Effect of graphitization temperature on microstructure of PAN-based high modulus graphite fibers

以日本东丽公司T800碳纤维为原料,经不同温度的连续石墨化处理得到性能不同的高模量碳纤维。利用X射线衍射（XRD）和激光拉曼光谱（Raman光谱）研究了5种自制PAN基高模量碳纤维（1^#,2^#,3^#,4^#,5^#）的微观结构。结果表明：随着石墨化温度的升高,石墨微晶尺寸L_c、L_a10、L_a110及取向度均逐渐增大,而d₀₀₂和取向角则逐渐减小。石墨化温度越高,碳纤维的石墨化程度越高,结晶度越大。     

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。     

高强高模PAN基石墨纤维的制备研究

以国产T800级PAN基碳纤维为原料,通过调整石墨化温度和牵伸率,制备出拉伸强度3.8 GPa和拉伸模量450 GPa的石墨纤维。研究发现,拉伸模量随石墨化处理的温度升高和牵伸比的增加而提高,而其拉伸强度随牵伸比的增加而下降。进一步分析石墨化处理过程中纤维微观结构参数发现,微观有序化和高取向是制备高强高模石墨纤维的关键。     

聚丙烯腈基高强高模石墨纤维结构研究

以聚丙烯腈纤维为先驱体,经连续热稳定化、碳化处理,制备出T800级碳纤维;进一步经连续石墨化处理后,制备出M50J级石墨纤维。采用SEM、元素分析、XRD和Raman等手段表征了碳纤维截面形貌、化学组成、石墨微晶及取向等结构。与进口M50J石墨纤维相比,国产M50J级碳纤维模量与其相当,但有更高的拉伸强度;同时两者间碳含量和石墨微晶尺寸相当,但国产纤维具有更高的取向程度和石墨化程度。M50J级碳纤维比T800级碳纤维具有更高的碳含量、更完善的石墨微晶结构及取向程度。     

PAN基碳纤维宏微观结构与拉伸强度的关联性

采用扫描电子显微镜、激光拉曼光谱仪、X射线衍射仪和X射线小角散射仪对市场采购的T300及T700碳纤维和实验室自制的SY300及SY700碳纤维的宏观和微观结构进行了表征和分析,比较了这4种碳纤维在宏观和微观之间的差异,并分析了这些差异对拉伸强度的影响。结果表明:宏观方面,拉伸强度与直径成反比关系,其数值大小与直径实验方法密切相关;微观方面,对于不同类型碳纤维的拉伸强度与石墨化程度和微晶厚度成正比,与微晶层间距和微孔大小成反比。对于同类型的碳纤维,其石墨化程度、微晶厚度及层间距相近,微孔尺寸是影响拉伸强度的最主要因素。     

热处理对PAN基碳纤维结构与性能的影响

以日本进口碳纤维(T300)和国产聚丙烯腈基碳纤维(GCF)为原材料,采用自制石墨化炉,在一定拉伸条件下,对T300及GCF进行1500～2100℃热处理,制备了不同性能的高模量聚丙烯腈基碳纤维(PAN-CFs)。采用广角X射线衍射、拉曼散射光谱、万能材料测试机等探讨了在热处理过程中PAN-CFs性能的演变规律,研究了PAN-CFs的力学性能与微观结构。结果表明:随着热处理温度升高,PAN-CFs的拉伸强度逐渐下降,拉伸模量逐渐上升,纤维的微晶尺寸和微晶取向度逐渐增大,石墨化程度越来越高,PAN-CFs的微观结构从二维乱层石墨结构向有序的三维层状结构发展。     

石墨化温度对人造石墨微观结构及电化学性能的影响

以油系针状焦为原料，在1 500～3 000℃范围内，探索不同石墨化温度对二次颗粒石墨微晶层间距d₀₀₂、微晶堆砌厚度L_c和微晶基面宽度L_a等微观结构的演变，揭示了碳原子从二维无序到三维有序排列的规律。研究结果表明：随着石墨化温度的升高，石墨微晶层间距逐渐减小，晶粒尺寸变大，同时石墨微晶的d₀₀₂与L_a的倒数具有一定的线性关系；同时研究了不同石墨化温度对二次颗粒电化学性能的影响，二次颗粒的首次比容量、首次效率及真密度随石墨化温度的升高而增加；温度在2500℃及以上时，充放电曲线呈U型且存在稳定的电压平台；石墨化温度在3 000℃时，油系针状焦的首次比容量和首次库伦效率分别可达343 mAh/g、94.7%。     

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。     

不同直径国产高强中模型碳纤维结构及其轴向压缩强度关系的研究

通过测量与比对东丽T300、T800H碳纤维的压拉比,验证了拉伸回弹法测量高强中模型碳纤维本征压缩强度的可行性。采用该方法测试了五种不同直径国产T800级高强中模型碳纤维的单丝压缩强度,并采用X射线衍射仪(XRD)、扫描电镜(SEM)分别表征其石墨微晶结构及断裂形态。探讨了碳纤维结构与力学强度的关联性。结果表明,当直径的变化有利于提升石墨微晶的基面宽度和取向度时,国家高强中模型碳纤维的轴向抗压性能得到强化,单丝压缩强度可达2. 8 GPa,压拉比为0. 52,显著高于东丽T800H的0. 42。碳纤维/环氧复合材料轴向压缩强度可达1 715 MPa,进一步验证了单丝压缩强度的研究结果。     

不同直径的T800级高强中模碳纤维的结构对比

对自制的两种不同直径的T800级高强中模碳纤维(NBF1,NBF2)的结构与性能进行了研究,并与日本东丽公司T800碳纤维进行了比较。结果表明:NBF1,NBF2的直径分别为5. 64,6. 31μm,均高于日本东丽公司T800碳纤维(5. 45μm),截面比日本东丽公司T800碳纤维规整; NBF1,NBF2的拉伸强度分别为5. 58,5. 56 GPa,略高于日本东丽公司T800碳纤维(5. 52 GPa),拉伸模量分别为293,295 GPa,略高于日本东丽公司T800碳纤维(290 GPa),断裂伸长率分别为1. 97%,1. 89%,均高于日本东丽公司T800碳纤维(1. 80%); NBF2的石墨微晶层间距为0. 352 7 nm,显著低于日本东丽公司T800碳纤维(0. 355 5 nm),NBF2具有更高的石墨化程度;碳纤维表面无序化程度越低,其拉伸强度越高。     

Isotropic carbon and graphite fibers from chemically modified coal-tar pitch

A precursor for a general purpose carbon fiber was prepared from coal tar pitch (CP) modified with 10 % p-benzoquinone (BQ) at 380 ?C for 3 hours. Such a modification raised the softening of the pitch from 85 ?C to 271 ?C at a yield of 43 %. The modified pitch was spun smoothly at a rate of 480 m/min into a fiber of 20 Μm diameter. The fiber was stepwise stabilized at 236 ?C (5 ?C/min) and 312 ?C (1 ?C/min) for 3 hours at each temperature. Successively,carbonization and graphitization were performed at 1,000 ?C and 2,400 ?C, respectively, for one hour. Both the carbonized and graphitized fibers exhibited tensile strength of 570 MPa. The structural parameters of carbon and graphite fibers were their orientation values of 56.2 and 58.1 %, relatively low Lc(002) of 11.24 and 25 å, and large interlayer spacing (d₀₀₂) of 3.86 and 3.49 å, respectively.     

碳纤维石墨化技术研究进展

碳纤维石墨化可以使其结构趋向于理想石墨结构，拉伸模量大幅提升，因此石墨化碳纤维广泛应用在航空航天等尖端技术领域。本文对比分析了碳纤维石墨化设备优缺点，详细介绍了激光超高温加热等新式石墨化方法及促进石墨化进程的相关工艺，进一步从微观结构层面分析影响力学性能的因素，为高模量碳纤维制备技术的研究提供理论及实践参考。指出目前主流的石墨体间接加热技术由于温度限制阻滞了碳纤维模量的进一步提升，克服高温限制且高效高质量、节能环保的石墨化技术是未来的发展趋势；应从组成碳纤维的分子层面去分析把握碳纤维的结构演变，进而优化控制石墨化工艺及设计相关石墨化设备，不断改善碳纤维石墨化结构，逐步趋向于力学性能的理论值。     

Structure of silicon-modified mesophase pitch-based graphite fibers

Silicon-modified mesophase pitch-based graphite fibers (SGF) were prepared from mixtures of mesophase pitch and silicon (Si) nanoparticles, followed by fiber spinning, thermo-oxidative stabilization, carbonization and graphitization. The morphology and microstructure as well as physical properties of the obtained graphite fibers were characterized. Compared with the unmodified graphite fibers (GF), SGF possessed the characteristic of the circular cross section, and no cracks along the fiber axis were observed. Based on the XRD and Raman analysis, Si nanoparticles added in the fiber resulted in the dissimilar orientation of graphitic pleats and changed the crystallite of the SGF. The angle of orientation and the ratio of the intensity of D-Raman peak and G-Raman peak for SGF were increased to 10.59° and 0.25, respectively, which were higher than that of the GF. The small-angle X-ray scattering experiment indicated that Si introduced in the fiber had no effect on the micropore size and pore size distribution compared with that of the GF. The tensile strength and modulus of the Si-modified carbon fibers was 2.42 and 138.8 GPa, respectively.     

Microcrystal structure evolution of mesophase pitch-based carbon fibers with enhanced oxidation resistance and tensile strength induced by boron doping

Mesophase pitch-based carbon fibers (MPCFs) with various concentration of boron were fabricated through an easy and effective strategy by treating stabilized fibers with boron acid solution. The microstructural evolution of boron-doped MPCFs was characterized. It was found that boron doping promoted high degree of graphitization with the decrease of interlayer spacing and the growth of crystallite dimension due to catalytic graphitization of boron to carbon. Boron doping significantly improved 5?wt% burn-off temperature of MPCFs increasing by 344?°C, and the tensile strength of MPCFs was also enhanced by 19%. Both of the outstanding oxidation resistance and mechanical performance of MPCFs was obtained due to effect of boron. The results demonstrated boron doping was a feasible way to produce high-performance MPCFs.     

The breaking strength of imperfect (real) polymer fibers

The thermodynamic fusion theory of strength of perfect polymer fibers of finite molecular weight is extended to include imperfect (i.e. real) fibers of incomplete crystallinity and orientation. Approximate equations for failure strength, strain, and work of failure are derived by extracting from the real visco-elastic fiber an equivalent reversible component suitable for thermodynamic analysis. This is facilitated by an explicit relationship between fiber breaking stress, σ_*, and breaking strain, _*, which is shown to be σ_*=0.632K_* (K=modulus) for constant strain-rate deformations. It is shown that fiber breaking time is equivalent to the fiber visco-elastic mechanical relaxation time. Experimental data shows that the activation energy of rupture of polyethylene fibers is not the activation energy of covalent bond rupture. Instead it agrees with the activation energy expected of crystal melting in accordance with the fusion theory of rupture. The activation volume of the polyethylene fibers also agrees with the value expected from this theory.     

The structure and properties of ribbon-shaped carbon fibers with high orientation

Using a naphthalene-derived mesophase pitch as a starting material, highly oriented ribbon-shaped carbon fibers with a smooth and flat surface were prepared by melt-spinning, oxidative stabilization, carbonization, and graphitization. The preferred orientation, morphology, and microstructure, as well as physical properties, of the ribbon-shaped carbon fibers were characterized. The results show that, the ribbon-shaped fibers possessed uniform shrinkage upon heat treatment, thereby avoiding shrinkage cracking commonly observed in round-shaped fibers. As heat treatment progressed, the ribbon-shaped graphite fibers displayed larger crystallite sizes and higher orientation of graphene layers along the main surface of the ribbon-shaped fiber in comparison with corresponding round-shaped fibers. The stability of the ribbon-shaped graphite fibers towards thermal oxidation was significantly higher than that of K-1100 graphite fibers. The longitudinal thermal conductivity of the ribbon fibers increased, and electrical resistivity decreased, with increasing the heat treatment temperatures. The longitudinal electrical resistivity and the calculated thermal conductivity of the ribbon-shaped fibers graphitized at 3000 °C are about 1.1 μΩ m and above 1100 W/m K at room temperature, respectively. The tensile strength and Young’s modulus of these fibers approach 2.53 and 842 GPa, respectively.     

高性能沥青基碳纤维制造——氧化碳化石墨化

本文论述了用于制造高性能碳纤维的中介相沥青初生纤维的氧化稳定化、碳化与石墨化过程及其对最终碳纤维力学性能与电导性能的影响;讨论了氧化碳化与石墨化温度、升温速率、中介相沥青原料种类与氧化稳定化程度、石墨化程度、抗张强度与模量、电阻率、纤维结构的关系;指出了五种加速氧化稳定化进程的有效措施。