Synthesis and pyrolysis mechanism of a novel polymeric precursor for SiBN ternary ceramic fibers

A novel polymeric precursor polyborosilazane (PBSZ) for SiBN ternary ceramic fibers was successfully synthesized from trichlorosilane (HSiCl₃), boron trichloride (BCl₃) and hexamethyldisilazane (HDMZ) by a simple one step reaction process. The chemical structures and ceramic yield of the PBSZ precursors were investigated by NMR spectroscopy, FT-IR and TGA. The preparation of PBSZ fibers was conducted in a lab-scale melt-spinning equipment at a spinning speed of 130 m/min. SiBN ternary ceramic fibers were obtained after the non-fusible treatment and pyrolysis of PBSZ fibers in an NH₃ atmosphere. The pyrolysis mechanism, high-temperature behavior and morphologies of the SiBN ternary ceramic fibers were investigated by NMR, XRD, TEM and SEM. The obtained SiBN ternary ceramic fibers had good flexibility, and possessed a tensile strength of 0.84 GPa with a diameter of ∼18 μm. Furthermore, these SiBN ceramic fibers exhibited excellent thermal stability, and maintained the amorphous state up to 1600 °C.     

硅硼氮纤维前驱体聚合物的扩链反应改性

以柔性链遥爪聚合物[双(3-氨丙基)封端的聚二甲基硅氧烷(BTA-PDMS)]为扩链剂,对聚硅硼氮烷进行扩链反应改性,既可以提高其相对分子质量,又在刚性分子链中引入柔性链段,这显著改善了前驱体聚合物纤维的柔韧性,有望实现易退绕的目的。     

新型耐高温氮化物陶瓷纤维研究进展

介绍了耐高温氮化物陶瓷纤维的种类及制备方法即有机聚合物先驱体转化法;综述了Si3N4,BN,SiBN,SiBN(C)陶瓷纤维的研究进展;重点介绍了SiBN(C)陶瓷纤维的研究现状,并与SiC纤维进行性能对比.指出具有耐高温、透波性等功能结构一体化的SiBN(C)陶瓷纤维是陶瓷纤维的重要发展方向,简化先驱体的合成过程及降...     

Pyrolysis of polyborosilazane and its conversion into SiBN ceramic

Abstract

The polyborosilazane was prepared by coammonolysis of boron trichloride and methyldichlorosilane with hexamethyldisilazane. The decarburisation process of the polyborosilazane under ammonia was studied. The results suggested carbon was effectively removed under ammonia and the removal of carbon mainly occurred during the temperature range of 400–600°C. After pyrolysed at 900°C under ammonia, the carbon content was only 0·29 wt-%. Further heat treatment at 1500°C under argon yielded SiBN ceramic. The structure and morphological properties of SiBN ceramic were studied by solid ²⁹Si nuclear magnetic resonance, X-ray diffraction and scanning electron microscopy. The results showed that the SiBN ceramic was amorphous and possessed a smooth surface. The contents of boron, silicon and nitrogen in the SiBN ceramic are 10·9, 42·6 and 38·48 wt-% respectively.     

Effects of boron content on the microwave-transparent property and high-temperature stability of continuous SiBN fibers

Owing to their high-temperature stability and microwave-transparent properties, SiBN fibers are promising reinforcement materials for microwave windows or radomes in harsh environments. This work investigates the high-temperature properties of continuous SiBN fibers with different boron contents. Compared with Si₃N₄ fibers, the SiBN fibers demonstrated superior high-temperature stability, retaining their original tensile strength up to 1600°C with a smooth surface and amorphous structure. The boron-containing microstructure improved the microwave-transparent properties of the SiBN fibers by decreasing their dielectric constant and loss. The values were stabilized at temperatures up to 1200°C. The high-temperature stability and microwave transparency of the SiBN fibers were likely contributed by the synergistic effect of the amorphous BN phase and the Si–N–B networks (the main existing state of the boron atoms).     

LaPO4 coating on alumina-based fiber: Strength retention of fiber and improvement of interfacial performances

The characteristics of the interface are the key factors that determine the mechanical properties and fracture behavior of fiber-reinforced ceramic matrix composites. Design and preparation of coatings which can preserve fiber strength and maintain appropriate interfacial bonding strength are of great challenges. LaPO₄ coating is a promising weak interface coating for oxide fiber reinforced oxide ceramic matrix composites. Through this coating, the toughening mechanism of the composite such as fiber pulling out and fiber debonding is triggered. The LaPO₄ coating was deposited on the surface of alumina-based fibers by a solution precursor heterogeneous precipitation method. The effects of different precursors and different deposition temperatures on fiber strength were studied, and the mechanism of the strength degradation of the coated fiber was analyzed. It was found that the fibers coated with phytic acid precursor and deposited at 90 °C had the highest tensile strength compared to other coated fibers. The retention of strength is attributed to its loosely stacked coating. Besides, a single fiber pullout test was carried out to evaluate the effect of the coating on the interface of the composites. The results show that the composites coated by depositing citric acid precursor and phytic acid precursor at 90 °C can reduce the interfacial bonding strength by 32.5% and 46.7%, respectively compared to uncoated composites. This study has potential application value in the preparation of ceramic matrix composites used in oxidation and high temperature environments.     

SiBN(C)陶瓷纤维先驱体的表征及熔融纺丝

以B(NHCH3)3和Si(NHCH3)4为小分子先驱体,在一定条件下通过共缩聚反应得到聚硅硼氮烷,经熔融纺丝得到SiBN(C)陶瓷先驱体纤维;采用红外光谱、核磁共振、元素分析等手段研究了小分子先驱体的配比对聚硅硼氮烷结构的影响.结果表明:聚硅硼氮烷存在B-N六元环、Si-N、Si-N-B、N-H等主要官能团,熔融纺丝...     

Effect of silica sol on phase transition of alumina-mullite fibers

Duplex oxide ceramic fibers have excellent high temperature properties. However, controlling the microstructure of duplex oxide ceramic fibers is difficult and complexed. In this work, the effect of silica sols affecting the interaction of precursor sol-gel particles on the high-temperature phase transition and microstructure of alumina-mullite fibers was investigated. The results show that the silica sol affects the particle interactions and distribution in the mixed sol. Alumina-mullite fibers prepared from non-homogeneous precursor sols generated α-Al₂O₃ at 1400 °C, while fibers prepared from homogeneous precursor sols required higher temperatures. In addition, mullite (3Al₂O₃:2SiO₂) with an orthogonal structure is more likely to be generated in the non-homogeneous Al₂O₃-SiO₂ precursor sol. The prepared alumina-mullite fibers have a tensile strength of up to 1.68 GPa. Finally, the mechanism of the influence of silica-sol properties on the final organization of the alumina-mullite fiber was further discussed.     

Effect of high-pressure vapor pretreatment on the microstructure evolution and tensile strength of zirconia fibers

High-strength zirconia (ZrO₂) continuous fibers, which are potential candidates as ultra-high temperature thermal insulators and reinforced materials, are typically fabricated by dry spinning an organozirconium precursor. However, the uncontrolled decomposition of organozirconium precursor usually occurs upon heat treatment that breaks the continuous fibers into pieces, resulting in the loss of tensile strength. Herein, in this contribution, we aimed to maintain the integrity of ZrO₂ precursor fibers during heat treatment. For this purpose, novel high-pressure vapor (HPV) pretreatment of ZrO₂ precursor fiber was introduced. The HPV pretreatment is considered to be efficient for the removal of the organics in precursor, promoting the formation of amorphous structures of Zr(OH)₄ and Zr(OH)₃HCO₃. Combining the studies of microstructures and tensile strengths, it was found that the amorphous structures played roles of cross-linking points, keeping the fibers integrity during the followed heat treatment. After HPV pretreatment, the high-strength ZrO₂ continuous fibers would be obtained by direct sintering in air without any atmosphere which substantially lowered the cost. The tensile strengths of sintered ZrO₂ continuous fibers pretreated by an optimized HPV procedure could reach up to as high as 1.299 GPa. The HPV pretreatment method provides a high-efficiency, low-cost technique for preparing high-quality ceramic fibers.     

Flexible TiO2 ceramic fibers near-infrared reflective membrane fabricated by electrospinning

Titanium oxide is a potential high temperature reflective material due to its high melting point, large refractive index, and suitable band gap. The flexible TiO₂ ceramic fibers membrane was successfully fabricated by sol–gel method using the polyacetylacetonetitanium (PAT) as the precursor. In order to obtain high-quality TiO₂ fibers, the PAT precursor with good stability and good spinnability was optimized by adjusting the molar ratio of acetylacetone to Ti to 1:1. The TiO₂ fibers heat-treated at 700?°C had a diameter of 400–500?nm. The crystal phase of TiO₂ fibers was anatase, and the surface of fibers was smooth without obvious defects. In addition, the TiO₂ ceramic fibers membrane heat-treated at 700?°C had good flexibility and tensile strength, and the average reflectance in the wavelength range of 500–2500?nm was up to 91.3%. The fibers membrane exhibits a significant reflection effect in the practical experiments and maintained good morphology of the fibers after 1200?°C test.     

Hybrid effect on mechanical properties of M40‐T300 carbon fiber reinforced Bisphenol A Dicyanate ester composites

Interply and intraply hybrid composites based on Bisphenol A Dicyanate ester (BADCy), high strength carbon fibers T300, and high modulus carbon fibers M40 were prepared by monofilament dip‐winding and press molding technique. The tensile, flexural, interlaminar shear properties and SEM analysis of the hybrid composites with different fiber content and fiber arrangement were investigated. The results indicated that the mechanical properties of intraply hybrid composites were mainly determined by fiber volume contents. When the ratio of fiber volume content was close to 1:1, the intraply hybrid composites possessed lowest tensile and flexural strength. The mechanical properties of interply hybrid composite mainly depended on the fiber arrangement, instead of the fiber volume contents. The hybrid composites using T300 fiber layout as outside layer possessed high flexural strength and low flexural modulus, which was close to that of T300/BADCy composites. The hybrid composites ([(M40)_x/(T300)_y]_S) using M40 fiber layout as outside layer and T300 fibers in the mid‐plane had high flexural modulus and interlaminar shear strength. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Study of SiC fiber axial compressive behavior using tensile recoil measurement

SiC fibers have been widely investigated as reinforcements for advanced ceramic matrix composites owing to their excellent high-temperature properties. However, the axial compressive strength of SiC fibers has not been thoroughly studied. In this study, the compressive behavior of two SiC fiber types containing different compositions and thermal degradation were characterized by tensile recoil measurements. Results illustrated that the SiC fiber compressive strength was 30%–50% of its tensile strength, after heat treatment at 1200℃–1800℃ for 0.5 h in argon. The fiber compressive failure mechanism was studied, and a “shear-bending-cleavage” model was proposed for the recoil compression fracture of pristine SiC fibers. The average compressive and tensile strengths of the pristine SiC-II fiber were 1.37 and 3.08 GPa, respectively. After treatment at 1800℃ for 0.5 h in argon, the SiC-II fiber compressive strength decreased to 0.42 GPa, whereas the tensile strength reduced to 1.47 GPa. The mechanical properties of the fibers degraded after high-temperature treatment. This could be attributed to SiC grain coarsening and SiC_xO_y phase decomposition.     

Fabrication and Characterization of Glass‐Ceramic Fiber‐Containing Cr3 + ‐Doped ZnAl2O4 Nanocrystals

Glass‐ceramic fibers containing Cr³⁺‐doped ZnAl₂O₄ nanocrystals were fabricated by the melt‐in‐tube method and successive heat treatment. The obtained fibers were characterized by electro‐probe micro‐analyzer, X‐ray diffraction, Raman spectrum and high‐resolution transmission electron microscopy. In our process, fibers were precursor at the drawing temperature where the fiber core glass was melted while the clad was softened. No obvious element interdiffusion between the core and the clad section or crystallization was observed in precursor fiber. After heat treatment, ZnAl₂O₄ nanocrystals with diameters ranging from 1.0 to 6.3 nm were precipitated in the fiber core. In comparison to precursor fiber, the glass‐ceramic fiber exhibits broadband emission from Cr³⁺ when excited at 532 nm, making Cr³⁺‐doped glass‐ceramic fiber a promising material for broadband tunable fiber laser. Furthermore, the melt‐in‐tube method demonstrated here may open a new gate toward the fabrication of novel glass‐ceramic fibers.     

Producing high‐quality precursor polymer and fibers to achieve theoretical strength in carbon fibers: A review

The precursor fiber quality has a large impact on carbon fiber processing in terms of its performance, production yield, and cost. Polyacrylonitrile precursor fibers have been used commercially to produce strong carbon fibers with average tensile strength of 6.6 GPa. There is a scope to improve the average tensile strength of carbon fibers, since only 10% of their theoretical strength has been achieved thus far. Most attempts to increase the tensile strength of carbon fibers have been made during the conversion of precursor fiber to carbon fiber. This review highlights the potential opportunities to enhance the quality of the polyacrylonitrile‐based precursor fiber during polymer synthesis, spinning, and postspinning. These high‐quality precursor fibers can lead to new generation carbon fibers with improved tensile strength for high‐performance applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43963.     

Estimate of carbon fiber’s fracture toughness based on the small angle X-ray diffraction

According to the Weibull theory, the micropore sizes were used to analyze the stress intensity factor of carbon fiber monofilament crack tip stress field. Based on the analysis of carbon fiber monofilament and multifilament tensile strength, diameter and micropore size get the relationship between carbon fiber monofilament tensile strength and the pore radius by the Guinier principle and Griffith fracture theory, thus to estimate carbon fiber fracture toughness. The results show that this method can implement the estimation of fracture toughness on the basis without destroying the structure of the carbon fibers; the fracture toughness of T300 estimated by the average pore size was 1.34 MPa·m^1/2, in accordance with data 1.25 and 1.32 MPa·m^1/2 by producing defects, errors are 7.2 and 1.5%, respectively.     

Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

Nextel? 610 alumina fibers and alumina‐YAG (yttrium‐aluminum garnet) matrices were used to make oxide‐oxide ceramic matrix composites (CMCs) with and without monazite (LaPO₄) fiber‐matrix interfaces. Twelve sequential aluminum oxychloride (AlOCl) infiltrations with 1 hour heat treatments at 1100°C and a final 1 hour heat treatment at 1200°C were used for matrix densification. This matrix processing sequence severely degraded CMC mechanical properties. CMC tensile strengths and interlaminar tensile (ILT) strengths were less than 10 MPa and 1 MPa, respectively. Axial fracture of Nextel? 610 fibers was observed after ILT testing, highlighting the extreme degradation of fiber strength. Extensive characterization was done to attempt to determine the responsible degradation mechanisms. Changes in Nextel? 610 fiber microstructure after CMC processing were characterized by optical microscopy, SEM, and extensively by TEM. In AlOCl degraded fibers, grain boundaries near the fiber surface were wetted with a glass that contained Y₂O₃/SiO₂ or Y₂O₃/La₂O₃/P₂O₅/SiO₂, and near‐surface pores were partially filled with Al₂O₃. This glass must also contain some Al₂O₃ and initially some chlorine. AlOCl decomposition products were predicted using the FactSage^® Thermochemical code, and were characterized by mass spectrometry. Effects of AlOCl precursors on monazite coated and uncoated Nextel? 610 fibers tow and filament strength were evaluated. A mechanism for the severe degradation of the oxide‐oxide CMCs and Nextel? 610 fibers that involves subcritical crack growth promoted by release of chlorine containing species during breakdown of intergranular glasses in an anhydrous environment is proposed.     

Plasma etching and plasma polymerization coating of carbon fibers. Part 2. Characterization of plasma polymer coated carbon fibers

Unsized AS-4 carbon fibers were subjected to RF plasma etching and/or plasma polymerization coating in order to enhance their adhesion to vinyl ester resin. Ar, N₂ and O₂ were utilized for plasma etching, and acetylene, butadiene and acrylonitrile were used for plasma polymerization coating. Etching and coating conditions were optimized in terms of plasma power, treatment time, and gas (or monomer) pressure by measuring the interfacial adhesion strength. Interfacial adhesion was evaluated using micro-droplet specimens prepared with vinyl ester resin and plasma etched and/or plasma polymer coated carbon fibers. Surface modified fibers were characterized by SEM, XPS, FT-IR, α-Step, dynamic contact angle analyzer (DCA) and tensile strength measurements. Interfacial adhesion between plasma etched and/or plasma polymer coated carbon fibers and vinyl ester resin was reported previously (Part 1), and characterization results are discussed is this paper (Part 2). Gas plasma etching resulted in preferential etching of the fiber surface along the draw direction and decreased the tensile strength, while plasma polymer coatings altered neither the surface topography of fibers nor the tensile strength. Water contact angle decreased with plasma etching, as well as with acrylonitrile and acetylene plasma polymer coatings, but did not change with butadiene plasma polymer coating. FT-IR and XPS analyses revealed the presence of functional groups in plasma polymer coatings.     

Synthesis,pyrolysis of a novel liquid SiBCN ceramic precursor and its application in ceramic matrix composites

SiBCN ceramic precursor, polyborosilazane, was synthesized through a novel method which used sodium borohydride as boron source. Vinyl silazane with SiCl was converted to vinyl silazane with SiH structure, followed by hydroboration reaction and subsequent high-temperature reaction to form soluble polyborosilazane liquid. The process of precursor-to-ceramic conversion was almost completed before 800 °C and the cross-linked polyborosilazane precursor exhibited higher ceramic yield 75.6% at 1200 °C. The SiBCN ceramic annealed at 1400 °C contained BN, SiN and SiC bonds with smooth and dense surface and still retained principally amorphous structure up to 1600 °C. In addition, the viscosity of the polyborosilazane was 65 mPa.s, which can efficiently prepare ceramic matrix composite by means of precursor infiltration and pyrolysis (PIP). The density of as-obtained ceramic matrix composite (CMC) was 1.82 g/cm³, and the average bending strength, bending modulus and tensile strength were 265.2 MPa, 37.5 GPa and 158.6 MPa, respectively.     

A novel polyborosilazane for high-temperature amorphous Si–B–N–C ceramic fibres

Polyborosilazane synthesised from BCl₃, HMeSiCl₂, and Me₃SiNHSiMe₃ is easy to cross-link for dehydrogenation of Si–H and N–H, which limits its practical applications for Si–B–N–C fibres on an industrial scale. Therefore, in this context, MeSiCl₃ was used instead of HMeSiCl₂ to synthesise a novel polyborosilazane with limited cross-linking density to fabricate Si–B–N–C fibres. The polyborosilazane synthesised from BCl₃, MeSiCl₃, and Me₃SiNHSiMe₃ exhibits good melt-processability and 1 km long polyborosilazane fibre can be obtained by melt spinning. Prior to pyrolysis, chemical curing with vapour HSiCl₃ at 80 °C was utilised to make the λ green fibres infusible. The as-cured fibres were subsequently pyrolyzed at 1200 °C in nitrogen atmospheres to provide Si–B–N–C ceramic fibres with ca. 1.5 GPa in tensile strength, ca. 160 GPa in Young's modulus, ca. 12 μm in diameter and keeping amorphous up to 1700 °C, which makes them to be promising reinforcements in ceramic matrix composites for high temperature applications.     

Effect of high-pressure vapor on the microstructure and mechanical properties of TiO2 continuous fibers

During the preparation of TiO₂ continuous fibers, the organic ligands of the precursor fibers are severely decomposed and generated a large amount of gas, which can reduce the fiber matrix strength. Tt is necessary to choose a suitable treatment strategy to avoid this and obtain high-quality TiO₂ continuous fibers. In this study, flexible continuous TiO₂ fibers with a diameter of about 30 μm were prepared using a high-pressure vapor pretreatment method. The high-pressure vapor pretreatment caused precursor hydrolysis, which promoted the decomposition of the organic ligands in a mild way and prevented fiber fracture caused by the violent oxidative decomposition. The crystallization temperature decreased by 120 °C because of the synergistic effects of vapor and pressure. The hydrolysis of the precursor and the reduction in the crystallization temperature were conducive to the formation of compact fibers with high strength. However, the presence of water vapor caused the fibers to undergo the dissolution-precipitation process simultaneously, forming a large number of defects, which was harmful to its strength. The sample 1501 composed of anatase and rutile showed the highest average tensile strength of 385 MPa because it had fewer defects than the other samples. Although the highest average tensile strength is lower than the reported value of 800 MPa, the method is easy to implement and solves the problem of organics decomposition, which is helpful for industrial preparation.