M. A. Timofeev

Impact of Fe Content in Laboratory - Produced Soot Aerosol on its Composition, Structure, and Thermo-Chemical Properties

Soot aerosol, which is a major pollutant in the atmosphere of urban areas, often contains not only carbonaceous matter but also inorganic material. These species, for example, iron compounds, originated from impurities in fuel or lubricating oil, additives or engine wear may change the physico-chemical characteristics of soot and hence its environmental impact. We studied the change of composition, structure, and oxidation reactivity of laboratory-produced soot aerosol with varying iron content. Soot types of various iron contents were generated in a propane/air diffusion flame by adjusting the doping amount of iron pentacarbonyl Fe(CO)5 to the flame. Scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy (EDX) was combined with cluster analysis (CA) to separate individual particles into definable groups of similar chemical composition representing the particle types in dependence of the iron content in soot. Raman microspectroscopy (RM) and infrared spectroscopy were applied for the characterization of the graphitic soot structure, hydrocarbons, and iron species. For the analysis of soot reactivity, temperature-programmed oxidation (TPO) was used. It is demonstrated that iron is most dominantly present in the form of amorphous Fe (III) oxide crystallizing to hematite α-Fe2O3 upon thermal treatment. Iron contaminations do not change the soot microstructure crucially, but Fe(CO)5 doping of the flame impacts hydrocarbon composition. Soot oxidation reactivity strongly depends on the iron content, as the temperature of maximum carbon (di)oxide emission T max follows an exponential decay with increasing iron content in soot. Based on the results of the thermo-chemical characterization of laboratory-produced internally mixed iron-containing soot, we can conclude that iron-containing combustion aerosol samples cannot be characterized unambiguously by current thermo-optical analysis protocols. Copyright 2012 American Association for Aerosol Research

Effect of the Electric Field of the Anode Sheath on the Growth of Aligned Carbon Nanotubes in a Glow Discharge

Arrays of aligned carbon nanotubes on silicon substrates were grown in the anode sheath of a dc glow discharge. In order to clarify the role of the electric field in the growth of nanotubes, numerical simulations of charged particle transport in the anode sheath were carried out in the drift-diffusion approximation. The distributions of the charged particle density and electric field are obtained. Possible mechanisms whereby the electric field influences the growth of aligned carbon nanotubes are analyzed. It is found that the nanotubes grow in the region in which the electric field is enhanced due to the depletion of positive ions in the anode sheath.

Microspectral analysis of dentine with femtosecond laser induced plasma

Microspectral analysis of dentine plasma produced by femtosecond laser radiation with intensities of I ∼ 1013−1015 W/cm2 in ambient atmosphere has been measured. C, O, Ca, Zn, Na, and Cu spectral lines were identified. The X-ray radiation with energies E > 30 keV has been observed upon laser beam intensities of I ∼ 5 × 1015 W/cm2.

Optical-microphysical and physical-chemical characteristics of Siberian biomass burning: Experiments in Aerosol Chamber

A series of experiments aimed at studying the effect of combustion regimes of typical Siberian biomasses on the optical, microphysical, and physical-chemical properties of smoke aerosols was performed in the Large Aerosol Chambe, Institute of Atmospheric Optics, Siberian Branch, Russian Academy of Sciences. A comprehensive data analysis showed that temperature regime of Siberian pine and coniferous tree burning has a key effect on the formation and time dynamics of all smoke characteristics. The polarization spectronephelometer measurements of light scattering are used to determine the size distributions and absorption indices of particles. Particles in the smoldering phase are weakly absorbing, but the mixed phase contains a strongly absorbing fine component produced in open flame phases. We studied microstructure characteristics of aerosols by the analysis of morphology and elemental composition. Groups of soot and organic particles were determined as micromarkers of emissions in open flaming and smoldering phases, respectively. The organic and elemental carbon contents, origin and concentration of chemical compounds in the water-soluble ion fraction exhibit a strong dependence on the combustion phase. Sugar anhydride (levoglucosan) was determined in the smoldering phase as a stable molecular marker of Siberian pine burning. A number of specific markers of coniferous wood burning were identified among the chemical compounds. Smoke aging is accompanied by condensation of organic and inorganic compounds, transformation of aerosol surface chemistry, and the formation of the group of potassium-rich particles, all demonstrating the complexity and variability of the chemical composition and microstructure of atmospheric aerosol pollution during Siberian forest fires.

Magnetic porous composite material: Synthesis and properties

A new method of obtaining magnetic porous composite materials is described, which is based on the self-propagating high-temperature synthesis (SHS) in the form of solid-phase combustion. The SHS process involves transformation of the nonmagnetic α-Fe2O3 particles (contained in the initial mixture) into magnetic Fe3O4 particles. The synthesized material comprises a porous carbonaceous matrix with immobilized Fe3O4 particles. The obtained composite has been characterized by electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements. The sorption capacity of the porous material has been studied.

Studying the morphology of nanocrystalline graphite field-emission cathode grown on a diamond grid

The morphology of a nanocrystalline graphite field-emission cathode based on a polycrystalline diamond grid has been studied in order to elucidate the nature of electron-emitting centers. Ribbonlike and cylindrical carbon nanostructures have been found on the emitter surface, which possess greater aspect ratios as compared to those of graphite microedges forming the cathode surface.

Light efficiency of cathodoluminescent screens excited by a runaway electron beam

A technique employing electron beams generated by an open gas discharge is proposed for measuring the light efficiency of phosphor coatings of cathodoluminescent screens. The total light efficiencies of various phosphor coatings in the medium excitation energy range (ɛ < 7 keV) are estimated with allowance for both the direct radiation flux outgoing from the phosphor screen and the backward radiation flux propagating along the exciting electron beam. The possibility is demonstrated of creating a high-luminance (∼20000 cd/m2) cathodoluminescent source with a light efficiency of ∼60 lm/W.

Growth and structure of epitaxial diamond films grown on Si(111) single crystals

Experiments on growing single-crystal diamond films on silicon crystals with (111) surface orientation have been performed. Results attesting to the possibility of obtaining thin heteroepitaxial films are presented.

Aerosol composition and microstructure in the smoky atmosphere of Moscow during the August 2010 extreme wildfires

This is a comprehensive study of the physicochemical characterization of multicomponent aerosols in the smoky atmosphere of Moscow during the extreme wildfires of August 2010 and against the background atmosphere of August 2011. Thermal–optical analysis, liquid and ion chromatography, IR spectroscopy, and electron microscopy were used to determine the organic content (OC) and elemental content (EC) of carbon, organic/inorganic and ionic compounds, and biomass burning markers (anhydrosaccharides and the potassium ion) and study the morphology and elemental composition of individual particles. It has been shown that the fires are characterized by an increased OC/EC ratio and high concentrations of ammonium, potassium, and sulfate ions in correlation with an increased content of levoglucosan as a marker of biomass burning. The organic compounds containing carbonyl groups point to the process of photochemical aging and the formation of secondary organic aerosols in the urban atmosphere when aerosols are emitted from forest fires. A cluster analysis of individual particles has indicated that when the smokiest atmosphere is characterized by prevailing soot/tar ball particles, which are smoke-emission micromarkers.

Synthesis of nanostructured zinc oxide films in propane flow

A new method is proposed for the synthesis of nanostructured zinc oxide (ZnO) films in propane that is used as a source of reactive carbon and carrier gas. The growth of films consisting of columnar ZnO structures under these conditions takes place at a relatively low temperature (about 630°C) of the evaporator.