PREVAIL projection reduction

PREVAIL projection reduction exposure with variable axis immersion lens... 

Projection reduction exposure with variabie axis immersion iens (PREVAiL) iithography... 

All these projections must be treated with caution since the science involved in the uptake of gases by coal is imperfectly understood and complications may arise. As the concentration and prevailing pressure of carbon dioxide increase, adsorption on the coal surface is replaced by absorption (or dissolution) into the structure of the coal. The coal loses its brittle nature and becomes rubbery the latter, in turn, leads to plastic flow. The extent to which this change in state occurs is dependent upon the carbon dioxide pressure, the temperature and the nature of the coal. A probable consequence of plastic flow would be the sealing of capillary channels in the coal and thereby a reduction in its capacity to absorb more gas. Another pertinent factor is that coal swells as carbon dioxide is absorbed and this, too, would cause a major decrease of permeability and consequent gas uptake. For both of these reasons, present estimates of the capability of coal seams to absorb carbon dioxide should be treated as tentative. 

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