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The advent of commercial nuclear power generation has created an increased need for thermodynamic data on metal-water systems at temperatures up to 350~ The entropy correspondence principle discovered by Criss and Cobble [J. Am. Chem. Soc., 86, 5385 and 5391 (1964)] provides an excellent means of estimating high-temperature partial molar ionic entropies and hence high-temperature heat capacities, from entropy values at 25~ It is therefore often possible to calculate both equilibrium constants and standard electrode potentials with surprising accuracy for elevated temperatures. Unfortunately, different conventions have been used by several authors in publishing calculated numerical data. One purpose of the present paper is to clarify these differences. In addition, a means of simplifying the calculations is described. This new approach permits rapid modification or augmentation of existing values when more accurate data become available, or When information at other temperatures is required. Values of Kw, the ionization product of water, and E~ the standard electrode potentials of silver-silver halide electrodes, are calculated as examples for temperatures up to 30O~ and these values are compared with available experimental data.

The dielectric relaxation model for ion current transients is tested against both new data obtained under potentiostatic conditions and data obtained by Dewald under galvanostatic conditions. A single set of system constants reproduces both sets of data. As has been already shown for the system A1/A12OJelectrolyte, some of the system constants appear to vary slightly with film formation conditions, a possible consequence of minor structural or compositional changes. The results of a-c impedance measurements made during steady-state film growth were also reproduced by the same set of system constants for frequencies below 1 kHz. Above 1 kHz, an anomalous increase in a-c conductance with increasing frequency was observed.The purpose of this paper (Parts I and I1 ~) is to test the dielectric relaxation model for ion current transients (1-8) against a variety of forms of data for the valve metal-oxide system Ta/Ta2OJelectrolyte

The objective of this research was to investigate the use of electrochemical noise (EN) for detecting stress corrosion crack (SCC) initiation in boiling water reactor (BWR) environments. Initial experiments examined the response of sensitized AISI Type 304 stainless steel (SS) in slow strain‐rate tensile (SSRT) tests in oxygenated, 288°C/10.4 MPa water, a laboratory simulation of the normal BWR environment. This combination of specimen condition and geometry assured abundant nucleation of intergranular cracks, with controllable propagation and arrest via changes in either loading or environment. In the latter case, addition of gaseous hydrogen was used to simulate BWR hydrogen water chemistry (HWC) and lower the specimen potential into a non‐cracking region. The SSRT tests provided an ideal platform for optimizing the electrochemical cell configuration, while establishing the nature of electrochemical potential and current noise (EPN and ECN) responses to crack initiation, propagation and arrest. The standard deviation of electrochemical potential, a measure of EPN amplitude, proved to be the best indicator of SCC initiation, but the degree of correlation depended upon both the periodicity of the calculation and the electrode configuration. Further development work is expected to lead to a useful, in‐plant sensor for real‐time detection of SCC activity.

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