This paper proposes a model inspired by the one

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This paper proposes a model inspired by the one proposed by the authors Hughes et al. 273 for a multilayer coating system. The protective coating proposed is to be produced in five steps (Fig. 16 ), using mainly sol–gel methods. The first step involves chemical activation of the metallic surface, aiming to improve further covalent interaction between the Si– O–Si groups of the OIH matrix and the oxo- and/or hidroxo-groups formed on the metallic surface. Addi- tionally, it is expected that this treatment will contrib- ute to improving the uniformity and distribution of the first OIH sol–gel layer deposited, providing full cover- age on a smoother substrate than that given by the chemical pretreatment. The second step of the pro- posed model consists of depositing a thin layer of OIH matrix gel. The sol–gel precursors used to produce this coating material should provide good adhesion with the activated metallic substrate and adequate curing process ensuring appropriate mechanical and support properties to the deposition of a second OIH gel layer. The composition of this and the other layers should be based on the same matrix composition in order to avoid sharp differences of the properties at the interface between the different layers preventing sur- face/interface tensions. This strategy also contributes to minimizing the differences in thermal and mechan- ical properties between the different layers. The deposition of this first layer is also necessary to ensure that the inhibitors and any other species, including self- healing agents, do not migrate toward the metallic surface except when in the presence of external aggressive agents. In this situation, the inhibitor action could be expanded to the vicinity of the metallic surface to stop the spread of corrosion. As observed by several authors, the relative amount of inhibitor could compromise OIH matrix stabil- ity, 94 , 99 , 117 , 120 , 130 so the presence of the first OIH layer also contributes to additionally enhance the protection against inhibitor mobility/migration or diffusion to- ward the metallic surface. The layer where the inhibitor is immobilized is produced in a third step and under adequate gelling conditions to minimize the curing demanding time and optimize the immobilization of the inhibitor species within this layer. Adjusting the gelling time (viscosity) of the gel precursor (of the deposited coating) by achieving an optimum viscosity value, allows the starting of the curing process immediately and during a short time. This methodology should also obtain a dense and smooth layer with a good adhesion to the previous OIH layer. The following step consists of producing a third OIH layer containing self-healing agents that contribute to guarantee the reversibility of the damages caused by a variety of factors such as usage, weathering, or loading damage. The reversibility mechanism could be trig- gered by the entrance of water and ions transported through the topcoat. This mechanism is inspired by the process that has been used for self-healing in polymer
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  • Fall '19
  • 1984, oIh, OIH coatings

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