Applications of sensitivity analysis to combustion chemistry

Combustion chemical models usually contain several hundred or thousand kinetic rate parameters. Most simulation packages calculate local concentration sensitivities, but it is frequently not easy to extract meaningful information from large sensitivity matrices. Principal component analysis is a simple post-processing technique that summarizes sensitivity information and also reveals the effect of simultaneously changing parameters.A new program package, called KINALC, has been created for the analysis of gas-phase reaction systems. This program is an extension to CHEMKIN based simulation programs. KINALC processes the concentration sensitivity information in four different ways and allows a comparison of the sensitivity information to other methods, based on the study of reaction rates and stoichiometry, for the analysis of complex mechanisms. KINALC is available through the World Wide Web.The various methods are illustrated by the analysis of a detailed chemical model for hydrogen combustion. Local sensitivity analysis of models of homogeneous hydrogen explosion and of premixed laminar hydrogen-air flame has been carried out and the sensitivity results reveal that the chemical processes are very similar in these physically different systems at the corresponding temperatures.     

Correlation of C1s chemical state intensities with the O1s intensity in the XPS analysis of anodically oxidized glass-like carbon samples

An XPS study of anodic oxidized glass-like carbon (GC) was conducted in order to investigate the inconsistency between O_1s/C_1s and oxygen concentration (Ocal.) calculated from the curve fitting results of the C_1s spectrum. Consideration of the asymmetric peak shape of the C_1s spectrum is normally done in order to obtain precise curve fitting results. However, it was found that the 2nd-carbon peak should also be taken into consideration in the curve fitting process in addition to the effect of asymmetric peak shape of carbon to obtain a consistent value of O_1s/C_1s. The 2nd graphitic peak is normally located +0.7–+0.8 eV away from the original C_1s spectrum. The ratio of the 2nd graphitic peak area in the C_1s spectrum increased as the electrical charge increased. However, the peak shapes of C_1s spectra of anodic oxidized GC after heat treatment at 1500 °C in argon atmosphere were almost the same as the C_1s of untreated GC. Although the origin of the 2nd graphitic peak is not well understood, it may be related to the amount of oxygen on the GC surface.     

Correlation between electrokinetic potential, dispersibility, surface chemistry and energy of carbon nanotubes

This paper proposes the correlation between the electrokinetic potential, dispersibility in solvents, surface energy and oxygen content of carbon nanotubes (CNTs) affected by functionalization. Colloidal systems consisting of CNTs with varying degrees of dispersion are prepared and characterized to evaluate CNT dispersibility and suspension stability in solvents with different polarities. The results show that an absolute value of zeta potential at about 25 mV is closely related to the micro- and macroscopic dispersion of CNTs, whereas a high absolute value of 40 mV is regarded as an indication of high quality CNT dispersion with much enhanced suspension stability in solvents. The absolute zeta potential value increases consistently with increasing degree of CNT functionality, the increase being most pronounced in a hydrophilic liquid such as water. A linear correlation is established between the surface energy of a CNT film and the oxygen to carbon ratio of CNT surface. The CNT dispersibility in a liquid is determined not only by their physical states, but also by the hydrophilicity and surface functionality of CNTs, all of which are reflected by zeta potential.     

XPS study of carbon nitride films deposited by hot filament chemical vapor deposition using carbon filament

Amorphous carbon nitride, a-CN_x, thin films were deposited by hot filament CVD using a carbon filament with dc negative bias voltage on the substrate. The effects of the negative bias and the filament components on the binding structure of the films are investigated by XPS. The composition ratio of graphite to amorphous carbon in the filaments affects the bonding structure of carbon and nitrogen in the films, although the nitrogen content in the films is almost same as 0.1. The nitrogen content in the films changes from 0.1 to 0.3 as the negative bias changes from 0 to − 300 V.     

A chemical ionization mass spectrometry method for the online analysis of organic aerosols

A new technique employing chemical ionization mass spectrometry (CIMS) is described that allows the composition of organic particles to be determined on the time scale of seconds. With this Aerosol CIMS technique, particles are vaporized thermally at temperatures up to 480 degrees C, and the resulting vapor is chemically ionized and detected with a quadrupole mass spectrometer. The separation of the vaporization and ionization steps allows greater control and more flexibility for the detection of condensed phases than with other chemical ionization methods. Consequently, composition can be correlated to volatility, providing an additional dimension of information. The use of a variety of positive and negative reagent ions, such as H(+)(H(2)O)(2), H(+)(CH(3)OH)(2), NO(+), O(2)(+), O(2)(-), F(-), and SF(6)(-), offers flexibility in the detection sensitivity and specificity. Furthermore, the degree of fragmentation of the resulting ion can be controlled, providing more straightforward identification and quantification than with other commonly used methods, such as electron impact ionization. Examples are given of the detection of aerosols consisting of organics with various functionalities, including alkanes, alkenes, alcohols, aldehydes, ketones, and carboxylic acids. Applications of this technique to laboratory studies of atmospherically relevant aerosol reactions are discussed.     

Characterization by XPS and SEM of reactive chemical vapour deposited boron carbide on carbon fibre

A process and apparatus used in the large-scale deposition of boron-based films on carbon fibres is described. The deposition occurs when the heated moving fibres react with a BCl₃-H₂ mixture. Among other advantages, such a process provides for continuous processing at atmospheric pressure. The properties of the as-deposited fibres, ex-Pan based, are discussed in terms of their use in material composites under ambient atmosphere. X-ray photoelectron spectroscopy shows that the filament surface consists of a B₄C-BN mixture.     

Applicability of the alkylation chemistry for chemical C-terminal protein sequence analysis

We have evaluated the alkylation chemistry first described some years ago by Boyd et al. which is now routinely applied in a commercial instrument. We have found that the low repetitive yields observed during these analyses are due to the formation of a major side product when alkylating the C-terminal thiohydantoin. This side product, resistant to the chemical cleavage methods currently used, was characterized by NMR experiments in solution. We further demonstrate that chemical C-terminal sequence analysis of proteins using the alkylation chemistry is feasable with low picomole amounts of material. High-sensitivity C-terminal sequencing allows a complementary approach by which a protein is first subjected to N-terminal Edman degradation followed by C-terminal sequence analysis, limiting the amount of material necessary for the characterization of the protein under study. This limited C-terminal sequence information is often sufficient to solve problems that cannot be solved by applying any other analytical method commonly used today.     

Chemical composition and surface chemistry of dc sputtered Pb-doped Bi-Sr-Ca-Cu-O thin films

X-ray photo-electron spectroscopy (XPS) studies were performed on dc sputtered superconducting Pb-doped Bi-Sr-Ca-Cu-O-films. A change in composition in as-deposited and annealed films was observed on the surface of the films. This may be related to the reduction in surface free energy due to the segregation of bismuth from bulk to the surface. Further, the change in binding energies of the constituent elements before and after the annealing were also observed. These results were correlated with the superconducting transition of the films after annealing.     

Influence of surface chemistry on inkjet printed carbon nanotube films

Carbon nanotube ink chemistry and the proper formulation are crucial for direct-write printing of nanotubes. Moreover, the correct surface chemistry of the self-assembled monolayers that assist the direct deposition of carbon nanotubes onto the substrate is equally important to preserve orientation of the printed carbon nanotubes. We report that the successful formulation of two single walled carbon nanotube (SWNT) inks yields a consistent, homogenous printing pattern possessing the requisite viscosities needed for flow through the microcapillary nozzles of the inkjet printer with fairly modest drying times. The addition of an aqueous sodium silicate allows for a reliable method for forming a uniform carbon nanotube network deposited directly onto unfunctionalized surfaces such as glass or quartz via inkjet deposition. Furthermore, this sodium silicate ingredient helps preserve applied orientation to the printed SWNT solution. Sheet resistivity of this carbon nanotube ink formula printed on quartz decreases as a function of passes and is independent of the substrate. SWNTs were successfully patterned on Au. This amine-based surface chemistry dramatically helps improve the isolation stabilization of the printed SWNTs as seen in the atomic force microscopy (AFM) image. Lastly, using our optimized SWNT ink formula and waveform parameters in the Fuji materials printer, we are able to directly write/print SWNTs into 2D patterns. Dried ink pattern expose and help orient roped carbon nanotubes that are suspended in ordered arrays across the cracks.     

Optimal surface chemistry for peptide immobilization in on-chip phosphorylation analysis

We investigated the optimal surface chemistry of peptide immobilization for on-chip phosphorylation analysis. In our previous study, we used a heterobifunctional cross-linker sulfosuccinimidyl-4-(N-maleimidomethyl) cyclohexane-1-carboxalate (SSMCC) to immobilize cysteine-terminated peptides on an amine-modified gold surface. The study revealed that the phosphorylation efficiency and rate were low (only 20% at 2 h) comparing with the reaction in solution. In this study, to improve the phosphorylation efficiency, the kinase substrates were immobilized via poly(ethylene glycol) (PEG), a flexible, hydrophilic polymer. An improvement in cSrc phosphorylation was achieved (60% at 1 h) from using a PEG-inserted peptide and SSMCC. However, no phosphorylation could be detected when the peptide was immobilized with a PEG-containing cross-linker. Fluorescence-labeled peptide studies revealed that the use of longer cross-linkers resulted in lower immobilization density. We considered that the flexible PEG linker was preferable to secure high phosphorylation efficiency for the immobilized peptide, probably due to the improvement of cSrc accessibility and peptide mobility, but the immobilization protocol is critical for keeping high density of the peptide immobilization. In addition, such an accelerating effect of PEG linker against on-chip phosphorylation of an immobilized peptide may depend on kinase structures or the position of the active center, because no improvement of on-chip peptide phosphorylation was observed in protein kinase A. However, PEG linker also did not suppress the phosphorylation in protein kinase A. Thus, we concluded that SSMCC and PEGylated peptide will be a good combination for the surface chemistry of on-chip phosphorylation in peptide array.     

Characteristics of multi-walled carbon nanotubes and background aerosols by carbon analysis; particle size and oxidation temperature

Novel carbonaceous nanomaterials such as carbon nanotubes and fullerenes have many beneficial characteristics as industrial materials, but exposure to these nanomaterials also poses health risks. As part of an exposure assessment, we characterized the following carbonaceous nanomaterials, using an aerosol carbon monitor: nine samples of multi-walled carbon nanotubes (MWCNTs), a sample of single-walled carbon nanotubes (SWCNTs), a standard sample of diesel exhaust particles (DEPs), and an ambient particulate matter (APM). The amounts of elemental carbon (EC) determined by the monitor coincided with the mass of MWCNTs calibrated by a microbalance. The carbonaceous nanomaterials were oxidized in three steps of oven temperatures (550, 700 and 920 °C) in this method. The portion of oxidized carbon at each temperature depended on the sample characteristic. We used the monitor to analyze the aerosol samples collected in five stages by a Sioutas cascade impactor (SCI), which collects size-segregated airborne particles having aerodynamic diameters from 6.6 μm to less than 0.25 μm. As MWCNTs aggregate/agglomerate easily, the size was of a good parameter to distinguish the MWCNTs from other materials. Two-dimensional mapping by size and oxidized temperature suggested the origin of the carbonaceous aerosol samples. Based on the results, we reanalyzed our previous data obtained at a factory manufacturing MWCNTs. The characteristics of workplace samples by particle size and carbon analysis were similar to those of MWCNT aerosol particles.     

Importance of carbon surface chemistry in development of iron-carbon composite adsorbents for arsenate removal

Micro/mesoporous activated carbon was oxidized and used either as received or after modification as a support for the deposition of iron oxyhydroxide. The prepared samples were applied as adsorbents of arsenate from water phase. The initial materials and those after adsorption were characterized using adsorption of nitrogen, - potentiometric titration, FTIR, EDX, XRD, AAS, and thermal analysis. The results obtained suggest that oxidation of the carbon support increases significantly the amount of iron oxyhydroxide species deposited on the surface and thus decreases their dispersions and the efficiency of arsenate immobilization in the carbon pore system. Iron hydroxyoxides react with arsenate forming salts. Moreover, a meso/microporous carbon surface contributes to changes in the toxicity of arsenic via reduction of As(V) to As(III). This is visible in the increased degree of carbon oxidation.     

XPS study of the surface chemistry of L-CVD SnO2 thin films after oxidation

In this paper we present the results of XPS study of the surface chemistry of L-CVD SnO₂ thin films onto Si(100) before and after subsequent additional oxidation. Moreover, the ageing effect was also studied in order to check the influence of ambient oxidation. As-deposited L-CVD SnO₂ thin films exhibit evident nonstoichiometry with the relative concentration [O]/[Sn] equal to 1.29 ± 0.1. After in situ oxidation at high temperature (800 K) the relative concentration [O]/[Sn] increases to 1.95 ± 0.05 which corresponds to the almost stoichiometric SnO₂. Almost the same relative concentration [O]/[Sn] of L-CVD SnO₂ thin films has been obtained after long term exposure to air. The oxidation states of L-CVD SnO₂ thin films in both cases were confirmed by the shape analysis of corresponding XPS O1s and Sn3d_5/2 peaks using the decomposition procedure. For the as-deposited L-CVD SnO₂ thin films a mixture of SnO and SnO₂ was observed, while for the oxidized L-CVD SnO₂ thin films the domination of SnO₂ was determined.     

Grafting the surface of carbon nanotubes and carbon black with the chemical properties of hyperbranched polyamines

Controlling the chemistry on the surface of new carbon materials is a key factor to widen the range of their applicability. In this paper we show a grafting methodology of polyalkylamines to the surface of carbon nanomaterials, in particular, carbon nanotubes and a carbon black. The aim of this work is to reach large degrees of covalent functionalization with hyperbranched polyethyleneimines (HBPEIs) and to efficiently preserve the strong chelating properties of the HBPEIs when they are fixed to the surface of these carbon materials. This functionalization opens new possibilities of using these carbon nanotubes-based hybrids. The results show that the HBPEIs are covalently attached to the carbon materials, forming hybrids. These hybrids emerge from the reaction of amine functions of the HBPEIs with carbonyls and carboxylic anhydrides of the carbon surface which become imine and imide bonds. Thus, due to the nature of these bonds, the pre-oxidized samples with relevant number of C=O groups showed an increase in the degree of functionalization with the HBPEIs. Furthermore, both the acid-base properties and the coordination capacity for metal ions of the hybrids are equivalent to that of the free HBPEIs in solution. This means that the chemical characteristics of the HBPEIs have been efficiently transferred to the hybrids. To reach this conclusion we have developed a novel procedure to assess the acid-base and the coordination properties of the hybrids (solids) by means of potentiometric titration. The good agreement of the values obtained for the hybrids and for the free HBPEIs in aqueous solution supports the reliability of the procedure. Moreover, the high capacity of the hybrids to capture Ni²⁺ by complexation opens new possibilities of using these hybrids to capture high-value metal ions such as Pd²⁺ and Pt²⁺.     

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high-temperature thermoplastics

The surface structure and morphology of several high strength polyacrylonitrile (PAN) based carbon fibres was studied with the scanning electron microscope (SEM) on the micrometre scale and the scanning tunnelling microscope (STM) down to the atomic scale. In addition, active surface area measurements were made to determine the number of bonding sites/unit area. Prior to the observations, the surfaces of some of the samples were subjected to either the commercial surface treatment or to oxidation in air or ozone in our laboratory. The roughness and number of bonding sites on each fibre surface was determined. These values will be correlated with the mechanical properties of composites made with these fibres and thermoplastic polymers in Part III of this study.     

内燃机燃烧测试分析系统的设计与开发

开发一套基于PC机的内燃机燃烧测试分析系统,并对气缸压力的采集,数据的匀化、光顺处理,动态上止点位置的确定等做介绍。利用测量的气缸压力曲线和能量守恒原理,在LabVIEW软件平台上编写出内燃机燃烧放热率计算程序,研究主要经验参数对放热率及缸内平均温度的影响。结果表明:采用Woschni传热公式计算的放热率曲线值高于采用Eichelberg传热公式和Sitkei传热公式计算的放热率曲线值。扫气系数φs的变化对气缸内平均温度有显著影响,φs=0.99时的缸内平均温度明显高于φs=0.95时的缸内平均温度,两者最高温度相差81.4 K。     

碳氮纳米结构材料的Raman和XPS分析

利用等离子体增强热丝化学气相沉积在不同条件下制备了不同结构的碳氮纳米结构材料。用扫描电子显微镜(SEM)、显微Raman光谱仪和X射线光电子谱(XPS)仪对它们的形貌和结构进行了分析。SEM照片表明在不同的生长条件下可制备出碳氮纳米尖锥、碳氮柱。Raman谱中位于1350和1607cm-1的D和G峰,表明制备的碳氮纳米结构材料主要由sp2碳组成。根据D和G峰的强度比,估计的sp2碳颗粒为4nm。XPS谱在398.4eV处显示出与氮有关的峰,表明制备的碳氮纳米结构材料中含有氮。对N1sXPS谱的峰进行拟合后,发现位于398.4eV的峰由位于398.3和约400.0eV的两个峰组成,分别与sp3和sp2 C—N键有关,表明材料中的部分碳原子被氮原子所替代。     

The effect of the cerium precursor and the carbon surface chemistry on the dispersion of ceria on activated carbon

Activated carbon-supported cerium dioxide (CeO₂/C) was prepared by impregnation of a commercial support (Norit R2030) with aqueous solutions of two different cerium precursors, [(NH₄)₂Ce(NO₃)₆] and Ce(NO₃)₃·6H₂O. The effect of carbon surface chemistry on the dispersion of ceria was studied by using two different carbon supports, the R2030 and the same material after an oxidation treatment with H₂O₂. Thus, four samples were obtained by combining the precursors and the supports. The prepared materials were characterized by thermogravimetry, nitrogen adsorption isotherms (77 K), X-ray diffraction, temperature-programmed desorption, temperature-programmed reduction and transmission electron microscopy, in order to study the degree of ceria dispersion over the supports. It was found that the best results in terms of ceria dispersion were obtained for the material prepared with the oxidized carbon and ammonium cerium nitrate as cerium precursor.