Swelling of Wood and Fiberboards in Liquid Ammonia

Study was made to determine if wood or fiberboards would be suitable insulating containers for storage of liquid ammonia. Species tested were Sitka spruce (Picea sitchensis) redwood (Sequoia sempervirens), and Douglas-fir (Pseudotsuga menziesii). Cross sections 1/8-inch thick in the fiber direction with the annual rings parallel to two opposite edges were used for the measurements. Half of the specimens were 2 inches long in the tangential direction by 0.5 inch wide, and half were 2 inches in the radial direction by 0.5 inch wide. Using an apparatus designed for this purpose, swelling in either water at 25?C. or liquid ammonia at about -36?C. was measured as a function of time-percent swelling versus the square root of time in minutes. In addition, similar specimens of the three softwoods, balsa, and specimens of a typical insulating board and typical untempered and tempered hardboard were soaked in either water or liquid ammonia and dried to obtain information on swelling and collapse of these materials. Liquid ammonia near its boiling point swells wood more rapidly than does water at room temperature. In the tangential direction the swelling for softwoods is 30 to 45 percent greater in liquid ammonia than in water. In the radial direction, the swelling of Sitka spruce and redwood is about the same as in water, but for Douglas-fir it is greater. The swelling of balsa is less in liquid ammonia than in water. However, a large internal swelling must occur because the cell walls are plasticized to such a degree that a very large amount of collapse occurs on subsequent drying. The softwood species also collapsed to a prohibitive degree on drying after soaking in liquid ammonia. The large collapse would make unlined wooden tanks unsuitable for storage of liquid ammonia. When lined with light rubber dam, the penetration of liquid ammonia is sufficiently small so that swelling and subsequent collapse on drying are not serious.

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