著者

木島 茂

出版者

Japan Society of Corrosion Engineering

雑誌

防蝕技術 (ISSN:00109355)

巻号頁・発行日

vol.17, no.9, pp.381-388, 1968-09-15 (Released:2009-11-25)

参考文献数

24

被引用文献数

7 1

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Arrhenius plots were made using data on uniaxially stressed specimens of Types 304, 303 Se, 201, and 431 stainless steels immersed in 35% MgCl2 solution at various temperatures, pH of which had been adjusted to 3 at 22°C by adding HCl. The reciprocal of time-to-failure was taken as the rate of stress-corrosion cracking. Although this is not exactly correct, the results were in good agreement with the Arrhenius' equation. Furthermore, it was found that both the activation energy and logarithm of the rate coefficient, i. e. the pre-exponential term, increased in direct proportion to the stress-level applied and, in addition, the lines illustrating the above relations breaked at a stress-level corresponding to 0.03% proof yield strength of Types 304 and 303 Se steels. As for the other steels such a break was not evidently observed.Arrhenius' equation describes only the temperature dependence of a reaction rate and does not include the entropy changes, so that the activation energy corresponds to the activation enthalpy. Thus, the stress-dependent term, associated with the rate coefficient but not with the enthalpy, should belong either to the entropy term, if it depends on stress, or to another rate coefficient of the probability expression in terms of the free energy, if it does not depend on stress.The analysis of the results leads to the following conclusions: (1) if stress influences entropy, applied stress effectively decreases the activation free energy, and on the other hand the activation enthalpy increases with increasing stress; (2) if the entropy does not depend on stress, applied stress extraordinarily increases the frequency factor that depends on stress. This would mean that the density of active sites is augmented to very high order. Both the activation enthalpy and free energy increase with increasing stress.In both cases, therefore, rate of stress-corrosion cracking increases with applied stress. It can not be made clear, however, on the basis of this kind of analysis, which view is true, and, furthermore, there would be a case in which stress could influence both the entropy and the frequency terms simultaneously. At present, one can only say that the stress-dependent term, associated with thermal excitement of atoms but not with potential energy, is a sort of environment-sensitive parameter that may be able to control the susceptibility to stress-corrosion cracking, although the detailed mechanism involved can not be clarified.