Conductivity for soot sensing: possibilities and limitations

In this study we summarize the possibilities and limitations of a conductometric measurement principle for soot sensing. The electrical conductivity of different carbon blacks (FW 200, lamp black 101, Printex 30, Printex U, Printex XE2, special black 4, and special black 6), spark discharge soot (GfG), and graphite powder was measured by a van der Pauw arrangement. Additionally the influence of inorganic admixtures on the conductivity of carbonaceous materials was proven to follow the percolation theory. Structural and oxidation characteristics obtained with Raman microspectroscopy and temperature programmed oxidation, respectively, were correlated with the electrical conductivity data. Moreover, a thermophoretic precipitator has been applied to deposit soot particles from the exhaust stream between interdigital electrodes. This combines a controlled and size independent particle collection method with the conductivity measurement principle. A test vehicle was equipped with the AVL Micro Soot Sensor (photoacoustic soot sensor) to prove the conductometric sensor principle with an independent and reliable technique. Our results demonstrate promising potential of the conductometric sensor for on-board particle diagnostic. Furthermore this sensor can be applied as a simple, rapid, and cheap analytical tool for characterization of soot structure.     

洋葱状纳米碳烟颗粒在基础油中的摩擦学性能

在SRV IV摩擦磨损试验机上,采用球-盘接触方式考察了不同载荷下碳烟颗粒在150SN基础油中的摩擦学性能。借助三维表面形貌仪、扫描电子显微镜、能谱仪、X射线光电子能谱仪及拉曼光谱探讨了载荷诱导的碳烟颗粒的减摩作用机理。结果表明,载荷对碳烟颗粒在150SN基础油中摩擦学特性有较大影响。低载荷时,碳烟颗粒可以改善基础油的抗磨性能;高载荷时,碳烟能够改善基础油的减摩性。载荷诱导的碳烟颗粒的减摩机理与其洋葱状的纳米结构有关,高载荷下碳烟颗粒外层的石墨微晶被剥离,在摩擦副表面形成了减摩层,使摩擦系数下降。     

Synthesis of carbon nanotubes by arc discharge in open air

In this work Carbon nanotubes have been synthesized by arc discharge in open air. A TIG welding ac/dc inverter was used as the power source for arc discharge. During each run of the arc discharge based synthesis, the anode was a low purity (approximately 85% C by weight) graphite rod. The effect of varying the atmosphere on the yield of soot of the carbon nanotube containing carbon soot has been studied. Various soots were produced, purified by oxidation and characterized to confirm formation of carbon nanotubes and their relative quality, using transmission electron microscopy, Raman spectroscopy, and XRD. It was found that the yield of soot formed on the cathode is higher when synthesis is carried out in open air than when carried out in a flowing argon atmosphere. When synthesized in open air, using a 7.2-mm-diameter graphite rod as anode, the yield of soot was around 50% by weight of the graphite consumed. Current and voltage for arcing were at identical starting values in all the experiments. This modified method does not require a controlled atmosphere as in the case of a conventional arc discharge method of synthesis and hence the cost of production may be reduced.     

微氧化处理对球形石墨结构及电化学行为的影响

研究了微氧化处理对球形石墨的晶体结构、表面形貌和电化学行为的影响. 采用XRD、Raman光谱和SEM等手段分析了样品的结构和形貌, 并采用恒电流充放电测试、粉末微电极技术和慢速扫描循环伏安法(SSCV)研究了微氧化前后石墨负极的电化学行为. 结果表明, 微氧化后石墨颗粒中的结构缺陷增多, 近表面区域的无序度增大, 面内平均晶粒尺寸L_a减小, 且菱形相含量降低, 石墨呈不规则的鳞片状, 部分层面的边缘有卷曲与刻蚀现象. 微氧化后石墨负极的第三次脱锂容量从345.5 mAh/g增加至381.4 mAh/g, 且其循环性能得到有效改善. 同时, 微氧化后锂离子较容易从石墨中脱出, 脱锂过程中一阶Li-GICs(lithium-graphite intercalation compounds, 简称Li-GICs)向二阶Li-GICs的阶转变可在较低的电位下发生.     

In situ studies of fuel oxidation in solid oxide fuel cells

Existing electrochemical experiments and models of fuel oxidation postulate about the importance of different oxidation pathways and relative fuel conversion efficiencies, but specific information is often lacking. Experiments described below present the first direct, in situ measurements of relevant chemical species formed on solid oxide fuel cell (SOFC) cermet anodes operating with both butane and CO fuel feeds. Raman spectroscopy is used to acquire vibrational spectra from SOFC anodes at 715 degrees C during operation. Both C4H10 and CO form graphitic intermediates. In the limit of a large oxide flux, excess butane forms ordered graphite but only transiently. At higher cell potentials (e.g., less current being drawn) ordered and disordered graphite form on the Ni cermet anode following exposure to butane, and under open circuit voltage (OCV) conditions the graphite persists indefinitely. The chemistry of CO oxidation is such that ordered graphite and a Ni-COO intermediate form only at intermediate cell potentials. Concurrent voltammetry studies show that the formation of graphite with butane at OCV leads first to decreased cell performance after exposure to 25 cm3 butane, then recovered performance after 75 cm3. CO voltammetry data show that at lower potentials the oxide flux through the YSZ electrolyte is sufficient to oxidize the Ni in the anode especially near the interface with the electrolyte.     

Radionuclides in Irradiated Graphite of Industrial Uranium–Graphite Reactors: Effect of Irradiation and Thermochemical Treatment on the Graphite Structure

The structure of irradiated graphite from decommissioned industrial uranium–graphite reactors was studied. The extent of disturbance of the graphite structure is closely correlated with temperature and integral neutral fluence. The perfection of the structure of graphite samples (data of X-ray diffraction and Raman spectroscopy) does not correlate with their radioactivity, which is due to low absolute concentration of the radionuclides. Mapping of the samples using Raman spectroscopy reveals spatial heterogeneity of the distribution of graphite lattice damages, which casts doubt on the representativeness of the spectra of individual points. The spatial distribution of domains differing in the crystal lattice perfection was studied for the first time and was compared with the radionuclide distribution. Satisfactory correlation between the radiographic and spectroscopic mapping data is observed for some samples. Irradiated graphite is strongly textured and contains amorphous microvolumes, which are probably radionuclide carriers. Thermochemical treatment (oxidation in O₂, thermal shock) leads to degradation of the irradiated graphite structure on the submicron level, accompanied by a drastic decrease in the mechanical strength of the samples.     

Carbon nanostructure examined by lattice fringe analysis of high-resolution transmission electron microscopy images

The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.     

鸟巢状CuCeZrOx三元复合氧化物的合成及其对碳烟颗粒的催化氧化性能研

采用尿素均相沉淀法合成了CuCeZrO_x(CCZ)三元复合氧化物催化剂。采用X射线衍射分析(XRD)、N₂-吸脱附测试、X射线光电子能谱(XPS)、扫描透射电镜(STEM)、程序升温还原(脱附、氧化)等技术, 考察煅烧温度对催化剂的物化性质和催化碳烟燃烧活性的影响。结果表明: 350℃煅烧产物CCZ-350表现出最优的催化活性: 在空速为12000 mL/(g_catalyst·h), O₂浓度为10vol%, NO浓度为500×10^-6, 催化剂和碳烟以10︰1质量比松散接触条件下, 碳烟颗粒最大燃烧速率温度T₅₀ = 407℃, 同时表现出极佳的抗水汽中毒和抗SO₂中毒性能, 这与活性组分的高度分散以及催化剂表面大量高活性吸附氧物种的存在有关。此外, 催化剂材料具有疏松多孔的鸟巢状结构, 有利于催化剂和碳烟颗粒的充分接触。该催化剂在柴油车尾气排放温度范围内(150~400℃)还能完全催化氧化柴油车尾气中CO、C₃H₆和C₃H₈等其他污染物, 显示出优异的催化净化柴油车尾气的综合性能。     

Lattice Boltzmann simulation on continuously regenerating diesel filter

To reduce particulate matter (PM) including soot in diesel exhaust gas, a diesel particulate filter (DPF) has been developed. Since it is difficult to observe the phenomena in a DPF experimentally, we have conducted a lattice Boltzmann simulation. In this study, we simulated the flow in a metallic filter. An X-ray computed tomography (CT) technique was applied to obtain its inner structure. The processes of soot deposition and oxidation were included for a continuously regenerating diesel filter. By comparing experimental data, a parameter of soot deposition probability in the numerical model was determined.     

基于工业化碳材料的锂氟化碳电池正极材料制备及性能EI北大核心CSCD

为实现锂氟化碳电池在更多领域的普遍应用,以工业化碳材料(活性炭、球形石墨、膨胀石墨和工业石墨烯)为碳源,制备了四种氟化碳正极材料。通过扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、拉曼光谱(Raman)、红外光谱(FTIR)、X射线能谱(XPS)、氮气吸脱附以及电化学测试等表征手段对材料的微观形貌、晶体结构、化学结构和电化学性能进行了系统的研究。研究表明:氟化工业石墨烯具有完全的单氟化碳结构、高比表面积以及稳定的碳结构,在20 mA·g^(-1)的放电电流下可以实现高达945.4 mAh·g^(-1)的比容量;氟化活性炭具有较多的半共价C-F键,其起始放电电压最高,但是由于其结构稳定性较差,电压平台快速下降,导致整体比容量较低;氟化膨胀石墨和氟化球形石墨与氟化工业石墨烯结构类似,但是由于高氟化碳原子(CF_(2)和CF_(3))的存在,其放电比容量要低于氟化工业石墨烯。不过在高放电电流密度下,氟化膨胀石墨、氟化球形石墨和氟化工业石墨烯的能量密度十分接近,因此,基于氟化膨胀石墨和氟化球形石墨的成本优势,氟化膨胀石墨和氟化球形石墨更适合于高功率应用场景。     

Amorphous carbon films in direct current magnetron sputtering from regenerative sooting discharge

We present results of carbon coatings on metal substrates in cylindrical hollow cathode (CHC) direct current magnetron sputtering. This is a new technique for making amorphous carbon films by CHC magnetron sputtering from a regenerative sooting discharge. The carbon films are deposited on Cu and Al substrates in a Ne atmosphere and compared with the films of carbon soot on the same materials produced from a conventional 80A arc discharge between graphite electrodes in a He background gas. Raman spectroscopy reveals the existence of graphite and diamond-like structures from the arc discharge while in CHC magnetron sputtering, graphite-like structures are dominant. X-ray diffraction data of samples from the arc discharge show nano-size precipitates of Al₄C₃ of rhombohedral and hexagonal form for the aluminium sample and probable formation of diamond and hexagonal carbon in copper whilst in magnetron sputtering we obtain amorphous carbon films. Scanning electron microscope images of the surface show a collection of loose agglomerates of carbon particles in the arc discharge whereas, for magnetron sputtering, structures are regular with smooth edges and fine grains.     

Amorphous carbon films in direct current magnetron sputtering from regenerative sooting discharge

We present results of carbon coatings on metal substrates in cylindrical hollow cathode (CHC) direct current magnetron sputtering. This is a new technique for making amorphous carbon films by CHC magnetron sputtering from a regenerative sooting discharge. The carbon films are deposited on Cu and Al substrates in a Ne atmosphere and compared with the films of carbon soot on the same materials produced from a conventional 80A arc discharge between graphite electrodes in a He background gas. Raman spectroscopy reveals the existence of graphite and diamond-like structures from the arc discharge while in CHC magnetron sputtering, graphite-like structures are dominant. X-ray diffraction data of samples from the arc discharge show nano-size precipitates of Al₄C₃ of rhombohedral and hexagonal form for the aluminium sample and probable formation of diamond and hexagonal carbon in copper whilst in magnetron sputtering we obtain amorphous carbon films. Scanning electron microscope images of the surface show a collection of loose agglomerates of carbon particles in the arc discharge whereas, for magnetron sputtering, structures are regular with smooth edges and fine grains.     

Synthesis and characterization of electrochemically-reduced graphene

Graphene has superior electrical conductivity than graphite and other allotropes of carbon because of its high surface area and chemical tolerance. Electrochemically processed graphene sheets were obtained through the reduction of graphene oxide from hydrazine hydrate. The prepared samples were heated to different temperatures such as 673 and 873 K. X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS), transmission electron microscopy (TEM), Raman spectra and conductivity measurements were made for as-prepared and heat-treated graphene samples. XRD pattern of graphene shows a sharp and intensive peak centred at a diffraction angle (2θ) of 26·350. FTIR spectra of as-prepared and heated graphene were used to confirm the oxidation of graphite. TEM results indicated that the defect density and number of layers of graphene sheets were varied with heating temperature. The hexagonal sheet morphology and purity of as-prepared and heat treated samples were confirmed by SEM–EDX and Raman spectroscopy. The conductivity measurements revealed that the conductivity of graphene was decreased with an increase in heating temperature. The present study explains that graphene with enhanced functional properties can be achieved from the as-prepared sample.     

Wavelength-dependent optical extinction of carbonaceous particles in atmospheric aerosols and interstellar dust

Optical extinction spectra for particles of structurally disordered carbonaceous material (carbon black, soot) are discussed in terms of the effects of size and shape and the difference between coagulated and coalesced particles. For this purpose, the orientation-averaged specific extinction for several compact and open aggregates of spherical particles is calculated and compared with the specific extincton by homogeneous particles, i.e., volume-equivalent sphere and elongated spheroids. The extinction spectra are calculated for wavelengths from 0.2 to 1000 microm by use of the optical constants for the carbonaceous materials of J?ger et al. [Astron. Astrophys. 332, 291 (1998)] and Schnaiter et al. [Astrophys. J. 498, 486 (1998)]. Comparisons with the model case of particles composed of graphite and with measurements of diesel soot aerosols are made.     

石墨烯-二硫化钼复合负极材料的制备及性能研究

借助机械球磨法, 成功地利用层状硫化物MoS₂对膨胀石墨实现了有效剥离, 得到石墨烯与MoS₂的复合材料。球磨处理后, 元素C均匀地分散在复合材料中。MoS₂ 与膨胀石墨的质量比越高, 得到的复合材料中具有石墨烯特征的石墨就越多, 但相应的石墨烯的缺陷也越多。优化后的复合材料用作锂离子电池负极材料时显示出良好的电池性能, 在小倍率0.1 Ah/g电流密度下充放电循环70次后, 电池容量仍保持在~ 570 mAh/g; 在大倍率1 A/g电流密度下充放电循环55次后, 电池容量仍能保持在~ 450 mAh/g。     

XPS analysis of combustion aerosols for chemical composition, surface chemistry, and carbon chemical state

Carbonaceous aerosols can vary in elemental content, surface chemistry, and carbon nano-structure. Each of these properties is related to the details of soot formation. Fuel source, combustion process (affecting formation and growth conditions), and postcombustion exhaust where oxidation occurs all contribute to the physical structure and surface chemistry of soot. Traditionally such physical and chemical parameters have been measured separately by various techniques. Presented here is the unified measurement of these characteristics using X-ray photoelectron spectroscopy (XPS). In the present study, XPS is applied to combustion soot collected from a diesel engine (running biodiesel and pump-grade fuels); jet engine; and institutional, plant, and residential oil-fired boilers. Elemental composition is mapped by a survey scan over a broad energy range. Surface chemistry and carbon nanostructure are quantified by deconvolution of high-resolution scans over the C1s region. This combination of parameters forms a distinct matrix of identifiers for the soots from these sources.     

Plasma oxidation of thermally grown graphenes and their characterization

We report the plasma oxidation of thermally synthesized graphenes and their characterization using Raman spectroscopy and atomic force microscope (AFM). A graphene was synthesized by thermal chemical vapor deposition with methane and transferred onto trench substrate to make suspended configuration in order to exclude substrate effects. The air plasma treatment at 0.4 W for 5 min and property characterization were alternately performed to address the effect of oxidation. After the oxidation, a drastic change in Raman spectra was observed, which implies that considerable structural changes occurred in the graphene. Interestingly, we observed from the Raman and AFM analyses that the number of layers can be reduced by the controlled plasma oxidation treatment. The results may open the possibility of graphene formation from graphite sheets through the precise control of plasma treatment conditions.     

Structure and electrochemical performance of nickel hydroxide synthesized by rapid quench method

Nickel hydroxide with amorphous structure has been synthesized successfully by chemical precipitation method combined with rapid quench technique. The microstructure and morphology of the prepared samples were analyzed by XRD, Raman spectra, IR spectra, and SEM. The electrochemical performance of the sample was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and charge/discharge tests. The discharge capacity of the amorphous nickel hydroxide is 330.0 mAh g⁻¹ at 0.2C, much higher than that of the theoretical capacity of β-nickel hydroxide (289.0 mAh g⁻¹). Moreover, the amorphous nickel hydroxide exhibits higher electrochemical reaction reversibility, lower electrochemical impedance, and better cyclic stability compared with β-nickel hydroxide.     

Stacking Defects in C60 Films

The structure of pollycrystalline C₆₀ films prepared by sublimation from 99.9% pure C₆₀ powder and from graphite soot was investigated by X-ray diffraction. A complex fcc (111) line was found in the former samples. Comparison of experimental and simulated (111) profiles allowed to assess quantitatively the degree of stacking disorder introduced during the growth of the film. Probabilities could be derived for continuation of already started fcc and hep sequences, thereby characterizing the statistical microstructure of the C₆₀ films. Also, the relative magnitudes of inter- and intra-layer disorder can be estimated. The films deposited from graphite soot show a high structural disorder.     

Nanostructure and reactivity of carbon particles from co-pyrolysis of biodiesel surrogate methyl octanoate blended with n-butanol

This paper presents nanostructure and reactivity of carbon particles (soot) from co-pyrolysis of biodiesel surrogate methyl octanoate blended with n-butanol at temperatures from 1023 K to 1223 K in a quartz tube flow reactor, as n-butanol concentration increases from 0 to 50% (mole fraction) in the mixed fuels. The soot structure was characterized by low and high resolution transmission electron spectroscopy (LRTEM and HRTEM) and X-ray diffraction (XRD). The soot reactivity was investigated by thermogravimetric analyzer (TGA). When the pyrolysis temperature increased, as well as the rise of n-butanol addition, soot presented the higher degree of graphitization with the larger fringe length and lower fringe tortuosity. TGA results revealed that the higher amount addition of n-butanol can induce the formations of less reactive soot, and soot yielded at lower temperatures was more reactive than that at high temperatures. In addition, the high correlations between soot reactivity with its nanostructure were given in details.