A new simple experimental approach is proposed for in situ mechanistic studies of the underpaint stability of metal/oxide/polymer interface under immersion. It allows an intelligent screening and fast ranking of conversion coatings on Zn alloys designed for further application of organic coatings. The approach is based on the application of a simple electrochemical aging protocol to the samples preliminary coated with a model epoxy-polymer. The latter is enough thin to allow local electrochemical impedance measurement and stable under this protocol, as revealed by attenuated total reflectance infrared spectroscopy (ATR-IR) and electrochemical impedance spectroscopy (EIS). The interface stability and degradation modes characterization is accessed via combined EIS, local electrochemical impedance spectroscopy and mapping (LEIS and LEIM) and in situ optical imaging.The developed approach allowed to discriminate two Zn alloy substrates, one with intact and another with slightly damaged Cr(III) conversion layer, for which no strong differences in the electrochemical behavior or average surface composition was visible prior to the epoxy-polymer application. The relative stability of two substrates with model thin coating, evaluated in the developed electrochemical test, correlated with the observations obtained for the same substrates coated with thick commercial epoxy primer after 1000 h of immersion. The proposed methodology offers the possibility of a rapid intelligent screening of various formulations of Cr(III)-based surface treatments for Zn based substrates designed for paint applications.
Accelerated migration tests which are commonly used to measure chloride diffusion in ordinary cement-based materials cannot be directly applied to composite with very low permeability, such as Ultra High-Performance Fiber Reinforced concretes (UHPFRC). In order to assess the UHPFRC enhancement on the structural durability, there is a critical need to accurately assess the permeability level of the material to chloride ions. The objective of this work is to adapt an existing set-up of accelerated chloride migration test in order to (i) better characterize the resistance of chloride ion penetration in UHPFRC; and (ii) to compare the resistance of chloride ion penetration between UHPC and UHPFRC. The material characterization, the set-up modifications of the existing accelerated migration test, the results are presented. In conclusion, the modification of the test-set-up allowed to accurately measure chloride transport of very low permeability UHPFRC and to shed light on the effect of the fiber reinforcement.
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