Optical anisotropy of carbonized coking- and caking-coal vitrains

The purpose of this work was to characterize in detail the optical anisotropy formed during carbonization of the range of coals used in the coking industry, the ultimate objective being to attain a better understanding of the coking process. Vitrains hand-picked from a series of coking and caking coals were carbonized to various temperatures between 380 and 1000 °C. The semicokes and cokes so produced were examined by polarized-light microscopy to determine the proportions of the different types of optical anisotropy developed during carbonization. The results demonstrated that coals normally grouped within one class of the coal classification system used by the National Coal Board can lead to cokes which are significantly different in terms of their optical anisotropy. The process of the anisotropic development during carbonization can be explained generally in terms of loss of volatile matter, variations in viscosity of the plastic mass, and distortion of ordered phases by the pressure of evolving gases. Differences in carbonization behaviour as judged by the coke anisotropy can be attributed to differences in the ‘molecular-structure’ of the parent coal. In this respect the oxygen in the coal is considered to be of primary significance.     

Influence of carbonization conditions on the development of different types of optical anisotropy in cokes

The vitrain components of a series of coal samples were carbonized at temperatures from 400 to 1000°C at different rates of heating ranging from 0.5 to 10°K/min and utilizing soaking times up to 24 hr. Polished specimens prepared from the carbonized products were examined microscopically under polarized light in order to determine the proportions of the various types of optical anisotropy present in them. The variations in heating rate and soaking time were found to exert little significant influence on the anisotropy developed in high-temperature cokes. But in semicokes produced at carbonization temperatures within the plastic range the influence of the carbonization conditions was much more pronounced with the effects being inter-related. Decreasing the heating rate or increasing the soaking time led to the optical anisotropy generally becoming detectable at lower carbonization temperatures. Fast heating rates caused an increase in the rate of transformation of the fine-grain mosaic anisotropy into coarser-grained types of anisotropy and increased soaking time led to enhanced anisotropic development in the semicokes produced at temperatures within the plastic range. The type of anisotropy developed in cokes is closely related to the release of volatile matter and the plasticity developed during carbonization and the conclusion is drawn that the balance between these factors controls the extent of the anisotropic development.     

Coal carbonization and coke anisotropy: some comments

Previously published work is presented in modified form to emphasise that, except under special circumstances, spherical mesophase units have not been observed during coal carbonization and that the viscosity of the fluid phase, considered so important during pitch carbonization, has no strong bearing on the size of anisotropic units found in metallurgical coke.     

Pore development during carbonization of coals

Changes in pore properties during carbonization at a constant heating rate and no external pressure were followed for bituminous and subbituminous coals by porosimetry, sorption and density measurements. Observations were supplemented by scanning electron microscopy and rate of volatilization measurements. All coals exhibited similar devolatilization behaviour and pore structure development, showing maximum micro and macropore volumes around 600 °C, and a partial collapse of pore structure after 800 °C. The micropore structure did not collepse in the case of non-caking coal. Pore volume maxima occur at least 100 °C above the temperature of the devolatilization rate maxima. Some interpretation is provided.     

Passivation of nanostructured silicon optical devices by thermal carbonization

Nanostructured silicon interference filters have been thermally carbonized by acetylene decomposition at different temperatures in order to passivate their high internal surface area. Stability has been studied by periodically measuring the optical spectrum of treated and untreated porous silicon filters stored in oxidizing environments. Experimental results show that thermal carbonization stabilizes the structures against oxidation, since treated samples show no significant shift of their optical spectra after storage in either ambient air or ethanol for up to two months. Moreover, the thermal carbonization process has no significant effect on the optical performance of the filters. Results show that thermal carbonization by acetylene decomposition provides an effective way to produce chemically stable porous silicon optical devices for biological and chemical sensing.     

煤化工低碳化发展技术进展

煤化工是煤炭利用的重要方向,对煤化工碳排放问题作了分析,介绍了二氧化碳化工利用技术进展,探讨了正在研究开发的二氧化碳转化新技术,为科学研究和工程项目实际应用展示了二氧化碳回收利用的美好前景,开发和利用二氧化碳转化为有机合成原料或燃料具有巨大的经济价值和重要的意义。     

聚丙烯腈热稳定化纤维在碳化过程中的结构变化研究

为研究聚丙烯腈(PAN)热稳定化纤维在连续碳化过程中的结构和力学性能变化,于300~1 300℃对PAN稳定化纤维进行热处理,然后采用傅里叶变换红外光谱(FTIR)分析仪、X射线衍射(XRD)仪、拉曼(Raman)光谱仪、元素分析仪及纤维强伸仪等表征了纤维的化学结构、微晶结构及拉伸强度。结果表明:当温度达到600℃时,纤维残余氰基消失,结构致密性增大,且强度略有增加;当温度升高到1 000℃时,纤维氧含量大幅降低,纤维由梯形结构转变为碳平面结构,晶面堆叠、晶粒尺寸及石墨化程度缓慢增加,拉伸强度逐渐提高;当温度超过1 000℃后,微晶结构进一步重排与完善,晶粒尺寸及堆叠层数出现较快增长,同时纤维拉伸强度出现较大提升,体密度先降低后升高。     

Particle size from optical anisotropy effects in scattered light

An original light-scattering method often suitable for the case of anisotropic particles is explained. Two particular values of the scattering angle θ are needed: θ_m, the angular position of the minimum of the H_h component, and θ_o, the angular value for which H_h = V_v. This method has been successfully applied to the case of copolymer single crystals.     

Change of pore properties during carbonization of coking coal

Porosimetry, sorption and density measurements are reported on two caking bituminous coals, West Virginia Jewel No. 2 medium volatile and a Pennsylvania Pittsburgh seam high volatile C, for final carbonization temperatures between 400 and 1000°C. Samples were not confined and heating rates of 3 and 8.2°/min were employed. The medium volatile samples exhibit pronounced maxima in pore volume, pore surface area and porosity between 600 and 800°C. These temperatures are considerably greater than the characteristic temperature and the temperature at which maximum dilation occurs. The high volatile C coal does not exhibit well defined maxima. Results are interpreted in terms of pore development mechanisms. A mathematical model for pore development is proposed and shown to correlate satisfactorily, the pore volume and surface area measurements.     

Observation of disclinations and optical anisotropy in a mesomorphic copolyester

We report observations carried out on a thermotropic copolyester which had been polymerized by the manufacturers with the random addition of aromatic groups into the conventional poly(ethylene terephthalate) chain. At elevated temperatures the material exhibits complex anisotropic effects in the quiescent mesomorphic state which are observed to be frozen into the material at room temperature. The copolyester is sensitive to surface effects and is possibly influenced by magnetic fields. Using the latter technique we were able to orient the polymer in a manner which enabled us positively to identify within the material the existence of disclinations with strengths of ±1. Finally surface replica electron microscopy revealed a morphological texture that complimented and extended that deduced from the optical studies.     

Mechanical properties of pitch-coal extrudates during the carbonization process

Combined thermogravimetric and thermomechanical measurements are used to investigate the carbonization of coal-pitch extrudates. Changes in mass and dimensions are measured as a function of temperature. Qualitative dynamic measurements help to elucidate the mechanical properties of interacting coal-pitch systems during the carbonization step.     

Microstructural evolution during charcoal carbonization by X-ray diffraction analysis

X-ray diffraction (XRD) of monolithic pieces of carbonized medium-density fiberboard (c-MDF) provided new insights on the microstructural evolution occurring during charcoal carbonization. Classical XRD theory was used to correlate the {002} peak intensity to the amount of carbon in large turbostratic crystallites and to bulk dimensional changes. This new analytical technique could be used to study the microstructural evolution of other monolithic carbon materials (including soft carbons) or of specific processes (including chemical activation). The quasipercolation model, a new ‘percolation-like’ model, was created based on XRD analysis of monolithic c-MDF. As the carbonization temperature (T_carb) increased above 600 °C, the large turbostratic crystallites grew very little, but the graphene sheets grew substantially. Volumetric shrinkage suggested that turbostratic crystallites were drawn closer together as the low-density disordered carbon was converted into high-density graphene sheets. At approximately 900 °C, the large graphene sheets and the large turbostratic crystallites significantly impinged on each other. The increased impingement of conductive phases with increasing carbonization temperature would cause the commonly observed nonmetal-metal transition of hard carbon materials. The quasipercolation model also suggested the source of the nanoporosity that is critical in activated carbons.     

污水污泥水热炭化过程中磷的迁移转化特性

利用SMT方法研究了污水污泥水热炭化固体产物中磷的赋存形态和分布。结果表明,水热炭化处理可以使污泥中的有机磷（OP）转化为无机磷（IP）。在实验条件范围内,污泥中的磷主要富集在水热焦中（R_TP＞70%）,且主要以无机磷（IP）形态存在。延长水热炭化时间或升高水热炭化温度,污泥中无机磷（IP）和非磷灰石无机磷（NAIP）均呈逐渐升高的趋势,而且水热炭化温度的影响程度显著大于水热炭化时间。水热炭化时间对磷灰石无机磷（AP）的影响不明显,但AP含量随水热炭化温度的升高而略微升高。结合XRD谱图分析发现,105℃烘干污泥中主要存在磷酸铝盐和磷酸铁盐两种含磷化合物;水热炭化处理促使焦磷酸盐转化为正磷酸盐,且磷在水热焦中基本以最稳定的正磷酸盐形式存在。该研究结果可为污泥的资源化利用及从污泥中回收磷资源提供理论参考。     

Optical anisotropy and non-linear optical properties of azobenzene methacrylic polymers

Photoinduced optical anisotropy has been studied in several methacrylic copolymers, either amorphous or liquid crystalline, with cyano azobenzene chromophores in the side chain. Illumination with linearly polarised 488 nm light gives rise to high and stable values of birefringence and dichroism, mainly in liquid crystalline films. Both dichroism and birefringence decrease with the azo content in the copolymer series while some increase can be achieved by the incorporation of biphenyl molecules to the copolymers. Photoinduced anisotropy disappears above the glass transition temperature in amorphous polymers, whereas it increases in liquid crystalline polymers (LCP) due to a thermotropic self-organisation.The non-linear optical (NLO) properties of the films have been studied by second harmonic generation (SHG) measurements. The intensity of the harmonic signal from in situ corona poled polymeric films has been measured. The effect of 488 nm light irradiation on the azo chromophores orientation and consequently on the NLO response of the films was investigated at different temperatures. The intensity and thermal stability of the second harmonic signals obtained after the two different (thermal and photoassisted) corona poling processes have been compared.     

Modifying ability of Ql-free coal-tar pitch to develop optical anisotropy in co-carbonizations

Carbonization properties of a Ql-free coal-tar pitch (CTP-ASM) prepared by selective precipitation were studied to evaluate it as a source for needle-coke. Its modifying ability for production of needlecoke in co-carbonizations with principal carbonizing substances which gave cokes of mozaic texture in single carbonizations was estimated by changing mixing ratios. The shape and size of the anisotropic optical texture in the co-carbonized coke were measured by point counting. CTP-ASM and Ashland A240, of eight additives, had the highest modifying ability in the co-carbonizations with Khafji vacuum residue. Both contained ca. 6% benzene-insolubles (Bl), and had f_a values of ≈0.9. Other additives of either lower or higher Bl or f_a showed less modifying ability. The modifying susceptibility of principal carbonizing substances varies with their structure and properties. Based on a systematic investigation of co-carbonizations the compatibility between a principal carbonizing substance and an additive is discussed from a viewpoint of their structural parameters.     

Coefficient variation of the mechanical properties of carbon fiber during carbonization

The approaches of the development for carbon fibers are how to improve their mechanical properties and to reduce the cost of the production as well as to maintain or to control the stability of their properties, i.e., the reproducibility. The coefficient variation of the mechanical properties immediately influenced the reproduction. In this paper, the effect of the operating conditions during carbonization on the coefficient variation of the properties for carbon fiber is discussed.     

Red mud pulp carbonization with scandium extraction during alumina production

In the existing technology for the processing of bauxites into alumina, scandium remains in red mud. The average scandium concentration in bauxites coming into processing from the Severoural’skoe and Srednetimanskoe deposits is studied. Bauxites are a rich potential source for the production of scandium. The fractional distribution of mud and the concentration of scandium in its fractions are determined. The concentration of scandium in aluminate solutions and that from mud fields is extremely low and amounts to <0.05 g/m3. The processing of mud with a soda solution results in the partial solubility of scandium with its complexing. For the precipitation of scandium, the solubilities of Al, Ga, Zn, and Sc compounds in alkalinesoda-hydrocarbonate solutions are studied under the conditions of reactive and gas carbonization. Zinc hydroxide is the best coprecipitant. The carbonization of red mud pulp provides for the partial recovery of scandium and reduces the toxicity of mud storage areas by converting the alkaline-carbonate liquid phase into a carbonate-hydrocarbonate one with a lower toxicity.     

煤焦油渣炭化过程中孔结构及表面分形特征

利用煤气化焦油渣为原料进行活性炭制备实验研究,对炭化过程焦油渣孔结构和表面特征进行研究,采用N₂吸附/脱附等温实验和表面分形理论研究炭化对焦油渣孔结构和表面特征的影响。结果表明：炭化物的吸附等温线倾向于表征微孔吸附特征的Ⅰ类吸附等温线;炭化物中具有发达的微孔结构、过渡孔结构和极不发达的大孔结构;随着温度和升温速率的提高,微孔结构先增加后又逐渐发展为过渡孔和大孔;对炭化物表面的分形特征进行研究发现,表面分形维数与BET比表面积、总孔容、平均孔径不存在直接关系,但是与微孔面积占比和微孔容积占比存在较好的一致性;焦油渣在炭化处理过程中随着温度的升高和升温速率加快,经历了“立体发展-逐渐衰落”的过程。当炭化终温850℃、升温速率20℃/min时,可以得到最优的活化前体。