When the corrosion of aluminum is uniform, its magnitude can be determined by "before and after" measurement of specimen thickness. This thickness can be determined by measuring the inductive properties of a coil in which the specmen is centered. The measurement is not sensitive to the presence on the specimen of small amounts of corrosion product oxide. High sensitivity can be achieved when: (1) the core of the coil fits closely around the specimen, (2) the specimen is carefully centered in the coil, and (3) the temperature is closely controlled.
A gauge is described in which as little as 0.03 mg/sq dm, or 10 Å, penetration of 1100 aluminum can be detected. Repeated readings on a particular sample, however, can cover a range of as much as five times the above figure. Use of the gauge is illustrated by curves of corrosion in distilled water.
