Oxygen diffusion/reaction coupling

In essentially neutral environments (pH = 7), in contact with air, the controlling reaction is the reduction of dissolved oxygen. For Case IV, the effects of galvanic coupling under conditions of oxygen diffusion control are analyzed by reference to Fig. 4.23. Again, metal B is repre-... 

Fig. 4.23 Schematic representation of polarization curves for the analysis of galvanic coupling when diffusion control of the oxygen reduction reaction is the dominant factor governing the corrosion rate...

A copper pipe and a pipe of unalloyed steel are joined as shown in Figure 3. Water with a resistivity of the order of 300 ohm cm is flowing through the pipeline. Assume that the oxygen reduction reaction is diffusion controlled on both materials, and that the dissolution of steel is activation controlled. Compare with a couple of examples in Seetion 7.3 (Figures 7.13 and 7.11). 

There are many solid state reactions with interesting morphologies in which other modes of transport besides ionic transport in the reaction product can be very important. As a first example, let us consider a reaction which normally occurs by the counter-diffusion of cations, as illustrated in Fig. 2-1 for the formation of spinels in the reaction couple AO/AB2 O4/B2 O3. It was assumed in this case that the mobility of the oxygen ions is negligible. However, if the reactant oxides AO and B2 O3 are very porous, then the reaction product AB2 O4 will also be porous. Furthermore, if the reaction product is an electronic conductor 1), as is generally... 

It also follows that if the solution is stirred the rate of arrival of oxygen at the cathode will be increased. This will result in a corresponding increase in the rate of bimetallic corrosion as is shown in Fig. 1.63 for the aluminium-mild steel couple in stirred 1 - On NaCl solution . The increase in galvanic corrosion rate will be in the inverse relation to the slope of the anodic polarisation curve of the more negative metal, provided that the cathodic reaction is not totally diffusion controlled. 

Oxidation of Anionic Polymers In the Solid State The ability of the macroradical and of the macroions to diffuse In the mixture, and to interreact Is responsible for the secondary products formation coupling reaction and alcoholate synthesis. To prevent the diffusion phenomenon, we have carried out the deactivation In the solid state. The living polymers have been prepared In benzene, with or without a solvating agent (THF or TMEDA) and the solution has been freeze dried before the oxygen introduction. The experimental results are collected in Table VII. 

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