Corrosion incongruent

Corrosion may be especially rapid under existing deposits where amine is absent and the pH level is lower than that of the bulk water, as incongruent phosphate effects and concentrating effects further contribute to the problem. 

Keywords PCM phase change latent heat melting heat storage cold storage corrosion phase separation incongruent melting subcooling nucleator products. 

In an environment with a constant redox condition (e.g., permanently aerated and/or constant pH), a condition not uncommon in industrial and environmental situations, corr could shift in the positive direction for a number of reasons. Incongruent dissolution of an alloy could lead to surface ennoblement. Alternatively, as corrosion progresses, the formation of a corrosion product deposit could polarize (i.e., increase the overpotential, i), for) the anodic reaction as illustrated in the Evans diagram of Fig. 4. Polarization in this manner may be due to the introduction of anodic concentration polarization in the deposit as the rate of transport of dissolved metal species away from the corroding surface becomes steadily inhibited by the thickening of the surface deposit i.e., the anodic half-reaction becomes transport controlled. 

Corrosion of the Pu-doped pyrochlore-based ceramics is by incongruent dissolution and segregation of secondary phases [40], Leach rates in 1-year PCT-B tests were found to be (in g/(m xday) Ca - 10, Gd - 10, Pu - 10, Zr - <10. The leach rate of Pu is reduced by one order of magnitude - from lO" g/(m day) in short tests (1 to 7 days) to 10 g/(m xday) after 112-324 days of interaction with water [105], Introduction of 8 to 15 wt.% of oxides of typical contaminants (F, Cl, Na, Mg, K, Na, Si, Al, Ga, Mo, W, etc.) yielded extra glass, perovskite, and Ca-Al-Ti phase instead of brannerite [117]. This does not affect or even improve the chemical durability with respect to actinides. 

Incongruent dissolution with the formation of crystalline reaction products is the third mechanism for the corrosion of ceramics. In this mechanism, on reaction between the ceramic and the solvent, a crystalline reaction product is formed. It happens in the dissolution of strontium titanate in an acid. The reaction is shown in Equation 5.2. 

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