Semi-quantitative analysis of the structural evolution of mesophase pitch-based carbon foams by Raman and FTIR spectroscopy

Graphitized carbon foams(GFms)were prepared using mesophase pitch(MP)as a raw material by foaming(450℃),pre-oxidation(320℃),carbonization(1000℃)and graphitization(2800℃).The differences in structure and properties of GFms prepared from different MP precursors pretreated by ball milling or liquid phase extraction were investigated and compared,and semi-quantitative calculations were conducted on the Raman and FTIR spectra of samples at each preparation stage.Semi-quantitat-ive spectroscopic analysis provided detailed information on the structure and chemical composition changes of the MP and GFm de-rived from it.Combined with microscopic observations,the change from precursor to GFm was analyzed.The results showed that ball milling concentrated the distribution of aromatic molecules in the pitch,which contributed to uniform foaming to give a GFm with a uniform pore distribution and good properties.Liquid phase extraction helped remove light components while retaining large aromatics to form graphitic planes with the largest average size during post-treatment to produce a GFm with the highest degree of graphitization and the fewest open pores,giving the best compression resistance(2.47 MPa),the highest thermal conductivity(64.47 W/(m·K))and the lowest electrical resistance(13.02μΩ·m).Characterization combining semi-quantitative spectroscopic ana-lysis with microscopic observations allowed us to control the preparation of the MP-derived GFms.

Preparation of a high-performance synthetic pitch from aromatic hydrocarbons containing N/Cl

The preparation of a synthetic pitch from aromatic monomers could easily regulate structure orientation at the molecu-lar level,which would be useful in fabrication.An isotropic synthetic pitch was prepared by a chlorine-and/or nitrogen-induced sub-stitution polymerization reaction method using aromatic hydrocarbon precursors containing Cl and N,which for this study were chloromethyl naphthalene and quinoline.This method was verified by investigating the structural changes under different synthesis conditions,and the synthesis mechanism induced by aromatics containing Cl was also probed.The result shows that the pyridinic N in quinoline contains a lone pair of electrons,and is an effective active site to induce the polymerization reaction by coupling with aromatic hydrocarbons containing Cl.The reaction between such free radicals causes strong homopolymerization and oligomeriza-tion.A higher reaction temperature and longer reaction time significantly increased the degree of polymerization and thus increased the softening point of the pitch.A linear molecular structure was formed by the Cl substitution reaction,which produced a highly spinnable pitch with a softening point of 258.6℃,and carbon fibers with a tensile strength of 1163.82 MPa were obtained.This study provides a relatively simple and safe method for the preparation of high-quality spinnable pitch.

A review of the catalytic preparation of mesophase pitch

Because of its high purity and excellent orientation, mesophase pitch is a superior precursor for high-performance car-bon materials. However, the preparation of top-notch mesophase pitch faces challenges. Catalytic polycondensation at low temperat-ures is more favorable for synthesizing mesophase pitch, because it circumvents the high-temperature free radical reaction of other thermal polycondensation approaches. The reaction is gentle and can be easily controlled. It has the potential to significantly im-prove the yield of mesophase pitch and easily introduce naphthenic characteristics into the molecules, catalytic polycondensation is therefore a preferred method of synthesizing highly spinnable mesophase pitch. This review provides a synopsis of the selective pre-treatment of the raw materials to prepare different mesophase pitches, and explains the reaction mechanism and associated research advances for different catalytic systems in recent years. Finally, how to manufacture high-quality mesophase pitch by using a cata-lyst-promoter system is summarized and proposed, which may provide a theoretical basis for the future design of high-quality pitch molecules.

Pitch-derived soft carbon composite with hard carbon fibers for high-rate and long-cycling K^(+) storage

Potassium-ion batteries(KIBs)have been seen as a competitive alternative to lithium-ion batteries(LIBs)due to their natural abundance,low cost and rocking chair-like operating mechanism similar to LIBs.Soft carbon has a lower voltage plateau compared to hard carbon and an easily modulated lattice structure compared to graphite,which provides particular advantages in KIBs anodes.Pitch has attracted much attention as a simple,readily available and inexpensive precursor for soft carbon,but its structure is easily damaged during cycling.Herein,the flexible film Pitch@CNF are prepared by uniformly winding reticulated carbon fibers on the surface of pitch-soft carbon via electrostatic spinning technique,which not only enables the pitch to maintain its structure well during cycling and withstand the volume expansion upon K^(+) insertion,but also is conducive to ionic transport of the three-dimensional reticulated structure.Meanwhile,the abundant pores on the carbon fibers can provide more K^(+) active sites.The prepared flexible self-supporting films can be used directly as electrodes without the addition of binders and conductive agents.The reversible capacity is 290 mAh·g^(-1)at a current density of 0.1 A·g^(-1),and the capacity retention rate is 83%after 500 cycles.

On the effect of pitch and yaw angles in oblique impacts of smallcaliber projectiles

A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study.The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea? software yielded the conclusions.The experimental verification proved that slight differences in the pitch-andyaw angles of a projectile upon an impact caused different damage types to the projectile’s core.The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results.An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study.The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.

Effect of Rigid Pitch Motion on Flexible Vibration Characteristics of a Wind Turbine Blade

Adynamic pitch strategy is usually adopted to improve the aerodynamic performance of the blade of awind turbine.The dynamic pitch motion will affect the linear vibration characteristics of the blade.However,these influences have not been studied in previous research.In this paper,the influences of the rigid pitch motion on the linear vibration characteristics of a wind turbine blade are studied.The blade is described as a rotating cantilever beam with an inherent coupled rigid-flexible vibration,where the rigid pitch motion introduces a parametrically excited vibration to the beam.Partial differential equations governing the nonlinear coupled pitch-bend vibration are proposed using the generalized Hamiltonian principle.Natural vibration characteristics of the inherent coupled rigid-flexible system are analyzed based on the combination of the assumed modes method and the multi-scales method.Effects of static pitch angle,rotating speed,and characteristics of harmonic pitch motion on flexible natural frequencies andmode shapes are discussed.It shows that the pitch amplitude has a dramatic influence on the natural frequencies of the blade,while the effects of pitch frequency and pith phase on natural frequencies are little.

Parametric investigation of railway fastenings into the formation and mitigation of short pitch corrugation

Short pitch corrugation has been a problem for railways worldwide over one century.In this paper,a parametric investigation of fastenings is conducted to understand the corrugation formation mechanism and gain insights into corrugation mitigation.A three-dimensional finite element vehicle-track dynamic interaction model is employed,which considers the coupling between the structural dynamics and the contact mechanics,while the damage mechanism is assumed to be differential wear.Various fastening models with different configurations,boundary conditions,and parameters of stiffness and damping are built up and analysed.These models may represent different service stages of fastenings in the field.Besides,the effect of train speeds on corrugation features is studied.The results indicate:(1)Fastening parameters and modelling play an important role in corrugation formation.(2)The fastening longitudinal constraint to the rail is the major factor that determines the corrugation formation.The fastening vertical and lateral constraints influence corrugation features in terms of spatial distribution and wavelength components.(3)The strengthening of fastening constraints in the longitudinal dimension helps to mitigate corrugation.Meanwhile,the inner fastening constraint in the lateral direction is necessary for corrugation alleviation.(4)The increase in fastening longitudinal stiffness and damping can reduce the vibration amplitudes of longitudinal compression modes and thus reduce the track corrugation propensity.The simulation in this work can well explain the field corrugation in terms of the occurrence possibility and major wavelength components.It can also explain the field data with respect to the small variation between the corrugation wavelength and train speed,which is caused by frequency selection and jump between rail longitudinal compression modes.

Analysis of Influence on Aerodynamic Noise of Wind Turbine Blades under Different Pitch Angles

Aiming at the influence of blade pitch Angle on aerodynamic noise of wind turbines, the sound field and flow field distribution at 0˚, 5˚, 10˚ and 15˚ are calculated by numerical simulation. Then, through the distribution of pressure field and velocity field calculated by flow field, the influence of different pitch angles on wind turbine blade aerodynamic noise and the reasons for its influence are analyzed. The results show that when the pitch Angle increases within 0˚ - 10˚, the aerodynamic noise pressure level of the blade decreases. However, the sound pressure level of aerodynamic noise increases in the range of 10˚ - 15˚. The changes of static pressure gradient and pressure pulsation on the blade surface make the aerodynamic noise change, and the changes of the two are positively correlated. At the same time, the fluid velocity and fluid motion state on the blade surface are closely related to the aerodynamic noise of the blade. The greater the fluid velocity, the more complex the fluid motion state and the greater the turbulent kinetic energy of the wind turbine blade, and the aerodynamic noise of the wind turbine blade will also increase.

Ultrafine red phosphorus confined in reasonably designed pitch-based carbon matrix built of well-interconnected carbon nanosheets for high-performance lithium and potassium storage

Red phosphorus has been well-recognized as promising anode materials for lithium-ion batteries(LIBs)and potassium-ion batteries(PIBs)due to its extremely high theoretical capacity and low cost.However,the huge volume change and poor electric conductivity severely limit its further practical application.Herein,the nanoscale ultrafine red phosphorus has been successfully confined in a three-dimensional pitch-based porous carbon skeleton composed of well-interconnected carbon nanosheets through the vaporization-condensation method.Except for the traditional requirement of high electric conductivity and stable mechanical stability,the micropores and small mesopores in the porous carbon matrix centered at 1 to 3 nm and the abundant amount of oxygen-containing functional groups are also beneficial for the high loading and dispersion of red phosphorus.As anode for LIBs,the composite exhibits high reversible discharge capacities of 968 mAh g^(-1),excellent rate capabilities of 593 mAh g^(-1)at 2 A g^(-1),and long cycle performance of 557 mAh g^(-1)at 2 A g^(-1).More impressively,as the anode for PIBs,the composite presents a high reversible capacity of 661 mAh g^(-1)and a stable capacity of 312 mAh g^(-1)at 0.5 A g^(-1)for 500 cycles with a capacity retention up to 84.3%.This work not only sheds light on the structure design of carbon hosts with specific pore structure but also open an avenue for high value-added utilization of coal tar pitch.

High accuracy non-equidistant method for singular perturbation reaction-diffusion problem

Singular perturbation reaction-diffusion problem with Dirichlet boundary condition is considered. It is a multi-scale problem. Presence of small parameter leads to boundary layer phenomena in both sides of the region. A non-equidistant finite difference method is presented according to the property of boundary layer. The region is divided into an inner boundary layer region and an outer boundary layer region according to transition point of Shishkin. The steps sizes are equidistant in the outer boundary layer region. The step sizes are gradually increased in the inner boundary layer region such that half of the step sizes are different from each other. Truncation error is estimated. The proposed method is stable and uniformly convergent with the order higher than 2. Numerical results are given, which are in agreement with the theoretical result.

Preparation of pitch precursor with excellent spinnability for general-purpose carbon fibre using coal tar pitch as raw material

Tetrahydrofuran(THF) extract of coal tar pitch(CTP) was used instead of blending CTP with pretreated pyrolysis fuel oil to prepare an isotropic pitch precursor with excellent spinnability for general-purpose carbon fibre through bromination-dehydrobromination. The feasibility and effectiveness of synthesising an isotropic pitch precursor derived from THF-soluble(CTP-THFs) is demonstrated in this study.The results show that CTP-THFs contains more light components than CTP;CTP-THFs and CTP monomer proportions were 62.52% and 45.32%, respectively. However, based on comparisons of CTP-THFsBr0 and CTPBr0 characterisations, CTP-THFs exhibits better polycondensation than CTP. Bromination-dehydrobro mination promotes polycondensation of pitch precursors, leading to greater carbon aromaticity in CTP-THFsBr5, CTP-THFsBr10, and CTP-THFsBr15 than that in CTP-THFsBr0 and CTPBr0. CTP-THFsBr5 and CTP-THFsBr10 have excellent spinnability even with softening points as high as 230 ℃. The pericondensed carbon and carbon aromaticity of CTP-THFsBr5 and CTP-THFsBr10 are high owing to the higher degree of polycondensation;however, they still possess a more linear molecular structure. The as-prepared carbon fibre exhibits homogeneity and uniformity, and the mechanical performance is comparable with that of commercial general-purpose carbon fibre products.

A Novel Non-Equidistant Grey GRM(1,1) Model Based on Reciprocal Accumulated Generating

Applying the reciprocal accumulated generating and the reconstruction method of GRM(1,1) model’s background value of non-equidistant sequence based on the exponential trait of grey model and the definition of integral for the problem of lower precision as well as lower adaptability in non-equidistant GM(1,1) model, the calculation formulas were deduced and a novel non-equidistant GRM(1,1) model generated by reciprocal accumulated generating was put forward. The grey GRM(1,1) model can be used in non-equidistant interval & equidistant interval time series and has the characteristic of high precision as well as high adaptability. Example validates the practicability and reliability of the proposed model.

The mitigation of pitch-derived carbon with different structures on the volume expansion of silicon in Si/C composite anode

The microstructures of carbon precursors significantly affect the electrochemical performance of Si/C composite anodes.However,the interaction between Si and carbon materials with different structures is still unclear.Pitch-based materials undergoing different thermal treatments are superior sources for synthesizing carbons with different structures.Herein,different types of mesophase pitch(domain,flow-domain and mosaic structure) obtained from controllable thermal condensation are utilized to prepare Si/C composite materials and the corresponding models are established through finite element simulation to explore the correlation between the lithium storage properties of Si/C composites and the structures of carbon materials.The results indicate that the flow-domain texture pitch P2 has a better ability to buffer the volume expansion of silicon particles for its highly ordered arrangement of carbon crystallites inside could disperse the swelling stress uniformly alongside the particle surface.The sample Si@P2 exhibits the highest capacity of 1328 mA h/g after 200 cycles at a current density of 0.1 A/g as well as the best rate performance and stability.While sample Si@P3 in which the mosaic texture pitch P3 composed of random orientation of crystallites undergoes the fastest capacity decay.These findings suggest that highly ordered carbon materials are more suitable for the synthesis of Si/C composite anodes and provide insights for understanding the interaction between carbon and silicon during the charging/discharging process.

Proton pitch angle distributions in the Martian induced magnetosphere: A survey of Tianwen-1 Mars Ion and Neutral Particle Analyzer observations

The pitch angle distributions of ions and electrons can be affected by various processes;thus,they can serve as an important indicator of the physical mechanisms driving the dynamics of space plasmas.From observations from the Mars Ion and Neutral Particle Analyzer onboard the Tianwen-1 orbiter,we calculated the pitch angle distributions of protons in the Martian induced magnetosphere by using information from the magnetohydrodynamically simulated magnetic field,and we statistically analyzed the spatial occurrence pattern of different types of pitch angle distributions.Even though no symmetrical features were seen in the dataset,we found the dominance of the field-aligned distribution type over the energy range from 188 to 6232 eV.Maps of the occurrence rate showed the preferential presence of a trapped-like distribution at the lower altitudes of the surveyed nightside region.Although our results are more or less restricted by the adopted magnetic field,they indicate the complexity of the near-Mars proton pitch angle distributions and infer the possibility of wave–particle interactions in the Martian induced magnetosphere.

Effects of Ethylene Tar-Based Pitch Coatings on the Electrochemical Properties of Graphite Anode Materials

To improve the electrochemical performance of graphite anode materials,pitches with various softening points(150℃,180℃,200℃,and 250℃)were prepared from ethylene tar and used to coat graphite through a liquid coating process.The effects of the softening point of the pitch and the coating amount on the microstructure and electrochemical properties of graphite were studied by methods including thermogravimetric analysis,X-ray diffraction,Raman spectroscopy,surface area analysis,scanning electron microscopy,transmission electron microscopy,and electrochemical testing.The graphite particles were coated uniformly by the pyrolytic carbon in the pitch.The coating changed the degree of graphitization,decreased the average specific surface area,and improved the electrochemical performance significantly.The best battery anode performance was obtained when the mass ratio of pitch to graphite was 10%,the heat treatment temperature was 1100℃,and the softening point of the pitch was 250℃.Under the optimum conditions,the irreversible capacity loss in the first cycle at 0.1 C was only 23 mAh/g,and the first Coulombic efficiency reached 94.2%.The capacity retention rate was 98.3%after 100 charge-discharge cycles at 0.1 C.

Tunable and efficient microwave absorption from mesophase pitch carbide with designable electromagnetic properties

In order to obtain the microwave absorption(MA)materials with light weight,high efficiency and tunable properties,the carbonized mesophase pitch(CMP)with the variation in carbonization temperatures and particle sizes were prepared and characterized.The carbonization temperature mainly controlled the graphitization degree of the CMP to affect their conductive loss.The carbon residues were generated on the CMP surface when the temperature was higher than 700℃,which contributed significantly to the polarization loss of the CMP.For scale regulation,the segregation between the particles in the paraffin ring caused by the reduction particles of CMP carbonization at 750℃(750 CMP)resulted in a significant reduction in conductive losses while improving their impedance matching.The 750 CMP over 300 mesh sieved had the strongest MA properties of-53 d B at 3.4 GHz within 5.5 mm.Moreover,the prepared CMPs were multi-layer compounded and optimized by CST microwave studio.The synergistic effect derived from the improved impedance matching and the enhanced interfacial polarization resulted in significant reflection loss in multi-layer CMP.Overall,these findings lead to the systematically regulation of carbon-based materials for MA,showing an attractive application prospect for the preparation of high-performance MA materials.

Feasibility Investigation of Bitumen Properties by Blending of Coal Tar Pitch

There are numerous methods and additives available to improve the durability and quality of road bitumen. A coal tar obtained by coal coking was distilled in a laboratory into fractions of initial boiling point IBP-180℃ (gasoline-like fuel), 180℃ - 360℃ (diesel-like fuel), and >360℃ (residue or coal tar pitch). The coal tar pitch was added into road bitumen by up to 1 - 5 wt% and investigated the alteration of physical and chemical properties. The physico-mechanical properties of coal tar pitch and bitumen blends, as well as the chemical group composition, were determined using standard techniques (MNS) and the SARA method, respectively. Results of 3% coal tar pitch addition into bitumen enhanced ductility by 12.4% and softening point by 1.6℃. We found that blending with bitumen coal tar pitch as a modifier could improve bitumen properties.

Operation State of theWind Turbine Pitch System Based on Fuzzy Comprehensive Evaluation

To ensure wind turbine(WT)safe operations and improve the utilization rate of wind energy,effective evaluation of the operation state of the pitch system is critical.Therefore,a new method was proposed to evaluate the operation state of the pitch system of WT based on fuzzy comprehensive evaluation.Firstly,based on SCADA data,the working state of the pitch system under rated power state and power state of WT were analyzed.Secondly,through the analysis of characteristic parameters and physical mechanism of the pitch system,the consistency principle of characteristic parameters,the stability principle of power under rated state,and the stability principle of blade angle underpowered state were obtained.Next,based on the aforementioned principles,the evaluation indexes were established,and the fuzzy comprehensive evaluation method was used to establish the operation state evaluation model of the pitch system under rated power state and under power state of the WT.Finally,an example was provided to verify the effectiveness of the method.The evaluation model established in this study can be used as a technical reference for the online monitoring of WT pitch systems to ensure the safe and stable operation of WTs.

基于模糊神经网络PID的煤矿掘进机俯仰控制研究

目前煤矿掘进机俯仰控制主要采用PID控制方法,在掘进机俯仰控制时变性与液压系统非线性情况下的控制精度不高。掘进机俯仰控制通过控制液压缸行程实现,将传统PID算法与模糊控制、神经网络等相结合,可有效提高液压缸行程控制精度。提出了一种基于模糊神经网络PID的煤矿掘进机俯仰控制方法。通过分析掘进机支撑部运动学关系,得到俯仰角与支撑部液压缸的数学关系;介绍了掘进机俯仰控制液压系统工作原理,建立了液压系统及其传递函数模型;将模糊控制与神经网络相结合,形成模糊神经网络,利用模糊神经网络优化PID控制参数,再结合支撑机构数学模型和液压系统传递函数模型,建立掘进机俯仰角模糊神经网络PID控制模型,实现煤矿掘进机俯仰机构自动精确控制。该方法可使掘进机俯仰机构更加快速、准确到达预设位置,解决掘进机俯仰控制中的时变性与非线性难题。仿真结果表明:模糊神经网络PID控制算法相较于模糊PID和PID控制算法,跟踪误差分别降低了69.34%和74.49%。通过液压缸位移控制模拟煤矿掘进机在突变工况和跟随工况下的俯仰控制,结果表明:模糊神经网络PID控制算法相比模糊PID和PID控制算法,俯仰控制跟踪误差最小,对位置信号的平均响应时间分别缩短了27.22%和50.33%,动态控制性能更好。

沥青基碳纤维的制备工艺、反应机理及调控方法

沥青基碳纤维是重要的工程碳纤维之一,在航空航天、国防军工等领域具有广泛应用。沥青基碳纤维制备流程长、影响因素多,归咎于对其制备工艺、反应机理及调控方法的认识不足,迄今工业化生产强度性能优异的沥青基碳纤维仍面临诸多困难。以碳纤维生产流程为主线,针对原料预处理、沥青前驱体调制、熔融纺丝、预氧化及炭化与石墨化的现状、方法、机理及调控进行深入探讨分析。沥青基碳纤维的原料有煤系、石油系、生物质系、高分子系和纯化合物,原料预处理方法主要有蒸馏和萃取;沥青前驱体的调制本质是以氢转移反应和自由基反应并行的液相炭化反应,包括环化、芳构化、低聚和缩聚等复杂的反应过程。芳烃低聚物在高温下缩聚形成稠环芳烃片状大分子的基本结构单元,基本结构单元经过热运动不断聚集,形成聚集体;由于范德华力作用使基本结构单元相互堆叠,形成平行堆积体,进而通过层积、堆积等过程形成基本构筑单元聚集体。基本构筑单元聚集体在不同反应条件下可以转变为长程无序、短程有序的难石墨化结构,也可以转变为长程有序、短程有序的易石墨化结构。以煤系、石油系和生物质系物质为原料调制沥青前驱体时,因其反应活性好,通常选用设备简单、操作容易、成本低廉的热缩聚法;而当以萘、甲基萘等纯化合物为原料时,因其反应活性差,需要较高的温度才能引发自由基反应,故通常采用催化合成法。熔融纺丝宏观上起到塑型的作用,通过改变纺丝参数和喷丝板的形状分别可以调节碳纤维的直径和形状;此外,熔融纺丝对中间相沥青前驱体的重排分子作用尤为明显,使得石墨微晶更易沿轴向一维排列形成有序的石墨晶体结构。为使沥青纤维在炭化过程中不发生融化,需要将沥青纤维由热塑性转变为热固性,即通过轻微的氧化反应,让沥青中的稠环芳烃分子经历氧化、缩合、分解和脱水,从而形成特定的交联结构,最终在纤维结构中生成一定量的含氧官能团。炭化是使预氧化后的纤维经过复杂的化学反应和结构转变形成具有炭材料分子结构特征的碳纤维。炭化过程中,石墨微晶发生重排,非碳原子被移除,碳元素含量进一步升高;经过石墨化后,石墨晶体结构更加完整、取向度更高,使碳纤维向石墨纤维转变,强度性能更加优异。另外,针对沥青基碳纤维的突破方向,提出了从分子维度定向可控制备的思路;并为碳纤维生产过程中耗时耗能的预氧化步骤的优化改进提供了具体方法。