Pre-oxidized Fiber Research Articles

Study on preparation of high cyclization degree and high strength pre-oxidized fiber by nitration

Study on preparation of high cyclization degree and high strength pre-oxidized fiber by nitration

Research on dynamic microwave low-temperature carbonization of high performance carbon fiber

Polyacrylonitrile precursor was obtained by one-step method of polymerization and spinning. After conventional pre-oxidation at 180–280 °C in air, the polyacrylonitrile pre-oxidized fiber was carbonized at 600–1000 °C by microwave heating and conventional heating in nitrogen. An infrared thermometer is used to detect the surface temperature of the fiber in real time. The dielectric loss tangent (tanδ) increases first and then decreases with increasing temperature. The intensity of the A line of the MCF-1000 sample increases, the G line gradually separates from the D line, and the ID/IG value decreases. Compared with CCF-700, the tensile strength of MCF-700 is increased by 10.06%. The microwave carbonization method creates excellent carbon fiber tensile strength at a temperature of 200 °C lower than the conventional carbonization temperature. The initial modulus of MCF-700 is 51.33% higher than that of CCF-700. Microwave carbonization can obtain carbon fiber with a higher initial modulus at a lower carbonization temperature.

Evolution and Regulation of Radial Structure of PAN Pre-Oxidized Fiber Based on the Fine Denier Model.

Affected by ambient oxygen and thermal diffusion mechanism, the radial structural distribution of polyacrylonitrile (PAN) fiber during the pre-oxidation process will be inherited to the carbon fiber, which had a remarkable effect on the mechanical properties of carbon fiber. It is important to understand the evolution mechanism of radial structure evolution of PAN fiber during the pre-oxidation process to manufacture the high-performance carbon fiber. In this paper, a series of fine denier model fibers were prepared by adjusting the oxygen concentration to describe the structural characteristics at different radial regions of pre-oxidized fibers. The evolution mechanism of the radial structure of pre-oxidized fiber, with the increase of heat treatment temperature, was studied by the methods of optical microscope, C13 nuclear magnetic resonance (13C-NMR), and thermogravimetric analyzer (TGA). The results showed that along the radial direction of pre-oxidized fiber from skin to core layer, the degree of cyclization changed little while the dehydrogenation and oxygen-containing structure gradually decreased. Specifically, the oxygen-containing functional groups in the core decreased to the lowest level or even disappeared. A moderate increase of temperature in the initial and middle pre-oxidation processes could effectively promote the formation of cyclized structure and stabilize cross-linked ladder structure in the skin region of the fiber. With it, the thermal stability of obtained pre-oxidation fiber was improved.

Mo2C nanoparticles coated tubular carbon nanofibers as a highly efficient electrocatalyst for the hydrogen evolution reaction

The development of highly effective and non-precious electrocatalysts for the hydrogen evolution reaction (HER) remains highly desirable. In this work, we report a facile strategy using preoxidized fiber films as a precursor to prepare a flower-like Mo2C-based electrocatalyst for the HER, in which the pyrolysis of a mixture of urea and ammonium molybdate tetrahydrate during thermal treatment realized nitrogen doping. The N–Mo2C/CNFs-900 electrocatalyst exhibits excellent HER activity with a small overpotential of 119 mV at 10 mA cm−2 in an alkaline solution and the Tafel slope was calculated to be 106.9 mV dec−1. N-M-9 demonstrated long term stability over 24 h. With an increase in temperature, MoO2 was gradually transformed into Mo2C and the formation of Mo2C was promoted upon nitrogen doping. This work provides a feasible approach to synthesize high performance HER electrocatalysts for renewable energy applications.

Evolution mechanism of cyclized structure of PAN-based pre-oxidized fiber during low temperature carbonization process

The low temperature carbonization process is an important stage to realize the structural transition from the organic cyclized structure of PAN based pre-oxidized fiber to the inorganic pseudo-graphite structure of the ultimate carbon fiber. In the present paper, the evolution mechanism of cyclized structure and aggregation structure of PAN stabilized fiber during low temperature carbonization was studied by means of TGA, 13C-NMR, XRD, XPS and Raman. The results indicated that when the heat-treated temperature was lower than 450 °C, the mainly chemical reactions were the dehydrogenation and pyrolysis reactions in acyclic linear molecular chain or partial cyclized structure. At this stage, the growth of cyclized structure was not obvious. While the original ordered structure was destroyed gradually and the internal stress increased significantly. It induced the cyclized structure to be further oriented. When the temperature was higher than 450 °C, the polycondensation and reconstruction in aromatic heterocyclic structure was more important. The early aromatic heterocycles had many different structural scales, poor homogeneity and many defects in the heterocycles. At this stage, a new pseudo-graphite crystalline structure gradually formed and the d-spacing of graphite layer decreased slightly and crystallites size increased slowly with the increase of heat-treated temperature. When the temperature was higher than 550 °C, the pseudo-graphite base structure gradually formed. The d-spacing were further reduced slightly, and the crystallites size increased slowly. A new ordered basis structure was gradually developed into carbon fiber.

Characterization of a polyaniline/pre-oxidized fiber felt electromagnetic wave absorbing composite

Firstly, a polyaniline/pre-oxidized fiber felt composite was prepared by in situ polymerization using pre-oxidized fiber felt as the substrate, aniline as the monomer, ammonium persulfate as the oxidant, and p-toluenesulfonic acid as the dopant. Secondly, the electromagnetic wave absorbing property and tensile property of the polyaniline/pre-oxidized fiber felt composite were investigated. Finally, the structure and composition were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, and differential scanning calorimetry. The results show that the reflection loss of the polyaniline/pre-oxidized fiber felt composite is the smallest at the 3000 MHz frequency, reaching –8.23 dB, and the average surface resistance is 2059.84 Ω, with good conductivity. The characterization analysis shows that polyaniline has been successfully loaded on the pre-oxidized fiber felt, and the protonation reaction occurs at the nitrogen atom on the imine -N-. The polyaniline structure is doped by p-toluenesulfonic acid with a certain degree of order and crystallinity, and the composite has good thermal stability.

The study on the electromagnetic properties of polyurethane coated pre-oxidized fiber felt composites

In this study, coated pre-oxidized fiber felt composites were prepared using the PU2540 polyurethane as a matrix and adopting a coating technology on the pre-oxidized fiber felt. Firstly, influences of wave-absorbing functional particles on the dielectric properties and shielding effectiveness of single-layer coated pre-oxidized fiber felt composites were analyzed and compared. Secondly, influences of the graphene content on the dielectric properties and shielding effectiveness of graphene coated pre-oxidized fiber felt composites were discussed. Results showed that values of the real and imaginary parts and loss tangent value of the dielectric constant for graphene coated pre-oxidized fiber felt composites were all larger than those of graphite coated pre-oxidized fiber felt composites, that is, the former had a stronger polarization ability, dissipation ability and attenuation ability to electromagnetic waves than the latter. However, the shielding effectiveness of the latter was larger than that of the former, that is, the shielding ability of graphite coated pre-oxidized fiber felt composites was better than that of graphene coated pre-oxidized fiber felt composites. When the graphene content was 15% of the mass of the polyurethane, the value of the imaginary part and loss tangent value of the dielectric constant for graphene coated pre-oxidized fiber felt composites were both the largest, and the dissipation ability and attenuation ability to electromagnetic waves were both the strongest.

A study of the heat insulation performance of pre-oxidized fiber felts of silica aerogel/silicon carbide composite coatings

In this article, pre-oxidized fiber felts of silica aerogel/silicon carbide composite coatings were prepared by the coating process and then compounding silica aerogel with silicon carbide powder as the infrared sunscreen on the pre-oxidized fiber felts. The influence of the ratio of the contents of the silica aerogel and silicon carbide as the infrared sunscreen on the heat insulation performance of coating composites of pre-oxidized fiber felts was discussed, and their mechanical properties were investigated. The results show that with increasing silicon carbide content in the composite coating, the coefficient of thermal conductivity increases gradually; when the working temperatures were 100, 150 and 200 °C, the coating composites of pre-oxidized fiber felts had the best heat insulation performance when the mass ratio of the silica aerogel and silicon carbide was 4:7. The working temperature and the steady-state temperature difference of the coating composites shows a linear relationship, so simple calculation methods of the coefficient of thermal conductivity for the coating composites were given at higher temperatures.

A study of the mechanical properties of pre-oxidized fiber felt/epoxy resin composite material

In this article, the pre-oxidized fiber felt composite material was firstly prepared by a mold press process, and the pre-oxidized fiber and resin were used as the reinforcing material and substrate of composite material, respectively. The pretreatment method of the pre-oxidized fiber felt and the impact of the amount of curing agent and the curing pressure on the mechanical properties of the composite material were studied, and the tensile and flexural properties were assessed to optimize the preparation process of composite material. Results show that when the curing agent accounts for 60% of the epoxy resin and the curing pressure is 3 MPa, the best tensile and flexural properties of the prepared composite material are achieved. The mechanical properties for the pretreated composite sheet prepared from pre-oxidized fiber were superior to those for the untreated sheet.

Dynamic oxidation and protection of the PAN pre-oxidized fiber C/C composites

Pre-oxidized fibers as reinforcement are candidates for reducing the overall cost of C/C composites with superior properties. This study investigated the dynamic oxidation and protection of the pre-oxidized fiber C/C composites (Pr-Ox-C-C). According to the Arrhenius equation, the oxidation kinetics of the Pr-Ox-C-C consisted of two different oxidation mechanism with the transition point was at about 700°C. Scanning electron microscopy investigation showed that oxidation initiated from the fiber/matrix interface of composites, whereas the matrix carbon was easily oxidized. To improve the anti-oxidant properties of Pr-Ox-C-C, a ceramic powder-modified organic silicone resin/ZrB2-SiC coating was prepared by the slurry method. The coated samples were subjected to isothermal oxidation for 320h at 700°C, 800°C, 900°C, 1000°C and 1100°C with incurred weight losses of − 1.6%, 0.77%, − 1.28%, 0.68% and 1.19%, respectively. After 110 cycles of thermal shock between 1100°C and room temperature, a weight loss of 1.30% was obtained. The Arrhenius curve presented four different phases and mechanisms for coating oxidation kinetics. The excellent oxidation resistance properties of the prepared coating could be attributed to the inner layer which was able to form B2O3-Cr2O3-SiO2 glass to cure cracks, and the ZrB2-SiC outer layer that could provide protective oxides to reduce oxygen infiltration and to seal bubbles.

KOH direct activation for preparing activated carbon fiber from polyacrylonitrile-based pre-oxidized fiber

The activated carbon fiber(ACF) was prepared from polyacrylonitrile-based pre-oxidized fiber(PANOF) by KOH direct activation. The influence of activation conditions including impregnation ratio(the mass ratio of PANOF to KOH), activation temperature and activation time on the pore structure and electrochemical properties of ACF was investigated, and the corresponding activation mechanism was proposed. The ACF prepared at an activation temperature of 800 °C and an impregnation ratio(the mass ratio of PANOF to KOH) of 1:2 for an activation time of 1 h in 6 mol/L KOH solution exhibits a specific surface area of 3029 m2/g, a mesoporosity of 84.2% and a specific capacitance of 288 F/g, and shows a good capacitive performance. The prepared ACF can be used as the electrode material for supercapacitors.

Comparative Analysis of Fibers for Thermal Protective Clothing

This paper firstly introduces the performance of some kinds of thermal protective clothing materials, for example, Nomex, Polysulfonamide fiber (PSA), polyphenylene sulfide fiber (PPS) and pre-oxidized fiber. Then mainly states the application status through investigation. According to their merits and demerits, we can improve clothes' comfort and functionality through blending. Finally, we should aim to gain more practical and environmental friendly thermal protective fibers.

Non-isothermal kinetic analysis of oxidative stabilization processes in PAN fibers

Non-isothermal kinetic analysis of oxidative stabilization processes in polyacrylonitrile (PAN) fibers was studied with the use of the differential scanning calorimetry (DSC) data. PAN terpolymer fibers consisting of acrylonitrile, methyl acrylate and itaconic acid were studied. Kinetic parameters and kinetic models of nitrile cyclization and oxidative destruction of chain fragments and functional groups were obtained. On the basis of these kinetic models constant heat flow temperature programs with maximum heat flow of 0.11 mW/mg for PAN fiber and 0.09 mW/mg for pre-oxidized PAN fiber were calculated. It was shown that simulated degree of conversion coincides within errors with cyclization index (CD) for stabilized fiber. CD can be used as an estimation of degree of conversion in research and practical applications. Technique of kinetic analysis, that was used, allows optimization of conditions for thermal stabilization for any required cyclization index and degree of conversion for the oxidative stabilization process in PAN fibers.

Soft X-ray spectromicroscopy dual-energy contrast image for element spatial distribution analysis

The detection of chemical speciation with spatial resolution of 30 nm has been implemented at BL08U soft X-ray spectromicroscopy endstation of Shanghai Synchrotron Radiation Facility. For each specimen, we scan two absorption images separately at two energies E1 and E2 near the absorption edge of the element with E1>E2. After calculating the signal ratio of each pair of the corresponding pixels’ optical density in the two absorption images, we can obtain the map of the spatial distribution of that element. Compared with the conventional analysis method of K-edge subtraction (KES), our ratio analysis method is more sensitive and accurate in identifying the spatial distribution of the interested elements, and the definition of the contrast threshold determining whether a pixel contains the interested element, is simpler and clearer in physics. Through the analysis and calculation of the spatial distributions of the oxygen element on a pre-oxidized polyacrylonitrile fiber cross-section, we can verify the effectiveness of the ratio analysis method compared to the traditional KES method. This ratio method provides a new analysis tool for fast mapping the distribution of trace elements.

Ｓｉ−Ｔｉ−Ｃ−Ｏ繊維結合型セラミックスの微細構造と特性

The microstructure and mechanical properties of Si-Ti-C-O fiber-bonded ceramics (Tyrannohex (R)) produced by hot-pressing pre-oxidized Si-Ti-C-O fibers with a surface oxide (SiO2 and TiO2) layer of 250, 430 and 580nm thickness were investigated. The hot-pressing temperature and pressure were 2023K and 50MPa, respectively. Tyrannohex, which was produced using the pre-oxidized fiber with a surface oxide layer of 250nm thickness, showed a close-packed structure with 90% of volume fraction (Vf) of the fiber. The interstices were packed by an oxide material, which existed on the surface of the raw fiber. It was observed that the oxide material changed to TiC-particle dispersed structure by a reaction between TiO2, which existed on the fiber's surface, and excess carbon in the fiber during hot-pressing. Moreover, an interfacial carbon layer (10-20nm) around the fiber was formed. Tyrannohex showed very high fracture energy (8900J/m2) by Chevron notched beam method. Tyrannohex (Vf=90%) showed elastic fracture behavior without any plasticity even at 1673K, because all the fibers were restricted by the close-packed structure. At all the contact points of the fibers, an interfacial carbon layer existed without oxide material. About 90% of the initial strength was maintained after heat-treatment in air for 1000 hours because of an effective formation of a protective oxide layer on the surface.