Preceramic Polymer Research Articles

Synthesis and Characterization of Meltable and Soluble Reticulating Polysilazane Modified via Melamine Toward SiCN Ternary Ceramics

The molecular structure of polymer has a great influence on the physical and chemical properties of polysilazane and the properties of ceramics pyrolyzed from the polysilazane. The polysilazane with reticulating molecular structure has good performance generally. The performance of the precursor can be effectively improved by reasonable molecular structure design and control of the synthesis process. In this paper, a reticulating polysilazane PSZ-M with outstanding meltability and solubility were synthesized via an aminolysis reaction between dichloromethylsilane (DCMS) and hexamethyldisilazane (HMDZ), and using the melamine as additive. The properties and the ceramization process of PSZ-M, as well as the molecular structure and properties of derived SiCN ceramic, were well studied. The melamine can be introduced via the dehydrogenation reaction between N–H and Si–H. The ceramics yield was enhanced to 63.18% at 900 °C after the introduction of melamine. The SiCN ceramics derived from the PSZ-M can remain amorphous when pyrolyzed below 1400 °C, the crystal phase of SiC, SiN4 were detected for 1500 °C treated samples. The using of melamine as an additive to synthesis polysilazanes has led to the development of a convenient approach for constructing polysilazanes with reticulating structure and ideal performance, which supports a strategy for the structure design of preceramic polymers.

Multiscale ceramic components from preceramic polymers by hybridization of vat polymerization-based technologies

A novel approach to fabricate ceramic structures at multiple scales in a single component, based on the hybridization of additive manufacturing technologies, was developed by combining 3D macro-stereolithography (Digital Light Processing, DLP) with two-photon lithography (2PL), to produce cm-sized sample geometries with sub-μm surface features. The preceramic structures in the sub-μm scale were realized by 2PL directly on easily manageable DLP macro-sized samples of the same ceramic composition. In this way, preceramic structures presenting both features typical of DLP printers (with a minimum size of around 50 μm) and features well below their resolution limit were realized. We report here, for the first time, the realization of polymer-derived ceramic SiOC ceramic components structured in 3D across several length scales (with micron and mesoscale 3D features), produced by pyrolysis at 1000 °C of preceramic parts, without shape distortion during the pyrolysis step.

Magnetically Actuated SiCN-Based Ceramic Microrobot for Guided Cell Delivery.

A silicon carbonitride (SICN) ceramic microrobot, biocompatible and magnetically activable, is developed for the delivery of viable cells to defective tissue by sequential steps of microstructuring, magnetization, and cell loading. The ceramic carrier of porous cylindrical framework is fabricated by 3D laser lithography using a photocurable preceramic polymer, chemically modified polyvinylsilazane, and subsequent pyrolysis at 600 °C under an inert atmosphere. Magnetic nanoparticles (MNP) are integrated into the surface-modified ceramic carrier by thiol-ene click reaction. Finally, the microrobot is loaded with fibroblast cells, which can be guided by a rotating external magnetic field. The proposed ceramic microrobot is mechanically durable, adequately controllable with external magnetic field, and quite compatible with mammalian cells.

Dong-Pyo Kim.

"My biggest motivation is the happiness that comes from scientific discussions. For me, science is a tool of good communication in friendship, irrespective of age, language, or culture. Guaranteed to make me laugh is finding similarities in human nature and science …" Find out more about Dong-Pyo Kim in his Author Profile.

Fabrication of porous boron nitride by using polyborazylene as precursor, polymethylmeth-acrylate as reaction agent

A novel process for the production of micro-molecular boron nitride foams has been developed through foaming of boron nitride preceramic polymer with the help of sacrificial microbeads of polymethylmethacrylate (PMMA), followed by pyrolysis under inert atmosphere. The process parameters of porous BN ceramics were studied by thermo gravimetric analysis, thermo mechanical analysis, X-ray diffraction, scanning electron microscopy, mercury porosimetry and elemental analysis. The microstructure and element composition of the porous ceramics were also studied by the above methods. The results showed that: when using polyborazylene from thermolization of borazine at 60°C as boron nitride precursor, PMMA microbeads with pore size of 25μm as sacrificial microbeads, adding into polyborazylene powder with 80 wt% in the foaming mixture. After warm-pressing the powders under 74MPa at 60°C, subsequently pyrolyzing the powders under ammonia to 1000°C then to 1450°C under nitrogen atmosphere, we can obtain boron nitride foams. Through scanning electron microscopy observation, X-ray diffraction analysis and porosity measurement, it was confirmed that the obtained boron nitride pieces were microcellular foams with homogeneous distributed pore size average at ∼19.15μm and had a mostly interconnected porosity of 79.06 vol%. The temperature should be increased to 1700-1800°C to prepare porous BN ceramic with a certain degree of crystallinity (layer spacing d002 = 0.335-0.333 nm)

Silicon Oxycarbide: Silicon Oxycarbide—Tin Nanocomposite as a High‐Power‐Density Anode for Li‐Ion Batteries (Adv. Sci. 19/2019)

In article number 1901220, Thomas Graule, Maksym V. Kovalenko, and co-workers present a new synthesis of Sn nanoparticles (NPs) embedded in a SiOC matrix via the pyrolysis of a preceramic polymer as a single-source precursor. This approach yields a homogeneous dispersion of Sn NPs in a SiOC matrix, which helps to buffer the volume changes of Sn and prevent particle aggregation upon lithiation/delithiation.

Preparation and structure of SiOCN fibres derived from cyclic silazane/poly-acrylic acid hybrid precursor.

Ceramic matrix composite (CMC) materials have been considered a desired solution for lightweight and high-temperature applications. Simultaneously, among all different CMC reinforcements, polymer-derived ceramic (PDC) fibres have gained attention for the intrinsic thermal stability and mechanical strength with simple and cost-effective synthesis techniques. Here, carbon-rich SiOCN fibres were synthesized via hand-drawing and polymer pyrolysis of a hybrid precursor of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasilazane (TTCSZ) and poly-acrylic acid (PAA). The type of silazane reported in this work is considered as a major precursor for SiCN; however, it is unspinnable, due to its unfavourable physical properties (low viscosity) and chemical structure (cyclic rather than linear structure). The introduction of PAA to TTCSZ to create a hybrid precursor remarkably improved the spinnability of the silazane and should be widely applicable to other unspinnable PDC pre-ceramic polymers. Investigations on the structural and compositional development of the fibres were mainly conducted via Raman spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance and thermo-gravimetric analysis to determine spinnability, free carbon content, cross-linking and pyrolysis behaviour of the fibres, respectively.

Combining Soft Polysilazanes with Melt-Shear Organization of Core-Shell Particles: On the Road to Polymer-Templated Porous Ceramics.

The preparation of ordered macroporous SiCN ceramics has attracted significant interest and is an attractive area for various applications, e.g., in the fields of catalysis, gas adsorption, or membranes. Non-oxidic ceramics, such as SiCN, own a great stability based on the covalent bonds between the containing elements, which leads to interesting properties concerning resistance and stability at high temperature. Their peculiar properties have become more and more important for a manifold of applications, like catalysis or separation processes, at high temperatures. Within this work, a feasible approach for the preparation of ordered porous materials by taking advantage of polymer-derived ceramics is presented. To gain access to free-standing films consisting of porous ceramic materials, the combination of monodisperse organic polymer-based colloids with diameters of 130 nm and 180 nm featuring a processable preceramic polymer is essential. For this purpose, the tailored design of hybrid organic/inorganic particles featuring anchoring sites for a preceramic polymer in the soft shell material is developed. Moreover, polymer-based core particles are used as sacrificial template for the generation of pores, while the preceramic shell polymer can be converted to the ceramic matrix after thermal treatment. Two different routes for the polymer particles, which can be obtained by emulsion polymerization, are followed for covalently linking the preceramic polysilazane Durazane1800 (Merck, Germany): (i) Free radical polymerization and (ii) atom transfer radical polymerization (ATRP) conditions. These hybrid hard core/soft shell particles can be processed via the so-called melt-shear organization for the one-step preparation of free-standing particle films. A major advantage of this technique is the absence of any solvent or dispersion medium, enabling the core particles to merge into ordered particle stacks based on the soft preceramic shell. Subsequent ceramization of the colloidal crystal films leads to core particle degradation and transformation into porous ceramics with ceramic yields of 18–54%.

Strong and light cellular silicon carbonitride – Reduced graphene oxide material with enhanced electrical conductivity and capacitive response

Steady graphene oxide (GO) scaffolds created by direct ink writing are used to develop a silicon carbonitride (SiCN) -graphene oxide hybrid material through a preceramic polymer route. For achieving mechanically stable GO scaffolds, the drying method is critical as the ink contains about 5 wt.% of GO, 10 wt.% of polyelectrolytes and 85 wt.% of water. The liquid preceramic polymer (polysilazane type) quickly infiltrates the 3D scaffolds, under vacuum conditions, entirely covering the GO network creating a replica of the original scaffold. The hybrid cellular structure -once thermally treated for GO reduction and ceramic conversion- consists of a network of reduced GO (∼10 wt.%) embedded in an amorphous SiCN matrix following the designed architecture. The 3D hybrid structures show notable electrical conductivity (890 S m−1 at room temperature), thermal stability and considerable strength, about 20 times higher than the single GO scaffold. The structures are tested as electrodes for supercapacitors, reaching a gravimetric capacitance of 39 F g−1 that remains stable after 7000 charge/discharge cycles.

Open-celled silicon carbide foams with high porosity from boron-modified polycarbosilanes

Open-Celled silicon carbide (SiC) foams were prepared from a mixture of a boron-modified polycarbosilane as a preceramic polymer and poly(methymetacrylate) (PMMA) microbeads as sacrificial agents. The process consists in the cross-linking of the liquid allylhydridopolycarbosilane (AHPCS, SiC precursor) with borane dimethylsulfide (BDMS, boron source) to form a solid boron-modified polycarbosilane with an adjusted cross-linking degree. The latter is mixed with PMMA microbeads (25 μm) in a 20:80 ratio and the mixture is warm-pressed at 120 °C forming consolidated green bodies to be pyrolyzed at 1000 °C under argon and to deliver open-celled SiC foams with an interconnected porosity of 73.4 vol%. These foams combine a low density with a compressive strength of 3.49 ± 0.56 MPa and a thermal and mechanical stability under argon up to 1300 °C. Ageing and microfiltration tests in the conditions of a primary loop of coolant in a Pressurized Water Reactor (PWR) showed that foams display a relatively high stability while retaining particles of 5 μm in diameter making these materials as appropriate candidates to work in separation techniques under harsh environments.

Silicon Oxycarbide-Tin Nanocomposite as a High-Power-Density Anode for Li-Ion Batteries.

Tin‐based materials are an emerging class of Li‐ion anodes with considerable potential for use in high‐energy‐density Li‐ion batteries. However, the long‐lasting electrochemical performance of Sn remains a formidable challenge due to the large volume changes occurring upon its lithiation. The prevailing approaches toward stabilization of such electrodes involve embedding Sn in the form of nanoparticles (NPs) in an active/inactive matrix. The matrix helps to buffer the volume changes of Sn, impart better electronic connectivity and prevent particle aggregation upon lithiation/delithiation. Herein, facile synthesis of Sn NPs embedded in a SiOC matrix via the pyrolysis of a preceramic polymer as a single‐source precursor is reported. This polymer contains Sn 2‐ethyl‐hexanoate (Sn(Oct)2) and poly(methylhydrosiloxane) as sources of Sn and Si, respectively. Upon functionalization with apolar divinyl benzene sidechains, the polymer is rendered compatible with Sn(Oct)2. This approach yields a homogeneous dispersion of Sn NPs in a SiOC matrix with sizes on the order of 5–30 nm. Anodes of the SiOC/Sn nanocomposite demonstrate high capacities of 644 and 553 mAh g−1 at current densities of 74.4 and 2232 mA g−1 (C/5 and 6C rates for graphite), respectively, and show superior rate capability with only 14% capacity decay at high currents.

Tailored Oxidation Barrier Coatings for Mo-Hf-B and Mo-Zr-B Alloys.

The cyclic oxidation response of Mo-14Hf-23B and Mo-14.8Zr-26B (compositions in at. %) was investigated in air at 800 °C, which is a critical temperature for Mo-based alloys because of the pesting phenomenon. Rapid oxidation was observed for the unprotected samples, and an oxidation protection coating was developed based on a preceramic polymer with silicon and boron as particulate fillers. Cyclic oxidation tests of the coated samples showed excellent oxidation protection: no Mo, Hf or Zr oxides were found after testing and a small mass gain in the initial stage of oxidation indicated the formation of a glassy protection layer on the alloys surfaces after exposure to air at 800 °C.

Study of a silicon-based preceramic for the processing of polymer-derived ceramics

Silicon-based preceramic polymers are an important type of precursor used in the processing of novel polymer-derived ceramics (PDCs), which includes the cross-linking and pyrolysis of the precursor. An integral study of physicochemical and rheological properties of a silicon-based preceramic regarding the variables that control the crosslinking and the characterization pyrolyzed material were accomplished. The precursor synthetized by the sol–gel method was characterized by density measurement, SEC, ATR-FTIR, NMR, and DSC. Flow properties in function of temperature and time, and viscoelastic properties as a function of deformation, frequency, temperature and time were studied by rotational and oscillatory testing, respectively. Also, the crosslinking process in the presence of a catalyst was studied by ATR-FTIR and dynamic tests. The phases generated at high temperature were characterized by XRD, Raman spectroscopy, and EDS. The results indicate that the studied precursor could be considered as a preceramic polymer for developing SiOC-based PDCs.

Polymer‐Derived Ultra‐High Temperature Ceramics (UHTCs) and Related Materials

Ultra‐high temperature ceramics (UHTCs) represent an emerging class of materials capable of providing mechanical stability and heat dissipation upon operation in extreme environments, e.g., extreme heat fluxes, chemically reactive plasma conditions. In the last few decades, remarkable research efforts and progress were done concerning the physical properties of UHTCs as well as their processing. Moreover, there are vivid research activities related to developing synthetic access pathways to UHTCs and related materials with high purity, tunable composition, nano‐scaled morphology, or improved sinterability. Among them, synthesis methods considering preceramic polymers as suitable precursors to UHTCs have received increased attention in the last few years. As these synthesis techniques allow the processing of UHTCs from the liquid phase, they are highly interesting, e.g., for the fabrication of ultra‐high temperature ceramic composites (UHT CMCs), additive manufacturing of UHTCs, etc. In the present review, UHTCs are in particular discussed within the context of their physical properties as well as energetics. Moreover, various synthesis methods using preceramic polymers to access UHTCs and related materials (i.e., (nano)composites thereof with silica former phases) are summarized and critically evaluated.

Radio Frequency and Microwave Heating of Preceramic Polymer Nanocomposites with Applications in Mold‐Free Processing

Here the authors demonstrate an oven‐free and mold‐free heating route to convert preceramic polymers to silicon carbide using carbon nanomaterials as susceptors. Silicon carbide is prized for its high thermal stability and low density and could be produced via slow oven heating of polycarbosilane (PCS). The authors show that addition of multiwalled carbon nanotubes (MWCNT) as susceptors to polycarbosilane results in rapid and volumetric heating upon exposure to microwaves and radio frequency. The authors assess microwave heating of polycarbosilane‐MWCNT composites; this process is capable of reaching pyrolysis temperatures, and the resulting crystal structure is cubic (β‐SiC). Dielectric properties of these composites in the radio frequency range is measured. The authors cure these composites using RF, and thermogravimetric data shows that the extent of cure for these samples is around 95%. The applicability of this study for 3D printing silicon carbides by successive iterations of layer deposition and rapid RF curing is demonstrated. The fly measurements of dielectric values of the 3D printing ink at different temperature while curing it is performed. The authors have also shown that these volumetric heating methods can rapidly cure polycarbosilane fibers to make silicon carbide fibers without melting them before crosslinking.

Synthesis, characterization, and ceramization of a carbon-rich SiCw-ZrC-ZrB2 preceramic polymer precursor

Abstract A precursor (PBSZ) for SiCw-ZrC-ZrB2 hybrid powder was synthesized by chemical reaction of phenol, paraformaldehyde, zirconium oxychloride, boric acid and tetraethylorthosilicate. Results show that zirconium, silicon and boron atoms have been successfully introduced into the branched structure. Decomposition of PBSZ is completed at 800 °C, and it gives amorphous carbon, SiO2, B2O3 and ZrO2 with a yield of 38% at 1200 °C. During the pyrolysis process, ZrB2 and SiC form at about 1500 °C, followed by the appearance of ZrC when the amount of B2O3 is limited. Highly crystallized ZrB2–ZrC–C powder with ZrB2 and ZrC grains evenly distributed in the carbon matrix together with randomly distributed SiC whiskers are obtained after heat-treated at 1800 °C. Further heated at 1900 °C, ZrB2 and ZrC grains grow from 200 to 500 nm, while SiC whiskers show a much smaller diameter size and tend to grow on the ZrB2–ZrC–C block surface. The morphology difference is caused by the larger gas supersaturation and accommodation coefficient of the pore channels on the block surface. In addition, defects of the carbon matrix are cumulated to the highest at 1500 °C and the structure-ordered carbon is obtained after heat treated at 1900 °C.

Tape casting of preceramic polymers toward advanced ceramics: A review

AbstractIn the last 20 years, tape casting, a standard wet‐shaping process to produce thin ceramics, has been applied to manufacture polymer‐derived ceramics (PDCs). Si‐based polymers, such as polysiloxanes and polysilazanes, also known as preceramic polymers (PCPs), have been used as precursors/binders replacing conventional raw materials and additives for tape casting process. Thermal processing of PCPs is carried out at lower temperatures in comparison with classical ceramic sintering, particularly of carbides and nitrides. Furthermore, polymeric precursors can be converted into hybrid or composite ceramics, when parts of the polymers remain unreacted. Inert or reactive fillers might be used to reduce both shrinkage and porosity inherently caused by the weight loss occurring during polymer pyrolysis while forming new ceramic phases in the final materials. Alternatively, pore formers might also be added to tailor pore shape, connectivity, and volume (macroporosity). Nevertheless, current equipment and process parameters for tape casting‐based products must be eventually adjusted to fit the characteristics of ceramic precursors. Therefore, the aim of this review is focused on listing and discussing the efforts to produce PDCs using tape casting as a shaping technique. Interactions of system components and effects of treatment, particularly thermal stages, on final microstructure and properties are stressed out. Gaps in the literature concerning processing optimization are pointed out, and suggestions are given for further development of PDCs produced by tape casting.

Processing of Mo silicide powders as filler particles in polymer-derived ceramic coatings for Mo-Si-B substrates

Oxidation resistant Mo5SiB2 powders, which will be used as filler particles in polymer-derived ceramic (PDC) coatings, are processed by mechanical alloying and heat treatment. After microstructural analysis of the silicide particles they are incorporated in a preceramic polymer slurry. Subsequent pyrolysis results in a multi-phase composite consisting of a silicon oxynitride matrix and homogeneously distributed Mo silicide particles. Using cyclic oxidation tests it is shown that the newly developed particle-filled PDCs are promising for future application as protective oxidation barrier coatings on Mo-based materials.

Synchrotron Microtomography of Polymer Derived Macroporous SiOC Ceramics

Porous ceramics have found immense applications in leading technological areas including porous burners, catalyst supports, and filtration media. It is extremely important to understand morphological features of highly porous ceramic bodies, and extract detailed quantitative information, including porosity, pore size distribution, interconnectivity, pore anisotropy, and sphericity. Synchrotron X‐ray microtomography has evolved as an excellent technique to acquire information on the complex three‐dimensional geometry and topology of reticulated structures. In this work, macroporous silicon oxycarbide ceramics are fabricated by positive replication of polyurethane sponge with the use of a preceramic polymer, and their topology has been studied by synchrotron X‐ray microtomography. Further, ceramic bodies have been prepared with progressive increase in the preceramic polymer concentration in the solution, and the ensuing change in the porous morphology of the structures have been studied. The results indicate the formation of excellent reticulated ceramics with 88–92% porosity, and with dense and uniform struts. The pore size distribution is uniform with very good sphericity and minimal anisotropy. The overall porosity indicates excellent interconnectivity with highly negative Euler numbers. The work presents a comprehensive analysis of reticulated ceramic bodies fabricated by preceramic polymer pyrolysis route.

First synthesis of silicon nanocrystals in amorphous silicon nitride from a preceramic polymer

We report the first synthesis of silicon nanocrystals embedded in a silicon nitride matrix through a direct pyrolysis of a preceramic polymer (perhydropolysilazane). Structural analysis carried out by XRD, XPS, Raman and TEM reveals the formation of silicon quantum dots and correlates the microstructures with the annealing temperature. The photoluminescence of the nanocomposites was investigated by both linear and nonlinear measurements. Furthermore we demonstrate an enhanced chemical resistance of the nitride matrix, compared to the typical oxide one, in both strongly acidic and basic environments. The proposed synthesis via polymer pyrolysis is a striking innovation potentially allowing a mass-scale production nitride embedded Si nanocrystals.