Long-range corrosion protection

Long-range corrosion protection of coating defects... 

Visual observations and spectroscopic investigations on the various aluminum alloys coated with doped polyaniline and doped polypyrrole indicate that there is no long-range electrode polarization phenomenon like that observed on mild steel-coated samples. The corrosion protection of aluminum using conducting polymers is affected by the composition of the aluminum alloy. Corrosion inhibition is controlled solely by anodic protection. Doped polyaniline coatings provide better corro-... 

The hydraulic oil must provide adequate lubrication in the diverse operating conditions associated with the components of the various systems. It must function over an extended temperature range and sometimes under boundary conditions. It will be expected to provide a long, trouble-free service life its chemical stability must therefore be high. Its wear-resisting properties must be capable of handling the high loads in hydraulic pumps. Additionally, the oil must protect metal surfaces from corrosion and it must both resist emulsification and rapidly release entrained air that, on circulation, would produce foam. 

Various surface analysis techniques show that silicate glasses rapidly develop surface compositional profiles when exposed to water. When water is present as a vapor an alkali-rich layer (presumably a hydrated alkali carbonate) forms over the SiOj-rich layer. Water as a liquid dissolves the alkali and leaves the silica-rich film. As long as this SiC -rich film is stable the rate of corrosion due to diffusion is reduced with exposure time. Addition of multi-valent species to the glass or reactant results in formation of a complex protective surface layer in the glass which may be stable over a wide range of environmental conditions. 

For pipe systems of stainless steel carrying chlorinated seawater, internal localized corrosion can be very efficiently prevented by the application of Resistance-controlled Cathodic Protection (RCP). A resistance is simply inserted between the sacrificial anode and the pipeline, and this makes a system that is particularly suitable when there is a low diffusion-limiting cathodic current in the critical potential range [10.29]. Typical of the method is that the current output from the anode is kept low, which has the consequence that the voltage drops are low and the protected pipe length from each anode is long. 

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