Microscopy, atmosphere control

Both heated stages [224] and ambient temperature gas environments [225,226] have been developed for use in electron microscopy and both are combined [227,228] in the controlled atmosphere instrument. Pressures of up to 30 kPa and temperatures up to 1500 K have been used in studies of a wide variety of solid—gas and catalytic reactions [ 229]. 

The experimental tools for this research were chronopotetiometry (galvanostatic cycling),25 atomic force microscopy (AFM),26,27 scanning electron microscopy (SEM), and X-ray diffraction (XRD).21,25 It should be mentioned that the AFM imaging was conducted in-situ under potential control and in a special homemade glove box filled with highly pure argon atmosphere. This system has been already described in detail in the literature.28... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Baker pioneered direct measurements of the onset of particle mobility on substrates using controlled atmosphere electron microscopy (17). He has pointed out the close relationship between the onset of particle motion as determined in his studies and the Tammann temperature (18). It is important to establish whether melting temperature decreases monotonically with particle size as indicated by the data of Buffat and Borel (7) or is equal to the Tammann temperature as hypothesized by Baker (18). 

Controlled atmosphere electron microscopy was used to directly follow the formation of carbonaceous deposits on supported ruthenium particles during reaction with acetylene (ref. 73). Under these conditions the major type of deposit was filamentous carbon, and its growth characteristics were found to depend on the nature of the support, specimen pre-treatment conditions, and the reaction temperature. When the reaction was performed on a graphite support the filaments were produced by the... 

A combination of controlled atmosphere electron microscopy and flow reactor techniques have been used to investigate the influence of hydrogen sulfide on the catalytic activity of cobalt. Changes in the behavior of cobalt were monitored by the use of probe reactions which are sensitive to the chemical nature of the catalyst surface. These included graphite gasification in oxygen and hydrogen, and carbon deposition from decomposition of hydrocarbons. 

Approaches and Methods to Study Thermal Stability of Model-Su[yoiled Catalysts. - A number of techniques can be applied to the investigation of model-supported catalysts. They include TEM, controlled atmosphere electron microscopy (CAEM), temperature-programmed... 

Among the established instrumental methods for determining metal dispersion, electron microscopy appears to be finding increasing favour and recent advances include the application of high-resolution and controlled-atmosphere electron microscopy to supported metal catalysts (Section 3). Recently, attempts have been made to estimate crystallite size from XPS intensities EXAFS also promises a still more complete description of the... 

Instrumental techniques successfully applied to investigation of model supported catalysts include TEM, CAEM (controlled-atmosphere electron microscopy), TPD, EXAFS, AES, XPS, STM, XRD, and Mdssbauer Spectroscopy. Analytical HRTEM and same area studies have demonstrated great promise for advancing mechanistic knowledge in this area of science. 

After storing the samples at each temperature for 1 week, they were rapidly thawed in a warm bath (at 310 K). They were then cultured on poly-L-lysine-coated 24-well plates or the MED probe, which is a plate used to measure nerve impulses, in an incubator (humidified atmosphere including 5% CO2 at 310 K) after replacing the cryoprotectant with the culture medium. The recovering neurons were first examined by phase-contrast microscopy and compared with control samples. The presence of neurons... 

Crystallization of the homogeneous glasses was performed in a vertical tube furnace with a controlled atmosphere (002/ 2 with a total flow rate of 200 ml per min.). This is tne same atmosphere used in the ash fusion test ( ). The quenched sample was analyzed by petrographic microscopy, powder X-ray diffraction and chemical analysis (to determine the ferrous/total iron ratio) using the method of Hey (2). 

Figure 8. Model of the transformations observed for tungsten oxide on an alumina film by controlled atmosphere electron microscopy.

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