Thermoanalytical studies of pitch pyrolysis

Characterization of pitches by thermal analysis techniques is highly relevant to the practical use of these materials, as they undergo heat treatments in all of their utilization processes. The aim of this work was to improve the interpretation of the complex DTA curves of pitches by comparison with model compounds. For this, TG/DTG/DTA was used to study under identical conditions the pyrolysis of a petroleum pitch and a coal tar pitch as well as a number of polycyclic aromatic hydrocarbons. Results were interpreted as a function of the molecular structure, pyrolysis reactivity and graphitizability of cokes from the hydrocarbons. It is concluded that condensation and polymerization, which are the most likely exothermal reactions predominant in petroleum pitches, indicate the presence therein of reactive molecules. Alternatively, endothermal phenomena such as distillation, depolymerization and cracking, predominant in coal tar pitches, suggest the presence of light, little reactive aromatic molecules.Financial support from DGICYT (project PB87-0456) is gratefully acknowledged.     

煤沥青的电化学加氢──Ⅰ．原料煤沥青的预处理和组成结构分析

为选择适于作为碳纤维原料的煤沥青，对三种中低温煤沥青的预处理和组成结构进行了研究，同时对其中的太钢煤沥青进行了热缩聚制取中间相沥青的结构变化分析。研究分析结果表明，只要经过合适的工艺路线进行处理，这三种煤沥青都有可能作为沥青基碳纤维的原料。     

Effect of rosin to coal-tar pitch on carbonization behavior and optical texture of resultant semi-cokes

Coal-tar pitch was modified with rosin, and carbonization behavior of the modified pitches and optical texture of resultant semi-cokes were studied in this paper. The carbonization behavior was studied by thermogravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy techniques, respectively. The optical texture of resultant semi-cokes was characterized by polarized-light microscopy. The results show that there are marked differences in the carbonization behavior of coal-tar pitch and the modified pitches. The modification results in a small decrease in carbonization yield by 1.2–3.2% when rosin content is kept at 5–15 wt.% of coal-tar pitch. The modified pitches have functional groups of cycloparaffin, double bonds, and carboxyl group, which gradually disappear and aromatization degree increases with increasing heat treatment temperature. Moreover, the modification contributes to a notable improvement in the optical texture of resultant semi-cokes which varies from coarse-grained mosaics to domains.     

煤焦油沥青不同改性产物炭化性质的比较研究

比较研究了几种改性煤焦油沥青的炭化性质，并从原料结构上给出了解释。结果表明：在同一热处理条件下形成的各种中间相沥青的光学显微结构区域的大小顺序为：Ｓ－ＬＤＯＨＦ－ＭＣＴＰ＞Ｓ－ＭＣＴＰ＞ＭＣＴＰ－ＰＳ＞ＭＣＴＰ共炭化沥青分子中含有较多的短烷基侧链和环烷结构，炭化时能形成可溶性较好的广域型中间相体；超临界抽提能调整沥青的族组成和分子量分布，使分子更易于均匀聚合和取向，超临界抽提沥青的炭化性能优于抽提     

Optical wave propagation in a cholesteric liquid crystal using the finite element method

Bragg reflections of cholesteric liquid crystals at normal and oblique incidences were investigated using the finite element method (FEM). Detailed FEM derivations together with the consideration of boundary conditions are given. Two methods for achieving broadband Bragg reflection are analysed: one is to use high birefringence liquid crystal in the uniform pitch structure, the other is to use the gradient pitch structure. In each case, the number of cholesteric pitches required for establishing the Bragg reflection was simulated.     

重质稠环芳烃的固体核磁共振光谱研究

以固体核磁共振光谱为主要分析手段,比较研究了两种合成中间相沥青吡啶不溶组分的结构。结果表明：均四甲苯基中间相沥青吡啶不溶组分具有较低的芳香度和缩合度,富含甲基和环烷结构,分子呈渺位结合实际合构型;与此相反,四氢萘基中间相沥青则呈现很高的芳香度和缩合度,芳环上仅带有一些甲基取代基,平均分子为完全迫位缩合构型,造成这种结构差异的原因在于前驱齐聚物的结构及缩聚程度的不同。     

Chemical activation of carbon mesophase pitches

This paper studies the chemical activation of mesophase pitches of different origins in order to obtain activated carbons suitable for use as electrodes in supercapacitors. The effect that the activating agent (NaOH, LiOH, and KOH), the alkaline hydroxide/pitch ratio, and the activation temperature had on the characteristics of the resultant activated carbons was studied. LiOH was found to be a noneffective activating agent, while activation with NaOH and KOH yielded activated carbons with high apparent surface areas and pore volumes. The increase of the KOH/pitch ratio caused an increase of the chemical attack on the carbon, producing higher burnoffs and development of porosity. Extremely high apparent surface areas were obtained when the petroleum pitch was activated with 5:1 KOH/carbon ratio. The increase of the activation temperature caused an increase of the burnoff, although the differences were not as significant as those derived from the use of different proportions of activating agent.     

Optical wave propagation in a cholesteric liquid crystal using the finite element method

Bragg reflections of cholesteric liquid crystals at normal and oblique incidences were investigated using the finite element method (FEM). Detailed FEM derivations together with the consideration of boundary conditions are given. Two methods for achieving broadband Bragg reflection are analysed: one is to use high birefringence liquid crystal in the uniform pitch structure, the other is to use the gradient pitch structure. In each case, the number of cholesteric pitches required for establishing the Bragg reflection was simulated.     

Thermotropic cellulose derivatives with flexible substituents. III. Temperature dependence of cholesteric pitches exhibiting a cholesteric sense inversion

For the thermotropic cholesteric mesophase of tri-o-(β-methoxyethoxy)ethyl cellulose (DP = 11), cholesteric pitches larger than 2 μm were precisely determined by microscopic observation and their temperature dependence was examined in the temperature range from 80°C to 140°C. In the initial temperature region of 80°C to 106°C, the pitch increases with increasing temperature. After the pitch diverges at 106°C, it decreases as temperature is raised further. This anomalous temperature dependence of pitch was associated with a thermally-induced inversion from right- to left-handed helicoidal structure which was first observed in this kind of cellulose derivatives.     

Study on selective reflection properties of chiral nematic liquid crystalline composites with a non‐uniform pitch distribution

The preparation is reported of particles of photopolymerisable monomer/chiral dopant composites with a crystalline (Cr)‐chiral nematic (N*) phase transition. By mixing particles with different pitches of the N* phase in the Cr phase and crosslinking the liquid crystal (LC) monomer molecules by photopolymerisation in the planarly oriented N* phase, an N*‐LC composite film with a non‐uniform pitch distribution was obtained. Experimental results show that the bandwidth of the reflection spectrum and the location of reflection band of the composite films can be controlled accurately by controlling the pitch lengths of the N* phase of the particles. Effects of polymerisation temperature and UV intensity on the non‐uniform pitch distribution of N*‐LC composite films were investigated.     

Comparison of the pitch induced from lamellar and nematic regions in some lyotropic liquid crystal systems

Lamellar phases (Lalpha) composed of decylammonium chloride(DACl), NH4Cl and H2O were doped with cholesteryl-2-ethoxyethoxyethyl carbonate (CEEC) and with (L-MA) or its racemic mixture (DL-MA). Lalpha phases of the novel intrinsic optically active L-serine hydrochloride decylester (L-SDE) and its racemic mixture (DL-SDE) were also prepared. From the chiral Lalpha phases, cholesteric phases (ChD) were induced with increased temperature and it was found that the pitch length shortened as the temperature was raised. This phenomenon is new for micellar cholesterics. The non-chiral Lalpha phases gave pseudo-isotropic and nematic regions with increased temperature. On the basis of these results and those in the literature, a new interpretation of the distorted micelle shape and the formation of the fingerprint texture is presented. The pitches induced from Lalpha regions were always larger than those obtained from nematic regions. From these results it is inferred that the interactions between the micelles in the cholesteric state at room temperature are of 'ideal' type. In addition, the temperature dependence of the pitch in micellar cholesterics is discussed.     

Direct exposure electron ionization mass spectrometry and gas chromatography/mass spectrometry techniques to study organic coatings on archaeological amphorae

Two different analytical approaches, direct exposure electron ionization mass spectrometry (DE-MS) and gas chromatography/mass spectrometry (GC/MS), were compared in a study of archaeological resinous materials. DE-MS was found to be an efficient fingerprinting tool for the fast screening of organic archaeological samples and for providing information on the major components. GC/MS appeared to be more efficient in unravelling the sample composition at a molecular level, despite the long analysis time and the need for a wet chemical pretreatment. Both procedures were applied to characterize the organic material present as coatings in Roman and Egyptian amphorae. DE-MS successfully identified abietanic compounds, hence a diterpenic resinous material could be identified and its degree of oxidation assessed. GC/MS enabled us to identify dehydroabietic acid, 7-oxodehydroabietic acid, 15-hydroxy-7-oxodehydroabietic acid, 15-hydroxydehydroabietic acid, retene, tetrahydroretene, norabietatriene, norabietatetraene and methyl dehydroabietate. These oxidized and aromatized abietanes provided evidence that the amphorae examined were waterproofed with a pitch produced from resinous wood of plants from the Pinaceae family. The chemometric evaluation of the GC/MS data highlighted significant chemical differences between the pitches found in the two archaeological sites, basically related to differences in the production techniques of the materials and in their degradation pathways.     

The alignment of nematic liquid crystals on photolithographic micro-groove patterns

The alignment of nematic liquid crystals on micro-groove patterns was studied. It has been found that the order of the alignments is determined by the edge shape, spacing, and line pitch of the micro-groove patterns. On coarse patterns, with pitches greater than 2 μm, striped patterns of the liquid crystal alignment were observed using polarized light which manifested different orientations of the liquid crystals on the top, edge, and bottom of the grooves, respectively. On fine patterns, with pitches less than 2 μm, a uniform device-quality alignment has been realized, with which twisted nematic cells were constructed in combination with the rubbed alignment layer on the opposite substrate. Their viewing angle characteristics and tilt orientations of the director were also investigated.     

The alignment of nematic liquid crystals on photolithographic micro-groove patterns

Abstract

The alignment of nematic liquid crystals on micro-groove patterns was studied. It has been found that the order of the alignments is determined by the edge shape, spacing, and line pitch of the micro-groove patterns. On coarse patterns, with pitches greater than 2 μm, striped patterns of the liquid crystal alignment were observed using polarized light which manifested different orientations of the liquid crystals on the top, edge, and bottom of the grooves, respectively. On fine patterns, with pitches less than 2 μm, a uniform device-quality alignment has been realized, with which twisted nematic cells were constructed in combination with the rubbed alignment layer on the opposite substrate. Their viewing angle characteristics and tilt orientations of the director were also investigated.     

Discontinuous change in the helical pitch of cholesteric liquid crystals by photoisomerization of a chiral azobenzene molecule

This paper describes the discontinuous change in the helical pitch of a cholesteric liquid crystal (ChLC) by means of the photoisomerization of chiral azobenzene molecules under homogenous alignment conditions. A mixture of E44, R811 and Azo was prepared in the ratio 68/28/4, respectively. R811 and Azo have opposite twisting abilities such that they induce right- and left-handed helices, respectively when added to E44. The mixture was injected into a glass cell having a 2 or 5 µm cell gap, and treated for homogeneous molecular orientation. The wavelength of selective reflection from the ChLC was shifted to shorter wavelengths by the trans-cis photoisomerization of Azo. The change in the helical pitch was not only discontinuous, but also dependent on the cell thickness. The discontinuous change in the helical pitch was estimated to be almost the same as the half turn of the helical pitch in each cell gap, and was dependent on the number of helical half pitches in the glass cell. The homogeneous alignment condition affects the photochemical change in the helical structure of the ChLC system.     

Monitoring the synthesis of new pitches from coal tar and its fractions by chromatography and related techniques.

The aim of this paper is to study the applications of chromatography and related techniques in the transformation of coal-derived products into pitches for specific uses. Anthracene oil, tar and pitch were thermally treated in the presence of air (and sulfur in the case of anthracene oil) in order to cause the polymerization/condensation of their components. The evolution of the components of the parent materials during the treatments was monitored by gas chromatography-mass spectrometry, gas chromatography-atomic emission detection, probe mass spectrometry and size-exclusion chromatography. From the results obtained, possible mechanisms for the transformation of coal-derived products into new pitches were established.     

烷基在针状焦形成中的作用

采用煤焦油沥青的甲苯可溶物和废聚苯乙烯共碳化制备针状焦,考察了中间相沥青中烷基含量对针状焦性能的影响。结果表明,通过添加废聚苯乙烯共碳化,中间相沥青中烷基的质量分数从12.0%增加到33.3%,可以制备出热膨胀系数更低、光学各向异性排列更好的针状焦。代表光学各向异性指数的两个量,在光学结构单元中,平行于热膨胀系数方向的轴向分矢量平均长度和光学结构单元的矢量平均长度,分别从20.8μm 和23.4μm增加到28.4μm和28.8μm,热膨胀系数从0.8×10^-6 /K降低到0.1×10^-6 /K。针状焦形成过程中中间相沥青的烷基含量增加使体系黏度降低,有利于光学各向异性相的融并和定向排列。烷基的增多在固化阶段产生足量的气体,在向外逸出过程中使融并中间相的芳香平面大分子沿轴向排列的更为规整。     

Photoinduced two-dimensional gratings based on dye-doped cholesteric liquid crystal films

This work elucidates photoinduced two-dimensional (2D) gratings in dye-doped cholesteric liquid crystal films. The helical pitch is increased by green-beam-induced trans-cis isomerization and a concomitant thermal effect. Two-dimensional gratings appear when the green beam is turned off. Grating formation results from elastic instability caused by restored strain arising from helical pitch reduction. Grating lifetime increases as green beam intensity increases and declines under irradiation with a strong red beam. Variation in grating spacing with green intensity with various pitches is also examined.     

Phenyl-substituted polycyclic aromatic compounds as intermediate products during pyrolytic reactions involving coal tars, pitches and related materials

Summary Several so far unreported phenyl-substituted polycyclic, aromatic compounds were detected in coal tars, coal tar pitches and ring furnace flue gases by their gas chromatographic retention and mass spectra. In the case of thiophene-derived compounds, the elemental sulfur traces obtained by GC-AED supplied further evidence of their identity. Pure authentic substances were synthesised and analysed by GC-MS and GC-AED to prove the identity of the unknown compounds. Concentration profiles of phenyldibenzofurans and phenyldibenzothiophenes in different coal tars, coal tar pitches and ring furnace flue gases are reported. Reaction mechanisms are proposed which suggest that during oxidative pyrolysis phenyldibenzofurans and phenyldibenthiophene are the intermediate products on the path from dibenzofuran and dibenzothiophene to triphenyleno[1,12-bcd]furan and benzobisbenzofurans, and the respective thiophenes.     

Discontinuous change in the helical pitch of cholesteric liquid crystals by photoisomerization of a chiral azobenzene molecule

This paper describes the discontinuous change in the helical pitch of a cholesteric liquid crystal (ChLC) by means of the photoisomerization of chiral azobenzene molecules under homogenous alignment conditions. A mixture of E44, R811 and Azo was prepared in the ratio 68/28/4, respectively. R811 and Azo have opposite twisting abilities such that they induce right- and left-handed helices, respectively when added to E44. The mixture was injected into a glass cell having a 2 or 5?µm cell gap, and treated for homogeneous molecular orientation. The wavelength of selective reflection from the ChLC was shifted to shorter wavelengths by the trans-cis photoisomerization of Azo. The change in the helical pitch was not only discontinuous, but also dependent on the cell thickness. The discontinuous change in the helical pitch was estimated to be almost the same as the half turn of the helical pitch in each cell gap, and was dependent on the number of helical half pitches in the glass cell. The homogeneous alignment condition affects the photochemical change in the helical structure of the ChLC system.