Abiotic Synthesis of Organic Compounds in Deep-Sea Hydrothermal Environments

Porous, well crystalline LiFePO 4 /C composites with different amounts of carbon have been prepared by a sol-gel technique. The thickness of carbon coatings (paintings) has been determined by high-resolution transmission electron microscopy. It is shown that carbon coating thickness can be controlled by the amount of carbon and it has an impact on the obtained reversible capacity. Furthermore, it is shown that atomic ratio of nonactive Fe(III) phase (presumably Fe 3 P) in as-synthesized LiFePO 4 /C composites depends on the amount of carbon in the composite. Using Mossbauer spectroscopy, we have confirmed that the nonactive Fe(III) remains nearly unchanged in the composite during cycling. The lowest amount of carbon in LiFePO 4 /C composites obtained from citrate anion as a gelling agent was 3.2 wt % and this particular amount corresponds to the carbon coating thickness of about 1-2 nm. The reversible capacity obtained from the above-mentioned composite delivers close to 80% of the theoretical capacity at room temperature with a current density of 170 mA/g (C/1 rate).

Impact of the Carbon Coating Thickness on the Electrochemical Performance of LiFePO4 / C Composites

The field of M ¨ ossbauer spectroscopy (MS) has recently enjoyed renewed visibility in the diverse geoscience communities as a result of the inclusion of M ¨ ossbauer

Mössbauer Spectroscopy of Earth and Planetary Materials

The syntheses of amorphous Fe(2)O(3) nanoparticles of varying size and morphology, their magnetic properties, crystallization mechanism, and applications are reviewed herein. The synthetic routes are classified according to the nature of the sample (powders, nanocomposites, films, coated particles). The contributions of various experimental techniques to the characterization of an amorphous Fe(2)O(3) phase are considered in this review, including some key experimental markers, allowing its distinction from nanocrystalline "X-ray amorphous" polymorphs (maghemite, hematite). We discuss the thermally induced crystallization mechanisms depending on transformation temperature, atmosphere, and the size of the amorphous particles that predetermine the structure of the primarily formed crystalline polymorph. The controversial description of the magnetic behavior, including an interpretation of the low-temperature and in-field Mossbauer spectra, is analyzed.

Amorphous iron(III) oxide--a review.

Thermal stability of Ti3SiC2 thin films

By use of a special deconvolution algorithm, it was possible to decompose the XPS O 1s signal into several components reflecting different oxygen bonds. The influence of exposure in vacuo, environmental atmosphere, distilled water, and in a polish solution as corrosive media on the surface of different glasses has been studied. The O 1s signals of fused silica, Na 2 O· n SiO 2 glasses, a BaO·SiO 2 and a BaOB 2 O 3 SiO 2 glass (Schott SK 16) were analyzed. On the glass surfaces, leached layers were formed and analyzed qualitatively and semiquantitatively by XPS and optical and infrared methods. As a reference, virgin surfaces of samples broken in ultrahigh vacuum have been used. The absolute binding energies as well as the shifts relative to the bridging oxygen in ≡SiOSi≡ have been determined for the first for silanol groups ≡SiOH in the surface layer (532.9±0.2 eV and 0.56±0.10 eV, respectively) and for water and/or hydronium bound oxygen (533.6±0.2eV and 1.25±0.10 eV, respectively). Silanol groups are formed in atmosphere as well as by the residual gas in vacuo. Details of the growth of the leached layer were studied, e.g. the dissolution of Ba ++ ions and the growth of the thickness of the leached layer.

Xps study of leached glass surfaces

In sodium silicate glasses, the fraction of differently bound Si species Q[i] (i = 0−4), depending on the number i of bridging oxygens bound to the quarternary silicon, is a function of stoichiometry and the Na/Si ratio. Sodium silicate glasses were investigated by high resolution X-ray photoelectron spectroscopy. To explain the differences in chemical shifts and linewidths of the O 1s signal of the bridging and the non-bridging oxygen as a function of alkali concentration, and extended glass model was developed. This new model takes into account the influence of the alkali concentration on the Q[i] distribution and on the appearance and concentrations of differently bound bridging oxygens as well as non-bridging oxygens. In principle, four different bonds for the non-bridging oxygens (NaOQ[i], i = 0−3) and seven different bonds for the bridging oxygens (Q[i]OQ[j], i, j = 1−4, |i − j| < 2), linking the different Q[i] species could exist. According to this ‘discrete bond model’, for each glass composition the number of these possible bridging and non-bridging oxygen species is limited to a maximum of two for each of them. An approximation of the measured X-ray photoelectron O 1s signal by a superposition of O 1s signals as calculated on the basis of this model allows an excellent reproduction of the experimental results if the glasses are non-phase-separated. In the case of phase separation, the measured spectrum shows only Q[i]OQ[i] bonds (with i = 1−4) identical to the bonding behaviour in the corresponding well-known crystalline phases. The chemical shifts of the non-bridging oxygens relative to the brodging oxygens (as well as the absolute binding energies), as measured by X-ray photoelectron spectroscopy, can be explained by changes in the relative concentrations and intensities of the different oxygen bonds as a function of glass composition. The energy differences between two energetically neighbouring bridging oxygens (i.e., Q[i]OQ[i] and Q[i]OQ[j] with |i − j| = 1) are equal (within the experimental error) for all bridging oxygen bonds in sodium silicate glasses and can be correlated with the cation field strengths of the modifying cations.

Discrete bond model (DBM) of sodium silicate glasses derived from XPS, Raman and NMR measurements

The structural differences in the surface region between freshly fractured and leached silicate glasses containing 16.7, 18.8 and 44.4 mol% PbO, respectively, were investigated by photoelectron spectroscopy (XPS). The optical properties and the thicknesses of leached layers were determined by reflection measurements. The binding energies of the O1s signal components for untreated samples can be ascribed to non-bridging (NBO) and bridging (BO) oxygen and oxygen associated with lead as network former (OPb). The binding energy of OPb was found to be 529.1 ± 0.2 eV. For quantitative conclusions, relative XPS sensitivity factors were determined for oxygen, silicon and lead in these glasses. The experimental NBO/BO/OPb ratio found is in good agreement with the NBO/BO/OPb ratio calculated by use of the `discrete bond model' (DBM). Leaching causes a removal of about 90% of the glass modifiers. The O1s signal of silanol groups and other O–H bonds formed appears at a higher binding energy as compared with the BO signal. Whereas the glasses with smaller Pb contents exhibit thin and well confined leached layers, on the glass with the larger Pb content a structured thick layer is formed. Its thickness growth follows a t -dependence expected for a diffusion controlled process. Pb at network forming sites is more stable with respect to leaching than network modifying Pb. After the removal of Pb from network modifying sites, in addition to the formation of silanol and other O–H bonds a rebinding between Si tetrahedra is found resulting in an increased density of the leached layer.

Changes of lead silicate glasses induced by leaching

The influence of phosphoric acid on steel and on its corrosion products: a Mössbauer spectroscopic approach

Langmuir-Blodgett mono- and multilayers of ferric stearate have been formed on oxidized silicon wafers. Thermodesorption of these layers was investigated by conversion electron Mossbauer and photoelectron spectroscopy and some complementary methods. Heating of samples in air up to 523 K leads to a desorption of the fatty acid chains, while the ferric ions are left on the substrate surface. These ions do not cluster laterally like it was found for Cd ions. They form a rather homogeneous, closed oxidic layer. This well defined layer may be used afterwards for further studies of surface reactions as well as interface and intra-layer interactions. The surface iron ions were found to exhibit a reasonably high recoilless fraction. Therefore, Mossbauer spectroscopy allows to follow chemical, structural, and magnetic changes of the iron ions even if the surface is covered by less than one monolayer.

CEMS/XPS study of iron stearate Langmuir-Blodgett layers

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