Atmospheric corrosion definition

The definition of TOW presented on ISO standard 9223 is the following The period during which a metallic surface is covered by adsorptive and/or liquid films of electrolyte that are capable of causing atmospheric corrosion .. In addition, the new document ISO WD/9223... 

The presence of water does not only create conditions for the existence of an electrolyte, but it acts as a solvent for the dissolution of contaminants [10], Oxygen plays an important role as oxidant element in the atmospheric corrosion process. The thickness of the water layer determines the oxygen diffusion toward the metallic surface and also the diffusion of the reaction products to the outside interface limited by the atmosphere. Another aspect of ISO definition is that a metallic surface is covered by adsorptive and/or liquid films of electrolyte . According to new results, the presence of adsorptive or liquid films of electrolyte perhaps could be not in the entire metallic surface, but in places where there is formed a central anodic drop due to the existence of hygroscopic particles or substances surrounded by microdrops where the cathodic process takes place. This phenomenon is particularly possible in indoor conditions [15-18],... 

We believe that the definition of this test is a prerequisite to rationalization of atmospheric corrosion responses. 

The definition of the powder surfaces tends to be in terms of the process for making it (23). This limits interpretation of their properties and also limits generalization of properties to surfaces which have been generated by atmospheric corrosion. Conversely, the LEED, Auger electron spectroscopy, photo emission properties, etc, are measured on fresh surfaces in UHV, because interpretation is difficult for more complex configurations and because experience has shown that these properties are profoundly modified and confused by exposure to real atmospheres. 

Corrosion may be broadly defined as the degradation of a material due to interaction with its environment. From this broad definition, it is evident that the material need not be man-made for instance the "weathering of granite tors on moorlands may be considered as corrosion of their crystal constituents by the atmosphere (rain, sun, wind, etc). In this chapter, however, it is only metallic corrosion that will be considered. 

The broadest definition of corrosion is the degradation of a material s properties or mass over time because of the effect of the environment. We can think of this in simpler terms by recognizing this process as the tendency for a material to return to its most thermodynamically stable state. For most metallic materials, this means the formation of oxides or sulfides, or other basic metallic compounds generally considered to be ores. For polymeric materials, the end result could be a variety of simple organic compounds. Only in vacuums or under inert atmospheres can corrosion processes be expected to halt entirely. In most cases, these processes are slow enough to afford useful and practical equipment life. 

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. 

Anderson and Reinhard (1939) observed definite differences in the corrosion rates of sheet zinc exposed during different periods of the day. Specimens were exposed for 8 hours per day and were stored in dry, unheated rooms for the other 16 hours. The test was planned so that a different group of specimens was exposed during each 8-hour period 08 15 to 16 15, 16 15 to (X) 15, and 00 15 to 08 15. The test continued for 6 years, and thus each set was exposed to the atmosphere of Palmerton, Pennsylvania, for a cumulative... 

The environmental boundaries of a liquid metal system are set by the containment material. This material may experience other types of corrosion on the exterior surface (of pipe or tubing for example), but it isolates the liquid metal from interaction with any external atmosphere. This specification of "contained and isolated" sets the limits for the liquid metal corrosion system. Other more genercJ areas of liquid metal/metal interaction, such as that produced when, for example, liquid steel or aluminum come into contact with materials employed in their production, are excluded by this definition. Liquid metal embrittlement will not be addressed. Information on this topic can be found elsewhere [1-3]. 

Corrosion of metals in sea water and sea atmosphere part 1 Definitions, basic information) (in German)... 

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