Deposit corrosion definition

The experimental results suggest that the deposition of NO2 into dew accelerates the corrosion of galvanized steel however, it is difficult to establish this definitively because the concentration of dissolved NOx in the dew is small, thus its... 

Dijfuse sources are highly dynamic, spread out pollution sources and their magnitude is closely related to meteorological factors such as precipitation. Major diffuse sources under this definition include surface runoff (load from atmospheric deposition), groundwater, erosion (load from eroded material), diffuse loads of paved urban areas (atmospheric deposition, traffic, corrosion) including combined sewer overflows, since these events occur discontinuously over time and are closely related to precipitation (it has to be pointed out that emissions from urban areas are also partly involved in the point source term, so these discharges are not constant in reahty). Both point and diffuse sources contribute to the total contaminant load of rivers. 

This definition excludes inhibitor films or other corrosion-protecting layers such as paint and so on, which have the same function as passive films but a different origin. Such films are formed from components in the electrolyte (inhibitors) or are deposited in a technical process (e.g. cathodic deposition of paint). 

One of the key factors in any corrosion situation is the environment. The definition and characteristics of this variable can be quite complex. One can use thermodynamics, e.g., Pourbaix or -pH diagrams, to evaluate the theoretical activity of a given metal or alloy provided the chemical makeup of the environment is known. But for practical situations, it is important to realize that the environment is a variable that can change with time and conditions. It is also important to realize that the environment that actually affects a metal corresponds to the microenvironmental conditions that this metal really sees, i.e., the local environment at the surface of the metal. It is indeed the reactivity of this local environment that will determine the real corrosion damage. Thus, an experiment that investigates only the nominal environmental condition without consideration of local effects such as flow, pH cells, deposits, and galvanic effects is useless for lifetime prediction. 

Using this definition, one finds both corrosion and deposit problems in the preboiler system that can manifest themselves as general corrosion, pitting, or erosion-corrosion. The deposit problem can result from either deposition of suspended sohds that should have been removed earlier in the clarifier unit, or else it may be caused by formation of adherent calcium, magnesium, or iron scales. 

This definition of overpotential is phenomenological and is always valid, irrespective of the reasons for the deviation of the potential from its reversible value. The overpotential is always defined with respect to a specific reaction, for which the reversible potential is known. When more than one reaction can occur simultaneously on the same electrode, there is a different overpotential with respect to each reaction, for any value of the measured potential. This situation is encountered most commonly during the corrosion of metals. When iron corrodes, for example, in a neutral solution, the overpotential may be + 0.4 V with respect to metal dissolution and -0.8 V with respect to oxygen reduction. During metal deposition, hydrogen evolution often occurs as a side reaction. At any given potential the overpotential with... 

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