Coupon Contamination Procedures

For each series of experiments, the same stainless steel coupon (4 cm X 3.5 cm X 0.1 cm) was precleaned, coated with the test contaminant, and then placed in the autoclave for testing. For precleaning, the coupon was either washed first in a chloroform bath, rinsed with acetone, and then dipped in an acetone bath or immersed in a 1,1,1-trichloroethane bath and wiped with a tissue to remove any residue. After precleaning, the coupon was weighed to determine when the mass of the coupon was within 0.1 mg of its original weight. This was set as the standard for perfect cleanness of the coupon. 

For the first two series of experiments, the coupon was submerged completely in one of the two test contaminants, patted lightly with a lint-free tissue to remove excess material, and weighed. Loading was controlled to 0.005 g from run to run to minimize effects of surface concentration differences. In later series, dopants were applied to one side of the coupon which was marked to designate an area so that the contaminated area would remain constant from run to run. The contaminants were applied to this area with a small, short-bristled paint brush. Contaminant mass for each of these series was kept constant from run to run to within 0.0001 g. 

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