Service life substrate corrosion effects

Primers are often used to help ensure an adequate service life and, indeed, the presence, and the chemical type, of any primer may play a crucial role in ensuring a long service life for the adhesive joint. For example, it will be shown later that the use of organometallic primers may be extremely beneficial and many commercial corrosion-inhibiting primers have been developed for use with epoxy aerospace adhesives following the above comments, it is probably not just a coincidence that many of the latter types of primers contain phenolic-based constituents. Examples of the effect of substrate surface pretreatments on joint durability were shown in Figs 4.16 and 4.17 and Table 4.15 further examples are illustrated in Fig. 8.8. 

Moisture has a profound effect on the service life of adhesive joints made with some adhesives between some adherends. This point has been made in the section on Water Sensitivity in Chapter 5. There are four aspects of the problem which need to be drawn together when looking at joints which have been exposed to moisture or are to be designed to withstand such exposure. These comprise the ability of moisture to diffuse through the adhesive, its susceptibility to displacement from the substrate, the corrosion susceptibihty of the substrate and, lastly, the role of any primer or sealing agent in modifying the first three considerations. 

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