中间相沥青纤维稳定化过程中的氧化动力学计算

为了定量测算稳定化中间相沥青纤维(MPPF)的交联程度,采用差示扫描量热法(DSC)对不同温度下MPPF恒温氧化稳定化过程中的热流随时间的变化进行测试.通过氧化反应和交联反应的连串反应机制对MPPF的恒温DSC曲线进行定量分析.计算结果表明,MPPF氧化稳定化过程中氧化反应和交联反应的活化能分别为59和67 kJ·mo...     

加压氧化对抑制中间相沥青纤维氧化粘连并丝的影响

为了解决中间相沥青纤维氧化稳定化过程中由于纤维表面发生小分子挥发以及低分子质量组分软化导致的粘连并丝问题,采用加压空气和加压氧气对中间相沥青纤维进行氧化稳定化热处理,研究氧气分压和氧化气体的总压力对沥青纤维氧化粘连的影响.利用悬垂度的测试表征氧化沥青纤维的粘连程度,悬垂度越大说明纤维粘连程度越小.结果 表明:空气中压力...     

中间相沥青纤维在不同氧气浓度下氧化稳定化过程的研究

研究了萘系中间相沥青在不同氧气浓度下氧化稳定化过程，以期改善炭纤维的力学性能和缩短氧化稳定化时间，与空气相比（氧含量为２１％），在较低的氧气浓度下（Ｏ２：１０％，Ｎ２：９０％，体积含量）氧化后的纤维，经过后续炭化处理，炭纤维的抗拉强度及模量有一定的提高，而最终氧化终温则一样；在较高的氧气浓度下（３０％，５０％）进行氧化稳定化，可使氧化终温比空气时降低２０℃左右，但炭纤维的抗拉强度及模量有所下降。元素分析数据及红外光谱表明在较高氧气浓度下，沥青纤维与氧气的反应速度大大加快，在不同氧气浓度下稳定化、炭化后而得的炭纤维断面结构及微晶参数没有很大差别。     

煤沥青纤维的不熔化处理

采用空气预氧化方法进行煤沥青纤维的不熔化处理,用红外光谱定性描述了预氧化过程,并运用动力学进行了定量计算,求出了增重为3％时,不同直径的纤维在不同温度下所需的预氧化时间。     

中间相沥青纤维的氧化

中间相沥青熔融纺丝可制得沿轴定向较好的沥青纤维。这些纤维虽然由芳烃大分子层片组成,有较高的软化点,但仍具有热塑性,因此在碳化以前必须进行不熔化处理,使之热固化,以防止碳化时纤维的熔融和融并,保持它们轴向择优定向的结构。故不熔化处理在碳纤维的制造过程中是一个关键的步骤。 本文通过在空气中加热中间相沥青纤维,研究了氧化工艺参数,氧化增重和最终碳纤维性能之间的关系,并试图从热力学和动力学的角度探讨中间相沥青纤维的氧化过程。     

中间相沥青纤维的氧化稳定化及炭化

本文主要研究了具有不同直径萘系中间相沥青纤维的氧化稳定化及炭化性质，结果表明，直径为１１μｍ和１６μｍ的细径中间相沥青纤维在空气中以０．５℃／ｍｉｎ的升温速度升至２６０℃至３２０℃，即可完成以后续的炭化过程中完全不融化，且抗拉强度和模量分别达到最大值，而对于直径分别为２５μｍ和４７μｍ的沥青纤维，既使最终氧化温度很高。在炭化后的纤维仍然形成所谓的“皮芯”结构，而且纤维越粗，“皮芯”结构中的芯部越大     

用连串反应表征沥青纤维的氧化动力学

沥青纤维在不熔化过程中,同时伴着氧的增加和脱除,含氧量的变化又会体现在沥青纤维的增重及失重上。使用热重分析仪(TG)研究沥青纤维在空气中的热氧化行为,考察了从120℃升温到410℃的质量变化,以及分别在230和290℃恒温过程中的质量变化。将氧化过程中含氧官能团的生成和脱除视为同时发生的两个连串反应,用连串反应动力学模拟计算了氧化过程中的纤维重量变化并计算了反应速率常数。结果表明:氧化和脱氧反应均为一级反应,用连串反应可以很好地拟合沥青纤维的氧化增重过程。用恒速升温的非等温动力学可以分别计算出氧化反应和脱氧反应的频率因子和活化能,并据此可以计算不同温度下两种反应的表观速率常数随温度的变化。低温时氧化反应速率常数k1明显大于脱氧反应速率常数k2,随着温度的升高,k1和k2均增大,但k2增加的速率k1,达到290℃时k1和k2相等,290℃后k2k1,与实验结果先增重后失重相吻合。同样用连串反应动力学模拟了恒温过程中纤维的质量变化,也具有很好的拟合度,但所得到的反应速率常数k1和k2与恒速升温反应相比明显要小,并对其原因进行了分析。     

煤沥青基中间相沥青的制备研究

以纯化的煤焦油沥青为原料,考察了热聚合温度和恒温时间对中间相沥青的收率、光学显微形态、软化点和族组成的影响.结果表明:反应温度在420℃,恒温5 h时得到了软化点为312℃的流线体型中间相沥青,其收率为79.1%;热聚合反应在相对较低的温度400℃,反应时间为10 h时形成了软化点为305℃、收率为81.4%的优质广域型可纺性中间相沥青.对该原料煤沥青而言,通过控制热聚合反应温度和恒温时间可以达到制备优质中间相的目的.     

沥青基带状纤维的预氧化研究

采用熔融纺丝工艺制备中间相沥青基带状纤维,分别于不同温度和不同时间进行氧化稳定化处理,采用红外光谱仪和元素分析测定预氧化纤维官能团和氧含量的变化,并采用扫描电镜和纤维强伸度仪等检测设备研究2 500℃石墨化纤维的结构和性能.实验结果表明：沥青分子在预氧化过程中与氧发生反应,生成了热固性的沥青大分子.氧化温度越高,氧化时间越长,带状纤维的氧含量越高.厚度为～35μm,宽度为～380μm的带状沥青纤维于氧气气氛经220℃下预氧化20h和2 500℃石墨化处理后,其拉伸强度可达1.75GPa,比240℃和260℃预氧化制得的石墨纤维的拉伸强度高.     

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。     

Evaluating multi-step oxidative stabilization behavior of coal tar pitch-based fiber

Oxidative stabilization is an important step for isotropic pitch-based carbon fiber preparation; coal tar pitch-based fiber is treated by multi-step oxidative stabilization under various conditions to investigate the oxidative stabilization mechanism. The chemical structure changes of isotropic pitch-based fiber during the oxidative stabilization and carbonization stage are systematically characterized by In-situ diffuse reflectance infrared Fourier transform, elemental analysis, mass spectroscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance, scanning electron microscope with an energy dispersive X-ray spectrometer. These results show that the oxygen distribution gradient in oxidative stabilized fiber radial direction become homogeneously with the increasing of oxidation temperature and time under multi-step oxidative stabilization. The resultant carbon fiber shows tensile strength of 942 ± 42 MPa and Young's modulus of 42.8 ± 3.1 GPa due to appropriate oxygen content, homogeneous oxygen distribution, more cross-link bond (C-O-C) content, higher aromaticity and lower weight loss introduced in multi-step oxidative stabilized pitch fiber. The multi-step oxidative stabilization provides synergy effect between reaction rate and the oxygen diffusion rate as well as eliminates the oxygen concentration gradient, it provides an time-saving and energy-effective method for the oxidative stabilization of isotropic pitch-based carbon material (pitch fiber, pitch microsphere, etc.) and improve the resultant carbon material performance.     

Injection and stabilization of mesophase pitch in the fabrication of carbon-carbon composites: Part II. Stabilization process

In the fabrication of carbon-carbon composites by mesophase injection through a fiber preform, it is essential to stabilize the flow-induced microstructure in the flow channels and to prevent relaxation and exudation of the mesophase. Oxidation stabilization studies were conducted on preforms injected with the naphthalene-based AR mesophase pitch. Oxidation mass gain (OMG) curves at 170, 222, and 270 °C were generated for 60°-wedges cut from full size composite disks. The rates of OMG at 170 °C of first- and second-cycle injection wedges and full-size disks were comparable to those using as-spun filaments 30 μm in diameter, and particles sieved to 200 to 340 μm. The results suggest that oxygen is accessible deep into a mesophase matrix and the transport is facilitated by connected array of shrinkage cracks. Oxidation at 170 °C has strong advantage over higher oxidation temperatures by having a higher carbon yield and lower OMG threshold and thus oxidation time required for stabilization. The 60°-wedges could be stabilized at 170 °C after a 25 h oxidation with a 7.2% OMG and attaining a carbon yield above 85%.     

Y形沥青基炭纤维的制备及不熔化处理对其性能的影响

采用Y形喷丝板，以中间相沥青为原料熔纺出Y形纤维，考察了Y形沥青纤维的纺丝特点。实验表明，Y形沥青纤维具有较高的分子取向，其炭化纤维具有较高的力学性能。研究了不溶化恒温时间对Y形炭纤维性能的影响，利用电子扫描显微镜（SEM）分析了纤维的微观结构。     

Investigation on promotion effect of oxidative stabilization for pitch-based fiber by co-carbonization of coal tar pitch and atmospheric residual

As a pivotal step in the preparation of carbon fiber, oxidative stabilization not only plays a crucial role in maintaining fibrous morphology but also contributes significantly to enhance mechanical properties of resultant carbon fiber. Due to high activation energy of pitch molecules reaction with oxygen and the sluggish diffusion of oxygen within the fiber, the improvement of oxidative stabilization efficiency faces significant challenges. Atmospheric residual (AR) has a high and easily oxidized aliphatic structure. Spinnable pitch is synthesized by co-carbonization of coal tar pitch (CTP) and AR at a ratio of 3:1 in this work. Its methylene bridge bond ratio is 4.45% and have an appropriate amount aliphatic structure, which makes pitch molecular more linear and naphthenic. Excessive addition of AR is detrimental to spinning performance. The most optimal oxidative stabilization temperature of as-spun fiber was 280°C, which is lower than that of fiber produced by CTP alone (300°C), displaying a higher oxidative stabilization efficiency. The obtained pitch-based carbon fiber shows excellent mechanical properties with tensile strength of 999.0 ± 80.1 MPa and Young's modulus of 57.7 ± 3.5 GPa. The co-carbonization by two different substances has been applied in manufacturing carbon fiber, providing a facile approach to accelerate the oxidative stabilization of pitch fiber.     

煤沥青球的氧化不熔化过程特性

氧化不熔化过程是煤沥青基球状活性炭制备中的核心工艺,对其过程特性和动力学机理的认识是实现氧化过程工艺优化的关键。本文以煤沥青萃取球为原料,通过实验研究,重点探讨了粒径范围、升温速率和氧化温度对其氧化不熔化过程的影响,并确定氧化动力学参数及其反应机理函数。结果表明：氧化不熔化过程可分为轻组分热解、初步氧化、氧化增重和恒温氧化失重4个阶段。煤沥青球经过氧化不熔化后,C、H含量减少,O含量增加,表面光滑平整。减小粒径并选取合适的升温速率（0.25～0.5℃·min^-1）以及氧化温度（275～325℃）,更有利于氧化不熔化快速稳定地进行。粒径范围为0.3～0.6 mm的煤沥青球在升温速率为0.5℃·min^-1、氧化温度为300℃的条件下活化能最小,各个阶段的值分别为83.34、293.19、302.25和357.05 kJ·mol^-1。     

Injection and stabilization of mesophase pitch in the fabrication of carbon-carbon composites. Part III: Mesophase stabilization at low temperatures and elevated oxidation pressures

Micrography and infrared spectroscopy were applied to explore microstructural stabilization of mesophase pitch at oxidation temperatures as low as 130 °C. AR mesophase pitch synthesized from naphthalene was drawn to rods and thick filaments with fine fibrous microstructures that coarsen upon carbonization without adequate stabilization. At 270 °C, the stabilization front advances rapidly to a depth of about 7 μm, after which no further growth is perceptible. At low temperatures, there is a time lag before a stabilized layer can be observed near the surface, but thereafter the stabilization front advances relatively rapidly. For longer oxidation times, the low-temperature stabilization depths can exceed those attained at higher temperatures. FTIR spectra confirmed chemical reactivity and the formation of oxygen-bearing functional groups even at the low oxidation temperatures. Oxidation under a moderate pressure of 0.7 MPa can be effective in raising the oxygen uptake and increasing the stabilization depths significantly. All evidences point to the advantageous use of lower oxidative temperatures: more effective penetration of stabilization depth, lessen destructive effects of over-oxidation, and potentially shorter processing times.     

纺丝温度对中间相沥青炭纤维结构性能的影响

以萘催化合成中间相沥青(MP-1)和热缩聚法制备中间相沥青(MP-2)两种中间相沥青为原料,对其进行簇组成分析、偏光显微镜观察及红外光谱分析,研究其组成及结构.采用实验室气压式单孔纺丝装置在不同温度下对两种中间相沥青进行熔融纺丝,探讨纺丝温度对炭纤维结构及性能的影响.研究表明:MP-1低温获得无规结构,高温出现中心放射状边缘洋葱皮混合结构;MP-2随纺丝温度升高依次出现无规结构、准洋葱皮结构和洋葱皮结构.中间相沥青原料的性质影响着纤维截面结构随纺丝温度变化的规律.     

On the chemistry of the oxidative stabilization and carbonization of carbonaceous mesophase

Two mesophase samples, one derived from a coal-tar pitch (M-A) and the other from a naphthalene-based pitch (M-B), were stabilized with air in a temperature range of 200-300 °C and then carbonized to 1000 °C. Elemental analysis and FTIR spectroscopy were used to monitor the changes produced by oxygen in the chemical composition of the mesophase samples at different stages of stabilization (from 200 to 300 °C) and after carbonization of the stabilized samples (from 300 to 1000 °C). The results show that oxidative stabilization is a dehydrogenative process, where the hydrogen removed is predominantly aliphatic and the oxygen uptake is mainly in the form of C-O-C and CO groups. The more aliphatic character of M-B accelerates the stabilization process with respect to M-A. M-B shows a higher weight gain and also a greater variety of oxygen-containing functional groups. As a result, the plasticity of M-B is more affected by changes in the stabilization temperature than that of M-A. Thus, the stabilization process is easier to control in the case of M-A. On carbonization, oxygen and hydrogen are removed from the stabilized samples and the carbons generated exhibit an increase in interlayer spacing and a decrease in crystallite size as the carbonization temperature increases.     

热聚合温度对煤液化沥青制备中间相沥青的影响

为制备优质的中间相沥青,以煤液化沥青为原料,在不同热聚合温度下制备中间相沥青,采用偏光显微镜、红外光谱仪、XRD、热分析等测试仪器对所得中间相沥青进行分析和表征。结果表明,温度对中间相沥青的收率、形貌和结构影响显著。随着温度升高,中间相沥青的收率降至86.2%,H含量降至3.96%,S含量有所下降,残炭率增大;中间相小球体的尺寸增大,逐渐出现融并现象,最终形成广域型中间相;煤液化沥青中的稠环芳烃、芳香烃的含量明显增加,烷烃成分则明显减少;煤液化沥青中的无定型区含量减少,分子的排列与取向性变好。选择低的热缩聚温度(410~420℃),适当延长反应时间有利于反应方向的控制,从而达到制备优质中间相的目的。