Acridines (acridine, 9-methylacridine and 9-propylacridine) and acridans (acridan, 9-methylacridan and 9-propylacridan) have been examined as corrosion inhibitors for aluminum by three types of coupon test as follows:
1) Adding an inhibitor alone in dilute HCl solution.
2) Pre-filmed coupon test in dilute HCl solution: the filmed coupon is prepared by dipping itself in the inhibitor-containing dioxane.
3) Adding tetralin solution of an inhibitor in salted water with a dispersant. As results, the efficiencies were summarized as follows:
1) acridines>acridans, 2) acridans>acridines
3) acridans>acridines
Acridines can always protect aluminum by filming metallic surface with an active form of resonance structures, while acridans can protect the metal only when they are released from their molecular-association of hydrogen bonding.
A lone pair of electrons of N-atom in acridans. may be donated only when released from hydrogen: bond association, but in acridines may always be donated from their active form.
Acridans show better inhibition only when they are adsorbed on the metal apart from their molecular-association, while acridines always give the same characteristics of inhibition comparatively as dissociated acridans.

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Three groups of zinc alloys were prepared, namely (1) binary alloys made by adding Hg, In, Ti, Sn, or Bi to extremely high-pure zinc, (2) ternary alloys made by adding Cd, Si, Mg, or Na to Zn-Al alloys of electrolytic zinc base, and (3) ternary alloys made by adding Si, Sn, Bi, or Mg to Zn-Al alloys of low grade (distilled) zinc base. With these samples, anodic potentials, current efficiencies, etc. were determined for more than 1, 000hrs at a constant current of 1.0mA/cm² in an artificial sea-water at room temperature. Furthermore, with some selected samples, the generating currents were measured for a week by coupling test pieces to a steel cathode maintained at a constant potential in sea-water.
The results obtained and the conclusions derived were summarized as follows:
(1) In the case of extremely high-pure zinc, the addition of less than 0.1% of Hg, Sn, Bi, In, Tl, Pb, Cd, or Al generally improves anode performance. Among them, Al, Cd, In, and Hg are most effective; Pb and Tl being less effective. Especially, in Zn-Hg alloy, anode efficiency reaches to 99%.
(2) In the case of Zn-Al alloys of high-pure zin, base, the addition of less than 0.1% of Cd, Sio Mg, or Na results in the performance similar tc or somewhat better performance than that of the base alloy. Especially the ternary alloy containing 0.03-0.05% of Cd or 0.02-0.05% of Si exhibits an anodic potential of -1.0 volt (SCE) and a current efficiency of 98%.
(3) In the case of Zn-Al alloys of low-grade zinc base, the addition of approximately 0.1% of Si, Sn, Bi, Mg, or Na results in nearly the same performance as that of the base alloy. Among them, the ternary alloy containing Si or Bi shows an anodic potential of -1.04 volts and a current efficiency of 98%.
(4) All the samples tested have so high a performance that, in the constant current test, little differences are observed among them. However, in the coupling current test carried out at a relatively high current density, marked differences in current appear. Moreover, in the latter test, it is found that Zn-Al alloys and the ternary alloys containing Al always show the ability to keep high currents, whereas the binary zinc alloys containing Hg, In, Cd, etc. show the tendency to decrease the currents rapidly with time.
(5) It was confirmed that binary or ternary zinc alloys containing Al are superior to the other binary zinc alloys tested in performance as galvanic anodes for use in sea-water.

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