Nitrogen critical enhancements

The thermal conductivity critical enhancement of nitrogen has been analyzed by Perkins et a/. (1991). An empirical expression with five adjustable coefficients was used in order to represent the experimental data in the vicinity but not very close to the critical point. Accordingly, the following expressions should not be tq)plied in the temperature range 123 to 129 K and in the density range 10.9 to 11.4 mol L . ... 

The active site on the surface of selective propylene ammoxidation catalyst contains three critical functionalities associated with the specific metal components of the catalyst (37—39) an a-H abstraction component such as Sb ", or Te" " an olefin chemisorption and oxygen or nitrogen insertion component such as Mo " or and a redox couple such as Fe " /Fe " or Ce " /Ce" " to enhance transfer of lattice oxygen between the bulk and surface... 

Similarly to N, most S pools are found in organic form in forest floor and soil humus. However, unlike nitrogen, there are important abiotic processes, especially sulfate sorption processes, which play a critical role in regulating sulfate dynamics in forest ecosystems. An example of this type of exposure pathway was shown in the Habbard Brook whole-tree harvesting experiment, where the decrease in sulfate output from the watershed was attributed to sulfate adsorption, which was enhanced by soil acidification from nitrification (see above). 

Foams, in the form of froths, are intimately involved and critical to the success of many mineral-separation processes (Chapter 10). Foams may also be applied or encountered at all stages in the petroleum recovery and processing industry (oil-well drilling, reservoir injection, oil-well production and process-plant foams). A class of enhanced oil recovery process involves injecting a gas in the form of a foam. Suitable foams can be formulated for injection with air/nitrogen, natural gas, carbon dioxide, or steam [3,5]. In a thermal process, when a steam foam contacts residual crude oil, there is a tendency to condense and create W/O emulsions. Or, in a non-thermal process, the foam may emulsify the oil itself (now as an O/W emulsion) which is then drawn up into the foam structure the oil droplets eventually penetrate the lamella surfaces, destroying the foam [3], See Chapter 11. 

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