抄録
We found that the aluminum surface was blackened in the boiling natural-water. Then, we examined the condition in which this discolouration occurred. As the experiments, aluminum and its alloys (1S, 2S, 52S, 61S, 17S) which were variously treated were boiled in the well-water, the distillated water and the well-water which was controlled PH. Table 1-11 and Photo. 1-11 show the results of these experiments. Summarizing these results, we have determined the conditions in which the discolouration occurres as follows.
(1) There should be neither oxid film nor other films which prevent the direct contact of the water on the aluminum surface before boiling in the natural water.
(2) Thc Tcmperature of water should be more than 80°C and the aluminum surface should be laid in the condition in which the oxid film is formed.
(3) The water should have any metallic ions and these ions should be in the condition in which they are able to act sufficiently.
The discolouration above mentioned seems to illustrate one of the delicate action of bare aluminum surface and to give us the kye with which we may be able to unlock the tightly closed door of the aluminum surface problems, for instance, activity and oxidation of aluminum surface and corrosion resistance of aluminum and its alloys, etc.
