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

Wang, Bin; Wu, Shuai; Li, Chenggao; Cao, Weiyu

doi:10.1088/2053-1591/ac3587

Cited by 10 publications

(4 citation statements)

References 21 publications

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“…For PAN, rapid shrinkage was observed in the temperature range of 300 to 400 °C. The molecular cyclization of PAN is typically reported to proceed below 400 °C, and carbonization through various mechanisms takes place around 400 to 600 °C. − Therefore, in the calcination, the as-spun nanofibers, consisting of a mixture of Mo precursor and PAN, undergo thermal decomposition and carbonization to form C nanofibers structure. Subsequently, metal species nucleate within the C nanofibers, as reported in several studies on metal/C nanofibers. ,− …”

Section: Resultsmentioning

confidence: 99%

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium

Oh,

Kim,

Kim

et al. 2024

J. Am. Chem. Soc.

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Fabricating nanoscale metal carbides is a great challenge due to them having higher Gibbs free energy of formation (ΔG°) values than other metal compounds; additionally, these carbides have harsh calcination conditions, in which metal oxidation is preferred in the atmosphere. Herein, we report oxocarbon-mediated calcination for the predictive synthesis of nanoscale metal carbides. The thermochemical oxocarbon equilibrium of CO–CO2 reactions was utilized to control the selective redox reactions in multiatomic systems of Mo–C–O, contributing to the phase-forming and structuring of Mo compounds. By harnessing the thermodynamically predicted processing window, we controlled a wide range of Mo phases (MoO2, α-MoC1–x , and β-Mo2C) and nanostructures (nanoparticle, spike, stain, and core/shell) in the Mo compounds/C nanofibers. By inducing simultaneous reactions of C–O (selective C combustion) and Mo–C (Mo carbide formation) in the nanofibers, Mo diffusion was controlled in C nanofibers, acting as a template for the nucleation and growth of Mo carbides and resulting in precise control of the phases and structures of Mo compounds. The formation mechanism of nanostructured Mo carbides was elucidated according to the CO fractions of CO–CO2 calcination. Moreover, tungsten (W) and niobium (Nb) carbides/C nanofibers have been successfully synthesized by CO–CO2 calcination. We constructed the thermodynamic map for the predictive synthesis of transition metal carbides to provide universal guideline via thermochemical oxocarbon equilibrium. We revealed that our thermochemical oxocarbon-mediated gas–solid reaction enabled the structure and phase control of nanoscale transition metal compounds to optimize the material–property relationship accordingly.

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Section: Resultsmentioning

confidence: 99%

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium

Oh,

Kim,

Kim

et al. 2024

J. Am. Chem. Soc.

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“…Xue et al [15,16] reported that the pre-oxidation degree of PAN-based pre-oxidized fiber in the skin was higher, while it was the lowest in the core due to the decrease of oxygen content. The skin-core structure of pre-oxidized fibers could be weakened through the thermal treatment at a lower temperature for a long time, according to the work [17,18]. However, it was also easy to form the excessive oxygenated functional groups in the fiber.…”

Section: Introductionmentioning

confidence: 99%

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

Wang

et al. 2022

Materials

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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.

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“…Related investigations have revealed the chemical reaction mechanism and product structure during the preoxidation process can be obtained by means of infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and Raman spectra. Furthermore, the mechanisms of 'cyclization reaction', 'dehydrogenation reaction' and 'oxidation reaction' were proposed in the research [21][22][23], as well as the structural models of 'trapezoidal structure', 'aromatic heterocycle', 'imine crosslinking', 'polyene amine' and 'spread crosslinking' [24][25][26]. However, the effect mechanism of characteristic structure on the formation and evolution of embryonic conjugate structure has not been well established.…”

Section: Introductionmentioning

confidence: 99%

Effect of ambient atmosphere on the formation and evolution of conjugated structure of pre-oxidized polyacrylonitrile

Wang

Shuai

et al. 2022

Mater. Res. Express

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The ambient atmosphere has the remarkable effect on the chemical reaction mechanism and the formation of characteristic chemical structures and conjugated structures for pre-oxidized PAN. In the present paper, fourier transform infrared spectroscopy (FT-IR) and ultraviolet visible spectroscopy (UV-vis) were used to characterize the variations of chemical reaction characteristic structures and conjugate structures of copolymerized PAN in nitrogen and air atmosphere, respectively. Combined with the multivariate reaction model proposed by the predecessors, it can be found thatthat two main conjugated structures (conjugated polyene and conjugated aromatic heterocycle) formed during the pre-oxidation process of copolymerized PAN . In nitrogen atmosphere, the formed main structure units were the conjugated diene and conjugated double ring with 1-2 double bonds. By contrast, the formed main units in air were the conjugated diene and conjugated tricyclic with a double bond. During the whole pre-oxidation process, the maximum unit numbers of conjugated double bonds and conjugated rings were no more than four and six, respectively. Increasing the heat treatment temperature was easy to form more conjugate structures than prolonging the heat treatment time. Furthermore, with the increase of heat treatment temperature or time in air, the main conjugate unit numbers had no obvious change, while the maximum unit numbers increased slightly. When exposed in nitrogen atmosphere , the main conjugated polycyclic structure was transformed into conjugated tricyclic structure after the heat treatment at 250 oC for more than 3 hours. In addition, when the heat treatment temperature and time were 280 oC for more than 4 hours, the main conjugated polyene structure was transformed into conjugated triene, andthe maximum conjugated unit numbers increased slightly with it.

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

Cited by 10 publications

References 21 publications

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium

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

Effect of ambient atmosphere on the formation and evolution of conjugated structure of pre-oxidized polyacrylonitrile

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