shell nanophase structure of ZrB2/ZrO2. The fabricated ceramic composites have a crystallized t-ZrO2 interface between ZrB2 and SiOC domains. The ceramic composites exhibit stable dielectric properties, which are relatively insensitive to temperature change from room temperature to 900 °C. The return loss exceeds − 10 dB, especially between 28 and 40 GHz, at the elevated temperatures. The stable high-temperature electromagnetic (EM) absorption properties are attributed to the stable dielectric and electrical properties induced by the core–shell nanophase structure of ZrB2/ZrO2. Crystallized t-ZrO2 serve as nanoscale dielectric interfaces between ZrB2 and SiOC, which are favorable for EM wave introduction for enhancing polarization loss and absorption. Existence of t-ZrO2 interface also changes the temperature-dependent DC conductivity of ZrB2/SiOC ceramic composites when compared to that of ZrB2 and SiOC alone. Experimental results from thermomechanical, jet flow, thermal shock, and water vapor tests demonstrate that the developed ceramic composites have high stability in harsh environments, and can be used as high-temperature wide-band microwave absorbing structural materials.

Influence of Ni on the structural evolution of polymer-derived SiOC ceramics

Polymer derived ceramics (PDCs) technique is an advanced method for preparing high performance ceramics, in which pyrolysis process is an important step. In order to study the effect of the Ni transition metal on the pyrolysis process of polysiloxane, different contents of Ni acetate tetrahydrate (Ni(ac)2·4H2O)-impregnated polysiloxane (PSO) precursors were pyrolyzed in argon atmosphere between 1000 °C and 1300 °C. The organic-inorganic conversion behavior of precursors, the elemental and structural characterization of the Ni-free and Ni-containing SiOC ceramics were investigated. The results revealed that the presence of Ni not only enabled the growth of carbon nanotubes (CNTs) but also promoted the crystallization of carbon and SiC phase during the pyrolysis process. Additionally, high Ni content and pyrolysis temperature raised the diameters of CNTs and crystallinity of turbostratic layer carbon and SiC.

3D printing of crack-free dense polymer-derived ceramic monoliths and lattice skeletons with improved thickness and mechanical performance

Previous research often failed to prepared polymer-derived SiOC ceramic components with dense and thick monoliths/skeletons based on additive manufacturing processes, due to the porosities and cracks generated during the pyrolysis process. Herein, we report a simple solution which combines the introduction of phenolic resin (PR) as an additive and the use of controlled strategy of pyrolysis, for the vat photopolymerization additively manufactured SiOC ceramics. As a result, crack-free dense monolith and lattice skeleton structural polymer-derived SiOC ceramics are successfully prepared despite the low ceramic yield of 19.3 wt% and large linear shrinkage of 50% generated after pyrolysis. The prepared dense monoliths possess a thickness of over 5 mm and the lattices show attainable maximum dense skeletons thickness of ~2 mm. The maximum dense thickness of the samples after pyrolysis is over 7 times that of other samples prepared based on additive manufacturing reported in the literature. As an indicator of dimensional retention, the specific dense thickness to ceramic yield ratio (T/Y) is deduced, resulting maximum values of 101.9 µm/(wt%) for lattice skeletons and 254.7 µm/(wt%) for monoliths. The former is even larger than that for dense monolith SiOC structures prepared by other conventional gel casting and isostatic pressing techniques with much higher ceramic yields of > 80 wt%, and is about 6.1 times the largest T/Y ratio (=16.7 µm/(wt%)) achievable in the AM-based works reported in the literature. This shows predominance of the current work over other types of polymer-derived ceramic structures prepared by additive manufacturing and even conventional methods. The lattice structures’ apparent density and specific strength reached 0.55 g/cm 3 and 6.6 × 10 4 N∙m/kg, respectively. The mechanical performance surpasses other structural polymer-derived ceramic structures with similar apparent density reported in the literature. Through the advanced characterization and analysis of material phase and morphology evolution during the pyrolysis process, the mechanism of defect-free densification is revealed. That is, the introduction of PR enables a highly smooth gas-releasing process due to the generation of ordered gas-releasing channels in the sample bodies during the pyrolysis process. As a result, the generation of cracks and defects was successfully prevented. Moreover, due to the high carbon residue of the PR, the samples containing 15 wt% PR in the preceramic state still possessed amorphous SiOC ceramics after pyrolysis at 1400 ℃, while 0 wt% PR samples showed SiC crystallization. Compared with similar materials reported, the ceramics prepared in this study exhibit enhanced structural and mechanical performance. The strategy investigated in the study can be a viable route for the additive manufacturing of high-performance crack-free and thick monolith and lattice skeleton SiOC ceramic structures based on vat photopolymerization.

Stereolithography-based additive manufacturing of polymer-derived SiOC/SiC ceramic composites

In order to overcome challenges typically encountered during additive manufacturing of ceramics via the polymer precursor route, a novel polymer-derived SiOC/SiC composite system suitable for advanced geometric designs achievable by lithography-based ceramic manufacturing was established. The photoreactive resin system filled with 20 wt% SiC exhibits suitable viscosity characteristics, adequate stability against sedimentation, and a fast photocuring behavior. After printing and pyrolytic conversion, SiC particulates were well-dispersed within the polymer-derived SiOC matrix. A direct comparison with the unfilled polysiloxane-based resin system showed that the addition of particulate SiC increases handleability, reduces shrinkage, and significantly increases critical wall thicknesses up to 5 mm. The biaxial Ball-on-Three-Balls testing methodology yielded a characteristic strength of 325 MPa for SiOC/SiC composites. The results highlight the high potential of particle-filled preceramic polymer systems toward the fabrication of high-performance SiC-based materials by lithography-based additive manufacturing.

Design paradigm for strong-lightweight perfect microwave absorbers: The case of 3D printed gyroid shellular SiOC-based metamaterials

Research on microwave absorbing (MA) metamaterials with multifunctional coupling designs is a burgeoning topic. Reported here is a design paradigm for architecting mechanically robust all-dielectric MA metamaterials reaching perfect electromagnetic wave absorption. First, we generalized rules of optimal permittivities for nonmagnetic materials reaching theoretically ultimate reflection loss (RL) smaller than −150 dB, and proposed a facile criterion for evaluating MA performance based on the offset of dielectric Cole-Cole curves from theoretical optimal values. Subsequently, electromagnetic tunable polymer-derived SiOC ceramics with the highest reported printing accuracy of 20 μm were developed as metamaterials matrix, and the strong-lightweight gyroid shell-cellular (shellular) is introduced to optimize the MA performance while balancing mechanical properties. Finally, as-fabricated gyroid shellular MA metamaterials exhibit an unmatched MA performance coupled with unparalleled mechanical properties: the minimum RL achieves the ceiling value of −70.3 dB, the effective absorption bandwidth spans the whole X-band, and the specific compressive strength is as high as 63.0 MPa/(g/cm3) at 0.606 g/cm3 ultralow density. Besides, the theoretical framework was well-established for guiding structural optimization and practical manufacturing of inhomogeneous metamaterials. This research advanced an unambiguous theoretical direction for the development of structure-function integrated MA metamaterials through the synergistic interaction among theory, computation, and experiment.

Ti doped SiOC precursor to activate gyroid sensing structures

Ti-doped polymer-derived SiOC ceramic has multi-functional sensing capability due to its semiconductive properties. Their mechanical and chemical stability provide reliable support for their long-term service and safe operation in extreme environments. The sensing properties of Ti-doped SiOC (SiTiOC) can be optimized by modulation carrier concentration. Meanwhile, it can be fabricated by 3D printing as structural-strengthened components, promising for abnormal environmental signals warning under harsh conditions. In this work, SiTiOC gyroid structures were constructed by vat photopolymerization. The resulting components had thermistor characteristics with a negative temperature coefficient. After the Ti doping, the structures exhibited a high conductivity of 1.10 S/m, as the Ti ions formed an efficient percolation network by introducing acceptor impurities. The structures also had piezoresistive capability as the conductive phases can generate a tunneling-percolation conduction effect. They can detect a strain of less than 0.5%. Furthermore, the structures can realize n-butanol sensing for their p-type semiconductor properties. The components also had an excellent mechanical performance with the compressive strength and Young's modulus of 92.83 MPa and 4.28 GPa, respectively, ensuring reliable service under pressure loading.

Thermochemical heat storage performances of magnesium sulphate confined in polymer-derived SiOC aerogels

The thermochemical heat storage performances of hygroscopic magnesium sulphate (MgSO4) can be improved by dispersing it within a porous matrix. However, the host material must be able to bear the intense stresses developed by the hydration of the salt. In this work, we report the first use of a polymer-derived SiOC ceramic aerogel as host for the confinement of MgSO4 for seasonal thermal energy storage, providing a way to easily tune its final porosity to achieve controllable mass fractions of salt in the so-obtained composite. Besides, the distinctive mesoporosity of ceramic aerogels guarantee a free path for water vapour to rapidly hydrate MgSO4 while avoiding the breakage of the composite. Vacuum impregnation of the aerogel samples led to a composite with a maximum of 59.1%wt of MgSO4.1 H2O and a complete hydration in 60 min under H2O saturated air.