The rate of hydrogen absorption into a potentiostatically polarized titanium was measured by using the nuclear chemical method, which was proposed in the previous report. The method consisted of the polarization, or the corrosion, of test specimen in a DC1-D₂O solution and the bombardment of deuterons with the Cockcroft-Walton accelerator. The amount of absorbed deuterium was estimated from the counting rate of neutrons.
Remarkable absorption was observed at more basic potential than -0.65V vs. S.C.E. and the rate of absorption increased with higher cathodic polarization. The growth of the hydrogen-absorbed layer obeyed the linear rate law rather than the Fick's diffusion law. These facts suggested that the some surface process would control the rate. Relatively high proportion such as 40 to 50%, in comparison with the electrochemical evolution of hydrogen, was observed at the potential region ranging from -1.1 to -1.3V.

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Stability of the passive 18-8 steel in acid solution is found to depend on the potential during the etching treatment as well as the passivation treatment. The potential of the steel during the passivation treatment is controlled by changing the concentration of nitric acid solution or by using a potentiostat. Also a constant potential of the steel during the etching treatment is attained in a dilute nitric acid solution or in a concentrated sulphuric acid solution with or without applying the external polarization. Stability which is decided by measuring the self-activation time in oxygen-free sulphuric acid solution increases with increasing the potential of the passivation treatment, and a critical potential, at which the stability changes abruptly, is admitted irrespective of the method of the passivation treatment, i. e., chemical passivation or potentiostatically controlled passivation. Structural changes of the passive film are concluded to take place at this critical potential of 0.4 volt (vs. SCE). Etching potential, also, changes the self-activation time of the passive steel treated at a constant passivation condition. The maximum stability is obtained at -0.32V of the etching potential. This fact is explained by assuming the selective enrichment of chromium on the surface bofore passivation.

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