Co-reporter:Xingmin Liu, Zhaoju Yu, Ryo Ishikawa, Lingqi Chen, ... Ralf Riedel
Acta Materialia 2017 Volume 130(Volume 130) pp:
Publication Date(Web):15 May 2017
DOI:10.1016/j.actamat.2017.03.031
For the first time, single-source-precursors (SSPs) were synthesized through chemical modification of a commercial poly(methylvinyl)silazane with chemically bonded graphene oxide and carbon nanotube hybrids (GO/CNTs). After pyrolysis of warm-pressed and consolidated SSP-powders at 1000 °C in Ar, monolithic SiCN ceramic nanocomposites modified with in-situ thermally reduced GO/CNTs, namely RGO/CNTs-SiCN, were successfully obtained. The SSP-derived nanocomposite exhibits significantly enhanced dielectric properties if compared with that of a physically-blended-precursor derived reference material. Moreover, the SSP-derived RGO/CNTs-SiCN composite containing 15.0 wt% GO/CNTs in the feed possesses an electromagnetic shielding effectiveness of 67.2 dB with a sample thickness of 2.00 mm, which is the highest value among all the reported graphene-based composites with comparable thickness.Download high-res image (269KB)Download full-size image
Co-reporter:Xingmin Liu;Ryo Ishikawa;Lingqi Chen;Xiaowei Yin;Yuichi Ikuhara;Ralf Riedel
Journal of Materials Chemistry C 2017 vol. 5(Issue 31) pp:7950-7960
Publication Date(Web):2017/08/10
DOI:10.1039/C7TC00395A
Single-source-precursors (SSPs) have been synthesized through chemical modification of poly(methylvinyl)silazane (HTT 1800) with graphene oxide (GO) via an amidation reaction catalyzed by ZnCl2. With the formation of an SSP, the restacking of GO was effectively prevented by the HTT 1800 grafted at the surface of GO. After pyrolysis of warm-pressed green bodies comprising the SSP, GO-HTT 1800, monolithic silicon carbonitride (SiCN) ceramic nanocomposites containing in situ thermally reduced graphene oxide (RGO), namely RGO–SiCN, were successfully prepared. The resultant RGO–SiCN nanocomposites possess versatile electromagnetic (EM) properties ranging from EM absorbing to shielding behavior. With 2.5 wt% GO in the feed, the final RGO–SiCN nanocomposite exhibits an outstanding minimal reflection coefficient (RCmin) of −62.1 dB at 9.0 GHz, and the effective absorption bandwidth reaches 3.0 GHz with a sample thickness of 2.10 mm. With the same GO content, the resultant RGO–SiCN nanocomposite prepared by mechanical blending exhibits a far inferior RCmin of −8.2 dB. This finding strongly supports the advantage of the developed SSP route suitable for the fabrication of RGO–SiCN nanocomposites with significantly enhanced EM properties. With 12.0 wt% GO content in the feed, the obtained RGO–SiCN nanocomposite reveals an excellent shielding effectiveness of 41.2 dB with a sample thickness of 2.00 mm.
Co-reporter:Zhaoju Yu, Yaxing Pei, Shuyi Lai, Shuang Li, ... Xinya Liu
Ceramics International 2017 Volume 43, Issue 8(Volume 43, Issue 8) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.ceramint.2017.01.117
Newly developed TiC-TiB2-SiC ceramic nanocomposites were successfully synthesized by a novel single-source-precursor approach, with allylhydridopolycarbosilane (AHPCS), bis(cyclopentadienyl) titanium dichloride (Cp2TiCl2) and triethylamine borane (TEAB) as starting materials. The obtained single-source-precursor was characterized by Fourier transform infrared spectra (FT-IR), which confirms that hydroboration (C=C/B-H) and dehydrochlorication (Si-H/Cp2TiCl2) reactions were involved to introduce B and Ti elements into the AHPCS chains. The structural evolution of single-source-precursors, phase composition and chemical composition of the obtained ceramics were investigated by FT-IR, X-ray diffraction (XRD) and elemental analysis. High temperature behavior of the resultant TiC-TiB2-SiC ceramic nanocomposites with respect to decomposition as well as crystallization was carefully checked by XRD and mass loss after annealing at high temperatures of 1600 and 1800 °C. Transmission electron microscopy (TEM) was used to further observe the microstructure of TiC-TiB2-SiC nanocomposites, which again confirms the crystalline phases consist of nanoscaled β-SiC, TiC and TiB2.
Co-reporter:Zhaoju Yu, Xingang Luan, Ralf Riedel
Journal of the European Ceramic Society 2016 Volume 36(Issue 15) pp:3551-3552
Publication Date(Web):November 2016
DOI:10.1016/j.jeurceramsoc.2016.06.001
Co-reporter:Zhaoju Yu, Yao Feng, Shuang Li, Yaxing Pei
Journal of the European Ceramic Society 2016 Volume 36(Issue 15) pp:3627-3635
Publication Date(Web):November 2016
DOI:10.1016/j.jeurceramsoc.2016.02.003
In this paper, we use methyl-terminated polydimethylsiloxane (PDMS) as a pore-former and allylhydridopolycarbosilane (AHPCS) as a preceramic precursor to fabricate mesoporous SiC(O) ceramics by using liquid-liquid phase separation combined with cross-linking and emulsion processing. The influence of the polymer-polymer miscibility on the formation of mesoporous SiC(O) ceramics was investigated, with PDMS (350 cP) as porogen and AHPCS and polysiloxane (PSO) as preceramic precursors, respectively. Mesoporous SiC(O) with a specific surface area of 87.83 m 2g−1 and an average pore size of ca. 5 nm was produced by pyrolysis of a polymeric gel obtained from AHPCS/PDMS blends. In contrast, with PSO/PDMS blend as the starting material, mesopores were not formed in the final ceramics. In case of the AHPCS/PDMS blends, the polymer-to-ceramic transformation, the formation and the characteristic features of the mesopores were investigated by FT-IR, TGA, OM, SEM and N2 sorption isothermal analysis. The polymer-polymer miscibility between the preceramic polymer and the porogen polymer significantly influences the formation of the mesoporous ceramics. The final mesoporous SiC(O) ceramic obtained at 900 °C can withstand up to 1400 °C without significant change of the porosity. The resultant mesoporous SiC(O) shows highly efficient adsorption towards a model organic dye, namely Rhodamine B.
Co-reporter:Zhaoju Yu, Le Yang, Hao Min, Pei Zhang, Anhua Liu, Ralf Riedel
Journal of the European Ceramic Society 2015 Volume 35(Issue 2) pp:851-858
Publication Date(Web):February 2015
DOI:10.1016/j.jeurceramsoc.2014.09.009
A novel hyperbranched polytitaniumcarbosilane (HPTiCS) was synthesized by a monomer route. The obtained HPTiCS contains dicyclopentadienyl titanium units, which exhibits excellent self-catalytic activation of the dehydrocoupling reaction during its cross-linking process. As a result, the 1200 °C ceramic yield of the pyrolyzed HPTiCS is 32 wt% higher than that of titanium-free hyperbranched hydridopolycarbosilane (HPCS). Compared with titanium-free HPCS-derived SiC, the resulting HPTiCS-derived SiC-based ceramic exhibits a significantly enhanced resistance toward the growth of the in situ formed β-SiC crystals as the matrix phase after being annealed at 1600 °C.
Co-reporter:Zhaoju Yu, Hao Min, Le Yang, Yao Feng, Pei Zhang, Ralf Riedel
Journal of the European Ceramic Society 2015 Volume 35(Issue 4) pp:1161-1171
Publication Date(Web):April 2015
DOI:10.1016/j.jeurceramsoc.2014.10.037
To investigate the influence of the architecture of preceramic polymers on the ceramic yield, two dendritic-like polycarbosilanes named as K3G3 and G3 were synthesized through different routes. The obvious difference in their molecular structures is related with the distribution of allyl groups. The decomposition and rearrangement reactions of the K3G3 occurred at lower temperatures compared with that of sample G3, due to the fact that the allyl groups in G3 are located in both inner and outer molecular layers while those in K3G3 are located in the outer layers, exclusively. As a result, the residual mass of the K3G3 at 1000 °C (18 wt%) is much lower than that of the G3 sample (35 wt%). The molecular weight of the dendritic-like polymers also has an important effect on their ceramic yield which increases from 34.6 to 67.6% with the increasing molecular weight of Gn (3 ≤ n ≤ 5).
Co-reporter:Qingbo Wen, Yeping Xu, Binbin Xu, Claudia Fasel, Olivier Guillon, Gerd Buntkowsky, Zhaoju Yu, Ralf Riedel and Emanuel Ionescu
Nanoscale 2014 vol. 6(Issue 22) pp:13678-13689
Publication Date(Web):10 Sep 2014
DOI:10.1039/C4NR03376K
A novel single-source precursor was synthesized by the reaction of an allyl hydrido polycarbosilane (SMP10) and tetrakis(dimethylamido)hafnium(IV) (TDMAH) for the purpose of preparing dense monolithic SiC/HfCxN1−x-based ultrahigh temperature ceramic nanocomposites. The materials obtained at different stages of the synthesis process were characterized via Fourier transform infrared (FT-IR) as well as nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation was investigated by means of MAS NMR and FT-IR spectroscopy as well as thermogravimetric analysis (TGA) coupled with in situ mass spectrometry. Moreover, the microstructural evolution of the synthesized SiHfCN-based ceramics annealed at different temperatures ranging from 1300 °C to 1800 °C was characterized by elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Based on its high temperature behavior, the amorphous SiHfCN-based ceramic powder was used to prepare monolithic SiC/HfCxN1−x-based nanocomposites using the spark plasma sintering (SPS) technique. The results showed that dense monolithic SiC/HfCxN1−x-based nanocomposites with low open porosity (0.74 vol%) can be prepared successfully from single-source precursors. The average grain size of both HfC0.83N0.17 and SiC phases was found to be less than 100 nm after SPS processing owing to a unique microstructure: HfC0.83N0.17 grains were embedded homogeneously in a β-SiC matrix and encapsulated by in situ formed carbon layers which acted as a diffusion barrier to suppress grain growth. The segregated Hf-carbonitride grains significantly influenced the electrical conductivity of the SPS processed monolithic samples. While Hf-free polymer-derived SiC showed an electrical conductivity of ca. 1.8 S cm−1, the electrical conductivity of the Hf-containing material was analyzed to be ca. 136.2 S cm−1.
Co-reporter:Zhaoju Yu, Le Yang, Hao Min, Pei Zhang, Cong Zhou and Ralf Riedel
Journal of Materials Chemistry A 2014 vol. 2(Issue 6) pp:1057-1067
Publication Date(Web):25 Nov 2013
DOI:10.1039/C3TC32088J
Hydrosilylation of vinyl ferrocene with allylhydridopolycarbosilane was used to synthesize a processable hyperbranched polyferrocenylcarbosilane (HBPFCS), which was characterized by combination of gel permeation chromatography, Fourier transform infrared (FT-IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation of the HBPFCSs was then investigated by FT-IR and 13C MAS NMR spectroscopy as well as by thermal gravimetric analysis (TGA). A self-catalytic effect of ferrocenyl units in the HBPFCS skeleton on dehydrocoupling was found during a curing process at 170 °C resulting in a high ceramic yield of ca. 80% at 1200 °C in Ar. Finally, microstructures and magnetic properties of the final ceramics were studied by techniques such as X-ray diffraction, energy dispersive spectroscopy, Raman spectroscopy, transmission electron microscopy and vibrating sample magnetometry. The final ceramic (pyrolysis temperature ≥900 °C) is characterized by a microstructure comprised of a SiC/C/Fe nanocomposite. Turbostratic carbon layers located at the segregated α-Fe crystal boundary avoid interdiffusion and explain the exclusive existence of α-Fe in a SiC/C matrix even at 1300 °C. Variations of the iron content in the HBPFCSs and of the pyrolysis conditions facilitate the control of the composition and ceramic micro/nanostructure, influencing in particular magnetic properties of the final SiC/C/Fe nanocomposite ceramic.
Co-reporter:Cong Zhou, Hao Min, Le Yang, Meiyu Chen, Qingbo Wen, Zhaoju Yu
Journal of the European Ceramic Society 2014 Volume 34(Issue 15) pp:3579-3589
Publication Date(Web):December 2014
DOI:10.1016/j.jeurceramsoc.2014.05.039
A novel polyborosilazane (PBSZ) precursor was synthesized by the reaction of copolysilazane (CPSZ) with dimethylaminoborane (DMAB). The resultant PBSZs were characterized by FT-IR and NMR spectroscopy. It was found that both, BH and NH bonds of DMAB, react with CPSZ leading to boron containing copolysilazanes. The polyborosilazanes were pyrolyzed at 900 °C in argon and the precursor-to-ceramic transformation was studied by TG-MS and FT-IR spectroscopy. The modification of CPSZ with DMAB enhances the cross-linking of the resulting PBSZ, which increases the final ceramic yield from 57.8% to 77.5–80.0%. Finally, the ceramics obtained at 900 °C were subsequently annealed at different temperatures ranging from 1200 to 1800 °C. The heat-treated products were characterized by X-ray powder diffraction and electron microscopy. Accordingly, the resulting SiBCN ceramics exhibit significantly enhanced high-temperature-resistance with respect to decomposition and crystallization as compared with boron-free CPSZ-derived SiCN ceramics. TEM results support that the thermal stability is due to the segregation of a BN(C) phase as interlayer between Si3N4 nanocrystals formed during heat-treatment of SiBCN at T > 1500 °C.
Co-reporter:Cong Zhou, Le Yang, Hao Geng, Qiang Zheng, Hao Min, Zhaoju Yu, Haiping Xia
Ceramics International 2012 Volume 38(Issue 8) pp:6815-6822
Publication Date(Web):December 2012
DOI:10.1016/j.ceramint.2012.05.080
Abstract
In this paper, Si–C–N–Fe magnetoceramics were obtained by pyrolysis of iron-modified polysilazane (PFSZ) precursors which were synthesized by using polysilazane (PSZ) and iron (III) acetylacetonate (Fe(acac)3) as starting materials. The as-synthesized PFSZ precursors were characterized by Fourier transform infrared spectroscopy (FT-IR) and gel permeation chromatography. The polymer-to-ceramic conversion of the PFSZ was studied by FT-IR and thermal gravimetric analysis. It is found that the ceramic yield of the PFSZ precursor is ca. 25% higher than that of the original PSZ. The crystallization behavior, microstructures and magnetic properties of the PFSZ-derived Si–C–N–Fe magnetoceramics were studied by techniques such as X-ray diffraction, transmission electron microscopy and vibrating sample magnetometer. The results indicate that the formed α-Fe nanoparticles are uniformly dispersed in amorphous Si–C–N(O) matrix, leading to the soft magnetization of the resultant Si–C–N–Fe ceramics. Moreover, the iron content and the magnetic properties of the Si–C–N–Fe ceramic could be easily controlled by the amount of Fe(acac)3 in the precursor.
Co-reporter:Zhaoju Yu, Cong Zhou, Ran Li, Le Yang, Siwei Li, Haiping Xia
Ceramics International 2012 Volume 38(Issue 6) pp:4635-4643
Publication Date(Web):August 2012
DOI:10.1016/j.ceramint.2012.02.045
Polyboronsilazane (PBSZ) precursors for SiBCN ceramics were prepared by using 9-borabicyclo-[1,3,3] nonane (9-BBN) and copolysilazanes (CPSZ) as starting materials, involving the hydroboration reaction between vinyl groups of PSZ and BH groups of 9-BBN under mild conditions. The as-synthesized PBSZ was obtained as a soluble liquid, which was characterized by FT IR and NMR. The polymer-to-ceramic conversion of PBSZ at a ceramic yield of 62.2–79.9% was investigated by means of FT IR and TGA. The crystallization behavior and microstructures of PBSZ-derived SiBCN ceramics were studied by XRD, SEM and HRTEM. The SiBCN ceramic began to crystallize at 1600 °C. Further heating at 1800 °C induced partial crystallization to give mixed XRD patterns for SiC, Si3N4, and BN(C). It is observed that the introduction of boron improves the thermal stability of SiBCN ceramics, especially under high temperatures of 1600–1800 °C. In addition, the introduction of boron significantly improves the ceramic density while inhibits the SiC crystallization.
Co-reporter:Zhaoju Yu, Le Yang, Junying Zhan, Cong Zhou, Hao Min, Qiang Zheng, Haiping Xia
Journal of the European Ceramic Society 2012 Volume 32(Issue 6) pp:1291-1298
Publication Date(Web):June 2012
DOI:10.1016/j.jeurceramsoc.2011.12.015
SiC/ZrC/C composites were prepared via pyrolysis of a polymeric precursor, namely AHPCS/Cp2ZrCl2 hybrid precursor prepared by the blend of allylhydridopolycarbosilane (AHPCS) and bis(cyclopentadienyl) zirconium dichloride (Cp2ZrCl2). The cross-linking and polymer-to-ceramic conversion of as-synthesized AHPCS/Cp2ZrCl2 were characterized by means of FTIR, 13C NMR, TGA, EDS, Raman spectroscopy and XRD. It is suggested that dehydrocoupling, hydrosilylation and dehydrochlorication are involved in the cross-linking of the hybrid precursor, which is responsible for a relatively high ceramic yield of 75.5% at 1200 °C. The polymer-to-ceramic conversion is complete at 900 °C, and it gives an amorphous ceramic. Further heating at 1350 °C induces partial crystallization, and then the characteristic peaks of β-SiC and cubic ZrC appear at 1600 °C. The effect of the composition of the hybrid precursor is also studied in the work.
Co-reporter:Siwei Li, Litong Zhang, Muhe Huang, Zhaoju Yu, Haiping Xia, Zude Feng, Laifei Cheng
Materials Chemistry and Physics 2012 Volume 133(2–3) pp:946-953
Publication Date(Web):16 April 2012
DOI:10.1016/j.matchemphys.2012.01.121
TiC–TiB2–SiC ceramics with enhanced yield and microstructure homogeneity were synthesized from hybrid polymer precursors. The polymer reactions and phase evolution were characterized through a variety of techniques. It had been found that the ceramic yield of allylhydridopolycarbosilane was increased after introduction of borazine and was further enhanced by subsequently adding proper amount of tetrabutyl titanate. The borazine favored cross-linking and induced B containing phases to facilitate the densification, while the Ti source was competent to fix B and excess C (which was redundant for the formation of SiC) as uniformly distributed TiB2 and TiC through sintering, respectively. An optimally thermal-stable TiC–TiB2–SiC structure was constructed by consuming the excess C as the Ti content rose to 5 wt.%, at the cost of a slightly reduced ceramic yield.Highlights► Hybrid polymer precursors were synthesized by reacting AHPCS with borazine and then with tetrabutyl titanate. ► A SiBCN ceramic with enhanced yield and thermal stable structure was obtained. ► A fine TiC–TiB2–SiC structure was established by optimizing the feeding content of the Ti source. ► Phase evolution of the composite was explored through cooperation of a variety of techniques.
Co-reporter:Ran Li;Cong Zhou;Le Yang;Siwei Li;Junying Zhan;Haiping Xia
Journal of Applied Polymer Science 2011 Volume 122( Issue 2) pp:1286-1292
Publication Date(Web):
DOI:10.1002/app.34274
Abstract
Tailorable copolysilazanes (CPSZs) with variable chemical structure and molecular weights were prepared by coammonolysis of dichloromethylsilane, dichloromethylvinylsilane, and trichloromethylsilane. The as-synthesized CPSZ was characterized by gel permeation chromatography, Fourier transformed infrared (FTIR) spectroscopy, and nuclear magnetic resonance spectroscopy. The CPSZ could be cured in an inert atmosphere at 180°C for 24 h. Pyrolysis behavior and structure evolution of the cured CPSZ were studied by means of thermal gravimetric analysis and FTIR. Hydrosilylation, transamination, dehydrogenation, and demethanation reactions were involved in the polymer-to-ceramic conversion of CPSZ. The ceramization process was complete at 900°C with a ceramic yield of 81–84%. Elemental analysis indicated that the compositions of final ceramics can be tailored by controlling the feed ratios of the starting chlorosilanes. Moreover, the microstructural evolution of the resultant SiCN ceramics was further investigated by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
Co-reporter:Zhaoju Yu;Junying Zhan;Cong Zhou;Le Yang
Journal of Inorganic and Organometallic Polymers and Materials 2011 Volume 21( Issue 3) pp:
Publication Date(Web):2011 September
DOI:10.1007/s10904-011-9483-9
A hybrid precursor of titanium-containing polycarbosilane is prepared by blending hyperbranched polycarbosilane (HBPCS) and tetrabutyl titanate (TBT), and then crosslinking at 160 °C, followed by pyrolyzing at high temperatures to afford SiC(Ti) ceramics. The crosslinking reaction of HBPCS–TBT hybrid precursor is investigated by FT-IR, solid state 29Si MAS NMR, and GPC. The results indicate that the crosslinking reaction takes place via condensation between the Si–H bond of HBPCS and butoxy group in TBT leading to the formation of Si–O–Ti bonds. The thermal properties and structural evolution of crosslinked hybrid precursor and the crystallization behavior and composition of final ceramics are investigated by TGA, FT-IR, Raman spectroscopy, XRD and energy dispersive elemental analysis. The ceramic yield of hybrid precursor is significantly enhanced by introduction of TBT. The ceramic yield at 1,400 °C is 83% for HBPCS–TBT-5 as measured by TGA. The Ti-content in the ceramic is controlled by varying the TBT content in the feed. The SiC(Ti) ceramic is amorphous at 900 °C. The characteristic peaks of β-SiC and TiC appear until 1,600 °C. The growth of SiC crystals is inhibited by the formation of TiC.
Co-reporter:Muhe Huang;Yunhui Fang;Ran Li;Tianhua Huang;Haiping Xia
Journal of Applied Polymer Science 2009 Volume 113( Issue 3) pp:1611-1618
Publication Date(Web):
DOI:10.1002/app.30071
Abstract
Liquid polycarbosilanes substituted by unsaturated groups were prepared by a one-pot synthesis with Cl2Si(CH3)CH2Cl, Cl3SiCH2Cl, and CH2CHCH2Cl (or HCCMgBr) as the starting materials. The as-received polycarbosilanes were characterized by gel permeation chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance and were confirmed to have hyperbranched structures. The polymer yield, SiH content, side reaction, unsaturated group content, and polymer structure are affected by the amount of the starting materials in feed. The thermal properties of the polycarbosilanes were investigated by thermogarvimetric analysis. The ceramic yield of allyhydridopolycarbosilane is about 60% and that of ethynylhydridopolycarbosilane is over 75%, indicating that the liquid polycarbosilanes have great potential to be promising precursors to SiC. Moreover, the compositions of the polycarbosilanes and the final ceramics can be tailored by controlling the amount of the starting materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Co-reporter:Zhaoju Yu, Shuang Li, Pei Zhang, Yao Feng, Xinya Liu
Ceramics International (1 April 2017) Volume 43(Issue 5) pp:
Publication Date(Web):1 April 2017
DOI:10.1016/j.ceramint.2016.12.104
In this paper, magnetic porous Ni-modified SiOC(H) ceramic nanocomposites (Ni/SiOC(H)) were successfully prepared via a template-free polymer-derived ceramic route, which involves pyrolysis at 600 °C of nickel-modified allylhydridopolycarbosilane (AHPCS-Ni) precursors synthesized by the reaction of allylhydridopolycarbosilane (AHPCS) with nickel(II)acetylacetonate (Ni(acac)2). The resultant Ni/SiOC(H) nanocomposites are comprised of in-situ formed nanoscaled Ni socialized with small amounts of NiO and nickel silicides embedded in the amorphous SiOC(H) matrix. The materials show ferromagnetic behavior and excellent magnetic properties with the saturation magnetization in the range of 1.71–7.08 emu g−1. Besides, the Ni/SiOC(H) nanocomposites are predominantly mesoporous with a high BET surface area and pore volume in the range of 253–344 and 0.134–0.185 cm3 g−1, respectively. The measured porosity features cause an excellent adsorption capacity towards a template dye acid fuchsin with the adsorption capacity Qt at 10 min of 80.7–85.8 mg g−1 and the Qe at equilibrium of 123.8–129.8 mg g−1.
Co-reporter:Zhaoju Yu, Le Yang, Hao Min, Pei Zhang, Cong Zhou and Ralf Riedel
Journal of Materials Chemistry A 2014 - vol. 2(Issue 6) pp:NaN1067-1067
Publication Date(Web):2013/11/25
DOI:10.1039/C3TC32088J
Hydrosilylation of vinyl ferrocene with allylhydridopolycarbosilane was used to synthesize a processable hyperbranched polyferrocenylcarbosilane (HBPFCS), which was characterized by combination of gel permeation chromatography, Fourier transform infrared (FT-IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation of the HBPFCSs was then investigated by FT-IR and 13C MAS NMR spectroscopy as well as by thermal gravimetric analysis (TGA). A self-catalytic effect of ferrocenyl units in the HBPFCS skeleton on dehydrocoupling was found during a curing process at 170 °C resulting in a high ceramic yield of ca. 80% at 1200 °C in Ar. Finally, microstructures and magnetic properties of the final ceramics were studied by techniques such as X-ray diffraction, energy dispersive spectroscopy, Raman spectroscopy, transmission electron microscopy and vibrating sample magnetometry. The final ceramic (pyrolysis temperature ≥900 °C) is characterized by a microstructure comprised of a SiC/C/Fe nanocomposite. Turbostratic carbon layers located at the segregated α-Fe crystal boundary avoid interdiffusion and explain the exclusive existence of α-Fe in a SiC/C matrix even at 1300 °C. Variations of the iron content in the HBPFCSs and of the pyrolysis conditions facilitate the control of the composition and ceramic micro/nanostructure, influencing in particular magnetic properties of the final SiC/C/Fe nanocomposite ceramic.
