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Some aspects of soot formation from gas phase molecules at high temperatures are still unclear. Aromatic π-radicals may be key elements for a change in the model of carbon clustering and particle formation. However, experimental investigations are still needed on the radical nature of molecules and particles in flames and on their roles in the transition from molecules to incipient molecular clusters and their further evolution to mature soot. In this paper, we present electron paramagnetic resonance (EPR) and Raman spectroscopy measurements of particles collected in an ethylene-rich premixed flame at various residence times during nucleation. The experimental results, combined with measurement of the particle size distribution by a differential mobility analyzer, are used to investigate the role of radicals in particle nucleation and rearrangement of aromatic molecules in just-nucleated particles. For all the sampled particles, an EPR signal typical of persistent carbon-centered aromatic radicals is measured. An abrupt change in the EPR signal intensity, which is characteristic of stronger supramolecular interactions, is observed when the size distribution changes from monomodal to bimodal, as confirmed by Raman spectroscopy. Our experimental results indicate strong involvement of π-radicals during particle nucleation and growth. The paramagnetic/radical nature of the sampled particles is discussed on the basis of recent studies on the role of resonantly stabilized radicals in soot nucleation. The presence of localized π-electrons on the edge of aromatic soot constituents and their role in carbon clustering are also discussed.

Incipient carbon nanoparticles, CNP, formed by incomplete hydrocarbon combustion are composed of polycyclic aromatic hydrocarbons [1,2] and exhibit a quantum dot behavior [3], which make them ideal for a wide range of applications. Flame synthesis offers a continuous and low-cost process for the production of inorganic nanoparticles, such as TiO2, with fine control of cristallinity and phase. Likewise, carbon nanoparticles, CNPs, with tailored size and optical and electronic properties can be produced by optimizing the flame process. The assembly of nanoparticles into a uniform thin film with precise control over chemical and physical properties poses a significant challenge. Thermophoretic sampling relies on the thermophoretic forces driving the particles in the hot flame towards a cold substrate inserted in the flame and can be used to produce nanostructured, self-assembled films that can lead to novel applications. In this work, CNP and CNP/TiO2 nanoparticles have been produced in premixed ethylene-air flames and thin films have been realized by thermophoretic deposition on silicon substrates with gold interdigitated electrodes. Scanning mobility particle sizer furnished the particle size distribution and Raman and optical spectroscopy chemico-physical and structural information. The electrical characterization of the films was conducted by measuring the IV characteristics which shows a good linearity in the interval [-5 V, 5 V] whereas non-linear phenomena appear for wider voltage ranges and hysteresis phenomena are also observed in carbon/TiO2 films. Impedance spectroscopy was used to investigate the films with respect to their microstructure. This method is indeed particularly useful for nanostructured films with inter-grain and grain-edge impedances and capacities. Finally, noise spectral density at low and very low frequency was measured to investigate the electron transport. The main source of noise is of thermal type for the carbon material, whereas carbon/TiO2 film shows a Fliker type, 1/f noise, consistent to a larger amount of localized states responsible for trapping/detrapping processes of charge carriers and charge fluctuations during the conduction process. [1] Schulz, F., Commodo, M., Kaiser, K., De Falco, G., Minutolo, P., Meyer, G., D`Anna, A., Gross, L., "Insights into incipient soot formation by atomic force microscopy" Proc. Combust. Inst. 37: 885-892 (2019). [2] Commodo, M., Kaiser, K., De Falco, G., Minutolo, P., Schulz, F., D`Anna, A., Gross, L., "On the early stages of soot formation: molecular structure elucidation by high-resolution atomic force microscopy" Combust. Flame 205, pp. 154-164. [3] Liu, C, Singh, A.V., Saggese, C., Tang, Q., Chen, D., Wan, K., Vinciguerra, M., Commodo, M., De Falco, G., Minutolo, P., D'Anna, A., Wang H. , Flame-formed carbon nanoparticles exhibit quantum dot behaviors, 2019, DOI:10.1073/pnas.1900205116

Carbon-based nanomaterials (CNPs) have attracted considerable interest because of their unique electronic, optical and mechanical properties. Among them, CNPs have become increasingly popular mainly due to their photoluminescence (PL) properties which make them ideal for bio-medical imaging or drug-delivery in addition to light-emitting devices because of their low toxicity, environmental friendliness, low cost and relatively simple synthesis processes. There are many routes for the synthesis of CNPs divided into top-down nano-cutting methods and bottom-up organic approaches. The first one includes laser ablation, arc discharge, chemical and electrochemical oxidation of large carbon structures; recently, starting from the pioneering work of Liu et al. [1], also the so called "candle soot" turned out to be an excellent precursor for the synthesis of CNPs for a variety of applications [2]. A wide set of studies indicates that the constituents of CNPs in flames are mainly PAHs of moderately size [3, 4]. Furthermore, there is a large body of evidence indicating a change in the electronic and optical properties of CNPs during their early stages of nucleation and growth [5] and recently, Liu et al. [6] demonstrated quantum dots behavior of the CNPs, in the particle range 4-23 nm, directly produced and collected from flames. Therefore, carbon particle nucleation and growth in flames can be exploited as a bottom up process for CNPs through direct sampling CNPs from a well-controlled flame reactor. In this work particle size has been measured on-line in aerosol phase by a differential mobility analyzer. Particles with different average sizes have been sampled and characterized for the first time by scanning tunneling microscopy/spectroscopy (STM/STS). The electronic properties, i.e., density of states and energy band gap, of flame-formed nanoparticles measured by STS have been correlated to nanostructure determined by Raman spectroscopy and the UV-visible absorption spectra and optical band gap determined by Tauc analysis. [1] H. Liu et al., Fluorescent Carbon Nanoparticles Derived from Candle Soot, Angew. Chem. Int. Ed. 46 (2007) 6473 -6475. [2] M.R. Mulay et al., Candle soot: Journey from a pollutant to a functional material, Carbon 144 (2019) 684-712. [3] F. Schulzet al., Insights into incipient soot formation by atomic force microscopy, Proc. Combust. Inst. 37, 2019, 885-892. [4] M. Commodo et al., On the early stages of soot formation: Molecular structure elucidation by high-resolution atomic force microscopy, Combust. Flame 205 (2019) 154-164. [5] M. Commodo et al., Physicochemical evolution of nascent soot particles in a laminar premixed flame: from nucleation to early growth, Combust. Flame 162 (2015) 3854-3863. [6] C. Liu et al., Flame-Formed Carbon Nanoparticles Exhibit Quantum, Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1900205116.

Recent advances in the literature have shown experimental evidences of a consistent amount of ?-radicals and cross-linked structures among the molecular constituents of just-nucleated soot particles. The inclusion of such experimental observations in the mechanism of soot particle formation will improve the comprehension of the physics and chemistry involved during the evolution of soot particles in flames. In this regards ?-radical could have a fundamental role, particularly at the onset of soot formation, when gas-phase molecules convert to a condensed-phase material. According to the literature of highly delocalized ?-radicals, two type of dimerization process can be taken into account. These are: a ?-stacking mechanism that occurs by forming multi-electron/multi-center delocalized bonds, thus covalent-like, with shorter intermolecular distances and stronger interactions with respect to van der Waal interactions; a conventional ?-bond formation, with longer distance and weaker strength than regular C-C bond. In this work we use density functional theory (DFT) with hybrid functional and localized Gaussian basis set (B3LYP/6-31G**) to analyze and classify two radicals having different topological structures in term of localization/delocalization of the unpaired electron, and in turn binding energy and optical band gap characteristics of the clustering of two different molecular radicals. The ambition of this study can be represented by the investigation of the two polycyclic aromatic, labeled as radical 1 (R1), and radical 2 (R2), experimentally determined by Atomic Force Microscopy (AFM) studies and calculated by ab-initio quantum investigations. As results the different clustering of the two polycyclic aromatic hydrocarbons with a couple of unpaired electron delocalized, in different spin multiplicity (Sz=1, 3), leads to a different reductions of the optical gap.

L'attività di ricerca condotta dall'unità IRC-CNR per il PAR 2016-2017 ha riguardato la messa a punto di procedure di sintesi e di deposizione di nanoparticelle di TiO2 e compositi TiO2/C ottenute per sintesi in fiamma su elettrodi commerciali. In particolare, metodi di sintesi di nanoparticelle in fiamma sono stati utilizzati allo scopo di modificare le proprietà superficiali degli elettrodi. Sono state prodotte nanoparticelle di TiO2 igroscopico e compositi TiO2/C depositate direttamente su elettrodi mediante deposizione temoforetica in modo da migliorarne i parametri elettrochimici.

PREMESSA: L'attività di ricerca condotta dall'unità IRC-CNR per il PAR 2016-2017 ha riguardato la caratterizzazione di elettrodi ricoperti di nanoparticelle di TiO2, TiO2/C e di sole particelle carboniose. Pe le due classi di materiali, F-CNP e F-CNP/TiO2, si è effettuata la caratterizzazione chimico-fisica mediante spettroscopia Raman, XRD, sessile drop.

Inflammation is central to the development of chronic obstructive pulmonary disease (COPD), caused by inhalation of noxious particles or gas, especially cigarette smoke (CS). Emerging genetic and pharmacological evidence suggests that IL-1-like cytokines are highly detected in the sputum and broncho-alveolar lavage (BAL) of COPD patients, implying the involvement of the multiprotein complex inflammasome. In order to understand the role of this complex in COPD, we isolated PBMCs from healthy volunteers (smoker and non-smoker) and COPD patients. To mimic environmental pollution, PBMCs were treated with ultrafine particulate matter (UFP

In spite of the advances in laser diagnostics in combustion, the effect of rapid laser irradiation on the physical/chemical properties of soot particles is far from being comprehensively understood. Optical properties, particle nanostructure and aggregate size of laser-irradiated soot particles are analyzed in this paper. Carbonaceous particles sampled from nitrogen-quenched diffusion flames of ethylene and methane are irradiated on-line by a 1064-nm short laser pulse. Wavelength-resolved extinction measurements in the visible range are used to follow their transformation by varying the laser energy density. A variation of the extinction coefficient of the irradiated particles compared to the extinction coefficient of the pristine ones is observed, especially for ethylene soot. The particle nanostructures are analyzed by Raman spectroscopy and the effect of laser irradiation on aggregate structure is evaluated by measuring particle size distributions. The results indicate that both soot nanostructure and optical properties are strongly dependent on the laser energy density when irradiated by a laser source. This is significant for ethylene soot, while for methane soot the degree of variation of such properties is less pronounced, at least in the investigated heating conditions. © 2020 Elsevier Inc.

Concentrated ternary mixture of nitric acid, sulfuric acid, and water are often used in the chemical industry for a wide range of applications. Among these, nitrations of organic substrates are the most common. Nevertheless, there is still a poor understanding of speciation of the acids in the mixtures, and different simplified or semiempirical approaches have been found in the literature to model nitration kinetics by mixed acids. Most of the found investigations are relevant in restricted ranges of experimental conditions, resulting in a fragmentary vision. In this work, most of the approaches found in the literature were reviewed in order to define their limits of validity, and new empirical equations for the estimation of nitronium ion concentration are proposed. Moreover, on the basis of original experimental data, a simplified model is proposed to calculate the dissociation of acids at varying experimental conditions, and the main assumptions reported in the literature were verified. Adopted simplifying assumptions were verified at sulfuric acid concentrations higher than 2.1 mol·L–1 and nitric acid concentrations ranging from 2.0 to 11 mol·L–1.

Report tecnico inerente le procedure di sintesi in fiamma di aerosol di nanoparticelle carboniose, metodo di deposizione degli aerosol carboniosi per la produzione di film carboniosi nanostrutturati e le procedure di "annealing" termico per la ristrutturazione di materiali carboniosi (PAR 2015 deliverable).

In this work, a set of four partially premixed ethylene–air laminar flames, characterized by different equivalent ratios, was studied. The aim was to investigate the effect of partial premixing on soot formation, which is a relevant parameter for real combustion devices. Quantitative and qualitative information on soot particles were obtained using a modified version of the thermophoretic particle densitometry (TPD) method. Particle thermal emissivity values were measured from the transient thermocouple temperature response. Results show that the emissivity of flame-formed carbon nanoparticles ranges from about 0.5 for soot precursor particles up to 0.95, i.e., the typical emissivity value attributed to mature soot particles. Particle volume fraction was then accurately evaluated by means of the TPD method, using the values of particle emissivity previously measured. The changing of particle features throughout the flame, evidenced by the variation in thermal emissivity, was further investigated using Raman spectroscopy. The analysis of Raman spectra showed that the increase in thermal emissivity follows a reduction in the hydrogen-to-carbon ratio of the investigated soot nanoparticles. Measurements performed with the TPD method also evidence that both particle emissivity and volume fraction are strongly affected by oxidation, which prevents to accurately measure soot concentration in oxidative regions of the flames. An attempt to include soot oxidation in the TPD method for a correct evaluation of volume fraction procedure is also illustrated. OH concentration profiles, obtained from a modeling analysis and validated by radical chemiluminescence measurements, were used in the TPD method to correct particle concentration due to oxidation.

To fulfill the requirement of energy sustainability, organic solar cells (OSCs) should combine the use of solar energy as a renewable energy source with materials that guarantee a clean energy solution based on an evaluation of the full lifecycle from cradle to grave. In this study, we investigated the possibility of using combustion-produced nanoparticles (CPNs) in blends with regioregular poly (3-hexylthiophene) (P3HT), as active layer in OSCs. We present a detailed characterization of the CPNs using Raman spectroscopy, light absorption, cyclic voltammetry and differential mobility analysis, showing their optimal features of band gap and size for use as electron acceptor materials. Moreover we present a spectroscopic investigation of the P3HT:CNPs blends, using static and dynamic fluorescence and transient absorption spectroscopy. P3HT exhibits strong quenching and shortened fluorescence lifetimes when mixed with CNPs. Interestingly, an efficient charge transfer was observed when a high loading of CNPs was added to the blend. © 2015 Elsevier Ltd. All rights reserved.

Recent advances in gas turbine combustor design are aimed at achieving low exhaust emissions, hence modern aircraft jet engines are designed with lean-burn combustion systems. In the present work, we report an experimental study on lean combustion in a liquid fuel burner, operated under a non-premixed (single point injection) regime that mimics the combustion in a modern aircraft engine. The flame behavior was investigated in proximity of the blow-out limit by an intensified high rate Charge-Coupled Device (CCD) camera equipped with different optical filters to selectively record single species chemiluminescence emissions (e.g., OH*, CH*). Analogous filters were also used in combination with photomultiplier (PMT) tubes. Furthermore this work investigates well-mixed lean low NOx combustion where mixing is good and generation of solid carbon particulate emissions should be very low. An analysis of pollutants such as fine particles and gaseous emissions was also performed. Particle number concentrations and size distributions were measured at the exhaust of the combustion chamber by two different particle size measuring instruments: a scanning mobility particle sizer (SMPS) and an Electrical Low Pressure Impactor (ELPI). NOx concentration measurements were performed by using a cross-flow modulation chemiluminescence detection system; CO concentration emissions were acquired with a Cross-flow modulation Non-dispersive infrared (NDIR) absorption method. All the measurements were completed by diagnostics of the fundamental combustor parameters. The results herein presented show that at very-lean conditions the emissions of both particulate matter and CO was found to increase most likely due to the occurrence of flame instabilities while the NOx were observed to reduce.

In this study, an improved version of the thermophoretic particle densitometry (TPD) method, introduced by McEnally et al. (1997) has been used for quantitative and qualitative characterization of soot particles generated in both premixed and diffusion flames. To this aim, the dependence of thermocouple temperature response on particle concentration and properties of collected material has been exploited. A variety of values for the thermal emissivity of flame-formed carbonaceous particles are measured, ranging from e ≈ 0.4–0.5 for freshly nucleated particles up to the value of e = 0.95, typical of a mature soot. The data demonstrate that a correct determination of e is necessary to accurately evaluate the particle volume fraction at the early stage of the soot formation, where particle concentration measurement is indeed particularly challenging. Raman spectroscopy analysis of the carbon particles has been conducted with the aim to better understand and to support the observed variation in the thermal emissivity of the carbon particles. In particular, the variation of thermal emissivity is showed to take up with a variation of hydrogen percentage and optical bandgap. Data also evidence that oxidation has a severe role in affecting both the determination by TPD of soot emissivity and soot concentration. In flame regions where soot oxidation occurs, the present formulation of TPD technique severely underestimate soot concentration.

This study reports the development of a one-step method for the production of antimicrobial protective coatings for aluminum surfaces with titania nanoparticles. An aerosol flame synthesis system was used to produce monodisperse, ultra-fine TiO 2 nanoparticles, which were directly deposited by thermophoresis onto plates of aluminum alloy by means of a rotating disc. Fuel-lean reactor conditions were used to synthesize pure anatase nanoparticles of 3.5 nm in diameter. Substrates were mounted onto the rotating disc that repetitively passes through the flame. Convection due to the rotational motion cooled the substrates, on which particles were deposited as films by thermophoresis. Such a system allowed to obtain submicron coatings of different thickness, by varying the total time of deposition. The antimicrobial activity of TiO 2 coatings was tested against the Gram positive bacterium Staphylococcus aureus . To determine the inhibition of biofilms formation, microbes were plated on TiO 2 coatings and a semi-quantitative colorimetric assay was performed using crystal violet. The tests showed that the TiO 2 coating obtained with t des =10 s inhibits up to 70-80% Staphylococcus aureus biofilm formation, and the inhibition of biofilms formation was confirmed by means of Scanning Electron Microscopy observation. Also, the antimicrobial properties of the coatings was enhanced by irradiating the samples in the UV region. The results of the present work are promising for using titania films as protective coatings for applications where an antimicrobial activity is required.

The objective of the present work is to assess the effect of pressure on nanostructure, morphology and dimension of soot particles from a set of co-flow methane/air laminar diffusion flames stabilized in a high-pressure combustion chamber. To this aim, particles produced in a pressure range between 5 and 20 bar have been collected by thermophoresis and characterized by means of Raman spectroscopy and Atomic Force Microscopy (AFM). First-order Raman spectra have been acquired at different heights above the burner for each pressure. No significant changes in the nanostructure and composition of soot particles were detected as a function of pressure, while nanostructure and composition have been observed to change with particle residence time within flame. From AFM measurements, Particle Size Distribution Functions (PSDs) have been obtained through a dimensional statistical analysis. PSDs have been found to be mostly bimodal, with a first particle mode below 10 nm slightly decreasing with pressure and a second particle mode between 10 and 20 nm rather constant with pressure. Moreover, a comparison between PSDs from AFM and PSDs from Transmission Electron Microscopy reported previously showed a good complementarity between those two techniques. This study represents a first attempt to characterize and correlate the structural and morphological properties of soot particles produced at high-pressures, which are the typical operating conditions of most practical combustion devices.

There is a constant need of new researches on combustion-generated particulate and techniques able to monitor an extended size range down to the smallest particles in order to provide exhaustive monitoring of air quality and provide new guidelines to update regulatory standards for limiting particulate emission. The main objective of the research program was to extend the characterization of particulate matter formation and growth in flame and in the exhaust of combustion system. 1) Development and characterization of a sampling method able to collect nanometric particulate matter from laboratory and practical combustion systems. 2) Sampling and analysis of the nanometric particulate at the exhausts of practical (domestic appliance and engines) systems. 3) Chemico-physical analysis of the sampled nanometric particulate matter by "ex situ" techniques. 4) Investigation of specific properties of combustion nanoparticles, which are of particular interest for environmental issues. Specifically: interaction of particles with water, which is of interest for health issue and climate effect related to cloud formation, and optical properties like emissivity, which are of interest for climate effect related to radiative balance.

Ultrafine particles (UFP) generated by combustion processes are often associated with adverse health effects. However, little is known about the inflammatory processes generated by UFP that may underlie their toxicological activity. Murine macrophages (J774.1 cells) and human peripheral blood mononuclear cells (PBMCs) were used to evaluate the molecular mechanism underlying the pro-inflammatory activity of UFP. The addition of soot particles to J774.1 cells induced a concentration-dependent release of IL-1α, IL-1β and IL-33 This effect was not associated with cell death and, in contrast to literature, was pronounced at very low concentrations (5–100 pg/ml). Similarly, UFP induced the release of IL-1α, IL-18 and IL-33 by PBMCs. However, this effect was solely observed in PBMCs obtained from smokers, as the PBMCs from non-smokers instead released higher levels of IL-10. The release of these cytokines after UFP exposure was caspase-1- and NLRP3 inflammasome-dependent in PBMCs from healthy smokers, whereas IL-1α release was calpain-dependent. These results show that UFP at very low concentrations are able to give rise to an inflammatory process that is responsible for IL-1α, IL-18 and IL-33 release, which is pronounced in PBMCs from smokers, confirming that these individuals are especially susceptible to inflammatory-based airway diseases once exposed to air pollution.

Rapporto finale/Relazione tecnico-scientifica per CONTRATTO PER LA PRESTAZIONE DI SERVIZI DI RICERCA IRC/MATERIAS S.r.l. (protocollo IRC n° 0001059 del 24/11/2017)

Soot formation in combustion represents a complex phenomenon that strongly depends on several factors such as pressure, temperature, fuel chemical composition, and the extent of premixing. The effect of partial premixing on soot formation is of relevance also for real combustion devices and still needs to be fully understood. An improved version of the thermophoretic particle densitometry (TPD) method has been used in this work with the aim to obtain both quantitative and qualitative information of soot particles generated in a set of laminar partially-premixed co-flow flames characterized by different equivalence ratios. To this aim, the transient thermocouple temperature response has been analyzed to infer particle concentration and emissivity. A variety of thermal emissivity values have been measured for flame-formed carbonaceous particles, ranging from 0.4 to 0.5 for the early nucleated soot particles up to the value of 0.95, representing the typical value commonly attributed to mature soot particles, indicating that the correct determination of the thermal emissivity is necessary to accurately evaluate the particle volume fraction. This is particularly true at the early stage of the soot formation, when particle concentration measurement is indeed particularly challenging as in the central region of the diffusion flames. With increasing premixing, an initial increase of particles is detected both in the maximum radial soot volume fraction region and in the central region of the flame, while the further addition of primary air determines the particle volume fraction drop. Finally, a modeling analysis based on a sectional approach has been performed to corroborate the experimental findings.

Soot inception in flames remains mostly unknown. What are, if any, the differences between inception particles formed in non-sooting and sooting flames, and to what extent soot formation is governed primarily by coagulation or by a different composition/aromatization of inception particles are open questions. In this work, the initial particle growth occurring in premixed flames of ethylene has been investigated. On line size-selected photoionization efficiency of inception particles produced in various flames has been measured. Structural/chemical differences of both nucleating and growing particles have been additionally investigated by off-line cyclic voltammetry, Raman spectroscopy, and light absorption. Results show that the size of aromatic domains within particles slightly increases when moving from flames in which the particle size distribution remains nearly constant and mono-modal in the nanometer range along the flame height, to flames in which particle coagulation gives rise to the formation of a second mode constituted by larger but still nanometric particles. Only in particles of this latter mode, d ≈ 10 nm, the first appearance of stacking of polyaromatic units is observed. On this basis, it has been hypothesized that two graphitization processes occur during the first stages of soot inception: a slight increase of in plane aromatic islands in primary particles and the formation of aromatic plane stacks in coagulated primary particles. This second type of coagulating-graphitization process explains the closure of the band gap observed in the grown particles respect to the primary ones, and hence the change of optical properties, towards the typical values observed in soot. © 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Carbon particulate matter derived from combustion consists of a variety of organic compounds, which often present features similar to carbon-based materials used in several brand new technologies. This consideration has recently provided the inspiration to check out the possible applications of these products in the field of material science and engineering. In this study, combustion-formed carbonaceous materials were collected from three different fuel-rich laminar premixed flames of ethylene and air, in order to characterize and correlate both the optical and the electrical properties. Physical and chemical properties of the particle have been tailored by changing the flame parameters, such as the fuel/air ratio, the particle residence time, and the sampling procedure, in order to produce particles with broadly different characteristics. We used Raman spectroscopy to characterize particle composition, and medium range order of carbonaceous particles sampled from the flame. UV-visible absorption spectroscopy was used to calculate the optical band-gap of the material by reporting the optical spectra in the form of Tauc plot. The electrical characterization was then performed by measuring I-V characteristics, i.e. current vs. voltage plots. Finally, a theoretical model based on tunneling effect has been checked for understanding the electrical conduction phenomenon through a thin film of carbonaceous nanoparticles.

Carbon nanoparticles in laminar premixed flames are broadly divided into two classes based on the bimodal shape of the particle size distribution and on the different chemical and physical properties that these particles present depending on the combustion conditions, such as residence time, equivalence ratio, and fuel chemical composition. The chemical and structural characteristics of carbon nanoparticles have been the subject of numerous works because these properties might be of relevance for particle reactivity and optical properties. Few information are available on their hydrophilic properties although these are of relevance for the human health, the climate change, in addition to the technological implementation of condensation nuclei particle counters in aerosol science, water scrubbers and electrostatic precipitators. The aim of this work is to investigate the hydrophilic/hydrophobic behavior of carbon nanoparticles formed in different flame conditions. Static contact angle measurements in addition to chemical and physical characterization of the carbon nanoparticles have been implemented. Results show that nanoparticles formed in richer flame conditions, are the most hydrophobic, whereas nanoparticles of organic carbon, formed in relatively leaner flame condition, appeared to be the most hydrophilic. The reason for a different water affinity of particles, and especially of the smaller organic carbon nanoparticles, has been discussed by analyzing the different material in terms of their chemical/structural composition and in terms of surface functionalities. While no significant differences have been found by Raman spectroscopy in terms of their carbon structure, the different hydrophilicity is explained in terms of the different amount of surface oxygen detected by X-ray photoelectron spectroscopy (XPS). Combustion conditions are therefore very important in outlining the hydrophilic/hydrophobic tendency of the carbon particles.

Nel contesto dell'ottimizzazione energetico-ambientale dei sistemi di generazione locale di energia, in coerenza con il Piano triennale della Ricerca di Sistema Elettrico 2012-2014, il presente progetto prevede un approccio integrato di: i) attività di ricerca inquadrabili nell'area d'intervento "C1-Risparmio di energia elettrica", dedicate alla messa a punto di tecniche di monitoraggio/controllo dell'efficienza energetica nonchè allo sviluppo di un sistema di cogenerazione ad alta efficienza, e ii) attività di ricerca che riguardano la messa punto di tecniche di misura di inquinanti specifici dei combustibili derivanti da biomasse/rifiuti e dell'effetto della composizione dei combustibili sulla qualità delle emissioni, contestualizzate nell'area d'intervento denominata "B1.1 Energia elettrica da biomasse".

This work reports a one-step method for the production of TiO2 nanoparticle coatings on aluminum alloys substrates. 5 nm diameter anatase nanoparticles have been synthesized by means of an Aerosol Flame Synthesis (AFS) system. A deposition system, constituted by a rotating disc, has been developed and operated to directly produce homogeneous nanostructured coatings by thermophoresis. Different coatings can be obtained by varying the total deposition time of the substrates. Electrochemical Impedance Spectroscopy (EIS) has been used to characterize the surface and the electrochemical behavior of the coatings. An improvement of the electrochemical properties due to the presence of nano-TiO2 coatings is demonstrated. © 2017 American Scientific Publishers All rights reserved.

Aluminum alloys are widely used in the aeronautic industry for their high mechanical properties; however, because they are very sensitive to corrosion, surface treatments are often required. TiO 2 has excellent resistance to oxidation and it is often used to improve the corrosion resistance of aluminum surfaces. Several coating procedures have been proposed over the years, which are in some cases expensive in terms of production time and amount of deposited material. Moreover, they can damage aluminum alloys if thermal treatments are required. In this paper, a one-step method for the coating of aluminum surfaces with titania nanoparticles is presented. Narrowly sized, TiO 2 nanoparticles are synthesized by flame aerosol and directly deposited by thermophoresis onto cold plates of aluminum AA2024. Submicron coatings of different thicknesses are obtained from two flame synthesis conditions by varying the total deposition time. A fuel-lean synthesis condition was used to produce 3.5 nm pure anatase nanoparticles, while a mixture of rutile and anatase nanoparticles having 22 nm diameter — rutile being the predominant phase —, was synthesized in a fuel-rich condition. Scanning electron microscopy is used to characterize morphology of titania films, while coating thickness is measured by confocal microscopy measurements. Electrochemical impedance spectroscopy is used to evaluate corrosion resistance of coated aluminum substrates. Results show an improvement of the electrochemical behavior of titania coated surfaces as compared to pristine aluminum surfaces. The best results are obtained by covering the substrates with 3.5 nm anatase-phase nanoparticles and with lower deposition times, that assure a uniform surface coating.

In the last decades, flame studies focused on particle inception mechanisms and the characterization of particle composition and properties have shown that flames operated in fuel-rich conditions produce a broad variety of CNPs with different morphology, chemical, physical, optical and electronic properties which depend on the flame conditions. Thus, flame combustion can be optimized to form tailored CNPs for specific applications [1, 2]. Besides particle properties, the assembly of nanoparticles into a uniform thin film with precise control over chemical and physical properties poses a significant challenge. Various techniques have been developed and studied over the years to create thin films of nanoparticles that can lead to novel applications, as electro-deposition of semiconductor and metal nanoparticles, the deposition of nanoparticle monolayers via the Langmuir-Blodgett technique, sol-gel chemistrybased deposition. Thermophoretic sampling is a technique often used to collect on a substrate isolated particles from flames for TEM or other single particles analysis techniques. This method relies on the thermophoretic forces driving the aerosol particles in the hot gas flame towards a cold surface inserted in the flame. In this work, carbon nanoparticles have been produced in a premixed ethylene-air flame and their potentiality as a medium for electronic applications has been investigated. To this aim, CNPs thin films have been achieved by the direct deposition of the flame-synthesized CNPs on multilayer substrates consisting on highly-doped (500 ?m thick) Silicon layers, thin (200 nm) SiO2 insulating barriers and gold electrodes (drain/source contacts) with interdigitated layout. The flame conditions examined in this work allow to produce CNPs that can roughly be distinguished into two classes: organic particles with diameter, D=2-10 nm, which have molecularlike spectroscopic properties, and soot particles, which are constituted by amorphous carbon in form of primary particles with D=10-50nm which can grow in chain like structures. CNPs have been characterized by measuring the size distribution by a Scanning Mobility Particle Sizer, and their physico-chemical properties by UV-visible light absorption and Raman spectroscopy. Current-voltage (IV) measurements recorded for all the synthesized films display a linear (ohmic) behavior for values of the applied voltages up to 10V. Moreover, it was found that the electrical conductivity (?) of these layers exhibit a distinctive dependence on the thickness following a rising behavior up to a maximum value of about 10-3 S/cm. Finally, by applying a further external voltage signal to the highly-doped Silicon substrate, working as the gate electrode in a field-effect transistor configuration, we have been able to modify reversibly the current flowing in the CNPs channels, thus revealing the possibility to evaluate also the charge carrier mobility (?) through the MOSFET model. Maximum ? values of about 10-4 cm2/volt*sec were estimated in this work.

s of the papers presented at the 39th Combustion Meeting Associazione Sezione Italiana del Combustion Institute

The mean size of flame-formed fluorescent carbonaceous nanoparticles was detected by in-situ time-resolved fluorescence anisotropy (TRFA) measurements. A long investigated coflowing laminar diffusion flame of ethylene was used as combustion system for both data comparison and for its importance in the field of particulate formation and emission control. From the analysis of the decay time of the fluorescence anisotropy, we estimated the diameter of particles selected by their ability to absorb and emit visible light, as a function of the flame radial position for several heights from the fuel nozzle. TRFA has allowed us to investigate intermediate classes of compounds between the UV absorbing particles and soot studied in previous works. These compounds have average sizes ranging from 10 to 20 nm. The technique proves to be applicable to the study of soot formation mechanisms, and specifically to follow the inception phenomenon based on the transition from the gas-phase to the solid particles.

In this study, the thermal oxidative stability of a kerosene-type Jet A-1 commercial aviation fuel has been investigated using a three-dimensional (3D) excitation/emission matrix fluorescence (EEMF) method. The fuel was thermally stressed in flow test conditions over a range of temperatures in the autoxidative regime. To determine the effect of dissolved oxygen on aviation fuel thermal stability, the measurements were conducted for both air-saturated and fully deoxygenated fuel samples. The increase in the fuel temperature results in a large red shift of the fluorescence signals for the air-saturated fuel; however, fully deoxygenated fuel showed no difference in the fluorescence spectra with respect to neat fuel. The observed increase in the emission wavelengths of the collected spectra may be attributed to the formation of high-molecular-mass compounds within the liquid fuel. These species are formed as a consequence of the chemical reactions activated during the thermal stressing process. The use of 3D ...

In modern gas-turbine aircraft, aviation fuel is routinely used as a coolant to remove waste heat loads from, for example, lubrication and secondary engine systems, in addition to its conventional role as the energy source through combustion. Theincreaseofthefueltemperatureactivatesseveralliquid-phasereactionsinvolvinghydrocarbonmolecules,dissolvedoxygen,and indigenous heteroatomic (O, N, and S) polar compounds. The result of such reactions is the formation of gums and solid deposits within the fuel lines, which are of concern for the maintenance of gas-turbine engines. In the present paper, the thermal oxidative stability of commercial aviation fuel was investigated by the positive electrospray ionization mass spectrometry (ESIMS) technique.Several classes ofpolarspecies,withdifferentlevels ofalkylation, were detected intheunstressed jet fuel.Themajorityof these compounds were characterized by a molecular mass within the range of 90� 250 Da. Thermally stressed jet fuel, under different experimental conditions, showed the presence of a broad molecular mass band of polar compounds in the range of 250� 400 Da. This class of soluble high-molecular-mass compounds was not detectable when the dissolved oxygen was removed from the fuel by nitrogen sparging. Consistent with previous findings in the literature, we postulate that aggregation processes of these species, through polymerization or clustering reactions, could be responsible for the formation and precipitation of insoluble compounds, which ultimately lead to the formation of the oxidative deposits.

Aviation fuel is used as a coolant to remove waste heat loads from an aircraft in addition to its conventional role as an energy source through combustion. As the fuel temperature increases, several reactions involving hydrocarbon molecules, dissolved oxygen, and impurities take place, which ultimately lead to the formation of gums and solid deposits. Ultraviolet−visible light absorption and fluorescence spectroscopy were used to study the degradation of commercial Jet A-1 as it was thermally stressed. Both techniques were shown to be highly sensitive to the chemical reactions occurring in the thermally stressed fuel that led to the formation of oxygenate products.

Soot volume fractions of binary mixtures of butane isomers, ethylene-butane isomers, and propanebutane isomers were evaluated experimentally in diffusion flames on both co- and counter-flow burners. Soot volume fractions were measured by two-dimensional line of sight attenuation of a broadband arc lamp generated light in co-flow flames, whereas in counter-flow flames, attenuation of a small radius laser beam was used. Binary mixtures of iso-butane and n-butane did not show any synergistic effects on soot formation. On the other hand, either n-butane or iso-butane addition to ethylene caused a strong synergistic effect in both types of flames that the soot volume fractions were higher than those of the individual mixture components under the same flame conditions. Binary mixtures of propane and butane isomers, however, didnotdisplay any measurable synergisticeffect onsoot formation.These observations were discussed in the light of mechanisms proposed by previous investigators to explain the synergistic effects detected in the flames of binary mixtures. Current results cast doubt on the universality of the dominance of any of the mechanisms previously proposed to explain the synergistic effects observed with some binary hydrocarbon mixtures. Most of the soot formation studies focus on single-hydrocarbon fuels because of the complex nature of soot mechanismsinflames.Ontheotherhand,mixturesofhydrocarbons, especially binary mixtures, are studied, although to a limited extent, to identify the probable soot formation channels associated with potential interactions between pyrolysis products of the hydrocarbons in the mixture. Several of these studies identified a synergistic effect when two pure hydrocarbons are mixed as the fuel. The synergistic effect in soot formation is described as the measured (or computed) increasesofthesootyieldofabinaryhydrocarbonmixtureover the soot concentrations of any of the two components in the mixture individually under similar flame conditions. The synergistic effect is observed if the addition of one single component fuel to another intensifies some production channels for the formation of soot by the interaction of the pyrolysisproductsofthesefuels.Availablefuelmixtureresults in the literature provide some insight into the precursors that might be the culprit for the synergistic effects. However, there exist significant disagreement among researchers about the results of the fuel mixture experiments and the interpretation of these results. 1-3

In this work we compare the results of several nanoparticle measurement techniques with the aim of investigating the formation of nanoparticles in non-sooting to slightly sooting flames. In slightly sooting conditions there is quite good agreement between Differential Mobility Analyser (DMA), Atomic Force Microscopy (AFM), and optical measurements on particle size and concentration. However, in rich flames below the onset of soot, DMA measures a strong drop-off in the total particle volume fraction at low fuel to air mixtures, which is not observed in optical or AFM measurements that detect a more gradual decrease in particle concentration with decreasing C/O and almost constant spectroscopic properties. The disagreement is significantly larger than experimental error and is only observed when the particle size distribution includes solely particles smaller than about 3 nm. Particle losses in the DMA sampling system does not seem to be the only possible reason for justifying the discrepancy with the other techniques. Further investigations are necessary in order to characterize chemically and physically this class of nanoparticles which constitute the earliest stage in the formation of particulate carbon.

Spectral optical techniques, including light extinction and laser induce fluorescence and incandescence measurements, are combined to characterize large-molecule soot precursors and soot in a slightly sooting flame of benzene at atmospheric pressure. Light absorption coupled to in-situ light scattering measurements and ex-situ Atomic Force Microscopy also allowed the evaluation of particle sizes. In the benzene flame high molecular mass structures with typical sizes of 3–4 nm are formed in the main oxidation region of the flame. The radical-rich flame environment in which these compounds are formed promotes their dehydrogenation increasing the level of their aromaticity. As a result, nanoparticles with typical sizes of about 5 nm, absorbing and fluorescing in the visible are formed. These compounds reach a maximum concentration just before the appearance of incandescent soot particles.

Interaction forces acting between combustion-generated carbon particles were studied by using atomic force microscopy (AFM). To this aim, carbon nanoparticles were produced in fuel-rich ethylene/air laminar premixed flames with different equivalent ratios Φ, and analyzed at a fixed residence time in the flame. Particles were collected on mica substrates by means of a thermophoretic sampling system and then analyzed by AFM. A characterization of particle dimension and morphology were performed operating AFM in semicontact mode, showing that the shape of the particles collected on a sampling plate is never spherical. Increasing the flame-equivalent ratio, particle shape moves from an almost atomically thick object to thicker compounds, indicating the transformation from particles made of small, defective graphene-like sheets to particles containing stacked aromatic layers. Attractive and adhesive forces between a titanium nitride probe and sampled particles were calculated from force-distance curves acquired in AFM force spectroscopy mode. Assuming that van der Walls forces are the main contribution to attractive forces, the measurement of attractive forces allowed the evaluation of the Hamaker constant for the carbon particles as a function of the flame-equivalent ratio. The comparison of the measured Hamaker constants with the values for benzene and HOPG, suggests a continuous increase of the aromatic domains and the three-dimensional order within the particles when the flame-equivalent ratio increases.

In this work we produce atomically thin carbon nanostructures which have a disk-like shape when deposited on a substrate. These nanostructures have intermediate characteristics between a graphene island and a molecular compound and have the potentiality to be used either as they are, or to become building blocks for functional materials or to be manipulated and engineered into composite layered structures.The carbon nanostructures are produced in a premixed ethylene/air flame with a slight excess of fuel with respect to the stoichiometric value. The size distribution of the produced compounds in aerosol phase has been measured on line by means of a differential mobility analyzer (DMA) and topographic images of the structures deposited on mica disks were obtained by Atomic Force Microscopy. Raman spectroscopy and XPS have been used to characterize their structure and the electronic and optical properties were obtained combining on-line photoionization measurements with Cyclic Voltammetry, light absorption and photoluminescence.When deposited on the mica substrate the carbon compounds assume the shape of an atomically thin disk with in plane diameter of about 20 nm. Carbon nano-disks consist of a network of small aromatic island with in plane length, La, of about 1 nm. Raman spectra evidence a significant amount of disorder which is in a large part due to the quantum confinement in the aromatic islands. Nano-disks contain small percentage of sp3 and the O/C ratio is lower than 6%. They furthermore present interesting UV and visible photoluminescence properties.

In this work, particle inception and early growth stages were investigated in an ethylene/air premixed flame by the evolution of the particle size and structure with flame residence time. Particle size distribution was measured by a scanning mobility particle seizer and chemical-physical investigation was carried out by Raman microspectroscopy, UV-visible light absorption and cyclic voltammetry. From early inception of particles, just downstream the flame front, to the formation of primary soot particles, in the post-oxidation flame zone, particles participate in a series of chemical and physical reactions that strongly modify their nanostructure and physicochemical properties, resulting in different optical and electronic characteristics. The results presented in this study show that the evolution from a mono-modal to a bi-modal size distribution is associated to a particle graphitization process consisting of a slight increase of the in plane average size of the polyaromatic units within the particles, La, and on the formation of stacks of polyaromatic planes. These outcomes suggest that in our flame conditions particle coagulation/coalescence has a major role in the initial soot formation, affecting both physical and chemical particle properties. © 2015 The Combustion Institute.

Atomic force microscopy (AFM) is a well-known scanning probe technique, mainly used for its capability to achieve topographic images with subnanometer resolution. In addition to surface topographies characterization, AFM is also a powerful tool for sensitive force spectroscopy measurements; in this operation mode, the forces acting between the AFM tip and the surface under investigation are recorded during approach and retract of cantilever to and from the sample, and plotted as force-distance curves. From these measurements, short-range attractive and adhesive forces can be quantitatively evaluated. The purpose of this work is to investigate attractive and adhesive forces of incipient and mature soot particles formed in flames across the soot threshold limit. To this aim, carbon nanoparticles were produced from fuel-rich ethylene/air laminar premixed flames, at a fixed height above the burner (HAB) of 15 mm, with different equivalent ratios ?. Particles were then collected on mica substrates by means of a thermophoretic sampling system and analyzed by AFM operating in contact and force spectroscopy modes. Attractive and adhesive forces between silicon probe and collected particles were both found to increase with flame equivalent ratio, moving from non-sooting flame conditions (?=1.85), in which 2-5 nm diameter organic carbon nanoparticles are mainly produced, up to fully-sooting conditions (?=2.58), in which 50-100 nm soot aggregates are mainly produced. As expected, adhesive forces are 5-7 times greater than attractive forces in the same conditions. This is evidenced by the fact that particle deformation and bonding with AFM tip occurring during contact results in a curve-distance hysteresis contribution. The measurement of the attractive force by the AFM force-distance curve allows the evaluation of the Hamaker constant for the different carbon particles. The Hamaker constant of investigated nanoparticles was also theoretically derived from Lifshitz theory; Van der Walls interactions were indeed calculated and compared to experimental data. The study of surface properties of flame-formed nanoparticles, by means of AFM force-distance spectroscopy, appears to be promising for a better understanding of the coagulation and coalescence phenomena between carbon particles in the soot formation process.

The effect of ethanol addition in ethylene laminar premixed flames on the characteristics of soot precursor nanoparticles was investigated by aerosol photoionization technique. The fifth harmonic of a Nd:YAG laser, 213 nm (5.82 eV), was used as ionization source, while a differential mobility analyzer (DMA) coupled to a Faraday cup electrometer was used for ionized particle classification and detection. Carbonaceous nanoparticles in the nucleation mode, i.e., with sizes ranging from 1 to 10 nm, show a photoionization charging efficiency clearly dependent on the percentage of ethanol used as dopant in the flame. In particular, we observed that the more ethanol was added as fuel, the lower the particle photo-charging efficiency was. This result indicates a modification in the nanoparticle chemical structure as the amount of ethanol is increased. These experimental evidences may be explained by a decrease of aromaticity of the particles and/or by the presence of oxygen bonds within the nanoparticles. Copyright © Taylor & Francis Group, LLC.

The synthesis of pure titania and carbon-titania nano-powders in a premixed atmospheric fuel-rich flame was studied. The variation of the flame C/O ratio allows to produce both pure titania and carbon-TiO2 nanoparticles. Raman Spectroscopy, X-ray Diffraction, Atomic Force Microscopy, Electrical Low Pressure Impactor and Scanning Electron Microscopy were used to characterize the synthesized nano-powders, in terms of crystallinity, phase content, size and morphology. Produced nano-powders with a dimension of 25-40 nm are composed by both rutile and anatase phases, with rutile being the predominant one. Reactive Oxygen Species analysis performed on the synthesized nano-powders showed that the inclusion of carbon in the nano-powders results in a reduced adverse health effect, in terms of ROS production.

Objective: We reviewed our experience with myocardial revascularization without cardiopulmonary by-pass (CPB) to evaluate early- and mid-term results compared with those obtained using CPB. Methods: From May 21 1997 to November 1998, 747 patients had isolated myocardial revascularization, 480 without CPB (Group A) and 267 with CPB (Group B). Exposure of the target vessels was obtained with four slings (two passed through the transverse sinus and two behind the inferior vena cava) and four deep pericardial sutures on the mobile pericardium around the left atrium (Lima stitches). The number of anastomoses/patient (when two or more conduits were used) was higher in Group B (3:1 ^ 1: 0v s 2:6 ^ 0:7, P , 0:001). More marginal branches were grafted in Group A (258 vs 239), but the percentage was higher in Group B (P , 0:001). Crude and risk adjusted mortality was similar in both groups, as well as cerebrovascular accident (CVA) and acute myocardial infarction incidences. Patients in Group A woke earlier, had less inotropes, lower creatinkinase myocardial band (CK‐MB) peak, lower bleeding and less transfusion, shorter Intensive Care Unit (ICU) and postoperative stay in hospital than patients in Group B. 266 anastomoses were checked; of these 98.5% were patent and 97.0% were patent and not restrictive. Conclusions: Myocardial revascularization without CPB can provide good early- and mid-term results in selected patients. Primary endpoints (death and acute myocardial infarction) were similarly independent from the technique used. Some of the secondary endpoints were favorable in Group A; however their importance is minor. Even if we feel that some high risk patients with severe comorbidities can benefit from CPB surgery; this aspect is difficult to demonstrate scientifically. q 1999 Elsevier Science B.V. All rights reserved.

Background:Left anterior descending artery grafting using the left internal mammary artery via a left anterior small thoracotomy (LAST) gained new popularity in 1994. We review our experience in 250 of 512 patients who underwent a LAST in single vessel left anterior descending artery disease from November 1994 to October 1997. Methods: Left anterior descending artery stabilization was obtained pharmacologically and mechanically. Two patients (0.8%) had percutaneous transluminal coronary angioplasty at a mean of 23 ± 5 days; 172 (68.8%) patients had early postoperative angiography. Results: Eight conduits were occluded (patency rate 95.30%). There was only one late death. Cumulative angiography and Doppler flow evaluation showed that 96.8% of the anastomoses were patent and 95.6% were both patent and nonrestrictive. At a mean follow-up of 16.3 ± 9.3 months, 9 (3.6%) patients had redo-surgery due to anastomotic/conduit failure and 249 (99.6%) patients were alive and asymptomatic. No patients had acute myocardial infarction. The 35-month actuarial survival rate was 99.6%± 0.4%, and the event-free survival rate for the entire experience was 93.7%± 1.3%. If only the last 157 patients are considered, at 18 months event-free survival was higher than in the entire group of patients (96.4%± 1.4% vs 93.7%± 1.390, p = 0.05). Conclusions: New instrumentation has made the operation easier and has contributed to its spread, along with increased experience and the end of the learning curve. At the moment we consider the LAST a more anatomical and physiological surgical approach to single vessel coronary disease. (J Card Surg 7998;73:306–309)

An applicability study of advanced measuring equipment for monitoring particulate emission has been performed

Photoelectric charging of particles is a powerful tool for online characterization of submicrometer aerosol particles. Indeed photoionization based techniques have high sensitivity and chemical selectivity. Moreover, they yield information on electronic properties of the material and are sensitive to the state of the surface. In the present study the photoionization charging efficiency, i.e., the ratio between the generated positive ions and the corresponding neutral ones, for different classes of flame-generated carbonaceous nanoparticles was measured. The fifth harmonics of a Nd:YAG laser, 213 nm (5.82 eV), was used as an ionization source for the combustion generated nanoparticles, whereas a differential mobility analyzer (DMA) coupled to a Faraday cup electrometer was used for particle classification and detection. Carbonaceous nanoparticles in the nucleation mode, i.e., sizes ranging from 1 to 10 nm, show a photoionization charging efficiency clearly dependent on the flame conditions. In particular, we observed that the richer the flame is, i.e., the higher the equivalent ratio is, the higher the photon charging efficiency is. We hypothesized that such an increase in the photoionization propensity of the carbonaceous nanoparticles from richer flame condition is associated to the presence within the particles of larger aromatic moieties. The results clearly show that photoionization is a powerful diagnostic tool for the physical-chemical characterization of combustion aerosol, and it may lead to further insights into the soot formation mechanism. © 2013 American Chemical Society.

Sviluppo di metodi di analisi delle caratteristiche del particolato fine e ultrafine