The critical potential of hydrogen absorption and the hydrogen absorption rate into titanium under catholic polarization have been measured in artificial sea water with flow velocity of 2.0m/sec and then the effect of flow velocity, dispersed sand, dissolved zinc ion and dissolved chlorine or oxygen gas on the hydrogen absorption rate of titanium have been examined. The results obtained are summarized as follows: (1) The critical potential of hydrogen absorption of titanium in artificial sea water lies in between -0.6 and -0.7V (vs SCE). (2) The hydrogen absorption rate increases as the potential becomes less noble and increases sharply at potentials less noble than -1.1V. (3) The hydrogen absorption rate decreases with increasing the flow velocity. (4) The dispersed sand, dissolved chlorine gas, or deaeration in sea water promote the hydrogen absorption. (5) The passive oxide film on the titanium surface obstructs the hydrogen absorption.

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The growth rate of hydride layer on the surface of titanium, which was cathodically polarized in sulfuric acid, was measured by application of the so-called etching method. The principle and the procedure of this method were rather simple; the specimen covered with a hydride layer was dissolved layer by layer by the short-time dipping in the dilute mixed solution of nitric and hydrofluoric acids, and the hydrogen-titanium ratio of the dissolved portions were determined from the weight loss of specimen and the volume of evolved hydrogen gas. From the data of a series of repeated dissolutions with a single specimen, the hydrogen concentration profile was depicted, and also the amount of hydrogen uptake and the thickness of layer were determined. The profile took a S-shaped curve and consisted of two steep and one flat branches. The results of the X-ray diffraction indicated that both of the outer steep and the flat branches corresponded to a single f. c. c. titanium hydride phase and the inner steep branch to the mixed phases of the f. c. c. and the hexagonal α-titanium. The increase of the cathodic current density and the raising of temperature both stimulated the hydrogen absorption. The rate law changed in accordance with various experimental parameters; for example, it was linear at lower current density and higher temperature, while parabolic at higher current density and lower temperature. Effects of the solution inpurities and the crystalline grain size were also investigated.

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The history of open recirculating cooling water treatment and recent “Alkaline Treatment” were described. In high concentration of Ca-hardness and M-alkalinity solution, CaCO₃ deposition was controlled by the addition of scale inhibitors such as phosphonates or poly-electrolytes and the corrosion of mild steel was also prevented by small amount of PO₄.

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