Ageing, pretreatment techniques

A number of techniques have been developed to convert corrosion-prone, clean surfaces to less reactive ones. Three common conversion processes are phosphating, anodizing, and chromating. These processes remove the inconsistent, weak surface on metal substrates and replace it with one that is strong, permanent, and reproducible.58 Figure 15.18 shows the effect of various pretreatments on the durability of aluminum alloy-epoxy joints subjected to aging in water at 50°C. 

It should be noted that the gas and vapor permeability of polymer membranes could be affected by pretreatment, ageing, plasticizatitm, crosslinking and/or crystallinity of the polymer and, in some cases, by the experimental conditions and measurement techniques employed. For example, the type of solvent(s) used in the casting of membranes may affect their permeability. 

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