Rachel Pflieger - Academia.edu (original) (raw)

Papers by Rachel Pflieger

Spectrochimica Acta Part B: Atomic Spectroscopy, 2008

The problem of correlation between the temperature of the target surface and the mass-spectromete... more The problem of correlation between the temperature of the target surface and the mass-spectrometer signal in laser-vaporization mass spectrometry has been analyzed theoretically. An approach based on statistical mechanics has been applied in order to describe the transient vaporization into vacuum of molecules effused from the area of the target surface struck by a laser pulse of moderate power density and time duration of some tens of ms (Langmuir vaporization). In particular, an expression for the intensity of the output signal of the mass spectrometer, I(l,t), has been derived as a function of the detection time, t, and of the distance, l, of the ionizing chamber of the spectrometer from the target. A simple numerical method for the calculation of I(l,t) according to the time profile of the target temperature is also provided. By fitting experimental I(t) values with the theoretical expression one can retrieve thermodynamic quantities involved in the sublimation/evaporation process of the molecular species analyzed, such as enthalpy and equilibrium vapor pressure (or, alternatively, vaporization coefficient). As an illustration, this fitting was performed on experimental measurements of pyrolytic graphite sublimation in the temperature range 3200-3700 K. The analysis developed will be useful for the interpretation of experimental datasets in order to retrieve hightemperature thermodynamic data, especially on high-melting materials. Research in this domain is being launched for nuclear materials, particularly for Generation IV advanced fuels.

Journal of Visualized Experiments, 2014

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules ... more The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO 2 powder in pure water yields stable colloids of plutonium due to both effects.

ACS Sustainable Chemistry & Engineering

There are typically signs of light degradation of ionic liquids by pyrolysis when used in electro... more There are typically signs of light degradation of ionic liquids by pyrolysis when used in electrochemistry or when submitted to high heat or to ultrasound irradiation for chemical reactions. Cavitation observed through sonoluminescence from dry hydrophobic ionic liquids under sonication leads to degradation by pyrolysis at the level of traces. The degradation products can hinder recycling ionic liquids and, in turn, hinder the beneficial of their use and development of efficient large-scale processes. Unfortunately, various experimental limitations have prevented structural determination. The problems include the following: ionic liquids are almost non-volatile, which excludes the use of classical analytical techniques, and degradation products are produced at very low concentrations, which complicates extraction and analysis. Reported here is the first structural determination of the degradation products of a hydrophobic bis(trifluoromethylsulfonyl)imide-based ionic liquid under ul...

Multibubble Sonoluminescence and Sonochemistry of F-Transition Elements

Proceedings of the 8th International Symposium on Cavitation, 2012

Effect of operational conditions on sonoluminescence and kinetics of H2O2 formation during the sonolysis of water in the presence of Ar/O2 gas mixture

Ultrasonics sonochemistry, Jan 14, 2015

Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra o... more Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204-362kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry...

Journal of visualized experiments : JoVE, 2014

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules ... more The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophoto...

Ultrasonics sonochemistry, 2014

Sonoluminescence spectra collected from 0.1 to 3.0M aqueous solutions of formic acid sparged with... more Sonoluminescence spectra collected from 0.1 to 3.0M aqueous solutions of formic acid sparged with argon show the OH(A(2)Σ(+)-X(2)Πi) and C2(d(3)Πg → a(3)Πu) emission bands and a broad continuum typical for multibubble sonoluminescence. The overall intensity of sonoluminescence and the sonochemical yield of HCOOH degradation vary in opposite directions: the sonoluminescence is quenched while the sonochemical yield increases with HCOOH concentration. By contrast, the concentration of formic acid has a relatively small effect on the intensity of C2 Swan band. It is concluded that C2 emission originates from CO produced by HCOOH degradation rather than from direct sonochemical degradation of HCOOH. The intensity of C2 band is much stronger at high ultrasonic frequency compared to 20 kHz ultrasound which is in line with higher yields of CO at high frequency. Another product of HCOOH sonolysis, carbon dioxide, strongly quenches sonoluminescence, most probably via collisional non-radiative...

The problem of correlation between the temperature of the target surface and the mass-spectromete... more The problem of correlation between the temperature of the target surface and the mass-spectrometer signal in laser-vaporization mass spectrometry has been analyzed theoretically. An approach based on statistical mechanics has been applied in order to describe the transient vaporization into vacuum of molecules effused from the area of the target surface struck by a laser pulse of moderate power density and time duration of some tens of ms (Langmuir vaporization). In particular, an expression for the intensity of the output signal of the mass spectrometer, I(l,t), has been derived as a function of the detection time, t, and of the distance, l, of the ionizing chamber of the spectrometer from the target. A simple numerical method for the calculation of I(l,t) according to the time profile of the target temperature is also provided. By fitting experimental I(t) values with the theoretical expression one can retrieve thermodynamic quantities involved in the sublimation/evaporation process of the molecular species analyzed, such as enthalpy and equilibrium vapor pressure (or, alternatively, vaporization coefficient). As an illustration, this fitting was performed on experimental measurements of pyrolytic graphite sublimation in the temperature range 3200-3700 K. The analysis developed will be useful for the interpretation of experimental datasets in order to retrieve hightemperature thermodynamic data, especially on high-melting materials. Research in this domain is being launched for nuclear materials, particularly for Generation IV advanced fuels.

The Journal of Physical Chemistry B, 2015

The multibubble sonoluminescence (MBSL) spectra of t-BuOH aqueous solutions submitted to power ul... more The multibubble sonoluminescence (MBSL) spectra of t-BuOH aqueous solutions submitted to power ultrasound at 20, 204, 362, and 613 kHz show emissions for the Δυ = −1 to Δυ = +2 vibrational sequences of C 2 * Swan system (d 3 Π g → a 3 Π u ). The Δυ=+2 emission overlaps with the CH(A−X) emission band. The maximal Swan band emission is observed when the MBSL of water itself is almost completely quenched. In general, MBSL is more intense at high-frequency compared to 20 kHz ultrasound. However, in the presence of Xe, the MBSL of C 2 * at 20 kHz is so bright that it can be seen by the unaided eye as a blue glow in the close vicinity of the ultrasonic tip. The intensity of the C 2 * band emission exhibits a maximum vs t-BuOH concentration: 0.1−0.2 M at 20 kHz and (1−8) × 10 −3 M at high-frequency ultrasound. Such a huge difference is attributed to a much smaller bubble size at high ultrasonic frequency or, in other words, to a much higher bubble surface/volume ratio providing more efficient saturation of the bubble interior with t-BuOH vapors and to the fact that high frequency bubbles remain active for many more cycles than 20 kHz ones, thus accumulating more hydrocarbon decomposition products. Simulation of the emission spectra using Specair software demonstrated the absence of thermal equilibrium for C 2 * radicals (T v > T r ), where T v and T r are the vibrational and the rotational temperature, respectively. In Ar, T v decreases with increasing t-BuOH concentration reaching a steady value in the concentration domain that corresponds to C 2 * emission maximum intensity. In the presence of Xe an extremely high T v is obtained, which is explained by the relatively low ionization potential of Xe providing a higher electron temperature of nonequilibrium plasma generated during bubble collapse. Analysis of the gaseous products of t-BuOH sonolysis reveals a significant sonochemical activity even at high t-BuOH concentration when MBSL is totally quenched, indicating that drastic conditions could be produced also within nonsonoluminescing cavitation bubbles.

Ultrasonics Sonochemistry, 2010

The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitr... more The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitric acid medium. In order to minimize the volume of radioactive waste it seems interesting to generate the reactive species in situ in such solutions using ultrasonic irradiation without addition of salt-forming reagents. This review summarizes for the first time the versatile sonochemical processes with uranium, neptunium and plutonium in homogeneous nitric acid solutions and heterogeneous systems. The dissolution of refractory solids, ultrasonically driven liquid-liquid extraction and the sonochemical degradation of the volatile products of organic solvent radiolysis issued from PUREX process are considered. Also the guidelines for required further work to ensure successful application of the studied processes at industrial scale are discussed.

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry B, 2013

This article focuses on the possibility of exciting some lanthanides (Ce 3+ , Tb 3+ , Gd 3+ , and... more This article focuses on the possibility of exciting some lanthanides (Ce 3+ , Tb 3+ , Gd 3+ , and Eu 3+ ) by ultrasound in aqueous solutions. Depending on the lanthanide ions and on the acoustic cavitation conditions (single-bubble or multibubble systems), the excitation mechanism is shown to be photoexcitation (e.g., for Ce 3+ ) or collision-induced excitation (e.g., for Tb 3+ ). The sonoluminescence of Tb 3+ is studied in detail at various ultrasonic frequencies, allowing quantification of the amount of quenching. The latter is much stronger in sonoluminescence than in photoluminescence due to the particular properties of acoustic cavitation. Complexation with citrate ions enhances manifold sonoluminescence of lanthanides due to reduction of intra-and inner-molecular quenching.

The Journal of Physical Chemistry A, 2012

The sonoluminescence (SL) spectra of OH-(A 2 Σ + ) excited state produced during the sonolysis of... more The sonoluminescence (SL) spectra of OH-(A 2 Σ + ) excited state produced during the sonolysis of water sparged with argon were measured and analyzed at various ultrasonic frequencies (20, 204, 362, 609, and 1057 kHz) in order to determine the intrabubble conditions created by multibubble cavitation. The relative populations of the OH-(A 2 Σ + ) v′ = 1−4 vibrational states as well as the vibronic temperatures (T v , T e ) have been calculated after deconvolution of the SL spectra. The results of this study provide evidence for nonequilibrium plasma formation during sonolysis of water in the presence of argon. At low ultrasonic frequency (20 kHz), a weakly excited plasma with Brau vibrational distribution is formed (T e ∼ 0.7 eV and T v ∼ 5000 K). By contrast, at highfrequency ultrasound, the plasma inside the collapsing bubbles exhibits Treanor behavior typical for strong vibrational excitation. The T e and T v values increase with ultrasonic frequency, reaching T e ∼ 1 eV and T v ∼ 9800 K at 1057 kHz.

The Journal of Physical Chemistry A, 2011

Spectroscopic studies of single-bubble sonoluminescence (SBSL) in water and aqueous sodium chlori... more Spectroscopic studies of single-bubble sonoluminescence (SBSL) in water and aqueous sodium chloride solutions with a defined concentration of argon were performed as a function of the driving acoustic pressure. The broad-band continuum ranging from 200 to 700 nm is characterized by fits using Planck's law of blackbody radiation. The obtained blackbody temperatures are in the range of 10 4 K and are revealed to be independent of the presence of a salt and the acoustic pressure, whereas the SL intensity increases by a factor of more than 10 within the studied acoustic pressure range. The different trends followed by SL intensity and blackbody temperatures question the blackbody model. In solutions with 70 mbar of argon, line emissions of OH • radicals and Na* are observed. The shape of the OH • radical emission spectrum is very similar to that in MBSL spectra, indicating the strong similarity of intrabubble conditions. An increase of the acoustic pressure causes the continuum to overlap the lines until they become indistinguishable. The emission line of Na* in NaCl is observed only at high NaCl concentrations. When sodium dodecylsulfate is used a pronounced Na* line is already observed in a 1 mM solution thanks to enrichment of sodium ions at the interface. The results presented in this work reveal the strong similarity of SBSL and MBSL under certain experimental conditions.

Journal of the American Ceramic Society, 2009

Although glass-RuO 2 composites are well known for their particular electrical properties, the re... more Although glass-RuO 2 composites are well known for their particular electrical properties, the reasons for their very low percolation thresholds are still subject to debate. In this paper, a detailed study of the influence of various experimental parameters (temperature, RuO 2 content, stirring, etc.) on the electrical conductivity and, in particular, on the percolation threshold in borosilicate glass-RuO 2 composites is presented. This percolation threshold is shown to increase by a factor of two (from 0.6 to 1.2 vol%) when stirring is applied during synthesis and by more than a factor of three (42.1 vol%) when a sol-gel route is used. Besides, the study of various synthesis temperatures reveals that the electronic part of the electrical conductivity is highly correlated to Ru solubility in the glass matrix. It can be concluded from these various experiments that both the presence of dissolved ruthenium in the glass matrix and the possibility of RuO 2 particles to rearrange in the melt in order to form kind of a network are necessary for a low percolation threshold. J ournal J. Am. Ceram. Soc., ]] []]] 1-7 (2009)

A Knudsen cell-mass spectrometer facility to investigate oxidation and vaporisation processes in nuclear fuel

Journal of Nuclear Materials, 2005

ABSTRACT Vaporisation processes in uranium oxide fuel were investigated under controlled oxidatio... more ABSTRACT Vaporisation processes in uranium oxide fuel were investigated under controlled oxidation conditions. A Knudsen cell with a mass spectrometer was adapted to feed an adjustable oxygen flux up to temperatures of 1900K producing an oxygen pressure in the cell ranging up to 1000Pa. Experiments were carried out on fresh and irradiated fuels, both pre-oxidised to U3O8 or oxidised online in the Knudsen cell, to measure effects associated with fuel sublimation in the form of different uranium-bearing oxides. Mass spectrometry, electromotive force measurements and thermo-gravimetric analysis were used to determine the vapour equilibrium conditions at fixed free oxygen potentials.

Journal of Nuclear Materials, 2010

An original approach to immobilize ruthenium species and then transform them into RuO 2 nanoparti... more An original approach to immobilize ruthenium species and then transform them into RuO 2 nanoparticles is presented that uses hybrid-functionalized glasses. First, different chemical graftings of functional groups (acetylacetonate, amine, nitrile, pyridine and thiol) in porous glass were used to extract ruthenium-containing complexes ([Ru(CH 3 N) 4 Cl 2 ] and Ru(NO)(NO 3 ) 3 ) from solutions. The best functional groups to selectively coordinate Ru complexes and thus extract it from the solutions have been determined. Then, the obtained Ru-containing composite glass was heated under air to remove the organic species and to obtain RuO 2 nanoparticles inside a glass with centimetre scale geometric form. The as-obtained materials were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen physisorbtion measurements, elemental analysis and X-ray diffraction (XRD).

Advances in the mass spectrometric study of the laser vaporization of graphite

Journal of Applied Physics, 2008

ABSTRACT Reliable experimental data on graphite vaporization and especially on carbon vapor compo... more ABSTRACT Reliable experimental data on graphite vaporization and especially on carbon vapor composition exist only up to 2500–3000 K. Data measured at higher temperatures are questionable due to several experimental limitations, such as the difficult temperature determination and the not straightforward correlation of measured temperatures and intensities of signals in mass spectra. That is why a new method of high-temperature mass spectrometry with laser vaporization was developed, in order to extend the accessible temperature range while overcoming these limitations and to shed more light on the still poorly known behavior of carbon at high temperatures. Thus, carbon sublimation relative partial pressures of the species C1, C2, C3, C4, and C5 were measured up to 4100 K. Moreover, the values of the relative vaporization coefficients of C1, C2, C3, C4, and C5, estimated by comparison of the experimentally obtained partial pressures with the predicted equilibrium ones, are proposed.

Journal of Applied Physics, 2011

Due to the chemically unstable nature of uranium dioxide its vapour composition at very high temp... more Due to the chemically unstable nature of uranium dioxide its vapour composition at very high temperatures is, presently, not sufficiently studied though more experimental knowledge is needed for risk assessment of nuclear reactors. We used laser vaporisation coupled to mass spectrometry of the produced vapour to study urania vapour composition at temperatures in the vicinity of its melting point and higher. The very good agreement between measured melting and freezing temperatures and between partial pressures measured on the temperature increase and decrease indicated that the change of stoichiometry during laser heating was very limited. The evolutions with temperature (in the range 2800-3400 K) of the partial pressures of the main vapour species (UO 2 , UO 3 and UO 2 + ) were compared with theoretically predicted evolutions for equilibrium non-congruent gas-liquid and gas-solid phase coexistence and showed very good agreement. The measured main relative partial pressure ratios around 3300 K all agree with calculated values for total equilibrium between condensed and vapour phase. It is the first time the three main partial pressure ratios above stoichiometric liquid urania are measured at the same temperature under conditions close to equilibrium non-congruent gas-liquid phase coexistence.

Thermodynamics of Refractory Nuclear Materials Studied by Mass Spectrometry of Laser-Produced Vapors

International Journal of Thermophysics, 2005

ABSTRACT A new method of high-temperature mass spectrometry (MS) with laser-induced vaporization ... more ABSTRACT A new method of high-temperature mass spectrometry (MS) with laser-induced vaporization (LIV) has been developed. The initial problem of LIV MS, consisting of an inadequate correlation between the temperature of the surface and the MS signal, was successfully overcome.The method was developed on graphite, of which fast time-resolved MS measurements (ca. 20ms) were performed over a large mass interval; the influence of geometrical parameters and of the laser pulse length on MS measurements was studied. Carbon sublimation relative partial pressures of C1, C2, C3, and C5 were measured up to 3810 K. This corresponds to a total pressure of about 0.8bar estimated independently by the integral mass flux using the Hertz–Knudsen equation. The vaporization of UO2 was studied at temperatures above ≈ 2500 K, where conventional Knudsen-cell mass spectrometry cannot be applied. The vaporization enthalpy obtained for the main species in UO2 vapor was in good agreement with that of conventional mass spectrometry.

Spectrochimica Acta Part B: Atomic Spectroscopy, 2008

The problem of correlation between the temperature of the target surface and the mass-spectromete... more The problem of correlation between the temperature of the target surface and the mass-spectrometer signal in laser-vaporization mass spectrometry has been analyzed theoretically. An approach based on statistical mechanics has been applied in order to describe the transient vaporization into vacuum of molecules effused from the area of the target surface struck by a laser pulse of moderate power density and time duration of some tens of ms (Langmuir vaporization). In particular, an expression for the intensity of the output signal of the mass spectrometer, I(l,t), has been derived as a function of the detection time, t, and of the distance, l, of the ionizing chamber of the spectrometer from the target. A simple numerical method for the calculation of I(l,t) according to the time profile of the target temperature is also provided. By fitting experimental I(t) values with the theoretical expression one can retrieve thermodynamic quantities involved in the sublimation/evaporation process of the molecular species analyzed, such as enthalpy and equilibrium vapor pressure (or, alternatively, vaporization coefficient). As an illustration, this fitting was performed on experimental measurements of pyrolytic graphite sublimation in the temperature range 3200-3700 K. The analysis developed will be useful for the interpretation of experimental datasets in order to retrieve hightemperature thermodynamic data, especially on high-melting materials. Research in this domain is being launched for nuclear materials, particularly for Generation IV advanced fuels.

Journal of Visualized Experiments, 2014

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules ... more The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophotoluminescence dominates in diluted solutions, and collisional excitation contributes at higher uranium concentration. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble, but then diffuse into the liquid phase and react with solution precursors to form a variety of products. For instance, the sonochemical reduction of Pt(IV) in pure water provides an innovative synthetic route for monodispersed nanoparticles of metallic platinum without any templates or capping agents. Many studies reveal the advantages of ultrasound to activate the divided solids. In general, the mechanical effects of ultrasound strongly contribute in heterogeneous systems in addition to chemical effects. In particular, the sonolysis of PuO 2 powder in pure water yields stable colloids of plutonium due to both effects.

ACS Sustainable Chemistry & Engineering

There are typically signs of light degradation of ionic liquids by pyrolysis when used in electro... more There are typically signs of light degradation of ionic liquids by pyrolysis when used in electrochemistry or when submitted to high heat or to ultrasound irradiation for chemical reactions. Cavitation observed through sonoluminescence from dry hydrophobic ionic liquids under sonication leads to degradation by pyrolysis at the level of traces. The degradation products can hinder recycling ionic liquids and, in turn, hinder the beneficial of their use and development of efficient large-scale processes. Unfortunately, various experimental limitations have prevented structural determination. The problems include the following: ionic liquids are almost non-volatile, which excludes the use of classical analytical techniques, and degradation products are produced at very low concentrations, which complicates extraction and analysis. Reported here is the first structural determination of the degradation products of a hydrophobic bis(trifluoromethylsulfonyl)imide-based ionic liquid under ul...

Multibubble Sonoluminescence and Sonochemistry of F-Transition Elements

Proceedings of the 8th International Symposium on Cavitation, 2012

Effect of operational conditions on sonoluminescence and kinetics of H2O2 formation during the sonolysis of water in the presence of Ar/O2 gas mixture

Ultrasonics sonochemistry, Jan 14, 2015

Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra o... more Ultrasonic frequency is a key parameter determining multibubble sonoluminescence (MBSL) spectra of water saturated with Ar/O2 gas mixtures. At 20kHz, the MBSL is quenched by oxygen. By contrast, at high-frequency ultrasound the maximal MBSL intensity is observed in the presence of Ar/20%O2 gas mixture. Nevertheless, oxygen has no influence on the shape of MBSL spectra. The effect of oxygen on MBSL is explained by oxygen dissociation inside the collapsing bubble which is much more effective at high ultrasonic frequency compared to 20kHz ultrasound. In contrast to MBSL, a higher yield of H2O2 is observed in Ar/20%O2 gas mixture whatever the ultrasonic frequency. At 20°C and 20% of oxygen the maximal yield of H2O2 is observed at 204-362kHz. The maximal yield of H2O2 is shifted to 613kHz when the bulk temperature is raised up to 40°C. Coupling of high-frequency ultrasound with mechanical stirring and intensive Ar/O2 bubbling improves H2O2 production. Comparison of MBSL and sonochemistry...

Journal of visualized experiments : JoVE, 2014

The chemical and physical effects of ultrasound arise not from a direct interaction of molecules ... more The chemical and physical effects of ultrasound arise not from a direct interaction of molecules with sound waves, but rather from the acoustic cavitation: the nucleation, growth, and implosive collapse of microbubbles in liquids submitted to power ultrasound. The violent implosion of bubbles leads to the formation of chemically reactive species and to the emission of light, named sonoluminescence. In this manuscript, we describe the techniques allowing study of extreme intrabubble conditions and chemical reactivity of acoustic cavitation in solutions. The analysis of sonoluminescence spectra of water sparged with noble gases provides evidence for nonequilibrium plasma formation. The photons and the "hot" particles generated by cavitation bubbles enable to excite the non-volatile species in solutions increasing their chemical reactivity. For example the mechanism of ultrabright sonoluminescence of uranyl ions in acidic solutions varies with uranium concentration: sonophoto...

Ultrasonics sonochemistry, 2014

Sonoluminescence spectra collected from 0.1 to 3.0M aqueous solutions of formic acid sparged with... more Sonoluminescence spectra collected from 0.1 to 3.0M aqueous solutions of formic acid sparged with argon show the OH(A(2)Σ(+)-X(2)Πi) and C2(d(3)Πg → a(3)Πu) emission bands and a broad continuum typical for multibubble sonoluminescence. The overall intensity of sonoluminescence and the sonochemical yield of HCOOH degradation vary in opposite directions: the sonoluminescence is quenched while the sonochemical yield increases with HCOOH concentration. By contrast, the concentration of formic acid has a relatively small effect on the intensity of C2 Swan band. It is concluded that C2 emission originates from CO produced by HCOOH degradation rather than from direct sonochemical degradation of HCOOH. The intensity of C2 band is much stronger at high ultrasonic frequency compared to 20 kHz ultrasound which is in line with higher yields of CO at high frequency. Another product of HCOOH sonolysis, carbon dioxide, strongly quenches sonoluminescence, most probably via collisional non-radiative...

The problem of correlation between the temperature of the target surface and the mass-spectromete... more The problem of correlation between the temperature of the target surface and the mass-spectrometer signal in laser-vaporization mass spectrometry has been analyzed theoretically. An approach based on statistical mechanics has been applied in order to describe the transient vaporization into vacuum of molecules effused from the area of the target surface struck by a laser pulse of moderate power density and time duration of some tens of ms (Langmuir vaporization). In particular, an expression for the intensity of the output signal of the mass spectrometer, I(l,t), has been derived as a function of the detection time, t, and of the distance, l, of the ionizing chamber of the spectrometer from the target. A simple numerical method for the calculation of I(l,t) according to the time profile of the target temperature is also provided. By fitting experimental I(t) values with the theoretical expression one can retrieve thermodynamic quantities involved in the sublimation/evaporation process of the molecular species analyzed, such as enthalpy and equilibrium vapor pressure (or, alternatively, vaporization coefficient). As an illustration, this fitting was performed on experimental measurements of pyrolytic graphite sublimation in the temperature range 3200-3700 K. The analysis developed will be useful for the interpretation of experimental datasets in order to retrieve hightemperature thermodynamic data, especially on high-melting materials. Research in this domain is being launched for nuclear materials, particularly for Generation IV advanced fuels.

The Journal of Physical Chemistry B, 2015

The multibubble sonoluminescence (MBSL) spectra of t-BuOH aqueous solutions submitted to power ul... more The multibubble sonoluminescence (MBSL) spectra of t-BuOH aqueous solutions submitted to power ultrasound at 20, 204, 362, and 613 kHz show emissions for the Δυ = −1 to Δυ = +2 vibrational sequences of C 2 * Swan system (d 3 Π g → a 3 Π u ). The Δυ=+2 emission overlaps with the CH(A−X) emission band. The maximal Swan band emission is observed when the MBSL of water itself is almost completely quenched. In general, MBSL is more intense at high-frequency compared to 20 kHz ultrasound. However, in the presence of Xe, the MBSL of C 2 * at 20 kHz is so bright that it can be seen by the unaided eye as a blue glow in the close vicinity of the ultrasonic tip. The intensity of the C 2 * band emission exhibits a maximum vs t-BuOH concentration: 0.1−0.2 M at 20 kHz and (1−8) × 10 −3 M at high-frequency ultrasound. Such a huge difference is attributed to a much smaller bubble size at high ultrasonic frequency or, in other words, to a much higher bubble surface/volume ratio providing more efficient saturation of the bubble interior with t-BuOH vapors and to the fact that high frequency bubbles remain active for many more cycles than 20 kHz ones, thus accumulating more hydrocarbon decomposition products. Simulation of the emission spectra using Specair software demonstrated the absence of thermal equilibrium for C 2 * radicals (T v > T r ), where T v and T r are the vibrational and the rotational temperature, respectively. In Ar, T v decreases with increasing t-BuOH concentration reaching a steady value in the concentration domain that corresponds to C 2 * emission maximum intensity. In the presence of Xe an extremely high T v is obtained, which is explained by the relatively low ionization potential of Xe providing a higher electron temperature of nonequilibrium plasma generated during bubble collapse. Analysis of the gaseous products of t-BuOH sonolysis reveals a significant sonochemical activity even at high t-BuOH concentration when MBSL is totally quenched, indicating that drastic conditions could be produced also within nonsonoluminescing cavitation bubbles.

Ultrasonics Sonochemistry, 2010

The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitr... more The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitric acid medium. In order to minimize the volume of radioactive waste it seems interesting to generate the reactive species in situ in such solutions using ultrasonic irradiation without addition of salt-forming reagents. This review summarizes for the first time the versatile sonochemical processes with uranium, neptunium and plutonium in homogeneous nitric acid solutions and heterogeneous systems. The dissolution of refractory solids, ultrasonically driven liquid-liquid extraction and the sonochemical degradation of the volatile products of organic solvent radiolysis issued from PUREX process are considered. Also the guidelines for required further work to ensure successful application of the studied processes at industrial scale are discussed.

The Journal of Physical Chemistry C, 2011

The Journal of Physical Chemistry B, 2013

This article focuses on the possibility of exciting some lanthanides (Ce 3+ , Tb 3+ , Gd 3+ , and... more This article focuses on the possibility of exciting some lanthanides (Ce 3+ , Tb 3+ , Gd 3+ , and Eu 3+ ) by ultrasound in aqueous solutions. Depending on the lanthanide ions and on the acoustic cavitation conditions (single-bubble or multibubble systems), the excitation mechanism is shown to be photoexcitation (e.g., for Ce 3+ ) or collision-induced excitation (e.g., for Tb 3+ ). The sonoluminescence of Tb 3+ is studied in detail at various ultrasonic frequencies, allowing quantification of the amount of quenching. The latter is much stronger in sonoluminescence than in photoluminescence due to the particular properties of acoustic cavitation. Complexation with citrate ions enhances manifold sonoluminescence of lanthanides due to reduction of intra-and inner-molecular quenching.

The Journal of Physical Chemistry A, 2012

The sonoluminescence (SL) spectra of OH-(A 2 Σ + ) excited state produced during the sonolysis of... more The sonoluminescence (SL) spectra of OH-(A 2 Σ + ) excited state produced during the sonolysis of water sparged with argon were measured and analyzed at various ultrasonic frequencies (20, 204, 362, 609, and 1057 kHz) in order to determine the intrabubble conditions created by multibubble cavitation. The relative populations of the OH-(A 2 Σ + ) v′ = 1−4 vibrational states as well as the vibronic temperatures (T v , T e ) have been calculated after deconvolution of the SL spectra. The results of this study provide evidence for nonequilibrium plasma formation during sonolysis of water in the presence of argon. At low ultrasonic frequency (20 kHz), a weakly excited plasma with Brau vibrational distribution is formed (T e ∼ 0.7 eV and T v ∼ 5000 K). By contrast, at highfrequency ultrasound, the plasma inside the collapsing bubbles exhibits Treanor behavior typical for strong vibrational excitation. The T e and T v values increase with ultrasonic frequency, reaching T e ∼ 1 eV and T v ∼ 9800 K at 1057 kHz.

The Journal of Physical Chemistry A, 2011

Spectroscopic studies of single-bubble sonoluminescence (SBSL) in water and aqueous sodium chlori... more Spectroscopic studies of single-bubble sonoluminescence (SBSL) in water and aqueous sodium chloride solutions with a defined concentration of argon were performed as a function of the driving acoustic pressure. The broad-band continuum ranging from 200 to 700 nm is characterized by fits using Planck's law of blackbody radiation. The obtained blackbody temperatures are in the range of 10 4 K and are revealed to be independent of the presence of a salt and the acoustic pressure, whereas the SL intensity increases by a factor of more than 10 within the studied acoustic pressure range. The different trends followed by SL intensity and blackbody temperatures question the blackbody model. In solutions with 70 mbar of argon, line emissions of OH • radicals and Na* are observed. The shape of the OH • radical emission spectrum is very similar to that in MBSL spectra, indicating the strong similarity of intrabubble conditions. An increase of the acoustic pressure causes the continuum to overlap the lines until they become indistinguishable. The emission line of Na* in NaCl is observed only at high NaCl concentrations. When sodium dodecylsulfate is used a pronounced Na* line is already observed in a 1 mM solution thanks to enrichment of sodium ions at the interface. The results presented in this work reveal the strong similarity of SBSL and MBSL under certain experimental conditions.

Journal of the American Ceramic Society, 2009

Although glass-RuO 2 composites are well known for their particular electrical properties, the re... more Although glass-RuO 2 composites are well known for their particular electrical properties, the reasons for their very low percolation thresholds are still subject to debate. In this paper, a detailed study of the influence of various experimental parameters (temperature, RuO 2 content, stirring, etc.) on the electrical conductivity and, in particular, on the percolation threshold in borosilicate glass-RuO 2 composites is presented. This percolation threshold is shown to increase by a factor of two (from 0.6 to 1.2 vol%) when stirring is applied during synthesis and by more than a factor of three (42.1 vol%) when a sol-gel route is used. Besides, the study of various synthesis temperatures reveals that the electronic part of the electrical conductivity is highly correlated to Ru solubility in the glass matrix. It can be concluded from these various experiments that both the presence of dissolved ruthenium in the glass matrix and the possibility of RuO 2 particles to rearrange in the melt in order to form kind of a network are necessary for a low percolation threshold. J ournal J. Am. Ceram. Soc., ]] []]] 1-7 (2009)

A Knudsen cell-mass spectrometer facility to investigate oxidation and vaporisation processes in nuclear fuel

Journal of Nuclear Materials, 2005

ABSTRACT Vaporisation processes in uranium oxide fuel were investigated under controlled oxidatio... more ABSTRACT Vaporisation processes in uranium oxide fuel were investigated under controlled oxidation conditions. A Knudsen cell with a mass spectrometer was adapted to feed an adjustable oxygen flux up to temperatures of 1900K producing an oxygen pressure in the cell ranging up to 1000Pa. Experiments were carried out on fresh and irradiated fuels, both pre-oxidised to U3O8 or oxidised online in the Knudsen cell, to measure effects associated with fuel sublimation in the form of different uranium-bearing oxides. Mass spectrometry, electromotive force measurements and thermo-gravimetric analysis were used to determine the vapour equilibrium conditions at fixed free oxygen potentials.

Journal of Nuclear Materials, 2010

An original approach to immobilize ruthenium species and then transform them into RuO 2 nanoparti... more An original approach to immobilize ruthenium species and then transform them into RuO 2 nanoparticles is presented that uses hybrid-functionalized glasses. First, different chemical graftings of functional groups (acetylacetonate, amine, nitrile, pyridine and thiol) in porous glass were used to extract ruthenium-containing complexes ([Ru(CH 3 N) 4 Cl 2 ] and Ru(NO)(NO 3 ) 3 ) from solutions. The best functional groups to selectively coordinate Ru complexes and thus extract it from the solutions have been determined. Then, the obtained Ru-containing composite glass was heated under air to remove the organic species and to obtain RuO 2 nanoparticles inside a glass with centimetre scale geometric form. The as-obtained materials were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), nitrogen physisorbtion measurements, elemental analysis and X-ray diffraction (XRD).

Advances in the mass spectrometric study of the laser vaporization of graphite

Journal of Applied Physics, 2008

ABSTRACT Reliable experimental data on graphite vaporization and especially on carbon vapor compo... more ABSTRACT Reliable experimental data on graphite vaporization and especially on carbon vapor composition exist only up to 2500–3000 K. Data measured at higher temperatures are questionable due to several experimental limitations, such as the difficult temperature determination and the not straightforward correlation of measured temperatures and intensities of signals in mass spectra. That is why a new method of high-temperature mass spectrometry with laser vaporization was developed, in order to extend the accessible temperature range while overcoming these limitations and to shed more light on the still poorly known behavior of carbon at high temperatures. Thus, carbon sublimation relative partial pressures of the species C1, C2, C3, C4, and C5 were measured up to 4100 K. Moreover, the values of the relative vaporization coefficients of C1, C2, C3, C4, and C5, estimated by comparison of the experimentally obtained partial pressures with the predicted equilibrium ones, are proposed.

Journal of Applied Physics, 2011

Due to the chemically unstable nature of uranium dioxide its vapour composition at very high temp... more Due to the chemically unstable nature of uranium dioxide its vapour composition at very high temperatures is, presently, not sufficiently studied though more experimental knowledge is needed for risk assessment of nuclear reactors. We used laser vaporisation coupled to mass spectrometry of the produced vapour to study urania vapour composition at temperatures in the vicinity of its melting point and higher. The very good agreement between measured melting and freezing temperatures and between partial pressures measured on the temperature increase and decrease indicated that the change of stoichiometry during laser heating was very limited. The evolutions with temperature (in the range 2800-3400 K) of the partial pressures of the main vapour species (UO 2 , UO 3 and UO 2 + ) were compared with theoretically predicted evolutions for equilibrium non-congruent gas-liquid and gas-solid phase coexistence and showed very good agreement. The measured main relative partial pressure ratios around 3300 K all agree with calculated values for total equilibrium between condensed and vapour phase. It is the first time the three main partial pressure ratios above stoichiometric liquid urania are measured at the same temperature under conditions close to equilibrium non-congruent gas-liquid phase coexistence.

Thermodynamics of Refractory Nuclear Materials Studied by Mass Spectrometry of Laser-Produced Vapors

International Journal of Thermophysics, 2005

ABSTRACT A new method of high-temperature mass spectrometry (MS) with laser-induced vaporization ... more ABSTRACT A new method of high-temperature mass spectrometry (MS) with laser-induced vaporization (LIV) has been developed. The initial problem of LIV MS, consisting of an inadequate correlation between the temperature of the surface and the MS signal, was successfully overcome.The method was developed on graphite, of which fast time-resolved MS measurements (ca. 20ms) were performed over a large mass interval; the influence of geometrical parameters and of the laser pulse length on MS measurements was studied. Carbon sublimation relative partial pressures of C1, C2, C3, and C5 were measured up to 3810 K. This corresponds to a total pressure of about 0.8bar estimated independently by the integral mass flux using the Hertz–Knudsen equation. The vaporization of UO2 was studied at temperatures above ≈ 2500 K, where conventional Knudsen-cell mass spectrometry cannot be applied. The vaporization enthalpy obtained for the main species in UO2 vapor was in good agreement with that of conventional mass spectrometry.