Mechanisms of Solid–Gas Reactions: Reduction of Air Pollutants on Carbons

Studying the behavior of surfaces at high temperatures is of great importance for understanding the properties of ceramics and associated surface-gas reactions. Atomic processes occurring on bulk crystal surfaces at high temperatures can be recorded by reflection electron microscopy (REM) in a conventional transmission electron microscope (TEM) with relatively high resolution, because REM is especially sensitive to atomic-height steps.Improved REM image resolution with a FEG: Cleaved surfaces of a-alumina (012) exhibit atomic flatness with steps of height about 5 Å, determined by reference to a screw (or near screw) dislocation with a presumed Burgers vector of b = (1/3)<012> (see Fig. 1). Steps of heights less than about 0.8 Å can be clearly resolved only with a field emission gun (FEG) (Fig. 2). The small steps are formed by the surface oscillating between the closely packed O and Al stacking layers. The bands of dark contrast (Fig. 2b) are the result of beam radiation damage to surface areas initially terminated with O ions.

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Residual Gas Reactions in the Electron Microscope: I. Qualitative Observations on the Water Gas Reaction

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100101207 ◽

1968 ◽

Vol 26 ◽

pp. 292-293

Author(s):

Richard E. Hartman ◽

Roberta S. Hartman ◽

Peter L. Ramos

Keyword(s):

Electron Beam ◽

Electron Microscope ◽

Gas Phase ◽

Absolute Temperature ◽

Residual Gas ◽

Gas Reactions ◽

Image Position ◽

The Right ◽

Water Gas ◽

Thinning Rate

The action of water and the electron beam on organic specimens in the electron microscope results in the removal of oxidizable material (primarily hydrogen and carbon) by reactions similar to the water gas reaction .which has the form:The energy required to force the reaction to the right is supplied by the interaction of the electron beam with the specimen.The mass of water striking the specimen is given by:where u = gH2O/cm2 sec, PH2O = partial pressure of water in Torr, & T = absolute temperature of the gas phase. If it is assumed that mass is removed from the specimen by a reaction approximated by (1) and that the specimen is uniformly thinned by the reaction, then the thinning rate in A/ min iswhere x = thickness of the specimen in A, t = time in minutes, & E = efficiency (the fraction of the water striking the specimen which reacts with it).

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Some Effects of Oxidant Air Pollutants (Ozone and Peroxyacetyl Nitrate) on the Ultrastructure of Leaf Tissues

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095066 ◽

1972 ◽

Vol 30 ◽

pp. 360-361

Author(s):

William W. Thomson ◽

Elizabeth S. Swanson

Keyword(s):

Air Pollutants ◽

Electron Microscopic Examination ◽

Peroxyacetyl Nitrate ◽

Electron Microscopic ◽

Growth Physiology ◽

Physiology And Biochemistry ◽

Entire Plant ◽

Leaf Tissues ◽

Gaseous Hydrocarbons ◽

The Individual

The oxidant air pollutants, ozone and peroxyacetyl nitrate, are produced in the atmosphere through the interaction of light with nitrogen oxides and gaseous hydrocarbons. These oxidants are phytotoxicants and are known to deleteriously affect plant growth, physiology, and biochemistry. In many instances they induce changes which lead to the death of cells, tissues, organs, and frequently the entire plant. The most obvious damage and biochemical changes are generally observed with leaves.Electron microscopic examination of leaves from bean (Phaseolus vulgaris L.) tobacco (Nicotiana tabacum L.) and cotton (Gossipyum hirsutum L.) fumigated for .5 to 2 hours with 0.3 -1 ppm of the individual oxidants revealed that changes in the ultrastructure of the cells occurred in a sequential fashion with time following the fumigation period. Although occasional cells showed severe damage immediately after fumigation, the most obvious change was an enhanced clarity of the cell membranes.

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Freeze-dried dispersions for automated SEM analysis of individual submicron airborne particulates

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122447 ◽

1992 ◽

Vol 50 (1) ◽

pp. 408-409

Author(s):

Karen A. Katrinak ◽

David W. Brekke ◽

John P. Hurley

Keyword(s):

Air Pollutants ◽

Size Range ◽

Sem Analysis ◽

Individual Particle ◽

Chemical Data ◽

Particle Analysis ◽

Bulk Analysis ◽

Airborne Particulates ◽

Freeze Dried ◽

Individual Particle Analysis

Individual-particle analysis is well established as an alternative to bulk analysis of airborne particulates. It yields size and chemical data on a particle-by-particle basis, information that is critical in predicting the behavior of air pollutants. Individual-particle analysis is especially important for particles with diameter < 1 μm, because particles in this size range have a disproportionately large effect on atmospheric visibility and health.

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