Chemical equilibrium IN Fe–O–H system at high temperatures

In a previous paper, Broom and the author have shown that the process by which equilibrium is reached between the oxides of carbon, methane, and hydrogen, on the one hand, and amorphous carbon on the other, at temperatures above 700°C. is essentially chemical in character. In the case of methane, some experiments were carried out at lower temperatures, and these appeared to indicate that, while the gas was still absorbed rapidly, it could be recovered reversibly, suggesting that the mechanism of absorption was distinct from that by which the chemical equilibrium was finally established. This observation led to the following experiments on argon, which is not supposed to be taken up by carbon at moderately high temperatures. As in the former experiments, the principle of allowing the gas to remain for several days in contact with the carbon was adhered to; for though the rate of absorption was at first rapid at all temperatures, the time taken for equilibrium to be established increased as the temperature fell, and ultimately became so long that it was impossible to obtain results of any value in a reasonable time. A good deal of the published work on adsorption of gases seems to be vitiated by the fact that the experiments have been too hurried.

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In situ REM imaging of surface processes on ceramic bulk crystals from 300 to 1670 K in a conventional TEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100087616 ◽

1991 ◽

Vol 49 ◽

pp. 660-661

Author(s):

Z. L. Wang ◽

J. Bentley

Keyword(s):

High Temperatures ◽

Image Resolution ◽

Atomic Processes ◽

Crystal Surfaces ◽

Beam Radiation ◽

Surface Areas ◽

Transmission Electron ◽

Reflection Electron Microscopy ◽

Gas Reactions

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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