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Accession Number:
AD0670297
Title:
THE PROTECTIVE ACTION OF CALCIUM-MAGNESIUM COATING DURING CATHODIC PROTECTION OF STEEL AND IRON IN SEA WATER
Corporate Author:
FOREIGN TECHNOLOGY DIV WRIGHT-PATTERSON AFB OH
Report Date:
1967-09-20
Abstract:
The protective action of white films formed on iron and steel surfaces in sea water under conditions of cathodic protection was studied. Three series of tests were performed with 16 Mn low-alloy steel. In the first series, specimens were exposed either to natural sea water or to 3 NaCl solution, and protected with a constant current. In the second series the specimens were first exposed to stagnant or stirred sea water and for 3 days protected with a high density, 40 microampsq cm, current to form uniform films and then current applied periodically in 24-hr cycles. Specimens of the third series were tested either in natural or artificial sea water with various current densities. The artificial sea water contained either Mg and Ca pH 7. 7, Mg alone pH 7.8, Ca alone pH 8.0, or no Mg and Ca pH 7.8. Experimental results showed that protection can be achieved in natural sea water at 25 microampsq cm and in 3 NaCl solution at 35 microampsq cm. Specimens pretreated with a higher current can be protected at 3.5 microampsq cm. The periodically applied current should have a density of 15-20 microampsq cm. Polarization of Ca-Mg films is 5-8.8 times that of Ca or Mg films, while polarization of Mg films is higher than that of Ca films. Polarization characteristics are affected by current density applied in forming the film. Film formation is more difficult on rusted metal surfaces and more complete in stirred sea water. Films formed at a pH exceeding 10 provide protection for metals films formed at pH 9 fail to protect.
Supplementary Note:
Edited trans. of Hai Yang Yu Hu Chao (Chinese People's Republic) v8 n1 p51-59, 1966.
Pages:
0022
Distribution Statement:
Approved for public release; distribution is unlimited.
File Size:
1.06MB
