Preceramic Precursor Research Articles

Low-temperature sintering of SiC ceramics using a mixture of preceramic precursor and metal nanoparticles

Polymer infiltration and pyrolysis (PIP) has a limitation in increasing the relative density of SiC ceramics above 90 %. This is due to the blockage of open pore channels. In this study, a new process that incorporates Ni and graphite nanoparticles into SiC preceramic precursor is examined. Ni nanoparticles react with the SiC precursor to form low melting point nickel silicide phases which infiltrate into pores of the bulk without a blockage problem. In later infiltration cycles, graphite nanoparticles are added to convert the nickel silicide to nickel carbide and silicon carbide, which may prevent the deterioration of mechanical strength at high temperature. The relative density of SiC ceramics in this study increases to 92 % and above, which is higher than that of SiC ceramics prepared by the traditional PIP. The results of this study show a pathway to process high density SiC ceramics at relatively low sintering temperatures.

ZrC/SiC composites from functionalised ZrC combining preceramic precursors and SPS

ZrC/SiC composites were obtained in situ using Spark Plasma Sintering (SPS), with a previous organic functionalisation of ZrC particles (ZrCf). It used the direct ceramisation/sintering of ZrCf/polycarbosilane mixture without any previous crosslinking steps. The prior functionalisation did not have an effect on either the relative density of the materials or the mechanical properties. However, larger SiC domains were observed around the functionalised ZrC particles, probably due to the hydrosilylation reaction between pendant alkene groups and Si-H from the commercial polycarbosilane. In addition, TEM analyses showed different features such as the presence of inter- and intra-granular SiC, and of a double layer at the grain boundaries between the ZrC and SiC phases, when avoiding functionalisation. The oxidation behaviour was also tested, and the prior functionalisation improved the properties of the final samples.

Hybrid HfC‐SiCN matrix for improved oxidation resistance of carbon fiber–reinforced mini‐composites

AbstractHafnium carbide (HfC) is an ultrahigh‐temperature ceramic with high melting point, chemical stability, hardness, and wear resistance. However, its low fracture toughness and poor thermal shock resistance limit its structural applications in extreme environments. In this study, co‐curing of liquid precursors was carried out prior to complete pyrolysis of individual polymeric precursors. First, HfC preceramic polymer precursor was cured, followed by silicon carbonitride (SiCN) precursor curing on a 2D carbon fiber (CF) cloth using the drop‐coating process. The infiltrated CFs were pyrolyzed at 800°C to achieve CF/HfC‐SiCN ceramic mini‐composites. The cross‐linked precursor‐to‐ceramic yield was observed to be as high as 65% when the procedure was carried out in an inert environment. Although stable up to 1200°C, CF/HfC‐SiCN samples demonstrated susceptibility to oxidation at 1500°C in ambient air. The oxidation of HfC in the presence of SiC leads to the formation of a hafnium‐containing silicate (HfxSiyOz) along with hafnia (HfO2). This compound of silicate and hafnia limits oxygen diffusion better than SiO2 and HfO2 individually. The incorporation of SiCN in HfC ceramic led to improved phase stability compared to a neat HfC system. The results of this study also show that the use of liquid‐phase precursors for HfC and SiCN in the polymer‐infiltrated pyrolysis method is a promising approach to fabricating high‐temperature structural ceramic matrix composites with good oxidation resistance.

Recent Advances in Preceramic Polysilazane Precursors in Additive Manufacturing

Si3N4/SiCN ceramics have been extensively explored for applications in the aerospace, mechanical engineering, and biomedical fields. Recently, there has been significant focus on the additive manufacturing (AM) of polymer-derived ceramic (PDC) technology for fabricating Si3N4/SiCN ceramics. The chemical structure and composition of the preceramic polymer precursors have a crucial influence on the performance of ceramic products. In this paper, recent advances in the use of polysilazane and polycarbosilazane precursors in AM are reviewed and an outlook for future development is presented. The findings of this study could spark inspiration and reflection regarding AM applications and synthetic technology. It is believed that the development of PDCs in ceramic fabrication will become more versatile and application-oriented and provide more freedom in the design of high-performance ceramics.

Single-source-precursor synthesis of dense monolithic SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C ceramic nanocomposite with excellent high-temperature oxidation resistance

A dense monolithic SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C ceramic nanocomposite containing high-entropy carbide phase was prepared using a single-source-precursor method combined with spark plasma sintering. The nanocomposites were characterized by a unique microstructure with a homogeneous dispersion of (Ti0.25Zr0.25Hf0.25Ta0.25)C@C core-shell nanoparticles within a β-SiC matrix. The atomic ratios of transition metal elements within the in situ generated (Ti0.25Zr0.25Hf0.25Ta0.25)C nanoparticles can be controlled precisely by molecular design of the preceramic precursors. Oxidation behavior of the SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C nanocomposite was investigated as well. The SiC/(Ti0.25Zr0.25Hf0.25Ta0.25)C exhibit excellent oxidation resistance between 1200 °C and 1500 °C due to the in situ generated continuous multiphase scales consisting of β-SiO2, HfTiO4, ZrSiO4, HfSiO4, and Ta2O5 that can be rapidly sintered during oxidation. Particularly, at 1200 °C, the parabolic oxidation rate constant (Kp) value is 1–2 orders of magnitude lower than that of similar SiC/HfC, SiC/(Hf, Ta)C, SiC/(Hf, Ti)C and SiC/(Hf, Zr, Ti)C nanocomposites.

Additive Manufacturing of High‐Temperature Preceramic‐Derived SiOC Hybrid Functional Ceramics

High‐temperature capable materials, metals, and ceramics are attracting significant interest for applications in extreme environmental conditions. Herein, a hybrid metal‐reinforced ceramic matrix material consisting of preceramic‐derived high‐temperature SiOC and copper nanoplates is reported, enabling the manufacturing of high‐temperature sensing electronics. The preceramic polymer precursors including polydimethylsiloxane and polydimethylsilane, together with copper nanoplates, are thermally converted into durable copper‐reinforced SiOC ceramics. The presence of copper in SiOC ceramics enhances its electrical conductivity, while SiOC suppresses oxygen uptake and acts as a shield for oxidation to achieve high‐temperature thermal resistance and negative temperature coefficient at high temperatures. A comprehensive electric and sensing performance, combined with cost‐effectiveness and scalability, can facilitate the utilization of hybrid Cu and SiOC composites in high‐temperature electronics.

Customized Nanostructured Ceramics via Microphase Separation 3D Printing.

To date, the restricted capability to fabricate ceramics with independently tailored nano- and macroscopic features has hindered their implementation in a wide range of crucial technological areas, including aeronautics, defense, and microelectronics. In this study, a novel approach that combines self- and digital assembly to create polymer-derived ceramics with highly controlled structures spanning from the nano- to macroscale is introduced. Polymerization-induced microphase separation of a resin during digital light processing generates materials with nanoscale morphologies, with the distinct phases consisting of either a preceramic precursor or a sacrificial polymer. By precisely controlling the molecular weight of the sacrificial polymer, the domain size of the resulting material phases can be finely tuned. Pyrolysis of the printed objects yields ceramics with complex macroscale geometries and nanoscale porosity, which display excellent thermal and oxidation resistance, and morphology-dependent thermal conduction properties. This method offers a valuable technological platform for the simplified fabrication of nanostructured ceramics with complex shapes.

The dielectric properties of polymer derived silicon oxycarbonitride film incorporated with TiO2 for electromagnetic wave absorption

The polysilazane preceramic precursor is applied as a coating on ceramic substrates and pyrolyzed at different temperatures to form a silicon oxycarbonitride ceramic film for its dielectric properties in the low-frequency range of 1–8 MHz. Additionally, the porous ceramic hollow matrix filled with the polysilazane preceramic precursor is pyrolyzed for dielectric measurement in the high-frequency range of 1–19 GHz. The results indicate that coating Al2O3 substrates with SiCNO reduces the absorption effect as the pyrolytic temperatures increase. Conversely, coating AlN substrates with SiCNO exhibits the opposite absorption effect. Incorporating titanium dioxide with SiCNO reduces the wave absorption effect within the temperature range of 700 °C–1100 °C. The loss tangent and electromagnetic wave loss of the porous ceramic hollow matrix filled with SiCNO are 4.06 × 10−2 and 4.41 × 10−2, respectively in the high-frequency range. These findings indicate the electromagnetic wave absorption ability of SiCNO composite.

A new strategy to prepare magnetoceramics by bulk pyrolysis of Fe-containing polyamide precursors

In this work, a new strategy was developed to prepare magnetoceramics through a bulk pyrolysis of novel Fe-containing polyamide preceramic precursors at low pyrolysis temperature. A series of novel polyamides with different chemical structures were synthesized by bulk Michael addition and polycondensation, and their structures were characterized. Polymer precursors (PPs) were prepared by direct melt blending polyamides and FeCl3, and polymer-derived ceramics (PDCs) were prepared via the pyrolysis of PPs. The polyamide structure with pendant pyridine groups in repeating units makes the Fe complexes uniformly dispersed in matrix. The relationship between magnetoceramic compositions and PP structures was investigated by TGA, XPS, XRD, FE-SEM, FE-TEM and VSM characterizations. Different chemical structures and Fe catalysis effect lead to different thermal decomposition processes of PPs. Increasing crystal-Fe content in PDCs contributes to higher magnetic properties. The morphology of crystal phases in PDCs relies on the structures of PPs and pyrolysis temperature. Different pyrolysis temperatures and chemical structures of PPs bring about different Fe crystal phases and carbon crystal state of nanosheets or nanofiber bundles.

Dual functional low surface energy coating of anti-corrosion / fouling via crosslinking polysilazane preceramic precursor incorporated with fluorine

A dual functional low surface energy coating with polysilazane preceramic precursor is developed to form a silicon-based polymeric film. The result shows that the lowest surface free energy of the fluorinated silicon-based polymeric film is about 28.43 mJ/m2 and its corrosion potential achieves 0.0899 V by the tafel polarization indicating that it has relatively low surface free energy with high corrosion resistance. The water contact angle of the silicon-based polymeric film with polysilazane preceramic precursor diluted in acetone crosslinked at 400 °C can achieve 126.8°. Polysilazane preceramic precursor incorporated with titanium dioxide, TiO2 is able to reduce the surface energy to lower than 30 mJ/m2 for anti-fouling application. Nanoindentation result shows the fluorinated silicon-based polymeric film has the higher elastic recovery rate, 77.3 % representing that fluoride dopant improves its surface toughness. The average hardness and reduced modulus of the silicon-based polymeric film are superior to that of the pure aluminum, showing that this dual functional low surface energy coating provides a relatively high surface strength with high toughness.

Defective structure of doped carbons obtained from preceramic polymers through Cl2‐ and NH3‐assisted thermolysis

AbstractThe processing parameters such as the heat treatment temperature, type of preceramic precursor, and post‐synthesis treatments are key factors for the development the different microstructures in polymer‐derived ceramics. Moreover, doping with different heteroatoms has increased the ability of the polymer‐derived ceramics to produce tunable nanostructures with a controlled pore size and distributions. A preceramic precursor containing P has been prepared from a commercial polysiloxane polymer and a phosphate alkoxide. It has been subjected to thermal treatments in N2, NH3, and Cl2 atmospheres in different order sequences to create differentiated microstructures either in the ceramic matrix and the carbon phase. The structural, textural, and spectroscopic characterization revealed that the P atoms play a key role in the evolution of the microstructure during the thermal treatments. If the chlorination is carried out before the treatment in NH3, a silicophosphate matrix is formed and prevents from nitrogen incorporation into the free carbon phase. On contrary, if the NH3 treatment is carried out before the chlorination, the carbon phase is predominantly modified by the incorporation of P atoms within the free carbon network.

Mesoscale Modeling of Phase Separation Controlled by Hydrosilylation in Polyhydromethylsiloxane (PHMS)-Containing Blends.

Controlling morphology of polysiloxane blends crosslinked by the hydrosilylation reaction followed by pyrolysis constitutes a robust strategy to fabricate polymer-derived ceramics (PDCs) for a number of applications, from water purification to hydrogen storage. Herein, we introduce a dissipative particle dynamics (DPD) approach that captures the phase separation in binary and ternary polymer blends undergoing hydrosilylation. Linear polyhydromethylsiloxane (PHMS) chains are chosen as preceramic precursors and linear vinyl-terminated polydimethylsiloxane (v-PDMS) chains constitute the reactive sacrificial component. Hydrosilylation of carbon–carbon unsaturated double bonds results in the formation of carbon–silicon bonds and is widely utilized in the synthesis of organosilicons. We characterize the dynamics of binary PHMS/v-PDMS blends undergoing hydrosilylation and ternary blends in which a fraction of the reactive sacrificial component (v-PDMS) is replaced with the non-reactive sacrificial component (methyl-terminated PDMS (m-PDMS), polyacrylonitrile (PAN), or poly(methyl methacrylate) (PMMA)). Our results clearly demonstrate that the morphology of the sacrificial domains in the nanostructured polymer network formed can be tailored by tunning the composition, chemical nature, and the degree of polymerization of the sacrificial component. We also show that the addition of a non-reactive sacrificial component introduces facile means to control the self-assembly and morphology of these nanostructured materials by varying the fraction, degree of polymerization, or the chemical nature of this component.

UV‐curable inorganic precursors enable direct 3D printing of SiOC ceramics

Abstract3D ceramic parts are of great interest for various applications including aerospace, defense, electronics, photonics, and biomedical. Yet, additive manufacturing of ceramics is challenging due to their poor machinability. Herein, two approaches based on the chemical modification of silicon resins to obtain UV‐curable preceramic precursors of SiOC are described. The dual functionality of the synthesized resins acting both as preceramic precursor and as photopolymerizable entity under UV light is exploited. A set of characterization techniques has allowed the investigation of the mechanisms involved in the synthesis of the inorganic SiOC precursors according to the following approaches: (1) blend of the silicon resin with photoactive monomers and (2) synthesis of a single source UV‐curable preceramic silicon resin. A correlation between the nature of the precursor and the properties of the derived SiOC is analyzed. From a technological point of view, the materials can be fabricated as dense or crack‐free porous customized objects with low mass loss and optimal surface quality.

Surface mechanical and electrochemical properties of zirconium oxide embedded silicon carbonitride ceramic composite film by polysilazane preceramic precursor

Wet chemical and pyrolytic process is used to reduce zirconium oxide uniformly distributed in liquidic polysilazane preceramic precursor via sodium borohydride and zirconium n-propoxide to form zirconium oxide embedded silicon carbonitride (ZrO2-SiCN(O)) ceramic composite film. Its average hardness (H*) and modulus of elasticity (E * ) achieve 11.54 GPa and 101.2 GPa, respectively. Its index of elastic strain to failure, H* /E * and fracture toughness index, H*3/E *2 can reach 0.114 and 0.115 GPa. The average hardness and reduced modulus of elasticity are enhanced 25.2% and 30.2% as ZrO2 embedded in SiCN(O) ceramic film. The copper foam is coated with SiCN(O) ceramic film as the working electrode whose corrosion potential achieve 0.52 V that is 23 times higher than that of the pure copper foam. Its lowest current density is 7.42 × 10−7 A m−2 that is one hundredth of the pure copper foam as the working electrode.

New Low-Temperature Method of Synthesis of Boron Carbide Matrix Ceramics Ultra-Dispersive Powders and their Spark Plasma Sintering

The ultra-dispersive powders of pre-ceramic precursors for boron carbide based composites were obtained by relatively low-temperature (at 200 – 1000 °C) synthesis from liquid charges containing available compounds such as salts and oxides. Boron carbide matrix ceramics were compacted by their reactive spark plasma sintering (SPS) at 1500 – 1700 °C. It is noted that the X-ray diffraction (XRD) peaks corresponding (m)ZrO2 and WC phases presented in the synthetic pre-ceramic precursors disappear after the SPS is conducted at 1500 °C. It is established that the addition of tungsten and cobalt compounds promotes both the low-temperature synthesis of ceramic components and sintering processes of their powders. Energy dispersive X-ray (EDX) analysis showed that the ceramics contain a small amount of Co (0.8 – 2 wt.%). The density of samples of cobalt-containing ceramics B4C–ZrB2–W2B5–Co is higher compared to that of cobalt-free ceramics B4C–ZrB2–W2B5.

Cobalt‐catalyzed tunable carbon microstructures from halogenated SiC preceramic precursors

AbstractCarbide‐derived carbons (CDCs) with highly graphitized domains, linear, oval‐shaped, and barrel‐like structures have been prepared from a silicon carbide preceramic precursor containing catalytic amounts of cobalt. The chlorination temperature as well as the amount of catalysts will determine the specific surface area, pore size, and morphology of the obtained carbons. At low chlorination temperature, an amorphous network with significant amount of double or single oxygenated bonds was obtained. At 700 and 800°C both linear graphitic domains and barrel‐like carbon dominate the microstructure with an increased presence of microporosity. There barrel‐like structures provided increased specific capacitance, although the high anisotropy of the structure compromises the energy density of the device. At 900°C, despite the disappearance of this cropped surface, the hierarchical pore distribution and low O content also induce an increase of the specific capacitance of the CDC samples regardless of their high percentage of micropores.

Silicon oxycarbide-tin nanocomposite derived from a UV crosslinked single source preceramic precursor as high-performance anode materials for Li-ion batteries

In this work, we report an innovative and facile UV light-assisted synthesis of a nanocomposite based on silicon oxycarbide (SiOC) and tin nanoparticles. SiOC ceramic matrix, containing a conductive free carbon phase, participates in lithium-ion storage, and buffers the volume changes of Li-alloying/de-alloying material. The reported synthesis procedure through a polymer-derived ceramic route involves the preparation of a single-source precursor by UV crosslinking of a preceramic polymer in the presence of a tin precursor. Pyrolysis of this starting precursor at 1000 °C leads to a homogenous distribution of tin nanoparticles (25–35 nm) within the SiOC ceramic matrix, which is crucial for electrochemical stability of the material. SiOC/Sn nanocomposite tested as an anode for Li-ion battery exhibits high reversible capacity values (603 mAh g−1 at the current density of 74.4 mA g−1), outstanding rate capability (524 mAh g−1 at 2232 mA g−1), and superior stability (494 mAh g−1 after 250 charge/discharge cycles).

Influence of the Pyrolysis Temperature and TiO2-Incorporation on the Properties of SiOC/SiC Composites for Efficient Wastewater Treatment Applications.

This study focuses on the development of porous ceramer and SiOC composites which are suitable for microfiltration applications, using a mixture of polysiloxanes as the preceramic precursor. The properties of the membranes—such as their pore size, hydrophilicity, specific surface area, and mechanical resistance—were tailored in a one-step process, according to the choice of pyrolysis temperatures (600–1000 °C) and the incorporation of micro- (SiC) and nanofillers (TiO2). Lower pyrolysis temperatures (<700 °C) allowed the incorporation of TiO2 in its photocatalytically active anatase phase, enabling the study of its photocatalytic decomposition. The produced materials showed low photocatalytic activity; however, a high adsorption capacity for methylene blue was observed, which could be suitable for dye-removal applications. The membrane performance was evaluated in terms of its maximum flexural strength, water permeation, and separation of an oil-in-water emulsion. The mechanical resistance increased with an increase of the pyrolysis temperature, as the preceramic precursor underwent the ceramization process. Water fluxes varying from 2.5 to 370 L/m2·h (2 bar) were obtained according to the membrane pore sizes and surface characteristics. Oil-rejection ratios of 81–98% were obtained at an initial oil concentration of 1000 mg/L, indicating a potential application of the produced PDC membranes in the treatment of oily wastewater.

Carbon fiber surface-modified by polymer derived ceramic incorporated with graphene to strengthen the mechanical and electrochemical properties of ceramic-carbon fiber composite

In this study, the carbon fiber surface is spray coated with polysilazane preceramic precursor and pyrolyzed at different pyrolytic temperatures to form the ceramic-carbon fiber composite (SiCN-CCFC) with dense layer of amorphous SiCN ceramic film. The specific strength and modulus of SiCN-CCFC are enhanced 44.26% and 15.37% with spraying 40 wt.% polysilazane preceramic precursor diluted in acetone and then pyrolyzing at 450 °C compared with those of the pure carbon fiber. The carbon fiber spray coated with 20 wt% polysilazane preceramic precursor with 0.5 wt.% graphene in acetone is pyrolyzed at 450 °C to form the graphene-reinforced ceramic-carbon fiber composite (SiCN-GRCFC) whose specific strength and modulus are enhanced 73.15% and 41.15%, respectively, compared with those of the pure carbon fiber. The results of potentiodynamic polarization reveal the electrochemical properties between the pure carbon fiber and SiCN-CCFC that the corrosion potential increases from −0.0971 V to 0.5862 V, the corrosion current density decreases from 1.72 × 10−2 to 1.32 × 10−7 mA⋅cm−2, and the corrosion rate extremely decreases from 9.98 × 10−2 to 9.54 × 10−7 mm∙year−1. The electrochemical properties between the pure carbon fiber and SiCN-GRCFC show that the corrosion potential increases from −0.0971 V to 0.5873 V, the corrosion current density decreases from 1.72 × 10−2 to 3.61 × 10−6 mA∙cm−2, and the corrosion rate extremely decreases from 9.98×10−2 to 2.88 × 10−5 mm∙year−1. Therefore, it can be concluded that the SiCN coating incorporated with additional graphene content can significantly enhance the mechanical properties and corrosion resistance of the commercial carbon fiber.

Design of carbon–ceramic composite membranes with tunable molecular cut-offs from a carboxylic benzoxazine ligand chelated to silica–zirconia

This study presents a concept that focuses on the structure design of preceramic resin precursors by the sol–gel method for fabricating carbon–ceramic molecular sieving membranes.