Preparation of nanostructured porous carbon composite fibers from ferrum alginate fibers

Nano‐microstructured porous carbon composite fibers (Fe₂O₃@C/FeO@C/Fe@C) were synthesized by the thermal decomposition of ferrum alginate fibers. The ferrum alginate fiber precursors were prepared by wet spinning, and calcined at 300–1000°C in high purity nitrogen. The resulting composite fibers consist of carbon coated Fe₂O₃/FeO/Fe nanoparticles and porous carbon fibers. All the prepared nanostructures were investigated using thermal gravimetry, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy, transmission electron microscope (TEM), and nitrogen adsorption–desorption isotherm. The results show that there are five stages in the decomposition process of the ferrum alginate fibers. Transitions between the five stages are affected by the decomposition temperature. XRD results show that maghemite (Fe₂O₃), wüstite (FeO), martensite (Fe) nanoparticles were formed at 300–500°C, 600–700°C, 800–1000°C, respectively. Scanning electron microscopy and TEM results indicate that the composite fibers consist of nanoparticles and porous carbon. The diameter of the nanosized particles increased from 100 to 500 nm with increasing reaction temperature. The nitrogen adsorption–desorption results also show that the composite fibers have a micro‐ and mesoporous structure. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Structure Evolution in Polyethylene-Derived Carbon Fiber Using a Combined Electron Beam-Stabilization-Sulphurization Approach

A new approach is described for the production of poly(ethylene) (PE) derived carbon fibers (CFs) that entails the melt spinning of PE fibers from a suitable precursor, their cross-linking by electron beam (EB) treatment, and sulphurization with elemental sulphur (S₈), followed by pyrolysis and carbonization. Instead of focusing on mechanical properties, analysis of CF structure formation during all process steps is carried out by different techniques comprising solid-state nuclear magnetic resonance spectroscopy, thermogravimetric analysis coupled to mass spectrometry/infrared spectroscopy, elemental analysis, energy dispersive X-ray scattering, scanning electron microscopy, Raman spectroscopy, and wide-angle X-ray diffraction. A key step in structure formation is the conversion of PE into poly(thienothiophene)s during sulphurization; these species are stabile under inert gas up to 700 °C as confirmed by Raman analysis. Above this temperature, they condense into poly(napthathienophene)s, which are then converted into graphite-type structures during pyrolysis.     

Preparation of ultra-thin PAN-based activated carbon fibers with physical activation

This study elucidates the stabilization and activation in forming activated carbon fibers (ACFs) from ultra-thin polyacrylonitrile (PAN) fibers. The effect of stabilization time on the properties and structure of resultant stabilized fibers was investigated by thermal analysis, X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy (SEM). Stabilization was optimized by the pyrolysis of ultra-thin PAN fibers in air atmosphere at 280°C for 15 min, and subsequent activation in steam at 1000°C for 0.75 to 15 min. Resultant ACFs were characterized by N₂ adsorption at 77 K to evaluate pore parameters, XRD to evaluate structure parameters, and field emission scanning electron microscopy (FESEM) to elucidate surface morphology. The produced ACFs had surface areas of 668–1408 m²/g and a micropore volume to total pore volume ratio from 78 to 88%. Experimental results demonstrate the surface area and micropore volume of 1408 m²/g and 0.687 cm³/g, respectively, following activation at 1000°C for 10 min. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Development of precursor ceramics using organic silicon polymer

This paper relates to the Bridge Building Award, which was presented to the author (Toshihiro Ishikawa) by the American Ceramic Society on 27 January 2020. We have developed many types of functional ceramics using polycarbosilane as a raw material. Since 1983, several grades of SiC-based fibers have been produced from polycarbosilane by Ube Industries, Ltd. Of these grades, we developed the highest heat-resistant SiC-polycrystalline fiber (Tyranno SA), which can withstand up to 2000°C, using an organic silicon polymer (poly-aluminocarbosilane) containing a small amount of aluminum as a precursor material. By employing curing (in air) and firing (in nitrogen atmosphere at 1300°C) processes using the precursor fiber, an amorphous fiber (Si-Al-C-O fiber) containing a small amount of aluminum was obtained; subsequent heat treatment at higher temperatures (~2000°C) in argon atmosphere led to carbothermal reduction (SiO₂ + 3C SiC + 2CO(g)) and a sintering process, producing the abovementioned SiC-polycrystalline fiber (Tyranno SA). In the same year, using the same raw precursor fiber (Si-Al-C-O fiber), we also developed a new type of tough, thermally conductive SiC composite (SA-Tyrannohex) with high strength up to 1600°C in air. This ceramic consists of a highly ordered, close-packed structure of very fine hexagonal columnar SiC-polycrystalline fibers with a thin interfacial carbon layer between them. Further, by using the polycarbosilane as a starting material, we successfully developed a strong photocatalytic fiber (TiO₂/SiO₂ fiber) with a gradient surface layer composed of TiO₂-nanocrystals, making the best use of controlled phase separation (bleed-out) of additives (titanium (IV) tert-butoxide) contained in polycarbosilane. In this paper, the story of the development of these materials and the subsequent progress will be described along with the historical background.     

Ti3SiC2 interphase coating in SiCf/SiC composites: Effect of the coating fabrication atmosphere and temperature

The SiC fibers were coated with Ti₃SiC₂ interphase by dip-coating. The Ti₃SiC₂ coated fibers were heat-treated from 900 °C to 1100 °C in vacuum and argon atmospheres to comparatively analyze the effect of temperature and atmosphere on the microstructural evolution and mechanical strength of the fibers. The results show that the surface morphology of Ti₃SiC₂ coating is rough in vacuum and Ti₃SiC₂ is decomposed at 1100 °C. However, in argon atmosphere, the surface morphology is smooth and Ti₃SiC₂ is oxidized at 1000 °C and 1100 °C. At 1100 °C, Ti₃SiC₂ oxidized to form a thin layer of amorphous SiO₂ embedded with TiO₂ grains. Meanwhile, defects and pores appeared in the interphase scale. As a result, the fiber strength treated in the argon was lower than that treated in vacuum. The porous Ti₃SiC₂ interphase fabricated under vacuum was then employed to prepare the SiC_f/SiC mini composite by chemical vapor infiltration (CVI) combined with precursor infiltration pyrolysis (PIP), and can effectively improve the toughness of SiC_f/SiC mini composite. The propagating cracks can be deflected within the porous interphase layer, which promotes fiber pull-outs under the tensile strength.     

Thermophysical property and electrical conductivity of titanium isopropoxide – polysiloxane derived ceramics

In this study, high temperature resistant Si-O-C-Ti has been successfully prepared based on the pyrolysis of polysiloxane (PSO) and titanium (IV) isopropoxide (TTIP) at 1200–1400 °C. PSO can homogeneously mix with TTIP to enhance its conversion to TiC. The carbothermal reactions between TiO₂ (product of thermal decomposition of TTIP) and carbon result in the formation of TiC. All the Si-O-C-Ti composites pyrolyzed at 1200–1300 °C are stable up to 1000 °C in an oxidizing air atmosphere. TiC leads to high electrical conductivity at elevated temperatures; the maximum conductivity is 1176.55 S/m at 950 °C, which is the first reported value of >1000 S/m conductivity for Si-O-C-Ti ceramics. However, too high a pyrolysis temperature, such as 1400 °C, can potentially ‘destabilize’ the Si-O-C-Ti system by consuming the free carbon and result in lower conductivities.     

A different chemical route to prepare hafnium diboride-based nanofibers: Effect of chemical composition

This study reports on the synthesis of hafnium diboride (HfB₂)-based nanofibers via electrospinning of polyhafnoxanesal (PHO)-based solution followed by pyrolyzing hafnium-boron containing polyvinylpyrrolidone precursor fibers by a moderate heat treatment at 1500°C under argon atmosphere. The influence of the molar ratios of C/Hf and B/Hf in preceramic polymer method is investigated on the final phase of HfB₂-based nanofibers. Structural, thermal, microstructural, and physical properties of the hafnium-based fibers are evaluated using Fourier transform infrared spectra (FTIR), thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffractometer (XRD), high-temperature X-ray diffraction (HT-XRD), field-emission scanning electron microscope/energy-dispersive spectrometer (FE-SEM/EDS), and Brunauer-Emmett-Teller (BET). The results unveiled that the acidic pH was the optimal condition needed for obtaining the single phase of HfB₂ nanofibers. The precursor fibers with the stoichiometric ratio of 1:4:5 of Hf:B:C prepared under the acidic conditions converted into pure HfB₂ nanofibers having rough and porous surface after pyrolysis at 1500°C for 2 hour in argon, whereas HfB₂-HfC composite nanofibers with smooth surface were produced in the neutral conditions. The HfB₂ nanofibers with a mean diameter of ~100 nm prepared under the acidic conditions showed a higher specific surface area compared to HfB₂-HfC composite nanofibers with a diameter of ~121 nm derived in the neutral conditions.     

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.     

Development of MgO:TiO2 thin films for gas sensor applications

In this study, structural, morphological and optical properties, and gas sensor performance of magnesium oxide (MgO) doped titanium dioxide (TiO₂) thin films were investigated in detail. Gas sensor metallic patterns were fabricated on Si substrate using traditional photolithographic technique. MgO doped TiO₂ thin films were deposited on formed Pt electrode surface by confocal sputtering (co-sputtering) system as the active layer. Thin film characterizations were realized by using secondary ion mass spectroscopy (SIMS), atomic force microscope (AFM) and UV–Vis Spectrometer (UV–Vis). Gas sensing measurements were performed by gas sensing test system against methane gas at working temperature of 300?°C. To evaluate deposition and thermal annealing effects on the sensing performance, sensors were tested under gas. The sensitivity and response/recovery time of gas sensors were measured in 1000?ppm. MgO doped TiO₂ based sensor at substrate temperature of 100?°C has high sensitivity and short response/recovery time.     

Ultrasonic-assisted preparation of AlON from alumina/carbon core-shell nanoparticle

An aluminium oxynitride (AlON) powder was synthesized by carbothermal reduction nitridation (CRN) method. For this purpose, first Al₂O₃/C core-shell nanoparticles were prepared by the pyrolysis of Al₂O₃/polyacrylonitrile (PAN) nanocomposite precursor at 800?°C for 2?h in an argon atmosphere. Alumina/PAN precursor was prepared by ultrasonic method at room temperature. Then, by two-step thermal treatment of Al₂O₃/C core-shell nanoparticles at 1500–1600?°C for 2?h, followed by subsequent heating at 1750?°C for 1?h in N₂ flow, AlON powder was synthesized. The sample was investigated via Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and CHNS elemental analysis.     

Heat treatment of silica-fiber-reinforced BN-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> matrix composite

A new wave-transparent composite reinforced by silica fibers with a hybrid matrix comprising BN and Si₃N₄ was prepared by precursor infiltration and pyrolysis, and it was heat-treated at elevated temperatures. The variations of the composite during heat treatments were characterized and investigated by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-received composite exhibits good mechanical properties, and it is almost amorphous. When treated at 1600°C, it turned brittle, and silica fibers in it were fused; the composite showed a good crystalline form. When treated at 2100°C, the composite broke into pieces, and the composition showed only BN. Si₃N₄ was decomposed, and silica fibers were volatilized. The presence of BN probably affected the phase transitions of silica fibers. __________ Translated from Novye Ogneupory, No. 8, pp. 49–52, August 2007.     

Synthesis of ZrC–SiC Powders by a Preceramic Solution Route

Homogenous liquid precursor for ZrC–SiC was prepared by blending of Zr(OC₄H₉)₄ and Poly[(methylsilylene)acetylene]. This precursor could be cured at 250°C and converted into binary ZrC–SiC composite ceramics upon heat treatment at 1700°C. The pyrolysis mechanism and optimal molar ratio of the precursor were investigated by XRD. The morphology and elements analyses were conducted by SEM and corresponding energy‐dispersive spectrometer. The evolution of carbon during ceramization was studied by Raman spectroscopy. The results showed that the precursor samples heat treated at 900°C consisted of t‐ZrO₂ (main phase) and m‐ZrO₂ (minor phase). The higher temperature induced phase transformation and t‐ZrO₂ converted into m‐ZrO₂. Further heating led to the formation of ZrC and SiC due to the carbothermal reduction, and the ceramic sample changed from compact to porous due to the generation of carbon oxides. With the increasing molar ratios of C/Zr, the residual oxides in 1700°C ceramic samples converted into ZrC and almost pure ZrC–SiC composite ceramics could be obtained in ZS‐3 sample. The Zr, Si, and C elements were well distributed in the obtained ceramics powders and particles with a distribution of 100 ~ 300 nm consisted of well‐crystallized ZrC and SiC phases.     

Synthesis and pyrolysis behavior of a soluble polymer precursor for ultra-fine zirconium carbide powders

A soluble polymer precursor for ultra-fine zirconium carbide (ZrC) was successfully synthesized using phenol and zirconium tetrachloride as carbon and zirconium sources, respectively. The pyrolysis behavior and structural evolution of the precursor were studied by Fourier transform infrared spectra (FTIR), differential scanning calorimetry, and thermal gravimetric analysis (DSC–TG). The microstructure and composition of the pyrolysis products were characterized by X-ray diffraction (XRD), laser Raman spectroscopy, scanning electron microscope (SEM) and element analysis. The results indicate that the obtained precursor for the ultra-fine ZrC could be a Zr–O–C chain polymer with phenol and acetylacetone as ligands. The pyrolysis products of the precursor mainly consist of intimately mixed amorphous carbon and tetragonal ZrO₂ (t-ZrO₂) in the temperature range of 300–1200 °C. When the pyrolysis temperature rises up to 1300 °C, the precursor starts to transform gradually into ZrC, accompanied by the formation of monoclinic ZrO₂ (m-ZrO₂). The carbothermal reduction reaction between ZrO₂ and carbon has been substantially completed at a relatively low temperature (1500 °C). The obtained ultra-fine ZrC powders exhibit as well-distributed near-spherical grains with sizes ranging from 50 to 100 nm. The amount of oxygen in the ZrC powders could be further reduced by increasing the pyrolysis temperature from 1500 to 1600 °C but unfortunately the obvious agglomeration of the ZrC grains will be induced.     

Processing,Mechanical Characterization,and Alkali Resistance of SiliconBoronOxycarbide (SiBOC) Glass Fibers

A borosilicate sol–gel solution is synthesized using a mixture of methyltriethoxysilane, dimethyldiethoxysilane, and boric acid. SiBOC gel fibers are produced from the as‐synthesized sol–gel solution using a spinning apparatus. Subsequently, SiBOC glass fibers are prepared through pyrolysis under argon atmosphere at 1000°C and 1200°C. Mechanical properties of the SiBOC glass fibers are studied by measuring the tensile strength and the elastic modulus. The results show a high tensile strength ?1300 and 1058 MPa, and a high Young modulus ?79 and 95.5 GPa, for the fibers prepared at 1000°C and 1200°C, respectively. Furthermore, alkali resistance of the SiBOC fibers is investigated by measuring the tensile strength after soaking them for 20 h in NaOH and Ca(OH)₂ solutions at 100°C. For comparison, the same measurements are performed on commercial AR and E glass fibers. The SiBOC fibers show excellent alkaline resistance and perform better than commercial AR fibers. Indeed, SiBOC fibers retain 80%–90% of the initial strength after Ca(OH)₂ attack.     

Synthesis,Characterization, and Microstructure of ZrC/SiC Composite Ceramics via Liquid Precursor Conversion Method

The ceramic precursor for ZrC/SiC was prepared via solution‐based processing using polyzirconoxane, polycarbosilane, and divinylbenzene. The precursor could be transformed into ZrC/SiC ceramic powders at relative low temperature (1500°C). The cross‐linking process of precursor was studied by FT–IR. The conversion from precursor into ceramic was investigated by TGA, XRD. The ceramic compositions and microstructures were identified by element analysis, Raman spectra, SEM, and corresponding EDS. The results indicated that the ceramic samples remained amorphous below 1000°C and t–ZrO₂ initially generated at 1200°C. Further heating to 1400°C led to the formation of ZrC and SiC with the phase transformation of ZrO₂ and almost pure ZrC/SiC could be obtained upon heat‐treatment at 1500°C. During heat treatments, the ceramic sample changed from compact to porous due to carbothermal reduction. The ceramic powders with particle size of 100 nm~400 nm consisted of high crystalline degree ZrC and SiC phases, and Zr, Si, C were well distributed at the different sites in ceramic powders. The free carbon content was lowered to 1.60 wt% in final ZrC/SiC composite ceramics.     

In-situ formation of titanium carbide in carbon-rich silicon oxycarbide ceramic for enhanced thermal stability

Silicon oxycarbide (SiOC) ceramic has attracted great attention as fascinating candidate of high-temperature material, however, its thermal stability is significantly limited by the phase separation at high temperature. Here, a TiC/SiOC ceramic was prepared by pyrolysis of a tetrabutyl titanate modified carbon-rich polysiloxane (TBT/PSO) precursor. The TiC phase is in-situ formed by the carbothermal reaction of TBT-derived amorphous TiO₂ phase with excess free-carbon phase during pyrolysis, and its size and amount increase with the pyrolysis temperature. The SiC phase appears at a higher temperature than the TiC phase and is hindered by the increased Ti content in the TBT/PSO precursor. Thus, the TiC/SiOC ceramic exhibits better thermal stability and crystallization resistance than the TiC-free SiOC ceramic under the thermal treatment (1500 °C) in argon atmosphere. The in-situ formation of metal carbide into the carbon-rich SiOC ceramic would further expand its application at high temperature environments.     

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.     

Phase stability (at 1000°C) of hollow t-ZrO2 fibers costabilized by lanthana and yttria

Yttrium-stabilized ZrO₂ (YSZ) hollow fibers derived from a ceiba template present a 25%–53% reduction in thermal conductivity compared with traditional YSZ solid fibers. However, after prolonged preservation at 1000°C, tetragonal ZrO₂ (t-ZrO₂) can easily transform to monoclinic ZrO₂ (m-ZrO₂), which destroys the hollow structure of the YSZ fibers and results in loss of the structural advantages for heat insulation. To overcome this, in this study, biomorphic lanthana and yttrium costabilized zirconia (LaYSZ) fibers with a hollow structure are fabricated by doping appropriate amounts of lanthanum in the raw materials of YSZ fibers. X-ray diffraction, scanning electron microscopy, and thermal conductivity measurements are utilized to confirm the phase-stability superiority of LaYSZ fibers to that of YSZ fibers under harsh conditions. After preservation at 1000°C for 150 hours, the m-ZrO₂ content in the LaYSZ hollow fibers increases from 0 to 3.4 mol%, whereas that in the YSZ fibers increases from 0 to 10.25 mol%. Furthermore, owing to their better phase stability at 1000°C, the morphologies and heat-insulating properties of LaYSZ fibers are more improved in several aspects compared with YSZ fibers.     

High-temperature mechanical properties of NextelTM 610 fiber reinforced silica matrix composites

Novel Nextel? 610 fiber reinforced silica (N610f/SiO₂) composites were fabricated via sol-gel process at a sintering temperature range of 800–1200?°C. The sintering-temperature dependent microstructures and mechanical properties of the N610f/SiO₂ composites were investigated comprehensively by X-ray diffraction, nanoindentation, three-point bending etc. The results suggested a thermally stable Nextel? 610 fiber whose properties were barely degraded after the harsh sol-gel process. A phase transition in the silica matrix was observed at a critical sintering temperature of 1200?°C, which led to a significant increase in the Young's modulus and hardness. Due to the weak fiber/matrix interfacial interaction, the 800?°C and 1000?°C fabricated N610f/SiO₂ composites exhibited quasi-ductile fracture behaviors. Specially, the latter possessed the highest flexural strength of ≈ 164.5?MPa among current SiO₂-matrix composites reinforced by fibers. The higher sintering-temperature at 1200?°C intensified the SiO₂ matrix, but strengthened the interface, thus resulting in a brittle fracture behavior of the N610f/SiO₂ composite. Finally, the mechanical properties of this novel composite presented good thermal stability at high temperatures up to 1000?°C.     

Fabrication and Properties of Electrospun PAN/LA–SA/TiO2 Composite Phase Change Fiber

A stabilized matrix to accommodate phase change materials is essential in the application and functioning of phase change materials. In this study, lauric–stearic acid eutectics and TiO₂ were doped with polyacrylonitrile solution to electrospin a composite phase change nanofibers. The surface morphology indicated typical nanofibrous structure of polyacrylonitrile/lauric–stearic/TiO₂ composite nanofibers, and the diameter of fiber increased with the increase in lauric–stearic eutectic mass ratio. Differential scanning calorimetry analysis showed the temperature of melting peak of polyacrylonitrile/lauric–stearic/TiO₂ nanofiber was around 25°C, which was lower than that of pure lauric–stearic eutectics. Latent heat value of the composite fibers gradually increased with the increase in lauric–stearic mass ratio. Thermal cycle test and thermogravimetric analysis showed that polyacrylonitrile/lauric–stearic/TiO₂ composite fibers were reversible thermal energy storage materials with good thermal stability below 100°C.