Silicon Carbonitride Ceramics Research Articles

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.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

Effect of the graphitization level of the free carbon on the temperature sensitivity of silicon carbonitride‐based pressure sensors

AbstractPolymer‐derived ceramics (PDCs) have recently attracted an increasing attention because of their applications for wireless passive pressure sensors in the harsh environment. However, due to the effect of temperature on the frequency of PDC‐based wireless passive pressure sensors, it is not beneficial to accurate measurement of pressure. In this paper, a dense polymer‐derived silicon carbonitride (SiCN) ceramic was prepared by precursor infiltration and pyrolysis (PIP) technique to reduce the temperature sensitivity of PDC–SiCN‐based pressure sensor. The open porosity and density of SiCN ceramics varied from 13.34% and 1.89 g/cm3 without PIP process to 3.24% and 2.09 g/cm3 after three PIP cycles, respectively. Raman spectroscopy revealed that the level of graphitization of free carbon in dense SiCN ceramics is higher than that in porous SiCN ceramics, which would lead to an increase in the conductivity of dense SiCN ceramics. After three PIP cycles, the conductivity increased by almost two orders of magnitude from 3.01E − 10 to 1.28E − 08 S/cm. In addition, SiCN ceramic discs after PIP cycles and without PIP were applied to wireless passive pressure sensor based on resonator, which were tested at high temperature, respectively. Results confirmed that the temperature sensitivity of PDC–SiCN‐based pressure sensor decreased from 220.5 to 50.8 kHz/°C by PIP process.

Design and fabrication of Al2O3f/SiCN composite with excellent microwave absorbing and mechanical properties

AbstractA new kind of structural and functional integration ceramic matrix composite material was prepared from high‐performance alumina (Al2O3) fibers and absorbing silicon carbonitride (SiCN) ceramics via a combination of polymer infiltration pyrolysis (PIP) and chemical vapor infiltration (CVI) methods. The Al2O3 fiber annealed at its cracked temperature had enhanced permittivity, because the sizing agent on the Al2O3 fiber surface was cracked into pyrolysis carbon. For PIP + CVI Al2O3f/SiCN composites, PIP SiCN matrix with low conductivity was used as the matching phase, while CVI SiCN matrix with medium permittivity and dielectric loss was regarded as the reinforcing phase distributed in porous PIP SiCN matrix and inter‐bundles of Al2O3 fiber to improve their mechanical and microwave absorption properties. The fracture toughness and flexural strength of Al2O3f/SiCN composite were determined to be 9.4 ± 0.5 MPa m1/2 and 279 ± 28 MPa, respectively. Based on the design principles for impedance matching, the Al2O3f/SiCN composites before and after oxidation were used as loss and impedance layers, respectively. It was found that the optimized composite had the lowest reflection coefficient (RC) of −70 dB and the effective absorption bandwidth covering the whole X‐band. In conclusion, Al2O3f/SiCN composite can serve as a high‐temperature structural material with excellent microwave absorption properties for aerospace applications.

Fabrication of hierarchically micro/meso/macroporous silicon carbonitride ceramic using freeze casting method with a silsesquiazane precursor

Hierarchically porous silicon carbonitride (SiCN) was prepared using the freeze casting method with silsesquiazane (SSQZ) as a precursor. As SSQZ possesses a highly branched structure, it can provide a higher cross-linking degree than linear polysilazane and thereby, improve the structural stability. The porous SiCN can be produced without collapsing the pore structures by removing the organic groups during the pyrolysis process due to the high cross-linking degree. In this study, we used the freeze casting method to introduce macropores. In addition, the effects of glycidyl-POSS and 1,7-octadiene diepoxide as additional cross-linking agents on the formation of porous ceramics were investigated. The Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses showed that SSQZ with cross-linking agents demonstrated a higher cross-linking degree and was successfully converted to SiCN ceramics. As a result, the porous SiCN ceramics exhibited an improved structural stability, specific surface area, and pore volume.

Polymer-derived SiCN ceramics as fillers for polymer composites with high dielectric constants

High-dielectric-constant (high-e) ceramic/polymer composites are an important class of advanced functional materials due to their applications in energy storage fields, such as embedded capacitors. Here, we synthesized novel polymer-derived silicon carbonitride (SiCN)-filled polyvinylidene fluoride (PVDF) composites by the tape-casting method. For comparison, commercial BaTiO3-filled PVDF composites were synthesized following the same process. The SiCN/PVDF composites showed much higher e than the BaTiO3/PVDF composites over a broad frequency range (10−1–106 Hz). Furthermore, the SiCN/PVDF composites showed ultrahigh e at low frequencies. The e of the 40 vol% SiCN/PVDF composite was as high as 2600 at 10−1 Hz. Although the dielectric breakdown strengths of the SiCN/PVDF composites were slightly lower than those of the BT/PVDF composites, the calculated maximum energy storage density of the 40 vol% SiCN/PVDF composites (17.5 J cm−3) was much higher than that of 40 vol% BT/PVDF (0.773 J cm−3) at 10−1 Hz. This is the first report on the use of polymer-derived ceramics as a component of ceramic/polymer composites. The results indicate that the polymer-derived SiCN ceramics can serve as promising ceramic fillers for high-e composites and that the obtained SiCN-filled composites have promising applications in energy storage fields.

Low‐frequency dielectric dispersion in polymer‐derived amorphous silicon carbonitride ceramics

AbstractThe dielectric response of polymer‐derived amorphous silicon carbonitride (PDC‐SiCN) material was studied over a wide frequency range from 1 mHz to 10 MHz. Aside from presenting a relaxation process over 105 to 0.03 Hz frequency range, the material showed a strong low‐frequency dielectric dispersion (LFDD), which resulted in extremely high permittivities (up to 105) at frequencies lower than 0.03 Hz. It is identified that this LFDD resulted from relaxation process was not induced by conductivity. Therefore, PDC‐SiCN material showed two relaxation processes. Based on its microstructure, two polarization mechanisms were proposed for PDC‐SiCN: a mechanism based on polarons generated by unpaired electrons present in the material and an interfacial polarization mechanism as a result of different properties of SiCxN4−x matrix and free‐carbon clusters. Interfacial polarization process was simulated based on a parallel plate model involving two different materials. The result indicated that the relaxation time of an interfacial polarization can be distributed over a broad time range in the material.

The influence of pyrolysis temperature on the electrochemical behavior of porous carbon-rich SiCN polymer-derived ceramics

Within this study we report on the impact of the pyrolysis temperature on the structural and electrochemical properties of porous carbon-rich polymer-derived silicon carbonitride (SiCN) ceramics. Microstructural features of the synthesized materials were characterized in detail and discussed with respect to the lithium storage properties. X-ray diffraction study reveals the amorphous nature of the pyrolysed ceramics up to 1100°C, while a crystalline SiC-phase is formed at 1400°C. Micro-Raman spectroscopy shows that pyrolysed samples contain a free disordered carbon phase which tends to order with increasing pyrolysis temperature. Galvanostatic cycling with potential limitation enables to monitor the lithiation and delithiation performance. High irreversible losses are identified during the first cycle lithiation due to formation of SEI. Nevertheless the highest electrode capacities are recorded for the sample pyrolysed at 900°C reaching a first cycle reversible capacity of 447mAh·g−1 and a 100th cycle reversible capacity of 534mAh·g−1 at a current of 72mA·g−1. Further it is found that the prepared materials offer improved high current lithium storage ability compared to dense SiCN ceramics reported in literature so far.

Meso-Structuring of SiCN Ceramics by Polystyrene Templates.

A simple one-pot synthesis of well-defined PS-silazane nano-composites (polystyrene, PS) is described. In contrast to the, thus far, used two-step procedure ((1) assembly of a PS template bed and (2) careful filling of the voids between the PS spheres), which is restricted to macro structuring, we are able to simply mix the PS template and a commercially available silazane precursor HTT-1800 in toluene. The key is the alteration of the zeta potential of the PS template leading to a homogeneous dispersion in the silazane-toluene mixture. Removal of solvent gives rise to a highly ordered PS-silazane nano-composites and subsequent pyrolysis leads to mesoporous silicon carbonitride (SiCN) materials. The one-pot procedure has two advantages: easy upscaling and the use of PS spheres smaller than 100 nm in diameter, here 60 nm. The PS template was characterized by photon correlation spectroscopy, zeta potential measurements, scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The resulting mesoporous SiCN materials were analyzed by SEM, transmission electron microscopy (TEM), nitrogen sorption analysis, and Fourier transform infrared measurements (FT-IR).

New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics.

Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

Quantitative study on structural evolutions and associated energetics in polysilazane-derived amorphous silicon carbonitride ceramics

Several important structural changes and their energetics during high-temperature annealing of polysilazane-derived amorphous silicon carbonitride ceramics were quantitatively studied. A 29Si solid-state NMR study indicated that the structural transition in the Si-containing area can be described by an equilibrium reaction, 4SiCN3=SiC4+3SiN4. The enthalpy and entropy for the reaction were calculated to be positive. Raman and electron paramagnetic resonance (EPR) studies revealed that the structural evolution within the free carbon area includes the graphitization of amorphous carbon and the lateral growth of nanographite, accompanied by a decrease in the point defect concentration. EPR results also suggested that the materials contain two kinds of point defects: carbon-dangling bonds at the edge and in the interior of the nanographite. It was found that the lateral growth of the nanographite followed a 2-D grain growth process, and that the decrease in the defect concentration was mainly due to the growth of the nanographite. The energetics of the structural changes was rationalized according to a simple structural model, and the effects of these changes on the stability of the materials were discussed.

Fabrication of Carbon Nanofiber and Silicon Carbonitride Ceramic Nanomposites by <i>In Situ</i> Growth during Ceramic Formation

Carbon nanofiber (CNF) and silicon carbonitride (SiCN) ceramic nanocomposites (SiCN/CNF) are fabricated by in-situ growth of CNFs in SiCN ceramics during ceramic transformation of polymeric precursors of polysilazanes (PSZ). Metal catalyst precursors are mixed into the polysilazane liquid forming metal particles from decomposition under heating during the pyrolysis. At certain temperatures, ethylene was introduced as a carbon source to induce the growth of CNFs over the metal particles in the ceramic body followed by heating to higher temperatures to complete the pyrolysis. In this way, bulk nanocomposites of SiCN/CNF are obtained as crack-free bodies although some pores are left in the sample. Scanning electron microscopy (SEM) analysis performed on the cross-section of nanocomposites revealed the distribution of needle-like nanofibers of diameter ~ 200 nm and exposed length of ~ 2 μm. The CNFs exhibited the unique multiscale nanostructure in micron hollow tubes with branched nanofiber walls. Energy dispersive X-ray spectrometer (EDX) detected carbon as the major element from the nanofibers confirming the formation of carbon nanofibers. Moreover, clusters of nanoparticles are formed on the ceramic surface from carbon depositions. The in-situ growth of CNFs in SiCN ceramics provides a one-step process potentially to be developed for fabrication of structural and functional SiCN/CNF nanocomposites.

Preparation and electrochemical performance of a porous polymer-derived silicon carbonitride anode by hydrofluoric acid etching for lithium ion batteries

Porous silicon carbonitride (SiCN) ceramics were pyrolyzed from poly(silylcarbondiimide) derivatives, followed by etching with different concentrations of HF aqueous solution (5, 10, 15 and 20 wt%). The morphologies, structures and electrochemical performances of the HF-etched SiCN materials were investigated. The results indicated that the surface of the HF-etched SiCN composites became rough and porous. SiCN-10-HF, one of four HF-etched SiCN samples, showed excellent electrochemical properties as an anode for lithium ion batteries. Charge–discharge measurements indicated that the SiCN-10-HF anode exhibited a high initial specific discharge capacity of 681 mA h g−1 at a current density of 40 mA g−1, which was 2.4 times that of the unetched SiCN anode. After 100 cycles, the discharge capacity of SiCN-10-HF anode delivered 229.3 mA h g−1, which was 5.0 times that of the unetched SiCN anode (45.6 mA h g−1). Additionally, the SiCN-10-HF anode exhibited high rate performance. At a current density of 190 mA g−1, the discharge capacity of the anode was 160 mA h g−1. It was deduced that the formation of nano-sized pores or holes on the surface of the SiCN materials in the HF-etching process not only offered new channels for the intercalation of Li+ but also relieved the volume expansion during the charge and discharge process, resulting in improved capacity, stable cycling and good rate capability.

Synthesis and Characterization of Ethylene‐Bridged Copolycarbosilazane as Precursors for Silicon Carbonitride Ceramics

An ethylene‐bridged copolycarbosilazane precursor of copolysilylethylenediamine (co‐PSDA) is synthesized by polycondensation of ethylenediamine with the mixture of vinylmethyldichlorosilane and methyldichlorosilane in the presence of triethylamine as acid absorbing agent. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR, 1H NMR and 13C NMR) spectral analysis of the as‐synthesized co‐PSDA suggests a structure of ethylene‐bridged polycarbosilazane having –Si–N–C–C–N– as backbone chain with –CH=CH2, –H and –CH3 attached to Si as side groups. Co‐PSDA can be cross‐linked at 80°C using 2, 2‐azobisisobutyronitrile as initiator through the polyaddition of the vinyl group and dehydrogenation/deamination of Si–H and N–H. Then the cross‐linked co‐PSDA precursor is pyrolyzed at 1000°C in argon, giving out amorphous silicon carbon nitride (SiCN) ceramics with a high ceramic yield of 76 wt%. The obtained SiCN ceramics consist of nitrogen‐rich silicon sites of SiN4 as predominant component and some SiCN3 sites, which should arise from the breaking of N–C bonds below 600°C and the formation of active N–Si bonds.

Full Dense SiCN Ceramics Derived from Polysilazane

Full dense silicon carbonitride (SiCN) ceramics have been prepared successfully by thermally induced ceramisation of polysilazane precursor at 1000°C, and subsequently annealing at 1200°C. The density and the hardness of the obtained ceramics were about 2.61g/cm3and 13GPa at the pyrolysis temperature of 1000°C, respectively. The density and hardness have a slight change with the increasing annealing temperature. This meas that the ceramics pyrolyzed at 1000°C were stable.

Hierarchical Porous Carbide‐Derived Carbons for the Removal of Cytokines from Blood Plasma

Series of silicon carbonitride ceramics are utilized to obtain hierarchically porous carbide-derived carbons (CDCs) for cytokine removal. The removal rate of TNF-α and IL-6, as two examples of pro- and anti-inflammatory cytokines, is proportional to the surface area of pores larger than the size of the protein molecule

Synthesis of Spherical Non‐Oxide Silicon Carbonitride Ceramic Particles

In this article, we report a simple technique for synthesizing spherical non‐oxide silicon carbonitride ceramic particles from a polysilazane precursor. In this technique, the spherical particles of the polysilazane precursor were synthesized first via a precipitation polymerization process and then converted to ceramic particles by pyrolysis. The resultant ceramic particles exhibited a close‐to‐perfect spherical shape and a narrow size distribution around 430 nm. The precipitation and pyrolysis processes were characterized using SEM, TEM, FTIR, and XRD to illustrate the formation mechanisms of the ceramic particles.

Effect of Pyrolysis Temperature on the Piezoresistivity of Polymer‐Derived Ceramics

Amorphous silicon carbonitride (SiCN) ceramics were synthesized by pyrolyzing a polysilazane at different temperatures between 900° and 1400°C. The microstructures and compositions of the materials obtained were analyzed using X‐ray diffraction, elemental analysis, and Raman spectroscopy. To study their piezoresistive behavior, the resistivity of the resultant materials were measured as a function of applied stress. We found that the piezoresistive behavior of all materials can fit the tunneling‐percolation model. The piezoresistive stress coefficient of the materials obtained at temperatures below 1200°C showed both reverse and logarithmical dependences on applied stress, but that of the materials obtained at higher temperatures showed only logarithmical dependence. We believe that the pyrolysis temperature induces a change in the free carbon structure thus, causing this effect on the piezoresistivity.

Electrochemical study of lithium insertion into carbon-rich polymer-derived silicon carbonitride ceramics

This paper presents the lithium insertion into carbon-rich polymer-derived silicon carbonitride (SiCN) ceramic synthesized by the thermal treatment of poly(diphenylsilylcarbodiimide) at three temperatures, namely 1100, 1300, and 1700 °C under 0.1 MPa Ar atmosphere. At lower synthesis temperatures, the material is X-ray amorphous, while at 1700 °C, the SiCN ceramic partially crystallizes. Anode materials prepared from these carbon-rich SiCN ceramics without any fillers and conducting additives were characterized using cyclic voltammetry and chronopotentiometric charging/discharging. We found that the studied silicon carbonitride ceramics demonstrate a promising electrochemical behavior during lithium insertion/extraction in terms of capacity and cycling stability. The sample synthesized at 1300 °C exhibits a reversible capacity of 392 mAh g −1. Our study confirms that carbon-rich SiCN phases are electrochemically active materials in terms of Li inter- and deintercalation.

Electrochemical studies of carbon-rich polymer-derived SiCN ceramics as anode materials for lithium-ion batteries

The electrochemical behavior of poly(phenylvinylsilylcarbodiimide)-derived SiCN ceramics as anode material for lithium-ion batteries is reported here for the first time. The novel carbon-rich silicon carbonitride (SiCN) ceramics have been synthesized by the thermal treatment of poly(phenylvinylsilylcarbodiimide) under argon atmosphere at five temperatures, namely 1100, 1300, 1500, 1700 and 2000 °C. The SiCN electrodes were prepared without any conducting additives and were tested in electrochemical two electrodes cell using cyclic voltammetry and galvanostatic techniques. The capacity of the carbon-rich SiCN samples was found to be stable upon galvanostatic cycling and reaches almost 300 mAh/g for the sample prepared at 1300 °C with oxygen as the impurity. The dependence of the microstructure, especially of the crystallinity of the segregated carbon phase and of the oxygen impurities on the electrochemical behavior of the SiCN material, was analysed. At all temperatures of thermolysis, the free carbon phase has been identified as “soft carbon”.