In situ aberration corrected-transmission electron microscopy of magnesium oxide nanocatalysts for biodiesels

Biofuels are promising renewable energy sources and can be derived from vegetable oil feedstocks. Although solid catalysts show great promise in plant oil triglyceride transesterification to biodiesel, the identification of active sites and operating surface nanostructures created during their processing is essential for the development of efficient heterogeneous catalysts. Systematic, direct observations of dynamic MgO nanocatalysts from a magnesium hydroxide-methoxide precursor were performed under controlled calcination conditions using novel in situ aberration corrected-transmission electron microscopy at the 0.1 nm level and quantified with catalytic reactivity and physico-chemical studies. Surface structural modifications and the evolution of extended atomic scale glide defects implicate coplanar anion vacancies in active sites in the transesterification of triglycerides to biodiesel. The linear correlation between surface defect density (and therefore polarisability) and activity affords a simple means to fine tune new, energy efficient nanocatalysts for biofuel synthesis. © 2009 Springer Science+Business Media, LLC.

In situ transmission electron microscopy ion irradiations of model iron-chromium alloys

Iron-chromium alloys are used as a model to study the microstructural evolution of defects in irradiated structural steel components of a nuclear reactor. We examine the effects of temperature and chromium concentration on the defect evolution and segregation behavior in the early stages of damage. In situ irradiations are conducted in a transmission electron microscope (TEM) at 300°C and 450°C with 150keV iron ions in single crystal Fe14Cr and Fe19Cr bicrystal to doses of 2E15 ions/cm^2. The microstructures resulting from annealing and irradiation of the alloy are characterized by analysis of TEM micrographs and diffraction patterns and compared with those of irradiated pure iron. We found the irradiation temperature to have little effect on the microstructural development. We also found that the presence of chromium in the sample leads to defect populations with small average loop size and no extended or nested loop structures, in contrast to the populations of large extended loops seen in irradiated pure iron. A very weak dependence was found on the specific chromium content of the alloy. Chromium was shown to suppress defect growth by inhibiting defect mobility in the alloy. While defects in pure iron are highly mobile and able to grow, those in the FeCr alloys remained small and relatively motionless due to the pinning effect of the chromium.

Al-based anodic oxide films structure observation using field emission gun scanning electron microscopy

In the present work, the anodic oxide films of Al, Al-Cu 4.5% and Al-Si 6.5% alloys are formed using direct and pulse current. In the case of Al-Cu and Al-Si alloys, the electrolyte used contains sulfuric acid and oxalic acid, meanwhile for Al the electrolyte contains sulfuric acid only. Al-Cu alloy was submitted to a heat treatment in order to decrease the effect of inter metallic phase theta upon the anodic film structure. Fractured samples were observed using a field emission gun scanning electron microscope JSM-6330F at (LME)/Brazilian Synchrotron Light Laboratory (LNLS), Campinas, SP, Brazil. The oxide film images enable evaluation of the pore size and form with a resolution similar to the transmission electron microscope (TEM) resolution. It is also observed that the anodizing process using pulse current produces an irregular structure of pore walls, and by direct cur-rent it is produced a rectilinear pore wall. (c) 2005 Elsevier B.V. All rights reserved.

Analysis of β-tricalcium phosphate granules prepared with different formulations by nano-computed tomography and scanning electron microscopy

International audience

Low impact to fixed cell processing aiming transmission electron microscopy

In cell culture, cell structures suffer strong impact due to centrifugation during processing for electron microscope observation. In order to minimise this effect, a new protocol was successfully developed. Using conventional reagents and equipments, it took over one week, but cell compression was reduced to none or the lowest deformation possible.

Identical Location Transmission Electron Microscopy Imaging of Site-Selective Pt Nanocatalysts: Electrochemical Activation and Surface Disordering

We have employed identical location transmission electron microscopy (IL-TEM) to study changes in the shape and morphology of faceted Pt nanoparticles as a result of electrochemical cycling; a procedure typically employed for activating platinum surfaces. We find that the shape and morphology of the as-prepared hexagonal nanoparticles are rapidly degraded as a result of potential cycling up to +1.3 V. As few as 25 potential cycles are sufficient to cause significant degradation, and after about 500–1000 cycles the particles are dramatically degraded. We also see clear evidence of particle migration during potential cycling. These finding suggest that great care must be exercised in the use and study of shaped Pt nanoparticles (and related systems) as electrocatlysts, especially for the oxygen reduction reaction where high positive potentials are typically employed.

Avaliação da rugosidade, corrosão e aderência bacteriana no titânio comercialmente puro após ação de fluoretos em diferentes períodos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pozzolanic activity of oil-refining catalyst: evaluation by electron and atomic microscopy

The reuse of waste fluid catalytic cracking (FCC) catalyst as partial surrogate for cement can reduce the environmental impact of both the oil-refinery and cement production industries [1,2]. FCC catalysts can be considered as pozzolanic materials since in the presence of water they tend to chemically react with calcium hydroxide to produce compounds possessing cementitious properties [3,4]. In addition, partial replacement of cement with FCC catalysts can enhance the performance of pastes and mortars, namely by improving their compressive strength [5,6]. In the present work the reaction of waste FCC catalyst with Ca(OH)2 has been investigated after a curing time of 28 days by scanning electron microscopy (SEM) with electron backscattered signal (BSE) combined with X-ray energy dispersive spectroscopy (EDS) carried out with a JEOL JSM 7001F instrument operated at 15 kV coupled to an INCA pentaFetx3 Oxford spectrometer. The polished cross-sections of FCC particles embedded in resin have also been evaluated by atomic force microscopy (AFM) in contact mode (CM) using a NanoSurf EasyScan 2 instrument. The SEM/EDS results revealed that an inward migration of Ca occurred during the reaction. A weaker outward migration of Si and Al was also apparent (Fig. 1). The migration of Ca was not homogeneous and tended to follow high-diffusivity paths within the porous waste FCC catalyst particles. The present study suggests that the porosity of waste FCC catalysts is key for the migration/reaction of Ca from the surrounding matrix, playing an important role in the pozzolanic activity of the system. The topography images and surface roughness parameters obtained by atomic force microscopy can be used to infer the local porosity in waste FCC catalyst particles (Fig. 2).

Atomic force microscopy assisted with electron and ion beam microscopy for the direct measurement of biostructures and DNA samples

Dissertation to obtain a Master degree in Biotechnology

3D solutions in transmission electron (Cryo) -microscopy in biology

One of the main problems in transmission electron microscopy in thebiological field is the tri-dimensionality. This article explains the technicalprocedures and requirements to prepare biological specimens preserving themclosest to their native state to perform 3D reconstruction of the macromolecularcomplexes and cellular structures in their natural environment.

A scanning electron microscope for ultracold quantum gases

This thesis presents a new imaging technique for ultracold quantum gases. Since the first observation of Bose-Einstein condensation, ultracold atoms have proven to be an interesting system to study fundamental quantum effects in many-body systems. Most of the experiments use optical imaging rnmethods to extract the information from the system and are therefore restricted to the fundamental limitation of this technique: the best achievable spatial resolution that can be achieved is comparable to the wavelength of the employed light field. Since the average atomic distance and the length scale of characteristic spatial structures in Bose-Einstein condensates such as vortices and solitons is between 100 nm and 500 nm, an imaging technique with an adequate spatial resolution is needed. This is achieved in this work by extending the method of scanning electron microscopy to ultracold quantum gases. A focused electron beam is scanned over the atom cloud and locally produces ions which are subsequently detected. The new imaging technique allows for the precise measurement of the density distribution of a trapped Bose-Einstein condensate. Furthermore, the spatial resolution is determined by imaging the atomic distribution in one-dimensional and two-dimensional optical lattices. Finally, the variety of the imaging method is demonstrated by the selective removal of single lattice site. rn

Unique structures in a tumor herpesvirus revealed by cryo-electron tomography and microscopy.

Gammaherpesviruses, including the human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, are causative agents of lymphomas and other malignancies. The structural characterization of these viruses has been limited due to difficulties in obtaining adequate amount of virion particles. Here we report the first three-dimensional structural characterization of a whole gammaherpesvirus virion by an emerging integrated approach of cryo-electron tomography combined with single-particle cryo-electron microscopy, using murine gammaherpesvirus-68 (MHV-68) as a model system. We found that the MHV-68 virion consists of distinctive envelope and tegument compartments, and a highly conserved nucleocapsid. Two layers of tegument are identified: an inner tegument layer tethered to the underlying capsid and an outer, flexible tegument layer conforming to the overlying, pleomorphic envelope, consistent with the sequential viral tegumentation process inside host cells. Surprisingly, comparison of the MHV-68 virion and capsid reconstructions shows that the interactions between the capsid and inner tegument proteins are completely different from those observed in alpha and betaherpesviruses. These observations support the notion that the inner layer tegument across different subfamilies of herpesviruses has evolved significantly to confer specific characteristics related to viral-host interactions, in contrast to a highly conserved capsid for genome encapsidation and protection.

Scanning electron microscopic study of the in situ effect of salivary stimulation on erosion and abrasion in human and bovine enamel

This in situ study investigated, using scanning electron microscopy, the effect of stimulated saliva on the enamel surface of bovine and human substrates submitted to erosion followed by brushing abrasion immediately or after one hour. During 2 experimental 7-day crossover phases, 9 previously selected volunteers wore intraoral palatal devices, with 12 enamel specimens (6 human and 6 bovine). In the first phase, the volunteers immersed the device for 5 minutes in 150 ml of a cola drink, 4 times a day (8h00, 12h00, 16h00 and 20h00). Immediately after the immersions, no treatment was performed in 4 specimens (ERO), 4 other specimens were immediately brushed (0 min) using a fluoride dentifrice and the device was replaced into the mouth. After 60 min, the other 4 specimens were brushed. In the second phase, the procedures were repeated but, after the immersions, the volunteers stimulated the salivary flow rate by chewing a sugar-free gum for 30 min. Enamel superficial alterations of all specimens were then evaluated using a scanning electron microscope. Enamel prism core dissolution was seen on the surfaces submitted to erosion, while on those submitted to erosion and to abrasion (both at 0 and 60 min) a more homogeneous enamel surface was observed, probably due to the removal of the altered superficial prism layer. For all the other variables - enamel substrate and salivary stimulation -, the microscopic pattern of the enamel specimens was similar.

Composite electrode of carbon nanotubes and vitreous carbon for electron field emission

In this work, the electron field emission behaviour of electrodes formed by carbon nanotubes (CNTs) grown onto monolithic vitreous carbon (VCarbon) substrates with microcavities is presented. Scanning electron microscopy was used to characterize the microstructure of the films. Tungsten probes, stainless steel sphere, and phosphor electrodes were employed in the electron field emission study. The CNT/VCarbon composite represents a route to inexpensive excellent large area electron emission cathodes with fields as low as 2.1 V mu m(-1). In preliminary lifetime tests for a period of about 24 h at an emission current of about 4 mA cm(-2), there is an onset degradation of the emission current of about 28%, which then stabilizes. Electron emission images of the composites show the cavity of the samples act as separate emission sites and predominantly control the emission process. The emission of CNTs/VCarbon was found to be stable for several hours. (c) 2008 American Institute of Physics.

Strong reduction of V(4+) amount in vanadium oxide/hexadecylamine nanotubes by doping with Co(2+) and Ni(2+) ions: Electron paramagnetic resonance and magnetic studies

In this work we present a complete characterization and magnetic study of vanadium oxide/hexadecylamine nanotubes (VO(x)/Hexa NT's) doped with Co(2)+ and Ni(2+) ions. The morphology of the NT's has been characterized by transmission electron microscopy, while the metallic elements have been quantified by the instrumental neutron activation analysis technique. The static and dynamic magnetic properties were studied by collecting data of magnetization as a function of magnetic field and temperature and by electron paramagnetic resonance. At difference of the majority reports in the literature, we do not observe magnetic dimers in vanadium oxide nanotubes. Also, we observed that the incorporation of metallic ions (Co(2+), S = 3/2 and Ni(2+), S = 1) decreases notably the amount of V(4+) ions in the system, from 14-16% (nondoped case) to 2%-4%, with respect to the total vanadium atoms (fact corroborated by XPS experiments) anyway preserving the tubular nanostructure. The method to decrease the amount of V(4+) in the nanotubes improves considerably their potential technological applications as Li-ion batteries cathodes. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3580252]