Rita D. Bonetto

Structural modelling of coprecipitated VTiO catalysts

Abstract A statistical study of the particle shape and size of pure V2O5 and TiO2, and samples of coprecipitated V2O5TiO2 catalysts with different V Ti ratios, has been performed. They were also characterized by XRD, EDAX, SEM and XPS. The results showed that pure vanadium pentoxide is compose by large square or needle-shaped particles, while pure titanium dioxide has small and rounded ones. VTiO samples presented an area and shape, depending on the V Ti ratio. These results and the spectroscopical characterization conducted to a particle model of the catalysts. Those VOTi samples with high V Ti ratio would have large V2O5 crystals acting as support of a V Ti O 2 solid solution. In contrast, those samples with a low V Ti ratio, would have the solid solution supporting vanadium pentoxide crystals.

Measuring Surface Topography with Scanning Electron Microscopy. I. EZEImage: A Program to Obtain 3D Surface Data

Scanning electron microscopy (SEM) is widely used in the science of materials and different parameters were developed to characterize the surface roughness. In a previous work, we studied the surface topography with fractal dimension at low scale and two parameters at high scale by using the variogram, that is, variance vs. step log-log graph, of a SEM image. Those studies were carried out with the FERImage program, previously developed by us. To verify the previously accepted hypothesis by working with only an image, it is indispensable to have reliable three-dimensional (3D) surface data. In this work, a new program (EZEImage) to characterize 3D surface topography in SEM has been developed. It uses fast cross correlation and dynamic programming to obtain reliable dense height maps in a few seconds which can be displayed as an image where each gray level represents a height value. This image can be used for the FERImage program or any other software to obtain surface topography characteristics. EZEImage also generates anaglyph images as well as characterizes 3D surface topography by means of a parameter set to describe amplitude properties and three functional indices for characterizing bearing and fluid properties.

Measuring Surface Topography by Scanning Electron Microscopy. II. Analysis of Three Estimators of Surface Roughness in Second Dimension and Third Dimension

Scanning electron microscopy (SEM) is widely used in surface studies and continuous efforts are carried out in the search of estimators of different surface characteristics. By using the variogram, we developed two of these estimators that were used to characterize the surface roughness from the SEM image texture. One of the estimators is related to the crossover between fractal region at low scale and the periodic region at high scale, whereas the other estimator characterizes the periodic region. In this work, a full study of these estimators and the fractal dimension in two dimensions (2D) and three dimensions (3D) was carried out for emery papers. We show that the obtained fractal dimension with only one image is good enough to characterize the roughness surface because its behavior is similar to those obtained with 3D height data. We show also that the estimator that indicates the crossover is related to the minimum cell size in 2D and to the average particle size in 3D. The other estimator has different values for the three studied emery papers in 2D but it does not have a clear meaning, and these values are similar for those studied samples in 3D. Nevertheless, it indicates the formation tendency of compound cells. The fractal dimension values from the variogram and from an area versus step log-log graph were studied with 3D data. Both methods yield different values corresponding to different information from the samples.

L-shell radiative transition rates by selective synchrotron ionization

Relative L-shell radiative transition rates were obtained for a number of decays in Gd, Dy, Er, Yb, Hf, Ta and Re by means of a method for refining atomic and experimental parameters involved in the spectral analysis of x-ray irradiated samples. For this purpose, pure samples were bombarded with monochromatic synchrotron radiation tuning the incident x-ray energy in order to allow selective ionization of the different atomic shells. The results presented are compared to experimental and theoretical values published by other authors. A good general agreement was found and some particular discrepancies are discussed.

Bulk and surface characterization of crystalline and plastic sulphur oxidized by two Thiobacillus species

Abstract This work studies the surface interaction between Thiobacillus ferrooxidans and Thiobacillus thiooxidans with crystalline and plastic elemental sulphur. The interaction mechanisms were analysed by fractal geometry which describes textural modifications of the substrate caused by bacterial action. The results demonstrated that the bacteria are able to produce two different effects depending on the substrates. Only surface smoothing (decrease on fractal dimension values) was detected on crystalline sulphur (this effect being stronger with T . ferrooxidans than with T . thiooxidans), but, perforation of the bulk was also observed in plastic sulphur

L-shell transition rates for Ba, Ta, W, Pt, Pb and Bi using electron microprobe

a ´´ ´ ´ (5000) Cordoba, Argentina ´ Abstract L-shell transition rates for several elements are obtained by means of a method for refining atomic and experimental parameters in electron probe microanalysis. An analytical function is used to account for the bremsstrahlung, characteristic peaks and detection artifacts from an irradiated material. The refinement procedure consists of minimizing the differences between the experimental X-ray spectrum and that predicted by means of the function proposed. In this work, the spectra considered were recorded with an energy dispersive system. The procedure is applied to Ta, W, Pt, Pb and Bi pure samples and a BaSO sample. More than ten transitions are studied for each 4 element. The results obtained are in agreement with data given in the literature. Finally, the optimization procedure is applied to the refinement of mass concentrations in a sample in which L-lines are strongly overlapped with K lines. 2002 Elsevier Science B.V. All rights reserved.

Experimental Method to Determine the Absolute Efficiency Curve of a Wavelength Dispersive Spectrometer

A method for the experimental determination of the absolute efficiency of wavelength dispersive spectrometers was developed, based on the comparison of spectra measured with a wavelength dispersive system and with an energy dispersive spectrometer. The aim of studying this parameter arises because its knowledge is necessary to perform standardless analysis. A simple analytical expression was obtained for the efficiency curve for three crystals ~TAP, PET, and LiF! of the spectrometer used, within an energy range from 0.77 to 10.83 keV. Although this expression is particular for the system used in this work, the method may be extended to other spectrometers and crystals for electron probe microanalysis and X-ray fluorescence.

Characterization of texture in scanning electron microscope images

Publisher Summary This chapter discusses numerically generated images and scanning electron microscope (SEM) images corresponding to sample surfaces of several origins, the identification of different parameters taken from measurements carried out on these images. Such parameters are used to identify the image texture characteristics and their relationship to the surface from which they result. For instance, the chapter analyzes the attainment of two parameters d per and d min suggested by Bonetto and Ladaga to characterize, together with the fractal dimension D, the texture of SEM images. This method is applicable to many images that are observed by SEM and that present a fractal behavior at one scale and a periodic behavior at another scale in the variogram. The chapter also discusses the development of an interactive program that helps in obtaining the previous parameters for isotropic or anisotropic samples from calculations carried out according to different directions in the image.

Statistical inference, state distribution, and noisy data

A method for finding the state distribution in a physical system, on the basis of a detailed analysis of the experimental response of the system to an external probe, is presented. The concomitant algorithm, based upon the maximum entropy principle, is specifically devised so as to take into account the presence of noise due to experimental errors in the response signal. The formalism is illustrated by recourse to two numerical problems and is applied to a realistic situation involving X-ray diffraction.