Stresses in oxides

Brigelius, R. (1985). Mixed disulphides biological functions and increase in oxidative stress. In Oxidative Stress (ed. H. Sier) pp. 243-272, Academic Press, London. 

K. Barla, R. Herino, and G. Bomchil, Stress in oxidized porous silicon layers, J. Appl. Phys. 59,439, 1986. 

Stresses in oxide layers have been measured by a variety of techniques, which include mechanical tests where bending of a specimen is observed, when the oxide is formed on only one side, or a change in specimen length can be detected. " Usually the most accurate techniques are those that directly measure strain in the oxide lattice. 

Convincing evidence of rare-earth elements leading to reduced internal stresses in oxide scales has been obtained by X-ray measurements by Choquet and Mevrel (1989), and by deflection techniques by Delaunay et al. (1980) and Huntz (1988) using thin... 

In addition to high permselectivity, the membrane must have low-elec trical resistance. That means it is conductive to counterions and does not unduly restrict their passage. Physical and chemical stabihty are also required. Membranes must be mechanically strong and robust, they must not swell or shrink appreciably as ionic strength changes, and they must not wrinkle or delorm under thermal stress. In the course of normal use, membranes may be expec ted to encounter the gamut of pH, so they should be stable from 0 < pH < 14 and in the presence of oxidants. 

Fig. 1.45 Breakdown of oxide film leading to a pit and crack when a high-strength steel is subjected to a tensile stress in a chloride solution (after Brown )...

Fig. 1.82 Oxidation of a convex surface by cation diffusion the compressive stress in the initially formed oxide may lead to (a) failure by buckling or to (b) void precipitation...

In some cases the number of oxide layers can be related directly to the number of breaks in the curve and there is then no doubt that the acceleration derives from repetitive stress-induced oxide cracking. 

Since there is an isotropic growth stress in the plane of the oxide it is necessary to consider the two principal stresses and given by... 

The rigidity of the y axis prevents the development of spherical surfaces for all but very small displacements. Morton suggests that the limit is reached when the displacement is equal to the metal thickness. This condition was satisfied in the high-temperature studies of Appleby and Tylecote and spherical doming of the disc specimen occurred. When the oxide is not very thin compared with the metal both the moduli for oxide and metal must be considered. Stringer" , in his excellent review of stress generation and relief in oxide layers, quotes a corrected formula, originally due to Brenner and Senderoff ... 

As indicated earlier, protective oxide scales typically have a PBR greater than unity and are, therefore, less dense than the metal from which they have formed. As a result, the formation of protective oxides invariably results in a local volume increase, or a stress-free oxidation strain" . If lateral growth occurs, then compressive stresses can build up, and these are intensified at convex and reduced at concave interfaces by the radial displacement of the scale due to outward cation diffusion (Fig. 7.7) . 

The reduced oxidation near sample corners is related to these stress effects, either by retarded diffusion or modified interfacial reactionsManning described these stresses in terms of the conformational strain and distinguished between anion and cation diffusion, and concave and convex surfaces. He defined a radial vector M, describing the direction and extent of displacement of the oxide layer in order to remain in contact with the retreating metal surface, where ... 

Cotton, B., Allshire, A., Cobbold, P. H., Muller, T., and Campbell, A. K. (1989). Pholasin a novel bioluminescent probe for monitoring oxidative stress in single cardiomyocytes. Biochem. Soc. Trans. 17 705-706. 

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