Near-Surface Layer during the Heterogeneous Heterophase Oxidation of Metals and Alloys and the Related Chemical and Technological Aspects

Resumo

In many cases, when metals and alloys are oxidized under the continuous regeneration of the direct oxidant taken in the amounts comparable with catalytic amounts, the near-surface layer of surface deposits of the products of oxidation of the metal and the reduction of the oxidant of the metal can be considered as a local zone of the macrocyclic stage of regeneration of the oxidant of the metal. The transfer of this stage to the volume phase is admissible and sometimes reasonable if the product of the reduction of the direct oxidant of the metal is soluble in the volume phase to a sufficient extent and the metal oxide is almost insoluble in the volume phase, where the metal exists in a higher oxidation state, or metal peroxide is used as an oxidant. If the indicated solubility of the reduction product of the primary oxidant of the metal is too low or entirely absent, its transfer to the volume phase due to the mechanical failure of the near-surface layer results in progressive self-retardation and also, in many cases, in the nearly entire termination of the oxidation process. The facts of the presence and mechanical failure of the near-surface layer on the metal and alloy favorable from the viewpoint of chemistry and technology are considered.