Corrosion-reaction rates

The rate at which the corrosion of the 2iac proceeds depends on the rates of the two half reactions (eqs. 8 and 12). Equation 8, a necessary part of the desired battery reaction, fortunately represents a reaction that proceeds rather rapidly, whereas the reaction represented by equation 12 is slow. le, the generation of hydrogen on pure 2iac is a sluggish reaction and thus limits the overall corrosion reaction rate. 

Some measure of control over corrosion also is obtained by limiting the salinity in the boiler (primarily the ions of sodium, chloride, and sulfate). These ions all increase the conductivity of boiler water electrolyte and thus enhance corrosion reaction rates. Also, chloride and sulfate ions affect the passivation process. 

These ionic salts all increase the conductivity of BW electrolyte and thus enhance corrosion reaction rates, so that strict limitations on the... 

Passivation is manifested in a polarization curve ( figiu e C2.8.41 dashed line) by a dramatic decrease in current at a particular onset potential (the passivation potential, U ). The corrosion reaction rate kinetics, i.e. the anodic current density, is lowered by several orders of magnitude. 

It is customary to assume that the corrosion reaction rate is so high that it plays no part in controlling the corrosion rate. As a result it is possible to postulate that the oxygen concentration at the interface is zero. 

Flue gas temperature measurement errors can cause difficulties in heat recovery systems. If a thermocouple can see cold recuperator tubes (i.e., if the T-sensor can radiate heat to cold recuperator tubes), it may read 100°F to 250°F (55°C to 139°C) lower than it actually is, so it will not be able to protect the recuperator tubes. The corrosion reaction rate of steel doubles with every 16°F to 18°F of temperature rise, so an error of 100°F in the flue gas temperature can reduce tube life to about one-third of its intended life. 

J. R. Scully and R. G. Kelly, Methods for Determining Aqueous Corrosion Reaction Rates, in AS M Handbook, Vol. 13A, Corrosion Fundamentals, Testing, and Protection, ASM International, Materials Park, OH, 2003, p. 73. 

As a general rule, the corrosion reaction rate in seawater increases as the temperature is increased. This applies only when the effect of temperature alone is a factor. Other variables such as oxygen concentration, diffusion rates, salinity, calcareous deposit formation, and biological activity vary as a function of temperature and must also be considered as to how it affects the overall corrosion rate of a material, component, or system. 

By taking the natural logarithm of Eq. (71) and dilferentiating with respect to pressure, the pressure dependence of the corrosion reaction rate in high temperature aqueous systems can be expressed as,... 

As illustrated by Eq. (80), the pressure effects on corrosion reaction rate can be attributed to the impact of pressure on the activation process and on volume concentration of the aggressive species. " " The volumetric concentrations (mol/1 of the solution) of the aggressive species, Ch+, in Eq. (80) is density-dependent and can be expressed in terms of the molal (mol/kg of solvent) concentration by... 

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