Time history, electrical resistivity

Figure 11 shows the electrical resistivity vs. time history for sample 8 with the metal content below the percolation threshold and for sample 11 above this threshold. The resistivity of sample 8 increases fast, i.e., for the 20 s of oxidation, resistance (R) grows three orders of magnitude, whereas the resistivity of sample 11 increases much slower, i.e., 1.5 times for 20 min. Kinetics of the curve for sample 8 (Fig. 11a) could be approximated by the dependency In(R) 1 / ln(t), and for sample 11 theR(f) dependency reveals R ln(f) (Fig. 11b). 

Soils differ widely in mineral content, texture and permeability, moisture, pH and aeration, presence of organic matter and microorganisms, and electrical resistivity. Because of these variations, the corrosion performance of buried aluminum varies considerably, and a clear understanding of its bdiavior has depend on the accumulation of many field corrosion tests and actual case histories over an extended period of time (Ref30,51,52). 

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