Pyrolysis Of Polymeric Precursors Research Articles

Microarchitected Compliant Scaffolds of Pyrolytic Carbon for 3D Muscle Cell Growth.

The integration of additive manufacturing technologies with the pyrolysis of polymeric precursors enables the design-controlled fabrication of architected 3D pyrolytic carbon (PyC) structures with complex architectural details. Despite great promise, their use in cellular interaction remains unexplored. This study pioneers the utilization of microarchitected 3D PyC structures as biocompatible scaffolds for the colonization of muscle cells in a 3D environment. PyC scaffolds are fabricated using micro-stereolithography, followed by pyrolysis. Furthermore, an innovative design strategy using revolute joints is employed to obtain novel, compliant structures of architected PyC. The pyrolysis process results in a pyrolysis temperature- and design-geometry-dependent shrinkage of up to 73%, enabling the geometrical features of microarchitected compatible with skeletal muscle cells. The stiffness of architected PyC varies with the pyrolysis temperature, with the highest value of 29.57±0.78GPa for 900°C. The PyC scaffolds exhibit excellent biocompatibility and yield 3D cell colonization while culturing skeletal muscle C2C12 cells. They further induce good actin fiber alignment along the compliant PyC construction. However, no conclusive myogenic differentiation is observed here. Nevertheless, these results are highly promising for architected PyC scaffolds as multifunctional tissue implants and encourage more investigations in employing compliant architected PyC structures for high-performance tissue engineeringapplications.

Preparation of polymer-derived SiOC-Cu ceramic composites and their tribological performance

Cu-containing silicon oxycarbide (SiOC) ceramic composites have been prepared by thermal pyrolysis of polymeric precursors and subsequent spark plasma sintering at 1600 °C. The resulting composites consist of SiO2, SiC, free carbon, and Cu-Si alloys. The microstructure of the composites has been identified via optical microscope and SEM. The mechanical properties, including the Vickers hardness, nano-indentation hardness, and Young’s modulus, of the SiOC composites have been assessed via indentation methods. The effects of Cu content on the tribological properties of the composites have additionally been investigated under different sliding frequencies against Al2O3 spheres at room temperature. It is shown that the introduction of the Cu-Si alloys is effective in reducing the friction coefficient of the material system, which decreases linearly from 0.27 of monolithic SiOC to 0.15 of SiOC with 7 wt% Cu content at 1 Hz. Raman spectroscopy has highlighted the friction-driven evolution of the free carbon phase in the SiOC ceramics. Finally, a correlation between the sliding frequency, Cu-Si content, and tribological properties of SiOC is established.

Polymer-derived W-doping (Zr, Hf, Nb, Ta)C high entropy ceramics: Preparation, Properties and DFT calculation

(Zr, Hf, Nb, Ta, W)C high entropy carbides nano-powders (average particle size less than 65 nm) with low oxygen content (0.2–1.4 wt%) were synthesized through pyrolysis of polymer precursors. Bulk ceramics were fabricated through the process of hot-pressing, and their characteristics were studied by both computational and experimental methods. Density functional theory was carried out to analyze the effects of defects and the W element on the melting point, hardness, modulus, and toughness of ceramics. The results showed that W content had limited influence on the melting points and the aforementioned mechanical properties of ceramics, while carbon vacancies lead to a significant decrease in melting point, hardness and modulus, with slight increases in toughness. Experimental results indicated that the grain size, grain boundary strength, and lattice distortion of ceramic bulks increased with the increase of W content, which affected the mechanical properties consequently. Ceramics with W content of 5 mol% exhibited the best experimental comprehensive performances, with the Vickers hardness, fracture toughness and flexural strength of 23.82 ± 0.49 GPa, 5.66 ± 0.22 MPa·m1/2 and 593.95 ± 15.71 MPa, respectively.

Energetics and structure of SiC(N)(O) polymer‐derived ceramics

AbstractThis study presents new experimental data on the thermodynamic stability of SiC(O) and SCN(O) ceramics derived from the pyrolysis of polymeric precursors: SMP‐10 (polycarbosilane), PSZ‐20 (polysilazane), and Durazane‐1800 (polysilazane) at 1200°C. There are close similarities in the structure of the polysilazanes, but they differ in crosslinking temperature. High‐resolution X‐ray photoelectron spectroscopy shows notable differences in the microstructure of all polymer‐derived ceramics (PDCs). The enthalpies of formation (∆H°f, elem) of SiC(O) (from SMP‐10), SCN(O) (from PSZ‐20), and SCN(O) (from Durazane‐1800) are −20 ± 4.63, −78.55 ± 2.32, and −85.09 ± 2.18 kJ/mol, respectively. The PDC derived from Durazane‐1800 displays greatest thermodynamic stability. The results point to increased thermodynamic stabilization with addition of nitrogen to the microstructure of PDCs. Thermodynamic analysis suggests increased thermodynamic drive for forming SiCN(O) microstructures with an increase in the relative amount of SiNxC4−x mixed bonds and a decrease in silica. Overall, enthalpies of formation suggest superior stabilizing effect of SiNxC4−x compared to SiOxC4−x mixed bonds. The results indicate systematic stabilization of SiCN(O) structures with decrease in silicon and oxygen content. The destabilization of PDCs resulting from higher silicon content may reach a plateau at higher concentrations.

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.

Recent Progress in Silicon Carbide-Based Membranes for Gas Separation.

The scale of research for developing and applying silicon carbide (SiC) membranes for gas separation has rapidly expanded over the last few decades. Given its importance, this review summarizes the progress on SiC membranes for gas separation by focusing on SiC membrane preparation approaches and their application. The precursor-derived ceramic approaches for preparing SiC membranes include chemical vapor deposition (CVD)/chemical vapor infiltration (CVI) deposition and pyrolysis of polymeric precursor. Generally, SiC membranes formed using the CVD/CVI deposition route have dense structures, making such membranes suitable for small-molecule gas separation. On the contrary, pyrolysis of a polymeric precursor is the most common and promising route for preparing SiC membranes, which includes the steps of precursor selection, coating/shaping, curing for cross-linking, and pyrolysis. Among these steps, the precursor, curing method, and pyrolysis temperature significantly impact the final microstructures and separation performance of membranes. Based on our discussion of these influencing factors, there is now a good understanding of the evolution of membrane microstructures and how to control membrane microstructures according to the application purpose. In addition, the thermal stability, oxidation resistance, hydrothermal stability, and chemical resistance of the SiC membranes are described. Due to their robust advantages and high separation performance, SiC membranes are the most promising candidates for high-temperature gas separation. Overall, this review will provide meaningful insight and guidance for developing SiC membranes and achieving excellent gas separation performance.

Development of SiC-ZrC-based ultra-high temperature ceramic coatings via composite method of polymer precursor pyrolysis plus gaseous reactive infiltration

SiC-ZrC-based composite coatings on carbon/carbon composites via ZrC polymer precursor pyrolysis (PPP) plus gaseous reactive infiltration (GRI) of Si or ZrSi 2 , separately denoted as GSIC and GZSIC, were comparatively studied to explore the feasibility and effectiveness of GRI of ZrSi 2 . This composite method by applying ZrSi 2 or Si was proven to similarly produce dense coatings with enhanced coating/substrate interfacial bonding strength for the formed zig-zag transition layer. Furthermore, the GRI of ZrSi 2 instead of Si further increased the UHTC (ZrC) content in the as-deposited coatings resulted from the reaction of infiltrated ZrSi 2 and pre-introduced graphite, enhancing the ablation resistance of the coatings for carbon/carbon composites due to the formed stable Zr-rich Zr-Si-O multiphase oxide. The average mass and linear ablation rates were −0.12 mg/s and 1.56 μm/s for GSIC and −0.3 mg/s and −0.53 μm/s for GZSIC specimens, respectively. The average linear ablation rate of the GZSIC specimen was decreased by ~134% when compared to the GSIC specimen. These results further indicate that the PPP + GRI method with metal silicide MeSi 2 (Me = Zr, Ti, Hf, Cr, etc.) will contribute to the optimal fabrication of dense composite coatings with controllable microstructure, adequate evenly-distributed ultra-high temperature ceramic (UHTC) phases, enhanced interfacial bonding strength and wide circumstance suitability for potential applications. The related work is ongoing in our laboratory. • SiC-ZrC-based coatings were made by precursor pyrolysis plus gaseous reactive infiltration. • Pre-introduced graphite reacted with infiltrated ZrSi 2 further improved ZrC content in the coatings. • The gaseous infiltrated ZrSi 2 instead of Si enhanced ablation resistance of the coatings. • The coating's linear ablation rate was reduced by ~134% as gaseous infiltrated with ZrSi 2 .

Highly porous nitrogen-doped carbon superstructures derived from the intramolecular cyclization-induced crystallization-driven self-assembly of poly(amic acid).

Hierarchically porous carbon nanomaterials have shown significant potential in electrochemical energy storage due to the promoted charge and mass transfer. Herein, a facile template-free method is proposed to prepare nitrogen-doped carbon superstructures (N-CSs) with multi-level pores by pyrolysis of polymeric precursors derived from the intramolecular cyclization-induced crystallization-driven self-assembly (ICI-CDSA) of poly(amic acid) (PAA). The excellent thermal stability of PAA enables the N-CSs to inherit the hierarchical structure of the precursors during pyrolysis, which facilitates the formation of meso- and macropores while the decomposition of the precursors promotes the creation of micropores. Electrochemical tests demonstrate the ultrahigh surface-area-normalized capacitance (76.5 μF cm−2) of the N-CSs facilitated by the hierarchically porous structure, promoting the charge and mass transfer, as well as the high utilization of pyridinic and pyrrolic nitrogen (12.9%) to provide significant pseudocapacitance contribution up to 40.6%. Considering the diversity of monomers of PAA, this ICI-CDSA strategy could be extended to prepare carbon nanomaterials with various morphologies, pore structures and chemical compositions.

Robust High‐Temperature Supercapacitors Based on SiC Nanowires

AbstractCurrently, the exploration of energy conversion/storage devices for high‐temperature operation with desired stability is still a grand challenge. In the present work, the high‐temperature supercapacitors (SCs) based on SiC nanowires as the electrode materials are reported, which are synthesized via pyrolysis of polymeric precursors followed by etching for creating more active sites with enhanced surface area. In 2.0 m KCl aqueous electrolyte, the as‐fabricated electrode based on etched SiC nanowires delivers a specific capacitance of 23.6 mF cm–2 (29.5 F g–1) at a current density of 0.2 mA cm–2 (0.25 A g–1), which is ≈3.3 times to that of the counterpart without etching (7.19 mF cm–2). The as‐constructed ionic‐liquid‐based SCs can endure the operation temperatures up to 150 °C with a capacitance retention of 80% for 10 000 cycles, which drops only ≈6% in comparison to that at 0 °C. Even under progressive variation in temperatures ranged between 0 and 150 °C, the capacitance retentions keep higher than 76% for 12 000 cycles, representing their promising to be serviced as robust SCs against high‐temperature harsh conditions for energy storage.

Synthesis of self-helix structure Si3N4 nanobelts and its reinforcement effect on HA coating

ABSTRACT A self-helix structure Si3N4 nanobelts reinforced hydroxyapatite (HSN/HA) coating has been synthesised on carbon/carbon composites by a combination method of catalyst-assisted pyrolysis of polymeric precursors and electrochemical deposition. The morphology, microstructure, and bonding strength of the coating were analysed. An individual Si3N4 nanobelt showed a self-helical shape. The bonding strength between HSN/HA coating and carbon/carbon composites reached 12.5 ± 0.72 MPa, higher than that of pure HA coating (6.38 ± 0.32 MPa). HSN/HA coating has the potential to apply to hard tissue substitution surgery in the future.

Ultraselective carbon molecular sieve membrane for hydrogen purification

Abstract Hydrogen is a green clean fuel and chemical feedstock. Its separation and purification from hydrogen-containing mixtures is the key step in the production of hydrogen with high purity (>99.99%). In this work, carbon molecular sieve (CMS) membranes with ultrahigh permselectivity for hydrogen purification were fabricated by high-temperature (700–900 °C) pyrolysis of polymeric precursor of phenolphthalein-based cardo poly(arylene ether ketone) (PEK-C). The evolution of the microstructural texture and ultramicroporous structure and gas separation performance of the CMS membrane were characterized via TG-MS, FT-IR, XRD, TEM, CO2 sorption analysis and gas permeation measurements. CMS membranes prepared at 700 °C exhibited amorphous turbostratic carbon structures and high H2 permeability of 5260 Barrer with H2/CH4, H2/N2 and H2/CO selectivities of 311, 142, 75, respectively. When carbonized at 900 °C, the CMS membrane with ultrahigh H2/CH4 selectivity of 1859 was derived owing to the formation of the dense and ordered carbon structure. CMS membranes with ultrahigh permselectivity exhibit an attractive application prospect in hydrogen purification.

Scalable growth of SiC quasi-aligned nanoneedle arrays and their electron emission behaviors under high temperatures

Scalable growth of SiC quasi-aligned nanoarrays on SiC wafer substrate was reported through the pyrolysis of polymer precursor by using Au as the catalysts. Differently to the conventional one-dimensional nanostructures often with cylindrical shape, the as-grown SiC nanowires possessed tapered configurations with sharp tips, enabling their desired formation with typical nanoneedle morphology. Their turn-on fields manifested a decline from 3.4 to 1.4 V/μm, when the temperatures were adjusted from room temperature to 400 °C, evidencing their excellent field emission performance. Furthermore, they behaved a high stability with no obvious current emission degradation when subjected to high temperature of 200 °C over 10 h, representing their promising applications in vacuum electronics with robust stability under high-temperature harsh conditions.

The influence of surface composition of carbon nanotubes on the photobioelectrochemical activity of thylakoid bioanodes mediated by osmium-complex modified redox polymer

A combination of photosynthetic biocatalysts with high surface area conductive materials mediated by an osmium-complex modified redox polymer (OsRP) holds promising features for the development of sustainable “green” systems for solar energy conversion. In this work we performed a comparative study of two types of carbon nanotubes (CNTs) synthesized by pyrolysis of polymeric precursors. Both CNTs were of similar morphology, but had a different surface C/O ratio. The CNTs were utilized as a support for immobilization of thylakoid membranes, electrochemically wired through the OsRP. The photobioanodes based on the CNTs with a higher C/O ratio exhibit a higher maximum photocurrent density of 97.1 ± 8.3 μA cm−2 at a light intensity of 400 W m−2 with reduced charge transfer resistance, but had lower operational stability. Our results demonstrate the significance of investigating of electrochemical communication between the photosynthetic component, the redox mediator and the support nanomaterial and may offer new opportunities for designing and optimization of mediated bioelectrochemical systems.

High‐Performance SiC Nanobelt Photodetectors with Long‐Term Stability Against 300 °C up to 180 Days

AbstractIn the present work, high‐performance photodetectors (PDs) based on a single B‐doped 3C‐SiC nanobelt, which are synthesized via catalyst‐free pyrolysis of polymeric precursors of polysilazane, are reported. The as‐built PDs have a high responsivity and external quantum efficiency of 6.37 × 105 A · W−1 and 2.0 × 108% under 405 nm light with a power density of 0.14 mW · cm−2 at 5 V, respectively. The detectivity of the PDs is measured to be of 6.86 × 1014 Jones. Moreover, the B‐doped 3C‐SiC nanobelt PDs exhibit a long‐term stability against 300 °C up to 180 days, suggesting their promising applications to be served under harsh conditions.

Polymer-derived Ta4HfC5 nanoscale ultrahigh-temperature ceramics: Synthesis, microstructure and properties

Nanoscale Ta4HfC5 ceramics were synthesized from curing and pyrolysis of novel polymer precursors which were synthesized by cohydrolysis and polycondensation of acetyl acetone coordinated tantalum alkoxide and hafnium alkoxide followed by blending with phenolic resin as carbon source. Pyrolysis of the polymer precursor at 1600 °C in vacuum produced Ta4HfC5 nanocrystallites with an average grain size of 21 nm and well-distributed elements, encapsulated by an amorphous carbon shell. Near full dense Ta4HfC5 monoliths can be prepared by spark plasma sintering (SPS) at 1600 °C with 10 vol% MoSi2 as an additive, of which the Vicker micro-hardness and flexural strength achieved 17.58 GPa and 466 MPa, respectively. The polymer precursor method shed light on the fabrication of ceramic matrix composites. Besides, the high electrical conductivity of 1.5 × 104 S/m entitled the ceramics to a prospective of utilization in microwave absorbing/shielding fields under harsh conditions.

Fabrication of N-doped 3C-SiC nanobelts with selected [formula omitted] top surface and their enhanced transverse piezoresistance behaviours

The piezoresistive effect of SiC low-dimensional nanostructures, together with their exclusive benefits of superior mechanical characteristics and could be integrated into the flexible devices that can withdraw large strain, promise to make a wide range of sensing devices application possible in the severe working conditions. In this work, we reported the transverse piezoresistance behaviours of n-type 3C-SiC nanobelts with selected (11¯0) top surface and N dopants. The single-crystalline SiC nanobelts were achieved by the means of direct pyrolysis of polymeric precursors without catalysts, which had an average N doping level of ~ 6.02 at% and a typical width-to-thickness ratio of ~ 8. It was disclosed that the transverse piezoresistance coefficient π[11¯0] reached the maximum 10.29 × 10–11 Pa−1 at a fixed external stress of 67.03 nN. Correspondingly, the gauge factor (GF) was calculated to be of ~ 61.7, which is higher than all the reported n-type SiC, intrinsic SiC, as well as most of the p-type SiC counterparted. The findings shed light on the fact that present n-type SiC nanobelts have the potential of becoming an outstanding contestant for the development of robust pressure sensors having elevated sensitivities.

Glassy carbon MEMS for novel origami-styled 3D integrated intracortical and epicortical neural probes

We report on a novel technology for microfabricating 3D origami-styled micro electro-mechanical systems (MEMS) structures with glassy carbon (GC) features and a supporting polymer substrate. GC MEMS devices that open to form 3D microstructures are microfabricated from GC patterns that are made through pyrolysis of polymer precursors on high-temperature resisting substrates like silicon or quartz and then transferring the patterned devices to a flexible substrate like polyimide followed by deposition of an insulation layer. The devices on flexible substrate are then folded into 3D form in an origami-fashion.These 3D MEMS devices have tunable mechanical properties that are achieved by selectively varying the thickness of the polymeric substrate and insulation layers at any desired location. This technology opens new possibilities by enabling microfabrication of a variety of 3D GC MEMS structures suited to applications ranging from biochemical sensing to implantable microelectrode arrays. As a demonstration of the technology, a neural signal recording microelectrode array platform that integrates both surface (cortical) and depth (intracortical) GC microelectrodes onto a single flexible thin-film device is introduced.When the device is unfurled, a pre-shaped shank of polyimide automatically comes off the substrate and forms the penetrating part of the device in a 3D fashion. With the advantage of being highly reproducible and batch-fabricated, the device introduced here allows for simultaneous recording of electrophysiological signals from both the brain surface (electrocorticography—ECoG) and depth (single neuron). Our device, therefore, has the potential to elucidate the roles of underlying neurons on the different components of µECoG signals. For in vivo validation of the design capabilities, the recording sites are coated with a poly(3,4-ethylenedioxythiophene)—polystyrene sulfonate—carbon nanotube composite, to improve the electrical conductivity of the electrodes and consequently the quality of the recorded signals. Results show that both µECoG and intracortical arrays were able to acquire neural signals with high-sensitivity that increased with depth, thereby verifying the device functionality.

A facile method to prepare ZrC nanofibers by electrospinning and pyrolysis of polymeric precursors

Zirconium carbide (ZrC) is one of the most attractive ultra-high temperature ceramics due to its excellent properties. ZrC nanofibers were fabricated via electrospinning and pyrolysis of a novel polymeric precursor, Polyzirconosaal (PZSA), with the addition of polyvinylpyrrolidone (PVP) as the spinning aid. The polymer PZSA was prepared from the chemical reaction between Polyzirconoxane (PZO) and Salicyl alcohol. The as-spun PZSA/PVP fibers were converted to ZrC nanofibers with a diameter ~200nm after carbothermal reduction at 1300°C in argon. The obtained ZrC nanofibers maintained its excellent fibrous morphology. The microstructures exhibited that nanoscale ZrC particles dispersed in the fibers containing free carbon. The average crystallite size of ZrC particles using Scherrer method was 42nm. The obtained ZrC nanofibers were characterized by XRD, SEM and TEM. The current material would be particularly useful for applications such as catalyst support, filters, gas storage, supercapacitors, and phase change material support in thermal management systems.

Morphological Analysis of the Amorphous Carbon Embedded Nickel-Silica Composite Submitted at Gradual Oxidation

Amorphous embedded nickel-silica composites can be directly obtained by Polymeric Precursor Method when the polymeric precursor is pyrolysed in controlled atmosphere. The metallic particles dispersion into the matrix composite is very important to material applications, but the resistance against the oxidation under extreme conditions is also required. In this work, nickel-silica nanocomposite sample was synthesized for containing amorphous carbon as matrix interphase through the direct route based on the Polymeric Precursor Method. The composite sample was obtained by pyrolysis of polymeric precursor at 600 oC for 1 hour under nitrogen flow and then submitted to oxidation in oxygen flow at 400 oC up to 7 hours. It was observed by Transmission Electron Microscopy the metallic nickel nanoparticles present high dispersion into matrix composite. However, in spite of the border of the composite particles are easily oxidized and originate nickel oxide phase, as proven by X-Ray Diffraction, the amorphous carbon phase acts as protective phase for the majority of the composite sample. By Nitrogen Adsorption-Desorption Isotherms at 77 K it was demonstrated the carbon phase also preserves significantly the mesoporous nature of the composite under oxidation process.

Morphological Characterization of Nickel-Silica Nanocomposite in Residual Carbon Obtained by Direct Polymeric Route

Nickel-silica nanocomposites can be obtained by direct chemical route, such as the Polymeric Precursor Method. That methodology type permits to obtain material powders with significant specific area and porosity suitable for reactive gases or fluids permeation, which are required characteristics for application in heterogeneous catalysis process. The composite material obtained from pyrolysis of polymeric precursor has its porosity strongly dependent from precursor constitution, which affects the decomposition kinetic. In this study, it was obtained a polyester precursor based on triethylene glycol, which has been submitted at pyrolysis at 600 oC for several times in nitrogen atmosphere. The nickel-silica nanocomposite obtained through that methodology presents a residual amorphous carbon phase playing an important rule on the mechanism of pore formation. Nickel nanoparticles nucleate with sizes close to 10 nm in diameter and are highly dispersed in a hybrid amorphous carbon-silica matrix. The composite pore volume, calculated through the JBH method, presents a continuous increasing as a function of pyrolysis time, reaching more than 0.15 cc/g after 7 hours from initial decomposition process.