Exploration of aluminum passivity by aqueous additives 25--40/degree/C: Potential application to ORNL Advanced Neutron Source (ANS)

In anticipation of an ORNL Advanced Neutron Source (ANS) and possible limitations on neutron flux because of aluminum oxide buildup on heat exchanger surfaces, an exploration was made of aqueous additives for inhibiting corrosion. This study has confirmed previous, extensive studies during 1955-1965 showing that aluminum corrosion is a function of acidity, temperature, nature and concentration of electrolyte additive, and other variables. The exploration confirms that phosphate ion (of the electrolyte ions explored) appears to be good corrosion inhibitor for aluminum in acidic media, depending upon acidity and concentration at a given temperature. Nitrate ion at 25-200/degree/C in acidic media does not inhibit as well, but at temperatures of 200-400/degree/C seems to be relatively good. As the temperature rises, the pH (25/degree/C) must be lowered for best inhibition. Surprisingly, an alkaline, one molar ammonium bicarbonate solution appears to provide good corrosion resistance at temperatures up to 180/degree/C, appearing to be the best corrosion-protection additive (to 180/degree/C) of those explored. 9 refs., 4 tabs