Carbonates, aqueous, environment-alloy

Compared with ferritic carbon and low-alloy steels, relatively little information is available in the literature concerning stainless steels or nickel-base alloys. From the preceding section concerning low-alloy steels in high temperature aqueous environments, where environmental effects depend critically on water chemistry and dissolution and repassivation kinetics when protective oxide films are ruptured, it can be anticipated that this factor would be of even more importance for more highly alloyed corrosion-resistant materials. 

In contrast to SCC of carbon and low-alloy steels in chloride, sulfide, and sulfuric acid environments by hydrogen-embrittlement mechanisms, cracking in several environments is attributed to passive-film cracking and/or active-corrosion-path anodic-dissolution penetration mechanisms (Ref 124). These environments include nitrates, hydroxides, ammonia, carbon-dioxide/carbonate solutions, and aqueous car-bon-monoxide/carbon-dioxide. Nitrate-bearing solutions are encountered in coal distillation and fertilizer plants hydroxide solutions in the production of NaOH and in crevices of steam boilers and ammonia cracking has occurred in tanks and distribution systems for agricultural ammonia applications. 

Figure 2.11. The complexity of the catalytic center in its reaction environment is illustrated here with a schematic of the hydgrogenation of glucose over carbon-supported Pd particles that are alloyed with Ru in an aqueous medium. The interaction between the metal and the support, the surface composition of Pd and Ru and possible nucleation of Ru clusters, the aqueous medium and its wetting of the metal and the support, the presence of other metal and support surface intermediates such as hydroxyl groups can all act to influence the catalytic reaction.

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