High-temperature corrosion continued oxygen

It is claimed that the cured materials may be used continuously in air up to 300°C and in oxygen-free environments to 400°C. The materials are of interest as heat- and corrosion-resistant coatings, for example in geothermal wells, high-temperature sodium and lithium batteries and high-temperature polymer- and metal-processing equipment. 

For oxidation of iron to occur at high temperatures, the oxygen partial pressure must be above that of the dissociation pressure of the appropriate corrosion products. For example, at ca. 700 °C, an oxygen partial pressure of greater than 10 Pa is required for wiistite to form. In air, of course, this condition is readily satisfied, at least initially. As oxidation continues and the film thickens and becomes coherent, an oxygen gradient across the film is established and the composition of the corrosion layer changes. 

High pressure water systems are also available that heat by continuously circulating hot water. The advantage is less corrosion than steam since the oxygen is not replenished in the closed circuit. Also, temperatures are more uniform than steam because, like hot oil, it is a dynamic system. These systems are expensive and costly to maintain. 

Corrosion of aluminum requires the presence of moisture and oxygen. Aeration and oxygenating conditions will accelerate corrosion. Conversely, deaeration will retard corrosion. The amount of water may be minuscule, and present as isolated droplets or a continuous film. Soft waters tend to be less corrosive than hard waters. At ambient temperatures aluminum initially reacts with high-purity water, but this ceases after a few days as a result of the development of... 

At higher temperatures sodium containing high oxygen concentrations is corrosive [6.21]. This is a particular problem with the secondary sodium left in the IHXs. In most cases this cannot be removed or circulated if the rest of the secondary sodium is dumped. It is therefore necessary to protect it from oxidation, especially if the reactor is to continue in operation. It is desirable to have a means of determining the impurity levels in the IHX secondary sodium. 

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