High resolution electron microscopy of a used automobile catalytic converter

This work is a study of a used automobile catalytic converter using mainly electron microscopy but also techniques such as x-ray powder diffraction, energy dispersive x-ray spectroscopy (EDS) and image simulation. The catalytic converter was used for ~ 80000 km in an ordinary car and partly with leaded fuel. The monolith could be identified as Mg2Al4Si5O18 (α- or β-cordierite). The lead contamination was detected all over the monolith but with a higher concentration in agglomerates on the cordierite surface. Small particles of elementary lead could be identified. The active metals (Pt and Rh) were mainly found as sintered particles (>10 nm) composed of both Pt and Rh. An unexpectedly high amount of Rh was found in these particles (Rh/Pt ratio ≥1). It was in some rare cases possible to image Pt or Rh particles with the initial size (~ 2 nm).Ce travail consiste en l'étude d'un pot d'échappement catalytique automobile par microscopie électronique principalement, et également par diffraction X sur poudres et microanalyse X par dispersion d'énergie. Ce pot d'échappement a été en service durant 80000 km sur une automobile courante dont une partie de la consommation était constituée d'essence au plomb. Le support a pu étre identifié comme Mg2Al4Si5O18 (Cordiérite α ou β). La contamination par le plomb a été detectée sur tout le support mais à plus forte concentration dans des agglomérats en surface de la cordiérite. Des petites particules de plombs ont été identifiées. Les métaux actifs (Pt et Rh) ont été principalement reconnus sous la forme de particules frittées (> 10 nm) composées de Pt et Rh. Une quantité importante, surprenante de Rh a été mise en évidence dans ces particules (Rh/Pt ≥ 1). Dans de rares cas, il a été possible de reconnaître des particules de Pt ou de Rh de taille initiale (≃ 2 nm)

A crystal growth scenario from HREM studies of pinakiolite related oxyborates

The Wadsley defects of pinakiolite related oxyborates (M3O2BO3, M = Mg, Mn, Fe, Al, Sb, Ti) have been studied with high resolution transmission electron microscopy (HREM) and microanalysis (EDX). Structure images of Al-ludwigite crystals show broad slabs of chestermanite with a higher content of antimony. Such chemical variations of structure changes and the nature of local defects support a suggested crystal growth model, including chemical twinning and a crystal growth front parallel to the (100) surface. A new synthetic member of the pinakiolite family, with a twin sequence of regular repeat of ludwigite- and chestermanite-like structures, was identified.Les défauts de Wadsley d'oxyborates de type pinakiolite (M3O2BO3, M = Mg, Mn, Fe, Al, Sb, Ti) ont été étudiés par microscopie électronique haute résolution et microanalyse X. Des images de structure de cristaux de ludwigite à l'aluminium montrent de larges lamelles de chestermanite avec une forte concentration d'antimoine. De telles variations chimiques liées au changement structural et la nature des défauts locaux suggèrent un modèle de croissance cristalline incluant le maclage chimique et un front de croissance cristalline parallèle à la surface (100). Un nouveau composé de synthèse de la famille de pinakiolites avec une séquence maclée d'une répétition régulière de structures de type ludwigite et clustermanite a été identifié

Self-healing and self-organized gold nanoparticle films at a water/organic solvent interface

Gold nanoparticles (5 nm and 20 nm) have been synthesized and stabilized with mercaptoundecanol. These particles, although insoluble in water or common organic solvents, spread as a thin film at the liquid-liquid interface between a water phase and an organic phase. Films of these gold nanoparticles have been observed both by conventional transmission electron microscopy of deposited samples and by cryo-transmission electron microscopy of plunge-frozen samples. The film can be monolayered and extend over centimeter-sized areas. The particle films spontaneously re-assemble and self-organize at the interface when disrupted. This self-healing capacity of the film should make it possible to build a device for continuous production and deposition of the film

Hurlbutite, the first Be mineral from Vastana iron mine, Skane, Sweden

Hurlbutite has been identified as the first Be mineral from the Vastan (a) over circle iron mine, Sk (a) over circle ne, Sweden. The mineral is yellowish to whitish and its microscopic habit is platy and porous. Associated minerals are pinkish apatite, hematite, quartz and svanbergite. The unit cell dimensions calculated from powder X-ray diffraction data are: a = 8.321(8) Angstrom, b = 8.834(8) Angstrom, c = 7.881(7) Angstrom, beta = 90.38(6)degrees. Energy dispersive X-ray analyses of Ca, Sr and P indicated the formula (Ca0.93Sr0.07)Be-2(PO4)(2). The presence of Be and O was qualitatively confirmed by parallel electron energy loss spectroscopy, and traces of B were also detected

Structure study of Bi2.5Na0.5Ta2O9 and B2.5Nam-1.5NbmO3m+3 (m=2-4) by neutron powder diffraction and electron microscopy

The crystal structures of Bi2.5Na0.5Ta2O9 and Bi2.5Nam-1.5NbmO3m+3 (m = 3,4) have been investigated.ysis of their neutron powder diffraction by the Rietveld anal patterns (lambda = 1.470 Angstrom). These compounds belong to the Aurivillius phase family and are built up by (Bi2O2)(2+) fluorite layers and (A(m-1)BnO(3m+1))(2-) (m = 2-4) pseudo-perovskite slabs. Bi2.5Na0.5Ta2O9 (m = 2) and Bi2.5Na2.5Nb4O15 (m = 4) crystallize in the orthorhombic space group A2(1)am, Z = 4, with lattice constants of a = 5.4763(4), b = 5.4478(4), c 24.9710 (15) and a = 5.5095(5), b = 5.4783(5), c = 40.553(3) Angstrom, respectively. Bi2.5Na1.5Nb3O12 (m = 3) has been refined in the orthorhombic space group B2cb, Z = 4, with the unit-cell parameters a = 5.5024(7), b = 5.4622(7), and c = 32.735(4) Angstrom. In comparison with its isostructural Nb analogue, the structure of Bi2.5Na0.5Ta2O9 is less distorted and bond valence sum calculations indicate that the Ta-O bonds are somewhat stronger than the Nb-O bonds. The cell parameters a and h increase with increasing m for the compounds Bi2.5Nam-1.5NbmO3m+3 (m = 2-4), causing a greater strain in the structure. Electron microscopy studies verify that the intergrowth of mixed perovskite layers, caused by stacking faults, also increases with increasing m. (C) 2002 Elsevier Science (USA)