Environmental-TEM

To check further on possible sintering, the corresponding PSD for the area were determined. Representative, the results for three different temperatures are shown as histograms in Fig. 5.13. For all temperatures the ADF show a sharp peak with a maximum at 1 nm, in accordance with the results for Pt4(, in Sect. 5.1.1 on carbon support. The similar shapes and stable peak maxima evidence that clusters are stable at temperatures up to 475 K on Si02 under UHV conditions. 

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The development of in situ environmental-TEM (ETEM) under controlled reaction environments to probe catalysis at the atomic level... 

Although environmental TEM instruments are now beginning to come on-line, a drawback of the TEM imaging completed to date is that they required operation at very... 

Synthesis Crozier et al. [40] have reported the gas-phase polymerization of polypropylene using Ziegler-Natta catalysis performed in an in situ environmental TEM. In this case, the monomer was introduced into the microscope and the probability of polymerization when the monomer strikes an active site was calculated using the available area of the catalyst. 

In addition to the numerous elemental characterisations of ambient particles, we have recently seen more applications in fundamental physico-chemistry. This includes laboratory studies on gas-particle reactions, e.g. sea salt or soil dust with nitric acid. Environmental SEM (ESEM) or environmental TEM (ETEM) does offer excellent future prospects in this field. In ESEM and ETEM, it is possible to obtain high quality images and to do some chemical analysis while the gaseous environment around the sample is controlled i.e. vacuum in the neighbourhood of the sample is not necessary, the relative humidity can be varied and a temperature around — 30 °C can be maintained). Ice nucleation properties of individual atmospheric particles have also been studied recently. Both ESEM and ETEM are relatively new techniques, of which the potential has not fully been explored. 

Objective lens and specimen stage is the heart of a transmission electron microscope. Modem objective lenses are a twin lens instead of a single lens. It has an upper and a lower pole-piece with a gap in between. The resolution of a microscope is directly determined by the pole-piece gap. Small pole-piece gaps allow high resolution, but limit tilt angles. A larger pole piece gap reduces resolution but allows other TEM applications such as tomography, cryo TEM, environmental TEM, and dynamic experiments. 

Analysis of soils is an important task in the environmental researches. Reliability of ICP-MS results of soil analysis mainly depends on chemical sampling. Recently microwave systems are widely used for preparation of different samples. Influence of microwave radiation on sample ensures a complete decomposition of sample, greatly increases the mineralization, and allows possible losses of volatile elements to be minimized. In the given study to intensify decomposition of soils we applied the microwave sample preparation system MULTIWAVE (Anton Paar, Austria and Perkin-Elmer, USA) equipped with rotor from 6 autoclaves with TEM reaction chambers of 50 ml volume. 

Bosveld, A.T.C. (2000). Biochemical and developmental effects of dietary exposure to PCBs 126 and 153 in common tem chicks. Environmental Toxicology and Chemistry 19, 719-730. 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

The particle size was below 50 nm (as determined by TEM image analysis), considerably smaller than that of the starting nanoemulsion, and showed a slight mean particle size increase and a broader size distribution with increasing O/S ratio, supporting the template effect of the nanoemulsion. The authors showed that these nanoparticles are interesting not only from a basic viewpoint but also for applications where safety and environmental concerns are important issues. 

The design of in situ atomic-resolution environmental cell TEM under controlled reaction conditions pioneered by Gai and Boyes (87,89) has been adopted by commercial TEM manufacturers, and latter versions of this in situ instrument have been installed in a number of laboratories. In situ atomic resolution-ETEM data demonstrated by Gai et al. (85-90) have now been reproduced by researchers in laboratories using commercial instruments examples include investigations of promoted ruthenium and copper catalysts in various gas environments (93) and detailed investigations of Ziegler-Natta catalysts (94). 

The immobilization of dissolved chemical species by adsorption and ion exchange onto mineral surfaces is an important process affecting both natural and environmentally perturbed geochemical systems. However, sorption of even chemically simple alkali elements such as Cs and Sr onto common rocks often does not achieve equilibrium nor is experimentally reversible (l). Penetration or diffusion of sorbed species into the underlying matrix has been proposed as a concurrent non-equilibration process (2). However, matrix or solid state diffusion is most often considered extremely slow at ambient temperature based on extrapolated data from high tem-... 

At the same time, one should notice that the real catalysts are applied in the gas/liquid environments at usually an increased temperature so that dynamic structural evolution of a real catalyst would not be probed in a conventional electron microscope. To bridge the gap, in situ environmental electron microscope is developed by placing a micoreactor inside the column of an electron microscope to follow catalytic reaction processes [58-62], However, the specimen in an in situ TEM may suffer from interaction with ionised gas (plasma), making the interpretation of in situ TEM study of catalytic reaction more complicated. Characterisation of static, post-reaction catalysts is still the most commonly used. Well-designed model catalysts and reasonable interpretation of the results are essential to a successful study. 

Table 5.2 Summary of selected analytical methods for molecular environmental geochemistry. AAS Atomic absorption spectroscopy AFM Atomic force microscopy (also known as SFM) CT Computerized tomography EDS Energy dispersive spectrometry. EELS Electron energy loss spectroscopy EM Electron microscopy EPR Electron paramagnetic resonance (also known as ESR) ESR Electron spin resonance (also known as EPR) EXAFS Extended X-ray absorption fine structure FUR Fourier transform infrared FIR-TEM Fligh-resolution transmission electron microscopy ICP-AES Inductively-coupled plasma atomic emission spectrometry ICP-MS Inductively-coupled plasma mass spectrometry. Reproduced by permission of American Geophysical Union. O Day PA (1999) Molecular environmental geochemistry. Rev Geophysics 37 249-274. Copyright 1999 American Geophysical Union...

The reduction of hematite with H2 at 387-610 °C has been followed in situ using TEM and an environmental cell (Rau et al., 1987). The reduction reaction started at nudeation sites on the edge of the sample and as the reaction proceeded, a particle showed four reaction zones consisting of umeacted hematite, lamellar magnetite, porous magnetite and finally porous iron (the temperature was too low for wiistite). 

The actual number of cells or percentage of microbial population that will be killed by an absorbed radiation dose depends also on various factors such as the inherent resistance of the particular organism, the growth stage, as well as environmental factors such as tem-... 

Let us now turn to the reduction of polyhalogenated C,- and C2-compounds. First we note that many of these compounds react by several reaction pathways that may yield different intermediate and/or final products. Furthermore, the relative importance of the various pathways will, in general, depend in a rather complex way on a variety of environmental factors including the nature of the reductant, tem-perature, pH, and presence of dissolved or particulate chemical species. The reason is that the reactive intermediates formed by transfer of one or two electrons to a polyhalogenated Cr or C2-compound may undergo a variety of subsequent... 

Spark source (SSMS) and thermal emission (TEMS) mass spectrometry are used to determine ppb to ppm quantities of elements in energy sources such as coal, fuel oil, and gasoline. Toxic metals—cadmium, mercury, lead, and zinc— may be determined by SSMS with an estimated precision of 5%, and metals which ionize thermally may be determined by TEMS with an estimated precision of 1% using the isotope dilution technique. An environmental study of the trace element balance from a coal-fired steam plant was done by SSMS using isotope dilution to determine the toxic metals and a general scan technique for 15 other elements using chemically determined iron as an internal standard. In addition, isotope dilution procedures for the analysis of lead in gasoline and uranium in coal and fly ash by TEMS are presented. 

The most recent developments in TEM also include the Environmental mode. In dedicated TEM, a differential pumping between the electron gun and the specimen stage allows the specimen to be surrounded by a gaseous atmosphere, with a pressure of a few millibars. Interestingly, the spatial resolution of the TEM is not seriously affected since atomic resolution is still attainable (31) and chemical reactions can be followed in situ. 

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