A low-cost rout for modification the polyacrylontrile(PAN) precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers wer...A low-cost rout for modification the polyacrylontrile(PAN) precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers were stabilized.The effect of UV irradiation on the chemical structure,orientation factor,density,crystallite size and morphology of the fibers in the process of stabilization was characterized by use of fourier transform infrared spectroscopy(FTIR),float-sink procedure,X-ray diffraction(XRD),scanning electron microscope(SEM),respectively.The results showed that UV irradiation could increase the density of the fibers in stabilization process.FTIR analysis indicated that the cyclization of nitrile groups was initiated at room temperature by UV irradiation.The transformation of C≡N groups to C=N ones was accelerated in the process of stabilization.The orientation factor of irradiated fibers was also increased.The crystallite size was decreased at first and increased later,and the better irradiation time of UV was 3 min according to the XRD test.SEM analysis indicated that irradiation could decrease the internal and surface defects of the stabilized fibers treated at 300 ℃.展开更多
Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mecha...Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mechanisms were both investigated.The specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated structure.However,the mechanical denudation of the sample only containing acicular crystals and the coating spallation caused by superfluous gaseous products of the sample with the sublayer composed of nanocrystals both indicate their inferior anti-ablation properties.It is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.展开更多
基金Funded by the National Natural Science Foundation of China (No. 51073098)the State Key Laboratory of Polymer Material Engineering(Sichuan University) (Nos.KF200901 and 2030925123008)
文摘A low-cost rout for modification the polyacrylontrile(PAN) precursor fibers was developed.The approach involved pretreatment PAN precursor fibers with UV irradiation for various periods of time before the fibers were stabilized.The effect of UV irradiation on the chemical structure,orientation factor,density,crystallite size and morphology of the fibers in the process of stabilization was characterized by use of fourier transform infrared spectroscopy(FTIR),float-sink procedure,X-ray diffraction(XRD),scanning electron microscope(SEM),respectively.The results showed that UV irradiation could increase the density of the fibers in stabilization process.FTIR analysis indicated that the cyclization of nitrile groups was initiated at room temperature by UV irradiation.The transformation of C≡N groups to C=N ones was accelerated in the process of stabilization.The orientation factor of irradiated fibers was also increased.The crystallite size was decreased at first and increased later,and the better irradiation time of UV was 3 min according to the XRD test.SEM analysis indicated that irradiation could decrease the internal and surface defects of the stabilized fibers treated at 300 ℃.
基金supported by the National Natu-ral Science Foundations of China(Nos.51727804,52130205,and 91860203)the National Key R&D Program of China(No.2021YFA0715803)The authors also thank the Analytical&Testing Center of Northwestern Polytechnical University for the characteri-zation of our samples.
文摘Tantalum carbon(TaC)alternate coatings with sublayers comprised of different crystallite morphologies were prepared on carbon/carbon composites by chemical vapor deposition.Their ablative behaviors and defending mechanisms were both investigated.The specimen with the sublayer composed of columnar crystals exhibited a better ablation resistance due to the toughness enhancement induced by the lami-nated structure.However,the mechanical denudation of the sample only containing acicular crystals and the coating spallation caused by superfluous gaseous products of the sample with the sublayer composed of nanocrystals both indicate their inferior anti-ablation properties.It is believed that the results will be helpful for the structural design and practical application of chemical vapor deposition(CVD)alternate coatings.