A comprehensive protocol for chemical analysis of flame combustion emissions by secondary ion mass spectrometry

International audienceRATIONALE. Time of flight secondary ion mass spectrometry (ToF-SIMS) is used to provide detailed information on the surface chemical composition of soot. An analytical protocol is proposed and tested on a laboratory flame, and the results are compared with our previous measurements provided by two-step laser mass spectrometry (L2MS). METHODS. This work details: (1) the development of a dedicated apparatus to sample combustion products from atmospheric flames and deposit them on substrates suitable for ToF-SIMS analysis; (2) the choice of the deposition substrate and the material of the sampling line, and their effect on the mass spectra; (3) a method to separate the contributions of soot and condensable gas based on impact deposition, and finally (4) the post-acquisition data processing. RESULTS. Compounds produced during flame combustion are detected on the surface of different deposition substrates and attributed a molecular formula based on mass defect analysis. Silicon and titanium wafers perform similarly, while the surface roughness of glass microfiber filters results in a reduced mass resolution. The mass spectra obtained from the analysis of different locations of the deposits obtained by impaction show characteristic patterns that are attributed to soot/condensable gas. CONCLUSIONS. A working method for the analysis of soot samples and the extraction of useful data from mass spectra is proposed. This protocol should help avoiding common experimental issues like sample contamination, while optimizing the setup performance by maximizing the achievable mass resolution

Application of ToF-SIMS for sulfur isotopic fractionation in sulfide phases of iron corrosion layers: determination of bacterial impact on the formation of these phases

International audienceTo a better understanding of the iron corrosion mechanisms, it is crucial to elucidate the role of bacteria. Thus, in order to have a diagnosis of the action of bacteria in the iron corrosion, the objective of this study is to determine by ToF-SIMS the isotopic sulfur fractionation δ 34 S in iron sulfides of (sub)micrometric size located in the corrosion product layers of the ferrous objects corroded in anoxic soils and marine environment. These iron sulfides may have two origins: an abiotic origin resulting in the dissolution/reprecipitation of sulfides from the surrounding medium (for example from pyrite in a soil) or a biotic origin by the action of the sulfate-reducing bacteria that reduce sulfate ions into sulfides leading to the formation of iron sulfides with ferrous ions issued from the aqueous dissolution of metal iron. A difference in the isotopic sulfur fractionation δ 34 S in the sulfur phases according to the abiotic or biotic origin of these phases is reported in the literature. Thus in this study, the isotopic sulfur fractionation δ 34 S in the iron sulfides formed in the corrosion product layers of iron was determined to identify the formation origin of these phases and the role of bacteria in the iron corrosion. After characterization of the distribution of the different iron sulfides within the layers (optical microscopy, SEM-EDS, μRaman spectroscopy), the local isotopic fractionation of sulfur is measured by the imaging and spectroscopy ToF-SIMS technique. Some important results have been obtained. First of all, the reproducibility and the accuracy of the method were established by the choice and the validation of a hydrothermal pyrite sample calibrated relatively to the international sulfur isotopic standard Canon Diablo Troilite. Secondly, it was observed that there was no or little variation in the isotopic sulfur fractionation δ 34 S with the degree of oxidation of sulfur. Finally, a noticeable difference in the isotopic sulfur fractionation δ 34 S between iron sulfides formed in laboratory under abiotic or biotic conditions was evidenced: δ 34 S is close to 0 in abiotic conditions whereas in biotic conditions it is shifted from 0 with values up to up to some tens per mil. These first results being promising, the study is actually in progress to determine the formation origin (abiotic/biotic) of the Fe-S present in the corrosion product layers of natural systems of iron corrosion, from soils, subaquatic and marine environments

Caractérisation de la charge d'espace aux joints de grains du spinelle MgAI2O4 (influence possible sur la superplasticité)

La déformation superplastique à hautes températures des céramiques polycristallines procède principalement par glissement aux joints de grains accommodé par la diffusion. On observe alors une vitesse de déformation reliée linéairement à la contrainte. Cependant, lorsque la taille de grain est faible (<1 m) , on constate à basses contraintes une diminution anormale de la vitesse de déformation. On parle alors de réaction d'interface et ce sont les processus d'émission et d'annihilation des défauts aux joints de grains qui contrôlent la vitesse de fluage. Dans les matériaux ioniques, les défauts étant chargés, la présence d'une charge d'espace peut expliquer un tel phénomène L'objectif de la thèse est de valider cette hypothèse pour le spinelle MgAl2O4. Pour cela, nous avons étudié la chimie des interfaces du spinelle à l'aide d'un MET associé à la microanalyse EDS. Nous avons mis en évidence un excès de lacunes de magnésium (de charge négative) dans le joint de grains. L'électroneutralité d'ensemble du matériau impose la présence d'une charge d'espace positive adjacente au joint de grains. La confrontation de nos résultats expérimentaux avec les équations théoriques de répartition de charge d'espace a permis d'évaluer la différence de potentiel entre le coeur des grains et la surface à 137 mV. Pour estimer l'influence possible d'une telle différence de potentiel, nous avons réalisé une étude du comportement thermomécanique du spinelle sous champ électrique. Nous avons constaté une augmentation des vitesses de croissance granulaire et de fluage lorsque l'échantillon est soumis à une différence de potentiel. Les mécanismes élémentaires de cet accroissement agissent tout comme la charge d'espace au niveau de l'interface grain/joint de grains en modifiant la cinétique de création et d'annihilation de défauts.LILLE1-BU (590092102) / SudocSudocFranceF

ToF-SIMS investigation of absorption of lead and bismuth in T91 steel deformed in liquid lead bismuth eutectic

International audienceThe time of flight secondary ion mass spectroscopy (ToF-SIMS) technique was employed to investigate the interaction of liquid lead-bismuth eutectic (LBE) atoms with the surface and subsurface of a T91 steel taking into account the contribution of plastic deformation. It is shown that both Pb and Bi can penetrate the steel network only in plastically deformed material. No microstructural interface (lath boundaries, grain boundaries...) was found to be preferential site for trapping Pb and Bi but clustering with molybdenum has been identified. Pb seems to be easier adsorbed than Bi because of its higher affinity with oxygen

ToF-SIMS analyses of brittle crack initiation of T91 steel by liquid sodium

International audienceTempering the martensitic T91 steel at 550 °C instead of 750 °C (recommended heat treatment) makes T91 more sensitive to liquid metal embrittlement. Especially, in liquid sodium, T91 tempered at 550 °C exhibited a brittle fracture while it was ductile in air. Liquid sodium initiated an intergranular crack which then propagated by transgranular mode in the bulk of the specimen. ToF-SIMS analyses were performed on dedicated Small Punch Test specimens in order to distinguish the contribution of the mechanical loading from the sodium environment. Controlled elastic or plastic deformations on pre immersed (503 °C during 169 h) and on as received materials were performed in liquid sodium at 450 °C. Sodium penetration at prior austenitic grains boundaries and at laths boundaries has been pointed out by TOF-SIMS. It is concluded that the sodium penetration requires plastic deformation

Une étude combinée XPS et ToF-SIMS pour une meilleure compréhension de la réactivité du formaldéhyde adsorbé à la surface d'une birnessite

National audienc

New preparation techniques for molecular and in-situ analysis of ancient organic micro- and nanostructures

Organic microfossils preserved in three dimensions in transparent mineral matrices such as cherts/quartzites, phosphates, or carbonates are best studied in petrographic thin sections. Moreover, microscale mass spectrometry techniques commonly require flat, polished surfaces to minimize analytical bias. However, contamination by epoxy resin in traditional petrographic sections is problematic for the geochemical study of the kerogen in these microfossils and more generally for the in situ analysis of fossil organic matter. Here, we show that epoxy contamination has a molecular signature that is difficult to distinguish from kerogen with time-of-flight secondary ion mass spectrometry (ToF-SIMS). This contamination appears pervasive in organic microstructures embedded in micro- to nano-crystalline carbonate. To solve this problem, a new semi-thin section preparation protocol without resin medium was developed for micro- to nanoscale in situ investigation of insoluble organic matter. We show that these sections are suited for microscopic observation of Proterozoic microfossils in cherts. ToF-SIMS reveals that these sections are free of pollution after final removal of a <10 nm layer of contamination using low-dose ion sputtering. ToF-SIMS maps of fragments from aliphatic and aromatic molecules and organic sulfur are correlated with the spatial distribution of organic microlaminae in a Jurassic stromatolite. Hydrocarbon-derived ions also appeared correlated with kerogenous microstructures in Archean cherts. These developments in analytical procedures should help future investigations of organic matter and in particular, microfossils, by allowing the spatial correlation of microscopy, spectroscopy, precise isotopic microanalyses, and novel molecular microanalyses such as ToF-SIMS

Detection of formaldehyde oxidation catalysis by MCR-ALS analysis of multiset ToF-SIMS data in positive and negative modes

International audienc

Combining sorption experiments and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) to study the adsorption of propranolol onto environmental solid matrices – Influence of copper(II)

International audienceThe bioavailability of pharmaceuticals is governed by their sorption in soils/sediments, as the retention processes determine their concentration in surface- and ground-water. The adsorption of these contaminants can involve various solid components such as organic matter, clays and metallic oxides, and their distribution among these solid components depends on contaminant and solid properties. In this paper we studied the adsorption of the pharmaceutical propranolol – a beta-blocker – on eight different solids (six soils, one sediment and one kaolinite-based sample) by batch experiments. The influence of contact time, propranolol concentration and pH was considered, as well as the presence of copper(II). The investigated solids displayed a wide variability in terms of CEC (cationic exchange capacity) and organic carbon and carbonates contents. The influence of pH was negligible in the pH range from 5.5 to 8.6. The adsorbed amounts were greatly dependent on the solid and two groups of solids were evidenced: three soils of high CEC and organic carbon contents which retained high amounts of propranolol, and three soils, the sediment and the kaolinite-based sample (low CEC and organic carbon content) displaying a low adsorption capacity for the beta-blocker. A linear model enabling the determination of the sorption parameters Kd and Koc was pertinent to describe the adsorption isotherms but the Koc values showed a great variability. It was shown that organic carbon content alone could not explain propranolol adsorption. The CEC value was identified as influent parameter and a simple empirical model was proposed to describe propranolol adsorption. At microscopic and molecular scales, ToF-SIMS experiments indicated (i) a decrease of potassium on the surface upon propranolol adsorption with a distribution of the beta-blocker similarly to alumino-silicates, iron and organic carbon on the surface confirming a cation exchange mechanism and (ii) the absence of degradation products and copper-propranolol complexes

Highly Active Noble-Metal-Free Copper Hydroxyapatite Catalysts for the Total Oxidation of Toluene

International audienceHydroxyapatite (Hap) supported Cu materials prepared by the wet impregnation method were designed as noble‐metal‐free catalysts for the total oxidation of toluene. Cu/Hap materials with different Cu loadings (2.5–20 wt %) calcined at 400 °C were characterized by using inductively coupled plasma optical emission spectroscopy, N2 physisorption, XRD, Raman spectroscopy, IR spectroscopy, X‐ray photoelectron spectroscopy, and time‐of‐flight secondary ion MS. The tenorite CuO phase was detected in all materials, and the libethenite Cu2(PO4)OH phase was observed for the sample with 20 wt % Cu. The presence of libethenite was accompanied by the formation of Ca2CO3H+ ions at the Hap surface. Residual NO3− species that interact with Cu and Ca were also found, and their amount increased with the increase of the Cu content in the sample. Interestingly, the specific activity in the total oxidation of toluene increased with the decrease of the Cu content in the catalyst. The rate per mole of Cu was increased by 10 times if the Cu content was decreased by four times. This noticeable result could be related to the presence of acid sites with a moderate strength as well as finely dispersed CuO species on the Hap, which allow the activation of toluene molecules and their oxidation through a redox mechanism. Moreover, Cu2.5 wt %/Hap showed a remarkably stable catalytic performance for 45 h time‐on‐stream, which evidences that this material has a high potential for applications in the removal of volatile organic compounds