Combining Raman Chemical Imaging and Scanning Electron Microscopy to Characterize Ambient Fine Particulate Matter

Raman chemical imaging and scanning electron microscopy (Raman/SEM) have been used in a preliminary study to determine the size, morphology, elemental and molecular composition, and molecular structure of fine particulate matter in several test samples and one ambient air sample. Raman chemical imaging and SEM, respectively, provide a way to spatially characterize a sample based on its molecular and elemental makeup. When combined, Raman chemical imaging and SEM provide detailed spatial, elemental, and molecular information for particulate matter as small as 250 nm. Initial studies demonstrate the potential of Raman/SEM for molecular and elemental determination of organic and inorganic fine particulate matter. This has been accomplished by analyzing samples with fine particulate matter using each method independently. Since both techniques are nondestructive, particles of interest can be relocated between instruments. Practical issues such as filter substrate compatibility and instrumentation compatibility are addressed. In addition, first results showing Raman/SEM chemical images from several standard materials, as well as ambient PM_2.5 samples, are reported.     

Characterization of Particulate Matter Morphology and Volatility from a Compression-Ignition Natural-Gas Direct-Injection Engine

The particulate matter (PM) emitted from a single-cylinder compression-ignition, natural-gas engine fitted with a High-Pressure Direct-Injection (HPDI) system distinctly different from a duel fuel engine was investigated, and characterized by size distribution, morphology, mass-mobility exponent, effective density, volatility, mixing state, and primary particle size using transmission electron microscopy (TEM), and tandem measurements from differential mobility analyzers (DMA) and a centrifugal particle mass analyzer (CPMA). Six engine conditions were selected with varying load, speed, exhaust gas recirculation (EGR) fraction, and fuel delivery strategy. An increase in engine load increased both the number concentration and the geometric mean diameter of the particulate. The fraction of the number of purely volatile particles to total number of particles (number volatile fraction, NVF) was found to decrease as load increased, although at the lower speed, partially premixed mode, the lowest NVF. All size distributions were also found to be unimodal. The size-segregated ratio of the mass of internally mixed volatile material to total particle mass (mass volatile fraction, MVF) decreased with load and with particle mobility-equivalent diameter. A roughly constant amount of volatile material is likely produced at each engine mode, and the decrease in MVF is due to the increase in PM number with load. Effective density and mass-mobility exponent of the non-volatile soot at the different engine loads were the same or slightly higher than soot from traditional diesel engines. Denuded effective density trends were observed to collapse to approximately the same line, although engine modes with higher MVFs had slightly higher effective densities suggesting that the soot structures have collapsed into more dense shapes—a suspicion that is confirmed with TEM images. TEM results also indicated that primary particle size first decreases from low to medium load, then increases from medium to high load. An increase in EGR was also seen to increase primary particle size. Coefficients were determined for a relation that gives primary particle diameter as a function of projected area equivalent diameter. A decrease in load or speed results in a stronger correlation.

Copyright 2015 American Association for Aerosol Research     

Fluorescence Microscopy Analysis of Particulate Matter from Biomass Burning: Polyaromatic Hydrocarbons as Main Contributors

New efficient approaches to the characterization of fly ash and particulate matter (PM) have to be developed in order to better understand their impacts on environment and health. Polycyclic aromatic hydrocarbons (PAH) contained in PM from biomass burning have been identified as genotoxic and cytotoxic, and some tools already exist to quantify their contribution to PM. Optical fluorescence microscopy is proposed as a rapid and relatively economical method to allow the quantification of PAH in different particles emitted from biomass combustion. In this study samples were collected in the flue gas of biomass-combustion facilities with nominal output ranging from 40 kW to 17.3 MW. The fly ash samples were collected with various flue gas treatment devices (multicyclone, baghouse filter, electrostatic precipitator); PM samples were fractionated from the flue gas with a DEKATI® DGI impactor. A method using fluorescence observations (at 470 nm), white-light observations and image processing has been developed with the aim of quantifying fluorescence per sample. Organic components of PM and fly ash, such as PAH, humic-like substances (HULIS) and water-soluble organic carbon (WSOC) were also quantified. Fluorescence microscopy analysis method assessment was first realized with fly ash that was artificially coated with PAH and HULIS. Total amounts of PAH in the three size fractions of actual PM from biomass burning strongly correlated with the intensities of fluorescence. These encouraging results contribute to the development of a faster and cheaper method of quantifying particle-bound PAH.

Copyright 2015 American Association for Aerosol Research     

Investigation on Particulate Oxidation from a DI Diesel Engine Fueled with Three Fuels

In this study, particles generated from a direct-injection (DI) diesel engine fueled with biodiesel, ultra-low-sulfur diesel (ULSD, <10 ppm-wt), and low-sulfur diesel (LSD, <500 ppm-wt) were investigated experimentally for their oxidation properties, using the thermogravimetric analysis (TGA), at five engine loads. Kinetic analysis of particulate oxidation was conducted based on the mass loss curves obtained from the TGA. The activation energy was found to be in the range of 142–175, 76–127, and 133–162 kJ/mol for the particulate samples for ULSD, biodiesel, and LSD, respectively. The particulate oxidation rate decreases with the increase of engine load for each fuel, and at each engine load, the oxidation rate decreases in the order of biodiesel, LSD, and ULSD. The primary particle size, nanostructure, and volatile fraction were also investigated for different particulate samples. The results indicate that the higher oxidation rate of biodiesel particles could be related to the smaller primary particle size, the more disordered nanostructure, and the larger volatile fraction, compared with the ULSD and LSD particles. The increase of sulfur content in a diesel fuel has a limited influence on primary particle size and nanostructure, while inducing a larger volatile fraction, which might be one of the reasons for the stronger oxidative reactivity of the LSD particles, compared with the ULSD particles.

Copyright 2012 American Association for Aerosol Research     

天然气/柴油双燃料发动机研究现状分析

随着世界传统能源的日益匮乏,以及排放污染问题的日益加重,天然气天然气/柴油双燃料发动机的开发和应用成为发动机行业新的研究热点。从传统燃料发动机面临的问题、新型燃料发动机发展前景和天然气发动机的特点分析了天然气/柴油双燃料发动机研究背景;综述了天然气/柴油双燃料发动机研究现状,提出了天然气/柴油双燃料发动机需要继续研究的方面,对开发和设计天然气/柴油双燃料发动机提供了一定的参考价值。     

Characterization of Exhaust Particulates from a Dual Fuel Engine by TGA,XPS, and Raman Techniques

Particulate matter (PM) emitted from a dual fuel engine is characterized using thermogravimetry, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Thermogravimetric analysis (TGA) provides the mass fractions of elemental carbon and volatile materials in PM; XPS provides the possible chemical compositions in the topmost layer of PM surface and Raman analysis provides the possible structure of the carbon presented in PM. Dual fuel engine uses both liquid (diesel) and gaseous fuels simultaneously to produce mechanical power and can be switched to only diesel fueling under load. The dual fuel engine is operated with natural gas and simulated biogases (laboratory prepared) and results are compared between the dual fueling and diesel fueling under the same engine operating conditions. Significantly higher volatile fractions in PM are obtained for dual fueling compared to diesel fueling complementing the gravimetric results. The maximum contribution of the graphitic carbon or aliphatic carbon such as hydrocarbons and paraffins (C═C or C─C) are found in the topmost atomic layers of both the diesel and dual fuel PM samples. The other chemical states are found to be the carbon-oxygen functional groups indicating significant oxidation behavior in the PM surface. Lesser aromatic content is noticed in the case of dual fuel PM than diesel PM. The carbon in dual fuel PM is found to be more amorphous compared to diesel PM. These characterizations provide us new information how the PM from a diesel engine can be different from that from a dual fuel engine.     

High-Resolution Electron Microscopy Investigation of Viscous Flow Creep in a High-Purity Silicon Nitride

The redistribution of intergranular amorphous films during creep deformation of Si₃N₄ has been studied by high-resolution transmission electron microscopy. The film thickness distribution of a high-purity Si₃N₄ material before and after creep was measured. A narrow range of film widths in the uncrept material and a bimodal distribution after creep were observed. These observations provided convincing evidence of the occurrence of viscous flow of intergranular amorphous films during creep deformation of Si₃N₄. Moreover, the creep response predicted by a viscous flow model was in good agreement with experimental data.     

Characterization of Particulate Matter from Direct Injected Gasoline Engines

The reactivity and reaction kinetics of particulate matter (PM) from direct injected gasoline (GDI) engines has been studied by O₂ and NO₂ based temperature programmed and isothermal step-response experiments, and the PM nano-structure has been characterized using HRTEM. The reactivity of the PM samples collected in filters during on-road driving was found to increase in the following order: Printex U < diesel < gasoline PI ≈ gasoline DI < ethanol for O₂ based combustion. The activation energies for O₂ and NO₂ based oxidation of PM collected from a GDI engine in an engine bench set-up was estimated to 146 and 71 kJ/mol respectively, which is comparable to corresponding values reported for diesel and model soot. Similar nano-structure features (crystallites plane dimensions, curvature and relative orientation) as observed for diesel soot were observed for gasoline PM.     

Resuspension of Particulate Matter from Carpet Due to Human Activity

This work investigated the resuspension and subsequent translocation of particulate matter (PM) from carpeted flooring surfaces due to walking. In addition, the effect of HVAC systems and ceiling fans on mixing and/or translocation of resuspended PM was studied. Testing took place both in a residence with a well-worn, soiled carpet and in an environmental test chamber. Prescribed walking occurred with PM measurements taken at multiple sampling heights. Scanning electron microscopy (SEM) of carpet fibers was used to determine the fraction of dust available for resuspension. These data, in conjunction with resuspended mass concentrations from this study, were used to generate emission factors by particle size for walking on both new and worn carpet.

Carpet loading does not affect the emission factor, indicating that the amount of resuspended PM is directly proportional to the available PM in the carpet. While relative humidity (RH) plays an important role in resuspension from new carpets, with high RH enhancing resuspension, it has the opposite affect with old carpets, with increased RH decreasing resuspension. With the HVAC system on, translocated particles 1.2 m horizontally from the source had number concentrations of approximately 20–40% of those at the source. With a ceiling fan on, extensive mixing was noted with little difference seen in particle resuspension by height. With the ceiling fan off, there was very little mixing present and particle size varied substantially by height.     

Electron Microscopy of Ferrites

This paper describes some electron microscopy studies of magnetic ferrites with special emphasis on LiFe₄O₈ and including some results on NiFe₂O₄ and SrFe₁₂O₁₈, The paper is concerned with analysis of the crystallography, defect structure, and phase transformations and their relations to magnetic properties, viz. coercivity and hysteresis characteristics.     

Glass-to-Metal Seal Interfacial Analysis using Electron Probe Microscopy for Reliable Solid Oxide Fuel Cells

The chemical compatibility between sealing glasses and interconnect materials for solid oxide fuel cells (SOFCs) has been studied in SOFC environments. Two borate-based glass compositions were sealed to interconnect materials, 441 stainless-steel (441SS) and Mn_1.5Co_1.5O₄-coated 441SS. The Mn_1.5Co_1.5O₄-coated 441SS coupons were analyzed as-received using X-ray diffraction (XRD) and electron probe microanalysis (EPMA) to obtain structural information and concentration profiles, respectively. The concentration profiles and the lack of Fe-containing phases present in the XRD spectrum show Fe is present throughout the coating, suggesting that Fe is partially substituted in the Mn_1.5Co_1.5O₄ spinel. The glass–metal coupons were heat treated in air at 750°C for 500 h. The specimens were analyzed by EPMA and scanning electron microscope (SEM) to obtain images of the glass microstructure at the interface, to verify seal adherence, and to record concentration profiles across the glass–metal interface, with an emphasis on Cr. In total, four seal configurations were tested and analyzed, and in all cases the glasses remained well adhered to the metal and coating, and there was no microstructural evidence of new reaction phases present at the interface. There was slight diffusion of Cr from the 441SS into the sealing glasses, and Cr diffusion was hindered by the coating on the coated 441SS samples.     

Investigation of the Structure of Zirconia Nanoparticles by High-Resolution Transmission Electron Microscopy

The structure of zirconia nanoparticles is investigated by high-resolution transmission electron microscopy (HRTEM). The structurally inhomogeneous nanoparticles with coherent interfaces (centaurs) are observed. The orientation relationships of the conjugated structures are determined.     

Investigation of Chocolate Surfaces Using Profilometry and Low Vacuum Scanning Electron Microscopy

In this study we establish the use of optical non-contact profilometry combined with low vacuum scanning electron microscopy (LV SEM) for the investigation of lipid surfaces. We illustrate, by using profilometry, a methodology for investigation of chocolate surface topology as a function of time, in the same area of interest. Both qualitative and quantitative data analysis has been performed for profilometry data. Further, relating these results to LV SEM images provides complementary topological information and hence a useful toolkit for the study of the chocolate surface prior and post fat bloom formation. For the demonstration of the successful combination of these two analytical techniques, white chocolate pralines were stored at two temperature-controlled conditions (at 18 °C, and cycled between 15 and 25 °C). Surface properties were then investigated during 36 weeks of storage. The surface images and the roughness parameters indicated distinct development of surface characteristics for the two storage conditions. From the results it is suggested that some imperfections, in the form of pores or protrusions, could play a role in fat bloom development and that there may be different main mechanisms of fat migration taking place for the different storage environments. In the present work, a positive correlation of profilometry data to chocolate surface characteristics and early bloom development has been established. There are indications that early prediction of fat bloom can be possible, however further work needs to be done to quantify prediction of fat bloom.     

Particulate Matter Soiling of Exterior Paints at a Rural Site

A soiling study was performed at an air monitoring site operated by the Research Triangle Institute in the relatively rural environmental conditions within Research Triangle Park, N.C. The study was designed to determine how various environmental factors contribute to the rate of soiling of white painted surfaces. Significant factors that were monitored were hourly rainfall and wind speed, and weekly data for dichotomous sampler measurements and total suspended matter concentrations. Gloss and flat white paints on hard-board were exposed vertically and horizontally, both protected and unprotected from rain for 16 wk. Measurements of exposed samples were taken at 2, 4, 8, and 16 wk. Reflectance was measured and scanning electron microscopy (SEM) stubs, which had been flush-mounted into the hardboard prior to painting, were removed at these times. Particle size distributions were determined by scanning electron microscopy. Major findings were: 1) reflectance change on sheltered surfaces was proportional to the fraction of the surface area covered by particles; 2) coarse mode particles contribute more than fine mode particles to soiling of both horizontal and vertical surfaces; 3) insoluble fine mode particles are not significantly washed off by rain; and 4) rain interacts with soluble particles to contribute to soiling by “staining” the surface.     

Electron Microscopy of Sintered Beryllia

Porosity, etching characteristics, and general microstructural features of extruded and sintered beryllium oxide were studied by electron microscope observation of surface replicas. Both pore structures and etching characteristics were shown to be related to the hemimorphic hexagonal crystal structure of BeO. A form of twinning possible only in hemimorphic systems was also observed.     

Transmission Electron Microscopy of Glass-Ceramics

A new technique has been developed by which thin sections of glass-ceramics can be prepared for direct observation by transmission electron microscopy. Techniques for identifying crystalline phases are discussed, and the degree of crystallinity in several glass-ceramics is presented.     

Investigation of Grain-Boundary Segregation in Ceramic Oxides by Analytical Scanning Transmission Electron Microscopy

Analytical scanning transmission electron microscopy (AEM) was used to study grain-boundary solute segregation in the systems MgO-NiO, A1₂O₃-Y, O₃, NiO-Cr₂O₃, and NiO-Al₂O₃. Electron beam spreading within the specimen was incorporated into a model to quantitatively measure solute segregation. Grain-boundary segregation occurred in A1₂O₃-Y₂O₃ and NiO-Cr₂O₃ but was not detected in MgO-NiO and NiO-Al₂O₃ specimens. These results and the quantitative measurements agree with equilibrium solute segregation theories. Microhard-ness measurements indicate no difference in hardness between the grain boundary and the matrix for Cr-doped NiO, a system in which segregation was detected.     

Problems in the Extraction of Polycyclic Aromatic Hydrocarbons from Diesel Particulate Matter

In this work, a comparison between Soxhlet, ultrasonic, and microwave-assisted extraction (MAE) (using hexane:acetone 1:1) of polycyclic aromatic hydrocarbons (PAHs) from SRM 1650 diesel particulate matter was made. As good recoveries were not obtained for the higher molecular weight compounds, MAE with toluene and dichloromethane was also tested. Achieved recoveries were compared with the results obtained in the same assays made with SRM 1648 urban particulate matter and real atmospheric particulate samples. In order to explain the difficulty of the extraction of PAHs from SRM 1650 in comparison to SRM 1648 and real atmospheric particulate samples, elemental analysis, X-ray diffraction, and particle analysis using scanning electron microscopy coupled to an automatic computer imaging system were also made. It is important to notice that SRM 1650 shows a high percentage of carbon and differences in the morphology of the particles between SRM 1650 and SRM 1648 were observed.     

北京市火电厂排放颗粒物的粒径分布

本文重点研究了北京市燃煤、燃油电厂锅炉的颗粒物排放及其粒径分布,静电除尘器的分级效率.文中对所采用的WY-Ⅱ型冲击式尘粒分级仪进行简要介绍,指出存在的问题,并提出建议.     

Electron Microscopy Study of Ordinary Portland Cement and Ordinary Portland Cement–Pulverized Fuel Ash Blended Pastes

Many ordinary portland cement (OPC) OPC–pulverized fuel ash (pfa) blended pastes of various ages have been examined using transmission electron microscopy, energy dispersive X-ray analysis, and scanning electron microscopy. In addition to the phases commonly identified in OPC pastes, such as CH, CSH, AFt, and AFm, we found areas of pooriy crystalline iron-containing material intermixed with CSH and needles of hydrotalcite-like composition. The iron-containing material may be the precursor of hydrogarnet phases identified in older pastes by other authors. In the pfa-blended cements, some of the pfa particles reacted to give a radially fibrillar gel, and others showed areas of well-crystallized hydrogarnet within the clearly defined outer boundary of the particle. Unreactive pfa particles had a rim of fibrillar CSH gel around the particle. The general fine-scale microstructure of the OPC-pfa-blended pastes was similar to that in OPC pastes alone, but the CSH gel material had a lower C:S ratio.