Redox Couples

TMPD shows promising behaviors as positive redox couple for flow batteries. The solubility (5 M) is greatly enhanced by elimination of hydrogen bonding. The redox stability is improved by shielding effect from methyl substitution. TMPD is electrochemically/chemically stable to give an excellent cycle performance.

Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.

Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C-H bonds as well as the aziridination of olefines. We report on the synthesis of the trigonal imido iron complexes [Fe(NMes)L 2 ] 0,À (L ¼ -N{Dipp}SiMe 3 ); Dipp ¼ 2,6-diisopropyl-phenyl; Mes ¼ (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN 3 ) with the linear iron precursors [FeL 2 ] 0,À . UV-vis-, EPR-, 57 Fe M össbauer spectroscopy, magnetometry, and computational methods suggest for the reduced form an electronic structure as a ferromagnetically coupled iron(II) imidyl radical, whereas oxidation leads to mixed iron(III) imidyl and electrophilic iron(II) nitrene character. Reactivity studies show that both complexes are capable of H atom abstraction from C-H bonds. Further, the reduced form [Fe(NMes)L 2 ] À reacts nucleophilically with CS 2 by inserting into the imido iron bond, as well as electrophilically with CO under nitrene transfer. The neutral [Fe(NMes)L 2 ] complex shows enhanced electrophilic behavior as evidenced by nitrene transfer to a phosphine, yet in combination with an overall reduced reactivity.

2,3-Dichloro-5,6-dicyanobenzoquinone (DDQ) is an electrochemical oxidation catalyst for a secondary amine, a model system for virtual hydrogen storage by removal of a hydrogen equivalent from an amine; a computational study provides mechanistic information.

Resumen. La seda del hilo de seguridad de araña es un material muy atractivo por sus excelentes propiedades mecánicas, por producirse de forma respetuosa con el medio ambiente y por ser biodegradable. Este material presenta una propiedad singular conocida como supercontracción: si se toma una fibra de seda obtenida por hilado forzado y se sumerge en agua permitiendo libremente el acercamiento de sus extremos, se produce un acortamiento de la longitud de la fibra hasta un 50%. Aún sin llegar a la inmersión en agua, el aumento de la humedad ambiental en un cierto intervalo también induce una fuerza de contracción. En este trabajo se estudia esta fuerza y su evolución en el tiempo para diversos valores de humedad relativa. La especie de araña empleada es Argiope trifasciata.

The tensile properties of the viscid silk of the spider Argiope trifasciata have been characterized. The tensile behaviour of viscid silk and the other constituent of the web, drag line silk, have been compared. All fibers have been retrieved from a single web, and characterized from tensile tests. The morphology of the fibers has been analysed from scanning electron microscope micrographs. Measured cross sectional areas have been used to re-scale force into stress. The viscid silk presents an elastomeric behaviour, although its tensile strength exceeds that of artificial fibers.

En el presente trabajo se estudia la influencia de la radiación UV sobre las propiedades mecánicas y las superficies de fractura de un polímero artificial bioinspirado en la seda de araña. Las fibras de seda de araña constituyen un material enormemente atractivo ya que su elevada resistencia y deformabilidad lo convierten en el material con mayor trabajo hasta rotura de los conocidos hasta el momento. Además se ha encontrado que posee una elevada biocompatibilidad y un comportamiento biodegradable. Debido a estas ...

Resumen. Se han estudiado las propiedades mecánicas del hilo víscido de la especie Argiope trifasciata, analizando su capacidad de absorción y disipación de la energía mecánica y el efecto del recubrimiento adherente, mediante ensayos de tracción simple hasta rotura y ciclos de carga y descarga. Así mismo, se han dado los primeros pasos en el análisis del estado de deformación y tensional de estos hilos en las telarañas. El estudio de la estuctura del material en estado original y después de eliminar el recubrimiento ...

A standardized and versatile electrochemical batch reactor that has wide applicability in both organic and inorganic synthesis and analytical electrochemistry has been developed. A variety of synthetic electrochemical transformations have been performed to showcase the versatility and demonstrate the reactor, including the synthesis of five Cu(I)-NHC, two Au(I)-NHC and one Fe(II)-NHC complex, as well as an Fe(III)-salen complex. The reactor is based on a commercially available vial with an adapted lid, making it inexpensive and highly flexible. It features a fixed interelectrode distance which is crucial for reproducibility, along with the ability to accommodate a variety of interchangeable electrode materials. The reactor has also been used in conjunction with a parallel plate allowing rapid screening and optimization of an organic electrochemical transformation. Cyclic voltammetry has been performed within the reactor on a range of imidazolium salt analytes with the use of an external potentiostat. The ability to use this reactor for both analytical and synthetic organic and inorganic chemistry is enabled by a flexible and characterizable design.

En las últimas décadas, ha existido un creciente interés por la fabricación, síntesis y preparación de nanopartículas bimetálicas (compuestas por dos elementos metálicos diferentes). Al combinar dos metales en estos nanomateriales, su desempeño muchas veces supera las propiedades asociadas con sus contrapartes monometálicas, y cambiando sus componentes y morfologías se puede modificar exitosamente su desempeño físico, eléctrico o químico. Ampliando de esta manera su campo de aplicación a áreas tales como administración de fármacos, óptica-electrónica, biosensores, separación química, materiales, biotecnología, nanoactuadores, bioimagen y bioterapia. La versatilidad de poder entender cómo combinar distintos elementos metálicos, en diferentes proporciones, a nivel nanométrico y de forma controlada, constituye un nuevo paradigma en la ingeniería de nanomateriales.

En el presente trabajo se analiza la modificación de la topografía de una púa escarificadora (SAE 1045) inspirada en la cutícula del bicho toro (Diloboderus abderus), con el objetivo de reducir la adherencia del suelo a la misma. Por tal motivo, se reportan los resultados experimentales de diferentes pruebas de campo, que corresponden a púas con distintas distribuciones geométricas de cavidades en su superficie. Asimismo, se investigó la evolución de la mojabilidad con el tiempo de ataque químico, con la finalidad de generar distintas jerarquías de rugosidades, imitando el efecto lotus.The present work analyses the modification of the topography of a plowshare (SAE 1045) inspired in the cuticle of a beetle called Diloboderus abderus, with the objective of reducing soil adhesion. Therefore, experimental results of different field tests corresponding to several plowshares with different geometric distributions of cavities are reported. Also, the evolution of wettability with time of e...

En el presente trabajo se analiza la modificación de la topografía de una púa escarificadora (SAE 1045) inspirada en la cutícula del bicho toro (Diloboderus abderus), que habita en nuestro suelo, con el objeto de reducir la adherencia del suelo. Por tal motivo, se reportan resultados experimentales de pruebas de campo que corresponden a una dada distribución geométrica de cavidades.

The electrochemical reduction of the complexes [CpNi(PR,),]', where R = C2H5, C3H7, C,H, or C6H5, [CpNi(diphos)]' and [CpNi(diars)]' in acetonitrile .is described and the data are compared with those for the complexes CpzNi, [Ni(PR3),]*+ and Ni(diphos)z'. In recent years there has been an increasing interest in the chemistry of nickel(I), for example its role as a catalyst in organic reactions (for review see ref. 1). In particular, it has been shown that, in aprotic media, a wide variety of ligands are able to stabilise (in both a thermodynamic and kinetic sense) this lower oxidation state of nickel. This paper describes the reductive electrochemistry of the complexes [CpNi(PR3),]', where R = C2HS, C3H7, C4H9 and CsHs, [CpNi(diphos)]' and [CpNi(diars)]' in acetonitrile and compares the data with that for nickelocene [2,3] and the nickel phosphine complexes [Ni(PR3)4]2+ and Ni(diphos),]*' [4,5].

Widely cited and accepted explanation of reaction mechanism of the case study reaction of chemical kinetics between Cr(III) ions and ethylenediaminetetraacetic acid (EDTA) contradicts modern chromium(III) coordination chemistry data. Absorption UV and visible light spectra were recorded during the reaction between aqueous solution of Cr(NO 3) 3 and EDTA in order to obtain new information about this reaction. Analysis of the spectra showed that only very small fraction of intermediates may be present in solution during the course of the reaction. The reaction scheme was established and according to it calculations based on a simplified model were carried out. Literature data for constants were used if known, otherwise, adjusted values of their sound estimates were applied. Reasonable agreement of the model calculations with the experimental data was obtained for pH values 3.8 and 4.5 but the model failed to reproduce measured rate of reaction at pH 5.5, probably due to the use of the oversimplified model.

The structure of molten Fe 2 SiO 4+x has been studied using both high-energy x-ray diffraction and Fe Kedge x-ray absorption near-edge structure (XANES) spectroscopy, combined with aerodynamic levitation and laser beam heating. A wide range of Fe 3+ contents were accessed by varying the levitation and atmospheric gas composition. Diffraction measurements were made in the temperature (T) and oxygen partial pressure ranges 1624(21) < T < 2183(94) K (uncertainties in parentheses) and-5.6(3) < ΔFMQ < +2.8(5) log units (relative to the Fayalite-Magnetite-Quartz buffer). Iron K-edge XANES measurements covered the ranges 1557(33) < T < 1994(36) K and-2.1(3) < ΔFMQ < +4.4(3) log units. Fe 3+ contents, x = Fe 3+ /ΣFe, estimated directly from the pre-edge peaks of the XANES spectra varied between 0.15(1) and 0.40(2). While these agree in some cases with semi-empirical models, notable discrepancies are discussed in the context of the limitations in both the models and in the calibrations used to derive oxidation state from XANES spectra. XANES pre-edge peak areas imply average Fe-O coordination numbers, n FeO , close to 5 for all Fe 3+ /ΣFe. Diffraction measurements yielded values of 4.4(2) < n FeO <

The problem of numerical determination of voltage potential inside three dimensional anisotropic media using values of the voltage potential on the boundary of the media has been solved. The convenient form of variational formulation of the problem has been derived. The numerical solution of the problem has been obtained by the method of local variations.

Nickel joins the fairly exclusive list of metals that can activate nitrile C-H bonds. We report the first example of the C-H activation of an acetonitrile ligand on a nickel center. The acetonitrile ligand formally loses a proton and undergoes a sharp flip to give a cyanomethyl ligand that is coordinated to the nickel atom. Structures of an initial N-bound acetonitrile-nickel complex and of a final cyanomethyl-nickel complex are both presented. JA105368P Figure 2. Molecular structure of 3. Key atoms are labeled. Only H atoms of the cyanomethyl ligand are shown (as isotropic spheres). Selected distances (Å) and angles (deg):

En este trabajo se estudia el rol de un lubricante sólido, bisulfuro de molibdeno (MoS 2), en la modificación del comportamiento tribológico, tensión-deformación y a fractura de un grado comercial de polietileno de alto peso molecular (HMWPE). Se observó que el lubricante sólido mejora la resistencia al desgaste del HMWPE, encontrándose una relación de carga que optimiza dicha propiedad. Sin embargo, las propiedades tensión-deformación y a fractura se ven claramente deterioradas.

Redox flow batteries (RFBs) have emerged as a prominent option for the storage of intermittent renewable energy in large and medium-scale applications. In comparison to conventional batteries, these systems offer the unique advantage of decoupling energy and power densities, which can be separately scaled. Flowing liquid electrolytes, stored in external adjacent tanks to the cell stack, allow the reversible conversion of chemical energy into electricity by exploiting the difference in oxidation states between electroactive species. RFBs are at an early stage of commercialization, but the energy density is still low for the widespread use and full implementation. The attractive physicochemical properties of ionic liquids (ILs), with adventurous electrochemical features over aqueous and organic electrolytes, have drawn growing interest for their use in energy devices. Due to their versatility, ILs can be applied in the main components of RFBs, showing great potential for the further development of the technology. For the first time, this work reviews the recent progress on the application of IL materials in RFBs, discussing their roles as i) supportive electrolytes and additives, ii) redox reaction media, iii) redox-active species and iv) electrolyte membranes. The advantages and limitations of the multiple functionalities of ILs in RFBs are detailed, underlining the promising prospects and future research trends in the field.

Studies related to novel electrolyte concepts for p-type dye sensitized solar cells (p-DSSCs) set focus on developing alternatives to the iodide/triiodide (I-/I 3-) redox couples, while attempts to improve the performance of the latter are scarce. In this study, we report on the first complete optimization of an I-/I 3 based electrolyte for p-DSSCs employing CuO-based photocathodes. Optimization of the electrolyte solvent, the effect of ionic liquids, and the concentrationdependent properties of various electrolyte additives were at the focal point. Electrochemical impedance spectroscopy (EIS) and intensity-modulated photovoltage and photocurrent spectroscopies complemented basic electrochemical and device characterization, leading to a sound understanding of charge injection, charge recombination, and charge transport. To this end, optimization of the aforementioned parameters enabled twofold device efficiencies of 0.156% compared to 0.078% for non-optimized devices.

2,3-Dichloro-5,6-dicyanobenzoquinone (DDQ) is an electrochemical oxidation catalyst for a secondary amine, a model system for virtual hydrogen storage by removal of a hydrogen equivalent from an amine; a computational study provides mechanistic information.

En este trabajo se estudia el rol de un lubricante sólido, bisulfuro de molibdeno (MoS 2), en la modificación del comportamiento tribológico, tensión-deformación y a fractura de un grado comercial de polietileno de alto peso molecular (HMWPE). Se observó que el lubricante sólido mejora la resistencia al desgaste del HMWPE, encontrándose una relación de carga que optimiza dicha propiedad. Sin embargo, las propiedades tensión-deformación y a fractura se ven claramente deterioradas.

This perspective invites conversation concerning base metal catalysis as a green and sustainable solution in industrial and academic contexts. We explore what it means to be 'sustainable' and provide information on current efforts in synthetic chemistry. We establish a definition of a base metal and reflect on what considerations might apply to that definition. Throughout, we offer recent case studies, highlighting topics relevant to ligand development, metal sourcing, recyclability, and comparative reactivity using precious metal relatives. We challenge non-specialist readers to consider how, where, and why base metal catalysts are utilized. Finally, we offer social context, asking broad questions relevant to social acceptability. For example, decisions related to catalyst development are often driven by factors including costliness, safety, social adoptability, and performance. How can we move base metal catalysis to the forefront? Does society really care if materials are fabricated from nickel instead of palladium or platinum? How can our community guide this knowledge translation? Is this a job for us alone?

En este articulo, se analiza el efecto de la incorporacion de fibras micrometricas de carbono (FC) y nanofibras de carbono (NFC), en una matriz termoplastica de polieter-eter cetona (PEEK), sobre las propiedades dinamico-mecanicas y tribologicas de los compuestos obtenidos. Se elaboraron compuestos de PEEK reforzado con fibras de carbono micrometricas y nanometricas mediante la tecnica de extruido y moldeado por inyeccion, en diferentes proporciones (0,6; 1; 3 y 5% en peso). Las probetas se enfriaron desde el estado fundido en un molde refrigerado con agua, obteniendo diferentes grados de cristalinidad. A fin de contrarrestar la disparidad de la cristalinidad, se realizo un tratamiento termico a las diferentes formulaciones, con el objeto de homogenizar la estructura cristalina del PEEK. Las propiedades dinamico-mecanicas mostraron incrementos de la rigidez por debajo de la temperatura de transicion vitrea para los sistemas que contenian refuerzo, siendo la concentracion con mayor c...

Se han estudiado conductores protónicos de alta temperatura (CPAT) fabricados por fusión de zona flotante asistida por láser (SrCe 0.9 Y 0.1 O 3-δ , SrCe 0.8 Y 0.2 O 3-δ , SrZr 0.9 Y 0.1 O 3-δ , SrZr 0.8 Y 0.2 O 3-δ , Sr 3 (Ca 1.18 Nb 1.82)O 9-δ y SrTi 0.95 Sc 0.05 O 3-δ). La caracterización microestructural se ha realizado mediante Microscopía Electrónica de Barrido y Transmisión (MEB, MET). Los materiales tienen una estructura celular, con células de anchuras entre 10-50 µm y regiones intercelulares superiores a 1 µm de espesor. El análisis de difracción indica que las células son cristalinas y que la región intercelular es amorfa. La MET revela que las células presentan múltiples defectos planares, separadas por regiones rotadas con la misma estructura cristalográfica. Las propiedades mecánicas a altas temperaturas fueron estudiadas a partir de ensayos de compresión bajo velocidad de deformación y carga constantes. Nuestros materiales resisten tensiones de 500 MPa a 700 ºC, 400 MPa a 1100 ºC y 370 MPa a 1300 ºC, observándose deformación plástica a 1100 ºC y 1300 ºC. El mejor comportamiento mecánico fue obtenido para los sistemas Sr 3 (Ca 1.18 Nb 1.82)O 9δ _ y SrZr 0.9 Y 0.1 O 3-δ. Las tensiones y resistencias en fluencia de estos sistemas son mejores que las de las cerámicas policristalinas CPAT de similar estructura y composición. Después de los ensayos mecánicos, las muestras fueron estudiadas por MEB y MET. La fractura comenzó a propagarse siguiendo las regiones intercelulares. En las muestras deformadas plásticamente se detecta la actividad de dislocaciones. Palabras clave: conductor protónico, solidificación direccional, alta temperatura, propiedades mecánicas. Microstructure and mechanical properties of high temperature protonic conductors fabricated by melt growth High temperature protonic conductors (HTPC) were successfully fabricated by melt growth using the laser heated floating zone method (SrCe 0.9 Y 0.1 O 3-δ , SrCe 0.8 Y 0.2 O 3-δ , SrZr 0.9 Y 0.1 O 3-δ , SrZr 0.8 Y 0.2 O 3-δ , Sr 3 (Ca 1.18 Nb 1.82)O 9-δ and SrTi 0.95 Sc 0.05 O 3-δ). Microstructural characterization was performed by scanning and transmission electron microscopy (SEM, TEM). The materials have a cellular microstructure, with cell width ranging between 10-50 µm and intercellular regions up to 1 µm thick. The diffraction analysis indicates that the cells are crystalline, and the intercellular regions are amorphous. TEM reveals that the cells present multiple planar defects, separating rotated regions with of same crystallographic structure. The high temperature mechanical properties were studied by compression tests performed under constant strain rate and constant load. Remarkable high temperature strengths of 500 MPa at 700 o C, 400 MPa at 1100 o C and 370 MPa at 1300 o C were measured, being the plastic deformation evident at 1100 ºC and 1300 ºC. The best mechanical behavior was obtained for the systems Sr 3 (Ca 1.18 Nb 1.82)O 9-δ and SrZr 0.9 Y 0.1 O 3-δ. The strengths and creep resistance of these systems are better than the ones of polycrystalline HTPC ceramics of similar structure and composition. After the mechanical tests, the samples were studied by SEM and TEM. The fracture started to propagate following the intercellular regions. In the plastically deformed samples, dislocation activity was found.

RESUMEN En este trabajo se presenta el estudio de la perovskita doble La2NiMnO6 como material de electrodo para supercapacitores. El óxido mixto fue preparado por ruta de precursores citrato (CIT). La muestra fue calcinada 4 horas a 800 ºC. El material fue caracterizado por DRXP, espectroscopía FTIR y microscopía SEM. El comportamiento capacitivo del material fue evaluado mediante voltamperometría cíclica y mediciones galvanostáticas de carga/descarga en medio alcalino y ácido. Los perfiles I/V fueron registrados variando las velocidades de barrido de 10 a 100 mV/s. Las curvas galvanostáticas de carga/descarga se registraron a diferentes densidades de corriente, con valores entre 3 y 17 A/g. Los valores más altos de capacitancia fueron obtenidos en medio alcalino. Se encontraron valores de capacitancia específica de 1681 F/g a una densidad de corriente de 3 A/g, potencia y energía específica de 2903 W/kg y 378 Wh/kg, respectivamente. Mientras que en medio ácido los valores fueron de...

Emerging research in the field of organometallic chemistry is centered on the development of new efficient catalysts for the production of useful organic products via group (nitrene, carbene, oxo) transfer chemistry. Nitrene, carbene and oxo transfer with 3d (base) metals allows for economically viable and sustainable alternatives to generate new CC , C-X, and X-X (X = N, O) bonds, as compared with precious metal catalysis or lengthy organic synthesis. This review specifically focuses on the evolving group transfer chemistry using mononuclear middle and late transition metal complexes in bulky alkoxide ligand environments. Bulky alkoxides are attractive ligand candidates for this chemistry because their steric and electronic properties generally lead to high-spin electrophilic reactive metal centers. Design and synthesis of well-defined alkoxide complexes are discussed first, with the focus on ''non-symmetric" alkoxides [OCR 2 R 0 ] developed mostly during the last decade. Variation of the size and the electronic nature of substituents in [OCR 2 R 0 ] allows for the selective formation of bis-or tris(alkoxide) ligand platforms. Next, the reactivity of these complexes in oxo, nitrene, and carbene transfer is described. The electronic structures and reactivity of discrete mononuclear oxo-alkoxide complexes M(OR) n (O) are discussed in the context of bioinorganic (photosystem II) and heterogeneous (zeolites) catalysis. In the chapters describing nitrene and carbene chemistry, the major emphasis is on the electronic structure and reactivity of novel M III (OR) 2 (Y Å) species (Y = NR, CR 2 , N 3 R, N 2 CR 2), which enables a multitude of coupling reactions including catalytic nitrene homocoupling, catalytic coupling of nitrenes and carbenes with isocyanides, as well as rare or unprecedented reductive coupling of azides and diazoalkanes.

This article studies the feasibility of a 1D radiative transfer model to compute the thermal source for a remote heating problem associated to the physics of the so-called plasmonic resonance (PR) in a synthetic polymeric material. The PR is responsible for converting the optical radiation from the incident laser beam into an equivalent thermal source and is achieved by embedding gold nanoparticles during the design of the synthetic polymer. Since the Radiative Transfer Equation cannot be analytically solved for a real experimental case, a two-staged simplified process is considered which requires the uncertainty quantification as a prior stage, in order to make an appropriate control of the resulting temperature profile. In this work, we include propagation errors for lattices of 1D, 2D and 3D geometries, due to the approximate laser source profile used, as well as those arisen from uncertainties in the thermal parameters and the ones derived from the variables involved in the design of the polymer. Computational simulations for a suitable experimental polymer are carried out using COMSOL®. Corresponding results show the scope of the reduced model in terms of a range of parameter values where it can be effectively used in practice.

En el presente trabajo se analiza la modificación de la topografía de una púa escarificadora (SAE 1045) inspirada en la cutícula del bicho toro (Diloboderus abderus), con el objetivo de reducir la adherencia del suelo a la misma. Por tal motivo, se reportan los resultados experimentales de diferentes pruebas de campo, que corresponden a púas con distintas distribuciones geométricas de cavidades en su superficie. Asimismo, se investigó la evolución de la mojabilidad con el tiempo de ataque químico, con la finalidad de generar distintas jerarquías de rugosidades, imitando el efecto lotus.The present work analyses the modification of the topography of a plowshare (SAE 1045) inspired in the cuticle of a beetle called Diloboderus abderus, with the objective of reducing soil adhesion. Therefore, experimental results of different field tests corresponding to several plowshares with different geometric distributions of cavities are reported. Also, the evolution of wettability with time of e...

En el presente trabajo se analiza la modificación de la topografía de una púa escarificadora (SAE 1045) inspirada en la cutícula del bicho toro (Diloboderus abderus), que habita en nuestro suelo, con el objeto de reducir la adherencia del suelo. Por tal motivo, se reportan resultados experimentales de pruebas de campo que corresponden a una dada distribución geométrica de cavidades.

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Elements in the lanthanides series are usually known under the name of rare earth elements (REE). In past decades, the use of these elements in industrial processes has increased exponentially with the development of novel technologies and applications. In addition to such growing industrial importance, and despite their relatively low concentrations in the Earth system, REE are sensitive markers of crystal-melt equilibria in geological systems. As a result, the study of lanthanides in materials, either as whole group or as single species, has become an important point of focus in both Geo-and Materials Sciences. Among REE, Ce and Eu are stable in many geological environments, with two different oxidation states (Ce 3+ /Ce 4+ and Eu 2+ /Eu 3+), hence, these two redox couples have been proposed as proxies for oxygen fugacity (fO 2) in different environments (oxybarometer). However, it is essential to understand the factors influencing redox mechanisms in order to use Ce/Eu distribution as fO 2 sensors. In this chapter, we present an overview of REE properties in minerals, melts, and glasses, and illustrate their importance through examples of applications in the fields of geochemistry, petrology, and mineralogy. OVERVIEW "The rare earths perplex us in our researches, baffle us in our speculations, and haunt us in our very dreams. They stretch like an unknown sea before us, mocking, mystifying and murmuring strange revelations and possibilities" (statement attributed to Sir William Crookes, 1902). The study of trace elements in silicate glasses is a key to understanding the influence of the chemical composition of glasses on the chemical, physical, and rheological

Water-sediment interactions were investigated in arsenic contaminated Holocene aquifers of the Red River floodplain, Vietnam, in order to elucidate the origin of the spatial variability in the groundwater arsenic concentration. The investigated aquifers are spread over an 8 x 13 km field area with sediments that varied in burial age from < 1 kyr to 11 kyr. The groundwater age ranged from less than 2 yr, up to a maximum near 90 yr. Groundwater As concentrations are between 0 and 6.5 µM and there are no simple correlations between the As concentration and groundwater age or aquifer sediment burial age. The aquifers are anoxic with up to 2 mM CH 4 and up to 0.5 mM DOC. The downward advective DOC flux is too small to support both methanogenesis and the reduction of As-containing Fe-oxides and sedimentary carbon is therefore considered the main carbon source for the redox processes. The groundwater H 2 concentration ranged between 0.1 and 4 nM. These values are intermediate between ranges characteristic for Fe-oxide reduction and methanogenesis and suggest that both processes take place simultaneously. The groundwater pe was calculated from the H 2 /H + and CH 4 /CO 2 redox couples, giving almost similar results that apparently reflects the pe of the bulk groundwater. The pe calculated for the As(III)/As(V) redox couple was found in disequilibrium with the other redox couples. Using the pe calculated from the CH 4 /CO 2 redox couple we show that the groundwater has a reducing potential towards Fe-oxides ranging from ferrihydrite to poorly crystalline goethite, but not for well crystalline goethite or hematite. Hematite and poorly crystalline goethite were identified as the Fe-oxides present in the sediments. Reductive dissolution experiments identify two phases releasing Fe(II); one rapidly dissolving that also contains As and a second releasing Fe(II) more slowly but without As. The initial release of Fe and As occurs at a near constant As/Fe ratio that varied from site to site between 1.2 and 0.1 mmol As/mol Fe. Siderite (FeCO 3) is the main sink for Fe(II), based on saturation calculations as well as the identification of siderite in the sediment. Most of the carbonate incorporated in siderite