Ceramization Research Articles

3D-printed polymer-derived ceramics with tunable cellular architectures

Ceramic materials possess high mechanical strength and environmental stability, but their brittleness limits their suitability for structural applications. A solution lies in using polymer-derived ceramics (PDCs), which offer enhanced toughness and versatility in shaping unlike traditional ceramic processing methods. This study explores tunable ceramic cellular architectures based on triply periodic minimal surface (TPMS) designs, fabricated via stereolithography (SLA) using a silicon oxycarbide precursor formulated for vat photopolymerization. By combining the preceramic polymer with a photoinitiator, crosslinkers, and other additives, intricate shapes are 3D-printed and then pyrolyzed under nitrogen, resulting in PDCs with complex TPMS geometries. The toughness, strength, and stiffness of the 3D-printed structures are evaluated through quasi-static compression experiments. Comprehensive material and microstructural characterizations of the PDCs are performed pre- and post-pyrolysis, employing visual inspection, X-ray micro-tomography, thermogravimetric analysis, energy dispersive X-ray spectroscopy, density, and rheological measurements. Optimization of 3D printing and pyrolysis parameters yields ceramic structures with 2.2 MPa compressive strength and 330 MPa stiffness with a lattice density of 0.5 g cm-3. The ceramic material, including porosity, had a maximum density of 1.63 ± 0.01 g cm-3. This low-cost SLA 3D printing technique is ideal for creating thin features and customized structures of bio-inspired, architectured ceramics. Furthermore, the process exhibits excellent printability, being compatible with common and cost-effective SLA, DLP, and LCD 3D printers.

High-pressure synthesis of fully dense polymer-derived SiCN ceramics: Structural evolution and mechanical properties

This study explored the microstructural evolution and mechanical behavior of dense amorphous SiCN ceramics by consolidating the PDCs-SiCN powder through high-pressure sintering at different temperatures. The results indicate that the SiCN ceramics remain in an amorphous state under pressures of 5 GPa and temperatures below 1200 ℃. As the temperature increases, the density increases steadily while the porosity decreases, exhibiting excellent properties with a porosity of 0.208 %, hardness and elastic modulus of 26.04±1.29 GPa and 223.8±6 GPa, respectively. As the temperature increases further, the amorphous three-dimensional network deteriorates, leading to a phase transition from amorphous to crystalline. This simultaneous presence of amorphous and crystalline phases can result in an increased formation of pores in ceramics. Precipitation of the soft phase “graphite” and the appearance of high porosity significantly diminish the mechanical properties of bulk ceramics. The high-pressure method represents an attractive avenue for the development of high-performance amorphous Si-based composite ceramics.

Deep-sea glass sponges-like hollow porous ceramic fiber aerogel: Fabrication, anti-shrinkage and thermal insulation

Ceramic aerogels prepared using the polymer-derived ceramics (PDCs) route were extensively applied in the thermal insulation field with lightweight and high-temperature resistance. However, ceramic aerogels were susceptible to weight loss and volume shrinkage at high temperatures, leading to the collapse of the aerogel structure and a reduction in thermal insulation performance. In this paper, inspired by the skeletal structure of deep-sea glass sponges, hollow porous MHP-SiC-CA ceramic fiber aerogel was prepared by electrostatic spinning. The anti-shrinkage property of ceramic fiber aerogel was improved through the circular and spindle-shaped pores on the surface of hollow fibers. The gas-solid phase interface was increased by the abundant nanopore structure, leading to enhanced reflection and refraction of thermal radiation within the aerogel. The heat conduction and heat convection of the aerogel were reduced with the hollow and porous structure. The results presented that the ceramic fiber aerogel exhibited excellent anti-shrinkage properties, high specific strength, and ultra-low thermal conductivity. The material was expected to provide novel perspectives for the development of ceramic fiber aerogels applicable to ultra-high-temperature environments.

Ultrafast high-temperature sintering of polymer-derived ceramic thick film sensors

Polymer-derived ceramics (PDCs) find extensive applications as sensitive materials in in-situ thin/thick film sensors (TFSs) co-fabricated with components. However, the prolonged high-temperature sintering steps of PDCs inevitably lead to severe thermal damage to their co-sintered substrates. In this study, we employed an ultrafast high-temperature sintering (UHS) method, achieving rapid sintering of preceramic polymer slurry sensitive films in just a few minutes. Through direct ink writing technology, we patterned the preceramic polymer slurry, followed by UHS to prepare high-temperature ITO/SiCN TFSs. UHS-ITO/SiCN exhibited high sensitivity of microstructure, composition, and electrical characteristics to UHS parameters. The obtained ITO/SiCN resistance grid showed high electrical conductivity (706.89 S m−1 at room temperature), highly dense surface structure and excellent oxidation resistance. In an air atmosphere, the resistance drift rate of the resistance grid at 900 °C was only 0.54 %·h−1 without any protective layers. Finally, we fabricated an ITO/SiCN heat flux sensor with high sensitivity (78.75 mV/(kW·m−2)), a wide range (94.8 kW m−2), and excellent repeatability. This work has the potential to expand the application of UHS in the manufacturing of novel in-situ TFSs integrated with components.

Two-step ALD process for non-oxide ceramic deposition: the example of boron nitride

Atomic layer deposition (ALD) based on polymer-derived ceramics (PDCs) chemistry is used for the fabrication of boron nitride thin films from reaction between trichloroborazine and hexamethyldisilazane. The transposition of the PDCs route to ALD is highly appealing for depositing ceramics, especially non-oxide ones, as it offers various molecular precursors. From a two-step approach composed of an ALD process forming a so-called preceramic film and its subsequent ceramization, conformal and homogenous BN layers are successfully synthesized on various inorganic substrates. In the first stage, smooth polyborazine coatings are obtained at a temperature as low as 90 °C. The saturation and self-limitation of the ALD gas-surface reactions are verified. Intriguingly, three ALD windows seem to exist and are attributed to change in ligand exchange. After the ceramization stage using a heat treatment, conformal near-stoichiometric BN layers are obtained. Their structure in terms of crystallinity can be adjusted from amorphous to well-crystalline sp2 phase by controlling the treatment temperature. In particular, a crystallization onset occurs at 1000 °C and well defined sp2 crystalline planes oriented parallel to the surface are noted after ceramization at 1350 °C. Finally, side-modification of the substrate surface induced by the thermal treatment appears to impact on the final BN topography and defect generation.

Tracking copper nanofiller evolution in polysiloxane during processing into SiOC ceramic.

Polymer-derived ceramics (PDCs) remain at the forefront of research for a variety of applications including ultra-high-temperature ceramics, energy storage and functional coatings. Despite their wide use, questions remain about the complex structural transition from polymer to ceramic and how local structure influences the final microstructure and resulting properties. This is further complicated when nanofillers are introduced to tailor structural and functional properties, as nanoparticle surfaces can interact with the matrix and influence the resulting structure. The inclusion of crystalline nanofiller produces a mixed crystalline-amorphous composite, which poses characterization challenges. With this study, we aim to address these challenges with a local-scale structural study that probes changes in a polysiloxane matrix with incorporated copper nanofiller. Composites were processed at three unique temperatures to capture mixing, pyrolysis and initial crystallization stages for the pre-ceramic polymer. We observed the evolution of the nanofiller with electron microscopy and applied synchrotron X-ray diffraction with differential pair distribution function (d-PDF) analysis to monitor changes in the matrix's local structure and interactions with the nanofiller. The application of the d-PDF to PDC materials is novel and informs future studies to understand interfacial interactions between nanofiller and matrix throughout PDC processing.

Dual-modified catalytic core-shell structure biomass carbon cotton fiber extends broadband electromagnetic waves absorption applications

Using vacuum impregnation method, the biomass carbon cotton fiber material was modified with polymer-derived SiCN ceramics and different Ni sources to successfully prepare the composite material. The electromagnetic microwave absorption properties of the material in the range of 2–18 GHz and the catalytic effect of different nickel sources were studied. The material modified by nickel nitrate hexahydrate forms a carbon fiber coated structure, improves impedance matching, enriches heterostructures, and increases electromagnetic synergistic loss, effectively enhancing the effective absorption bandwidth (EAB) reaches 4.72 GHz, the minimum reflection loss (RLmin) is −47.79 dB, and the thickness is only 1.32 mm. The results of CST show that the radar cross section of CFPN-2 material is −36.86 dB m2, and it has obvious effect of optimizing impedance matching.

Influence of Si3N4 fillers and pyrolysis profile on the microstructure of additively manufactured silicon carbonitride ceramics derived from polyvinylsilazane

ABSTRACT In this work, various methods were used to improve the printability of a photocurable polyvinylsilazane resin filled with silicon nitride particles for digital light processing. The developed resin was used as a preceramic polymer for polymer-to-ceramic conversion. The pyrolysis-induced structural changes of the additively manufactured objects were evaluated by comparing samples with different thicknesses, filler amounts and heating profiles. The printed green body retained its original geometry better and showed fewer cracks due to the addition of silicon nitride particles to the resin. Based on the thermally induced changes in a polyvinylsilazane resin system, a customized heating profile for the pyrolysis process was developed, which contributed to the reduction of pores and cracks while the average pyrolysis heating rate remained relatively high. This work provides insight into the pyrolysis of additively manufactured preceramic polymer green bodies and highlights various strategies for additive manufacturing of polymer-derived ceramics.

Reinforcement induced microcracking during the conversion of polymer-derived ceramics

This study investigates the role of discontinuous reinforcement on the microcracking of a preceramic polymer matrix during polymer to ceramic conversion. The material system comprised a carbosilane-based, preceramic polymer reinforced with mullite particles. The preceramic resin slurry was formulated for photopolymerization on a digital light projection 3D printer. Micro X-ray computed tomography, using a synchrotron light source, monitored a printed composite part during pyrolysis. The conversion of the carbosilane matrix into Si(O)C generated microcracks in the matrix that radially extended from particles. The likelihood of microcrack formation positively correlated with particle size. The largest particles (>104 µm3 volume or >60 µm side length) always abutted microcracks, while the matrix surrounding smaller particles (<5 µm) was free of microcracks. Numerical calculations showed the particles resist the shrinking matrix during its conversion. This created tensile stresses within the matrix. The driving force for microcrack growth was also analyzed with regard to the influence of matrix material parameters, particle form-factor and crack length. These results reveal the need to consider the form factor of discontinuous reinforcements, with regard to the material properties of the polymer-derived ceramic, in order to reduce or eliminate defects in the final part.

Graphite-assisted structural design of hierarchically porous SiC(rGO) PDCs with excellent capacity in thermal protection/insulation and load bearing for hypersonic vehicles

High flight speed of hypersonic vehicles will push thermal insulation composites to achieve balanced enhancement of high porosity with increasing load-bearing capability. Herein, hierarchically porous SiC(rGO) polymer-derived ceramics (PDCs) with lightweight, heat-insulating, anti-ablative and tough engineered merits, are designed from polycarbosilane-vinyltriethoxysilane-graphene oxide precursors by re-pyrolysis/graphite-assisted decarburization. Graphite pore-forming agents tightly coupled with SiOxCy/Cfree(rGO) by C-dangling bonds, can inhibit SiOxCy decomposition, increase ceramic network disorder and expedite concurrent removal of Cfree. SiO2 generated from Si-dangling oxidation bonding, efficiently densifies framework to retain mechanical performances, and meanwhile creates more interfaces to enhance phonon scattering. Such structure similar to nodular cast iron confers low thermal conductivity (0.11 W·m-1·K-1), particularly, fully preserves good compressive strength (5.4 MPa) for SiC(rGO)40%. Under both cyclic butane flame ablation (∼1300 °C) and long-term oxidation for 7200 s, self-healing effect of SiO2 imbues products with good structural integrity, shedding light on the opportunity to apply any thermal protection system.

Correlation the microstructure and magnetic properties of Fe-Ni-Mo soft magnetic composites fabricated via polymer-derived ceramics

The coatings play a crucial role in enhancing the performance of soft magnetic composites (SMCs). This study aims to create coatings for Fe-Ni-Mo SMCs using polysilazane (PSZ) as the precursor. The transformation mechanism of the PSZ/resin mixture is studied by analyzing functional groups and chemical bonds at various temperatures. During the self-polymerization process of PSZ at 350 °C, N–H, C = C–H, Si-H bonds, –CH3, and Si-CH3 groups undergo crosslinking reactions to form C–C and Si-N bonds. When the temperature reaches 600 °C, PSZ polymer cleavage, O-Si-C and Si-N-Si bond dominate in the coating. Additionally, PSZ can effectively enhance the heat resistance of silicone resin through its reaction with Si-OH groups, which has a significant effect on increasing the resistivity of SMCs and reducing high frequency core loss. Optimizing the PSZ content to 0.5 wt% enhances the magnetic properties of Fe-Ni-Mo SMCs, resulting in a μe of 74.0 at 100 kHz and a corresponding core loss (Pcv) of 547.7 mW/cm3 at 100 kHz/100 mT. The findings provide valuable insights for optimizing PSZ content to improve magnetic performance in SMCs.

Heterogeneous interface engineering of SiBCN/Ni fibers extends enhanced electromagnetic wave absorption properties

Faced with severe electromagnetic wave (EMW) pollution, the development of high-performance EMW absorbers remains a formidable challenge. In this study, SiBCN/Ni fibers containing uniformly dispersed Ni2Si nanoparticles were synthesized by electrospinning method with polymer-derived ceramics method, and their electromagnetic properties were evaluated. The low permeability threshold of the fibers ensures sufficient conduction loss effect. The in situ grown Ni2Si nanoparticles provide a magnetically coupled network, which is more conducive to obtaining excellent impedance matching. Furthermore, the presence of β-SiC, SiO2, and Si2N2O generates numerous heterogeneous interfaces (e.g., C-SiC and C-Ni2Si), leading to enhanced interfacial polarization through the accumulation of charges. As a result, the prepared SiBCN/Ni fibers exhibit impressive EMW absorption properties. At a Ni content of 1 wt%, the effective absorption band (EAB) is 4.32 GHz (13.68–18 GHz). At a Ni content of 1.5 wt%, the minimum reflection loss (RLmin) is −52.98 dB, and the sample has excellent radar scattering capabilities, which is verified by CST Microwave Studio simulations. Therefore, SiBCN/Ni fibers are promising as excellent EMW absorbing materials in practical applications.

Macroporous polymer-derived ceramics produced by standard and additive manufacturing methods: How the shaping technique can affect their high temperature thermal behavior

This work proposes the processing of porous ceramic lattices via three polymer-derived ceramic routes, namely powder bed fusion and infiltration, fused filament fabrication and replica, and a direct replica of a foamed polymer. A common feature in the processing of these lattices is the use of the same polysilazane as the preceramic source for the Si-C-N-O network that builds up during ceramization.We adopted rotated cube, honeycomb and randomized cellular geometries as a matter of comparison for thermal exchange when an air flow is forced through the structures up to 1050 °C. The three procedural pathways are discussed in their limitations regarding geometry, polymer-to-ceramic conversion, high-temperature heat exchange performance and durability. In this regard, while rotated cube geometry results in the best thermal exchange and highest pressure drop, we show a correlation between chemical composition and high temperature oxidation of the Si-C-N-O network, possibly attributed to the selection of the processing routes.

Subtractive manufacturing of polymer-derived ceramic composite thick film sensor based on ultrafast laser etching

Polymer-derived ceramics (PDCs) are increasingly recognized as promising materials for high-temperature thin/thick film sensors (HTTFSs). However, a large linewidth and poor dimensional accuracy have severely restricted the practical application of PDCs HTTFSs. Our study employed a picosecond laser to precisely pattern the polymer-derived ceramic (PDC) thick film while applying no obvious damage to the interface between ceramic and substrate. Through parameters optimization, the laser-affected area was minimized to 6 μm wide, and a minimum feature size of about 30 μm was achieved. Furthermore, 7 rounds of high-temperature tests of the patterned film revealed good temperature-resistance repeatability within a temperature range of up to 800 °C. To demonstrate practical application potential, we successfully fabricated a heat flux sensor, and it exhibited a sensitivity of 1.32 mV/(kW/m2), a response time of 600 ms, and excellent repeatability over a range of 0–75.4 kW/m2. In summary, this paper proposes a novel approach toward miniaturizing the linewidth of the polymer-derived ceramics thick film sensor, showing significant potential for precise measurements in extreme environments.

Vat photopolymerization 3D printing SiBCN ceramic metamaterials with strong electromagnetic wave absorption

Starting from the simulation prediction, SiBCN polymer-derived-ceramic metamaterials, integrating both structure and function in a single component, were obtained using vat photopolymerization technology starting from a preceramic polymer. The low-density gyroid triply periodic minimal surface (TPMS) structures used in this study increases the multiple reflection loss of electromagnetic wave (EMW) in the macro-interpenetrating channel structure, generates surface characteristics (stair-stepping effect) structure interface polarization, and improves microwave absorption characteristics. The possible multiple reflection effects of a gyroid structure on electromagnetic waves are discussed by Computer Simulation Technology simulation. At the same time, the precipitated phases in polymer derived ceramics (PDCs) were adjusted by controlling the pyrolysis temperature. The results show that the crystal phases (such as β-SiC and C) precipitated in the gyroid structure sample pyrolyzed at 1200°C enrich the heterogeneous interface polarization in the material. In addition, C forms a (semi-)conductive network, which increases the conductivity loss. The effective absorption bandwidth (EAB, RL<-10 dB) of the samples pyrolyzed at 1200°C was 3.09 GHz (thickness of 2.21 mm) and the minimum reflection loss (RLmin) was −70.6 dB (thickness of 2.31 mm), indicating that the samples have favorable EMW absorption properties and great potential for applications, providing a foundation for the preparation of high-performance lightweight structural ceramics.

Strengthened and toughened SiHfBCN-based high-temperature resistant adhesive with SiC NWs

To further improve the performance of binders, a SiHfBCN-based high-temperature resistant adhesive was successfully synthesized by Polymer-Derived Ceramics (PDC) route using TiB2, Polysiloxane (PSO) and short SiC nanowires as fillers. The effect of short SiC nanowires on the adhesive strength at room temperature and high temperature, as well as the reinforcing mechanism was studied. Compared with the adhesive without SiC nanowires, after curing (at 170 °C) and pyrolysis (at 1000 °C) in air, the appropriate adding of SiC nanowires upgrades the room temperature and high temperature (at 1000 °C in air) adhesive strength to (12.50 ± 0.67) MPa (up by about 32%) and (13.11 ± 0.79) MPa (up by about 106%), respectively. Attractively, under the synergistic impact of the nanowire bridging, nanowire breaking, nanowire drawing and crack deflection, the optimized adhesive exhibits multi-stage fracture, causing the increscent fracture displacement.

Rational design of SiBCN ceramics with excellent attenuation to strong electromagnetic-wave-absorbing properties at low frequency

To achieve strong electromagnetic wave absorbing properties, it is important to have good impedance matching, moderate electrical conductivity, and high polarization loss, particularly at low frequency. However, meeting these requirements for polymer-derived ceramics remains challenging. This paper proposes a simple approach to addressing this challenge by adjusting the crystallinity and defects of SiBCN ceramics. The addition of Sm as a catalyst and tailored heating temperatures were used to create SiBCN ceramics with adjustable crystallinities and defective nanograins. The controlled crystallinity provided good impedance matching, while the tailored defective nanograins offered high polarization loss. The combination of these factors results in high-performance electromagnetic wave absorption, with the SiBCN ceramics achieving a minimum reflection loss of −59.13 dB at 3.6 GHz and an effective attenuation bandwidth of 6.87 GHz with a thickness of 2.22 mm. This study provides an effective strategy for the design and fabrication of strong EMW absorbing materials.

Achieving High-Temperature Stable Structural Color through Nanostructuring in Polymer-Derived Ceramics.

Structural colors offer a myriad of advantages over conventional pigment-based colors, which often rely on toxic chemical substances that are prone to UV degradation. To take advantage of these benefits in demanding environments, there is growing interest in producing structural colors from ceramics. Polymer-derived ceramics (PDCs) emerge as a compelling choice, presenting two distinct advantages: their enhanced shape ability in their polymeric state associated with impressive temperature resistance once converted to ceramics. This study pioneers the fabrication of noniridescent structural colors from silicon oxycarbide (SiOC) PDC, enabled by the nanostructuring of an inverse photonic glass within the PDC material. This design, a functionally graded material with an inverse photonic glass (FGM-PhG) structure, leverages the innate light-absorbing properties of SiOC, yielding a vivid structural color that maintains its saturation even in white surroundings. This study elucidates the process-structure-properties relationship for the obtained structural colors by investigating each layer of the functionally graded material (FGM) in a stepwise coating deposition process. To further emphasize the exceptional processing flexibility of PDCs, the three-step process is later transferred to an additive manufacturing approach. Finally, the FGM-PhG structural colors are demonstrated to have remarkable thermal stability up to 1000 °C for 100 h, possibly making them the most thermally stable ceramic structural colors to date.

Fast Solution Blow Spinning of Lotus-Leaf-Inspired SiO2 Nanofiber Sponge for High Efficiency Purification.

Massive production of SiO2 nanofibers with both high durability and exceptional performance remains a significant challenge. Herein, a novel approach was introduced to achieve the massive production of SiO2 nanofibers with lotus-leaf-inspired surfaces by combining solution blowing spinning (SBS) and the polymer-derived ceramics method. Based on the SBS technique, three types of precursor nanofiber products were fast spined with methyl silsesquioxane polymer and polymethyl hydrogen siloxane employed as Si sources. The flow rate of the SBS spined Si-based ceramic nanofibers was enhanced to 20 mL·h-1. Furthermore, through the integration of hydrophobic-oleophilic SiO2 nanoparticles into the precursor solution, SiO2 nanofibers with lotus-leaf nanoprotrusion surfaces were fabricated. Nanoparticle-decorated SiO2 fibers demonstrated excellent hydrophobicity (138.3°), compression resilience (∼60%), proficiency in organic pollutant adsorption, high-temperature resistance (∼1100 °C), and outstanding thermal insulation properties (thermal conductivity of 0.0165 W·(m·K)-1).

Designed fabrication of lightweight SiC(Hf, rGO) bulk composites derived from Hafnium-modified precursors for hypersonic vehicle components

Demand for SiC-based polymer-derived ceramics (PDCs) employed as hypersonic vehicle components with light weight, high strength, excellent high-temperature/ablation resistance is increasingly urgent. Herein, bulk SiC(Hf, rGO) nanocomposite PDCs were fabricated via re-pyrolyzing ball-milling blends of unique SiC(Hf, rGO)p/polyhafniumcarbosilane-vinyltriethoxysilane-graphene oxide (PHVG). Highly cross-linked PHVG can effectively optimize compact formability and improve ceramic yield. In-situ formed HfO2 embedded in ceramic network toughens microstructure, while interfacial HfOSi increases structure disorder to improve high-temperature properties. As demonstrated, SiC(Hf, rGO) modified by 3 wt.% Hf and re-pyrolyzed at 1300 °C possess good mechanical performances including hardness (5.83 GPa), fracture toughness (4.29 MPa·m1/2), compressive strength (181.83 MPa) and flexural strength (46.55 MPa). More interestingly, self-healing HfO2(HfSiO4)/SiO2 protective layer emerging during 20 min surface ablation test at 1300 °C, timely covers defects and avoids destructive structure, thus retains stable structure and mechanical properties of specimens. Such nanocomposites can promote uses in thermal protection systems (TPS) for hypersonic vehicles against extreme high-temperature environments.