For the purpose of obtaining performance data on zinc anode for use in cathodic protection of salt-manufacturing apparatus, laboratory works were carried out.
Anodic potentials and current efficiencies on zinc of various purity and some kinds of zinc alloys were determined in boiling brines at constant current densities ranging from 5 to 30mA/cm
2. The results and conclusions obtained are as follows:
(1) The tendency for zinc anode to become passive, which is liable to occur in sea-water at ordinary temperature or in fresh water at elevated temperatures, is not observed for zinc except for that of low purity.
(2) Both high-purity zinc and all zinc alloys keep for a long time an anodic potential of -1.0 volt (SCE) and exhibit such a high current efficiency of 90-99%.
(3) Zinc alloys tested show an anode performance of same level as compared with that of high-purity zinc. However, Zn-Al alloys have a tendency to become brittle in hot brine.
(4) In the case of a concentrated brine, in which some salts might deposit to zinc surfaces, the increase in anodic potential of zinc may occur at a lower current density such as 5mA/cm
2.
(5) For the cathodic protection of salt-manufacturing apparatus, high-purity zinc should be used at higher current densities more than 10mA/cm
2.
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