The influence of two-stage isothermal treatment on the change in the linear dimensions of the fiber, the average sizes of the coherent scattering regions, the texture and phase composition of the polyacrylonitrile fib...The influence of two-stage isothermal treatment on the change in the linear dimensions of the fiber, the average sizes of the coherent scattering regions, the texture and phase composition of the polyacrylonitrile fiber in the process of isothermal thermal stabilization is considered by the methods of dilatometry and X-ray diffraction analysis. It is shown that preliminary short-term heat treatment at a lower temperature affects the process of structural transformations of the polyacrylonitrile fiber material and the formation of a new highly dispersed phase of the thermally stabilized fiber.展开更多
Different polyacrylonitrile （PAN） precursor fibers that displayed various thermal properties were studied by using differential scanning calorimetry （DSC）. Results showed that some commercial PAN precursor fibers ...Different polyacrylonitrile （PAN） precursor fibers that displayed various thermal properties were studied by using differential scanning calorimetry （DSC）. Results showed that some commercial PAN precursor fibers displayed double separated peaks and these fibers were of high quality because of their process stability during their conversion to carbon fibers of high performance. Some fabrication processes, such as spinning, drawing, could not apparently change the DSC features of a PAN precursor fiber. It was concluded that the thermal properties of a PAN precursor fiber was mainly determined from its comonomer content type and compositions.展开更多
The effect of structural evolution polyacrylonitrile (PAN) on mechanical properties was investigated in stabilization and carbonization. PAN spun fibers were stabilized in a convection oven with a constant tension for...The effect of structural evolution polyacrylonitrile (PAN) on mechanical properties was investigated in stabilization and carbonization. PAN spun fibers were stabilized in a convection oven with a constant tension for various times at 250℃. Fourier Transform Infrared spectroscopy (FTIR) and gel fraction results suggested that intra and intermolecular stabilization reactions occurred simultaneously. X-ray diffractograms revealed a disruption of crystalline structure and an appearance of pre-graphitic structure of PAN fibers due to stabilization. These structural changes by stabilization resulted in the significant decrease of tensile properties of fibers. In Raman spectra with heat treated fibers from 400℃ up to 1200℃, the intensity ratio of the D to G bands (ID/IG) decreased as heat treatment temperature increased, indicating an increase of basal plane of graphitic layer of heat treated fibers. Tensile strength of heat treated fibers at 1200℃ was found to be as high as 2.2 GPa.展开更多
Orientation of copolymer polyacrylonitrile （PAN） chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of...Orientation of copolymer polyacrylonitrile （PAN） chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.展开更多
Thermal stabilization is an important process in carbon fibers＇ production, during which the polyacryloni-trile fibers are heated from 180℃ to 280 ℃ in air. In this study, the samples were characterized by X-ray di...Thermal stabilization is an important process in carbon fibers＇ production, during which the polyacryloni-trile fibers are heated from 180℃ to 280 ℃ in air. In this study, the samples were characterized by X-ray diffraction,Fourier infrared spectroscopy, differential scanning calorimetry, small angle X-ray Scattering（SAXS） and mechanicaltensile tests. A new rule was suggested by the results of structural characterization for the cyclization, dehydrogena-tion and oxidation reactions that were observed to be drastic from 200 ℃ to 220 ℃, from 220 ℃ to 250 ℃, and inthe later period of the thermal stabilization reactions, respectively. The sizes, shapes and distributions of the sealedmicropores were obtained from the SAXS data. The breaking elongation was significantly affected by the drasticcyclization and dehydrogenation reactions. The breaking force was affected considerably by the bigger micropores,especially from 220 ℃ to 250 ℃, owing to the drastic dehydrogenation reactions.展开更多
For the wide application as thermal protection materials,it is very necessary for mullite ceramics to improve fracture toughness.In this paper,the laminated and stitched carbon fiber cloth preform reinforced mullite(C...For the wide application as thermal protection materials,it is very necessary for mullite ceramics to improve fracture toughness.In this paper,the laminated and stitched carbon fiber cloth preform reinforced mullite(C/mullite)composites were prepared through the route of sol impregnation and heat treatment using the Al2O3-SiO2 sol with a high solid content as raw materials.The C/mullite composites showed a flexural strength of 228.9 MPa that was comparable to that of dense monolithic mullite although the total porosity reached 13.4%.Especially,a fracture toughness of 11.2 MPa·m1/2that was 4–5 times that of dense monolithic mullite was obtained.Strength deterioration due to the carbothermal reduction between carbon fiber and the residual SiO2 in matrix was found above 1200℃.A pyrolytic C(Py C)coating was deposited on carbon fibers as interfacial coating.The chemical damage to carbon fibers was obviously alleviated by the sacrifice of PyC coating.Accordingly,the C/PyC/mullite composites kept strength unchanged up to 1500℃,and showed much higher strength retention ratio than C/mullite composites after annealing at 1600℃.展开更多
A novel bifunctional comonomer 3-ammoniumcarboxylate-butenoic acid-methyl ester （ACBM） was synthesized tor preparing poly[acrylonitrile-co-（3-ammoniumcarboxylate-butenoic acid-methyl ester）] [P（AN-co-ACBM）] copo...A novel bifunctional comonomer 3-ammoniumcarboxylate-butenoic acid-methyl ester （ACBM） was synthesized tor preparing poly[acrylonitrile-co-（3-ammoniumcarboxylate-butenoic acid-methyl ester）] [P（AN-co-ACBM）] copolymer as a carbon fiber precursor. Differential scanning calorimetry results show that the P（AN-co-ACBM） exhibits a significantly improved stabilization performance compared with polyacrylonitrile （PAN）, such as lower cyclization temperature and smaller rate of heat release, which is mainly attributed to the initiation of ACBM through an ionic cyclization mechanism. Simultaneously, the rheological analysis shows that P（AN-co-ACBM） possesses better spinnabilitv than PAN.展开更多
Acrylonitrile(AN)/1-vinyl-3-ethylimidazolium bromide(VIMB) copolymer was prepared via solution polymerization using dimethyl sulfoxide(DMSO) as a solvent and azodiisobutyronitrile as an initiator. The effects of comon...Acrylonitrile(AN)/1-vinyl-3-ethylimidazolium bromide(VIMB) copolymer was prepared via solution polymerization using dimethyl sulfoxide(DMSO) as a solvent and azodiisobutyronitrile as an initiator. The effects of comonomer VIMB on the polymerization, rheological properties of the polymer solution and thermal properties of the copolymer were investigated. The ionic liquid VIMB resulted in higher polymerization conversion ratio and higher average molecular weight when copolymerized with AN than itaconic acid(ITA). Rheological measurements indicated that the transition shear rate increased linearly with increasing temperature for P(AN/ITA)/DMSO solution, while an exponential growth with temperature was observed for P(AN/VIMB)/DMSO solution. The exothermic peaks of DSC curves in N_2 appeared at 276.67 and 257.34 °C for P(AN/VIMB) and P(AN/ITA), respectively. As a potential comonomer of AN for PAN carbon fibers, the VIMB resulted in about 7% higher char yield in N_2, and 23.7% less weight loss at 600 °C in air than ITA copolymer.展开更多
文摘The influence of two-stage isothermal treatment on the change in the linear dimensions of the fiber, the average sizes of the coherent scattering regions, the texture and phase composition of the polyacrylonitrile fiber in the process of isothermal thermal stabilization is considered by the methods of dilatometry and X-ray diffraction analysis. It is shown that preliminary short-term heat treatment at a lower temperature affects the process of structural transformations of the polyacrylonitrile fiber material and the formation of a new highly dispersed phase of the thermally stabilized fiber.
基金supported by the National Natural Science Foundation of China under grant No.59783002by the Natural Science Foundation of Henan under grant Nos.200510465008 and 0523021200.
文摘Different polyacrylonitrile （PAN） precursor fibers that displayed various thermal properties were studied by using differential scanning calorimetry （DSC）. Results showed that some commercial PAN precursor fibers displayed double separated peaks and these fibers were of high quality because of their process stability during their conversion to carbon fibers of high performance. Some fabrication processes, such as spinning, drawing, could not apparently change the DSC features of a PAN precursor fiber. It was concluded that the thermal properties of a PAN precursor fiber was mainly determined from its comonomer content type and compositions.
文摘The effect of structural evolution polyacrylonitrile (PAN) on mechanical properties was investigated in stabilization and carbonization. PAN spun fibers were stabilized in a convection oven with a constant tension for various times at 250℃. Fourier Transform Infrared spectroscopy (FTIR) and gel fraction results suggested that intra and intermolecular stabilization reactions occurred simultaneously. X-ray diffractograms revealed a disruption of crystalline structure and an appearance of pre-graphitic structure of PAN fibers due to stabilization. These structural changes by stabilization resulted in the significant decrease of tensile properties of fibers. In Raman spectra with heat treated fibers from 400℃ up to 1200℃, the intensity ratio of the D to G bands (ID/IG) decreased as heat treatment temperature increased, indicating an increase of basal plane of graphitic layer of heat treated fibers. Tensile strength of heat treated fibers at 1200℃ was found to be as high as 2.2 GPa.
基金supported by the National Natural Science Foundation of China(Nos.51073011 and 50673011) the,National High Technology Research and Development Program of China("863 Program",No.2006AA06Z382)the National Basic Research Program of China("973 Program",No.2006CB605304)
文摘Orientation of copolymer polyacrylonitrile （PAN） chains during their deformation prior to stabilization and the further effect on the stabilization were investigated in detail. Results reveal that the orientation of PAN chains presents a saturation point of 69.51% when the deformation ratio reaches approximately 1.07, meanwhile the cyclization rather than the oxidation has a stronger dependence on the orientation of PAN chains during stabilization. The cyclization is facilitated that the cyclization degree is increasing while the activation energy is decreasing obviously as a consequence of the developing orientation of PAN fibers before the saturation point; however, it is restrained during the further deformation of PAN fibers after the point. The resulting carbon fibers obtained from the PAN fibers prepared at the saturation point possess the highest mechanical properties of 4.07 GPa in tensile strength and 249.0 GPa in tensile modulus.
文摘Thermal stabilization is an important process in carbon fibers＇ production, during which the polyacryloni-trile fibers are heated from 180℃ to 280 ℃ in air. In this study, the samples were characterized by X-ray diffraction,Fourier infrared spectroscopy, differential scanning calorimetry, small angle X-ray Scattering（SAXS） and mechanicaltensile tests. A new rule was suggested by the results of structural characterization for the cyclization, dehydrogena-tion and oxidation reactions that were observed to be drastic from 200 ℃ to 220 ℃, from 220 ℃ to 250 ℃, and inthe later period of the thermal stabilization reactions, respectively. The sizes, shapes and distributions of the sealedmicropores were obtained from the SAXS data. The breaking elongation was significantly affected by the drasticcyclization and dehydrogenation reactions. The breaking force was affected considerably by the bigger micropores,especially from 220 ℃ to 250 ℃, owing to the drastic dehydrogenation reactions.
基金supported by the Open Foundation of Science and Technology on Thermostructural Composite Materials Laboratory (Grant No. 614291102010117)the Science Innovation Foundation of Shanghai Academy of Spaceflight Technology (Grant No. SAST2015043)the National Natural Science Foundation of China (Grant No. 11572277)
文摘For the wide application as thermal protection materials,it is very necessary for mullite ceramics to improve fracture toughness.In this paper,the laminated and stitched carbon fiber cloth preform reinforced mullite(C/mullite)composites were prepared through the route of sol impregnation and heat treatment using the Al2O3-SiO2 sol with a high solid content as raw materials.The C/mullite composites showed a flexural strength of 228.9 MPa that was comparable to that of dense monolithic mullite although the total porosity reached 13.4%.Especially,a fracture toughness of 11.2 MPa·m1/2that was 4–5 times that of dense monolithic mullite was obtained.Strength deterioration due to the carbothermal reduction between carbon fiber and the residual SiO2 in matrix was found above 1200℃.A pyrolytic C(Py C)coating was deposited on carbon fibers as interfacial coating.The chemical damage to carbon fibers was obviously alleviated by the sacrifice of PyC coating.Accordingly,the C/PyC/mullite composites kept strength unchanged up to 1500℃,and showed much higher strength retention ratio than C/mullite composites after annealing at 1600℃.
基金supported by the National Natural Science Foundation of China(Nos.51073031, 20971021 and 20974018)Doctoral Dissertation Innovation Project(No.BC201004)
文摘A novel bifunctional comonomer 3-ammoniumcarboxylate-butenoic acid-methyl ester （ACBM） was synthesized tor preparing poly[acrylonitrile-co-（3-ammoniumcarboxylate-butenoic acid-methyl ester）] [P（AN-co-ACBM）] copolymer as a carbon fiber precursor. Differential scanning calorimetry results show that the P（AN-co-ACBM） exhibits a significantly improved stabilization performance compared with polyacrylonitrile （PAN）, such as lower cyclization temperature and smaller rate of heat release, which is mainly attributed to the initiation of ACBM through an ionic cyclization mechanism. Simultaneously, the rheological analysis shows that P（AN-co-ACBM） possesses better spinnabilitv than PAN.
基金supported by the National Natural Science Foundation of China (no.U1362205)
文摘Acrylonitrile(AN)/1-vinyl-3-ethylimidazolium bromide(VIMB) copolymer was prepared via solution polymerization using dimethyl sulfoxide(DMSO) as a solvent and azodiisobutyronitrile as an initiator. The effects of comonomer VIMB on the polymerization, rheological properties of the polymer solution and thermal properties of the copolymer were investigated. The ionic liquid VIMB resulted in higher polymerization conversion ratio and higher average molecular weight when copolymerized with AN than itaconic acid(ITA). Rheological measurements indicated that the transition shear rate increased linearly with increasing temperature for P(AN/ITA)/DMSO solution, while an exponential growth with temperature was observed for P(AN/VIMB)/DMSO solution. The exothermic peaks of DSC curves in N_2 appeared at 276.67 and 257.34 °C for P(AN/VIMB) and P(AN/ITA), respectively. As a potential comonomer of AN for PAN carbon fibers, the VIMB resulted in about 7% higher char yield in N_2, and 23.7% less weight loss at 600 °C in air than ITA copolymer.
