Electrochemical Concepts Research Articles

Analysis of Oxide Wedging during Environment Assisted Crack Growth

Abstract The formation of nonsoluble corrosion products can cause a wedging action within cracks which has the potential to either promote stress corrosion cracking or suppress corrosion fatigue cracking. The magnitude of these effects is dependent on the specifics of the material-environment system, as well as the applied load history. Simple models, based on combining electrochemical and fracture mechanics concepts, have been formulated and shown to be useful in analyzing oxide wedging within cracks. These models were used in conjunction with measured oxide induced crack openings in turbine discs to conclude that oxide wedging does not significantly influence stress corrosion cracking in turbine discs containing NDE-detectable flaw sizes. The measured residual stress intensities were found to be between 10 and 20 MPa·m1/2, these being about 20 to 30% of the applied stress intensities. The major contribution to the measured residual stress intensities was shown to be due to oxide contact remote from the ...

Electrochemical properties of the interface between two immiscible electrolyte solutions: Part III. The general case of the galvani potential difference at the interface and of the distribution of an arbitrary number of components interacting in both phases

The distribution equilibrium between two immiscible electrolyte solutions is studied on the basis of electrochemical concepts. The paper continues the theoretical analysis which was developed in ref. 1, extended for the case of interaction among arbitrary components taking place in both phases.

Water oxidation to oxygen by cerium(IV) ions mediated by ruthenium dioxide catalyst

Cerium(IV) ions are shown to oxidize water to O2 in the presence of RuO2 catalyst in 0.5 mol dm–3 H2SO4 solution. The yield of oxygen depends strongly on the relative concentrations of Ce4+ and RuO2. High ratios of Ce4+ to RuO2 favour corrosion of the catalyst, a fact which is explained by electrochemical concepts. Our results are discussed in relation to an earlier proposition concerning the mechanism of the water oxidation reaction by Ce4+ ions in this system.

Water adsorption on metal surfaces: an electrochemical viewpoint

Recent results of water adsorption in ultra-high vacuum, both on clean metal surfaces and in the presence of a coadsorbate, are compared with classical models of the electric double layer at a metal-electrolyte interface. It is concluded from this comparison that the electrochemical concepts regarding the microscopic structure of this important boundary require major revision, although further adsorption experiments are necessary to construct and improved, alternative model.

The study of solid surfaces by electrochemical methods

Abstract The basic concepts of electrochemistry at the solid-electrolyte interface are discussed in this article with special emphasis on surface physical aspects. The electrochemical environment is shown to provide several unique experimental possibilities for the study of metal and semiconductor surfaces. Chemisorption processes, which are associated with charge transfer across the interface, can be studied with great accuracy, even when only submonolayer amounts are adsorbed. Semiconductor electrodes have recently received increasing attention and their fundamental properties, as well as selected experimental results, are described here. The optical reflectance of metal electrodes measures sensitively overlayers and the electric charge on the surface, both of which can easily be controlled by the voltage applied to the electrochemical cell. The final topic is photo-emission, which is usually associated with ultra high vacuum conditions but which, when studied at a metal-electrolyte contact, can be used to obtain complementary information, particularly at low excitation energies.

Fundamental Interpretation of the Salt Effects on Limiting Flashover Voltages of the Salt-Contaminated SiO2 Plates in Terms of Solid-State Electrochemistry

The interpretation of the limiting flashover voltages (LFOV) observed on SiO2 insulator plates contaminated by nine common salts (NaCl, NaNO3, Na2SO4, MgCl2, Mg(NO3)2, MgSO4, CaCI2, Ca(NO3)2 and CaSO4) has been carried out in terms of the concepts of solid-state electrochemistry. On the basis of the hypothesis that the salt under the active electrode is dry during flashover, it has been shown that the LFOV values for various salts are roughly related to their heats of formation per equivalent and bandgap values. The alternative hypothesis that the salt under the active electrode is wet has also been examined and the possibility of interpreting the salt effects on LFOV values in the context of this hypothesis has been explored.

The correlation of XPS analysis with electrochemical history in aqueous corrosion

The response of the surface composition of aluminium brass to electrochemical polarization is sea water has been studied by XPS in an attempt to elucidate the behaviour of condenser tube surfaces in marine environments. Individual specimens were polarized at 100 mV intervals between +100 and −1200 mV (SHE) for a charge transfer of 500 mA s. The rather complex spectra were normalised using Jorgenson's factors to permit meaningful discussion of the surface chemistry. In addition an ion etching was used to remove the high surface coverage of carbon molecules picked up from solution. The validity of each of these techniques, necessary for examination of samples removed from the aqueous phase, is discussed. In the present case they permit the observation of a strong correlation between the Mg ++/Cl − ratio and the surface potential. The movement of the ratio gives a nice demonstration of cathodic basicity and anodic acidity in accord with electrochemical concepts. This result may be of practical use in ascertaining whether corrosion pits on industrial plant are still active.

Sur quelques aspects caractéristiques des oxydes électrolytes solides

From experimental results and those in the literature, an attempt is made to describe some characteristic aspects of solid oxide electrolytes having a fluorite structure, in particular the range of physico-chemical stability and the changes of ionic conductivity associated with temperature, partial pressure of oxygen and composition. It appears that the usual concepts of solution electrochemistry and in particular the notion of equivalent conductivity can be transposed to solid oxide electrolytes, the ionic defects, the carriers of effective charge, being analogous to ions in solution. The study of the changes of equivalent conductivity with concentration of oxide-ion vacancies and the crystal parameter in the system ZrO 2-CeO 2-Y 2O 3 provides, in particular, simple explanations of certain characteristics of the total ionic conductivity.

Electrochimie des oxydes semi-conducteurs mixtes electroniques-ioniques. Systeme zircone-oxyde-de-cerium

Defect oxides are at once electronic and ionic semi-conductors. Electrochemical methods developed for aqueous solutions and molten salts can be used to determine the characteristics of these materials.Thermodynamic and electrochemical concepts can be used to interpret the phenomena observed during the passage of electric current through oxides when they are in contact with purely electronic conductors.The experimental study of binary mixtures of zirconium and cerium oxides, which are at once ionic and electronic conductors, has interest from the point of view of electrodes for magnetohydrodynamic energy conversion

ELECTROCHEMICAL PRECIPITATION OF BLOOD CELLS ON METAL ELECTRODES: AN AID IN THE SELECTION OF VASCULAR PROSTHESES?

face is a critical factor. A variety of experiments have contributed to characterization of the bloodintimal interface and to an understanding of some of the simpler electrochemical concepts which may be of importance in the highly complex process of clotting. Among these are (1) measurement in vivo of vascular transmural potential differences;' (2) demonstration of the tendency to form a clot on the vessel wall beneath the positively polarized member of an electrode pair applied in vivo;2' 3 (3) observation of clot formation both in vivo and in vitro on a positively polarized electrode of an electrode pair inserted in blood ;2' 3 (4) observation of spontaneous clot formation on platinum in vitro or on solid-walled plastic tubes inserted as prostheses in vivo;2 4 (5) measurement of transmural flux, mural adsorption, concentration, and the turnover rates of Na24, K42, Ca45, and Cl6 by blood vessel walls;'-7 (6) demonstration of the negative charge on the pores of blood vessel wall by electroosmnosis;-8 and (7) demonstration in vivo of longitudinal streaming potential produced by pulsatile blood flow.' Several aspects of these experiments have suggested the importance of physicochemical surface phenomena in the initial stages of the clotting process. This concept led us to study the interaction between the cellular components of blood and polarized metal electrodes, in an effort to distinguish between processes of an electrostatic and a more specifically chemical nature. These experiments' indicated that human erythrocytes and leukocytes in suspension in Krebs' solution at physiological pH values were deposited on both platinum or gold electrodes at electrode potentials (VH) more positive than approximately +0.33 volt with respect to the normal hydrogen electrode. If the potential was made less positive than this value, the cells were redispersed. Similarly, platelets in plasma containing acid citrate dextrose (ACD) deposited at about +0.40 volt. Although no detailed explanation of this phenomenon has yet been provided, it is nevertheless clear that the role of electrochemical interactions, possibly including charge transfer between the electrode and appropriate chemical groups on the surface of the cellular species, merits further consideration as an initiator of thromnbus formation. The experiments described above suggest that deposition of blood components on prosthetic devices may be avoided by using metals which, because of the nature of their interaction with the plasma, do not spontaneously acquire excessively positive potentials. This requirement is met by those metals near the

A Correlation of Some Terms Used in Theoretical Inorganic and Organic Chemistry

On the momentous occasion, in 1834, of the reading of Dumas' paper on substitution before the Academy of Sciences at Paris, the opening guns were fired in a long and bitter struggle between Berzelius, on the one hand, and the French school, headed by Laurent and Dumas, on the other. This extended argument marked the parting of the ways for inorganic and organic chemistry. Inorganic chemistry continued to use and to develop the electrochemical theory; organic chemists, however, abandoned the electrochemical theory almost entirely and contented themselves with the development and application of structural theory. There is admittedly some basis for this divorce of inorganic and organic chemistry. Whereas a great many of the reactions encountered in inorganic chemistry are ionic in character, relatively few organic molecules are ionized in solution. In organic reactions ions are postulated as existing, if at all, only as unstable and transient intermediates. With the development of the modern electronic theory, however, and its application to organic chemistry, it has become apparent that this separation is more superficial than real. Although organic molecules are not ordinarily ionized, nevertheless they are thought to be activated by the development, either permanently or incipiently, of positive and negative centers within the molecule, and a vast majority of organic reactions are initiated by the attack of the positive center of one molecule upon the negative center of another. Consequently, similar electrochemical concepts actually underlie both theoretical inorganic and organic chemistry. As a result of the separate development of these two divisions, however, the science has become cluttered with a dual system of nomenclature so that two completely unrelated, if not conflicting, sets of terms are often employed to describe similar or identical theoretical concepts or principles. The result is that the student of organic chemistry is compelled to learn a completely new and unfamiliar set of names for an old and familiar set of ideas. It is the purpose of this paper to correlate certain similar concepts of in-