沥青流变性质的研究方法

介绍了几种沥青流变性的表征方法。表征可以用表观粘度、法向应力差、蠕变柔量和动态粘弹参数等物理量、这些参数可以描述沥青流变性的不同方面。同时也介绍了用这些参数对沥青流变性的研究状况。     

中间相沥青的纺丝——中间相沥青的流变性和可纺性

为了调制出适宜于纺丝的中间相沥青,考察中间相沥青的流变行为和可纺性是必不可少的。本工作从几种不同原料热处理而得的中间相沥青的流变行为着手,比较了同种原料中间相沥青的粘度—温度曲线与软化点、中间相含量及中间相沥青可纺性之间的关系。不同原料中间相沥青,由于中间相分子大小和性质的不同,流变行为和可纺性能并不遵循同种原料中间相沥青的规律。这对进一步改进中间相沥青的调制工艺及进一步优化熔融纺丝工艺具有一定的指导意义。     

中间相沥青纤维氧化及碳化的研究

以石油系催化裂化渣油为原料，调制出可纺性的中间相沥青，并纺出均匀的中间相沥青纤维。用热分析法和元素分析法，确定了最佳氧化条件。利用X射线衍射技术（XRD）及透射电镜（TEM）对中间相沥青碳纤维进行了表征，求得了结构参数。并研究了碳化过程中，结构、性能与温度的依存关系。     

中间相沥青纤维氧化及炭化的研究

以石油系催化裂化渣油为原料，调制出可纺性的中间相沥青，并纺出均匀的中间相沥青纤维。用热分析法和元素分析法，确定了最佳氧化条件。利用X-射线衍射技术（XRD）及透射电镜（TEM）对中间相沥青炭纤维进行了表征，求得了结构参数、并研究了炭化过程中，结构、性能与温度的依存关系。     

中间相沥青可纺性的评价

在用沥青制取高性能纤维的生产中,沥青的可纺性是影响产品质量的关键因素。要达到稳定连续生产,必须正确选取控制参数。本文对中间相沥青纺丝期间的流变特性做了分析,通过实验,得到了一种评价中间相沥青纺丝性能的方法。该方法是通过中间相沥青的流变特性——剪切和拉伸粘度的测定,评价可纺性和选择纺丝温度区间。同以往的经验法相比。克服了随机性较大的缺点。对中间相沥青纺丝工艺有一定的指导和参考价值.     

沥青－重油共炭化制取中间相沥青基炭纤维初探

利用工业重油三线芳烃和煤焦油沥青共炭化改善沥青的炭化性质，调制可纺性中间相沥青。本文主要考察了共炭化反应条件对沥青改性的影响，不同热缩聚条件与所得中间相沥青的软化点，光学各向异性含量和可纺性的关系，并对中间相沥青进行初步熔纺及后处理，制得强度较高的炭纤维，讨论了由此途径制取高性能沥青基炭纤维的工艺特点。     

中间相沥青基炭纤维的研制

对不同的中间相沥青原料进行了微型纺丝机的试纺工作，探讨了中间相沥青的可纺性及炭纤维性能与中间相沥青性能的关系；采用自制的落球粘度计研究了BS－9中间相沥青原料的流变性能随温度变化的规律；同时对以BS－9为原料获得的沥青纤维进行了不熔化、炭化处理，研究了预氧化最终温度对炭纤维性能的影响。研究表明：中间相沥青本身的性质影响其可纺性并最终影响炭纤维的性能，在熔融纺丝过程中，要与纺丝工艺参数相互协调；落球法提供的可纺温度与微型纺丝机的纺丝实验基本吻合，为今后纺丝温度的选取提供了理论依据；不熔化处理温度是影响炭纤维性能的关键因素。以BS－9为原料，在本实验条件下，得到直径为10.03μm、拉伸强度为1.96GPa的沥青基炭纤维。     

石脑油渣油的共炭化改质

研究了石脑油渣油和催化裂化澄清油共炭化后所得的中间相沥青的性质。光学显微结构和各向异性含量的变化、中间相沥青基本组成的变化指出了石脑油渣油和催化裂化澄清油的共炭化并不遵循简单的叠加原理。两者混合后共炭化所得的中间相沥青粘度有效地降低,流动性得到改善,从而使中间相沥青的可纺性大为提高。所有这些结果显示了重质渣油的共炭化可改善中间相沥青的性能,而有利于中间相沥青碳纤维的制造。     

熔融纺制的沥青基炭纤维

虽然沥青基炭纤维可以熔融纺制,但中间相沥青的流动性使得它极难处置。同许多液体一样,中间相沥青也可以是非牛顿型的。但其粘度对温度的敏感性要比大多数熔融纺丝物料的感性高得多。在本研究中,应用能量平衡和力平衡来论证工艺参数和原料性质对中间相可纺性的影响。研究结果表明:在熔融纺丝期间,温度与中间相粘度的相关性会产生丝的应力,这种应力接近丝的抗拉强度极限。因此,在沥青基炭纤维形成过程中,控制温度和传热速率是极为关键的。     

煤直接液化沥青制备中间相沥青炭纤维的研究北大核心

中间相沥青基炭纤维的性能直接取决于纺丝用中间相沥青,煤直接液化沥青因其饱和烃含量高,氢碳比高,高温融变性好,硫含量低等优点成为制备纺丝用中间相沥青的优良前驱体。本文以煤直接液化沥青为原料,研究不同热缩聚工艺对中间相沥青组成和结构的影响,通过考察其偏光织构、软化点、喹啉不溶物含量、黏温曲线和纺丝时长等指标综合评价可纺性。采用高低温结合多段聚合工艺制得具有大融并体结构、可纺性优良的中间相沥青,并进一步制得具有理想微观形貌的纤维,其拉伸强度为2.03 GPa,拉伸模量达到581 GPa。     

Flow of molten mesophase pitch

The rheological behavior of molten mesophase pitch has become a subject of major scientific curiosity as well as of technological importance. With the exception of a few recent studies, the early experimental techniques were not entirely adequate for precise rheological characterization of such a complex fluid as molten mesophase pitch. A reasonably extensive literature, therefore, does not seem to exist on mesophase pitch rheology. The factors which could contribute to the difficulties of accurately measuring the apparent viscosity of carbonaceous anisotropic materials are discussed herein. A Couette-flow instrument has been modified for measuring the apparent viscosity of mesophase pitch, circumventing most of the experimental difficulties. The reliability of this apparatus has been tested by cross checking the apparent viscosity measurements with the values measured from two other rheometers, Instron Capillary and Seiscor/Han, for a number of fluids. Changes in rheological properties that occur during the transformation of a commercial pitch into a totally anisotropic pitch have now been studied by an improved technique on the modified Couette apparatus. The rheology of two mesophase pitches, made from model compounds, have also been investigated for comparison.     

Modified characteristics of mesophase pitch prepared from coal tar pitch by adding waste polystyrene

The toluene soluble of coal tar pitch was carbonized with waste polystyrene. The properties of mesophase pitches were characterized using polarized light optical microscope, apparent viscometer, FT-IR, ¹H NMR and X-ray diffractometer. After adding the waste polystyrene into the toluene soluble of coal tar pitch, the soluble mesophase were was increased from about 9% to 52% and the mesophase pitches were changed from 74% with coarse mosaic texture to 100% with flow domain texture. The mesophase pitches were transformed from thixotropy to unthixotropy. By waste polystyrene added into the toluene soluble of coal tar pitch, the methylene group was increased a lot. The presence of more alkyl groups modified the characteristics of mesophase pitches and improved the assembly of mesophase pitch molecules.     

A novel method to obtain a petroleum-derived mesophase pitch suitable as carbon fibre precursor

This paper studies a novel method for the preparation of mesophase pitches suitable as carbon fibre precursors. A series of thermally treated petroleum pitches with mesophase contents ranging from 10.8 to 52.2 vol.% was obtained from pitch A-240. Separation of the phases was initially attempted by hot filtration, a suitable method for separating the phases in thermally treated coal-tar pitches. Although filtration failed for the petroleum samples, the behaviour observed led to the development of a new separation method that consists in the sedimentation of the mesophase. This method, after optimisation, yielded pitches with mesophase contents up to 97 vol.%, which were easily spun into carbon fibres of reasonable mechanical properties.     

Effects of borane-pyridine complex on the mesophase pitch formation from decant oil

Mesophase pitches were prepared by adding 0.5 to 2 wt.% of a borane-pyridine complex to a decant oil in a tubing bomb reactor and heating in a fluidized-sand bath held at 500 °C for 30, 45, and 60 min, respectively. The mesophase pitches were analyzed using thermal gravimetric analysis, X-ray diffraction and polarized-light microscopy. Growth and coalescence of mesophase spheres were hindered, while the crystallinity of mesophase pitches was increased when the materials were heat treated with the boron compound. The addition of the borane-pyridine complex also accelerated the coke formation.     

Computational rheology of carbonaceous mesophases

Mesophase pitches are multicomponent discotic nematic liquid crystals (DNLCs), whose characteristic molecular weight is intermediate between low molar mass and polymeric nematic liquid crystals. Flow modelling of these fluids is performed using a previously formulated mesoscopic viscoelastic rheological theory [J. Non-Newtonian Fluid Mech. 94 (2000) 87] that takes into account flow-induced texture transformations. A complete extra stress tensor equation is developed from first principles for liquid crystal materials under non-homogeneous arbitrary flow. This mesoscopic viscoelastic model has been adapted to describe the rheology of flow-aligning thermotropic DNLCs as models of mesophase pitches. We develop a fundamental understanding of the relations between rheology and flow of carbonaceous mesophases using theory and simulation by characterizing the steady and transient shear rheological material functions of flow-aligning DNLCs. Predictions for simple shear flow (under non-homogeneous conditions) for the apparent shear viscosity and first normal stress differences are presented. The predicted relations among rheological properties, shear-induced microstructure, processing conditions and material parameters of discotic mesophases are characterized and discussed.     

Mesophase pitches for 3D-carbon fibre preform densification: rheology and processability

Synthetic mesophase pitches, produced from naphthalene (ARA24, ARA24r), were examined in terms of fluidity and thermal stability in comparison with other mesophase, isotropic pitches, or mesophase pitch/softening molecules blends. Their interest for carbon/carbon (C/C) composites processing by liquid impregnation or vacuum transfer inside three-dimensional carbon preform is discussed. Viscosity versus reduced temperature plots is reported on the same graph to compare the studied pitches and to define a suitable C/C processing window. Methylnaphthalene-based pitch is a good candidate with viscosity and stability adapted to the processing temperature and high carbon yield.     

Rheological characteristics of mesophase pitch

Rheological characteristics of two pretreated petroleum pitches, during their transformation to mesophase, have been studied by using rotalional viscometer. Simultaneously, the formation, growth, coalescence of mesuphase spheres, and the alignment of coalesced mesophase were observed by Hot-Stage-Cinema-Microscope, discussed with the results of viscosity change and the Q.I. content. It is found that both pretreated pitches were Newtonian fluids at low temperature, but behaved pseudoplastics as increase of mesophase content above 390C. Shear thinning behaviour was also apparent in the shear rate range of 1.9–20 sec⁻¹ at temperature above 390C. The apparent viscosity-temperature curves of this pyrolysed pitches were much affected by the pretreatment conditions.     

The role of low-molecular-weight components in the pyrolysis of pitches

Two pitches of different volatile contents, obtained from the same coal tar by different procedures, were characterized by elemental analysis, solubility, ¹H n.m.r., donor—acceptor ability, FT-i.r., extrography and size-exclusion chromatography. Their pyrolysis behaviour was followed by hot-stage microscopy and thermogravimetric analysis. The pitches were carbonized in a horizontal furnace and the resulting cokes were characterized by optical microscopy. Three partly devolatilized pitches were prepared by thermal treatment of the two pitches and their pyrolysis behaviour was compared in terms of mesophase development and optical texture of coke. The results indicate a significant influence of low-molecular-weight components of pitch on the development of mesophase but no effect on the subsequent optical texture of the coke.     

Rheological investigation of coal-tar pitch during its transformation to mesophase

Rheological characteristics of two coal-tar pitches, during their transformation to mesophase, have been followed by rotational viscometry. In certain instances samples were also taken, enabling the mesophase microstructure to be correlated with the flow behaviour. Flow curves established that the pitches are Newtonian liquids at low temperatures, but non-Newtonian character appears at temperatures above 380 °C. Scanning the viscosity-temperature curve of a binder pitch showed that the viscosity began to change, as a result of polymerization processes, at about 240 °C. In both pitches the apparent viscosity, at all rates of shear, increased very rapidly at temperatures above 420 °C when the mesophase content was in excess of 25%. Shear-thinning behaviour was apparent and a peak in the apparent viscosity-temperature curves appeared at all the rates of shear investigated. It is suggested that the systems can be regarded as emulsions. Initially an emulsion of mesophase in isotropic liquid exists but this transforms, at higher temperatures, to one of isotropic liquid in mesophase. The maximum in the apparent viscosity appears to correspond to the phase inversion point.