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Alkaline Earth (alkaline + earth)

Distribution by Scientific Domains
Polymers and Materials Science28%

Terms modified by Alkaline Earth

  • alkaline earth metal
    		•

    Selected Abstracts

    Lead(II) Potentiometric Sensor Based on 1,4,8,11-Tetrathiacyclotetradecane Neutral Carrier and Lipophilic Additives

    ELECTROANALYSIS, Issue 11 2008
    Mohamed
    Abstract A potentiometric sensor for lead(II) ions based on the use of 1,4,8,11-tetrathiacyclotetradecane (TTCTD) as a neutral ionophore and potassium tetrakis-(p -chlorophenyl)borate as a lipophilic additive in plasticized PVC membranes is developed. The sensor exhibits linear potentiometric response towards lead(II) ions over the concentration range of 1.0×10,5,1.0×10,2,mol L,1 with a Nernstian slope of 29.9,mV decade,1 and a lower limit of detection of 2.2×10,6,mol L,1 Pb(II) ions over the pH range of 3,6.5. Sensor membrane without a lipophilic additive displays poor response. The sensor shows high selectivity for Pb(II) over a wide variety of alkali, alkaline earth and transition metal ions. The sensor shows long life span, high reproducibility, fast response and long term stability. Validation of the method by measuring the lower limit of detection, lower limit of linear range, accuracy, precision and sensitivity reveals good performance characteristics of the proposed sensor. The developed sensor is successfully applied to direct determination of lead(II) in real samples. The sensor is also used as an indicator electrode for the potentiometric titration of Pb(II) with EDTA and potassium chromate. The results obtained agree fairly well with data obtained by AAS. [source]

    A Novel Al(III)-Selective Electrochemical Sensor Based on N,N,-Bis(salicylidene)-1,2-phenylenediamine Complexes

    ELECTROANALYSIS, Issue 16 2006
    B. Gholivand
    Abstract A polyvinylchloride membrane sensor based on N,N,-bis(salecylidene)-1,2-phenylenediamine (salophen) as membrane carrier was prepared and investigated as a Al3+ -selective electrode. The sensor exhibits a Nernstian response toward Al(III) over a wide concentration range (8.0×10,7,3.0×10,2,M), with a detection limit of 6.0×10,7,M. The potentiometric response of the sensor is independent of the pH of the test solution in the pH range 3.2,4.5. The electrode possesses advantages of very fast response and high selectivity for Al3+ in comparison with alkali, alkaline earth and some heavy metal ions. The sensor was used as an indicator electrode, in the potentiometric titration of aluminum ion and in determination of Al3+ contents in drug, water and waste water samples. [source]

    Asymmetrical Schiff Bases as Carriers in PVC Membrane Electrodes for Cadmium (II) Ions

    ELECTROANALYSIS, Issue 8 2005
    Hossein Mashhadizadeh, Mohammad
    Abstract 5-[((4-Methyl phenyl) azo)- N -(6-amino-2-pyridin) salicylaldimine] (S1), and 5-[((4-methyl phenyl) azo)- N -(2-diamino-2-cyano-1-ethyl cyanide) salicylaldehyde] (S2) with N and O donor atoms are effective ionophores to make Cd2+ -selective membrane electrodes. The electrodes based on S1 and S2 exhibits a Nernstian or near-Nernstian response for cadmium ion over a wide concentration range 1.5×10,1,7.5×10,7 with a slope of 28 and 2.0×10,1,4.0×10,7 with a slope of 22, respectively. They have quick response and can be used for three or four months without any divergence in potential. The proposed sensors show fairly good selectivity over some alkali, alkaline earth, transition and heavy metal ions. The electrodes based on S1 and S2 can be used in the pH range 3.5,9. These electrodes were used as an indicator electrode in potentiometric titration of cadmium ion with EDTA and in the direct determination of cadmium ion in aqueous solutions. [source]

    Copper Ion Selective Membrane Electrodes Based on Some Schiff Base Derivatives

    ELECTROANALYSIS, Issue 15-16 2003
    S. Sadeghi
    Abstract A series of Schiff base derivatives were studied to characterize their abilities as a copper ion carrier in PVC membrane electrodes. The electrode based on 2,2,-[4,4,diphenyl-methanebis(nitrilomethylidyne)]-bisphenol exhibits a Nernstian response for copper ions over the activity range 8.0×10,6,1.0×10,1 mol L,1 with detection limit of about , mol L,1 of copper ion in comparison with two other Schiff bases. The response time, pH effect and other characteristics of the electrodes were studied in a static mode. The effect of the methyl group substitute on Schiff base structure with SO2 bridging group in different positions with respect to OH group was studied. The results show that behavior of the electrodes is not considerably influenced by the position of methyl substitute. The selectivity coefficients were determined with modified fixed interference method (FIM) and matched potential method (MPM). The proposed electrodes comparatively show good selectivity with respect to alkali, alkaline earth and some transition metal ions. The electrodes were used for the determination of copper in black tea, multivitamin and mineral capsule and as an indicator electrode in potentiometric titration of copper ion. [source]

    Direct Current Plasma Emission Spectrometric Determination of Major, Minor and Trace Elements in Microwave Oven Acid Leachates of Powdered Whole Coal Samples

    GEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 1 2005
    Sandro Fadda
    DCP-AES; échantillons de charbon; four à micro-ondes; éléments facilement ionisables; effets de matrice. Major concentrations of Al2O3, Fe2O3, MgO, CaO, Na2O and K2O, minor levels of TiO2, P2O5 and thirty petrologically, geochemically and environmentally significant trace elements have been determined in microwave oven acid leachates of whole powdered coal samples by direct current plasma-atomic emission spectrometry (DCP-AES). A single sample preparation procedure was suitable for all the determinations with no additional dilution step for major elements solution. Dried samples (0.5 g) were treated in low-pressure PFA digestion vessels with HF/HCl/HNO3/HClO4 acids to quantitatively extract the analytes from the bulk material, while leaving the major part of organic matrix as a residue. The major constituents of geological samples, in particular the easily ionised elements (EIEs) such as alkali and alkaline earths, may complicate the instrumental determinations in DCP-AES because of differential enhancements of elemental emission intensities and stray light interferences. Taking account of these factors, the coal matrix is considered to have very low major oxide totals as compared to many other common geo-environmental and related materials (rocks, sediments, soil, ashes etc.). The sample size employed here, while yielding a relatively concentrated solution to cover a wide range of elemental determinations, provided a sample matrix that significantly diminished interferences for DCP measurements. The need for closely matching the unknowns and calibrators was eliminated except for overall acidity and an excess quantity of caesium for EIE buffering. Calibration of the spectrometer was accomplished by simple aqueous single element solutions as high concentration calibrators in addition to a reagent blank as a low concentration calibrator. Two point working curves were established to allow for the maximum concentrations of each element expected in the unknowns. The precision of determinations under routine conditions as well as the reproducibility of the leaching and precision of instrumental measurements have been evaluated. Relative standard deviations (RSD) were of 1,2% for those elements whose concentrations in solid samples were well above the limits of quantification. Method detection limits in the buffered solutions were also evaluated. To evaluate the accuracy of the microwave oven-DCP method a suite of eight certified coal reference materials of differing rank, were analysed with good agreement with the certified and/or available published data. Results are presented for the uncertified major oxides in the AR series reference materials. Les concentrations en éléments majeurs: Al2O3, Fe2O3, MgO, CaO, Na2O et K2O, en éléments mineurs TiO2, P2O5 et en 30 éléments en trace dont le comportement est important en Pétrologie, en Géochimie et en Environnement, ont été analysées par spectrométrie d'émission atomique à plasma à courant direct (DCP-AES), dans des lessivages acides effectués dans un four à micro-ondes sur des échantillons de charbon mis en poudre. Ce mode préparatoire unique est adaptéà toutes les déterminations sans qu'il soit nécessaire d'effectuer une dilution supplémentaire pour l'analyse des éléments majeurs. Les échantillons préalablement desséchés (0.5 g) sont traités dans les pots de PFA de basse pression, avec un mélange d'acides HF/HCl/HNO3/HClO4, afin d'extraire quantitativement les analytes du matériel géologique, tout en laissant la plus grande part de la matrice organique sous forme résiduelle. Les constituants majeurs de ces échantillons géologiques, en particulier les éléments facilement ionisables (EIEs) tels que les alcalins et les alcalino-terreux, peuvent compliquer l'analyse en DCP-AES à cause des rendements variables des intensités d'émission élémentaires et des interférences de raies de lumière. Mais là dessus, la matrice de charbon se révèle être bien plus pauvre en oxydes majeurs que les autres matériaux géologiques, environnementaux ou de type proche (roches, sédiments, sols, cendres). La taille d'échantillon retenue ici, tout en fournissant une solution relativement concentrée qui permet la détermination de beaucoup d'éléments, fournit une matrice qui diminue significativement les interférences lors de la mesure par DCP-AES. Le besoin d'avoir les solutions d'échantillons et les solutions de calibration avec des matrices très proches est donc éliminé, mis à part pour l'acidité totale et la quantité excessive de Césium pour tamponner les EIE. La calibration du spectromètre est faite avec des solutions mono- élémentaires aqueuses, pour déterminer les points de concentrations élevées et avec le blanc de réactifs pour le point de concentration basse. Les courbes de calibrations sont déterminées avec 2 points, pour autoriser l'analyse de concentrations maximales pour chaque élément dans les échantillons inconnus. La précision des déterminations en conditions de routine ainsi que la reproductibilité de l'opération de lessivage et la précision instrumentale des analyses ont étéévaluées. Les déviations standards relatives (RSD) sont de 1,2% pour tout élément dont les concentrations dans le solide sont au dessus des limites de quantification. Les limites de détection de la méthode dans les solutions tamponnées ont aussi étéévaluées. Enfin, pour évaluer la justesse de cette méthode "micro-ondes - DCP" huit charbons certifiés matériaux de référence de différents types ont été analysés, et sont en bon accord avec les données certifiées ou seulement disponibles publiées. Les données sur un certain nombre d'oxydes d'éléments majeurs actuellement non certifiés sont présentées pour les matériaux de référence AR. [source]

    Lanthanum Chromite-Based Interconnects as Key Materials for SOFC Stack Development

    INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2004
    Natsuko Sakai
    The historical investigations on the physicochemical and transport properties of lanthanum chromite-based perovskite oxides are reviewed to evaluate the compatibility as interconnects in solid oxide fuel cells. These materials improve sinterability in air. This has led to investigations on other physicochemical properties of these materials, such as thermal expansion, mechanical strength, and chemical stability. Lanthanum and chromium ion can be substituted by alkaline earths or transition metals, and this translates into a large flexibility in physicochemical properties. However, the formation of oxygen vacancies in a reducing atmosphere can result in an undesirable isothermal expansion or oxygen permeation. The chemical stability of these materials is governed by the fast cation diffusion at the grain boundary of the polycrystals. [source]

    Properties of Ionic-Conducting ,-Bi2O3 Containing Mixed Dopants

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2002
    Stephen D. Nunn
    ,-Bi2O3 compositions were prepared to evaluate the effect on properties of using mixed dopants. Baseline compositions containing 28 mol% of the alkaline-earth oxides CaO, SrO, or BaO were used for comparison. When the alkaline earths were combined in pairs to dope the bismuth oxide, the resulting properties were intermediate between the baseline end members. The data suggest that the transformation temperature for forming the high-conductivity ,1 phase can be varied continuously over a temperature range of about 565° to 750°C. Utilization of additional additives having different ionic size or valence charge compared with the alkaline earths resulted in no observed property changes that could be attributed to the additive alone. The most important variables influencing the conductivity level and phase transformation temperature of ,-Bi2O3 were the type and the amount of the alkaline-earth dopant in the composition. [source]