Preparation of Si–C–N–Fe magnetic ceramic derived from iron-modified polysilazane

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.     

Pyrolysis synthesis of Si–B–C–N ceramics and their thermal stability

Si–B–C–N ceramics were synthesized by co-pyrolyzing hybrid polymeric precursors of polycarbosilane (PCS) and polyborazine (PBN). The pyrolysis behavior and structural evolution of the hybrid precursor, the microstructure and composition of the prepared Si–B–C–N ceramics were fully investigated. It was found that the copyrolysis of hybrid polymeric precursors in Ar led to the release of CH₄, CH₃NH₂ and CH₃CN gases at temperatures ranging from 200 to 1100 °C, and finally resulted in the formation of amorphous Si–B–C–N ceramics. In particular, the Si–B–C–N ceramics formed from the hybrid precursor with PBN/PCS mass ratio of 1 could keep amorphous state up to the annealing temperature of 1800 °C with weight change of only 2.08%. But this amorphous ceramics would decompose to form crystalline SiC, BN and Si₃N₄ at 2000 °C. Additionally, compared with PCS-derived SiC ceramics, the Si–B–C–N ceramics showed improved anti-oxidation performance up to 1300 °C due to the formation of borosilicate layers covering the ceramics.     

Preparation of conductive Si/C/N/Ni ceramic nanocomposites using phenyl-substituted polysilazane and nickelocene as precursors

In this study, a conductive Si/C/N/Ni nanocomposite was prepared using phenyl-substituted polysilazane and nickelocene (NiCp₂) as precursors. Ni-related nanoparticles were uniformly distributed throughout the Si/C/N/Ni nanocomposite without aggregation because of the large number of nitrogen atoms in the silsesquiazane used as a precursor of the matrix. In addition, the nickel silicide crystalline phase and turbostratic carbon phase grew in the matrix of the Si/C/N/Ni nanocomposite at low temperatures because NiCp₂ acted as a catalyst. Moreover, NiCp₂ contributed to the increase in the turbostratic carbon crystallinity through the dehydrogenation reaction, resulting in an improved electrical conductivity of the Si/C/N/Ni nanocomposite.     

Paper derived SiC–Si3N4 ceramics for high temperature applications

Biomorphic Si₃N₄–SiC ceramics have been produced by chemical vapour infiltration and reaction technique (CVI-R) using paper preforms as template. The paper consisting mainly of cellulose fibres was first carbonized by pyrolysis in inert atmosphere to obtain carbon bio-template, which was infiltrated with methyltrichlorosilane (MTS) in excess of hydrogen depositing a silicon rich silicon carbide (Si/SiC) layer onto the carbon fibres. Finally, after thermal treatment of this Si/SiC precursor ceramic in nitrogen-containing atmosphere (N₂ or N₂/H₂), in the temperature range of 1300–1450 °C SiC–Si₃N₄ ceramics were obtained by reaction bonding silicon nitride (RBSN) process. They were mainly composed of SiC containing α-Si₃N₄ and/or β-Si₃N₄ phases depending on the nitridation conditions. The SiC–Si₃N₄ ceramics have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and Raman spectroscopy. Thermal gravimetric analysis (TGA) was applied for the determination of the residual carbon as well as for the evaluation of the oxidation behaviour of the ceramics under cyclic conditions. The bending strength of the biomorphic ceramics was related to their different microstructures depending on the nitridation conditions.     

The characteristics of Ni–Co–Mn–O precursor and Li(Ni1/3Co1/3Mn1/3)O2 cathode powders prepared by spray pyrolysis

Ni–Co–Mn–O precursor powders with spherical shape and dense structure were prepared by spray pyrolysis from a spray solution containing a drying control chemical additive (DCCA) and polymeric precursors. In contrast, the Ni–Co–Mn–O precursor powders obtained from a spray solution without additives had a hollow and porous morphology. Ni–Co–Mn–O precursor powders with a spherical shape and dense structure yielded Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode powders with a spherical shape and fine size by means of a solid-state reaction with lithium hydroxide. The mean size of the spherical cathode powder was 1.1 μm. The discharge capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O₂ powders with spherical shape and filled morphology was 195 mA h g⁻¹ at a current density of 0.1 C. The discharge capacities of the cathode powders with spherical shape and filled morphology at 55 °C decreased from 183 to 154 mA h g⁻¹ by the 30th cycle at a current density of 0.5 C.     

Synthesis and growth of SiC/SiO2 nanocables decorated with laminated porous ceramics from filter paper and polymericprecursor

A simple and efficient way to synthesize the SiC/SiO₂ nanocables decorated with the laminated porous ceramics by pyrolysis of filter papers impregnated with silicone resins in flowing argon atmosphere has been successfully developed. The phase composition of the laminated porous ceramics was measured by X-ray diffraction. The morphology and microstructure of the samples were analyzed by scanning electron microscopy and transmission electron microscopy. The experimental results show that the nanocables composed of crystalline SiC core coated with a shell of amorphous SiO₂ were observed in the interfacial channels and pores of the laminated ceramics. The diameters of SiC cores were 40–80 nm and the thicknesses of SiO₂ shells were 4–10 nm. The increase of the pyrolysis temperature caused an increase in the amount of SiC/SiO₂ nanocables. Finally, a vapor–liquid–solid (VLS) process was discussed as the growth mechanism of the nanocables.     

Up-scalable preparation of nano zirconium carbide powder in liquid polymeric precursor and its pyrolysis mechanism

Nano size ZrC powder was prepared by liquid polymeric precursor method. Zirconium n-butoxide (Zr(OⁿBu)₄) and benzoylacetone (BA) were mixed directly with different molar ratios to synthesize transparent liquid zirconium carbide single-source precursors. The carbon content in the precursor could be changed by adding different amount of BA. X-ray pure ZrC was obtained when the molar ratio of BA/Zr(OⁿBu)₄ was 4.6:1. The viscosity of the precursor was very low (<8 mPa s) without the addition of solvents. Zirconium carbide powders were fabricated by the pyrolysis at 800 °C in argon and subsequent heating at various temperatures in vacuum for carbothermal reduction reaction. The pyrolysis behavior, phase composition and transformation, and microstructure of the as-fabricated ZrC powders were analyzed. The gases of CH₄, CO and CO₂ released due to decomposition and evaporation of the organic component and transformation from ZrO₂ to ZrC during pyrolysis resulted in total 60–70% mass loss. The average grain size of the synthesized X-ray pure ZrC powders was less than 30 nm. Meanwhile, the pyrolysis mechanism of nano zirconium carbide powder was deduced.     

Preparation and characterization of carbon membranes made from poly(phthalazinone ether sulfone ketone)

Carbon membranes were prepared from a novel polymeric precursor of poly(phthalazinone ether sulfone ketone) (PPESK), of which the changes of microstructure and chemical compositions during pyrolysis from 500 °C to 950 °C were monitored by thermal gravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It has been found that the weight loss of the PPESK precursor up to 800 °C is about 43.0 wt%. After the heat treatment, the typical chemical structure of the PPESK precursor disappears, at the same time a graphite-like structure with more aromatic rings is formed. The interlayer spacing (i.e., d value) decreases from 0.471 nm to 0.365 nm as the pyrolysis temperature increases. The gas permeation performance of carbon membranes has been tested using pure single gases including H₂, CO₂, O₂ and N₂. For the carbon membrane obtained by carbonizing the PPESK precursor at 800 °C, the maximum ideal permselectivities for H₂/N₂, CO₂/N₂ and O₂/N₂ gas pairs could reach 278.5, 213.8 and 27.5, respectively.     

Facile synthesis of hexagonal boron nitride fibers with uniform morphology

Hexagonal boron nitride (h-BN) fibers were synthesized via the polymeric precursor method using boric acid (H₃BO₃) and melamine (C₃H₆N₆) as raw materials. The precursor fibers were synthesized by a water bath and BN fibers were prepared from the precursor at 1600 °C for 3 h in flowing nitrogen atmosphere. The products were characterized by X-ray powder diffraction, Fourier transformation infrared spectroscopy, thermogravimetry and scanning electron microscopy. The results showed that h-BN fibers with uniform morphology were successfully fabricated. The well-synthesized fibers were 1–2 μm in diameter and 200–500 μm in length.     

前驱体法制备Si-C-N-M基高性能陶瓷的研究进展

综述了聚合物前驱体热解转化法制备高性能Si-C-N-M基陶瓷的研究进展，着重介绍了3类Si-C-N-B基陶瓷前驱体（主链或侧基含有环硼氮烷或含硼杂环的聚硼硅氮烷、含硼聚硅氮烷和含硼聚硅基碳化二亚胺）及Si-C-N-Al基陶瓷前驱体。     

Synthesis of CuGa2O4 nanoparticles by precursor and self-propagating combustion methods

Copper gallate spinels, CuGa₂O₄, have been synthesized by two wet chemical routes: precursor method and self-propagating combustion involving a glycine-nitrate system. All complex precursors have been characterized by chemical analysis, infrared spectroscopy (IR), ultraviolet visible spectroscopy (UV–vis), electron paramagnetic resonance spectroscopy (EPR), thermal analysis and scanning electron microscopy (SEM). The copper gallate spinel oxides have been further investigated by X-ray diffraction (XRD), SEM, IR, UV–vis, magnetic measurements and EPR. The crystallite size of the copper gallate was found about 280 Å.     

Evaluation of plasma sprayed alumina–40 wt% titania and partially stabilized zirconia coatings on high density graphite for uranium melting application

Ceramic coatings have been proposed on high density graphite crucibles for the application of uranium consolidation and distillation of molten salt in pyrochemical reprocessing of metallic fuels. Towards this, uranium melting experiments were carried out on plasma sprayed partially stabilized zirconia (PSZ) and Al₂O₃–40 wt% TiO₂ (A40T) coated high density graphite samples at 1350 °C using induction heating system for evaluating the compatibility of these coatings with molten uranium. The coated high density graphite samples were characterized before and after uranium melting test by scanning electron microscopy attached with energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy. Microstructural observations revealed that no significant reaction layer or product was formed between uranium and PSZ coating, while uranium significantly adhered to A40T coating. PSZ coating offers better stability and protection to high density graphite crucibles from the chemical attack by molten uranium.     

Polysiloxane‐Derived Ceramics Containing Nanowires with Catalytically Active Tips

By direct foaming of a Pt‐containing polysiloxane precursor, macroporous ceramics were generated by pyrolysis at 1400°C under nitrogen or argon. The growth of nanowires was induced via a vapor–liquid–solid mechanism in which the Pt particles acted as deposition site for the decomposition gases released upon pyrolyzing the preceramic polymer. SEM, HR‐SEM, TEM/EDX, and XRD investigations revealed that pyrolysis under argon atmosphere leads to short SiC nanowires of only a few micrometers length and under nitrogen atmosphere Si₃N₄ nanowires evolved, with length of several 10 μm. In both cases the tips of the nanowires mainly consisted of PtSi. In contrast to samples pyrolyzed at 600°C, the components after higher temperature pyrolysis showed moderate‐specific surface areas of 55–67 m²/g. In CO oxidation experiments, a good catalytic activity was found for the Pt silicide particles, suggesting that despite their relatively large size, their location at the tips of the nanowires affords them good reactivity.     

Polymeric liquid precursor of multi-component ZrC–SiC ceramic

Polymeric liquid ceramic precursors for the production of multi-component ZrC–SiC ceramics were prepared by reactive blending of polyzirconoxanesal, phenylacetylene-terminated polysilane and bisphenol-A type benzoxazine. The polymeric liquid precursors of ZrC–SiC ceramic have the processing capability of Precursor-Infiltration-and-Pyrolysis technique in ceramic composites fabrication. The thermal cure reactions included by the catalytic polymerisation of ethynyl groups, the ring opening polymerisation of benzoxazine rings, and the condensation of zirconate with phenolic hydroxyl and Si–H at 200–350°C. The monolithic ceramics were formed upon pyrolysis at 1000, 1200 and 1600°C in a yield of 65, 62 and 40%, respectively. X-ray diffraction and SEM–EDS results revealed that almost pure, elemental, uniformly distributed ZrC–SiC multi-component ceramic monolith was obtained through pyrolysis at 1600°C via carbothermal reduction of ZrO₂.     

High-temperature phase and microstructure evolution of polymer-derived SiZrCN and SiZrBCN ceramic nanocomposites

A zirconium and a zirconium/boron containing single-source precursor were synthesized via chemical modification of a commercially available polysilazane (Durazane 1800) with tetrakis (dimethylamido) zirconium (IV) (TDMAZ) as well as with both TDMAZ and borane dimethyl sulfide complex, respectively. The polymer-to-ceramic transformation of the precursors into SiZrCN and SiZrBCN ceramics as well as the thermal evolution of their phase composition and microstructure was studied. The pyrolysis of the precursors led to the formation of amorphous SiZrCN and SiZrBCN ceramics. Interestingly, the as prepared SiZrBCN ceramic was single-phasic and fully featureless; whereas SiZrCN exhibited the presence of nano-sized ZrO₂ particles; however, only very localized in close proximity to internal surfaces. Heat treatment at higher temperatures induced crystallization processes in both prepared ceramics. Thus, at temperatures beyond 1500°C, cubic ZrC_xN_y, β-Si₃N₄ as well as β-SiC were generated. It was shown that the incorporation of B into SiZrCN suppressed the crystallization of ZrC_xN_y and, in addition, impeded the reaction of SiN_x with C, resulting in an improved thermal stability of SiZrBCN compared to SiZrCN ceramic. Moreover boron was shown to be mainly located in the sp²-hybridized “free” carbon present in SiZrBCN, forming a turbostratic BCN phase which has been unequivocally detected by means of high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDS).     

Synthesis of lanthanum beta-alumina powders by the polymeric precursor technique

La-β-Al₂O₃ (LaAl₁₁O₁₈) powders were synthesized by the polymeric precursor technique using lanthanum nitrate and aluminum nitrate. The transformations during thermal treatment of the precursor solution with ethylene glycol and citric acid were evaluated by thermal analysis. Fourier transform infrared spectroscopy analysis was performed after calcinations of the polymeric resin for determination of residual carbon. The specific surface area was evaluated by the BET method. Fine powders with ∼121 m²/g specific surface area and 20 nm average particle size were obtained and observed by scanning and transmission electron microscopy. Nearly single phase LaAl₁₁O₁₈ was obtained after pressing and sintering these powders at 1600 °C with small additions of MgO. The sintered pellets were characterized by X-ray diffraction and scanning electron microscopy. Impedance spectroscopy measurements carried out in the 1000–1200 °C range show the electrolytic behavior of the La-β-Al₂O₃ pellets, suggesting their application as solid electrolytes in high temperature potentiometric oxygen sensors.     

Molecular design for thermally stable SiZrBOC structure from single source precursor with high ceramic yield

A new type of high-temperature-resistant SiZrBOC ceramics was prepared by sol-gel method using polymethyl-hydro siloxane (PMHS), boric acid (B(OH)₃), and n-propyl zirconate (Zr(OPr)₄) as raw materials. After high-temperature pyrolysis, the SiZrBOC precursor was transformed into a crystalline ceramic material with a yield of 89.5 wt%. Fourier infrared spectroscopy (FT-IR) and thermogravimetric analysis (TGA) were applied to characterize the polymer-ceramic conversion process and thermal behavior of ceramic precursors. According to the results, the addition of boron elements led to the formation of Si-O-B links in the system. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to study the phase composition and microstructure of SiZrBOC ceramics. Finally, the oxidation test at 1200 °C revealed that SiZrBOC ceramics with a boron/zirconium molar ratio of 2.5:1 exhibited the best oxidation resistance at a weight gain of 0.4 wt% only.     

The synthesis of SiCON ceramics through precursor method

A polymeric precursor, polysiloxazane (PSON), for SiCON ceramics has been synthesized by the partial hydrolysis of MeViSiCl₂, MeHSiCl₂, and MeSiCl₃ followed by ammonolysis reaction of the hydrolyzed intermediates with NH₃. The structure and thermal properties of the polymeric precursor were investigated by means of Fourier transfer infrared spectra (FTIR), ¹H‐NMR, ²⁹Si‐NMR, gel permeation chromatography, and thermogravimetric analysis. The structure of the SiCON ceramics derived from the pyrolysis of PSON was characterized by FTIR and X‐ray diffraction. The as‐synthesized PSON produced mainly α‐Si₃N₄ crystalline phase during pyrolysis at 1500°C under N₂ atmosphere, whereas when pyrolyzed at 1500°C under Ar atmosphere, crystalline phases of α/β‐SiC and/or α‐Si₃N₄ were detected. © 2012 Wiley Periodicals, Inc. J fAppl Polym Sci, 2012     

Low-temperature synthetic route for boron carbide

Boron carbide is one of the hardest materials with diamond-like mechanical properties, and is already used for a variety of applications including armor plating, blasting nozzles, and mechanical seal faces, as well as for grinding and cutting tools. It is produced on an industrial scale by classical carbothermal reduction of boric oxides at high temperatures, but the formation of pure boron carbide in processed forms, such as films and fibers, is difficult. As an alternative to high-temperature powder techniques, there is recently great interest in the development of polymer precursors to produce ceramic materials. The aim of the present work is to develop a cost effective and low-temperature manufacturing process to synthesize boron carbide from cheap and easily available raw materials. The initial objective of our research is the design and synthesis of a new type of boron–carbon polymer, which would serve as precursor for boron carbide. The polymeric precursor is synthesized by the reaction of boric acid and polyvinyl alcohol that after pyrolysis at 400 °C and 800 °C gives boron carbide. The polymeric precursor and its pyrolyzed products are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). X-ray diffraction shows that boron carbide (B₄C) obtained from this method has an orthorhombic crystal structure. It is a unique low-temperature (∼400 °C) synthetic route for boron carbide.     

Micro-crystallization of the infrared transmitting chalcogenide glass in GeSe2–As2Se3–PbSe system

Micro-crystallization of the chalcogenide glass 40GeSe₂–50As₂Se₃–10PbSe has been studied in order to obtain infrared transmitting glass ceramics. Differential scanning calorimetry, IR transmission spectroscopy, X-ray diffraction, scanning electronic microscopy and thermal dilatancy have been used for characterizing the crystallization process. Performing thermal treatment on the glass sample at 250 °C (40 °C higher than T_g) for 10 h, we obtained a glass ceramic containing well-dispersed micro-crystals (<50 nm) and the obviously decreased thermal expansion coefficient.