Marino Battagliarin

High conductivity and chemical stability of BaCe1−x−yZrxYyO3−δ proton conductors prepared by a sol–gel method

High-temperature proton conductors are promising as electrolytes for intermediate-temperature solid oxide fuel cells. Among them, BaCeO3-based materials have high proton conductivity but rather poor chemical stability. In contrast, barium zirconates are rather stable, but have poorly reproducible densities and conductivities. In this study, the investigation of BaCe1−x−yZrxYyO3−δ solid solutions (x = 0, 0.10, 0.20, 0.30, 0.40; y = 0.15, 0.20) was undertaken, with the final aim of finding a composition having both high conductivity and good stability. The influence of the modified sol–gel Pechini synthetic approach on the powder morphology, and of a barium excess on the densification were demonstrated. Single-phase perovskite powders were prepared and high density pellets were obtained at temperatures lower than those commonly employed. Stability tests demonstrated that the Zr introduction into doped barium cerate greatly enhanced the chemical stability, particularly for Zr ≥ 20%. The proton conductivities, measured in a humidified H2/Ar atmosphere by impedance spectroscopy, were only slightly influenced by the Zr amount. Overall, BaCe1−x−yZrxYyO3−δ solid solutions having Zr ≈ 20–40% and Y ≈ 15–20% showed good chemical stability and high conductivity.

Synthesis, characterization and properties of water-soluble gold nanoparticles with tunable core size

Robust, water-soluble gold clusters protected by monolayers of ligands containing a short alkyl chain (C7) close to the gold surface and a triethylene glycol monomethylether unit (TEG) to impart solubility in water and other polar solvents were prepared and characterized. Thiol 7 (N1-{2-[2-(2-methoxyethoxy)ethoxy]ethyl}-8-sulfanyloctanamide) constitutes a good and versatile capping agent for the preparation of these nanoparticles. By tuning the Au/thiol ratio and sodium borohydride addition rate, nanoparticles with different core diameters ranging from 1.5 to 4.2 nm, as determined by TEM analysis, could be obtained. The size distribution of the gold cores appears to become broader as the Au/thiol ratio used to prepare the nanoparticles increases. Characterization of these nanoclusters also by NMR, UV-Vis and FTIR spectroscopies is reported. Solubility properties have been studied in a large variety of solvents and different solubility behaviors were observed for nanoparticles of different sizes. Exchange reactions were carried out successfully with small (1.9 nm) and large nanoparticles (4.2 nm) using dodecanethiol as the entering thiol. This demonstrates that these materials can be used for the preparation of nanoclusters with different functional groups soluble in polar solvents including water. The synthetic procedure described represents a facile route to tailoring the size and solubility properties of Au nanoparticles.

A fitting method for the determination of crystallinity by means of X-ray diffraction

A best-fitting version of the X-ray diffraction method of Gehrke & Zachmann [Makromol. Chem. (1981). 182, 627–635] for crystallinity determination, which is a modification of the method developed by Ruland [Acta Cryst. (1961). 14, 1180–1185], is presented. The data, corrected and normalized to electron units (e.u.), are plotted as I(s)s2 vs s and fitted by pseudo-Voigt functions for the crystalline peaks added to a background scattering IB(s)s2, with IB(s) = (1 − Xc)Iam(s) + Xc〈f(s)2〉[1 − exp(−ks2)], where Iam is the experimental intensity of a completely amorphous sample (also corrected and normalized to e.u.), 〈f(s)2〉 is the mean square atomic scattering factor in the material, Xc is the degree of crystallinity and k is a factor which includes either thermal or lattice disorder, where s = 2(sin θ)/λ. The use of the scattering of the amorphous sample in this non-integral form of the Ruland equations overcomes the problem, encountered with other procedures, of locating the continuous (background) scattering with accuracy. The degree of crystallinity and the disorder factor are supplied directly by the optimization process. Furthermore, the line broadening analysis which allows the determination of crystallite size is automatically obtained as a by product. Samples of polyethylene terephthalate (PET) with different degrees of crystallinity are investigated. The results are compared with those obtained by other methods which do not use fitting techniques.

Crystallinity of Polymers by X-ray Diffraction: A new fitting Approach

Abstract A new method for determining the crystallinity fraction of semi-crystalline polymers from X-ray powder diffraction measurements is presented. Using the scattering of an amorphous sample of the same material and a convenient expression for the disorder factor, the method can lead to precise separation of the crystalline and amorphous contributions by a fitting procedure. In this way, the crystallinity fraction and the disorder factor are automatically obtained. The method is applied to polyethylene terephthalate.

Sol-gel zirconia spheres for catalytic applications

Abstract Zirconia spheres have been prepared by gel supported precipitationprocedure, yielding high surface area materials retaining good mechanical resistance, proper shape, and narrow distribution dimensions in the range 0.01–2 mm. Spheres of 1.7 mm diameter have been characterized after calcination at four different temperatures (573–1073K). One of these samples has been used as support for the preparation of a 0.98% Pt catalyst showing good activity in the low temperature methane catalytic combustion.