An analysis of the relationship between the heat fluxes in the combustion of a single magnesium p... more An analysis of the relationship between the heat fluxes in the combustion of a single magnesium particle in an oxygen-containing medium shows that vapor-state combustion is possible only in the case where an appreciable portion of magnesium oxide condenses on the droplet surface.
Off-the-shelf calorimeters are typically used for hydrocarbon-based fuels and not designed for si... more Off-the-shelf calorimeters are typically used for hydrocarbon-based fuels and not designed for simulating metal powder oxidation in gaseous environments. We have developed a method allowing a typical bomb calorimeter to accurately measure heat released during combustion and achieve nearly 100% of the reference heat of combustion from powder fuels such as aluminum. The modification uses a combustible organic dispersant to suspend the fuel particles and promote more complete combustion. The dispersant is a highly porous organic starch-based material (i.e. packing peanut) and allows the powder to burn as discrete particles thereby simulating dust-type combustion environments. The demonstrated closeness of measured Al heat of combustion to its reference value is evidence of complete metal combustion achieved in our experiment. Beyond calorific output under conditions simulating real reactive systems, we demonstrate that the calorimeter also allows characterization of the temporal heat r...
Experiments were designed to investigate two regimes of metal particle combustion: fast and slow ... more Experiments were designed to investigate two regimes of metal particle combustion: fast and slow burning regimes. Stress-altering aluminum particles had been shown to produce a distinctly faster burning rate compared to untreated aluminum particles. The root cause for the differences in burning rate had been unclear. In this study, stress-altered and untreated aluminum particles were reacted as dispersed powder in a closed bomb calorimeter designed to monitor the transient temperature changes resulting from energy release upon combustion. The product residue was analyzed for size and species concentration. Results showed metastable γ-alumina that is associated with nano-oxide formation was in substantially higher concentration for stress-altered particle reactions that produced greater energy transfer rates. The increased energy transfer rate corresponded to higher radiant energy emission owing to condensation of nano-oxide particles. This study justifies condense-luminescence as a ...
This paper deals with nanoparticle generation by a glowing wire generator (GWG). The glowing cham... more This paper deals with nanoparticle generation by a glowing wire generator (GWG). The glowing chamber has been customized enabling using either single- or double-wire attached to the electrodes. The double-wire configuration was expected to significantly extend the operation window of the GWG. The undertaken measurements of the particle size distribution revealed, however, an anomalous behaviour of the particle size evolution depending on the applied voltage. At low voltages (<1.1V), the double-wire configuration allows for a substantial particle enlargement (up to two times) as compared to the single-wire configuration, which looks promising for the development of industrial aerosol generators. However, when the voltage exceeded the above value, the opposite behaviour was detected, i.e., some decrease in the particle size for the double-wire configuration was observed. This anomalous behaviour was attributed to interplay between nucleation and coagulation in the system. The corresponding mechanisms are discussed in this paper.
On a pu ameliorer les performances de collections de nanoparticles de phosphore en ameliorant cer... more On a pu ameliorer les performances de collections de nanoparticles de phosphore en ameliorant certaines des proprietes de leur materiau, telles que la cristallinite, et on a pu former des afficheurs en utilisant ces particules de taille submicronique. Ce sont des procedes de traitement ameliores qui ont contribuees a cette amelioration des particules qui presentent une cristallinite elevee et un haut niveau d'homogeneite de taille. On peut obtenir des dispersions et des composites a partir de poudres de collections de ces particules submicronique.
L'invention porte sur des nanoparticules de silice creuses qui peuvent avoir des enveloppes n... more L'invention porte sur des nanoparticules de silice creuses qui peuvent avoir des enveloppes non poreuses bien definies avec une faible fragmentation d'enveloppe et une bonne aptitude a la dispersion. Ces particules creuses bien definies peuvent etre formees par l'oxydation controlee des nanoparticules de silicium dans un solvant organique. Les nanoparticules creuses peuvent avoir des dimensions submicroniques de particules secondaires. Les nanoparticules de silice creuses peuvent etre incorporees dans des composites polymeres, tels que des composites a faible indice de refraction, pour des applications appropriees.
The application of pyrometry to retrieve particle temperature in particulate-generating flames st... more The application of pyrometry to retrieve particle temperature in particulate-generating flames strictly requires the knowledge of the spectral behavior of emissivity of light-emitting particles. Normally, this spectral behavior is considered time-independent. The current paper challenges this assumption and explains why the emissivity of oxide nanoparticles formed in flame can change with time. The suggested phenomenon is related to transitions of electrons between the valence and conduction energy bands in oxides that are wide-gap dielectrics. The emissivity change is particularly crucial for the interpretation of fast processes occurring during laser-induced experiments. In the present work, we compare the response of titania particles produced by a flame spray to the laser irradiation at two different excitation wavelengths. The difference in the temporal behavior of the corresponding light emission intensities is attributed to the different mechanisms of electron excitation duri...
This paper attempts to demonstrate the importance of the nanoparticle charge in the synthesis fla... more This paper attempts to demonstrate the importance of the nanoparticle charge in the synthesis flame, for the mechanism of their evolution during formation processes. An investigation was made of MgO nanoparticles formed during combustion of magnesium particles. The cubic shape of nanoparticles in an unaffected flame allows for direct interpretation of results on the external flame charging, using a continuous unipolar emission of ions. It was found that the emission of negative ions applied to the flame strongly affects the nanoparticle shape, while the positive ions do not lead to any noticeable change. The demonstrated effect emphasizes the need to take into account all of the phenomena responsible for the particle charge when modeling the nanoparticle formation in flames.
Abstract Flame Synthesis conditions significantly affect nanoparticles properties. Understanding ... more Abstract Flame Synthesis conditions significantly affect nanoparticles properties. Understanding thermal regime in flames can be very useful for tuning nanoparticles with specific properties. In this work, information on thermal status is obtained through the analysis of light emission from nanoparticles during synthesis and under an external laser irradiation. We focus on the dependence of the particle temperature on laser fluence as reported in our previous work. We discuss temperature plateau observed in the low laser fluence regime as attributed to non-isothermality, that means the local coexistence of partially solidified particles at melting point and much hotter particles in a flame spray.
Mailing envelopes containing pathogenic spores of bacillus anthraxes, which have recently been us... more Mailing envelopes containing pathogenic spores of bacillus anthraxes, which have recently been used by terrorists to infect humans, calls for a new investigation to identify a level of possible contamination of ambient air as a result of the opening of such envelopes. Here we show that opening an envelope and unfolding a letter aerosolize microbial particles located inside and create
An analysis of the relationship between the heat fluxes in the combustion of a single magnesium p... more An analysis of the relationship between the heat fluxes in the combustion of a single magnesium particle in an oxygen-containing medium shows that vapor-state combustion is possible only in the case where an appreciable portion of magnesium oxide condenses on the droplet surface.
Off-the-shelf calorimeters are typically used for hydrocarbon-based fuels and not designed for si... more Off-the-shelf calorimeters are typically used for hydrocarbon-based fuels and not designed for simulating metal powder oxidation in gaseous environments. We have developed a method allowing a typical bomb calorimeter to accurately measure heat released during combustion and achieve nearly 100% of the reference heat of combustion from powder fuels such as aluminum. The modification uses a combustible organic dispersant to suspend the fuel particles and promote more complete combustion. The dispersant is a highly porous organic starch-based material (i.e. packing peanut) and allows the powder to burn as discrete particles thereby simulating dust-type combustion environments. The demonstrated closeness of measured Al heat of combustion to its reference value is evidence of complete metal combustion achieved in our experiment. Beyond calorific output under conditions simulating real reactive systems, we demonstrate that the calorimeter also allows characterization of the temporal heat r...
Experiments were designed to investigate two regimes of metal particle combustion: fast and slow ... more Experiments were designed to investigate two regimes of metal particle combustion: fast and slow burning regimes. Stress-altering aluminum particles had been shown to produce a distinctly faster burning rate compared to untreated aluminum particles. The root cause for the differences in burning rate had been unclear. In this study, stress-altered and untreated aluminum particles were reacted as dispersed powder in a closed bomb calorimeter designed to monitor the transient temperature changes resulting from energy release upon combustion. The product residue was analyzed for size and species concentration. Results showed metastable γ-alumina that is associated with nano-oxide formation was in substantially higher concentration for stress-altered particle reactions that produced greater energy transfer rates. The increased energy transfer rate corresponded to higher radiant energy emission owing to condensation of nano-oxide particles. This study justifies condense-luminescence as a ...
This paper deals with nanoparticle generation by a glowing wire generator (GWG). The glowing cham... more This paper deals with nanoparticle generation by a glowing wire generator (GWG). The glowing chamber has been customized enabling using either single- or double-wire attached to the electrodes. The double-wire configuration was expected to significantly extend the operation window of the GWG. The undertaken measurements of the particle size distribution revealed, however, an anomalous behaviour of the particle size evolution depending on the applied voltage. At low voltages (<1.1V), the double-wire configuration allows for a substantial particle enlargement (up to two times) as compared to the single-wire configuration, which looks promising for the development of industrial aerosol generators. However, when the voltage exceeded the above value, the opposite behaviour was detected, i.e., some decrease in the particle size for the double-wire configuration was observed. This anomalous behaviour was attributed to interplay between nucleation and coagulation in the system. The corresponding mechanisms are discussed in this paper.
On a pu ameliorer les performances de collections de nanoparticles de phosphore en ameliorant cer... more On a pu ameliorer les performances de collections de nanoparticles de phosphore en ameliorant certaines des proprietes de leur materiau, telles que la cristallinite, et on a pu former des afficheurs en utilisant ces particules de taille submicronique. Ce sont des procedes de traitement ameliores qui ont contribuees a cette amelioration des particules qui presentent une cristallinite elevee et un haut niveau d'homogeneite de taille. On peut obtenir des dispersions et des composites a partir de poudres de collections de ces particules submicronique.
L'invention porte sur des nanoparticules de silice creuses qui peuvent avoir des enveloppes n... more L'invention porte sur des nanoparticules de silice creuses qui peuvent avoir des enveloppes non poreuses bien definies avec une faible fragmentation d'enveloppe et une bonne aptitude a la dispersion. Ces particules creuses bien definies peuvent etre formees par l'oxydation controlee des nanoparticules de silicium dans un solvant organique. Les nanoparticules creuses peuvent avoir des dimensions submicroniques de particules secondaires. Les nanoparticules de silice creuses peuvent etre incorporees dans des composites polymeres, tels que des composites a faible indice de refraction, pour des applications appropriees.
The application of pyrometry to retrieve particle temperature in particulate-generating flames st... more The application of pyrometry to retrieve particle temperature in particulate-generating flames strictly requires the knowledge of the spectral behavior of emissivity of light-emitting particles. Normally, this spectral behavior is considered time-independent. The current paper challenges this assumption and explains why the emissivity of oxide nanoparticles formed in flame can change with time. The suggested phenomenon is related to transitions of electrons between the valence and conduction energy bands in oxides that are wide-gap dielectrics. The emissivity change is particularly crucial for the interpretation of fast processes occurring during laser-induced experiments. In the present work, we compare the response of titania particles produced by a flame spray to the laser irradiation at two different excitation wavelengths. The difference in the temporal behavior of the corresponding light emission intensities is attributed to the different mechanisms of electron excitation duri...
This paper attempts to demonstrate the importance of the nanoparticle charge in the synthesis fla... more This paper attempts to demonstrate the importance of the nanoparticle charge in the synthesis flame, for the mechanism of their evolution during formation processes. An investigation was made of MgO nanoparticles formed during combustion of magnesium particles. The cubic shape of nanoparticles in an unaffected flame allows for direct interpretation of results on the external flame charging, using a continuous unipolar emission of ions. It was found that the emission of negative ions applied to the flame strongly affects the nanoparticle shape, while the positive ions do not lead to any noticeable change. The demonstrated effect emphasizes the need to take into account all of the phenomena responsible for the particle charge when modeling the nanoparticle formation in flames.
Abstract Flame Synthesis conditions significantly affect nanoparticles properties. Understanding ... more Abstract Flame Synthesis conditions significantly affect nanoparticles properties. Understanding thermal regime in flames can be very useful for tuning nanoparticles with specific properties. In this work, information on thermal status is obtained through the analysis of light emission from nanoparticles during synthesis and under an external laser irradiation. We focus on the dependence of the particle temperature on laser fluence as reported in our previous work. We discuss temperature plateau observed in the low laser fluence regime as attributed to non-isothermality, that means the local coexistence of partially solidified particles at melting point and much hotter particles in a flame spray.
Mailing envelopes containing pathogenic spores of bacillus anthraxes, which have recently been us... more Mailing envelopes containing pathogenic spores of bacillus anthraxes, which have recently been used by terrorists to infect humans, calls for a new investigation to identify a level of possible contamination of ambient air as a result of the opening of such envelopes. Here we show that opening an envelope and unfolding a letter aerosolize microbial particles located inside and create
Uploads