从发展低碳经济角度评价各向同性焦的潜在价值

通过阐述各向同性焦的质量特性,论证了利用其优越的天然特性研发生产各向同性石墨的可行性,展望通过技术创新,突破采用等静压成型技术产品规格不能大型化和成品率低的瓶颈,自主支撑我国电解铝节能减排、核石墨和半导体硅及光伏产业用各向同性石墨等低碳经济产业前景。     

各向异性叠前时间偏移技术在普光三维连片资料处理中的应用

各向异性广泛存在于地下介质中,原有的各向同性叠前时间偏移成像精度较低,各向异性叠前时间偏移技术不但有效解决了各向异性问题对成像精度的影响,而且能够解决共反射点道集大偏移距校正过量的问题。本文在理论分析的基础上提供了一套各向异性叠前时间偏移的流程,在做好各向同性叠前时间偏移的基础上,求取各向异性参数。然后进行各向异性叠前时间偏移。并以普光三维连片资料处理为例,将各向同性及各向异性叠前时间偏移成像效果进行了对比。实验证明,各向异性叠前时间偏移技术有效地提高了复杂构造的成像精度。断层更加清晰,断点归位更加准确。地震资料的横向分辨率得到了提高。     

一种制备各向同性焦的方法

介绍了一种以煤沥青为原料制备各向同性焦的方法,实现了各向同性焦和各向异性焦原料预处理的联产工艺。该方法的关键在于原料的调制及焦化工艺参数的选择。     

树脂基碳纤维丝束本构方程的研究

分析了三维完全各向异性、三维正交各向异性和横观各向同性材料的本构关系,提出树脂基碳纤维丝束采用横观各向同性的本构方程,并基于该方程,通过隐式计算模块Abaqus/Standard中的牛顿迭代法求解材料的拉伸性能,与试验作对比。结果表明:拉伸应力—应变关系曲线与试验值比较吻合,能较好地模拟树脂基碳纤维丝束的形变,较准确地反映拉伸力学响应;该本构方程模型能够有效地预测碳纤维复合材料的拉伸力学行为。     

沥青基碳纤维的性能和用途

<正>沥青基碳纤维具有高弹性模量、高热导率、低热膨胀率(尺寸稳定)等性能。沥青基碳纤维按原料分为液晶性各向异性沥青和非液晶性各向同性沥青。以各向异性沥青为原料制得的碳纤维易石墨化,通过高温烧制,可取得高强度、高弹性模量的碳纤维长丝;而以各向同性沥青为原料制成的碳纤维难以石墨化,高温烧制后石     

生物质碳化衍生物强化相变材料各向热导率的研究进展

相变材料由于具有较高的潜热值和良好的温度控制性能,已经被广泛应用于建筑节能、余热废热回收、电池热管理、太阳能热能储存等领域。然而,相变材料在固-液相变过程中的泄漏和导热性能差等缺点限制了它们的进一步发展。生物质碳化衍生物具有的多孔微观结构和良好的导热性克服了相变材料相变时的液漏和自身导热能力差等问题,成为相变材料良好的载体选择。由于生物质碳化衍生物多孔碳材料具有各向同性和各向异性的结构,因此,生物质碳化衍生物多孔碳材料强化相变材料的热导率分为各向同性热导率强化和各向异性热导率强化。     

沥青中喹啉不溶物对沥青炭化行为及沥青焦结构的影响

沥青中的喹啉不溶物对炭化行为,以及对沥青焦性质的影响直接关系到沥青焦的制造和炭素电极的生产。增加喹啉不溶物可产生更多的各向同性焦,用焦炭粒直接测定的热膨胀系数(CTE)是受喹啉不溶物类型的强烈影响。原始类型喹啉不溶物数量的增多,可使CTE(体积)从3.2增到17.4×10~(-6)K~(-1),反之派生类型喹啉不溶物对CTE的影响甚微。沥青粘结剂焦结炭的结构受沥青喹啉不溶物的影响较强烈,结果使炭素制品强度明显的提高。     

横向各向同性介质中地震波射线正演

在给定的理论模型下,研究了各向异性的存在对地震波传播速度的影响,用一种逐段迭代的射线追踪方法进行了横向各向同性介质中的走时正演,得到了相应的时距曲线。并通过用该时距曲线结果与基于各向同性介质模型假设所得到的时距曲线结果进行对比,验证了该射线追踪方法的有效性和精确性。该射线追踪方法理论上适用于任何界面模型,可以追踪到任意给定的精度,是一种值得推广的射线追踪方法。     

沥青基炭复合材料的制备及力学各向异性性质的探讨

采用新型的模压半炭化成型工艺在大气环境下制备出了高密度、低成本的焦炭颗粒增强沥青基炭复合材料（CRPCC）。研究了焦炭颗粒的种类对CRPCC材料的力学各向异性性质的影响。结果表明：由于沥青焦Ⅰ的颗粒形状系条状或棒状，故用其制备的CRPCC材料的力学性能具有明显的各向异性，且各向异性系数高达25％；而沥青焦Ⅱ和冶金焦的颗粒形状为多角形或准球形，故用它们制备的CRPCC材料基本上都是各向同性的。     

特种石墨的分类、市场和生产(续)

3三高石墨的生产简介 高纯石墨的生产流程根据产品是各向同性石墨还是各向异性石墨，采用哪一种成型工艺而定，一般可分为3种，见图1。三高石墨的生产与石墨电极生产有相似之处，技术关键问题简要介绍如下：     

Co-carbonization of Ashland A240 petroleum pitch with alkali metal carbonates and hydroxides

Petroleum pitch was co-carbonized with the carbonates and hydroxides of Li, Na, K, Rb and Cs, using 1–15 wt% of the salt. The resultant 1173 K carbons were examined by optical microscopy to assess quantitatively the components of the optical texture. The half-peak widths of the (002) diffraction bands were determined and the porosity and surface topography of fracture surfaces of the carbons were monitored by scanning electron microscopy. The aim of the study was to assess how the anisotropic carbon of pitch coke can be replaced by isotropic carbon via addition of alkali salts with a view to the optimization of commercial gasifiers. The effectiveness of the alkali carbonates was Li < Na < K< Rb < Cs, with hydroxides being more effective than carbonates. The optical texture changed abruptly from small domains to isotropic with residual anisotropic carbon in the isotropic matrix. The half-peak widths increased with increasing isotropic carbon content.     

Kinetics of the coke shrinkage process during calcination

The dimensional changes of raw isotropic and anisotropic coke occurring during calcination at 500–1200°C are examined under isothermal conditions using a high temperature dilatometer. The isothermal dimensional analysis is adapted to the coke shrinkage process by placing a coke sample into a dilatometer and measuring the expansion and contraction of the coke as a function of temperature and time. The apparent activation energy of the coke shrinkage process is computed from the experimental deformation rate data.     

The role of liquid crystals in the formation of graphitizable carbons (cokes)

The formation of cokes and graphites proceeds via the creation from the isotropic fluid phase of carbonization of pitch and coal, of lamellar nematic liquid crystals or mesophase. This anisotropic fluid, deformable mesophase, develops as spheres within which constituent molecules are stacked parallel to an equatiorial plane. This type of structure facilitates coalescence to a coherent mass which eventually forms a graphitisable carbon. The ‘onion-skin’ structure of mesophase spheres cannot so coalesce. Different optical textures of cokes and graphites owe their origin to different chemical reactivities and fluidities of mesophase, the lower the fluidity the smaller the size of the optical texture. Mesophase from lameller molecules is compared with conventional rod-like nematic liquid crystals. Structures in needle-cokes, metallurgical coke, coke from solvent refiend coal and carbon fibre from pitch are discussed in terms of formation and properties of lamellar nematic liquid crystals.     

Composition of pore-wall material in metal-lurgical coke: Considerations of strength,gasification and thermal stress

The optical texture of metallurgical cokes consists of anisotropic carbon made up of mozaics, 0.5–10 μm in size of flow-type anisotropy, 10–60 μm in size, as well as inert and isotropic material. Cokes from different coal sources possess optical textures which are different, being composed of different extents of the above components. The study examines the optical texture of polished surfaces of cokes and relates changes in surface topography caused by gasification by carbon dioxide at 1173 K, by heat treatment to 2073 k and by etching with atomic oxygen at 293 k to the optical texture. The results support a model to explain the strength of coke and its resistance to breakage caused by gasification, mechanical and thermal stresses, in terms of the size, orientation and bonding of the varied components which constitute the composite structure of coke material.     

A microscopic approach to determine the origin and mechanism of coke formation in fractionation towers

This study investigated the deposition of coke in a fractionation tower following thermal cracking of heavy feedstocks. A simple microscopic technique was used to determine whether the coke formed in situ in the fractionator or was formed elsewhere (e.g. in the reactor vessel) and was subsequently entrained in the vapour phase. The reflectance of coke types, mode of occurrence, and distributions from the bottom to the top of the fractionator were used to interpret the range of temperatures responsible for coke formation. Both isotropic and anisotropic (mosaic) coke was observed in the samples. The anisotropic textural features indicated that asphaltenes carry-over was a minor problem and that the vast majority of the isotropic coke precursors were the maltenes present in the gas phase that entered the fractionator. The formation of perfectly spherical mesophase was attributed to the gas oil stream itself used to quench the vapours exiting the thermal cracking vessel. Microscopic evidence, along with metals concentration in the coke at various locations of the operation provided useful information as to the nature of the coke precursors.     

Classification of carbon in Canadian fly ashes and their implications in the capture of mercury

Fly ashes produced from Canadian power plants using pulverized coal and fluidized bed combustors were examined for their carbon content to determine their ability to capture mercury. The feed coal used in these power plants were lignite, subbituminous, high and medium volatile bituminous, their blends, and also blends of coal with petroleum coke (Petcoke). The carbon and mercury content of the coals and fly ashes were determined using the ASTM standard method and by the cold vapour atomic absorption spectrometry method. The carbon content of the fly ash was concentrated by strong acid digestion using HCl and HF. The quantitative and qualitative analyses of the carbon concentrate were made by using a reflected light microscope. The results show that the carbon content of fly ash appears to be partially related to depositional environment during coalification and to the rank of the coal. The Hg captured by the fly ash depends on the rank and blend of the feed coals and the type of carbon in the fly ash. The isotropic vitrinitic char is mostly responsible for the capture of most Hg in fly ash. The inadvertent increase in carbon content due to the blending of coal with petroleum coke did not increase the amount Hg captured by the fly ash. The fly ash collected by the hot side electrostatic precipitator has a low Hg content and no relation between the Hg and carbon content of the ash was observed. These results indicate that the quantity of carbon in the fly ash alone does not determine the amount Hg captured. The types of carbon present (isotropic and anisotropic vitrinitic, isotropic inertinitic and anisotropic Petcoke), the halogen content, the types of fly ash control devices, and the temperatures of the fly ash control devices all play major roles in the capture of Hg.     

Optimal preparation of oxidized coal

The oxidation index is an important characteristic of coal and coal batch, indicating the change in coking properties on oxidation. The coke obtained from coal batch containing poorly clinkering oxidized coal has a higher content of isotropic carbon and a lower content of anisotropic carbon. That explains its increased reactivity and impaired mechanical and postreactive strength. The oxidation on storage is greatest for small coal classes (<0.5 mm). Preliminary removal of <0.5 mm oxidized coal markedly improves the reactivity and also the mechanical and postreactive strength. A method of preparing oxidized coal for coking is proposed: finer grinding (until the content of the ≤1 mm class is 100%). That considerably reduces the influence of the oxidized coal on the quality of the coke produced.     

Carbonization of aromatic hydrocarbons—IV: Reaction path of carbonization catalyzed by alkali metals

The carbonization path of aromatic hydrocarbons catalyzed by alkali metals has been investigated to elucidate how aromatic hydrocarbons were converted into the isotropic coke, compared to the same reaction catalyzed by aluminum chloride which gave the anisotropic needle-like coke. Attempts were made to identify the intermediate products by means of elemental analyses, NMR, and mass spectroscopy, and the process was followed by the analysis of evolved gases. Effects of the catalyst migration at the intermediate step of carbonization on the properties of produced coke were also investigated to know when the destiny of the coke was determined. These results indicate that the isotropic nature of the coke obtained from the aromatic hydrocarbons with alkali metals is due to the extensive dehydrogenation of the intermediate at the early stage of carbonization at ca. 250°C. The dehydrogenation may raise the melting point of the carbonizing material. Other factors influencing the nature of the coke are considered to be unimportant in the present case.     

Structure in cokes from coals of different rank

A range of bituminous coals has been carbonized to 1273 K. Polished surfaces of the solid products, carbons or cokes, are examined for optical texture by optical microscopy. Fracture surfaces of the carbons are examined by scanning electron microscopy (SEM). The carbon from the lowest rank coal (NCB Code No. 702) is isotropic and fracture surfaces are featureless. Carbons from coals of ranks 602, 502 are optically isotropic but fracture surfaces are granular (size 0.1–0.2 μm), indicating small growth units of mesophase. In the carbon/coke from a 401 coal, the anisotropic optical texture and grain size are both ≈0.5–10 μm diameter. Coke from a coking coal (301a, 301b) has a layered structure extending in units of at least 20 μm diameter with sub-structures ~ 1.5 μm within the layers, indicating perhaps that the bedding anisotropy of these coals is not totally lost in the fluid phase of carbonization. The carbons from the higher rank coals have the bedding anisotropy of the parent coal. The combined techniques of optical microscopy and SEM (both before and after etching of the fracture surfaces of coke in chromic acid solution) reveal useful detail of structure in carbons/cokes and of the mechanism of carbonization of coking coals.     

Isotropic and anisotropic microporosity development upon chemical activation of carbon fibers, revealed by microbeam small-angle X-ray scattering

A sub-micrometer size beam (0.5 μm diameter) in a position-resolved small angle X-ray scattering set-up (μSAXS) has been used for the characterization of chemically activated carbon fibers (ACF). These materials have been prepared from isotropic carbon fibers (pitch carbon fibers) and anisotropic carbon fibers (PAN-based carbon fibers) by chemical activation with KOH and NaOH. The μSAXS experimental set-up made it possible to analyze different regions of a single fiber across its diameter and to distinguish the structural features already existing in the raw fibers or being created during the activation process. The results showed that depending on the precursor, the chemical activation process produces isotropic or anisotropic development of porosity. It was observed that chemically ACF prepared from isotropic carbon fibers present an isotropic development of the porosity and that a high micropore volume is developed not only in the external region of the fiber, but also in the core. On the other hand, in the case of anisotropic PAN-based carbon fibers the existence of two regions with different structure was detected by μSAXS measurements across the fiber diameter: an anisotropic external ring and a more isotropic fiber core. The results showed that these two regions remain after chemical activation and that the activating agents are reaching the fiber core. It seems that the more isotropic fiber core is activated easier by NaOH than KOH.