causes a 3 0 % expansion at ordinary temperatures. No increase i n vol ume occurs above this value. I r radiated coal tars release gas rapidly, developing little volume increase. Because of limited flexibility at or dinary temperatures, coal tars and enamels are not considered feasible for use as buried membranes. They could possibly be modified to the nec essary flexibility. Additional plasticization would be expected to involve modification in the direction of i n creased gas formation and increased retention of that formed. A honeycomb structure develops in asphalt on irradiation. The voids are not continuous, and membranes 0.5 inch thick would be expected to have self-healing properties. Under hydrostatic pressure they could re main leak-tight. Additional i n stallations are required to study the effects of gas evolution on membrane seepage control. A suggested form would involve a two-layer construc tion—the layer i n contact with the subgrade having optimum flexi bility and heat and radiation re sistance, and the inner layer of low viscosity asphalt capable of releasing gas rapidly to provide self-healing properties. Fluxing of the two ma terials should be very slow, or can be prevented by a suitable intermediate barrier. Chemical attack of solutions con taining nitric acid is very severe at temperatures of 150° to 225° F. Use of membranes at these temperatures should be considered only for solu tions which contain less than 1 % strong oxidizing acids. Salt solu tions or alkaline solutions are confinable at temperatures up to 200° F. without undue attack or softening of the membrane when the initial softening point is at least 270° F. When earth barriers are used to re tard the flow of membrane lining, solution temperatures can be i n creased. Limited testing of pre fabricated membranes indicates poor resistance to both acids and alkalies.
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Our authors like to hear from readers. If you have questions or comments, or both, send them via The Editor, l/EC, 1155 16th Street N.W., Washington 6, D.C. Letters will be forwarded and answered promptly.
Aqueous system
TITLE
Food products
I Other'
COMPANY
C1TV
7QNE
STATE
VOL. 50, NO. 8
•
AUGUST 1958
91 A
