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1.
《Journal of the European Ceramic Society》2014,34(10):2163-2167
The electric conductivity of polymer-derived SiBCNs pyrolyzed at different temperatures was studied. We showed that the boron impeded the graphitization of the free-carbon phase in the SiBCN, leading to a higher characteristic temperature and activation energy as compared to the SiCN. Such an impeding effect is due to the interaction between h-BN and graphite phase. We also provided a credible evidence to show that the increase in the electric conductivity of the SiBCN with pyrolysis temperature is likely due to the increase in the conductivity of the free-carbon phase. 相似文献
2.
Kewei Wang Baisheng Ma Xuqin Li Linan An 《Journal of the American Ceramic Society》2014,97(7):2135-2138
We studied the electric conductivity and structure of polymer‐derived carbon‐rich amorphous SiC pyrolyzed at different temperatures. The conductivity of the material increased drastically with pyrolysis temperature followed an Arrhenius relationship with the activation energy of ~3.4 eV. Raman and X‐ray photoelectron spectroscopy analysis revealed that the order of free carbon phase increased with pyrolysis temperature, accompanied by sp3→sp2 transition. The activation energy for such a structure change was 3.1–3.8 eV, which is close to that for the conductivity change. We thus believe that the increase in the conductivity was mainly due to the increase in conductivity of the free carbon phase. 相似文献
3.
Enhanced electric conductivity of polymer‐derived SiCN ceramics by microwave post‐treatment
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Gang Shao Wenfeng Peng Chao Ma Wanyu Zhao Jingxia Guo Yuqi Feng Hailong Wang Rui Zhang Linan An 《Journal of the American Ceramic Society》2017,100(3):842-847
The effect of microwave treatment on the electric conductivity and structure of a polymer‐derived SiCN ceramic is studied. It is found that the conductivity of the microwave‐treated sample is about 40 times higher than that of the conventional heat‐treated one at the same temperature and dwell time conventionally. The X‐ray diffraction patterns show that both samples are amorphous without obvious crystallization. Raman analysis reveals that the microwave‐treated sample exhibited a narrower full width at half maximum and upper‐shift of G peak. X‐ray photoelectron spectroscopy spectra show that there is a significant sp3‐to‐sp2 transition of free carbon in the microwave‐treated sample. These results suggest that the microwave‐treatment can induce a distinct structure evolution of the free carbon, which contributes to the remarkable enhancement of the conductivity of the sample. 相似文献
4.
Yuxi Yu Chenhao Huang Jie Xu Jian Zhu Minghui Cong Jingyuan Song Shengnan Xia 《Journal of the American Ceramic Society》2021,104(10):5067-5076
Polymer-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. 相似文献
5.
Van Lam Nguyen Caterina Zanella Paolo Bettotti Gian Domenico Sorarù 《Journal of the American Ceramic Society》2014,97(8):2525-2530
SiOCN ceramics have been prepared by the polymer pyrolysis method. The preceramic polymers were synthesized from a polysiloxane cross‐linked with two different N‐containing compounds: a silazane or a ternary amine. The corresponding SiOCN ceramics were obtained by pyrolysis in nitrogen atmosphere at five different temperatures from 1000°C to 1400°C. The electrical conductivity of the powdered SiOCN ceramic samples was determined by the powder‐solution‐composite technique. The results show an increase in room temperature AC conductivity of three orders of magnitude, from ≈10?5 (S/cm) to ≈10?2 (S/cm), with increasing pyrolysis temperature from 1000°C to 1400°C. Furthermore, the electrical conductivity of the amine‐derived SiOCN is three to five times higher than that of the silazane‐derived ceramic at each pyrolysis temperature. The combined structural study by Raman spectroscopy and chemical analysis suggests that the increase of electrical conductivity with the pyrolysis temperature is due to the sp3‐to‐sp2 transition of the amorphous carbon phase. The higher conductivity of the amine‐derived SiOCN is also discussed considering features like the volume% of the free‐carbon phase and its possible N‐doping. 相似文献
6.
《Ceramics International》2020,46(5):5594-5601
Highly porous polymer-derived SiCN(O) and SiOC ceramics with low thermal conductivity were developed by replicating polyurethane (PU) foams. The PU templates were impregnated with polysilazane or polysiloxane precursor, followed by pyrolysis at different temperatures (1200 °C - 1500 °C) yielding SiCN(O) or SiOC ceramic foams, respectively. The swelling and cross-linking behavior of the used precursors had a significant impact on the morphology of the prepared foams. The samples had bulk densities ranging from 0.03 g.cm-3 to 0.56 g.cm-3 and a total porosity in the range from 75 to 98 vol%. Fourier transform infrared (FT-IR), Raman spectroscopy, X-ray diffraction (XRD) were employed to follow the structural evolution together with morphological characterization by scanning electron microscopy (SEM). The obtained ceramics were thermally stable up to 1400 °C, and the linear thermal expansion coefficient values of the porous SiCN(O) and SiOC components in the temperature range from 30 to 850 °C were found to be ~1.72 x 10-6.K-1 and ~1.93 x 10-6.K-1, respectively. Thermal conductivity (λ) as low as 0.03 W.m-1 K-1 was measured for the SiCN(O) and SiOC foams at room temperature (RT). The λ of the ceramic struts were also assessed by using the Gibson-Ashby model and estimated to be 2.1 W.m-1 K-1 for SiCN(O), and 1.8 W.m-1 K-1 for SiOC. 相似文献
7.
《Journal of the European Ceramic Society》2003,23(5):781-789
Electrical properties of monolithic, amorphous SiCxNyHz-ceramics derived from 1,3,5-trimethyl-1,3,5-trivinylcyclotrisilazane via polymer pyrolysis were investigated from room temperature to 400 °C using impedance spectroscopy. Depending on the pyrolysis temperature Tp, the d.c. conductivity varies up to 8 orders of magnitude. The temperature dependence of samples pyrolysed at low temperatures (Tp=700–1200 °C) follows a Mott law, whereas samples pyrolysed at high temperature (Tp=1400 °C) show an Arrhenius dependence. Structural changes during pyrolysis were characterized by solid state magic angle spinning nuclear magnetic resonance spectroscopy, Raman spectroscopy and X-ray diffractometry. NMR and especially Raman measurements indicate the formation of sp2-carbon atoms, which rearrange towards graphitic-like domains with increasing pyrolysis temperature. This observation can explain the related increase of the d.c.-conductivity. 相似文献
8.
L. Ribeiro A. Bezerra C. Gervais S. Bernard R. Machado G. Motz 《Journal of the European Ceramic Society》2021,41(6):3285-3291
The influence of pyrolysis temperature on the oxidation resistance of carbon-rich SiCN ceramics derived from reaction of acrylonitrile with a commercially available oligosilazane (HTT1800) and its subsequent pyrolysis in nitrogen atmosphere was evaluated. The investigation of the oxidation behavior reveals that the final pyrolysis temperature plays an important role in the oxidation resistance of the developed SiCN/C nanocomposites. Increasing the pyrolysis temperature promotes an ordering of the free-carbon phase and consequently, an improvement of the oxidation resistance is noticed. However, starting phase separation during annealing at 1500 °C reduces slightly the protection effect provided by the oxidation resistant Si3N4 phase. 相似文献
9.
Xiaoling Liu Jimei Xue Fan Yang Fang Ye Xiaomeng Fan Laifei Cheng 《Journal of the American Ceramic Society》2020,103(11):6255-6264
A 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. 相似文献
10.
《Diamond and Related Materials》2001,10(9-10):1921-1926
Amorphous SiCN films were prepared on Si (100) substrates by nitrogen ion-assisted pulsed-laser ablation of an SiC target. The dependence of the formed chemical bonds in the films on nitrogen ion energy and the substrate temperature was investigated by an X-ray photoelectron spectroscopy (XPS). The fractions of sp2 CC, sp3 CC, and sp2 CN bonds decreased, and that of NSi bonds increased when the nitrogen ion energy was increased without heating during the film preparation. The fraction of sp3 CN bonds was not changed by the nitrogen ion irradiation below 200 eV. Si atoms displaced carbon atoms in the films and the sp3 bonding network was made between carbon and silicon through nitrogen. This tendency was remarkable in the films prepared under substrate heating, and the fraction of sp3 CN bonds also decreased when the nitrogen ion energy was increased. Under the impact of high-energy ions or substrate heating, the films consisted of sp2 CC bonds and SiN bonds, and the formation of sp3 CN bonds was difficult. 相似文献
11.
《Journal of the European Ceramic Society》2014,34(3):589-598
Porous SiCN ceramics were successfully fabricated by pyrolysis of a kind of polysilazane. The effects of annealing temperature on the microstructure evolution, direct-current electrical conductivity, dielectric properties, and microwave absorption properties of SiCN in the frequency range 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, SiC, Si3N4 and free carbon nanodomains are gradually formed in the SiCN. Both the SiC and free carbon nanodomains lead to the increases of the complex relative permittivity and loss tangent of SiCN. With the increase of the annealing temperature, the average real permittivity, imaginary permittivity and loss tangent increase from 4.4, 0.2 and 0.05 to 13.8, 6.3 and 0.46, respectively. The minimum reflection coefficient and the frequency bandwidth below −10 dB for SiCN annealed at 1500 °C are −53 dB and 3.02 GHz, indicating good microwave absorption properties. 相似文献
12.
Si3N4–SiCN composite ceramics were successfully fabricated through precursor infiltration pyrolysis (PIP) method using polysilazane as precursor and porous Si3N4 as preform. After annealed at temperatures varying from 900 °C to 1400 °C, the phase composition of SiCN ceramics, electrical conductivity and dielectric properties of Si3N4–SiCN composite ceramics over the frequency range of 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, the content of amorphous SiCN decreases and that of N-doped SiC nano-crystals increases, which leads to the increase of electrical conductivity. After annealed at 1400 °C, the average real and imaginary permittivities of Si3N4–SiCN composite ceramics are increased from 3.7 and 4.68 × 10?3 to 8.9 and 1.8, respectively. The permittivities of Si3N4–SiCN composite ceramics show a typical ternary polarization relaxation, which are ascribed to the electric dipole and grain boundary relaxation of N-doped SiC nano-crystals, and dielectric polarization relaxation of the in situ formed graphite. The Si3N4–SiCN composite ceramics exhibit a promising prospect as microwave absorbing materials. 相似文献
13.
Pradeep Vallachira Warriam Sasikumar Gurdial Blugan Nicola Casati Eirini Kakkava Giulia Panusa Demetri Psaltis Jakob Kuebler 《Ceramics International》2018,44(17):20961-20967
Polymer derived SiOC and SiCN ceramics (PDCs) are interesting candidates for additive manufacturing techniques to develop micro sized ceramics with the highest precision. PDCs are obtained by the pyrolysis of crosslinked polymer precursors at elevated temperatures. Within this work, we are investigating PDC SiOC ceramic monoliths synthesized from liquid polysiloxane precursor crosslinked with divinylbenzene for fabrication of conductive electromechanical devices. Microstructure of the final ceramics was found to be greatly influenced by the pyrolysis temperature. Crystallization in SiOC ceramics starts above 1200?°C due to the onset of carbothermal reduction leading to the formation of SiC and SiO2 rich phases. Microstructural characterisation using ex-situ X-ray diffraction, FTIR, Raman spectra and microscopy imaging confirms the formation of nano crystalline SiC ceramics at 1400?°C. The electrical and mechanical properties of the ceramics are found to be significantly influenced by the phase separation with samples becoming more electrically conducting but with reduced strength at 1400?°C. A maximum electrical conductivity of 101 S?cm?1 is observed for the 1400?°C samples due to enhancement in the ordering of the free carbon network. Mechanical testing using the ball on 3 balls (B3B) method revealed a characteristic flexural strength of 922?MPa for 1000?°C amorphous samples and at a higher pyrolysis temperature, materials become weaker with reduced strength. 相似文献
14.
《Ceramics International》2019,45(14):17344-17353
The processing of 3D carbon fiber reinforced SiCN ceramic matrix composites prepared by polymer impregnation and pyrolysis (PIP) route was improved, and factors that determined the mechanical performance of the resulting composites were discussed. 3D Cf/SiCN composites with a relative density of ∼81% and uniform microstructure were obtained after 6 PIP cycles. The optimum bending strength, Young's modulus and fracture toughness of the composites were 75.2 MPa, 66.3 GPa and 1.65 MPa m1/2, respectively. The residual strength retention rate of the as-pyrolyzed composites was 93.3% after thermal shock test at ΔT = 780 °C. It further degraded to 14.6% when the thermal shock temperature difference reached to 1180 °C. The bending strength of the composites was 35.6 MPa after annealing at 1000 °C in static air. The deterioration of the bending strength should be attributed to the strength degradation of carbon fibers and decomposition of interfacial structure. 相似文献
15.
Zhao Zhang Quan Li Sanat Chandra Maiti Xingchen Shen Jian He Fei Peng Ranjendra K. Bordia 《International Journal of Applied Ceramic Technology》2023,20(2):1060-1070
Polymer-derived amorphous SiCN has excellent high-temperature stability and properties. To reduce the shrinkage during pyrolysis and to improve the high-temperature oxidation resistance, Y2O3 was added as a filler. In this study, polymer-derived SiCN–Y2O3 composites were fabricated by mixing a polymeric precursor of SiCN with Y2O3 submicron powders in different ratios. The mixtures were cross-linked and pyrolyzed in argon. SiCN–Y2O3 composites were processed using field-assisted sintering technology at 1350°C for 5 min under vacuum. Dense SiCN–Y2O3 composite pellets were successfully made with relative density higher than 98% and homogeneous microstructure. Due to low temperature and short time of the heat-treatment, the grain growth of Y2O3 was substantially inhibited. The Y2O3 grain size was ∼1 μm after sintering. The composites’ heat capacity, thermal diffusivity, and thermal expansion coefficients were characterized as a function of temperature. The thermal conductivity of the composites ceramics decreased as the amount of amorphous SiCN increased and the coefficient of thermal expansion (CTE) of the composites increased with Y2O3 content. However, the thermal conductivity and CTE did not follow the rule of mixture. This is likely due to the partial oxidation of SiCN and the resultant impurity phases such as Y2SiO5, Y2Si2O7, and Y4.67(SiO4)3O. 相似文献
16.
《Ceramics International》2023,49(10):15829-15841
In this study, we investigated the tunable porous structure of SiCN(O)-derived ceramic aerogels by changing the molecular structure of the polysilazanes from linear to branched. We also studied the effect of molecular structure on the thermal insulation properties of ceramic aerogels. As the percentage of branched molecular structure in the polysilazane precursor increased, the internal microscopic pore structure of the aerogels changed from macroporous to mesoporous. The specific surface areas and pore volumes of the ceramic aerogels prepared with different precursors increased after pyrolysis at 1000 °C, ranging from 3.7 to 255.9 m2/g and 0.01–0.36 cm3/g, respectively. The corresponding thermal conductivities increased slightly as the aerogels contracted after pyrolysis. The low thermal conductivity (0.046 W/(m·K) at minimum) can be attributed to the decrease in pore size caused by adjusting the precursor structure, which limits the thermal conduction of gas in the porous aerogel materials. 相似文献
17.
Gian Domenico Sorarù Getnet Kacha Renzo Campostrini Andrea Ponzoni Maurizio Donarelli Arun Kumar Gino Mariotto 《Journal of the American Ceramic Society》2017,100(10):4611-4621
In this work the room temperature electrical conductivity of Si(B)OC glasses made via polymer pyrolysis at 1200°C and 1400°C (maximum temperature) and having different amount of boron was measured. When B content is increased from zero (pure SiOC glass) up to B/Si=0.5 the electrical conductivity increases in 2 orders of magnitude from 4.09±0.64×10?5 up to 2.93±1.91×10?3 with a corresponding decrease in the activation energy from about 1.08 to 0.51 eV. This results shows for the first time that the electrical conductivity of Si‐based polymer‐derived ceramics can be controlled by the amount of the doping element. The structure of the Si(B)OC glasses has been studied with different techniques including FT‐IR, XRD and Raman spectroscopy. The Raman study indicates that B partially substitutes C into the sp2 C planes of the free carbon phase forming trigonal BC3 units. Accordingly, the evolution of the electrical properties with the B content has been correlated with the corresponding structural evolution and a hypothesis is presented to rationalize the role of boron on the electrical conductivity of SiOBC glasses. 相似文献
18.
Ravi Mohan PrasadGabriela Mera Koji Morita Mathis MüllerHans-Joachim Kleebe Aleksander GurloClaudia Fasel Ralf Riedel 《Journal of the European Ceramic Society》2012,32(2):477-484
Herein we report on the thermal decomposition of SiCN polymer-derived ceramics leading to materials with high specific surface area and defined pore sizes. The ceramics were obtained by means of pyrolysis of a carbon-rich poly(diphenylsilylcarbodiimide) precursor and by varying the thermolysis parameters, namely temperature, annealing time and using additional annealing steps. The thermal decomposition of SiCN ceramics is correlated with the carbothermal reaction of amorphous silicon nitride phase with excess carbon and this detrimental event leads to high specific surface area up to 568 m2 g−1 and micro- and mesopores formation in these materials. High-resolution TEM investigations have confirmed that the pores are embedded only in the carbon phase. Moreover, the relationship between the pore sizes and the organization of free carbon phase is discussed. 相似文献
19.
Yuyu Zhang Jia Sun Yuqi Wang Ralf Riedel Qiangang Fu 《Journal of the American Ceramic Society》2023,106(7):4220-4232
Different kinds of carbon nanomaterials, free carbon (Cfree), graphene, and N-containing graphene (NG), in single-source-precursors-derived SiCN ceramics, were in situ generated by modifying polysilazane with divinylbenzene, dopamine hydrochloride and melamine, respectively. Adjusting the carbon source brings phase structure and electromagnetic wave absorption (EMA) properties differences of SiCN/C ceramics. In situ Cfree enhances the EMA capacity of SiCN ceramics by improving their electrical conductivity of 9.2 × 10−4 S/cm. The electrical conductivity of SiCN ceramics with 2D graphene sheets balloons to 2.5 × 10−3 S/cm, causing poor impedance match thus leading to a worse EMA performance. In situ NG in SiCN ceramics has a low electrical conductivity of 5.6 × 10−8 S/cm, making for excellent impedance match. The corrugated NG boosts dielectric loss, interfacial, and dipole polarization. NG-SiCN nanocomposites possess an outstanding EMA performance with RLmin of −61.08 dB and effective absorption bandwidth of 4.05 GHz, which are ∼2.4 times lower and ∼4 times higher than those of SiCN, respectively. 相似文献
20.
《Journal of the European Ceramic Society》2022,42(13):5476-5483
In this study, we present a DLP 3D-printing strategy for the fabrication of SiCN ceramic matrix composites (CMCs). The polysilazane-based preceramic polymer containing inert fillers was UV-cured into a green body and then converted to SiCN CMCs after pyrolysis. The introduced fillers (Si3N4 particles and Si3N4 whiskers) as reinforcements are well dispersed in the matrix, which can not only effectively reduce the linear shrinkage and weight loss, but also greatly improve the mechanical properties of the SiCN CMCs. The bending strength of the SiCN CMCs reinforced with 10 wt% Si3N4 whiskers (without surface polished) reached 180.7 ± 15.6 MPa. Furthermore, the effect of fillers content on microstructure and porosity of the SiCN CMCs are discussed, and it was found that the excessive fillers led to increased pore defects and decreased continuity of the matrix, thereby reducing the mechanical properties of the SiCN CMCs. This strategy provides a promising ceramic manufacturing technique to fabricate polymer‐derived CMCs with complex-shaped and high-performance for potential demanding applications. 相似文献