Wechselwirkung von dreiwertigen Lanthaniden und Actiniden mit Aluminiumoxiden und -hydroxiden

Die vorliegende Arbeit beschäftigt sich mit der Wechselwirkung von dreiwertigen Lanthaniden und Actiniden (Eu(III), Gd(III) und Cm(III)) mit den Aluminiumoxid/-hydroxidphasen Korund/Saphir (alpha-Al2O3), Gibbsit (alpha-Al(OH)3) und Bayerit (beta-Al(OH)3) sowie den Al-Polyoxokationen „Al13“ (Al13O4(OH)24(H2O)127+) und „GaAl12“ (GaO4Al12(OH)24(H2O)127+). Die Ergebnisse sollen zu einem besseren Verständnis der Wechselwirkungen von Radionukliden an der Wasser-Mineralphasen-Grenzfläche im Nah- und Fernfeld eines nuklearen Endlagers in tiefen geologischen Formationen beitragen, wobei die Retention insbesondere durch Sorptions- und Einbaureaktionen an/in Mineralphasen beeinflusst wird. Batch-Untersuchungen zur Wechselwirkung von Eu(III) mit den Mineralphasen Korund (alpha-Al2O3) und Bayerit (beta-Al(OH)3) zeigen im Bereich niedriger Metallkonzentrationen ([M(III)] ~ 1E-7 M) ähnliche oberflächennormierte logKd-Werte, was auf die Existenz sehr ähnlicher Oberflächengruppen und damit auf die Bildung von hydroxidischen Strukturen auf der Aluminiumoxidoberfläche zurückgeführt werden kann. Ähnliche logKd-Werte wurden in früheren Untersuchungen auch für die Sorption von Eu(III) an gamma-Al2O3 beschrieben. TRLFS-(time resolved laser fluorescence spectroscopy)-Untersuchungen zur Sorption von Cm(III) an Korund und Bayerit zeigen eine ähnliche Cm(III)-Speziation, wobei im pH-Bereich 3 < pH < 13 drei sorbierte Cm(III)-Spezies voneinander unterschieden werden können ([Oberfläche-Cm(OH)x(H2O)5-x]3-x mit x = 0, 1, 2). Vergleichbare Cm(III)-Spezies werden anhand von spektroskopischen Befunden auch auf den Oberflächen der Saphir (001)-Einkristalle sowie den Al(III)-Clustern „Al13“ und „GaAl12“ angenommen. Im Fall von Gibbsit führt der hohe isoelektrische Punkt zu einer erst bei pH 5.5 beginnenden M(III)-Sorption, wobei eine Cm(III)-Spezies der Art Gibbsit-Cm(H2O)5 übersprungen wird und sich wahrscheinlich direkt der erste Cm(III)-Hydrolysekomplex ausbildet. Weiter kann eine in kleinen Konzentrationen vorliegende, eingebaute Cm(III)-Spezies nachgewiesen werden, deren Bildung durch Al(OH)3-Ausfällung als Folge einer - bezüglich der Löslichkeit von kristallinem Gibbsit - übersättigten Suspension ermöglicht wird. Mit Ausnahme der Saphir (110)-Oberfläche weisen die TRLFS-Ergebnisse damit auf eine ähnliche Koordination des Metallkations an den Oberflächen der Aluminium(hydr)oxide hin. In Übereinstimmung dazu können anhand von Gd(III)-EXAFS-Untersuchungen ähnliche M(III)-Bindungsplätze auf Oberflächen von Gibbsit, Bayerit und Korund bestimmt werden. Im Fall von Gibbsit und Bayerit ist eine M(III)-Sorption sowohl an die Basal-, wie auch an die Kantenflächen möglich, wobei das Metallkation über zwei oder drei Aluminolgruppen an die Oberflächen gebunden wird (bi- bzw. tridentate Koordination). Eine entsprechende Zuordnung ist für Korund aufgrund der sphärischen Morphologie der Aluminiumoxidpartikel ohne die Ausbildung definierter Kristallflächen nicht möglich. Die Ergebnisse der EXAFS-Untersuchungen zeigen weiter, dass die Metallionen offensichtlich an unterschiedliche Oberflächenplätze gebunden werden können, so dass von mehreren nebeneinander vorliegenden M(III)-Oberflächenspezies ausgegangen werden kann. Zusammenfassend zeigen die im Rahmen dieser Arbeit erhaltenen Ergebnisse, dass eine Kombination verschiedener Untersuchungsmethoden die Aufklärung der Prozesse, die (dreiwertige) Kationen an der Wasser-Aluminium(hydr)oxid-Grenzfläche eingehen können, erleichtert. So können mit Hilfe der Cm(III)-TRLFS unterschiedliche M(III)-Oberflächenspezies an den verschiedenen Aluminium(hydr)oxid-Phasen bestimmt werden, während die EXAFS-Untersuchungen den Metallkationen definierte Bindungsplätze zuordnen. Jedoch weisen die Ergebnisse darauf hin, dass die Existenz verschiedener, in unterschiedlicher Koordination vorliegender M(III)-Oberflächenspezies wahrscheinlich ist. Weiter können neben Sorptionsreaktionen auch Einbaureaktionen in (amorphe) Al(OH)3-Festphasen nachgewiesen werden

Rapport final du projet européen CatClay sur les processus de migration des cations dans les roches argileuses indurées

International audienceIn the framework of the feasibility studies on the radioactive waste disposal in deep argillaceous formations, it isnow well established that the transport properties of solutes in clay rocks, i.e. parameter values for Fick’s law, are mainlygoverned by the negatively charged clay mineral surface. While a good understanding of the diffusive behaviour of non-reactiveanionic and neutral species is now achieved, much effort has to be placed on improving understanding of coupledsorption/diffusion phenomena for sorbing cations. Indeed, several cations known to form highly stable surface complexes withsites on mineral surfaces migrate more deeply into clay rock than expected. Therefore, the overall objective of the EC CatClayproject is to address this issue, using a ‘bottom-up’ approach, in which simpler, analogous systems (here a compacted clay,‘pure’ illite) are experimentally studied and modelled, and then the transferability of these results to more complex materials, i.e.the clay rocks under consideration in France, Switzerland and Belgium for hosting radioactive waste disposal facilities, isverified. The cations of interest were chosen for covering a representative range of cations families: from a moderately sorbingcation, the strontium, to three strongly sorbing cations, Co(II), Zn(II) and Eu(III). For the 4 years of this project, much effort wasdevoted to developing and applying specific experimental methods needed for acquiring the high precision, reliable data neededto test the alternative hypotheses represented by different conceptual-numerical models. The enhanced diffusion of the sorbingcations of interest was confirmed both in the simpler analogous illite system for Sr2+, Co(II) and Zn(II), but also in the naturalclay rocks, except for Eu(III). First modelling approach including diffusion in the diffuse double layer (DDL) promisinglysucceeded in reproducing the experimental data under the various conditions both in illite and clay rocks, even though someassumptions made have to be verified. In parallel, actual 3D geometrical pore size distributions of compacted illite, and in lessextent, clay rock samples, were successfully determined by combining TEM and FIB-nt analyses on materials maintained in awater-like saturation state by means of an extensive impregnation step. Based on this spatial distribution of pores, first numericaldiffusion experiments were carried at the pore scale through virtual illite, enabling a better understanding of how transferpathways are organized in the porous media. Finally, the EC CatClay project allowed a better understanding of the migration ofstrongly sorbing tracers through low permeability ‘clay rock’ formations, increasing confidence in our capacity to demonstratethat the models used to predict radionuclide migration through these rocks are scientifically sound

Measurement of anisotropic diffuse scattering with synchrotron radiation

Anisotropic diffuse scattering of the 1D conductor K-hollandite has been measured at a synchrotron source and compared with measurements with a rotating anode. The intensity gain of more than one order of magnitude and the ability to adjust the wavelength provide the counting statistics in a few hours that are necessary for a quantitative analysis of diffuse phenomena. The main advantage of a synchroton source is the high resolution throughout reciprocal space (low and high Q). Thus, commensurate/incommensurate positions of diffuse layers may be distinguished, weak diffuse maxima become detectable and small peak shifts of diffuse modulations clearly visible

NEAR INFRARED PHOTOLUMINESCENCE OF THE HYDROGENATED AMORPHOUS SILICON THIN FILMS WITH IN-SITU EMBEDDED SILICON NANOPARTICLES

The intrinsic hydrogenated silicone layers with embedded silicon nanoparticles were grown in-situ at 250°C on glass substrates by the radio frequency plasma enhanced chemical vapor deposition (CVD) from silane highly diluted in hydrogen. The changes in the optical absorption coefficient were detected by the photothemal deflection spectroscopy (PDS). The transition from amorphous to crystalline phase for samples deposited at 5−6% silane concentration correlates to the crystalline volume fraction about 50% as detected by Raman spectroscopy and the high resolution transmission electron microscopy (HRTEM). The room temperature photo-luminescence increases significantly with increased crystallinity volume fraction but diminishes abruptly when crystallinity volume fraction exceeds above 80%. The photoluminescence intensity strongly correlates with the presence of isolated silicon nanoparticles in the mixed amorphous and crystalline phase. The strongest photoluminescence was found in the sample with mixed phase of amorphous matrix and isolated silicon nanoparticles and the crystalline volume fraction about 50%

2D kovový wolfram

2D metallic material is an important group member in 2D material family. Many applications have been applied in the catalysis and devices. In this paper, we present a novel method to prepare the tungsten 2D material, which is simple and powerful. The W thin film is deposited via magnetron sputtering. As-deposited tungsten thin film is able to be exfoliated with wet and dry methods. We show a clear layered structure of the tungsten thin film from the cross sectional view. Via the exfoliation, an large area 2D tungsten monolayer is obtained. After oxidation, the 2D material shows potentials in electric signal transport.2D kovový materiál je důležitým členem skupiny ve skupině 2D materiálů. Mnoho aplikací bylo použito v katalýze a v dalších zařízeních. V tomto příspěvku představujeme novou metodu přípravy wolframového 2D materiálu, která je jednoduchá a výkonná. Tenký film W je nanášen magnetronovým rozprašováním. Takto nanesený tenký film wolframu lze odlupovat mokrými a suchými metodami. V řezu vrstvou presentujeme jasnou vrstvenou strukturu wolframového tenkého filmu. Prostřednictvím exfoliace se získá velkoplošná 2D monovrstva wolframu. Po oxidaci ukazuje je 2D materiál slibný v přenosu elektrického signálu

The Effect of Monovalent Electrolytes on the Deprotonation of MAl12 Keggin Ions

We study the deprotonation of MAl12 Keggin ions in monovalent electrolyte solutions of varying composition and concentration by potentiometric titration. The structures exhibit very steep deprotonation, where the singly coordinated aquo groups lose protons within a narrow pH range. Once the deprotonation is substantial, the Keggin ions start to aggregate by dehydration and linkage of terminal functional groups into hydroxo-bridges. In the present study, we address three aspects with our experiments. We test the cation-specificity, the anion-specificity and the overall effect of electrolyte concentration with respect to the deprotonation behavior. Our results show that the cation series in chloride systems does not show any ion-specificity and all the curves coincide for the 100&nbsp;mM solutions, whereas the anion series in sodium systems does. The most structure-making anion (bromate) used in this study causes aggregation of the Keggins prior to the onset of aggregation in the presence of border-line and structure-breaking anions (chloride, nitrate and perchlorate). For the latter, no significant difference is observed. The fluoride ion causes a completely different behavior. No significant deprotonation pH effect is observed where deprotonation occurs in the absence of fluoride. At even higher pH, massive consumption of hydroxide occurs. Some possible scenarios for the behavior of the fluoride-containing systems are discussed

The Effect of Monovalent Electrolytes on the Deprotonation of MAl12 Keggin Ions

We study the deprotonation of MAl Keggin ions in monovalent electrolyte solutions of varying composition and concentration by potentiometric titration. The structures exhibit very steep deprotonation, where the singly coordinated aquo groups lose protons within a narrow pH range. Once the deprotonation is substantial, the Keggin ions start to aggregate by dehydration and linkage of terminal functional groups into hydroxo-bridges. In the present study, we address three aspects with our experiments. We test the cation-specificity, the anion-specificity and the overall effect of electrolyte concentration with respect to the deprotonation behavior. Our results show that the cation series in chloride systems does not show any ion-specificity and all the curves coincide for the 100&nbsp;mM solutions, whereas the anion series in sodium systems does. The most structure-making anion (bromate) used in this study causes aggregation of the Keggins prior to the onset of aggregation in the presence of border-line and structure-breaking anions (chloride, nitrate and perchlorate). For the latter, no significant difference is observed. The fluoride ion causes a completely different behavior. No significant deprotonation pH effect is observed where deprotonation occurs in the absence of fluoride. At even higher pH, massive consumption of hydroxide occurs. Some possible scenarios for the behavior of the fluoride-containing systems are discussed. 1