Microscopic and spectroscopic investigation of the calcite surface interacted with Hg(II) in aqueous solutions

The interaction of the {101¯4} cleavage surface of calcite with Hg(CH3COO)2 aqueous solutions with concentration of 5 mM Hg(II) (pH ≈3.5), was investigated using microscopic and spectroscopic techniques. In situ atomic force microscopy experiments showed that surface microtopography changes significantly as a result of the interaction, and that the initial rhombic etch pits induced by H2O dissolution are rapidly transformed to deeper etch pits exhibiting an unusual triangular shape. The growth of these etch pits is strongly anisotropic, moving faster along the [22¯1] direction than along the [010] direction (with step-retreat velocities of ~12 nm s –1 and ~4 nm s–1, respectively). The modified etch pits are due to Hg(II) sorption in the surface, rather than due to the effect of the acetate anion. The sorption (adsorption and probably absorption also) of Hg(II), in the first minutes of the interaction, is shown by X-ray photoelectron spectroscopy. After ~2 h, the triangular etch pits are interconnected to form larger hexagonal etch pits, while Hg(II)-bearing phases (confirmed later by SEM-EDS) grow onto the surface through a heterogeneous nucleation process. The crystal growth of orthorhombic (montroydite-type) hydrated Hg(II) oxide (HgO·nH2O) on the surface of calcite was confirmed by XRD patterns and FT-IR spectra from samples exposed for longer times to Hg(CH3COO)2 solution

Electron spectroscopic investigation of Sn coatings on glasses

Float glasses of different thicknesses and a conducting tin oxide glass have been investigated using Photo and Auger Electron Spectroscopy induced by AlKα X-rays. On the basis of measured chemical XPS shifts in the binding energies the chemical state of Sn (+2 or +4) incorporated on the float glasses could not be assigned. The use of the Auger parameter allows to separate relaxation and chemical contributions. The derived true chemical shifts of Sn on float-glasses are larger than those of SnO and/or SnO2 due to the larger ionic environment of the glass matrix. Ar+ or HF etching reveals that the concentration of Sn decreases exponentially as a function of depth from the surface. © Springer-Verlag 1996

X-ray photoelectron spectroscopic investigation of conducting polymer blends

Electrochemically prepared films of conducting polymers of polypyrrole and polythiophene and their blends with polyamide have been investigated by X-ray photoelectron spectroscopy. In the N1s region of the spectra of films containing polypyrrole the peak corresponding to N+ at 402.0 eV is separated from that of neutral N. The intensity of the N+ peak can be correlated with the electrical conductivity of the films and the spectroscopically derived ratio of F/N+ is close to 4 indicating that one BF4 - dopant ion is incorporated for every oxidized nitrogen center. In the spectra of films of polythiophene and its blends peaks corresponding to S and S+ can not be resolved but again the F/C ratio correlates with the electrical conductivity. © Springer-Verlag 1996

Surface spectroscopic studies of Cs+, and Ba2+ sorption on chlorite-illite mixed clay

The sorption behavior of Cs+, and Ba2+ on natural clay was investigated using ToF-SIMS, XPS, and XRD. The natural clay was composed mainly of chlorite and illite in addition to quartz and calcite. Depth profiling up to 70 Å was performed at 10 Å steps utilizing ToF-SIMS to study the amount of sorbed Cs+ and Ba2+ as a function of depth in the clay matrix. The results suggest that Cs+ and Ba2+ ions were sorbed primarily by ion exchange coupled with hydrolytic sorption. According to ToF-SIMS and XPS results, the total sorbed amount of Ba2+ was larger than that of Cs+. Quantitative determination of the primary cations within the analyzed clay before and after sorption indicated that for Ba2+ sorption, Ca2+, Mg2+ and for Cs+ sorption Ca2+, K+ were the major exchanging ions. The XRD spectra of Ba-sorbed clay contained new peaks that were identified as BaCO3

Interaction of Calcium Carbonates with Lead in Aqueous Solutions

Pure calcium carbonate (calcite and aragonite) solid materials of different particle size (100-200 ím fragments and millimeter-sized single crystals) were interacted with Pb in aqueous solutions at room temperature under atmosphericPCO2. In the case of the micrometer-sized samples, the macroscopic investigation using a batch-type treatment procedure (solutions between 10 and 1000 mg/L Pb) and ICP-AES, SEM-EDS, and powder-XRD showed that the metal is readily removed from the aqueous media by both materials and indicated the sorption processes (mainly surface precipitation leading to overgrowth of cerussite and hydrocerussite crystals) taking place in parallel with surface dissolution processes. The various processes occurring at the calcium carbonate solid-water interface were clearly distinguished and defined in the case of the millimeter-sized samples interacted with 1000 mg/L Pb using a combination of wet-chemical, in-situ (AFM) and exsitu (AFM, SEM) microscopic, and surface spectroscopic (XPS, 12C-RBS) techniques. The in-situ AFM data revealed the dissolution processes on the surface of the calcium carbonates and the simultaneous heterogeneous nucleation of lead carbonate phases and confirmed the secondary dissolution of lead carbonate crystals grown epitaxially from the initial nuclei. The XPS spectra confirmed that adsorption of Pb occurs simultaneously to dissolution at short interaction times (less than 10 min, prior to precipitation-nucleation/crystal growth) in the case of both CaCO3 polymorphs and that the calcite surface with adsorbed Pb may have an aragonite-type character. The 2CRBS spectra indicated that absorption (incorporation of Pb2+ ions) also takes place in parallel at the surface layers of the calcium carbonates, resulting in formation of solid solutions

XPS studies of MCM 41 postmodified by a Schiff base copper complex

Preliminary studies of the distribution of the copper complex in MCM 41 postmodified by a Schiff base (salen) copper complex have been carried out using x-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS). AAS showed 1.3 at% (atomic %) (0.65 mmolg(-1)) of copper loading, which is in close agreement with 1.5 at% obtained from XPS analysis. Nitrogen sorption (77 K) shows a change from a Type IV to a Type I isotherm on postmodification, indicating a change in porosity of the material from mesoporous to microporous. This change in porosity corresponds to a reduction in surface surface area (from 813 m(2)g(-1) to 332 m(2)g(-1)) and pore volume (from 0.39 cm(3)g(-1) to 0.02 cm(3)g(-1)). The XPS argon ion etching results suggest that about a third of the copper complex is going inside the pores, thereby narrowing some pores and blocking others. The remaining copper complex goes on to the external surface of the material. This hypothesis is consistent with the observed changes detected by nitrogen sorption studies on postmodification of MCM 41

A photoelectron spectroscopic investigation of conducting polypyrrole-polyamide composite film

X-ray photoelectron spectrum of the electrochemically prepared polypyrrole and polypyrrole-polyamide composite films exhibit an additional strong high binding energy peak at 402.0 eV corresponding to N+ moieties. Intensity of this peak is significantly reduced upon electrochemical reduction. Atomic concentrations derived from the observed N+ and F (stemming from the dopant BF4-) peaks reveal a slightly higher cation/anion ratio for this composite and suggest that the composite has a different chemical composition than the corresponding polymers. © 1995 Elsevier Science B.V

Creep cavitation evolution in polycrystalline copper under conditions of stress relaxation

Creep in metals and alloys has been observed and studied extensively over the past century. Most studies are based on constant load or less frequently on constant stress conditions. Under certain stress regimes during the period of service, such as creep-fatigue (cyclic), and under displacement-controlled loading the stress can relax. This paper uses novel millimetre length-scale beam bend geometry test specimens with constant displacement to simulate stress relaxation and explore cavity nucleation and early-stage growth/closure in a model polycrystalline material, namely oxygen-free high-conductivity copper. The role of changing grain size over the range 43 μm–2350 μm has been explored. Power-law creep theoretical modelling and finite element analyses have been adopted to predict creep relaxation and explain cavity nucleation and early-stage growth/closure for the test conditions. The results are compared with the experimental observations. The overall experimental and modelling outcomes are considered with respect to the underlying creep damage mechanism.</p

Interaction of calcite with Cr(III) and evidence for direct inorganic formation of vaterite

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Investigating the mechanical behaviour of Fukushima MCCI using synchrotron Xray tomography and digital volume correlation

A primary target towards the clean-up operation of the Fukushima disaster is the retrieval of Molten Core-Concrete Interaction (MCCI) products, presently residing on the basement of the damaged nuclear reactor Units 1–3. MCCI is a fusion of materials, composed of both nuclear fuel cladding and neighbouring structural components. Determining the currently unknown, physical and mechanical properties of MCCI is essential for successful and timely retrieval. In this paper, we aim to experimentally quantify the mechanical properties of a material fabricated to resemble MCCI. A small-scale representative specimen was mechanically tested using Hertzian indentation stepwise loading. Synchrotron X-ray computed tomography was conducted at several loading stages to reveal the sample microstructure and mechanical degradation. The acquired tomograms were analysed by digital volume correlation to measure full-field displacements and strains developed within the sample volume. Young’s modulus and Poisson ratio were determined via this combined methodology