Zirconia-alumina multiphase ceramic fibers with exceptional thermal stability by melt-spinning from solid ceramic precursor

Zirconia-alumina multiphase ceramic fibers with 80 wt% (Z80A20 fiber) and 10 wt% (Z10A90 fiber) proportions of zirconia were prepared via melt-spinning and calcination from solid ceramic precursors synthesized by controllable hydrolysis of metallorganics. The zirconia-alumina multiphase fibers had a diameter of about 10 µm and were evenly distributed with alumina and zirconia grains. The Z80A20 and Z10A90 ceramic fibers had the highest filament tensile strength of 1.78 GPa and 1.87 GPa, respectively, with a peak value of 2.62 GPa and 2.71 GPa. The Z80A20 ceramic fiber has superior thermal stability compared to the Z10A90 ceramic fiber and a higher rate of filament strength retention due to the stability in grain size. After heat treatment at 1100 °C, 1200 °C, and 1300 °C for 1 h respectively, the filament tensile strength retention rate of Z80A20 ceramic fibers was 87 %, 80 %, and 40 %. While Z10A90 ceramic fiber was fragile after being heated at 1300 °C. The results showed that the high zirconia content facilitated the fiber's thermal stability.     

Effect of hafnium oxide on continuous aluminum oxide-mullite-hafnium oxide composite ceramic fibers

The Al₂O₃-mullite-HfO₂ (AMH) ceramic fiber with a 20 wt% of HfO₂ has demonstrated good tensile strength and good high-temperature stability due to the tiny diameter and small grains even at high temperatures. To investigate the effect of HfO₂ on crystal behavior and high-temperature performance, continuous AMH ceramic fibers with different HfO₂ contents (0 wt%, 10 wt%, and 50 wt%) were prepared by melt-spinning of polymer precursors. The effect of HfO₂ on the crystal form transition process, mechanical properties, and high-temperature resistance of AMH fibers was studied by in-situ XRD and STEM. The AMH fibers with 50 wt% HfO₂ had the highest strength retention rate of 78.33% after heat treatment at 1200 °C for 0.5 h. After 0.5 h of heat treatment at 1500 °C, the grain size of the AMH fibers with 50 wt% HfO₂ was still less than 200 nm.     

Preparation and stereolithography of SiC ceramic precursor with high photosensitivity and ceramic yield

Stereolithography of ceramic precursors is a valuable additive manufacturing technology for complex ceramic parts. In this study, a new SiC ceramic precursor—liquid hyperbranched polycarbosilane (LHBPCS) grafting acrylate group was synthesized by chlorinating some Si–H groups of LHBPCS with Cl₂ followed by reacting with hydroxyethyl acrylate. The reaction processes and structures of intermediate reactant and target product were confirmed by FT-IR and ¹H NMR. According to photolithography experiment and hardness test under UV light, the synthesized LHBPCS had high photo-curing activity. Thermogravimetric analysis indicated it also possessed high ceramic yield (the ceramic yield at 1000 °C was 74.4%). After shaping with stereolithography, defect-free green bodies could be got. When heated to 1000 °C, the transparent yellow green bodies transformed into black SiC rich ceramic parts and 18.3–25.1% linear shrinkage associated with the precursor-to-ceramic conversion was observed. Because the shrinkage in the pyrolysis stage was nearly isotropic and the shrinkage was lower than other reported data, no obvious deformation or crack was found in the pyrolyzed parts.     

Enhancing thermal stability of oxide ceramic matrix composites via matrix doping

To overcome the main limitation of oxide ceramic matrix composites (Ox-CMCs) regarding thermal degradation, the use of matrix doping is analyzed. Minicomposites containing Nextel 610 fibers and alumina matrices with and without MgO doping were produced. The thermal stability of the minicomposites was evaluated considering their microstructure and mechanical behavior before and after thermal exposures to 1300 °C and 1400 °C for 2 h. Before heat treatment, both composite types showed very similar microstructure and tensile strength. After heat treatment, densification, grain growth and strength loss are observed. Furthermore, the MgO dopant from the matrix diffuses into the fibers. As a result, abnormal fiber grain growth is partially suppressed and MgO-doped composites show smaller fiber grains than non-doped composites. This more refined microstructure leads to higher strength retention after the heat treatments. In summary, doping the matrix can increase the overall thermal stability without impairing the room-temperature properties of Ox-CMCs.     

Modification of polycarbosilane as a precursor with high ceramic yield for oxygen-free SiC fibers

Polycarbosilane (PCS) was modified by addition of 1 wt% polyborazine and subsequent heat treatment at 70-400 °C. The modified PCS exhibited highly improved ceramic yield from original 63% to 78% by heating at 70 °C for 10 h. The molecular weight of the PCS modified at higher temperatures markedly increased, then was rendered infusible but soluble PCS in organic solvent on heating at 300 °C. H-NMR indicated that original PCS was enhanced by dehydrocoupling reaction between Si-H groups. Solution of the modified PCS was hand-drawn to fibers, followed by direct pyrolysis up to 1,400 °C without air-curing step to convert into oxygen-free SiC fibers. The morphology and crystalline phase were determined by SEM and XRD analysis, respectively. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8-10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University. Mr. Cao worked at CNU under co-advisor system.     

Preparation of highly crystalline titanium-based ceramic microfibers from polymer precursor blend by needle-less electrospinning

The aim of the present contribution is to study the influence of the post-spinning heat - treatment of single TiO₂/PVP precursor fibers on the properties and morphology of the final titanium-based microfibers. The post-spinning treatment conditions were: calcination in air at 450–600?°C and pyrolysis in argon at 1000–1700?°C. Calcination resulted in a production of anatase-rich and pure rutile fibers. The use of an alternative sintering method, the low-temperature plasma treatment, led to the crystallization of the composite Magnéli phases/polymer fibers. As a result of the same one precursor, pyrolysis at 1000?°C, the Carbon/TiO₂ composite fibers were obtained. Rising the treatment temperature in inert atmosphere led to the formation of the titanium carbide fibers. The formation process and all the obtained products were characterized by differential scanning calorimetry accompanied with thermogravimetric analysis (DSC/TGA), scanning and transmission electron microscopy (SEM, TEM), X-ray diffraction (XRD), and image analysis techniques.     

Oxidation resistance and thermal stability of the SiC-ZrB2 composite ceramic fibers

In this study, continuous SiC-ZrB₂ composite ceramic fibers were synthesized from a novel pre-ceramic polymer of polyzirconocenecarbosilane (PZCS) via melt spinning, electron beam cross-linking, pyrolysis, and finally sintering at 1800°C under argon. The ZrB₂ particles with an average grain size of 30.7 nm were found to be uniformly dispersed in the SiC with a mean size of 59.7 nm, as calculated using the Scherrer equation. The polycrystalline fibers exhibit dense morphologies without any obvious holes or cracks. The tensile strength of the fibers was greater than 2.0 GPa, and their elastic modulus was ~380 GPa. After oxidation at 1200°C for 1 hour, the strength of the fibers did not decrease despite a small loss of elastic modulus. Compared to the advanced commercial SiC fibers of Tyranno SA, the fibers exhibited improved high-temperature creep resistance in the temperature range 1300-1500°C.     

Fabrication and characterisation of boron doped barium stabilised bismuth cobalt oxide nanocrystalline ceramic composite

Abstract

In this paper, the fabrication and characterisation processes of both boron doped and undoped barium stabilised bismuth cobalt oxide nanocrystalline ceramic powders using polymeric precursor were reported. Obtained boron doped barium stabilised bismuth cobalt oxide nanocrystalline ceramic powders, which have been synthesised by polymeric precursor technique at temperatures below 900°C and at atmospheric condition, were characterised by X-ray diffraction, Fourier transform infrared and scanning electron microscopy techniques. According to X-ray results, fcc and bcc phases coexist in the samples of the nanocrystalline ceramic powders. Crystallite sizes for body centred cubic structure were calculated using Scherrer equation for both boron doped and undoped samples. In addition, lattice parameters were calculated for all samples.     

Single-source-precursor synthesis,microstructure and high temperature behavior of TiC-TiB2-SiC ceramic nanocomposites

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.     

Low-loss insulating-conductive ceramic composite with giant permittivity and high permeability using glass phase as separating layer

The control of dielectric loss in insulating-conductive ceramic composites is of great significance for the enhancement of the comprehensive performance of next-generation devices. In this work, a low-activity precursor co-sintering method was proposed to prepare low-loss BaTiO₃(BTO)/Ni_0.5Zn_0.5Fe₂O₄(NZFO) ceramic composite by using 2PbO–B₂O₃(PBO) glass as insulating layer. XRD and SEM were used to reveal the phase composition and the morphology of the composite. Results showed that the conductive networks can be successfully cut off by PBO glass separating layer inside the composite (1−x)BTO/xNZFO where x is the molar fraction of NZFO ferrite, giving rise to decreased dielectric loss in a wide compositional range between x=0.1–0.7 while retaining considerable effective permittivity and initial permeability. Excess amount of PBO glass is not favorable for the formation of separating layer due to the chemical reactions occurring between the constituent phases and the glass phase; meanwhile, accompanied by the decrement in dielectric loss, the initial permeability of the composite decreases linearly with increasing PBO content.     

Formation of inorganic (TaC,TaN) fibers by thermal decomposition of cellulose acetate–tantalum alkoxide precursor gel fibers

Precursor gel fiber was formed by extruding cellulose acetate spinning solution into Tantalum (Ta) pentaethoxide acetone solution in a coagulation bath. Gel formation must be due to the coordination of Ta to OH and CO groups on the pyranose ring. The resultant precursor gel fiber was converted into carbide (TaC) or nitride (TaN) fibers by pyrolyzing them in Ar, N₂, or NH₃ atmospheres. TaC and TaN fibers can be obtained near theoretical temperatures calculated from thermodynamics data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4320–4324, 2006     

前驱体热解法制备Al2O3的物相转变及其合成

本文着重考查了Al2O3的前驱体一碳酸铝铵沉淀的形成过程及煅烧过程物相变化，发现可通过调节反应条件和加入合适的表面活性剂，来控制碳酸铝铵晶核的形成及晶体的生长速度，有效地阻止了Al2O3的团聚，并在温度1150摄氏度下制备出分散的Al2O3，其平均粒径为－2um，比表面为－3m^2/g。     

Polymer-derived ceramic/graphene oxide architected composite with high electrical conductivity and enhanced thermal resistance

A low temperature method for the fabrication of architected ceramic composites contining graphene is developed based on the infiltration of lightweight graphene oxide (GO) micro-lattices with a preceramic polymer. Self-supported highly porous three-dimensional (3D) GO structures fabricated by direct ink writing are infiltrated with a liquid organic-polysilazane (a compound of Si, C, H, N), and subsequently pyrolyzed at temperatures of 800–1000?ºC to activate the ceramic conversion. These ceramic composites replicate the patterned GO skeleton and, whereas the graphene network provides the conductive path for the composite (electrical conductivity in the range 0.2–4?S?cm^?1), the ceramic wrapping serves as a protective barrier against atmosphere, temperature (up to 900?°C in air) and even direct flame. These structured composites also show hydrophobicity (wetting angle above 120°) and better load bearing capacity than the corresponding 3D GO lattice. The process is very versatile, being applicable to different liquid precursors.     

Elytra-mimetic ceramic fiber aerogel with excellent mechanical,anti-oxidation,and thermal insulation properties

High-performance thermally insulating aerogel with low density, high porosity, and low thermal conductivity characteristics was widely used in heat insulation. However, the large-scale application of aerogel was still limited by its brittleness and infrared radiation transparency at high-temperature. Fiber composite aerogel had achieved significant progress, but its anti-oxidation ability was poor, and its thermal insulation required further improvement at ultra-high temperatures. Herein, inspired by the structure of elytra, nanoparticle fiber (NF) was prepared by electrospinning of coaxial fiber loaded with opacifier and antioxidant nanoparticles. The NF was incorporated into the SiBCN aerogel to prepare NF/SiBCN ceramic fiber aerogel. The mechanical properties were improved by fiber networks. The shell structure increased the antioxidant properties. Heat conduction and heat convection were suppressed by the aerogel, while heat radiation was reduced by the coaxial fiber. The results showed that the ceramic fiber aerogel exhibited superior mechanical, antioxidant, and ultra-low thermal conductivity properties.     

A hybrid ceramic-polymer composite fabricated by co-curing lay-up process for a strong bonding and enhanced transient thermal protection

A hybrid ceramic-polymer composite is fabricated by a co-curing lay-up process by combining a carbon nanotube (CNT) reinforced ceramic composite thin film with a carbon fiber reinforced polymer (CFRP) composite substrate. The ceramic nanocomposite thin film has good flexibility, thermal conductivity and high temperature tolerance. The polymer composite substrate is a carbon fiber reinforced bismaleimide composite that is widely used in aerospace and automotive industries. Finite element analysis (FEA) is used to investigate the maximum survival temperature with different thicknesses of the ceramic nanocomposite. The resultant hybrid composite shows good structural integrity and displays a pull-off bonding strength up to 8.3?MPa. In addition, thermal study illustrates that such a flexible CNT reinforced ceramic composite can effectively protect CFRP in an elevated temperature environment by delaying transient thermal conduction.     

Design and synthesis of a novel spinnable polyborazine precursor with high ceramic yield via one-pot copolymerization

Synthesis of spinnable precursors with high ceramic yield is a crucial issue in BN fibers manufacturing by polymer-derived ceramics (PDCs) route. Spinnability and high ceramic yield are the basis of precursor processability, formability, and mechanical properties. Herein, based on DFT simulation, we designed and synthesized a novel polymer precursor poly[2-propylamino-4,6-bis(methylamino) borazine-co-tri(methylamino) borazine] (PPMAB) via a facile one-pot copolymerization strategy. The random copolymerization model of condensations was obtained through DFT calculation. The molecular chain structure, molecular weight, and molecular weight distribution were optimized by adjusting the synthesis conditions. The precursor PPMAB-1:1 with a high ceramic yield of 62.43% and concentrated molecular weight distribution (PDI < 1.3) was obtained. Rheological performance research revealed the excellent and stable spinnability of PPMAB-1:1 by the tunable viscosity and low flow activation energy (23.61 kJ/mol). As a demonstration of spinnability, continuous BN fiber with a fine diameter (>10 km, 7.60 ± 1.13 μm, and 1.6 GPa) was obtained after melt spinning. The present work effectively improved the ceramic yield and spinnability of polyborazine precursors. Simultaneously, it can be used extensively as a universal method to prepare multifunctional copolymers with precise structure control.     

Fabrication and characterization of TiO2/poly(dimethyl siloxane) composite fibers with thermal and mechanical stability

The mechanical stability of titania (TiO₂) nanofibers was improved by fabricating TiO₂/poly(dimethyl siloxane) (PDMS) composite fibers using a combination of hybrid electrospinning and sol‐gel methods, followed by heat treatment at 250°C for 3 h. The compositions (90/10, 80/20, and 70/30, w/w) of the TiO₂/PDMS composite fibers were varied by adjusting the flow rate of the PDMS sol with the flow rate of TiO₂ sol fixed. There was no significant change in morphology and average diameter of the as‐spun TiO₂/PDMS fibers after heat treatment. Both the tensile strength and modulus of the TiO₂/PDMS composite fibers increased gradually with increasing PDMS content up to 30 wt %. In addition, from the photo‐degradation reaction of methylene blue, the photocatalytic activity of TiO₂/PDMS composite fibers was strongly dependent on the TiO₂ content (%) in the composite fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Nanoplates forced alignment of multi-walled carbon nanotubes in alumina composite with high strength and toughness

Although the strengthening and toughening effects on ceramic composites are expected to be maximized by alignment of multi-walled carbon nanotubes (MWCNTs) in matrices, this concept has been rarely realized in practice due to the lack of convenient processing strategy. Here, the alignment of MWCNTs in alumina composite can be readily obtained by using α-Al₂O₃ nanoplates as raw powder. With the assistance of vacuum filtration and pressure in sintering, the highly aligned MWCNTs in alumina matrix are formed in in-plane direction. Accordingly, the strength and toughness in 1.5 wt% MWCNTs/alumina composite are improved by 58 % and 66 % with respect to monolithic alumina, respectively. Transmission electron microscopy observation reveals that the MWCNTs under great compressive residual stress are mainly embedded inside the grains, leading to much stronger grain boundaries. Meanwhile, the toughening effect is mainly attributed to the highly energy dissipating bridging and pullout, owing to the very effective load transfer.     

Enhanced surface area and thermal stability of mesoporous zirconia fibers modified by various oxides and the reinforcement mechanism

In the present work, four oxides (SiO₂, TiO₂, LaO_1.5, or CeO₂) were selected as additives to increase the surface areas and the pore wall stability of mesoporous zirconia (ZrO₂) fibers in virtue of enhancing the skeleton stability and hindering the grain growth. The preparation, characterization, and thermal evolution of mesoporous ZrO₂ fibers incorporated with different amounts of oxide additive and simultaneously combined with heat treatment via water vapour are presented. The effects of different oxide additives on the crystallization and phase transformation of mesoporous ZrO₂ fibers were investigated by X-ray diffraction. N₂ adsorption-desorption studies were conducted to investigate the changes in the porous structure of the ZrO₂ fibers heat-treated at different temperatures. Scanning electron microscopy confirmed the mesoporous structure of the ZrO₂ fibers. The oxide-added ZrO₂ fibers heat-treated in the presence of water vapour exhibited a mesoporous structure with increased surface areas and thermal stability. The related reinforcing mechanisms were proposed. It was deduced that water vapour promoted the removal of the soft template, leading to the formation of a mesoporous structure with a high surface area. Meanwhile, the increase in the surface areas of mesoporous ZrO₂ fibers with the incorporation of the oxide additive was mainly due to the enhanced thermal stability of the porous walls. The relationship between the mesoporous structure stability and the zirconia phase stability was fully discussed. This work provides a new route for enhancing the surface areas and structure thermal stability of mesoporous ZrO₂ fibers.     

Wet-spinning assembly of continuous and macroscopic graphene oxide/polyacrylonitrile reinforced composite fibers with enhanced mechanical properties and thermal stability

Polyacrylonitrile (PAN) composite microfibers with different contents of graphene oxide (GO) were fabricated via wet-spinning route in this work. Based on nonsolvent-induced phase separation theory, N,N-dimethyl formamide/water mixture system was employed as coagulation bath, nonsolvent (water) diffused into PAN spinning solution and led to a quick PAN fiber solidification. Nematic liquid crystal state of GO dispersions and GO/PAN spinning solutions were determined via polarized optical microscopy images, and the morphology and structure of the composite fibers were characterized via scanning electron microscope, Transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. 1 wt % GO/PAN composite fibers exhibited outstanding mechanical properties, 40% enhancement in tensile strength and 34% enhancement in Young's modulus compared with pure PAN fiber. The results of dynamic mechanical analysis indicated that the composite fiber with 1 wt % GO performed the best thermal mechanical property with 5.5 GPa and 0.139 in storage modulus and loss tangent, respectively. In addition, thermogravimetric analysis showed that thermal stability of the composite fibers enhanced with the increasing GO contents. GO/PAN composite fibers can be as the candidate of carbon fiber precursor, high performance fibers, and textiles applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46950.