Effect of intercalation on electrical and mechanical properties of C/C composites

The work is concerned with modification of C/C composites by intercalation of copper chloride. The samples of composites were made from graphite fibres and carbon matrix derived from mesophase pitch and from phenol-formaldehyde resin. The samples were prepared by impregnating graphite fibres with a liquid pitch or polymer solution to obtain unidirectional laminates. The laminates were used to prepare the composites which were then subjected to carbonization and graphitization up to 2150 °C. The work discusses the problem relevant to the effect of intercalation on mechanical and electrical properties of composites. The studies indicated that both mesophase pitch-based composites and phenolic-derived carbon-carbon composites changed their electrical and mechanical properties upon intercalation with copper chloride. Electrical conductivity of both types of composites decreased as a result of the damages formed during intercalation.     

On the rank-dependence of coal tar secondary reactions

The secondary reactions of volatile compounds, including coal tar and light gases, accounts for a great portion of soot formation and the subsequent heat release and pollutant emissions in the combustion zone. While coal primary pyrolysis has been extensively studied over the last few decades and several network pyrolysis models has been developed to describe this process, coal secondary pyrolysis is still not well understood. The Babcock and Wilcox Company has been investigating coal secondary pyrolysis in order to develop a comprehensive mechanism for inclusion in predictive computational fluid dynamics and coal combustion models. Supportive experiments were carried out in an entrained-flow reactor. Tar was extracted from the pyrolysis byproducts of seven coals of widely-distributed rank at temperatures ranging from 923 to 1473 K, and analyzed by ¹³C NMR. Tars formed from higher rank coals generally demonstrated higher sooting propensities. This rank-dependent sooting propensity is associated with tar’s chemical structure properties. With increased heat treatment severity, tar molecules lose a substantial amount of aliphatic attachments, and the average size of substitution per cluster decreases. Compared to tars formed from high-rank bituminous coals, those formed from low-rank sub-bituminous coals have a larger attachment portion, higher averaged substitution, and higher oxygen-containing functional groups. These differences contribute to the higher cracking propensity observed for low-rank coal tars.     

Nano-SiC implantation into the structure of carbon/graphite materials made by pyrolysis (carbonization) of the precursor system coal tar pitch/poly(dimethylsiloxane)

Conversion of the air-cured poly(dimethylsiloxane) {–O–Si(CH₃)₂–}_n to SiC during co-pyrolysis with a coal tar pitch is studied with reference to the related SiO₂/pitch system. Each binary mixture is first homogenized at 160 °C followed by carbonization at 500 °C under argon to afford initial carbonizates. In both cases, one part of the initial carbonizate is further pyrolyzed at 1300 °C and another part at 1650 °C under an argon flow resulting in composite products. All products are studied with FT-IR, XRD, and XPS spectroscopic methods supplemented with SEM and ‘wet’ Si-analyses, when applicable. Carbothermally assisted conversion of both silicon precursors to nanocrystalline SiC embedded in the evolving C-matrix, i.e. nano-SiC/C composites, is evident only after the 1650 °C carbonization stage.     

程序升温气化过程中氮的释放规律研究

采用 U 型管反应系统研究了不同煤种在程序升温条件下在四种气氛中反应时燃料氮的释放规律.研究发现热解时主要的含氮产物为 HCN,如果煤中含有较多的氧,即使在惰性气氛下也会释放出 NO.没有检测到 NH3 的生成,证实NH3 来源于 HCN 在焦表面的二次反应.N2O 仅在有氧气氛中气化时生成,说明氧气是 N2O 生成的必要条件.气化时的总固定氮 TFN 高于热解时,且气化剂中 O2 含量越高则总固定氮 TFN 越高.     

辐照和碳化对SiC空心微球的影响

以聚碳硅烷(PCS)为原料,通过炉内成球技术制备SiC空心陶瓷微球,讨论辐照交联和高温碳化对SiC陶瓷微球化学成分、成键结构和表面特性的影响。结果表明,PCS在热处理过程中的失重率约为35%,其分解温度在400~800℃之间。微球经电子束辐照后会生成以Si—C—Si和Si一O一Si骨架结构为主的三维网络交联结构。碳化过程使Si—C_32键,Si—H键和C—H键断裂,生成以Si—C为主的无定形态Si(C。辐照的均化作用使高温热处理碳化的微球能够维持完好的球壳结构,且具有更好的表面粗糙度和平整性。     

Compact structured silicon/carbon composites as high-performance anodes for lithium ion batteries

Compact-structured silicon/carbon composites consisting of silicon, graphite, and coal tar pitch pyrolysis carbon are prepared via two heating procedures after liquid solidification. The first heating procedure plays a key role in the formation of compact-structured silicon/carbon composites, in which the coal tar pitch has a good fluidity at 180 °C above the softening temperature, and it is easy to form a uniform coating on the surface of materials. At the same time, the fluidic coal tar pitch could also fill the voids between particles to form compact-structured silicon/carbon composites. As-prepared silicon/carbon composites exhibit moderate reversible capacity of 602.4 mAh g^?1, high initial charge-discharge efficiency of 82.3%, and good cycling stability with the capacity retention of 93.4% at 0.1 A g^?1 after 50 cycles. It is noteworthy that the synthetic method is scalable which is suitable for mass production.     

煤中氯对多环芳烃生成的影响研究

本文在管式炉上研究了煤中氯对多环芳烃生成的影响,测定了煤中氯含量不同时多环芳烃生成量的变化,并分析了在不同气氛下不同含氯量的煤燃烧时多环芳烃与二(?)英生成的相互关系.实验结果表明,在空气中燃烧及氮气气氛热解条件下,随着氯含量的增加,多环芳烃呈减少趋势;氯代反应是导致多环芳烃生成量减少的一个主要原因.     

Silicon/carbon nanocomposites used as anode materials for lithium-ion batteries

Silicon/carbon nanocomposites are prepared by dispersing nano-sized silicon in mesophase pitch and a subsequent pyrolysis process. In the nanocomposites, silicon nanoparticles are homogeneously distributed in the carbon networks derived from the mesophase pitch. The silicon/carbon nanocomposite delivers a high reversible capacity of 841 mAh g^?1 at the current density of 100 mA g^?1 at the first cycle, high capacity retention of 98 % over 30 cycles, and good rate performance. The superior electrochemical performance of nanocomposite is attributed to the carbon networks with turbostratic structure, which enhance the conductivity and alleviate the volume change of silicon.     

煤系针状焦原料在成焦过程中的XRD结构分析

低QI(原生喹啉不溶物)含量的软沥青（SCTP）是制备煤系针状焦的优选原料,研究其在成焦过程中的结构变化有助于高品质针状焦的研制。基于样品的X射线衍射（XRD）数据,利用Smarsly团队开发的CarbX软件对其全谱拟合,定量出SCTP在不同炭化温度（400,500,600,800,1 000,1 200和1 400 ℃）下的微晶结构参数,进而在纳米尺度下研究SCTP的热致结构变化情况。结果表明,随炭化温度升高,微晶堆垛的石墨烯层大小L_a从初始沥青的10.3 Å逐步增大到1 400 ℃的47.9 Å,但在500 ℃前L_a增加缓慢,只有当温度超过800 ℃后,L_a才显著增大,这表明需要800 ℃以上的高温才能使交联石墨烯层内的原子重组,进而导致微晶长大。然而,石墨烯碳网的C—C键长l_cc受温度的影响很小,在1.41~1.42 Å范围内变化。由于SCTP在液相炭化成半焦过程中存在中间相转化,导致微晶堆垛高度L_c在500 ℃前逐步增大,在500 ℃时达到最大（L_c=31.1 Å）,随后由于半焦进一步热解缩聚,使L_c逐步减小,在1 000 ℃时达到最低点（L_c=15.4 Å）,超过1 000 ℃后又开始增大。与L_c的变化趋势相同,堆垛的石墨烯层数N从原始沥青的2.66层增加到500 ℃的约9.05层,随后减小到1 000 ℃的4.55层,超过1 000 ℃后又开始增大。由于500 ℃前样品仍处于沥青态,所以此阶段微晶的石墨烯层间距a₃都较大,约为3.50 Å。当在500 ℃变为半焦后,a₃迅速减小至3.44 Å。随后温度升高,a₃在1 000 ℃达到最小（a₃=3.39 Å）,1 000 ℃后又开始增大,这表明焦炭经历了收缩再膨胀过程。通过CarbX软件拟合样品的XRD数据,除了可得到样品炭微晶的主要尺寸（L_a,L_c,N,a₃）信息外,还可获得这些参数的分散性（k_a,k_c,σ₃,ε₃）以及堆垛的取向性（q）、均匀性（η）和无序碳含量（c_un）等信息,有利于深入了解样品的微观结构,有助于优质针状焦的生产。     

利用小角X射线散射技术研究煤干馏过程中的孔隙结构变化

煤干馏是煤炭高效利用的重要途径之一。同步辐射小角X射线散射(Small Angle X-Ray Scattering,SAXS)技术是研究煤干馏过程中内部孔隙结构变化的常用手段。本文利用SAXS对山西余吾烟煤干馏过程(100~1200℃,温度梯度100℃)进行了表征,并对分形维数和粒径分布的变化进行了分析。结果发现煤干馏过程中,散射图像类似,具有各向同性特征,始终保持表面分形结构,且分形维数总体上呈现增大的趋势;随着煤干馏温度的升高,粒度分布发生了显著变化,充分反映了煤在不同干馏阶段的结构特征,对后续的煤炭研究具有一定的指导意义。     

Liquid-crystalline characteristics of cellulose derivatives: Binary and ternary mixtures of ethyl cellulose,hydroxypropyl cellulose,and acrylic acid

Phase behavior in binary and ternary mixtures of ethyl cellulose (EC), hydroxypropyl cellulose (HPC), and acrylic acid (AA) was investigated by optical techniques including polarized-light microscopy (POM), refractometry, UV absorption, and circular dichroism (CD) spectrophotometries, and laser-light scattering. Both derivatives of cellulose formed a cholesteric liquid-crystal phase in concentrated solutions in AA. EC and HPC homopolymer solutions in AA showed iridescent colors in the concentration range of 42–50 wt% and 65–80 wt%, respectively. In the 30–50 wt% HPC/AA solutions, an optical image with fingerprint-like patterns was observed between crossed polars. CD revealed that the cholesteric helical sense was right-handed in the HPC/AA mesophase, while the EC/AA mesophase formed left-handed structures. Anisotropic samples of HPC/AA and EC/AA also showed a POM image with a grid-like texture, which was much coarser in the former system compared with that in the latter. A phase diagram constructed for the ternary system EC/HPC/AA was divided into five distinct regions: (1) isotropic (I) monophase, (2) I + HPC mesophase (HLC), (3) I + HLC + EC mesophase (ELC), (4) HLC + ELC, and (5) anisotropic monophase, with the optical appearance changeable depending on polymer composition and concentration. In region 5 the anisotropic system was apparently monophasic in POM observations; however, CD and UV results indicated that the biphasic separation into the two cholesteric structures still occurred. Optical anisotropy and phase behavior were also examined for the EC/ HPC binary blends prepared from solutions and melt.     

Characterization of Coal Tar Pitch Oils by Nuclear Magnetic Resonance

Nuclear Magnetic Resonance (NMR) spectrometry has been used to characterize coal tar pitch oils, which had been obtained from a low-temperature carbonization of high volatile bituminous coal. NMR provides data on hydrogen distribution in coal oils and structural correlations established on elution chromatographic, on distillation fractions, and on the residues remaining after distillation. This research is the first report on the hydrogen distribution of coal tar pitch oils by NMR.     

Chemical transformation of iron compounds during the process of coal pyrolysis in steam

When the content of sulphur in hard coal is higher than 1.5% weight, such coal cannot be used as fuel in thermal-electric power stations due to environmental protection. Such coal can be used as a raw product in various chemical processes in which many valuable substances are obtained. This study is a small part of a major project looking for improved ways of utilizing sulphur-rich coals. Mössbauer measurements were carried out for semi-cokes obtained from sulphur-rich coal in the pyrolysis process in a steam atmosphere in the temperature range of 300–800 °C. Results of these measurements showed that during the pyrolysis process, pyrite transformed completely into iron oxides (magnetite and hematite), whereas illite transformed only partly even at the highest temperatures. Unfortunately, it was not possible to identify some products of the illite transformation.     

Characterization and organic electric-double-layer-capacitor application of KOH activated coal-tar-pitch-based carbons: Effect of carbonization temperature

The present study reports the influence of pre-carbonization on the properties of KOH-activated coal tar pitch (CTP). The change of crystallinity and pore structure of pre-carbonized CTPs as well as their activated carbons (ACs) as function of pre-carbonization temperature are investigated. The crystallinity of pre-carbonized CTPs increases with increasing the carbonization temperature up to 600 °C, but a disorder occurs during the carbonization around 700 °C and an order happens gradually with increasing the carbonization temperatures in range of 800–1000 °C. The CTPs pre-carbonized at high temperatures are more difficult to be activated with KOH than those pre-carbonized at low temperatures due to the increase of micro-crystalline size and the decrease of surface functional groups. The micro-pores and meso-pores are well developed at around 1.0 nm and 2.4 nm, respectively, as the ACs are pre-carbonized at temperatures of 500–600 °C, exhibiting high specific capacitances as electrode materials for electric double layer capacitor (EDLC). Although the specific surface area (SSA) and pore volume of ACs pre-carbonized at temperatures of 900–1000 °C are extraordinary low (non-porous) as compared to those of AC pre-carbonized at 600 °C, their specific capacitances are comparable to each other. The large specific capacitances with low SSA ACs can be attributed to the structural change resulting from the electrochemical activation during the 1st charge above 2.0 V.     

The measurement of various molecules of pyrolysis gas of coal by using VUV-SPI-TOFMS

We developed and tested a system that combines a vacuum ultraviolet single photon ionization time-of-flight mass spectrometer (VUV-SPI-TOFMS) with a Fourier transform-infrared (FT-IR) spectrometer and used it for the simultaneous detection of the various compounds generated during the pyrolysis of coal. We characterized the performance of the system, including its limits of detection and time resolution. We also determined the various compounds that could be detected using the system. The instrument exhibited a laboratory-determined detection limit that was in the parts per billion volume (ppbv) range and a detection time of 10 s for most of the aromatic compounds generated during the pyrolysis process. In addition, using this system, it was possible to determine the correlation between the pyrolysis temperature and the various compounds generated from different types of coals during the pyrolysis process.     

Effect of pressure on soot formation in the pyrolysis of <Emphasis Type="Italic">n</Emphasis>-hexane and the oxidation of fuel-rich mixtures of <Emphasis Type="Italic">n</Emphasis>-heptane behind reflected shock waves

The results of detailed kinetic simulations of the formation of soot particles in the pyrolysis of n-hexane–argon mixtures and in the oxidation of fuel-rich (φ = 5) n-heptane–oxygen–argon mixtures behind reflected shock waves at pressures of 20–100 bar and a constant concentration of carbon atoms or a constant fraction of argon in the initial mixture within the framework of a modified reaction mechanism are reported. The choice of n-hexane and n-heptane for examining the effect of pressure on the process of soot formation was motivated by the availability for these hydrocarbons of experimental measurements in reflected shock waves at high pressures (up to ~100 bar). The temperature dependences of the yield of soot particles formed in the pyrolysis of n-hexane are found to be very weakly dependent on pressure and slightly shifting to lower temperatures with increasing pressure. In general, pressure produces a very weak effect on the soot formation in the pyrolysis of n-hexane. The effect of pressure and concentration of carbon atoms in the initial mixture on the process of soot formation during the oxidation of fuel-rich n-heptane mixtures behind reflected shock waves is studied. The results of our kinetic simulations show that, for both the pyrolysis of n-hexane and the oxidation of fuel-rich n-heptane–oxygen mixtures, the influence of pressure on the process of soot formation is negligible. By contrast, the concentration of carbon atoms in the initial reaction mixture produces a much more pronounced effect.     

Acoustic emission technique for monitoring the pyrolysis of composites for process control

Carbonization is the first step in the heat and pressure treatment (pyrolysis) of composites in preparing carbon-carbon parts. These find many uses, including aircraft brakes, rocket nozzles and medical implants. This paper describes the acoustic emissions (AE) from various stages of the manufacturing process of carbon-carbon composites. This process involves carbonization at a high temperature and this results in both thermal expansion and volume change (due to pyrolysis in which a sacrificial polymer matrix is converted to carbon). Importantly the resultant matrix is porous and has a network of small intra-lamina cracks. The formation of these microcracks produces AE and this paper describes how this observation can be used to monitor (and eventually control) the manufacturing process. The aim is to speed up manufacture, which is currently time-consuming. The first section of the paper describes the design of unimodal waveguides to enable the AE to propagate to a cool environment where a transducer can be located. The second part of the paper describes various experimental observations of AE under a range of process conditions. In particular, this paper presents a technique based on detecting acoustic emissions and (1) uses wire waveguides to monitor parts within the autoclave to 800 degrees C, (2) monitors microcracking during pyrolysis, (3) uses a four-level threshold to distinguish between low- and high-amplitude cracking events, (4) recognizes the occurrence of harmful delaminations, and (5) guides the control of the heating rate for optimum efficiency of the pyrolysis process. In addition, supporting data are presented of in situ measurements of porosity, weight loss, cross-ply shrinkage, and mass spectroscopy of gases emitted. The process evolution is illustrated by the use of interrupted manufacturing cycle micrographs obtained by optical, scanning acoustic (SAM) and scanning electron (SEM) microscopy. The technique promotes in-process monitoring and control but also contributes to current understanding of pyrolysis.     

Effect of physical disturbance on the structure of needle coke

Through different preparation technology, this paper reports that the needle coke is prepared with coal-tar pitch under the effect of magnetic field and ultrasonic cavitation. It studies the effect of physical disturbance on the structure of needle coke. The structure of needle coke is characterized by scanning electron microscope and x-ray diffractometer, and the influence mechanism is analysed. Results showed that the structure and property of needle coke could be effectively improved by magnetic field and ultrasonic cavitations, such as degree of order, degree of graphitization and crystallization. Comparatively speaking, the effect of magnetic field was greater. The graphitization degree of needle coke prepared under the effect of magnetic field is up to 45.35%.     

Study of phase behavior in a system of linear hydrogen-bonded carboxylic acid homologues

The system of hydrogen-bonded liquid crystals formed from binary mixtures p-n-heptyloxybenzoic (I) acid and p-n-undecloxybenzoic (II) acid has been investigated by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, and scattering and dielectric measurements. The T–X phase diagram was obtained for this system. All mixtures show enantiotropic smectic and nematic phases. The crystalline phase represents a (α, β) solid solution. At the 2:1 ratio of I to II, an intermediate phase – co-crystal γ – is formed. The co-crystal γ possesses a much wider mesophase range than the corresponding initial components. In contrast to mixtures based on the solid solutions having a positive anisotropy, the co-crystal shows a negative dielectric anisotropy in the mesophase.     

Determining a 'safe' high-mass limit in matrix-assisted laser desorption/ionisation time-of-flight mass spectra of coal derived materials with reference to instrument noise

Three methods for determining a 'safe' estimate for high-mass limits of MALDI spectra of coal derived liquids were explored, using a sample of coal-tar pitch and its pyridine-insoluble fraction. Co-addition of increasing numbers of single-shot spectra (10, 30, 50 and 100 pulses) showed visually observable reductions in noise levels, consistent with robust and statistically meaningful signals. Three separate types of post-acquisition calculation were used to identify high-mass limits of the spectra. (i) A literature method indicated high-mass limits similar to those observed visually-as a shift from baseline at the highest masses, nearly 350 000 u for the coal tar pitch and about 390 000 u for its pyridine insoluble fraction. (ii) Comparing instrument signal with pre-selected multiples of the standard deviation, upper mass estimates of between 40-60 000 u for the coal-tar pitch and about 95 000 u for its pyridine-insoluble fraction were found. (iii) Calculation of the slope was used to identify 'lift-off' of the spectrum from baseline. The angle between the smoothed spectrum and the baseline was matched to a pre-selected value (e.g. 0.5 degrees and 1 degrees ). However, the arbitrary specification of the key parameter did not establish this last method on a firm basis. The choice of a criterion for estimating high-mass limits of MALDI spectra remains a semi-quantitative procedure; a reasonably conservative high-mass limit may be estimated by comparison of signal with five times the standard deviation. However, evaluation of size exclusion chromatograms of the present samples using polystyrene standards suggests that molecular mass distributions of pitch samples arrived at by MALDI mass spectrometry are, at least partly, determined by the limitations of available instruments. Copyright 1999 John Wiley & Sons, Ltd.