制备聚丙烯腈基高模量碳纤维的高温热处理技术

指出高温热处理是制备高模量碳纤维的关键技术;介绍了制备PAN基高模量碳纤维的3种高温热处理技术。     

激光石墨化过程中激光功率和牵伸力对聚丙烯腈基碳纤维化学结构和微观结构的影响

采用自制的高温激光石墨化平台对聚丙烯腈（PAN）基碳纤维进行石墨化处理,分别在不同激光功率和不同牵伸力条件下制备了多种碳纤维实验样品,利用拉曼光谱和XRD射线衍射研究了不同条件下碳纤维样品的化学结构和微观结构。结果表明：在牵伸力不变时,随着激光功率的增大,碳纤维石墨化程度提高,当激光功率增大到一定值时,单方面继续提高激光功率对于提高碳纤维石墨化程度的影响将变小;在激光功率一定时,随着牵伸力的增大,石墨微晶尺寸L_c、L_a均逐渐增大,而d₀₀₂和取向角逐渐减小,在激光石墨化过程中,施加一定的牵伸力可以促使碳纤维中的石墨微晶沿纤维轴方向择优取向,改善微晶尺寸、减少石墨微晶层间距、提高微晶堆砌层数。     

Catalytic graphitization of electroless Ni-P coated PAN-based carbon fibers

Catalytic graphitization of electroless Ni-P coated PAN-based carbon fibers is reported. PAN-based carbon fibers with and without electroless Ni-P coatings were heat treated and the structural changes were followed by X-ray diffraction and Raman spectroscopy, both of which indicate that the graphitization of PAN-based carbon fibers was enhanced in the presence of the coating. The graphitization was shown to be better for electroless Ni-P coated PAN-based carbon fibers heat treated at 1400 °C than for uncoated fibers heat treated at 2400 °C.     

PAN基碳纤维连续石墨化过程中的取向性

利用XRD研究了PAN基碳纤维在连续高温石墨化和热牵伸石墨化过程中纤维内石墨微晶沿纤维轴择优取向性的变化。结果表明：碳纤维中石墨微晶的择优取向性随石墨化温度的提高和热牵伸的增大而增加。两种工艺中纤维的拉伸模量均随微晶取向性的增加而增大,但在获得相同的模量下其取向参数却不同;碳纤维的拉伸模量不仅仅取决于石墨微晶的择优取向,而且与晶体的大小有关。另外,经过3000℃的高温处理后,纤维的择优取向参数Z仅为14.71°,说明纤维中乱层石墨的层面仍没有高度取向。     

Raman spectrum of modified PAN-based carbon fibers during graphitization

Graphite fibers were developed from polyacrylonitrile (PAN) fibers which were modified with potassium permanganate. After the transitional temperature, the formation of graphite structures commenced, the crystals increased in thickness, and the preferred orientation of the fiber crystals increased. The Raman specific absorption peak of noncrystalline carbon layers (1360 cm⁻¹) weakened with the increase in the graphitization temperature, whereas the degree of graphitization rose. The results of this analysis indicate that manganese has the effect of catalyzing graphitization, thus increasing the mechanical properties of the graphite fibers. © 1996 John Wiley & Sons, Inc.     

聚丙烯腈基碳纤维高温石墨化综述

针对高模量碳纤维制备的关键工艺环节,综述总结了石墨化的基本工艺和石墨化高温处理过程纤维组成、结构的变化以及对最终碳纤维力学性能的影响,以期为我国高强高模碳纤维研发提供借鉴。综述结果表明,一步法石墨化高温处理有利于保持纤维的高强度特性,该工业化技术具有发展潜力;1 800℃前后纤维密度为先降后升;随着纤维对石墨晶体结构逐渐完善,层间距减少,模量提高;催化石墨化以及强磁场或射线处理可促使纤维石墨晶体结构的完善,但不易工业化实施;石墨化过程中适施应力是一项保持纤维强度和提高模量的有效措施。     

热处理温度对PAN基碳纤维微观结构的影响

利用X射线衍射、元素分析、拉曼光谱研究了不同热处理条件下聚丙烯腈基碳纤维(PAN-CFs)微观结构和元素含量的变化,定义了PAN-CFs石墨微晶长度和石墨微晶体积。结果表明:随着热处理温度升高,纤维中氮元素含量不断减小;石墨微晶长度、微晶宽度、微晶堆叠厚度以及微晶体积均不断增大;纤维的空隙率不断增加,空隙率增加的原因为氮元素的脱出和微晶体积的增大;纤维的石墨化程度不断增加。     

PAN基高模量碳纤维成型过程中的结构性能关联性

以实验室自制T800级聚丙烯腈（PAN）基高强中模碳纤维为原料，经连续石墨化处理得到M50J级、M55J级高模量碳纤维，以X射线衍射（XRD）、Raman光谱为表征手段研究了高强碳纤维向高模量碳纤维转变过程中石墨微晶、取向、微孔含量、石墨化度等石墨特征结构的演变规律，并开展了PAN基碳纤维石墨特征结构与力学性能的关联性研究。研究结果表明：在高强碳纤维向高模量碳纤维转变过程中，随着石墨微晶层间距d ₀₀₂的下降以及石墨微晶堆砌厚度L _c的增加，碳纤维的拉伸模量逐渐提升；石墨微晶层间距和微晶取向是影响碳纤维拉伸强度的两个主要因素，石墨微晶层间距d ₀₀₂值增加、石墨微晶取向越高，纤维拉伸强度也越高；在高模量碳纤维的成型过程中，纤维内部微孔含量随着石墨化程度的提高而降低；经过高温石墨化处理后，碳纤维的拉伸强度会随着Raman光谱中无序结构D峰和石墨特征结构G峰积分强度比值I _D /I _G的下降而下降。     

Tensile properties of ultrahigh strength PAN-based, ultrahigh modulus pitch-based and high ductility pitch-based carbon fibers

The tensile properties and fracture behavior of ultrahigh tensile strength PAN-based (T1000GB), ultrahigh modulus pitch-based (K13D) and high ductility pitch-based (XN-05) carbon fibers have been investigated. The statistical distributions of the tensile strength were characterized. The Weibull modulus for the T1000GB, K13D and XN-05 fibers were calculated to be 5.9, 4.2 and 7.9, respectively. The results clearly show that for PAN- and pitch-based carbon fibers, the Weibull modulus decreases with an increase in the tensile modulus and the mean tensile strength.     

The microstructure of intercalated graphite fibers

A study of the microstructure of two types of graphite fibers GY70, a polyacrylotrinitrile (PAN) based fiber and UC4104B a pitch based fiber, is reported. These high modulus fibers were modified by intercalation with the donors K, Rb, Cs and the acceptors FeCl₃, AlCl₃. Several experimental techniques were used, to elucidate the effects of intercalation on the microstructure of the graphite fibers. These include scanning and transmission electron microscopy and small and wide angle X-ray diffraction.     

Elastic modulus and bend strength of a nuclear graphite at high temperature

The elastic modulus of a nuclear graphite was measured in the range from room temperature to 1400°C by the ultrasonic pulse echo method. Little or no change in the elastic modulus was observed up to 450°C. Above 500°C, however, it increased almost linearly with increasing temperature. The fractional increase was about 10% at 1000°C and 24% at 1400°C. The four-point bend test was also measured at temperatures between room temperature and 1200°C. Changes in bend strength with temperature were found to parallel to those of the elastic modulus. The mechanism for the correlation between the bend strength and the elastic modulus, as well as the effect of moisture on the strength, was discussed.     

Effect of graphite oxide on graphitization of furan resin carbon

Graphite oxide (GO) was used to accelerate the graphitization of furan resin carbon. The effects of the GO content and the heat-treatment temperature (HTT) on the graphitization of furan resin carbon were investigated. The X-ray diffraction results indicate that the graphitization extent of furan resin carbon increases with the increase of the GO content and the HTT.     

Influence of continuous stabilization on the physical properties and microstructure of PAN-based carbon fibers

A continuous stabilization and carbonization process was used to prepare polyacrylonitrile (PAN)-based carbon fibers. The stepwise stabilization of PAN fibers was tried at various temperatures. The effect of stepwise stabilization on the physical properties and microstructure of the final carbon fibers is reported in this article. The fixed temperature in stepwise stabilization is kept below the fusion temperature of PAN precursors to avoid overstabilization of the fibers. The optimum stepwise stabilization process not only increases the amount of ladder polymer in stabilized fiber but also improves the physical and mechanical properties of the resultant carbon fibers. The formation of closed pores from open pores in carbon fiber occurs at 1100°C, but the formation of closed pores occurs at 200°C lower for carbon fiber developed from overstabilized fiber. The effect of continuous stepwise stabilization on the properties of resulting stabilized fibers and the variation in physical properties, element composition, and microstructure of carbon fibers during the carbonization process are also reported in this article.     

Comparative study of the structure and microstructure of PAN-based nano- and micro-carbon fibers

The work presents results on the manufacture and comparative assessment of the structure and microstructure parameters of polyacrylonitrile polymer (PAN)-based carbon nano- and micro-fibers. Using the same polymer solution, PAN nano- and microfibers were obtained. The PAN nanofibers were obtained by electrospinning, and microfibers were spun using the conventional solution-spinning method. The PAN-based fiber precursors were annealed to 1000 °C, 2000 °C and to 2800 °C. Using X-ray diffraction and Raman spectroscopy, the structural and microstructural parameters of both types of carbon fibers were examined. The morphology of PAN nanofibers and carbon nanofibers (CNF) were studied by SEM. Both types of ex-PAN carbon fibers (nano and micro) have similar the c-axis spacing (d₀₀₂) values and crystallite sizes after heat treatment to 2000 °C presenting turbostratic structure. HR-TEM images of low temperature CNF show uniform microstructure with the misoriented small carbon crystallites along the fiber axis. The ratio of the integrated intensities of the D and G peaks for carbon nanofibers after heat treatment at 2000 °C was distinctly higher in comparison to carbon microfibers (CF). After additional annealing the fibers to 2800 °C a better structural ordering show CNF. The crystallite sizes (L_c, L_a) in CNF were distinctly higher in comparison to the crystallites in CF. CF consist of two carbon components, whereas CNF contain three carbon components varying in structural and microstructural parameters. One of carbon phases in CNF was found to have the interlayer spacing close to graphite, i.e. d₀₀₂=0.335 nm.     

Melt transcrystallization of polyethylene on high modulus polyethylene fibers

A polytheylene composite was prepared and tested. It was consisted of a high-density polyethylene (HDPE) matrix and uniaxial gel-spun high-modulus PE fiber. Aided by the similarity between matrix and fiber, transcrystallization of HDPE melt on the PE fiber surface was generated. Nucleating agents were not employed. The transcrystalline growth of HDPE on the PE fiber surface was found to consist of an inner and an outer zone. The inner zone, 2–3 μm thick, is composed of HDPE crystals nucleated on the PE fiber surface. Photomicrographs showed a well-defined region of row-nucleated HDPE on the surface of PE fiber. This means the fibrils of HDPE were found to grow out from the PE fiber axis and HDPE crystallites are oriented in planes perpendicular to the PE fiber axis. The fiber in the composite induced the transcrystalline growth of HDPE on the PE fiber surface at higher temperature than on cooling the melt. For 36 wt% fiber, the increase was 2.5°C, also resulting in ～ 10% more crystals. Crystallization of a composite with 50 wt% fiber at 124°C involved two steps: The first a fast transcrystallization of HDPE on the PE fiber surface followed by the bulk crystallization of the HDPE.     

烧成温度对高铬砖显微结构的影响

利用扫描电子显微镜分析了 170 0℃、174 0℃、1780℃、182 0℃和 186 0℃烧成后高铬砖的显微结构。结果表明 :高铬砖的烧成温度不是越高越好 ,而是有一个合适的烧成温度 174 0℃。在该烧成温度下制得的高铬砖 ,其基质中的Cr2 O3晶粒尺寸适中 ,基质组织结构致密 ,基质和颗粒结合紧密 ,无裂纹 ,并且其力学性能最佳。